\r\n\tmolecular and imaging methods for detection and identification of plant diseases have many limitations that will be discussed in this book. This sparked interest in the development of minimally invasive and substrate general spectroscopic
\r\n\ttechniques that can be used directly in the field for confirmatory plant disease diagnostics.
\r\n\tThis book will also discuss recent progress in development of reflectance, infrared, Raman and surface-enhanced Raman
\r\n\tspectroscopy for detection and identification of plant diseases. It will also present advantages and disadvantages of these optical spectroscopy methods compared to the most common molecular and imaging techniques.
\r\n\tThe book also aims to discuss specific plant diseases, their symptoms and available methods of treatment.
",isbn:"978-1-83962-516-9",printIsbn:"978-1-83962-515-2",pdfIsbn:"978-1-83962-517-6",doi:null,price:0,priceEur:0,priceUsd:0,slug:null,numberOfPages:0,isOpenForSubmission:!1,hash:"daef7c0ea5e568cfc5ae1613a74634b3",bookSignature:"Dr. Dmitry Kurouski",publishedDate:null,coverURL:"https://cdn.intechopen.com/books/images_new/10113.jpg",keywords:"PCR, ELISA, UAV, Satellite, Spectroscopic Diagnostics, Wheat, Sorghum, Rice, Corn, Fungal Pathogens, Viral Pathogens, Bacterial Pathogens",numberOfDownloads:117,numberOfWosCitations:0,numberOfCrossrefCitations:0,numberOfDimensionsCitations:0,numberOfTotalCitations:0,isAvailableForWebshopOrdering:!0,dateEndFirstStepPublish:"June 10th 2020",dateEndSecondStepPublish:"September 15th 2020",dateEndThirdStepPublish:"November 14th 2020",dateEndFourthStepPublish:"February 2nd 2021",dateEndFifthStepPublish:"April 3rd 2021",remainingDaysToSecondStep:"4 months",secondStepPassed:!0,currentStepOfPublishingProcess:4,editedByType:null,kuFlag:!1,biosketch:"Assistant Professor Kurouski obtained his Ph.D. at the State University of New York. He is an Assistant Professor at Texas A&M University. His experience includes working as a Senior Research Scientist at Boehringer-Ingelheim Pharmaceuticals and at Chemistry Department at Northwestern University, USA.",coeditorOneBiosketch:null,coeditorTwoBiosketch:null,coeditorThreeBiosketch:null,coeditorFourBiosketch:null,coeditorFiveBiosketch:null,editors:[{id:"264297",title:"Dr.",name:"Dmitry",middleName:null,surname:"Kurouski",slug:"dmitry-kurouski",fullName:"Dmitry Kurouski",profilePictureURL:"https://mts.intechopen.com/storage/users/264297/images/system/264297.jpeg",biography:"Dr. Dmitry Kurouski obtained his Ph.D. in Analytical/Physical Chemistry at State University of New York, Albany, USA. He is an Assistant Professor at Texas A&M University, at Department of Biochemistry & Biophysics. His experience includes working as a Senior Research Scientist at Boehringer-Ingelheim Pharmaceuticals and at Chemistry Department at Northwestern University, USA. He received numerous honors and awards for his continuous work in the field.",institutionString:"Texas A&M University",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"1",totalChapterViews:"0",totalEditedBooks:"1",institution:{name:"Texas A&M University",institutionURL:null,country:{name:"United States of America"}}}],coeditorOne:null,coeditorTwo:null,coeditorThree:null,coeditorFour:null,coeditorFive:null,topics:[{id:"5",title:"Agricultural and Biological Sciences",slug:"agricultural-and-biological-sciences"}],chapters:[{id:"74757",title:"The Trends in the Evaluation of Fusarium Wilt of Chickpea",slug:"the-trends-in-the-evaluation-of-fusarium-wilt-of-chickpea",totalDownloads:13,totalCrossrefCites:0,authors:[null]},{id:"74639",title:"Diagnosis of Fungal Plant Pathogens Using Conventional and Molecular Approaches",slug:"diagnosis-of-fungal-plant-pathogens-using-conventional-and-molecular-approaches",totalDownloads:41,totalCrossrefCites:0,authors:[null]},{id:"74600",title:"Blister Blight Disease of Tea: An Enigma",slug:"blister-blight-disease-of-tea-an-enigma",totalDownloads:65,totalCrossrefCites:0,authors:[null]}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"},personalPublishingAssistant:{id:"184402",firstName:"Romina",lastName:"Rovan",middleName:null,title:"Ms.",imageUrl:"https://mts.intechopen.com/storage/users/184402/images/4747_n.jpg",email:"romina.r@intechopen.com",biography:"As an Author Service Manager my responsibilities include monitoring and facilitating all publishing activities for authors and editors. From chapter submission and review, to approval and revision, copyediting and design, until final publication, I work closely with authors and editors to ensure a simple and easy publishing process. I maintain constant and effective communication with authors, editors and reviewers, which allows for a level of personal support that enables contributors to fully commit and concentrate on the chapters they are writing, editing, or reviewing. I assist authors in the preparation of their full chapter submissions and track important deadlines and ensure they are met. I help to coordinate internal processes such as linguistic review, and monitor the technical aspects of the process. As an ASM I am also involved in the acquisition of editors. Whether that be identifying an exceptional author and proposing an editorship collaboration, or contacting researchers who would like the opportunity to work with IntechOpen, I establish and help manage author and editor acquisition and contact."}},relatedBooks:[{type:"book",id:"7059",title:"Amyloid Diseases",subtitle:null,isOpenForSubmission:!1,hash:"d9a197d34d3d6006af726d577060f928",slug:"amyloid-diseases",bookSignature:"Dmitry Kurouski",coverURL:"https://cdn.intechopen.com/books/images_new/7059.jpg",editedByType:"Edited by",editors:[{id:"264297",title:"Dr.",name:"Dmitry",surname:"Kurouski",slug:"dmitry-kurouski",fullName:"Dmitry Kurouski"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"6418",title:"Hyperspectral Imaging in Agriculture, Food and Environment",subtitle:null,isOpenForSubmission:!1,hash:"9005c36534a5dc065577a011aea13d4d",slug:"hyperspectral-imaging-in-agriculture-food-and-environment",bookSignature:"Alejandro Isabel Luna Maldonado, Humberto Rodríguez Fuentes and Juan Antonio Vidales Contreras",coverURL:"https://cdn.intechopen.com/books/images_new/6418.jpg",editedByType:"Edited by",editors:[{id:"105774",title:"Prof.",name:"Alejandro Isabel",surname:"Luna Maldonado",slug:"alejandro-isabel-luna-maldonado",fullName:"Alejandro Isabel Luna Maldonado"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"1591",title:"Infrared Spectroscopy",subtitle:"Materials Science, Engineering and Technology",isOpenForSubmission:!1,hash:"99b4b7b71a8caeb693ed762b40b017f4",slug:"infrared-spectroscopy-materials-science-engineering-and-technology",bookSignature:"Theophile Theophanides",coverURL:"https://cdn.intechopen.com/books/images_new/1591.jpg",editedByType:"Edited by",editors:[{id:"37194",title:"Dr.",name:"Theophanides",surname:"Theophile",slug:"theophanides-theophile",fullName:"Theophanides Theophile"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"3092",title:"Anopheles mosquitoes",subtitle:"New insights into malaria vectors",isOpenForSubmission:!1,hash:"c9e622485316d5e296288bf24d2b0d64",slug:"anopheles-mosquitoes-new-insights-into-malaria-vectors",bookSignature:"Sylvie Manguin",coverURL:"https://cdn.intechopen.com/books/images_new/3092.jpg",editedByType:"Edited by",editors:[{id:"50017",title:"Prof.",name:"Sylvie",surname:"Manguin",slug:"sylvie-manguin",fullName:"Sylvie Manguin"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"3161",title:"Frontiers in Guided Wave Optics and Optoelectronics",subtitle:null,isOpenForSubmission:!1,hash:"deb44e9c99f82bbce1083abea743146c",slug:"frontiers-in-guided-wave-optics-and-optoelectronics",bookSignature:"Bishnu Pal",coverURL:"https://cdn.intechopen.com/books/images_new/3161.jpg",editedByType:"Edited by",editors:[{id:"4782",title:"Prof.",name:"Bishnu",surname:"Pal",slug:"bishnu-pal",fullName:"Bishnu Pal"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"72",title:"Ionic Liquids",subtitle:"Theory, Properties, New Approaches",isOpenForSubmission:!1,hash:"d94ffa3cfa10505e3b1d676d46fcd3f5",slug:"ionic-liquids-theory-properties-new-approaches",bookSignature:"Alexander Kokorin",coverURL:"https://cdn.intechopen.com/books/images_new/72.jpg",editedByType:"Edited by",editors:[{id:"19816",title:"Prof.",name:"Alexander",surname:"Kokorin",slug:"alexander-kokorin",fullName:"Alexander Kokorin"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"1373",title:"Ionic Liquids",subtitle:"Applications and Perspectives",isOpenForSubmission:!1,hash:"5e9ae5ae9167cde4b344e499a792c41c",slug:"ionic-liquids-applications-and-perspectives",bookSignature:"Alexander Kokorin",coverURL:"https://cdn.intechopen.com/books/images_new/1373.jpg",editedByType:"Edited by",editors:[{id:"19816",title:"Prof.",name:"Alexander",surname:"Kokorin",slug:"alexander-kokorin",fullName:"Alexander Kokorin"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"57",title:"Physics and Applications of Graphene",subtitle:"Experiments",isOpenForSubmission:!1,hash:"0e6622a71cf4f02f45bfdd5691e1189a",slug:"physics-and-applications-of-graphene-experiments",bookSignature:"Sergey Mikhailov",coverURL:"https://cdn.intechopen.com/books/images_new/57.jpg",editedByType:"Edited by",editors:[{id:"16042",title:"Dr.",name:"Sergey",surname:"Mikhailov",slug:"sergey-mikhailov",fullName:"Sergey Mikhailov"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"371",title:"Abiotic Stress in Plants",subtitle:"Mechanisms and Adaptations",isOpenForSubmission:!1,hash:"588466f487e307619849d72389178a74",slug:"abiotic-stress-in-plants-mechanisms-and-adaptations",bookSignature:"Arun Shanker and B. Venkateswarlu",coverURL:"https://cdn.intechopen.com/books/images_new/371.jpg",editedByType:"Edited by",editors:[{id:"58592",title:"Dr.",name:"Arun",surname:"Shanker",slug:"arun-shanker",fullName:"Arun Shanker"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"878",title:"Phytochemicals",subtitle:"A Global Perspective of Their Role in Nutrition and Health",isOpenForSubmission:!1,hash:"ec77671f63975ef2d16192897deb6835",slug:"phytochemicals-a-global-perspective-of-their-role-in-nutrition-and-health",bookSignature:"Venketeshwer Rao",coverURL:"https://cdn.intechopen.com/books/images_new/878.jpg",editedByType:"Edited by",editors:[{id:"82663",title:"Dr.",name:"Venketeshwer",surname:"Rao",slug:"venketeshwer-rao",fullName:"Venketeshwer Rao"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}}]},chapter:{item:{type:"chapter",id:"61096",title:"The Relationship between Instructional Leadership Style, Trust and School Culture",doi:"10.5772/intechopen.75950",slug:"the-relationship-between-instructional-leadership-style-trust-and-school-culture",body:'\nSchool effectiveness is the all efforts of schools to make changes to improve level of students’ achievements, and this term has been widely used since the 1960s [1]. Instructional leadership is a term which has been used after the work of Edmonds [2], Bossert et al. [3], Hawley and Rosenholtz [4], and Purkey and Smith [5] on effective schools in the United States and has been accepted as a core element of school leadership [6]. Researchers of effective school movement during the 1980s compared effective schools with ineffective ones regardless of socioeconomic status and family background of their students. This body of research had drawn attention of policymakers and scholars that instructional leadership of the principals, who focus highly on teaching and learning, is needed for school effectiveness. According to Lezotte [7], the principal as an instructional leader communicates the mission to the staff, students and parents in an effective school, and the principal as a coach, a partner and a cheerleader will have to develop his/her skills. Lezotte [7] proposed seven correlates of effective schools as follows:
Instructional leadership
Mission which is clear and focused
Environment which is safe and orderly
Climate with high expectations for success
Frequent tracking of student progress
Home-school relations which are positive
Student time on task and opportunity to learn
During the 1980s, many models of instructional leadership were introduced by the researchers. Researchers have used the model proposed by Hallinger and Murphy [8] most frequently in their research about instructional leadership. This model proposes three dimensions of instructional management and ten instructional leadership functions as follows:
\nDimension 1: School mission is defined:
School goals are framed clearly.
