Open access peer-reviewed chapter

Microwave Antennas Suggested for Biomedical Implantation

Written By

Kasturi Sudam Patil and Elizabeth Rufus

Submitted: July 7th, 2021 Reviewed: October 4th, 2021 Published: January 18th, 2022

DOI: 10.5772/intechopen.101060

From the Edited Volume

Antenna Systems

Edited by Hussain Al-Rizzo and Said Abushamleh

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Abstract

In the twenty-first century, there is an enormous development in various areas: microwave sensors have played an important role in medical devices, because of population growth and public awareness of the health of medical devices, they have become an ever-increasing technology. Microwave antenna sensors can be used to monitor human body temperature, implantable defibrillators, pacemakers, continuous glucose monitoring, heart failure detection, and so on. Antennas are also used as flexible sensors to monitor physiological parameters. Therefore, microwave sensors are used for wireless communication in various biomedical applications. The design of such antennas has gained considerable attention for dealing with issues such as miniaturization, biocompatibility, patient safety, improvement in communication quality, etc. The objective of this paper is to prove an overview of the requirements, design steps, and testing of a microwave antenna used in biomedical implantation. In this chapter, various antennas used in medical applications are described in detail. Also, antenna designing and testing requirements are discussed.

Keywords

  • implantable antennas
  • dual-band antennas
  • sensors
  • vivo test

1. Introduction

In latest years, microwave antennas have performed an important role in implantable biomedical devices. Millions of people around the world improved and saved their lives with the help of implants [1]. Implantable antennas play a role in creating a simulation environment, checking results, and fulfilling diagnostic purposes. With population growth and health awareness, people are more concerned about their health. Implantable medical devices (IMD) play an important role now a days. It is used to continuous monitoring of human body temperature [2], implantable cardioverter defibrillators and pacemakers [3], for continuous glucose monitoring [4], to detect heart failure [5], rectenna [6], and so on. In IMD an antenna is one of the essential parts. To design biocompatible antennas according to parameters, consider the required size, shape, miniaturization, impedance matching, biocompatibility, patient safety, and low power consumption [7, 8].

In the twenty-first century flexible electronics developing towards bio-integrated electronics for curvilinear biological skin, tissue, and organs considering patient’s safety [9]. Diagnosis and treatment are application areas of antenna, diagnosis can be done with help of magnetic resonance imaging (MRI), biomedical telemetry, and wireless capsule endoscopy [10]. Integrated implantable antenna plays important role in bi-directional communication for controlling and monitoring external equipment. The implantable antenna must be biocompatible, human tissues are conductive and it can be short circuit while coming into contact with metallization [11].

These are operated in very low frequencies such as medical implants communication system (MICS) band (402–405GHz) & Industrial, Scientific and Medical (ISM) bands (2.4–2.4835GHz) [12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]. In 1999, Federal Communications Commission (FCC) decided the frequency range of Medical Implant Communications Service (MICS) operating on frequency range 402–405 MHz. It consists of a low-power, high-speed, non-voice transmission that is useful in the manufacture of implantable medical devices [24]. The design of an implantable antenna is challenging due to biocompatibility issues miniaturization, loss of transmission path in the human body, safety issues, and so on.

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2. Different research areas for an antenna in biomedical application

Biomedical telemetry allows the measurement of physiological signals at some distance, these signals would be wired or wireless communication technologies. It helps to transmit and receive the data in a certain distance range. One of the developments in this field is an IMD. IMD consists of an antenna, electronic circuit, battery, and sensors. The antenna is built-in, it helps to transmit the signal from the human body to the exterior device. For this purpose following types of antennas are preferred.

2.1 Dual-band implantable antennas

The medical industry is continuously developing efficient and advanced systems that are suitable for the human body. In previous years, the ISM band was mainly used for antenna design [25], but the United States Federal Communications Commission (FCC) and the European Radio-communications Committee (ERC) allocated a frequency for biomedical telemetry [24, 26]. Communication between implants and the external unit is easy with the MICS band and ISM band used to send the awake signal to an external unit. MICS band is similarly intended for data communication, the ISM band is wilful for startup signals.

To design dual-band, implantable antennas is a shift between sleep and wake-up mode for conserving energy and increasing the lifetime of antennas. The dual-mode operation generally improves the lifetime of the battery [27]. The advantage of a differentially fed dual-band implantable antenna can be connected easily with differential circuits, useful to help eliminate loss introduced by baluns and matching circuits [28, 29]. From the following Table 1, we can observe that Differential feed antenna is generally operated on two nearly frequencies/frequency bands such as 433.9 and 542.4 MHz [28, 34] and MICS (402–405 MHz) and ISM (2.4–2.48 GHz) [35, 36, 38]. Also dual-band antennas operated on two frequency bands such as MICS (402–405 MHz) and ISM (2.4–2.48 GHz) [27, 29, 33, 37, 40] 1.4 and 2.4GHz [39].

Ref.Title and year of publicationFrequency bandsAntenna typeAntenna dimensionsApplication
DimensionSubstrateεrThickness
[27]Characterization and testing of skin mimicking material for implantable antennas operating at ISM band (2.4–2.48GHz) (2008)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Dual band22.5 × 22.5 × 2.5 mmRogers RO321010.20.635 mmGlucose monitoring
[30]Dual-band microstrip patch antenna based on the short-circuited ring and spiral resonators for implantable medical devices (2010)MICS (402–405 MHz) And ISM (2.4–2.48 GHz).Dual band micro strip patch antenna1375.4 mm3ARLON100010.21.27 mmMedical application
[28]Differentially fed dual-band implantable antenna for biomedical applications (2012)433.9and 542.4 MHzDifferential feed dual band antenna27 × 14 × 1.27 mmRogers 601010.20.635 mmNeural signal recording
[29]Compact dual-band antenna for implantable devices (2012)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Dual band antenna16.5 × 16.5 × 2.54 mmRogers301010.21.37 mmMedical application
[31]Dual-band implantable antenna with open-end slots on ground (2013)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Dual band antenna19 × 19.4 × 1.27 mmRogers301010.21.27 mmBiomedical telemetry application
[32]A broadband implantable and a dual-band on-body repeater antenna: design and transmission performance (2014)Medradio 401–406 MHz & ISM (2.4–2.48GHz)Dual band
  1. Broad band implantable antenna

