This chapter reviews the most significant advancements in the context of metamaterial (MTM) leaky wave antennas (LWAs). A brief review of the mechanism of leaky wave radiation along with an important class of MTMs known as composite right/left-handed (CRLH) structures is presented. Then, recent outstanding works in the area of CRLH LWAs are reported in detail. These works include the application of electronic control, substrate integrated waveguides, dual band and wideband performance, ferrite loaded waveguides, and split-ring-resonator (SRR)-based MTMs in LWAs. Also, the benefits of LWAs to design high gain active structures, reflecto-directive systems, wideband dual-layer substrate integrated waveguide antennas and conformal antennas are discussed.
Part of the book: Modern Antenna Systems
This chapter discusses various approaches for calculating the modified Mie-Lorenz coefficients of the graphene-based multilayered cylindrical and spherical geometries. Initially, the Kubo model of graphene surface conductivity is discussed. Then, according to it, the formulations of scattering from graphene-based conformal particles are extracted. So, we have considered a graphene-wrapped cylinder and obtained its scattering coefficients by considering graphene surface currents on the shell. Later, a layered nanotube with multiple stacked graphene-dielectric interfaces is introduced, and for analyzing the plane wave scattering, graphene surface conductivity is incorporated in the transfer matrix method (TMM). Unlike the previous section, the dielectric model of graphene material is utilized, and the boundary conditions are applied on an arbitrary graphene interface, and a matrix-based formulation is concluded. Then, various examples ranging from super-scattering to super-cloaking are considered. For the scattering analysis of the multilayered spherical geometries, recurrence relations are introduced for the corresponding modified Mie-Lorenz coefficients by applying the boundary conditions at the interface of two adjacent layers. Later, for a sub-wavelength nanoparticle with spherical morphology, the full electrodynamics response is simplified in the electrostatic regime, and an equivalent circuit is proposed. Various practical examples are included to clarify the importance of scattering analysis for graphene-based layered spheres in order to prove their importance for developing novel optoelectronic devices.
Part of the book: Nanoplasmonics
The integral equation (IE) method is one of the efficient approaches for solving electromagnetic problems, where dyadic Green’s function (DGF) plays an important role as the Kernel of the integrals. In general, a layered medium with planar, cylindrical, or spherical geometry can be used to model different biomedical media such as human skin, body, or head. Therefore, in this chapter, different approaches for the derivation of Green’s function for these structures will be introduced. Due to the recent great interest in two-dimensional (2D) materials, the chapter will also discuss the generalization of the technique to the same structures with interfaces made of isotropic and anisotropic surface impedances. To this end, general formulas for the dyadic Green’s function of the aforementioned structures are extracted based on the scattering superposition method by considering field and source points in the arbitrary locations. Apparently, by setting the surface conductivity of the interfaces equal to zero, the formulations will turn into the associated problem with dielectric boundaries. This section will also aid in the design of various biomedical devices such as sensors, cloaks, and spectrometers, with improved functionality. Finally, the Purcell factor of a dipole emitter in the presence of the layered structures will be discussed as another biomedical application of the formulation.
Part of the book: Electromagnetic Wave Propagation for Industry and Biomedical Applications
There are two main approaches for developing solar cells, including photovoltaic and photothermal technologies. Photovoltaic solar cells benefit from an active region whose performance can be improved by embedding nanoparticles with different shapes and materials. Photothermal solar cells are broadband absorbers, enabling electromagnetic energy absorption in the solar radiation region. Since the solar spectrum is expanded from 120 to 1000 THz, the device bandwidth engineering and its efficiency enhancement through utilizing nanoparticles, multiresonance configurations, and multilayered structures are necessary. Moreover, using chemically inert materials with high thermal conductivities results in stable performance under different environmental conditions. Thus, in this chapter, various photovoltaic and photothermal solar cells will be discussed, emphasizing their design principles. The chapter mainly considers absorption bandwidth enlargement, absorption efficiency enhancement, and material selection considerations. In this regard, solar cells designed with plasmonic materials, transition metals, refractory metals, and carbon materials are presented. Notably, the potential of two-dimensional graphene material in the solar cell design is revealed, and a lightweight graphene-based solar cell with near-perfect coverage of the whole solar spectrum is introduced.
Part of the book: Solar Panels - Recent Advances and Future Prospects [Working title]