School goals are communicated clearly.
Dimension 2: Instructional program is managed:
Instruction is supervised and evaluated.
Curriculum is coordinated.
Student progress is monitored.
Dimension 3: Positive school climate is created:
Instructional time is protected.
Professional development is promoted.
High visibility is maintained.
Incentives for teachers are provided.
Incentives for learning are provided.
Dimension 1 proposes that academic goals of the schools should be clear as they are discussed and reviewed with staff regularly. These goals have to be supported and incorporated into daily life by the staff. Principals should communicate the school goals to teachers, students and parents through the formal communication channels such as the school handbook and assemblies or informal ones such as parent and teacher conferences [6]. Mission is a body of goals determined for bringing vision to life. Schools should have certain goals. The basic mission of the school is to ensure that the environment needed to deliver high-quality education to students is created. There may be different viewpoints among teachers as regards the mission of the school; thus, the instructional leader is responsible for developing a shared mission based on stronger values. School principals may create an effective public relations system so as to announce the school objectives to the stakeholders as public relations is related to providing an effective communication channel through which the target audience can be notified about institutional objectives especially academic ones, of the school and developed expectations for education, student, teacher and academic success. Defining a good school vision and assertive mission is not sufficient alone. Goals of the school must be put into life by planning and reviewed constantly depending on changing and developing conditions and redefined when necessary so that they are up to date.
\nDimension 2 requires principles to have high knowledge in the school’s instructional program, commitment for the improvement of school and expertise in teaching and learning so that the principal can coordinate and control academic program of the school [6]. Ensuring coordination between curriculum and activities in school is one of the important roles of a school principal. The purpose of inspection in schools is to increase the effectiveness of all school activities and to obtain high-quality education. Inspection applied by school principals includes focusing on teaching-learning processes. Ensuring the goals of their school are translated into classroom activities is the main task of the school principals. Teaching can be monitored in classroom through semi-official classroom inspections, then concrete feedback can be given to teachers on certain classroom activities, and it is ensured that they reach the desired level. A school principal who aims the development of education-teaching and teachers in the school are obliged to inspect and evaluate what happens at the school. The evaluation must not be with the purpose of scaring but inspiring. The working environment and trust must be established so that teachers will not feel any fear at the time of evaluation. In order to ensure that teachers perform their roles better, he/she acts with them, leads them, inspires them for self-development and keeps their motivation high. The purpose of course inspection is to obtain direct information about student success and ensure that the missing points are corrected, provide feedback to the course teacher about the negative aspects and encourage them in developing the positive aspects, which is a milestone in the road to success [9]. The school principal can discuss the test results with the staff and provide them with interpretive analyses so that student weaknesses can be diagnosed and results of changes that were made in the school’s instructional program can be evaluated [6]. The school principal should create an evaluation system which appraises the academic success of students with the purpose of rewarding success and improvement displayed by students [10].
\nDimension 3 proposes that if high standards, expectations and culture of continuous learning and improvement are developed, an academic press can be created by the schools [6]. Time planning is one of the most important elements at school. The opening, closing, holiday and resting times, class hours and breaks of a school are elements that interest the time dimension of teaching. The activity periods at school have to be determined according to priorities and effectively planned; it is also necessary that the school principal has a special time plan and has time management skills. Attention must be paid to ensure that teaching time is used for teaching and implementing new skills and concepts and it is not interrupted. This can be monitored and evaluated by school principals through regular classroom visits and enforced with school policies. The top priority of school principals is to provide the environment needed for supporting the professional development of teachers related to school goals so that they can:
Ensure participation of teachers in several in-service training activities
Organize seminars, conferences, workshops, etc., for improvement of teachers in the school
Inform teachers on all kinds of education opportunities outside the institution
When the school principal observes classrooms, strolls in the building regularly and participates in personal development activities actively, teachers and students perceive the manager as a visible being. This also strengthens communication between stakeholders of education. An effective leader should value the success of both teachers and students. If they know that they will be rewarded due to a superior performance, they will be highly motivated to succeed better. Many researchers defined the characteristics of instructional leaders and their roles in effective schools [3, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26] as follows:
Assertive
Self-confident
Strong disciplinarians
Calm
Decisive
Persuasive
Resists against hindrances
Keeps high motivation for success
Takes risks
Strong
Directive leader
Not strictly bureaucratic
Adopts democracy
Good communicators
Good role models
Orients strong results
Has power of purpose
Encourages other members of the school to be involved in decision-making
Systematically monitors student progress
Has high visibility during supervision
Visits classes
Observes teaching and then responds to those observations
Experts in curricular development
Experts in teaching
Develops a common sense of vision among all members of the school
Evaluates the achievement of basic objectives
Focuses on building school culture
Focuses on academic press
Focuses on high expectations for student achievement
Perceived as the person of a difficult work who pays effort to learn
Performs lifelong learning, pioneers his/her environment for their learning
Shows high level of performance
Communicates easily and dynamically sets targets
Has detailed information about teaching planning and learning theories
Aware of the problems in the class
Able to determine pedagogical objectives themselves
Sets balance between their behaviors and values at school and in social life
Supports empowerment and controlling for sustainability
Prefers changing by risk-taking to sticking with the status quo and innovation to stability
Individuals who execute education-teaching activities recruiting their power from expertise
Able to create an organizational culture
Manifests coherent education philosophy
Until the 1990s, researchers focused on school principals as leaders who frame goals of the schools, maintain great expectations for teachers and students, promote development of teachers, supervise instruction, coordinate curriculum, monitor progress of the students and develop school program as an expert [27]. Researchers have put a great emphasis on the leadership skills of principals in effective schools since the end of the 1970s, and they have considered that these skills are one of the main factors of school effectiveness [25]. Democratic and also participative organization of schools conflicted with the hierarchic position of instructional leadership in the late 1980s during effective school restructuring movement which aimed to empower teachers accepted as professional educators (Marks and Louis 1997 as cited in [21]). Because of the limitations of instructional model focused on principals, attention was switched to transformational leadership and subsequently to distributed leadership [28].
\nIncrease in responsibilities and accountability of school leadership created the need for leadership distribution in schools. Hall and Hord [29] did a research related to fruitful change in schools and concluded that it is impossible for school principals to do it alone. This means that teaching cannot be improved by only school principal, and this work should be distributed across the school leaders [30, 31]. Then school leadership was reconceptualized as distributed leadership [32]. Distributed leadership is a collective action that can be exercised by the school principal, their assistants, heads of departments, teacher leaders and other members who aim the improvement of school [33, 34, 35, 36, 37]. Hargreaves and Goodson [38] note that distributed leadership is not an end in itself; it is distributed among instructional leaders. Instructional leaders share the responsibility of supervision of instruction, staff and curricular development.
\nDuring the 1990s, consideration of the role of teachers as leaders increased [39]. Principals have more chance to spend time in the classrooms of small primary schools to monitor teaching, but they may need teacher leaders or heads of departments to engage in curriculum in large secondary schools [40]. Youngs and King [41] stress that principals may build the capacity of school with the aid of teacher leaders. According to results of the studies done by Marks and Printy [21], schools become high-performing organizations when teachers share the instructional leadership with school principals. In this frame, it was defined who the teacher leaders are and what they do. Department chairs, curriculum managers, coaches, specialists, professional development coordinators, consultants, mentor teachers, resource teachers and demonstration teachers can be teacher leaders. Some of the teacher leaders can focus on different subjects or different grades, or they may focus on only one subject or one grade level [42]. Many of the teacher leaders may have full-time leadership role out of their classes, or some may take responsibility both as teacher and part-time leader [43]. Roles of teacher leaders for improvement of instruction and enhancing student learning are identified by researchers as follows:
Promoting school vision
Accepting school goals
Strengthening school culture [44]
Conducting workshops for professional development
Co-planning and modeling lessons
Observing teaching and providing feedback
Collecting and analyzing data
Facilitating dialog
Giving reflective critique
Promoting shared practices among teachers [45]
Peer coaching idea was first explored by Showers and Joyce [46]. They suggested that teachers should coach each other in complimentary ways. Coaching is a class-based support given by qualified, knowledgeable individuals to teachers and coaches to explore the ways on how to increase teaching practices of the teachers by using their own students [47]. Applications of coaching differ both within and between schools [48]. Coaches may focus one subject or grade or may work across grades or schools like teacher leaders, and they can be teacher leaders who coach in addition to classroom teaching, or they can be from outside the school [49]. Roles of peer coaches were identified by the researchers as follows:
Focusing on the needs of teachers [50]
Helping teachers plan and organize teaching lessons
Managing activities
Demonstrating lessons
Organizing materials
Analyzing data
Supporting whole-school reform
Building school capacity [52]
Teachers believe that coaches are not useful if they spent more time on management and administrative duties than their needs [51]. Based on the results of studies, it was noted that the quality of teachers’ instructional practices for class discussions improved [53] and also student achievement increased with coaching program [33, 54, 55].