  2. Dual–Band On–Body Repeater Antenna

  1. 3.99mm3

  2. 6720mm3

  1. Roger RO 3210

  2. FR4

  1. 10.2

  2. 4.4

  1. 0.635 mm

  2. 1.6 mm

The human trunk
[33]Miniaturized dual-band implantable antenna for wireless biotelemetry (2014MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Dual band antenna10.2 × 10.2 × 0.675 mmRogers301010.20.635 mmBiomedical applications especially human head or human arm implantable wireless communication
[34]Design and in vitro test of a differentially fed dual-band implantable antenna operating at MICS and ISM bands (2014)433.9and 542.4 MHzDifferential feed dual band antenna13.4 × 16 × 0.835 mmRogers RO 321010.20.635 mmWireless medical telemetry services
[35]A novel differentially fed compact dual-band implantable antenna for biotelemetry application (2015)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Differential feed dual band antenna22 × 23 × 1.27 mmRoger 301010.20.635 mmNear field biotelemetry
[36]Miniaturized differentially fed dual-band implantable antenna: design, realization, and in vitro test (2015)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Differential feed dual band antenna27 × 9 × 1.27 mmRoger 301010.20.635 mmBiomedical application
[37]Miniaturized dual-band implantable antenna for wireless biotelemetry (2016)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Dual band8.75 × 7.2 × 0.5 mmRogers 601010.20.25 mmWireless telemetry
[38]Differentially fed compact dual-band implantable antenna for biotelemetry (2016)MICS (402–405 MHz) and ISM (2.4–2.48 GHz).Differential feed dual band antenna22 × 23 × 1.27 mmRoger301010.20.635 mmBiotelemetry
[39]Dual-band implantable antenna with circular polarization property for ingestible capsule application (2017)1.4 and 2.4GHzDual bandRogers 301010.20.635 mmIngestible capsule application
[40]Dual-band electrically coupled loop antenna for implant applications (2017)(2.4 and 4.8 GHz).Dual band
  1. FR4

  2. RO4003

  1. 4

  2. 3.37

  1. 1.6 mm

  2. 0.5 mm

Implant application
[41]Dual-band (2.4–4.8 GHz) implantable antenna for biomedical telemetry applications(2.4 and 4.8 GHz).Dual-band12 × 12 mmRogers301010.20.635 mmBiotelemetry application

Table 1.

Dual-band and differential fed implantable antennas.

2.2 Circularly polarized antenna

Implantable antennas can communicate wirelessly with an external device. This is currently a great approach to stored physiological and real-time monitoring systems for biomedical telemetry [42]. Due to the effect of multipath distortion, communication with the help of far-field radio frequency (RF) link telemetry is sometimes affected. Since circularly polarized antenna preferred to the reduction of multipath and improvement of bit-error-rates can be achieved by circular polarization [43]. The design of the circular polarized (CP) antenna is difficult and needs to be miniaturized. Here, good circular polarization is achieved with a limited size [44]. Circular polarization has a special advantage in that it becomes insensitive between transmitter and receiver [45].

An Implantable patch antenna was first described with capacitive loading in [43], its axial ratio bandwidth is below 3 dB is narrow about 1.63%. [43]. In a circularly polarized helical antenna, measured impedance is 40% and axial radial bandwidth is 32.6% [46]. Similarly, in a loop antenna, simulated impedance and axial ratio bandwidth is 18.2%. [44]. Broadband CP implantable antenna exhibits its axial ratio bandwidth is 6.09% and wide impedance is 16.05% [45]. A miniaturized complementary split ring resonator (CSRR) was designed 915 MHz and its axial ratio bandwidth was 2.4% and impedance bandwidth is 12.2% [47]. Recent research on the CP ISM band antenna contained axial ratio −18.2% and impedance bandwidth 6.2% [48]. Recent work of CP ISM band at 915GHz consists axial ratio bandwidth and impedance band with 1.2 and −29% respectively [49]. Table 2 shows all recent information about the circularly polarized antenna.

Ref.Title and year of publicationFrequency of operationDepthAntenna dimensionsGain [dBi]Axial ratio BW
DimensionSubstrateεrThickness
[43]Capacitively loaded circularly polarized implantable patch antenna for ISM band biomedical applications (2014)2.4GHz4 mm skin10 × 10 × 1.27 mmRogers 301010.20.635 mm−22∼1.63%
[46]Circularly polarized helical antenna for ISM-band ingestible capsule endoscope systems (2014)2.4GHz50 mm muscleΠ × 5.52 mm × 3.81Rogers 301010.20.635 mm−32∼32.6%
[44]Miniaturized circularly polarized loop antenna for biomedical applications (2015)2.4GHz2 mm skin13 × 13 × 1.27 mmRogers 301010.20.635 mm−14∼2.4%
[45]Broadband circularly polarized implantable antenna for biomedical application (2016)2.4GHz5 mm muscle10 × 10 × 1.27 mmRogers 301010.20.635 mm−22.33∼6.09
[47]A miniaturized CSRR loaded wide-beam width circularly polarized implantable antenna for subcutaneous real-time glucose monitoring (2017)915 MHz4 mm skin8.5 × 8.5 × 1.27 mmRogers 301010.20.635 mm−27∼1.5%
[48]Miniaturized circularly polarized implantable antenna for ISM-band biomedical devices (2017)915 MHz3 mm skin15 × 15 × 1.27 mmRogers 301010.20.635 mm−32∼18.2%
[49]Circularly polarized implantable antenna for 915 MHz ISM-band far-field wireless power transmission (2018)915 MHz4 mm skin11 × 11 × 1.27 mmRogers 301010.20.635 mm−29∼1.2%

Table 2.

Circular polarized antennas for biomedical applications.

2.3 Capsule antennas

Capsule endoscopy is a diagnostic technology for gastrointestinal (GI) imaging that complements conventional endoscopy. An ingestible electronic radio telemetry capsule, first developed in 1957, is used to measure pressure and temperature [50]. It consists of the ability to transmit detailed information in real-time like growing heatstroke among the athletes while transmitting information to the receiver it simultaneously monitoring body temperature [51]. The approximate size of the capsule is 11 × 26 mm, in this small size it consists CMOS imager, light-emitting diode, transmitter, batteries, antennas, detailed track of the digestive system. Also, for prevention conditions such as gastroparesis and iron deficiency anemia [52, 53].

Wireless telemetry is used for real-time diagnostics, which is easy for disease diagnosis. The capsule orientation is random, but a robust continuous communication link for biomedical telemetry is quite a challenge to develop stable and secure communication links for capsule devices. The antennas are designed and must be characterized electromagnetically [54, 55]. Figure 1 shows in detail information about a biomedical capsule. It has eight different parts such as optical dome, lens holder, short focal length lens, light-emitting diode, CMOS Imager, batteries, radio telemetry transmitter, and antenna.

Figure 1.

Detail digestive track of a biomedical capsule.