\nVarious and numerous definitions have been made regarding organizational culture. According to Schwartz and Davis [56], organizational culture is the whole of beliefs and expectations shared by members of the organization and the norms that shape the behaviors of groups and individuals in the organization. Some of the scientists who are interested in the concept treat the organization’s culture as a set of widely shared beliefs about how people behave at work and the values that make it possible to distinguish which goals and tasks are important [57].
\nAccording to another point of view in the literature, organizational culture is the common beliefs and values that develop over time in an organization [58]. Hellriegel and Slocum [59] describe an organization’s culture as a complicated structure that is composed of beliefs, ideas, expectations, attitudes, behaviors and values shared by members of the organization. Organizations are social systems. The most important elements of this social system are the people. These people, who make organizations dynamic, come to life with their knowledge, manners and beliefs, or briefly “culture,” which they surround. Organizations are made up of people with different cultures. Social gaze, beliefs, rewards or punishment expectations, flexibility and fatalistic beliefs, that is, social expectations, which are shaped in the culture in which humans are located, cause them to look at the same phenomenon in the same context [60]. These people have come together with a number of professional criteria, and as a natural consequence of being a group, they have formed a system of beliefs and values that are relatively different from other organizations but within themselves. This system is “organization culture.” School culture can change in time in order to obtain higher student achievement as the profiles enrolling at the school vary from one year to the other and a school should adapt itself to them [61].
\nIn order to be able to compete in a constantly changing environment, the organization must adapt itself to this change, continually learn and practice what they learn [62]. Every organization should demonstrate value-based management. In other words, according to the development of events, there should be a set of values and decisions in the face of developing situations that do not take daily decisions [63].
\nEven though the definition of culture is difficult to measure and it causes some concerns, organizational culture offers a variety of benefits to its leader and organizational members [64, 65]. Organizational culture contributes to the organizational leadership in working more effectively and harmoniously with the organizational leader, as well as by providing regular procedures for the strategy and methods of putting the work into practice. Organizational culture leads to the emergence of new leaders who are identical in qualities to individuals who work within it and of its members. It provides a solid relationship between the individuals working in organizational culture and benefits such as contributing to the formation of cooperative working teams.
\nIn their research, Kowalski et al. [66] stated that one of the most important elements of school cultures is sharing. According to Robbins [67], management refers to one of the functions of communication as providing sharing. As for Senge [68], communication manager has been included in the factors that make a leader. In the organizations, it is possible to produce, share, interpret and understand the meaning of organizational communication in the processes of management functions such as effective coordination of managers [69, 70]. In this context, it can be said that there is an important share of communication in the formation of organizational culture, which is expressed as organizational integration and assumptions leading to external compatibility [65, 67]. The creation and strengthening of school culture are seen as a fundamental necessity for supporting and sustaining success in school [71].
\nFinnan [72] notes that school culture is not a static element but is constantly being built and shaped through reflection and interactions between individuals.
\nSchool culture gives a sense of formal identity and draws a way for organizational processes through organizations, legends, rituals, meanings, values and norms [73].
Values: The values and actions of individuals in the organization are measured and evaluated. Values are wider and tighter when compared to norms. To legitimize norms, they must originate from cultural values [74].
Beliefs: According to Schein [75], beliefs direct the behaviors of members of an organization by telling them how they should think and feel. The more beliefs are similar and shared by people, the more they become settled and distinct in the culture. Reaching the goals will be easier when beliefs are internalized in an organization [75].
Norms: Norms are invisible elements. If organizations want to improve the performance and increase the profitability of their employees, the first element they need to focus on is norms [76].
Heroes: Heroes are important people who make organization culture or adopt organization culture. At the same time, the heroes are symbolic of the organization culture. In many organizations, heroes are role models [74].
Stories and tales: In relation to the organization, they are important events that members live or listen [74].
Language: One of the key elements of communication is the language and, at the same time, cultivation [74].
Symbols: Symbols are symbols and words in organizational culture. These include special meanings. Essential values forming the basis of the organization are expressed by symbols [74].
According to some researchers, several and various dimensions of school culture are determined. These dimensions are as follows:
\n1. Democratic management and participation
\nA democratic school management includes determination of representatives through elections, a transparent management philosophy, providing a free working environment to the employees, entrenching a system which allows employees and students to express themselves freely and creating a culture which adopts equality as a common value, etc., [78]. Some studies showed that the subordinates of participatory leaders have higher satisfaction than the subordinates of some rampant leader types and that an increase in participation and cooperation level also increases the level of identification of employees with their organizations; other studies indicated that there is a meaningful relation between increase in morals and efficiency and more participation and that when workers determine production targets themselves, they determined a target which is above normal levels and that they surpassed this target in a short period of time (Roethlisberger and Bavelas cited in Davis [77]), (cited in [79]). As a result, it can be thought that success is inevitable in organizations which have a democratic school culture.
\n2. Cooperation, support and trust
\nCooperation can be defined in general terms as “a working partnership or business partnership created by individuals with same purposes and interests.” Support is the degree of help and sincerity provided by managers to their subordinates [80]. In his definition of school culture, Senge underlines the need to support the process between attitudes, values and habits. The existence of a supported professional community prevents teachers from giving in to exhaustion and empowers and motivates them (cited in [81]). There are stronger relations between education employees who enjoy an environment of trust, as a result of which they can display common stance in the face of problems and everybody can make contribution to the solution. If an environment of trust cannot be created, the relations between employees are damaged and sharing and cooperation are reduced.
\n3. The relation between school and environment
\nThe most important and explicit feature of school culture is that it receives the raw material (student) that it processes from the society, subjects them to the necessary education process and gives back to the society. It is also distinguished form other organizations in that all formal and informal organizations around the school direct or influence it. The development of a child at school must be in the same direction with the sensitiveness that the family shows to education. In this sense, two advantages of cooperation between family and school can be mentioned: first, the interest shown by the family to school and student provides motivation. Second, families that are familiar to the structure, values and standards of the school can direct their children in a better way [82]. A strong connection established between school and environment will have a positive impact on school culture.
\n4. Integration and sense of belonging
\nA distinct result of a strong culture is low employee turnover rate. In a strong culture, there is a high level of agreement among members on what the organization represents. Such a unity of purpose stimulates the senses of organizational belonging of employees, as a result of which the tendencies of employees to leave the organization are reduced [80]. Integration is the psychological commitment between an individual and the organization. This situation involves not only engagement of the individual to work and commitment to the organization but also his/her beliefs about the dominant values of the organization. Members of an organization can integrate with the group and the organization as well as its objectives through some shared cultural elements. For this reason, it is essential that the manager imposes an awareness of “us” in the organization so that employees benefit organizational integration and sense of belonging. In addition, in order to create a sense of belonging and community at the school, a stable group based on long-term togetherness is needed above all. Long-term togetherness of the staff is essential in terms of integration. Frequent turnover of managers or employees has a negative impact on the development of integration. On the other hand, the feeling of being a community is related to the sense of being a community that is related to all members of the school community accepting themselves as a part of the school and integrating with the school (Alavi et al., [83]).
\nAs an organization, school is an organization which adds the behavior needed to reach preset educational objectives in a planned manner and within a certain period. It is a system operating under public surveillance where transfer of knowledge and skills is realized in a programmed and systematic manner [78].
\nFeatures of a school organization can be listed as follows:
The most important and explicit feature of a school is that the raw material that it processes is human who comes from and goes back to society.
School has some values. The task of a school is to reconcile and balance these values.
School is a special environment. A controlled environment is created by developing programs that will ensure the behavioral changes desired to occur in the student.
School is an organization which is affected by and affects the environment.
School is the leading organization which ensures cultural change.
It is an organization which teaches cultural values to students and creates change in the cultural structure of the society.
School has a unique culture and personality.
School is a bureaucratic organization [84].
Although the definition of culture is difficult to measure and causes some concerns, organizational culture offers a variety of benefits to this organizational leader and organizational members [64, 65].
Organizational culture contributes to the organization’s staff to work more effectively and harmoniously with the organizational leader, as well as providing regular procedures for laying out business strategies and methods so that they can work effectively.
It increases commitment to the vision of the school.
A positive and effective school culture has many benefits such as increasing commitment to the school, developing trust toward school and the management, preventing destructive conflicts, shaping the behaviors and expectations of teachers and students at the school and increasing school success, etc., [65].
It increases the effectiveness and efficiency at school (such as academic success of students, performance of teachers) [85].
Trust can be shown as one of the most important factors in interpersonal relations and interaction. It has been subject to studies in the fields of organization, management and organizational behavior since the 1980s [86].
\nCummings and Bromiley [87] define trust as a mutual belief between individuals or groups that they will not use the opportunities to obtain advantage by keeping the promises of a group or individual made to other group or individual. Studies on organizational trust examine trust under three main headings. These are:
\nAccording to Hosmer [91], the five characteristic features of trust are as follows:
Helpfulness (thinking about the wellness of others)
Honesty (sticking to rightness)
Consistency (showing similar behaviors in similar situations)
Openness (sharing opinions and knowledge freely)
Competence (being skilled)
Handy [92] stated that trust:
Is not blind
Is strict
Requires limits
Requires constant learning
Requires being connected
Requires contact
Has to be earned
Trust is fragile; for this reason, it is not expected to show continuity. The behaviors which develop and preserve trust can be listed as follows (Covey 2004 cited in [93]):
Sharing essential information about oneself
Accepting weaknesses and errors
Asking for help and using the skills and experiences of others
Accepting the questions and information about the scope of your irresponsibilities
Giving the benefit of trust to others before reaching negative conclusions
Being willing to be influenced
Taking risk in offers for feedback and help
Refraining from abusing others who are open to criticism
Spending time and energy on cooperative benefit
Behaving in fairness and stability
Keeping promises
The recommendations for repairing trust in the case that trust is reduced or breached can be listed as follows [93]:
Sincere apologies
Not allowing the affected person to affect you
Keeping promises
Establishment of organizational trust at schools is not an easy task. Education institutions are environments where changes in terminal behaviors are targeted and within this framework interpersonal relations are experienced in the most intense manner. Ensuring the formation of trust in education institutions can lead to developments which will affect the quality of relations with teachers, students and parents in the short term and the entire social life in the long term. School is an organization which produces services, and this service can be highly qualified only if a positive intra-organizational environment is provided. Good relations between the employees, specification of the tasks and responsibilities and also talented employees willing to show their work have critical roles in the formation of trust in the institution [94].
\nTrust and the reflections of trust phenomenon in organizations, meaning organizational trust, have been mentioned so far. In the end of theoretical explanation, details will be given about the reflection of trust and the phenomenon of organizational trust in the school. The place of trust phenomenon at schools is close to, if not more important than, the position of the trust phenomenon in other organizations as schools are institutions that are established to create behavioral change in individuals. Most part of school product constitutes the behavioral changes in the people that it educates. There are very few types of organizations where human element is as dominant as school. In an institution where human element is dominant, trust, which keeps people together and which is the result of relations between them, has huge importance. According to Tshanmen-Moran et al. [95], trust is necessary to achieve success at school and to establish a better environment between managers and teachers in terms of education. The five basic criteria for creating trust at school are helpfulness, trustworthiness, competence, honesty and openness. We can list the benefits that a strong organizational trust level can provide to the school as follows:
It lays the foundation of a broad-based development and change that will be ensured at school.
It gives hope to teachers about regulations and changes made at school.
It ensures that teachers know each other better.
It shows whether the works and operations at school are conducted in a healthy manner [96].
Trust toward colleagues and school makes teachers open to innovation and change [97].
A trustworthy school climate ensures that teachers think about how to provide a better learning environment [98].
According to Bryk and Schneider [99], below are the actions that can be taken to create a sustainable climate of trust at school:
School personnel having the competence for performing their job
All employees being open and honest in their relations
Transparency between managers and employees
Taking into consideration the development and efficiency of school, trust represents a critical point. Trust lays the foundation of performing good and effective work at schools, whereas lack thereof appears as a factor which hinders such a development. At schools where trust does not exist, detachment between teachers and students and an unhealthy climate of communication exist. At schools with low level of trust, leaders pay effort to satisfy small interest instead of working for the group and the school. When lack of trust claims the school culture, it is not possible for the school to perform efficient work. In order to assure positive change at schools, we have to create an environment of relations based on trust. For the solution of many problems faced at schools, creating a trust-based working environment is the preliminary condition [100].
\nSchool culture is a phenomenon that is created by students, teachers, administrators, parents and other school staff members, and it is acquired in the form of habits, beliefs, perceptions, behaviors and norms. School culture influences every aspect of how a school functions including the methods of communication and the style of leadership of the school. Organizational trust in schools may not be formulated without school culture and the stakeholders of education as principals, teachers, students and parents. Quality of the communication among leaders of education, teachers and students plays an important role in constructing trust in a school. Trust will increase the motivation and morals and improve cooperation, school culture, organizational commitment and the impact of the instructional leaders on teams. How do the instructional leaders gain trust of others? Teacher leaders can gain trust of teachers if they help them as peers not as expert supervisors and avoid to give strict feedback about the teaching activities of the teachers [45]. They have to be facilitators by pointing out the weaknesses and showing the ways to increase the effectiveness of the activities. Teacher leaders are more effective when they are supported by the principals [40]. Principals may inform the teachers about the roles and importance of teacher leaders to increase school effectiveness and may provide sufficient time for them to work together [35]. Coaching can be effective when supported by the principals [101] and the teachers [102]. Principals can explain the importance of coaching to the teachers for improving teaching [37]. The works of the instructional leaders of a school are complementary of each other so that they have to trust and support each other. In this way, leadership can contribute to improve student learning by shaping the conditions and school climate based on the school objectives which target to meet the needs of contemporary society. Different perceptions among teachers and school administrators on educational leadership may cause problems regarding the organization of the school. This may in turn become a source of organizational conflict.
\nTaking into consideration the impact on the shaping of school culture, weaknesses and training needs of instructional leaders to succeed in their mission can be analyzed, and education opportunities can be provided to improve their instructional leadership qualifications; then measures can be taken against the factors that restrict instructional leadership. It is necessary that school leaders are aware of the importance of instructional leadership and positive, cooperative school culture is structured and developed at schools in order to ensure the effectiveness of schools and student success. In context of distributed leadership, principals, teacher leaders, deputy heads or coaches should work together, support each other as instructional leaders to reach the goals of the school. This may happen only in a climate of trust and mutual support which becomes an integral part of school culture. So school leaders should establish trusting relationships with each other if they place priority on effective instruction, student success and school improvement.
\nWith the rapid development of science and technology, Internet of Things (IoT) plays an increasingly important role in the next evolution of the Internet through turning data into information, knowledge, and wisdom [1]. More recently, multiple type applications based on IoT have been developed, including health testing, safe home, intelligent transportation, logistics supply, environmental protection, infrastructure testing, and security [2]. Sensor nodes in the IoTs are widely distributed and require independent, mobile, sustainable, and maintenance-free capabilities. Under the current technologies, most sensors require an external power source to drive their operation, wherein the battery is extensively applied. However, the life cycle of the battery is limited, and replacing the battery for the massive sensors is a huge project, which consumes a lot of manpower and material resources and increases the maintenance cost. In addition, the regularly replaced battery generates a large amount of harmful substances, which seriously endangers the environment and human health. Therefore, a clean and sustainable power source should be provided to satisfy the requirement of driving these small electronic devices sustainably.
Harvesting of the ambient environment energy, as an eco-friendly and renewable collecting energy method, is regarded as a promising and effective strategy to realize continuous powering for these small electronic equipment [3]. Some possible technologies have been exploited for collecting energy from surrounding environment, such as solar cells that collect energy from sunlight [4] and thermoelectric generators that harvest energy from temperature difference [5]. However, as constrained by the intermittency nature of sunlight, the low output of thermoelectric generators, these energy harvesting technologies cannot ensure the continuous operation of electronic devices. Owing to its abundant reserves and widespread, mechanical energy are increasingly utilized to extract and convert into electricity based on different mechanisms, including electromagnetic generator (EMG) [6], piezoelectric nanogenerator (PENG) [7, 8], and triboelectric nanogenerator (TENG) [9]. Considering the large-scale power generation of EMG and low output power of PENG, TENG has been demonstrated as a promising approach for harvesting ambient mechanical energy due to the desirable features of simple structure, flexibility, low cost, light weight, high efficiency, and high power density at low frequency [10]. The operation of TENGs is depended on triboelectrification (or contact electrification) and electrostatic induction [11], and the fundamental theory is according to Maxwell’s displacement current and change in surface polarization [12]. Since the first invention of TENG in 2012, it has been extensively investigated and well confirmed that the potential of wide application is ranging from powering small electronic devices for self-powered systems, functioning as active sensors for medical, infrastructural, human-machine, environmental monitoring, and security [13, 14, 15, 16, 17, 18, 19, 20]. Various types of wasted mechanical energies in our daily life, such as human motion, vibration, wind, and flowing water can be utilized by different TENG structures. Based on these characteristics, TENG can be utilized as a small-scale energy harvester for driving mass electronic equipment continuously.
TENGs are derived from the coupling effect of contact electrification and electrostatic induction. Contact electrification, as known as static electricity and contact charging, is a common phenomenon in many manufacturing environments and has been known for thousands of years. During the process of contact electrification, the dissimilar material/surface becomes charged after contacting with each other. After contacting, the opposite’s triboelectric charge is produced on the surface of dissimilar materials with different electron affinities. Driven by external mechanical motion, the materials will be separated resulting in potential difference between the two electrodes on the back side of the materials. To maintain the electrostatic equilibrium, the free electrons in the electrodes will be driven to flow in external circuit to balance the induced potential difference, thus converting mechanical energy into electrical energy. According to the different structure designs of electrodes or moving manners of the triboelectric layer in TENGs, four different modes of TENGs have been build [9], as elaborated as follows.
The mechanism of vertical contact-separation mode can be elaborated largely by an example. As shown in Figure 1a, the simplest structure of TENG includes two metal electrodes and a dielectric film, in which two metal films work as top electrode and back electrode attached to dielectric film, respectively [21, 22]. When mechanical movement is applied in the unit, the top electrode and dielectric film will contact with each other, and thus the dielectric layer and electrode will get positively charged and negatively charged, respectively, due to the triboelectrification. Once they are separated by a short distance, the potential difference between the two electrodes will be induced, which will drive electrons to flow from the back electrode to the top electrode, resulting in a pulse current with an external circuit connected. If they are brought into contact again, the electrons will flow back and the current will be reversed.
The four fundamental modes of triboelectric nanogenerators: (a) vertical contact separation mode, (b) in-plane contact-sliding mode, (c) single-electrode mode, and (d) freestanding triboelectric-layer mode [9].
The basic structure of TENG in this model is the same as that of the vertical contact-separation mode. The difference is from the motion mode of the top electrode (Figure 1b). In the original state, the top electrode and dielectric film fully overlap and intimately contact with each other, leading to the oppositely charged surfaces. With the top electrode sliding outward, the contact surface area will decrease gradually until the complete separation of the two surfaces. The separated surface creates a potential difference across the two electrodes, generating a current flow from the top electrode to the bottom electrode. When it slides backward, then there will be a reversed current flow to balance the potential difference [23, 24].
As displayed in Figure 1c, the single-electrode mode TENG has only one bottom electrode connected to the ground [25, 26]. After contact with the top material, the two surfaces will get charged owing to the triboelectric effect. During the process of an approaching and departing of top material, the local electrical field distribution caused by charged surfaces will change. Then, there will be potential difference change between the bottom electrode and the ground, and electrons exchange between them to maintain the potential change.
As for the freestanding triboelectric-layer mode, it is the only one that the motion part is a dielectric layer [10], as shown in Figure 1d. The dielectric layer and two electrodes are in the same order, and the gap distance between the two symmetric electrodes should much smaller than the size of dielectric layer. At the original position, the state of dielectric layer and electrode is the same as what is in the lateral-sliding mode. The dielectric layer and electrode will get oppositely charged, respectively, once the motion occurs as before mentioned. When the dielectric layer is sliding forward and backward, there will be a potential difference between the two electrodes due to the change of overlapped area, which drives the electron exchanges between them.
In order to satisfy the requirement of harvesting mechanical energy from multiple type motions, various TENGs have been fabricated based on the four modes illustrated above.
Given the collection features of small scale, low frequency, and irregularity, human biomechanical motions are considered to be accessible, renewable, and the most abundant energy sources. TENG can collect this energy and convert it into electricity. Since it is first reported in 2012, TENG harvesting mechanical energy from human biomechanical movements has been fully developed.