Various antenna designs for capsule antennas have been designed and developed in the literature, including multilayer spiral, multilayer helical, dipole, and complementary split resonator antennas. Antenna performance can be done with help of matching, radiation patterns, link budget, and characterization of wireless medical telemetry characterization. Wireless medical telemetry services (WMTS), industrial scientific and medical (ISM) band used for performance evaluation [56]. Table 3 shows design techniques, operating frequency, the radiation performance of capsule antenna.

Ref.Title and year of publicationAntenna typeSize of capsuleG [dBi]Approach towards miniaturizationFrequency of operation (MHz)Phantom Details in (mm)
SizeShapeTissue
[55]Conformal ingestible capsule antenna: A novel chandelier meandered design (2009)Multilayer Spiral26 × Ø11−26Meanders1400200 × 350 × 350BoxMuscle
[57]Design, realization and measurements of a miniature antenna for implantable wireless communication systems (2011)Multilayer helical32 × Ø10−29Stacking: four layersDual-band110 × Ø80CylinderMuscle
[58]New flexible medical compact antenna: design and analysis (2012)Microstrip17 × Ø7−33Meanders, shorting, λ/4 SIR434Ø200Cylinderεr = 49.6, σ = 0.51
[59]a novel conformal antenna for ingestible capsule endoscopy in the medradio band (2013)Microstrip24 × Ø10−30Meanders, shorting4021003CubeMuscle
[60]Circularly polarized helical antenna for ISM-band ingestible capsule endoscope systems (2014)Loop w/CSRR26 × Ø11−32Stacking: three layers24501003CubeMuscle
[61]A broadband flexible implantable loop antenna with complementary splitring resonators (2015)Assym. Dipole25 × Ø10−25MultibandØ180 × Ø100 × 50Elliptical cylinderMuscle
[62]Bandwidth enhancement of an implantable antenna (2015)Assym. Dipole24 × Ø11−37Meanders4021803CubeSkin
[63]Robust ultraminiature capsule antenna for ingestible and implantable applications (2017)Microstrip17 × Ø7−22Dielectric loading, λ/2 SIR434Ø100SphereMuscle
[64]In vivocharacterization of a wireless telemetry module for a capsule endoscopy system utilizing a conformal antenna design antenna (2018)Multilayer helical30 × Ø10−23Meanders433190 × 190 × 190cubeMuscle

Table 3.

Capsule antennas: Literature.

In [57] capsule is off-entered, the antenna operates in MedRadio 403 MHz and ISM 2.45 MHz bands and gain is for 403 MHz, [58] capsule is off-entered and distance to a surface is 10 mm. The bandwidth almost covers 403Mhz, ISM 434,868, 915, and 2.45GHz bands. The gain is about 434 MHz [61]. In [62] capsule is off-centered and the distance to a surface is 3 mm. The motivation is to improve the transmission range of a miniature in a body, but there are some difficulties such as poor radiation efficiency, strong coupling to biological tissues with loss and scattering, antenna impedance detuning, etc. Capsule antenna also considered for animal biotelemetry, electromagnetic properties of some animal tissue differ from humans. High robustness can reduce impedance detuning [63].

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3. Implantable antenna design requirements of an antenna

The implantable antenna design expects a small antenna size, broadband, low profile, and efficient antennas that can be used for data transmission, health monitoring, etc. The effective design depends on miniaturization, bandwidth, tuning, biocompatibility, patient safety, etc.

3.1 Miniaturization

In the case of an implantable antenna, an antenna supposes to be implanted in the human body, therefore the size must be should be minimized. Miniaturization becomes very important today because dimensions of half-wavelength (λ/2) and quarter wavelength (λ/4) antennas at low-frequency bands, ISM, MICS band makes them useless for designing implantable antennas. Generally, for the implantable antenna design MICS (402–405 MHz), ISM (Industrial, Scientific, and Medical 2.4–2.48 GHz) and Med Radio (401–406 MHz) bands are useful. While design, human tissue is designed with high relative permittivity, due to this antenna miniaturization being challenging. When a biocompatible layer with low permittivity is inserted around the antenna, the effective permittivity decreases. Various miniaturization methods are shown below.

3.1.1 High permittivity dielectric substrate

One of the techniques for reducing the size of the implantable antenna is to use a high dielectric constant substrate. In general, due to the high permittivity, the effective wavelength is shortened and the resonance frequency changes to a lower frequency. Table 4 shows in detail a list of materials used for the design of the implantable antenna. For reducing the size of the implantable antenna, one can use a high permittivity substrate.

MaterialDielectric constantRef.
Rogers RO321010.2[27, 32, 34]
ARLON 100010.2[30]
Roger 601010.2[28, 37]
Rogers 301010.2[29, 31, 33, 35, 36, 38, 39, 41, 43, 44, 45, 46, 47, 48]
FR44.6[32, 40]
RO40033.7[40]
RT/Duroid 60022.94[54]
MACOR6.1[7]
Alumina9.4[65]
RT/Duroid 601010.2[66, 67]
Rogers TMM13i12.2[68]

Table 4.

List of materials used for implantable antenna design.

Generally, Roger 3010/Roger RO 3210/Rogers6010/ RT/Duroid6010, ARLON1000, Alumina, MACOR, FR4, RO4003, etc. substrate materials utilized for the design of the implantable antenna. The relative permittivity of Roger 3010/Roger RO 3210/Rogers6010/RT/Duroid6010 is 10.2 shown in the table. In [68] miniaturization achieved by high permittivity substrate material used i.e., Rogers TMM13i. (εr = 12.2).

3.1.2 To improve impedance matching

The loading technique is used to improve impedance matching. In [29] the shorting strip is used as an inductive loading and compensates for the capacitive effect on the structure. Inductive loading capacitive loading plays an important part in this method, it is used to offset the imaginary part of the impedance. Therefore, a good impedance match is obtained at the desired frequency [42]. In [44], miniaturization was achieved by loading four patches and high impedance lines to form slow wave propagation, 54.4% miniaturization was achieved. In [61] antenna impedance matching was obtained with help of CSRR, which introduces negative permittivity (capacitance) and reduces the large inductive part of the loop antenna. Hence, less reflection and large radiation occur. In [69, 70] inductive loading techniques are used for miniaturized antenna size. Capacitive loading technique used in [71], antenna size reduced about 72% with help of circularly polarized microstrip patch antenna at the frequency of interest (fixed operating frequency).

3.1.3 Lengthening of the current flow path of radiator

Gain reduction can be possible by keeping a high relative dielectric constant of materials and planar inverted F antenna (PIFA) type antenna with structures like meandered, spiral, slot, etc. The longer the path of the radiator, the resonant frequency can be shifted towards a lower resonant frequency. Hence, size can be reduced. In [47] the antenna is square shape (case a), on which the current path is short and the resulting resonant frequency is 4.5GHz. As considering lower resonant frequency, to increase the effective length of the current path four C-shaped slots surrounding the patch edges (case b). CSRR is one of the MTM (Metamaterial) structures, it offers negative permeability values. So, the electrical length of this MTM unit cell is smaller than the wavelength at operating frequency (case3). A circular CSRR is loaded in the center of the patch and resonant frequency shift occurs at 2.45GHz. In [55] meandered dipole structure gives vector current alignment which helps miniaturization.

3.1.4 High frequency

As we know, a higher operating frequency will result in a shorter wavelength. Hence, an antenna that can be designed at a higher frequency will result in, small volume. In literature implantable antennas works in frequency bands like MedRadio 401–406 MHz [32, 72], MICS (Medical implants communication Service) 402–405 MHz [7, 27, 29, 30, 31, 33, 35, 36, 54, 65, 70, 71, 73, 74, 75, 76, 77, 78, 79, 80] and ISM (Industrial, Scientific and Medical) 2400–2480 MHz [32, 33]. In literature, it’s reported that the MICS band is more preferably used for the design of the implantable antenna. In [56] an implantable antenna and capsule antenna were designed at wireless telemetry services (WMTS) band 1395–1400 MHz for performance evaluation and it is used for remote monitoring of patient’s health.

3.1.5 Adding shorting pin

Shorting point is another method to miniaturize the size. In this technique, a shorting pin is inserted in between the patch plane and ground plane which increases the effective size of the antenna and reduces physical dimensions. In literature reported as [6, 7, 27, 29, 31, 54, 66, 73, 74, 75, 76, 77, 81] etc. consists shorting pin. Which helps miniaturize the size of the antenna. In [63] half-wave stepped impedance resonator (SiR) technique with two impedance steps, low-to-high and high-to-low to reduce the size of the antenna. In [67] antenna is miniaturized by adding two kinds of rectangular slots onto the annular ring.

3.2 Patient safely

Due to the propagation of electromagnetic field causes rise in temperature in human tissue, to evaluate this heat issue SAR is used. Generally, issues related to patient safety limit maximum allowable power incident on the implantable antenna. The rate of energy deposited per unit mass of tissue is called a Specific Absorption Rate (SAR). SAR is an internationally accepted FCC (Federal Communication Commission) guideline. For example, IEEE C95.1-1999 patient safety standard restricts the specific average of over 1 g of tissue in the shape of a cube to less than 1.6 W/kg ((SAR1g, max1.6 W/kg), IEEE C95.1-1999 is found to restrict transmission power up to 5.186 mW [82] and ANSI/IEEE C95.1-2005 standard restricts the Specific Absorption Rate averaged over any 10 g of tissue in the shape of cube less than 2 W/kg (SAR10g, max2 W/kg), IEEE C95.1-2005 is found to restrict transmission power up to 30.17 mW [83]. To attenuate electromagnetic interference, MedRadio regulations restrict effective radiated power of implantable antenna to 25 μW [84], power transmission is restricted to 50 mW. In [61] CSRR reduces the electric far-field of antenna this power absorption and SAR also reduced. As a result, radiation power increases, antenna radiation, and gain are increased.

SAR can be defined with the following equation,

SAR=σE22ρE1

where, ρ(Kg/m3) is mass density, σ(S/m) is conductivity and |E| is electric field intensity.

3.3 Biocompatibility

Biocompatibility is one of the necessary conditions while designing an implantable antenna to preserve patients’ safety. Human tissues are conductive, if they were allowed direct contact with metallization then there is a chance of short circuit. For long-term implantation, it’s crucial to handle biocompatibility and prevention from short circuits. Most of the materials from Table 4 are not biocompatible materials. There are different biocompatible materials reported in literature like macor [7], alumina [65], PDMS, Parylene C film, polyimide, PEEK (polyetheretherketone), polyethylene, silastic MDX4-4210 [46], etc. For thickness of encased biocompatible coating material can also affect the antenna performance [85].

3.4 Wireless communication ability

In the current scenario, an implantable antenna acts as a transmitting device, and an external device acts as receiving device as shown in Figure 2. Assuming far-field communication, the link power budget can be described as in terms of [43, 86, 87],

Figure 2.

Wireless communication link between IMD and external device.

Link MargindB=LinkCN0RequiredCN0E2
Link MargindB=Pt+GtLf+GrNoEbNo10log10Br+GcGdE3

Where Pt is transmitted power, Gt is transmitted antenna gain, Lf is path loss in free space, Gr gain of receiving antenna, and N0 is the noise power density. Also, Path loss can be given as,

LfdB=20log4ΠdλE4

Where d is the distance between transmitter and receiver.

Impedance Mismatch loss is given as,

LimpdB=10log1Γ2E5

Where Γis the reflection coefficient.

For, wireless communication, Link C/N0 must exceed than required C/No, in uplink transmission input power of the transmitter antenna is limited for safety purposes. Received power can be given as,

pr=pt+Gt+GrLfLimpepE6

Where epis polarization mismatch loss between transmitter and receiver.

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4. Antenna design and testing

4.1 Antenna design

While designing an antenna one should follow the following characterization of implantable antenna:

  • Consider, operating frequency bands: MICS (402–405 MHz), ISM (2.4–2.48GHz), MedRadio (401–406 MHz) according to application.

  • Design a low-profile antenna that fulfills conditions (tissue properties, dielectric constant, conductivity, etc.) of the human body.

  • Evaluation of simplified geometry for a designed implantable antenna in the human torso.

  • Further, evaluation and testing of the designed antenna in terms of radiation efficiency, return loss and bandwidth, etc.

  • Formation of links between transmitter and receiver antennas, estimate the performance of communication links used in an implantable antenna, fulfillment of SAR limitations, and maximum Effective radiating power.

  • Table 5 shows volume occupied by an implantable antenna in the literature.