Compared to the discrete devices, complex integrated TENGs can perform multiple functions with the merits of higher output performance, better adaptability, and sustainably. Based on the high-efficient and sustainable TENGs, various integrated TENGs have been developed for harvesting energy from human biomechanical movements. Zhu et al. introdued a packaged power-generating insole with built-in flexible multi-layered TENGs that harvested mechanical pressure during normal walking to power portable and wearable consumer electronics [27]. Bai et al. developed a flexible multilayered TENG by intergrating five layers of units on a zigzag-shaped Kapton substrate to gain pressure from normal walking [28]. Because of the unique structure and nanopore-based surface modification on the metal surface, the instantaneous short-circuit current (Isc) and the open-circuit voltage (Voc) can reach 0.66 mA and 215 V with an instantaneous maximum power density of 9.8 mW/cm2 and 10.24 mW/cm3. Triggered by press from normal walking, the TENG attached onto a shoe pad was able to instantaneously drive multiple commercial LED bulbs.
For improving the output current, Yang et al. designed an integrated rhombic gridding-based TENG to harvest vibration energy from natural human walking [29]. The newly designed TENG consists of PTFE nanowire arrays and aluminum nanopores with the hybridization of both the contact-separation mode and sliding electrification mode. Herein, Voc of the TENG could be up to 428 V, and Isc was near 1.395 mA with the peak power density of 30.7 W/m2. Moreover, based on the TENG, a self-powered backpack was developed with a considerably high vibration-to-electric energy conversion efficiency of 10.62(±1.19)%. When a person walks naturally carrying the designed backpack with a total weight of 2.0 kg, the power harvested from the body vibration is high enough to simultaneously light all the 40 LEDs.
Based on a high-output TENG, Niu et al. developed an universal self-charging system exclusively driven by random body motion for sustainable operation of mobile electronics [14]. In this system, a multilayered attached-electrode contact-mode TENG is utilized to effectively collect the energy from human walking and running (Figure 2a). The basic working principle of attached-electrode contact-mode TENGs is shown in Figure 2b. The structure of multi-unit TEMG, shown in Figure 2c, consists of 10–15 layered TENGs which used a Kapton film (a thickness of 125 μm) as the substrate and is shaped into a zigzag structure. A surface modified thin aluminum foil and fluorinated ethylene propylene (FEP) layer are utilized as the triboelectric materials. Figure 1d displays the small volume and lightweight of as-fabricated TENG (5.7 × 5.2 × 1.6 cm/29.9 g for a 10-layer TENG and 5.7 × 5.2 × 2.4 cm/43.6 g for a 15-layer TENG). As shown in Figure 2e,f, a human walking can drive this TENG to generate about 2.2 μC short-circuit transferred charge and about 700 V voltage output when embedded the TENG in the shoe insoles.
(a) System diagram of a TENG-based self-powered system, (b) working mechanism of an attached-electrode contact-mode TENG, (c) structure of the designed multilayer TENG, (d) photo of an as-fabricated TENG, (e) triboelectric charge output, and (f) Voc output of the as-fabricated TENG [14].
Shen et al. proposed a humidity resisting triboelectric nanogenerator to harvest energy from human biomechanical movements and activities for wearable electronics [30]. The obtained HR-TENG is fabricated by a nanofibrous membrane via electrospinning method. Under a relative humidity of 55%, the current and voltage output of the self-powered unit can still reach as high as 28 μA and 345 V, corresponding to a power density of 1.3 W/m2 with hand tapping. With the relative humidity raising from 30 to 90%, its electrical output still kept a relatively high level. A wide-range of electronics such as an electronic watch, a commercial calculator, a thermal meter, and a total of 400 LEDs has demonstrated to be successfully powered from human biomechanical movements under different ambient humidities.
Textile-based device is highly desirable for wearable electronics due to its low-mass, durable, flexible, and conformable [31]. As the most efficient power sources, textile substrate-based TENGs are fabricated for the features of simple structure, wide material choices, and low cost [32, 33, 34, 35, 36, 37]. Series efforts have been made to develop fabric TENGs for harvesting mechanical energy induced from body motions to sustainably drive wearable electronics [34, 38]. Lee et al. reported an electrical response of a textile substrate-based TENG including nanostructured surface provided by Al nanoparticles and polydimethylsiloxane (PDMS) [32]. The obtained TENG can power wearable electronics using low-frequency mechanical movements driven by human arm activity. Under the simple folding-releasing stage of an arm near 90o, the output voltage and current of 139 V and 39 μA are achieved, respectively.
To enhance the output performance, a highly stretchable 2D fabric was developed as a wearable TENG for harvesting footstep energy during walking to driven wearable electronic devices [39]. The fabric-structured TENG composes by Al wires and PDMS tubes with a high-aspect-ratio nanotextured surface with vertically aligned nanowires. It shows a stable high-output voltage and current of 40 V and 210 μA, corresponding to an instantaneous power output of 4 mW. The TENG also exhibits high robustness behavior even after 25% stretching, enough for use in smart clothing applications and other wearable electronics. Seung et al. reported a fully flexible, foldable nanopatterned wearable TENG with high power-generating performance and mechanical robustness [40]. Both a silver (Ag)-coated textile and PDMS nanopatterns based on ZnO nanorod arrays on a Ag-coated textile template are used as active triboelectric materials. A high voltage and current output with an average value of 170 V and 120 μA, respectively, are obtained from a four-layer-stacked wearable TNG under the compressive force of 10 kgf. Notably, there are no significant differences in the output voltages measured from the multilayer-stacked WTNG over 12,000 cycles, confirming the excellent mechanical durability of WTNGs. Without external power sources, the fabricated wearable TENG can drive the LEDs, LCD, and the keyless vehicle entry system, exihibting the potential applications in self-powered smart clothes, health care monitoring and self-powered wearable devices, and even personal electronics. Tian et al. demonstrated a high-performance double-layer-stacked triboelectric textile (DTET) for harvesting human motion energy [41]. Both the Ni-coated polyester conductive textile and the silicone rubber are adopted as effective triboelectric materials. A high output Voc of 540 V and an Isc of 140 μA can be obtained from the DTET with the size of 5 × 5 cm2, corresponding to a high peak surface power density of 0.892 mW/cm2 at a load resistance of 10 MΩ. The output peak signal of the DTET can be used as a trigger signal of a movement sensor to design movement monitoring equipment. With only the energy harvested from walking, running, or flapping, the DTET can directly light up 100 LEDs connected serially and drive portable electronics, such as competition timer, digital clock, and electronic calculator.
Owing to the high power density, stable cycle life, good safety, and potentials in integration into flexible wear, introducing supercapacitors as energy-storing devices into a fabric TENG show promising prospects. Pu et al. introduced a self-charging power textile for harvesting human motion energy. The self-charging power textile was fabricated by weaving the yarn supercapacitors together with a fabric TENG into an individual fabric [42]. Based on the integrated system, the motion-charging process is carried out by charging the yarn supercapacitors by the contact-separation motions between the TENG cloth and a common cotton cloth. The yarn supercapacitors and the fabric TENG endowed the excellent flexibility and weaveability of the self-charging power textile. Chen et al. developed a self-charging power textile, consisting of a fabric triboelectric nanogenerator and a woven supercapacitor, which can simultaneously harvest and store body motion energy to sustainably drive wearable electronics [43]. Utilizing traditional weaving craft, contact-separation mode and free-standing mode FTENG are designed and fabricated on a piece of textile by weaving the cotton, carbon, and PTFE wires. Combined with the energy-storing component, utilizing RuO2-coated carbon fiber and cotton threads, the obtained self-charging power textile can harvest energy from common daily activities such as running and walking to drive the wearable electronics, such as an electric watch.
For developing low-cost TENG, paper served as a supporting component for preparing TENG for the first time [44]. Paper-based TENGs represent an low-cost, light-weight, and environmentally friendly energy harvesting methodology. Nowadays, different types of paper-based TNEG have been designed and prepared for harvesting energy from human biomechanical movements [45]. Xia et al. proposed a X-shaped paper TENG formed from a ballpoint ink layer coated by painting with a commercial brush pen for harvesting mechanical energy from human walking [46]. In this design, paper served as both a component of the triboelectric pairs and a supporting component. When a brush pen is painted on the paper, the maximum values of current and voltage output can be achieved at 326 V, 45 μA, corresponding to a power density of 542.22 μW/cm2. The staked X-shaped paper TENG is proposed to increase the output performance and harvest the mechanical energy generated by motion of the human body, which can directly light up 101 blue high-power LEDs with a working voltage of 3.4 V.
Additionally, various efforts have been made to promote the development of TENGs for harvesting biomechanical energy based on external devices attached to the human body. In them, human skin-based TENGs are developed for converting biomechanical energy induced from human body itself into electronic energy. According to these series TENGs, human skin is used as one of the triboelectric materials with the single-electrode-mode. With the contact/separation between an area of human skin and a PDMS film, a Voc up to −1000 V, a short-circuit current density of 8 mA/m2, and the corresponding power density of 500 mW/m2 on a load of 100 MΩ were obtained from the skin-based TENG delivers, which could be used to directly drive tens of green light-emitting diodes [47]. Due to its fantastic features, skin-based TENGs are developed to transform physical parameters such as pressure, sliding, and other physiological variables into electronic signals, which exploit potential application. For realizing visual-image recognition, a self-powered brain-linked vision electronic-skin (e-skin) for mimicking retina is achieved from polypyrrole/polydimethysiloxane (ppy/PDMS) triboelectric-photodetecting pixel-addressable matrix [48]. The e-skin can directly transmit photodetecting signal into brain for participating in the vision perception and behavioral intervention. Besides visual-image recognitio, more functional sensors including sliding sensor [49], touch screen [50], pressing sensor [51], and motion sensors [52] are also deeply explored.
In order to satisfy the requirement of self-powered, highly stretchability, and transparency of triboelectric skins, different materials including silicone rubber [53], metal nanowire [54, 55], and conductive polymer [56] are widely studied. To introduce the characteristic of instilling self-healing and further enhance the performance of energy generation, stretch ability, transparency, and slime-based ionic conductors were first used as transparent current-collecting layers of TENG for harvesting mechanical [57]. The ionic-skin TENG consists of a silicone rubber layer with a thickness of 100 ± 10 μm, utilized as the triboelectrically negative material, a slime layer (a crosslinked poly(vinyl alcohol) gel) with a thickness of 1 mm that works as the ionic current collector, and a VHB tape with a thickness of 1 mm as the substrate (Figure 3a). Figure 3b shows the photograph of the real highly transparent ionic-skin TENG. As depicted in Figure 3c, the resulting ionic-skin TENG displays a transparency of 92% transmittance for visible light. The mechanism of the ionic-skin TENG is based on the single-electrode mode, wherein human skin and silicone rubber serve as frictional layer, respectively (Figure 3d). Figure 3e shows the digital photographs of the fabricated ionic-skin TENG suffering various mechanical deformations including uniaxial stretching up to 700% strain as well as folding and rolling. The produced slime exhibits high ionic conductivity due to the presence of positive (Na+) and negative ions (B(OH)4−), which is measured using electrochemical impedance spectroscopy (Figure 3f). Thanks for the series of design, the energy-harvesting performance of ionic-skin TENG is 12-fold higher than that of the silver-based electronic current collectors. Besides, fabricated ionic-skin TENG can recover its property even suffering 300 times of complete bifurcation, exhibiting an autonomously self-healing capacity.