Ref.Simulation tissueBand (MHz)Miniaturization techniqueVol. (mm3)
Dielectric materialSubstrate shapeDielectric constantPatch shapeShorting pinPatch stacking
[73]Skin402–405Rogers 3210Rectangular10.2Spiral10,240
[54]2/3 muscle402–405RT/duroid 6002Rectangular2.94WaffleYes6480
[73]Skin402–405Rogers 3210Rectangular10.2SpiralYes6144
[7]2/3 muscle402–405MACORSpiral6.1SpiralYes3457.4
[30]Skin402–405ARLON1000Square6.1MeanderedYes1375.4
[27]Skin402–405
2400–2480
Rogers 3210Rectangular10.2MeanderedYes1265.6
[74]Skin402–405Rogers 3210Rectangular10.2SpiralYes1200
[75]Skin402–405Rogers 3210Rectangular10.2MeanderedYes1200
[66]2/3 muscle402–405RT/duroid6010Rectangular10.2SpiralYes823
[81]Muscle402–405Rogers 3210Rectangular10.2Π-shapedYes791
[31]Skin402–405
2400–2480
Rogers3010Rectangular10.2Π-shaped with two meandered stripYes487.8
[76]Skin402–405Rogers 3210Circular10.2Hook-slottedYesYes335.8
[77]Vitreous humor402–405Rogers 3210Square10.2SpiralYesYes273.6
[6]Skin402–405
433–435
2400–2480
Rogers 3210Square10.2Comb and Π-shapedYesYes254
[78]Skin402–405Rogers 3210Circular10.2MeanderedYesYes203.6
[79]Human chest muscle401–406Rogers 3010Square10.21. square patch;
2. square patch with a central square slot
3. meandered square ring
4. meandered square ring with shorting pin
YesYes198.4
[71]Skin402–405Rogers 3210Square10.2SpiralYesYes190
[70]Skin402–405Rogers 3210Circular10.2Hook slottedYesYes149.2
[65]Skin402–405Rogers 3210Square10.2Hook slottedYesYes121.6
[67]Skin2400–2480Roger3010Circular10.2Two rectangle slots onto the annular ring120.69
[33]Skin402–405
2400–2480
Rogers 3210Rectangular10.2Spiral dipole67.8
[80]Skin402–405AluminaCircular9.4MeanderedYesYes32.7
[37]Human head model402–405
2400–2480
Rogers 3210Rectangular10.2Serpentine31.5
[72]Skin401–406Rogers RT/duroid 6010,Rectangular10.2l shaded reactive loading18.1

Table 5.

Volume occupied by MICS, ISM and medradio band implantable antenna and its miniaturized techniques: A literature.

Following commercial tools are used for designing an implantable antenna such as computer simulation tool (CST) Microwave Studio, High-Frequency Structure Simulator (HFSS), Advanced Designed System (ADS), and XFDTD. In [55] for analyzing electromagnetic characteristics of the implantable antenna inside head and body, Finite-difference-time-domain (FDTD) and Spherical dyadic Green’s function (DGF), etc. functions are applied. In [83] Antenna simulated using FDTD overall efficiency improved and suitable design obtained in minimal time with help of a genetic algorithm.

In general, a one-layer skin model is widely used for implantable antenna design. Although, 2/3 muscle model and three-layer tissue (skin, fat, muscle) mode are also typically for antenna designing. These three models make simulation efficient and measurement easier as this model is made from different materials to active accurate permittivity and conductivity.

In [26] implantable antenna designed with FDTD method including 2/3 muscle model. In [28, 33] antenna simulated in HFSS and CST respectively and a single-layer skin model is used. To design an implantable antenna in a realistic environment then it must evaluate within accurate human body models such as the human Voxel model shown in Figure 3. For neural recording systems and wireless endoscope systems, an accurate human model is required. For different biomedical applications, the implant’s position and depth could be a different and single layer or three-layer modeling used according to application. In Figure 4 one-layer tissue model is shown.

Figure 3.

Front and side view of CST human voxel mode used for simulation testing of various antenna.

Figure 4.

One layer tissue model.

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5. Testing

5.1 In-vitro test

The meaning of In-Vitro is an outside living organism, this test is relatively easy and practically implementable because testing exists inside the phantom. Phantom is a container (cube or box) with liquid or gel material, it consists of the electrical properties of biological tissue. Fabricated prototype inserted in tissue phantom and measured. Phantoms are generally prepared with the help of deionized water, sugar, salt, etc. If sugar concentration is increased, the permittivity of tissue significantly decreases and conductivity slightly increases and if salt concentration increased, it results in permittivity of tissue decreases and conductivity significantly increases. The mixture must be properly heated and stirred to avoid air bubble formation and poured inside the phantom. In [88] Measurement of liquids electrical properties (εr and μ) was conducted with a dielectric probe kit or open-ended coaxial cable. Generally, reflection coefficient, path loss, communication link, and polarization factor, etc. measured in vitro vest, as observed in the literature. Generally, prototype antennas are connected with a network analyzer through a coaxial cable, inserted in a tissue phantom, and measured.

5.2 In-vivo test

In-vivo test, testing performed inside animal tissue. There are two methods for Vivo testing, embedding an implantable antenna inside donor animals and surgically implanting an antenna inside a live animal. In [64, 89] dual bands MICS (402–405 MHz) and ISM (2.4–2.48GHz) tested in vivo. A vivo testing protocol must be developed before the experimental investigation. Pre-surgical preparation, anesthesia, etc. should be needed. In [89], two antennas were implanted in three different rats. Due to surgical procedure variation, affect exhibited on return loss frequency response. Dielectric properties of live tissue generally depend on frequency, age, temperature, sex, etc. parameters. In [90, 91, 92, 93] in vivo testing was performed to explore the effect of live tissues on antenna performance. In [91] biocompatible capsule device was implanted inside a live pig body for temperature monitoring. Two circular polarized antennas were tested in rat muscle in [93].

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6. Conclusion

In this paper, microwave antennas for biomedical applications are presented. A brief overview of different antenna types and the needs of the implantable antenna is given. The design of an implantable antenna mainly depends on miniaturization, biocompatibility, wireless communication ability, and patient safety. Different types of antenna, frequency bands for the design of the implantable antenna, miniaturization techniques, etc. were studied. Implantable medical devices now a day are used for physical monitoring, diagnosis purposes. Many other factors will come into the picture when these antennas are integrated with any biomedical device. Low battery power is one of the main constraints. While designing an implantable antenna, dimensions of antenna, patient safety, lower power consumption, efficiency, battery lifetime, etc. should be considered.

References

  1. 1. Greatbatch W, Homes CF. History of implantable devices. IEEE Engineering in Medicine and Biology Magazine. 1991;10(3):38-41
  2. 2. Scanlon WG, Evans NE, Mc Creesh ZM. RF performance of a 418MHz radio telemeter packed for human vaginal placement. IEEE Transactions on Biomedical Engineering. 1997;44(5):427-430
  3. 3. Wessels D. Implantable pacemakers and defi brillators: Device overview and EMI considerations. In: Proceedings of the IEEE International Symposium on Electromagnetic Compatibility (EMC 2002). New York: IEEE; 2002
  4. 4. Yilmaz T, Karacolak T, Topsakal E. Characterization and testing of skin mimicking material for implantable antennas operating at ISM band (2.4 GHz–2.48 GHz). IEEE Antennas and Wireless Propagation Letters. 2008;7:418-420
  5. 5. Chow EY, Ouyang Y, Beier B, Chappell WJ, Irazoqui PP. Evaluation of cardiovascular stents as antennas for implantable wireless applications. IEEE Transactions on Microwave Theory and Techniques. 2009;57(10):2523-2532
  6. 6. Huang F, Lee C, Chang C, Chen L, Yo T, Luo C. Rectenna application of miniaturized implantable antenna design for triple-band biotelemetry communication. IEEE Transactions on Antennas and Propagation. 2011;59(7):2646-2653
  7. 7. Soontornpipit P, Furse CM, Chung YC. Design of implantable microstrip antennas for communication with medical implants. IEEE Transactions on Microwave Theory and Techniques. 2004;52(8):1944-1951
  8. 8. Gosalia K, Humayun MS, Lazzi G. Impedance matching and implementation of planar space-filling dipoles as intraocular implanted antennas in a retinal prosthesis. IEEE Transactions on Antennas and Propagation. 2005;53(8):2365-2373
  9. 9. Kim D-H, Viventi J, Amsden JJ, Xiao J, Vigeland L, Kim YS, et al. Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics. Nature Mater. 2010;9(6):511-517
  10. 10. Kaur G, Kaur A, Toor G, Dhaliwal B, Pattnaik S. Antennas for biomedical applications. Biomedical Engineering Letters. 2015;5:203-212
  11. 11. Gabriel C, Gabriel S, Corthout E. The dielectric properties of biological tissues: I. Literature survey. Physics in Medicine and Biology. 1996;41:2231-2249
  12. 12. Aleef TA, Hagos YB, Minh VH, Khawaldeh S, Pervaiz U. Design and simulation-based performance evaluation of a miniaturized implantable antenna for biomedical applications. Micro and Nano Letters. 2017;12(10):821-826
  13. 13. Herth E et al. A biocompatible and flexible polyimide for wireless sensors. Microsystem Technologies. 2017:1-9
  14. 14. Asili M et al. Flexible microwave antenna applicator for chemo-thearapy of breast. IEEE Antennas and Wireless Propagation Letters. 2015;14:1778-1781
  15. 15. Asili M, Green R, Seran S, Topsakal E. A small implantable antenna for medradio and ISM bands. IEEE Antennas and Wireless Propagation Letters. 2012;11:1683-1685
  16. 16. Jung YH et al. A compact parylene-coated WLAN flexible antenna for implantable electronics. IEEE Antennas and Wireless Propagation Letters. 2016;15(560):1382-1385
  17. 17. Huang Y, Alrawashdeh R, Cao P. Flexible meandered loop antenna for implants in MedRadio and ISM bands. Electronics Letters. 2013;49(24):1515-1517
  18. 18. Scarpello ML et al. Design of an implantable slot dipole conformal flexible antenna for biomedical applications. IEEE Transactions on Antennas and Propagation. 2011;59(10):3556-3564
  19. 19. Asili M et al. Flexible microwave antenna applicator for chemo-thermotherapy of the breast. IEEE Antennas and Wireless Propagation Letters. 2015;14:1778-1781
  20. 20. Emami-Nejad H, Mir A. Design and simulation of a flexible and ultra-sensitive biosensor based on frequency selective surface in the microwave range. Optical and Quantum Electronics. 2017;49(10):320
  21. 21. Yilmaz T, Karacolak T, Topsakal E. Characterization and testing of skin mimicking material for implantable antennas operating at ISM band (2.4 GHz–2.48 GHz). IEEE Antennas and Wireless Propagation Letters. 2008;7:418-420
  22. 22. Yang S, Liu P, Yang M, Wang Q, Song J, Dong L. From flexible and stretchable meta-atom to metamaterial: A wearable microwave meta-skin with tunable frequency selective and cloaking effects. Scientific Reports. 2016;6(2015):1-8
  23. 23. Bahrami H, Porter E, Santorelli A. Flexible sixteen antenna array for microwave brest cancer detection. 2015;62(10):2516-2525
  24. 24. European Radiocommunications Commission (ERC) Recommendation 70-03 Relating to the Use of Short Range. In: European Conference of Postal and Telecommunications Administration, CEPT/ERC 70-03, Annex 12, 1997. Medical Implant Communications Service (MICS) FederalRegister, Rules Regulations, 64, 240, ; 1999. pp. 69926-69934
  25. 25. ITU. International Telecommunications Union-Radiocommunications (ITU-R), Radio Regulations, Section 5.138 and5.150. Geneva, Switzerland: ITU;
  26. 26. European Radiocommunications Commission (ERC) Recommendation 70-03 Relating to the Use of Short Range. In: European Conference of Postal and Telecommunications Administration; CEPT/ERC 70-03, Annex 12; 1997
  27. 27. Karacolak T, Hood AZ, Topsakal E. Design of a dual-band implantable antenna and development of skin mimicking gels for continuous glucose monitoring. IEEE Transactions on Microwave Theory and Techniques. 2008;56:1001-1008
  28. 28. Duan Z, Guo Y, Xue R, Je M, Kwong D. Differentially fed dual-band implantable antenna for biomedical applications. IEEE Transactions on Antennas and Propagation. 2012;60(12):5587-5595
  29. 29. Liu C, Guo Y-X, Xiao S. Compact dual-band antenna for implantable devices. IEEE Antennas and Wireless Propagation Letters. 2012;11:1506-1511
  30. 30. Sánchez-Fernández CJ, Quevedo-Teruel O, Requena-Carrión J, Inclán-Sánchez L, Rajo-Iglesias E. Dual-band microstrip patch antenna based on short-circuited ring and spiral resonators for implantable medical devices. IET Microwaves Antennas and Propagation. 2010;4(8):1048-1055
  31. 31. Xu L-J, Guo Y-X, Wu W. Dual-band implantable antenna with open-end slots on ground. IEEE Antennas and Wireless Propagation Letters. 2012;11:1564-1567