(a) Schematic diagram of the IS-TENG. (b) Digital photo of the highly transparent IS-TENG. (c) Transmittance spectra of the slime (ionic conductor) and the IS-TENG with respect to a glass slide. (d) Schematic illustration of the working mechanism of the IS-TENG. (e) Digital photos of the IS-TENG under various mechanically deformed states such as axial strain up to 700%, rolled, and folded. (f) EIS measurement of the slime (ionic conductor) [57].
For versatile scavenging mechanical energy induced from arbitrary mechanical moving objects such as humans, a new mode of triboelectric nanogenerator is first demonstrated based on the sliding of a freestanding triboelectric-layer between two stationary electrodes on the same plane [58]. With two electrodes alternatively approached by the tribo-charges on the sliding layer, electricity is effectively generated due to electrostatic induction. To reduce the direct friction between triboelectric layers for energy loss, a linear grating-structured freestanding triboelectric-layer nanogenerator (GF-TENG), consisting of a freestanding triboelectric layer with grating segments and two interdigitated metal electrodes, was developed for high-efficiency harvesting vibration energy from human walking [59]. As shown in Figure 4a, 60 commercial LEDs (Nichia NSPG500DS) can be lighted up instantaneously with the motion of hand sliding under a slow speed and a small displacement. The GF-TENG can also havest energy from the monement of car for powering electronic components on the vehicle (Figure 4b). Four identical extension springs are used to suspend and anchore the triboelectric layer, as displayed in Figure 4c. Owing to the structure, the obtained GF-TENG can scavenge the mechanical energy from people’s walking motion when it is bonded to human legs (Figure 4d). An excellent stability and maxmiun energy conversion efficiency of 85% are realized at a matched load resistance of 88 MU under the noncontact mode (Figure 4e).
Applications of GF-TENG for harvesting a wide range of mechanical energy. (a) Harvesting energy from sliding of a human hand. (b) Harvesting energy from acceleration or deceleration of a remote control car. (c) Device structure for noncontact GF-TENG. (d) Harvesting energy from people walking by noncontact GF-TENG and the real-time measurement of Isc. (e) Total conversion efficiency of noncontact GF-TENG for harvesting slight vibration under different load resistances [59].
Vibration, as a type of common mechanical phenomena, ubiquitously exists in ambient environment in a variety of forms and wide range of scales. Therefore, vibration can be regarded as a sustainable source of power for driving small electronics if it can be effectively collected. Contributing to the distinctive working mechanism, TENG has been proposed recently and proved a promising approach for scavenging mechanical energy from vibration, especially in the low-frequency range. To date, a variety of device and machine-based TENGs have been applied to convert mechanical energy induced from vibration into electric energy.
Chen et al. presented a harmonic-resonator-based TENG as a sustainable power source and an active vibration sensor [60]. The harmonic-resonator-based TENG, held a multilayer structure consisting of aluminum with nanoporous surface as contact electrode and nanowire-modified PTFE as frictional layer, is the first TENG that can harness random and tiny ambient vibration. It can effectively respond to vibration frequencies ranging from 2 to 200 Hz with a considerably wide working bandwidth of 13.4 Hz.
The above-mentioned harmonic resonator-based TENG with a simple structure design can only scavenge vibration energy from a single direction. In practice, vibrations in living environments generally display multiple motion directions. With this in mind, a three-dimensional TENG (3D-TENG) was designed for harvesting random vibration energy from multiple directions [61]. The 3D-TENG has a multilayer structure with circular acrylic as supporting substrates, as shown schematically in Figure 5a. The cylindroid core of the 3D-TENG lies at the center of the acrylic substrate with a bottom diameter of 3 cm. On the top of the core, an iron mass is mobile and suspended by three identical springs with an included angle of 120° between each other. The designed structural symmetry ensures that the whole system has a constant resonant frequency in arbitrary in-plane directions. A layer of PTFE film as one contact surface is adhered onto the bottom side of circular iron mass with a deposited copper thin film as the back electrode. Attached to the bottom acrylic substrate, an aluminum thin film with nanopore modification plays dual roles as a contact electrode and the other contact surface. The scanning electron microscopy (SEM) images of aluminum nanopores can be observed in Figure 5b. A photograph of the real 3D-TENG device is shown in Figure 5c. Owing to the conical-shaped spring structure, the 3D-TENG can operate in a hybridization mode combining with the vertical contact-separation mode and the in-plane sliding mode, which is beneficial to harvest random vibrational energy in multiple directions over a wide bandwidth.
3D triboelectric nanogenerator: (a) schematic of a 3D-TENG, (b) SEM image of nanopores on an aluminum electrode, and (c) a photograph of the fabricated 3D-TENG [61].
For better sensitivity response to external disturbance, a suspended 3D spiral structure was integrated with a TENG for energy harvesting and sensor applications [62]. Operating in the vertical contact-separation mode, the desired TENG with unstable mechanical structure can balance itself when be oscillated, which makes it a superior choice for vibration energy harvesting and vibration detection. The newly designed TENG has a wide working bandwidth of 30 Hz in low-frequency range with a maximum output power density of 2.76 W/m2 on a load of 6 MΩ.
Beyond that, a spherical three-dimensional TENG (3D-TENG) with a single electrode, consisting of an outer transparent shell and an inner polyfluoroalkoxy (PFA) ball, was designed for scavenging ambient vibration energy in full space [63]. By working at a hybridization of both the contact-separation mode and the sliding mode, the 3D-TENG can deliver a maximal output voltage of 57 V, a maximal output current of 2.3 μA, and a corresponding output power of 128 μW on a load of 100 MΩ, which can be used to directly drive tens of green light-emitting diodes. Moreover, the TENG is utilized to design the self-powered acceleration sensor with a detection sensitivity of 15.56 V/g.
Besides multiple motion directions, ambient vibrations generally exhibit a wide spectrum of frequency distribution. To solve this problem, a TENG with a wavy-structured Cu-Kapton-Cu sandwiched between two flat nanostructured PTFE films was designed for broadband vibration energy harvesting [64]. The core of the wavy structure is composed of a set of metal rods (with a diameter of 1/4 in.), as shown in Figure 6a. PTFE films are processed with inductively coupled plasma (ICP) etching to produce the nanostructures shown in Figure 6b, which would largely enhance contact electrification. The device structure is schematically shown in Figure 6c, accompanied by a magnified schematic in Figure 6d and a picture of a real device in Figure 6e. This structure design allows the TENG to be self-restorable after impact without the use of extra springs and converts direct impact into lateral sliding. Based on the wavy structure, the TENG can harvest vibrational energy from 5 to 500 Hz, and the generator’s resonance frequency was determined to be ∼100 Hz at a broad full width at half-maximum of over 100 Hz, producing a Voc of up to 72 V, an Isc of up to 32 μA, and a peak power density of 0.4 W/m2.
(a) Schematic of the method to fabricate wavy Kapton films. (b) SEM image of the ICP-processed PTFE film surface. (c) Schematic of the device structure. (d) Magnified schematic of the device, showing that the wavy core is in periodical contact with the nanostructures on the PTFE films. (e) Photograph of an as-fabricated TENG device before packaging [64].
After that, an elastic multiunit TENG was also realized to efficiently harvest low-frequency vibration energy over a wide frequency range [65]. The obtained TENG can provide a maximum instantaneous output power density of 102 W/m3 at as low as 7 Hz and maintain its stable current outputs over a wide frequency range (from 5 to 25 Hz). Besides, it can act as an active vibration sensor to monitor the running status of equipment. Moreover, by combining the TENG with a power management unit to form a self-charging power unit, the vibration energy harvesting from ambient environment, such as an operating machine and running bicycle, can sustain power electronics such as thermometers, humidity sensors, speedometers, and a micro-meteorological instrument.
For improving the lower output current, a multi-layered stacked TENG was reported as a cost-effective, simple, and robust approach for harvesting ambient vibration energy [66]. The 3D-TENG has a multilayered structure with acrylic as supporting substrates, as schematically shown in Figure 7a. A photograph of an as-fabricated TENG and SEM image of the PTFE nanowires is shown in Figure 7b-c. With superior synchronization, the 3D-TENG produces a short-circuit current as high as 1.14 mA and an Voc up to 303 V with a remarkable peak power density of 104.6 W/m2. As a direct power source, it is capable of simultaneously lighting up 20 spot lights as well as a white G16 globe light.
Three-dimensional triboelectric nanogenerator. (a) Schematic of a 3D-TENG. (b) SEM image of nanopores on aluminum electrode. (c) A photograph of the as-fabricated 3D-TENG [66].
To reduce the direct friction between triboelectric layers, a liquid-metal-based TENG (LM-TENG) was developed for high-efficiency vibration energy harvesting [67]. Owing to an intimate contact between the liquid metal and the polymer dielectric layer, the direct friction between triboelectric layers for energy loss is effectively reduced, resulting in high effective contact, shape adaptability, and low friction coefficient with solid. Therefore, the LM-TENG exhibits an output charge density of 430 μC/m2, which is four to five times higher than that in the case if the electrode is solid film.
On the other hand, soft electrode can effectively increase the contact intimacy between the triboelectric layers [68]. Xu et al. reported a novel soft and robust TENG made of a silicone rubber-spring helical structure with nanocomposite-based elastomeric electrodes for harvesting arbitrary directional vibration energy and self-powered vibration sensing [69]. The schematic diagram and a photo of the S-TENG are shown in Figure 8a,c, respectively. As displayed, the TENG exhibits a helical structure based on the integration of elastomer and spring. A mixing well silicone rubber and carbon nanofiber, which can be stretched up to the strain of 133%, serves as the elastomeric electrode (Figure 8b). The working mechanisms of the S-TENG under vertical and horizontal vibration are shown in Figure 8d,e, respectively. Under external vertical vibration excitation, the distance between a helical structure’s adjacent surfaces changes, forming a contact-separation mode TENG. Under horizontal vibration excitation, the S-TENG’s helical structure’s adjacent surfaces can contact on one side and separate on the other side, also forming a contact-separation mode TENG. Under the resonant states of the S-TENG, its peak power density is found to be 240 and 45 mW/m2 with an external load of 10 MΩ and an acceleration amplitude of 23 m/s2. Additionally, the dependence of the S-TENG’s output signal on the ambient excitation can be used as a prime self-powered active vibration sensor that can be applied to monitor the acceleration and frequency of the ambient excitation.