  32. 32. Kiourti A, Costa JR, Fernandes CA, Nikita KS. Broadband implantable and a dual-band on-body repeater antenna: Design and transmission performance. IEEE Transactions on Antennas and Propagation. 2014;62(6):2899-2908
  33. 33. Xu L-J, Guo Y-X. Miniaturized dual-band implantable antenna for wireless communication. IEEE Antennas and Wireless Propagation Letters. 2014;13:1160-1163
  34. 34. Zhu D, Guo Y-X, Je M, Kwong D-L. Design and in vitro test of a differentially fed dual-band implantable antenna operating at MICS and ISM bands. IEEE Transactions on Antennas and Propagation. 2014;62(5):2430-2440
  35. 35. Liu Y, Chen Y, Lin H, Juwono FH. A novel differentially fed compact dual-band implantable antenna for biotelemetry application. IEEE Antennas and Wireless Propagation Letters. 2016;15:1791-1194
  36. 36. Lei W, Guo Y-X. Miniaturized differentially fed dual band implantable antenna: Design, realization, and in vitro test. Radio Science. 2014;50:959-967
  37. 37. Cho Y, Yoo H. Miniaturized dual-band implantable antenna for wireless biotelemetry. Electronics Letters. 2016;52(12):1005-1007
  38. 38. Liu Y, Chen Y, Lin H, Juwono FH. Differentially fed compact dual band implantable antenna for biotelemetry. In: IEEE International Symposium on Antennas and Propagation; 26 June 2016. New York: IEEE; 2014. pp. 1-2
  39. 39. Dhun Z, Xu L. Dual band implantable antenna with circular polarization property for ingestible capsule application. Electronics Letters. 2017;53(16):1090-1092
  40. 40. Akbarpour A, Chamaani S. Dual-band electrically coupled loop antenna for implant applications. IET Microwaves, Antennas and Propagation. 2017;11(7):1020-1024
  41. 41. Blauert J, Kiourti A. Dual-band (2.4 GHz–4.8 GHz) implantable antenna for biomedical telemetry applications. International Applied Computational Electromagnetics Society Symposium (ACES). 2018:1-2
  42. 42. Kiourti A, Nikita KS. A review of implantable patch antennas for biomedical telemetry: Challenges and solutions. IEEE Antennas and Propagation Magazine. 2012;54(3):210-228
  43. 43. Liu C, Guo YX, Xiao S. Capacitively loaded circularly polarized implantable patch antenna for ISM band biomedical applications. IEEE Transactions on Antennas and Propagation. 2014;62(5):2407-2417
  44. 44. Xu LJ, Guo Y-X, Wu W. Miniaturized circularly polarized loop antenna for biomedical applications. IEEE Transactions on Antennas and Propagation. 2015;63(3):922-930
  45. 45. Li H, Guo Y-X, Xiao S-Q. Broadband circularly polarized implantable antenna for biomedical application. Electronics Letters. 2016;52(7):504-506
  46. 46. Liu C, Guo Y, Xiao S. Circularly polarized helical antenna for ISM-band ingestible capsule endoscope systems. IEEE Transactions on Antennas and Propagation. 2014;62(12):6027-6039
  47. 47. Liu XY, Wu ZT, Fan Y, Tentzeris EM. A miniaturized CSRR loaded wide-beamwidth circularly polarized implantable antenna for subcutaneous real-time glucose monitoring. IEEE Antennas and Wireless Propagation Letters. 2017;16:577-580
  48. 48. Zhang K, Liu C, Liu X, Guo H, Yang X. Miniaturized circularly polarized implantable antenna for ISM-band biomedical devices. International Journal of Antennas and Propagation. 2017;2017
  49. 49. Liu C, Zhang Y, Liu X. Circularly polarized implantable antenna for 915 MHz ISM-band far field wireless power transmission. IEEE Antennas and Wireless Propagation Letters. 2018;17(3):373-376
  50. 50. Mackay RS, Jacobson B. Endo radiosonde. Nature. 1957;179:1239-1240
  51. 51. Visser HJ, Kamp NAAO, Aben MJH, Woolde JHS, Bartels LW, Bakker CJG, et al. An analytical model for intravascular MR antennas. In: Proceedings of Antennas and Propagation Society International Symposium. Nice, France: IET; 2007. pp. 1-9
  52. 52. Given Imaging, M2A capsule camera [Internet]. Available from: //www.givenimaging.com/
  53. 53. Iddan G, Meron G, Glukhovsky A, Swain P. Wireless capsule endoscopy. Nature. 2000;405:417
  54. 54. Kim J, Rahmat-Samii Y. Implanted antennas inside a human body: Simulations, designs, and characterizations. IEEE Transactions on Microwave Theory and Techniques. 2004;52(8):1934-1943
  55. 55. Izdebski PM, Rajagopalan H, Rahmat-Samii Y. Conformal ingestible capsule antenna: A novel chandelier meandered design. IEEE Transactions on Antennas and Propagation. 2009;57(4):900-909
  56. 56. Rajagopalan H. Wireless medical telemetry characterization for ingestible capsule antenna designs. IEEE Antennas and Wireless Propagation Letters. 2012;11:1679-1683
  57. 57. Merli F, Bolomey L, Zurcher J-F, Corradini G, Meurville E, Skrivervik AK. Design, realization and measurements of a miniature antenna for implantable wireless communication systems. IEEE Transactions on Antennas and Propagation. 2011;59(10):3544-3555
  58. 58. Mahe Y, Chousseaud A, Brunet M, Froppier B. New flexible medical compact antenna: Design and analysis. IEEE Transactions on Antennas and Propagation. 2012;2012
  59. 59. Psathas KA, Kiourti A, Nikita KS. A novel conformal antenna for ingestible capsule endoscopy in the medradio band. In: Proceedings of 34th Progress in Electromagnetics Research Symposium (PIERS). Stockholm, Sweden; 2013. pp. 1899-1902
  60. 60. Liu C, Guo YX, Xiao S. Circularly polarized helical antenna for ISM-band ingestible capsule endoscope systems. IEEE Transactions on Antennas and Propagation. 2014;62(12):6027-6039
  61. 61. Alrawashdeh RS, Huang Y, Kod M, Sajak AAB. A broadband flexible implantable loop antenna with complementary split ring resonators. IEEE Antennas and Wireless Propagation Letters. 2015;14:1506-1509
  62. 62. Xu LJ, Guo YX, Wu W. Bandwidth enhancement of an implantable antenna. IEEE Antennas and Wireless Propagation Letters. 2015;14:1510-1513
  63. 63. Nikolayev D, Zhadobov M, Le Coq L, Karban P, Sauleau AR. Robust ultraminiature capsule antenna for ingestible and implantable applications. IEEE Transactions on Antennas and Propagation. 2017;65(11):6107-6120
  64. 64. Faerber J, Cummins G, Pavuluri SK, Record P, Rodriguez A, Lay H, et al.In vivocharacterization of a wireless telemetry module for a capsule endoscopy system utilizing a conformal antenna design antenna. IEEE Transactions on Biomedical Circuits and Systems. 2018;12(1):95-106
  65. 65. Liu WC, Chen SH, Wu CM. Bandwidth enhancement and size reduction of an implantable PIFA antenna for biotelemetry devices. Microwave and Optical Technology Letters. 2009;51(3):755-757
  66. 66. Huang W, Kishk AA. Embedded spiral microstrip implantable antenna. Hindawi International Journal of Antennas and Propagation. 2011:1-6
  67. 67. Li R, Guo Y, Zhang B. A miniaturized circularly polarized implantable annular-ring antenna. IEEE Antennas and Wireless Propagation Letters. 2017;16:2566-2569
  68. 68. Lee CWL, Kiourti A, Volakis JL. Miniaturized fully-passive brain implant for wireless neuro potential acquisition. IEEE Antennas and Wireless Propagation Letters. 2017;16:645-648
  69. 69. Kim J, Rahmat-Samii Y. Implanted antennas inside a human body: Simulations, designs, and characterizations. IEEE Transactions on Microwave Theory and Techniques. 2004;52(8):1934-1943
  70. 70. Liu WC, Chen SH, Wu CM. Implantable broadband circular stacked PIFA antenna for biotelemetry communication. Journal of Electromagnetic Waves and Applications. 2008;22(13):1791-1800
  71. 71. Liu WC, Yeh FM, Ghavami M. Miniaturized implantable broadband antenna for biotelemetry communication. Microwave and Optical Technology Letters. 2008;50(9):2407-2409
  72. 72. Bakogianni S, Koulouridis S. An implantable planar dipole antenna for wireless medradio-band biotelemetry devices. IEEE Antennas and Wireless Propagation Letters. 2015;15:234-237
  73. 73. Soontornpipit P, Furse CM, Chung YC. Miniaturized biocompatible microstrip antenna using genetic algorithm. IEEE Transactions on Antennas and Propagation. 2005;53(6):1939-1945
  74. 74. Kim J, Rahmat-Samii Y. SAR reduction of implanted planar inverted F antennas with non-uniform width radiator. In: IEEE International Symposium on Antennas and Propagation. New York: IEEE; 2006
  75. 75. Kim J, Rahmat-Samii Y. Planar inverted F antennas on implantable medical devices: Meandered type versus spiral type. Microwave and Optical Technology Letters. 1996;48(3):567-572
  76. 76. Lee CM, Yo TC, Luo CH. Compact broadband stacked implantable antenna for biotelemetry with medical devices. In: Proceedings of the IEEE Annual Conference on Wireless Microwave Technology (WAMICON 2006). New York: IEEE; 2006
  77. 77. Permana H, Fang Q, Cosic I. 3-layer implantable microstrip antenna optimized for retinal prosthesis system in MICS band. In: Proceedings of the IEEE International Symposium on Bioelectronics and Bioinformatics (ISBB 2011). New York: IEEE; 2011
  78. 78. Kiourti A, Nikita KS. Miniature scalp-implantable antennas for telemetry in the MICS and ISM bands: Design, safety considerations and link budget analysis. IEEE Transactions on Antennas and Propagation. 2012;60(8):3568-3575
  79. 79. Li H, Guo Y, Liu C, Xiao S, Li L. A miniature-implantable antenna for medradio-band biomedical telemetry. IEEE Antennas and Wireless Propagation Letters. 2015;14
  80. 80. Kiourti A, Christopoulou M, Nikita KS. Performance of a novel miniature antenna implanted in the human head for wireless biotelemetry. In: IEEE International Symposium on Antennas and Propagation. New York: IEEE; 2011. pp. 392-395
  81. 81. Lee CM, Yo TC, Huang FJ, Luo CH. Band width enhancement of planar inverted-F antenna for implantable biotelemetry. Microwave and Optical Technology Letters. 2009;51(3):749-752
  82. 82. IEEE. IEEE Standard for Safety Levels With Respect to Human Exposure to Radiofrequency Electromagnetic Fields, 3 kHz to 300 GHz, IEEE Standard C95.1. New York: IEEE; 1999
  83. 83. IEEE. IEEE Standard for Safety Levels With Respect to Human Exposure to Radiofrequency Electromagnetic Fields, 3 kHz to 300 GHz, IEEE Standard C95.1. New York: IEEE; 2005
  84. 84. International Telecommunication Union. Recommendation ITU-R SA. 1346. Geneva, Switzerland: International Telecommunication Union; 1998
  85. 85. Merli F, Fuchs B, Mosig J, Skrivervik A. The effect of insulating layers on the performance of implanted antennas. IEEE Transactions on Antennas and Propagation. 2011;59(1):21-31
  86. 86. Kiourti A, Costa JR, Fernandes CA. Miniature implantable antennas for biomedical telemetry: From simulation to realization. IEEE Transactions on Biomedical Engineering. 2012;59(11):3140-3148
  87. 87. Karacolak T, Cooper R, Topsakal E. Electrical properties of rat skin and design of implantable antennas for medical wireless telemetry. IEEE Transaction on Antennas and Propagation. 2009;57(9):2806-2812
  88. 88. Zajicek R, Oppl L, Vrbaf J. Broadband measurement of complex permittivity using reflection method and coaxial probes. Radio Engineering. 2008;17:14-19
  89. 89. Karacolak T, Cooper R, Butler J, Fisher S, Topsakal E. In vivo verification of implantable antennas using rats as model animal. IEEE Antennas and Wireless Propagation Letters. 2010;9:334-337
  90. 90. Kawoos U, Tofighi M-R, Warty R, Kralick FA, Rosen A. In-vitro and in-vivo trans-scalp evaluation of an intracranial pressure implant at 2.4 GHz. IEEE Transactions on Microwave Theory and Techniques. 2008;56:2356-2365
  91. 91. Kiourti A, Psathas K, Lelovas P, Kostomitsopoulos N, Nikita KS. In vivo tests of implantable antennas in rats: antenna size and inter-subject considerations. IEEE Antennas and Wireless Propagation Letters. 2013;12:1396-1399
  92. 92. Merli F, Bolomey L, Gorostidi F, Fuchs B, Zurcher JF, Barrandon Y, et al. Example of data telemetry for biomedical applications: An in vivo experiment. IEEE Antennas and Wireless Propagation Letters. 2015;14:783-786
  93. 93. Liu C, Guo Y-X, Jegadeesan R, Xiao S. In vivo testing of circularly polarized implantable antennas in rats. IEEE Antennas and Wireless Propagation Letters. 2013;12:1396-1399

Written By

Kasturi Sudam Patil and Elizabeth Rufus

Submitted: July 7th, 2021 Reviewed: October 4th, 2021 Published: January 18th, 2022