(a) The device schematic of the S-TENG. Note that the gray silicone rubber layer containing a spring forms a base on which other layers can be built, and the black silicone rubber layer along with the electrode layer forms a contact-separation pair. Both top and bottom electrodes are made of carbon nanofiber-mixed silicone rubber. (b) SEM image of the carbon nanofiber for preparing the elastomeric electrode. (c) Photo of the as-prepared S-TENG. Working mechanisms of the S-TENG under (d) vertical vibration excitation and (e) horizontal vibration excitation [69].
Water energy deriving from rainwater, ocean waves, and waterfalls has been regarded as an alternative renewable energy resource source without polluting the environment. Energy harvesting from water has been further reinforced due to the abundant reserves and little dependence on environmental conditions. Through decades of exploration, a variety of wave energy converting devices and machines based on TENG has been invented to harvesting energy from water.
Liquid-solid-mode TENGs for harvesting liquid-wave energy have drawn much attention for the features of relatively stable output and durability [70, 71, 72]. For the liquid–solid-mode TENG, contact separation is the main representative strategies applied to scavenge water energy [73, 74]. A hydrophobic surface on water-solid TENGs is beneficial for inducing separation at the interface of liquid and solid [75]. Based on this, Zhu et al. reported a liquid-solid electrification-enabled TENG based on a FEP thin film for harvesting energy from a variety of water motions [76]. Owing to the modification of aligned nanowires, the thin film with a property of hydrophobicity can increase the contact area at the liquid-solid interface, leading to enhanced surface charging density and thus electric output at an efficiency of 7.7%. Due to the creation of continuous contact separation between water and the solid surface, a cylindrical water TENG was designed by using a hydrophilic surface along with the hydrophobic surface to control the water flow inside a packaged system for enhanced electrostatic induction [77].
Generally, an effective way of integrating a number of electrodes together to make them area scalable is helpful for promoting output power density. On the other hand, the electric power is highly affected by nanostructures at the solid/liquid interface. According to this, a flexible thin-film TENG was reported for harvesting kinetic wave energy [78]. Because of the integration method that use an array of surface-mounted bridge rectifiers to connect multiple parallel electrode together, the induced current between any pair of electrodes can be constructively added up, leading to a significant enhancement in output power and realizing area-scalable integration of electrode arrays. However, the thin-film TENG is only applicable to regular water waves that interact with the TENG through a linear water level. For improving the adaptive means of harvesting water energy, a networked integrated TENG was fabricated for harvesting energy from interfacing interactions with water waves of various types [79]. Additionally, interdigital electrode-based TENGs were designed in the contact-sliding mode for the harvesting of triboelectric energy from water [80], resulting in a higher output performance than those of one- and two-electrode-based TENGs.
Beside liquid-solid-mode TENGs, other structure TENGs were designed for harvesting water energy generating by flowing water, such as multi-layered disk structure [81], floating buoy structure [82], radial-arrayed rotary structure [10], and so on. Although many water-based TENGs have been fabricated, there is a lack of effort in realizing TENG harvesting water energy directly on the fabric/textile, due to the poor water resistance of the fabrics related to their intrinsic hydrophilicity that can be ascribed to their abundant hydrophilic groups, and the strong adsorption capacity because of their large specific surface area [83]. For realizing the practical wearable device harvesting energy from water flow, Xiong et al. reported a wearable fabric-based WTEG with additional self-cleaning and antifouling performance for the first time [83]. This is realized with the preparation of hydrophobic cellulose oleoyl ester nanoparticles by a nontoxic esterification method and nanoprecipitation technology based on the microcrystalline cellulose. In this study, PET fabric-based WTEG can generate the output power density of 0.14 W/m2 at a load resistance of 100 MΩ.
There are two parts to water wave energy including the electrostatic energy from the contact electrification between water and surrounding media and the mechanical impact energy. For simultaneously scavenging both the energy from water, some works have been well done. For example, Su et al. presented an all-in-one hybridized TENG based on the conjunction of liquid-solid interfacial electrification enabled TENG and impact-TENG for harvesting water wave energy and as a self-powered distress signal emitter [84]; Lin et al. designed a fully integrated TENG for harvesting water energy and as a self-powered ethanol nanosensor, which contained a water-TENG unit to collect the electrostatic energy of water and a contact-TENG unit to collect the mechanical/kinetic energy of water [85]; Cheng et al. developed a water wheel hybridized TENG, composed of a water-TENG part and a disk-TENG part, for simultaneously harvesting the two types of energies from the tap water flowing from a household faucet [86]. Based on a unique structure design, the hybridized TENGs are shown to be suitable for harvesting multiple types of energies from water.
During a working process, the acting surfaces of the above mentioned TENGs will be exposed to ambient atmosphere, which will limit their applications in some cases. The interface electrification was seriously affected by humidity, causing a quick decline of the surface charge density [87]. In order to improve the performance of TENGs under harsh conditions with the presence of water, fully enclosed or packaged TENGs should be developed for tolerating the environment. So far, different designs were developed based on packaged TENG such as wavy-shaped models [88], fully packaged contact-separation configurations [89, 90, 91], and rolling spherical structure [92]. Wang et al. designed a freestanding, fully enclosed TENG that encloses a rolling ball inside a rocking spherical shell for harvesting low-frequency water wave energy [93]. An image of the fabricated TENG floating on water is shown in Figure 9a. Figure 9b shows the schematic diagram of the freestanding structured design that consists of one rolling ball and two stationary electrodes. To enhance the electric output of the TENG, nanowire arrays are fabricated on the surface of the Kapton film (Figure 9c) that provides a large contact area to generate more triboelectric charges on the surface. Through the optimization of materials and structural parameters, a spherical TENG of 6 cm in diameter actuated by water waves can provide a peak current of 1 μA over a wide load range from a short-circuit condition to 10 GΩ, with an instantaneous output power of up to 10 mW. This rolling-structured TENG is extremely lightweight, has a simple structure, and is capable of rocking on or in water to harvest wave energy. Additionally, rolling spherical TENGs and coupled TENG networks have been demonstrated to harness the water wave energy because of the advantages of light-weight, small-resistance under the water wave motions, and easy to be integrated [94, 95].
Device structure, basic operations of the freestanding-triboelectric-layer-based nanogenerator (RF-TENG) with a rolling Nylon ball enclosed. (a) Photograph of a rocking nanogenerator floating on water. (b) Schematic diagrams of freestanding-structured design. (c) SEM image of nanorod structure on the Kapton surface [93].
For enhancing the output current and enlarging the practical applications of packaged TENG, introducing a spring structure into the TENG can store the kinetic energy from water impact and later convert into electric power via residual vibrations [96]. Combining the advantages of spring structure and integrated multilayered structure, Xiao et al. demonstrated a kind of spherical TENG with spring-assisted multilayered structure for harvesting water wave energy [97]. The introduction of spring structure enhances the output performance of the spherical TENG by transforming low-frequency water wave motions into high-frequency vibrations, while the multilayered structure increases the space utilization, leading to a higher output of a spherical unit. The structure of spherical TENG designed with spring-assisted multilayered structure floating on water surface is schematically shown in Figure 10a. Figure 10b displays a photograph of as-fabricated spherical TENG device, and the inset shows the photograph of the device in the water waves. The working principle of each TENG unit is demonstrated in Figure 10c. The periodic movement of the mass block under the triggering of water waves, which leads to the contact and separation between two surfaces of the top aluminum foil and FEP film, produces periodic electric output signals. Owing to its unique structure, the output current of one spherical TENG unit can reach 120 μA, which is two orders of magnitude larger than that of previous rolling spherical TENG, and a maximum output power up to 7.96 mW is realized as triggered by the water waves.
(a) Schematic diagram of the spherical TENG with spring-assisted multilayered structure floating on water, and schematic representation enlarged structure for the zigzag multilayered TENG with five basic units. (b) Photographs of the as-fabricated TENG device. (c) Working principle of each TENG unit of the spherical TENG [97].
Wind energy can be a renewable energy sources for energy harvesting on account of widespread and absolute abundance. The practical application of traditional wind power in our daily life is largely limited by the extra-large volume, high cost of installation, noise and geographical environment. In this regard, TENG is one of the most alternative wind energy conversion strategies on accord of its small scale, low cost, simple fabrication routes, and portability [98]. In order to harvest wind energy, flutter-driven structure [99, 100] and rotational structure [101, 102] are the two main methods for preparing wind-driven TENG.
Flutter-driven structure TENG for harvesting wind energy was realized by Yang et al. for the first time [103]. As displayed in Figure 11, the TNEG is composed of two layers of Al foils and a FEP film laying in midair of a cuboid acrylic tube. The Al foils act as both triboelectric surfaces and electrodes, respectively. The FEP film is fixed one side, leaving the other side freestanding. The FEP film will vibrate periodically to contact the two Al foils inducing from wind, resulting in an output signal in an external circuit. Output voltage and current about 100 V and 1.6 μA are achieved, and a corresponding output power of 0.16 mW is realized under a loading resistance of 100 MΩ.
(a and b) The structure and photograph of the first reported flutter-driven mode WD-TENG [103].
Although single-side fixed-based TENG exhibits good performance for scavenging wind energy, the stability of output performance is a challenge because of the arbitrary fluttering of the FEP film. For solving the problem, an elasto-aerodynamics-driven TENG, consisting of a Kapton film with two Cu electrodes fixed on two ends in an acrylic fluid channel, was reported for scavenging air-flow energy [104], where the flutter effect of Cu electrodes was induced to contact two triboelectric materials of the PTFE films and the Kapton film to realize the output performance of the device.
Based on flutter-driven structure, many other efforts have been made to enhance the performance of TENG through optimizing the structure or the morphologies of material surface design. A lightweight and freestanding flag-type woven TENG, consisting of conductive belts of Ni-coated polyester textiles and Kapton film-sandwiched Cu belts, was designed for scavenging high-altitude wind energy from arbitrary directions [105]. When wind fluttering is applied in each woven unit, wind energy converts into electrical energy induced by the interlaced interactions between the Kapton film and a conductive cloth under wind-introduced fluttering of the flag. Besides, a flutter-driven TENG, consisting of a flag and a counter plate arranged in parallel with interwoven microstructure, was fabricated for harvesting wind energy based on contact electrification caused by the self-sustained oscillation of flags [106]. As shown inFigure 12, a flexible flag and a rigid plate are arranged in face to face in order to prepare a wind-driven energy-harvesting system using fluttering behavior. Owing to the design, interaction between them can lead to a rapid periodic contact and separation, and that movement can be successfully employed for converting the kinetic energy of the wind into electrical energy.
Schematic diagrams of a wind tunnel and the structural design of a flutter-driven triboelectric generator including surface characteristics of (i) a highly flexible flag, (ii) a counter plate, and (iii) the fabrication of the counter plate [106].
For rotational structure, wind cup is a main method for scavenging wind energy. Deriving from the conventional wind cup structure, a rotary structured TENG was presented for scavenging weak wind energy in our environment [101]. As illustrated in Figure 13, the rotary structured TENG is composed of a framework, a shaft, a flexible rotor blade, and two stators. When wind flowing is utilized in the rotation of the shaft and the flexible rotor, a flexible and soft polyester (PET) rotor blade with a PTFE film adhered at the end will periodically sweep across the Al electrodes. In this process, a consecutive face-to-face contact and separation between PTFE film and Al electrodes are produced, regarding as the basic process for generating electricity.
The schematic diagram showing the structural design of the R-TENG, with the enlarged picture showing the nanowire-like structures on the surface of PTFE [101].
Aiming to improve the robustness and lifetime of wind-driven TENG, a freestanding disk-based TENG was fabricated to harvest wind energy through automatic transition between contact and noncontact working states [102]. The major structure of the disk-based TENG includes two parts: the rotational inner acrylic barrel that connects with the freestanding rotor of the disk TENG and the stationary outer barrel that connects with the stator of the TENG. Two bearings are used to link the two parts and enable the relative rotation. Benefiting from the unique structural design, the TENG can work in the noncontact state with minimum surface wear and also transit into contact state intermittently to maintain high triboelectric charge density.
Besides serving as a power source for running some electric devices, wind-driven TENG is also expected to be utilized as various self-power systems by integrating with other electric devices. Chen et al. introduced the first self-powered air cleaning system focusing on sulfur dioxide (SO2) and dust removal as driven by the electricity generated by natural wind, with the use of rotating TENG [107]. Another common wind-driven TENG-based self-power system is the wind speed sensor. Kim et al. prepared wind-driven TENG based on rolling motion of beads for harvesting wind energy as a self-power wind speed sensor [108]. Wen et al. fabricated a blow-driven TENG, acting as an active alcohol breath analyzer, which is featured as high detection gas response of ~34 under an optimized sensor working temperature, fast response time of 11 s as well as a fast recovery of 20 s [109].
Aiming to simultaneously harvesting multitypes of energies from various sources, TENG has been hybridized with various other energy harvester strategies from the environment. It is well known that solar irradiance is another clean and renewable energy sources. To develop a practical method to simultaneously scavenge solar and mechanical energies, the concept of a hybridized energy harvester integrating TENG and solar cell was presented [110, 111]. Based on lightweight and low cost, fabric-based material is served as the ideal strategy utilized to fabricate these kinds of hybrid generator [112]. Chen et al. presented a foldable and sustainable power source by fabricating an all-solid hybrid power textile with economically viable materials and scalable fabrication technologies [34]. The wearable all-solid hybrid power textile has a single-layer interlaced structure, which is a mixture of two polymer-wire-based energy harvesters, including both a fabric TENG to convert mechanical movement into electricity and a photovoltaic textile to gather power from ambient sunlight, as schematically illustrated in Figure 14a,b, respectively. An enlarged view of the interlaced structure is presented for both the fabric TENG (Figure 14c) and photovoltaic textile (Figure 14d). Under ambient sunlight with mechanical excitation, like human motion, car movement, and wind blowing, the as-woven textile was capable of generating sufficient power for various practical applications, including charging a 2 mF commercial capacitor up to 2 V in 1 min, continuously driving an electronic watch, directly charging a cell phone, and driving the water splitting reactions.
Structural design of the hybrid power textile. (a and b) Schematic illustration of the hybrid power textile, which is a mixture of two textile-based all-solid energy harvesters: fabric TENG (a) and photovoltaic textile(b). Enlarged view of the interlaced structure of both the fabric TENG (c) and the photovoltaic textile (d) [112].
Aiming to largely collect the energy from mechanical motions, an integrated TENG and an electromagnetic generator (EMG) for concurrently harvesting mechanical energy are a promising way. By integrating two kinds of mechanical energy harvesting units, the weight of the EMG can be reduced and the total output power can be increased to expand the potential applications [113, 114, 115, 116, 117]. In them, rotational structure is the typical strategy utilized to simultaneously convert mechanical energy into electrical energy from one rotating motion. By integrating an EMG and a TENG, a rotation-based hybrid generator is first fabricated to generate a high output that can sustainably drive a commercial globe light with an intensity of illumination up to 1700 lx [118]. As illustrated in Figure 15a, the main structure of the hybrid generator consists of an EMG including the top and bottom layers (1 and 5) and a TENG including the middle layers (2, 3, and 4) with the planar structures, where the rotator and the stator are composed of layers 1 and2 and layers 3–5, respectively. The corresponding photographs of each layer are displayed in Figure 15b. Based on the relative rotation between the rotator and the stator, the hybrid generator simultaneously collects biomechanical energy from human hand-induced rotating motions. In order to compare the two generators with each other systematically, Guo et al. fabricated a water-proof triboelectric-electromagnetic hybrid generator, including a fully enclosed packaging of TENG achieved by the interactions between pairs of magnets as the noncontact mechanical transmission forces [119]. Systematic study of the influences of the designed parameters, including the segment’s number of the TENG, the rotation speed, and the arrangement of the coils, on the electrical outputs of the WPHG were performed experimentally. The result demonstrated that TENG can produce a stable voltage to power commercial electronic device even under a low rotation speed compared with EMG.
(a) Schematic diagram of the designed hybridized nanogenerator. (b) Photographs of the hybridized nanogenerator [118].
Besides the above mentioned, other strategies have been applied to intergrate with TENG for collecting other types of energies. Lee et al. presented a flexible hybrid cell to simultaneously harvest thermal and mechanical energies from skin temperature and body motion [120]. For fabricating the hybrid cell, ZnO nanowires are grown on the sputtered-coated seed layer surface of a thin Al substrate. And then, a 2-μm thick poly(methyl methacrylate) (PMMA) layer is coated on the surface of the as-grown ZnO nanowires, and a thin Al substrate is stacked on the PMMA-coated layer to be used as the top electrode. Owing to the structure design, the hybrid cell can simultaneously harvest thermal and mechanical energies so that the energy resources can be effectively and complementarily utilized for power sensor network and micro/nanosystems. Addtionally, combining the TENG with piezoelectric nanogenerator (PENG) is a alternative manner for concurrently collecting mechnical energy. Guo et al. developed an all-fiber hybrid piezoelectric-enhanced TENG that fabricated by electrospinning silk fibroin and poly(vinylidene fluoride) (PVDF) nanofibers on conductive fabrics [121]. Contributing to the large specific surface area of nanofibers and the extraordinary ability of silk fibroin to donate electrons in triboelectrification, the hybrid nanogenerator exhibited an outstanding electrical performance, with a power density of 310 μW/cm2, so that it can be regarded as a self-powered wearable microsystem for falling-down detection and timely remote alarm.
In order to seek an intelligent life, trillions of electronic device for the Internet of Things are requisite with higher personal, portable, complex, multifunctional, and smart. Aiming to maintain the normal working status of these small electronic devices sustainably, an effective technology to harvest small-scale energy from renewable natural resources is highly desirable. Given the collection characteristics of simple structure, flexibility, low cost, light weight, high efficiency, high power density, and environmental friendly, the invention of TENG is served as an promising small-scale energy harvester who can convert mechanical motions into electricity, even at low frequency. Futhermore, TENGs can also be utilized to transform physical parameters such as pressure, sliding, and other physiological variables into electronic signals, which directly reflected the information of mechanical stimuli and environmental conditions without an external power source. By extensively investigating, TENG can effectively harvest mechanical energy in almost any form based on the four fundamental modes, and thus can regard as the self-powered sensors for a wide application under diffident mechanical triggerings. In the future, the continuous endeavors on TENGs will lagerly enhance their output performance. Based on deeply investigating the fundamental menchanism of triboelectrification, it is possible to realize the ultrahigh charge density of TENG via material modification, structure design, or condition optimization. Besides the output perfoermance, the durability and output stability is the other bottleneck that limited the application of TENG, especially comparing with the traditional generator. It might overcome through fabricating new materials or coupling modes of operations. Based on the above discussion and analysis, it can be anticipated that TENG will soon become an ideal small-scall energy haverter with broad application as self-powered sensors through the world wide efforts.
The authors like to thank the financial supports from the National Key R & D Project from Minister of Science and Technology (2016YFA0202704), Beijing Municipal Science & Technology Commission (Z171100000317001, Z171100002017017, Y3993113DF), and National Natural Science Foundation of China (Grant No. 61774016, 21773009, 51432005, 5151101243, 51561145021).
There is no conflict of interest.
If your research is financed through any of the below-mentioned funders, please consult their Open Access policies or grant ‘terms and conditions’ to explore ways to cover your publication costs (also accessible by clicking on the link in their title).
\n\nIMPORTANT: You must be a member or grantee of the listed funders in order to apply for their Open Access publication funds. Do not attempt to contact the funders if this is not the case.
",metaTitle:"List of Funders by Country",metaDescription:"If your research is financed through any of the below-mentioned funders, please consult their Open Access policies or grant ‘terms and conditions’ to explore ways to cover your publication costs (also accessible by clicking on the link in their title).",metaKeywords:null,canonicalURL:"/page/open-access-funding-funders-list",contentRaw:'[{"type":"htmlEditorComponent","content":"Book Chapters and Monographs
\\n\\nMonographs Only
\\n\\nBook Chapters and Monographs
\\n\\n\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\nMonographs Only
\\n\\nLITHUANIA
\\n\\nBook Chapters and Monographs
\\n\\n\\n\\nBook Chapters and Monographs
\\n\\n\\n\\nBook Chapters and Monographs
\\n\\n\\n\\nSWITZERLAND
\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\\n\\n\\n\\nBook Chapters and Monographs
\\n\\nBook Chapters and Monographs
\n\nMonographs Only
\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\nBook Chapters and Monographs
\n\nBook Chapters and Monographs
\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\nBook Chapters and Monographs
\n\n\n\nMonographs Only
\n\n\n\nLITHUANIA
\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\n\n\nSWITZERLAND
\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\n\n\nBook Chapters and Monographs
\n\n