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Multi-band terahertz (THz) absorber based on a non-symmetric double-sided graphene comb resonator array is designed and simulated by the finite element method (FEM) in CST Software. Then, an equivalent circuit model (ECM) based on admittance with a fast MATLAB code is proposed to analyze the absorber in the THz region. The admittance-based ECM approach could be used for any metamaterial absorber containing one layer of resonators sandwiched between two dielectric slabs and backed by a metal layer consisting of a layer of resonators with a thickness much smaller than the minimum wavelength in the considered wavelength range. The proposed absorber is dynamically tunable with a one-layered resonator array. It has strong linear dichroism (LD) response of 98% and the frequency range of 0.7–5 THz with absorption > 96%: two absorption bands for TE mode and three for TM mode. The proposed absorber can be used in polarization-sensitive devices and systems in the THz region. The ECM model of the metastructure was derived to provide an efficient approach to analyzing the performance of the absorber. The FEM simulation results are in good agreement with the ECM ones.

This dissertation deals with design and characterization of functional structures for scattering of electromagnetic waves. An abundance of these structures can be found in nature, such as the structural coloration in the feathers of a peacock, the scales of butterflies and the shell of scarab beetles. Human design of structures providing specific interactions with electromagnetic waves have a long history. Today, these structures can be found in everyday products and applications like the filter of a microwave oven, shaded windows, polarizing glasses and 3D movies. A high demand of functional structures is also found in more advanced applications such as antenna design, electromagnetic scattering reduction for stealth applications, and in satellite communication systems.The dissertation consists of a general introduction and nine scientific papers, of which the majority have been published in peer-reviewed international journals. The general introduction sets the stage for the technical details contained in the included papers. Fundamental relations and scattering concepts in electromagnetic theory are presented, alongside with the approaches for design, optimization and experimental characterization of functional structures. The included papers can be divided into two main tracks: Papers I–VI concern satellite communications and Papers VII–IX are related to electromagnetic scattering characterization and reduction.In Papers I–V circular polarization selective structures for satellite communication applications are designed and characterized numerically and experimentally. A novel concept design is presented providing more than double the frequency bandwidth of previous designs. Furthermore, an experimental procedure and a data post processing scheme are presented for accurate characterization of circular polarization selective structures. In Paper VI a multiphysics study of a triaxial weave functioning as a reflector antenna surface is presented. The electromagneti

Many types of electromagnetic (EM) absorbers have been developed to convert EM energy into heat and to absorb EM waves. However, multilayer EM absorbers are complicated to design, fabricate and dispose of. In this work, we present a simple and scalable design method to achieve a single-layer electromagnetic absorber with a high absorption coefficient in a wide range of frequency bands. On the basis of the design, we develop two types of non-woven fabrics with high porosity in which the fibres are coated with multi-walled carbon nanotubes (MWCNTs). The absorption coefficients exceed 0.9 for the 5-mm-thick MWCNT-coated non-woven fabric measured in the 50-67 GHz range. An absorption coefficient of 0.94 at 5.8 GHz is expected to be obtained by using 50-mm MWCNT-coated fabric with a lower MWCNT content. The present MWCNT-coated non-woven fabrics will be useful materials for high-performance EM absorbers.

Many types of electromagnetic (EM) absorbers have been developed to convert EM energy into heat and to absorb EM waves. However, multilayer EM absorbers are complicated to design, fabricate and dispose of. In this work, we present a simple and scalable design method to achieve a single-layer electromagnetic absorber with a high absorption coefficient in a wide range of frequency bands. On the basis of the design, we develop two types of non-woven fabrics with high porosity in which the fibres are coated with multi-walled carbon nanotubes (MWCNTs). The absorption coefficients exceed 0.9 for the 5-mm-thick MWCNT-coated non-woven fabric measured in the 50-67 GHz range. An absorption coefficient of 0.94 at 5.8 GHz is expected to be obtained by using 50-mm MWCNT-coated fabric with a lower MWCNT content. The present MWCNT-coated non-woven fabrics will be useful materials for high-performance EM absorbers.

Many types of electromagnetic (EM) absorbers have been developed to convert EM energy into heat and to absorb EM waves. However, multilayer EM absorbers are complicated to design, fabricate and dispose of. In this work, we present a simple and scalable design method to achieve a single-layer electromagnetic absorber with a high absorption coefficient in a wide range of frequency bands. On the basis of the design, we develop two types of non-woven fabrics with high porosity in which the fibres are coated with multi-walled carbon nanotubes (MWCNTs). The absorption coefficients exceed 0.9 for the 5-mm-thick MWCNT-coated non-woven fabric measured in the 50-67 GHz range. An absorption coefficient of 0.94 at 5.8 GHz is expected to be obtained by using 50-mm MWCNT-coated fabric with a lower MWCNT content. The present MWCNT-coated non-woven fabrics will be useful materials for high-performance EM absorbers.

This article shows the most relevant results, related to the optimum design of a multilayer electromagnetic absorber for the wireless communications range. It was designed through two optimization strategies, a metaheuristic (Particle Swarm Optimization [PSO]) and a deterministic one (Interval Analysis). Despite achieving similar results, the last one proved to require an increased amount of computation time. Nevertheless, and due to its nature, the solution achieved was unique, while in PSO the results reproducibility was low, possibly due to the high complexity of the objective function., En este artículo se presentan los principales resultados asociados con el diseño óptimo de un absorbedor electromagnético plano multicapa, para el rango de frecuencias de las comunicaciones inalámbricas. Se diseñó mediante dos estrategias de optimización: una metaheurística (el algoritmo de enjambre de partículas) y otra determinística (el análisis de intervalos). A pesar de que se alcanzaron resultados similares, el método de intervalos mostró consistentemente un mayor tiempo de cómputo. Sin embargo y dada su naturaleza, su solución fue única, mientras que el método de enjambre de partículas mostró una limitada reproducibilidad en sus resultados, debido posiblemente al alto grado de complejidad de la función objetivo.

This article shows the most relevant results, related to the optimum design of a multilayer electromagnetic absorber for the wireless communications range. It was designed through two optimization strategies, a metaheuristic (Particle Swarm Optimization [PSO]) and a deterministic one (Interval Analysis). Despite achieving similar results, the last one proved to require an increased amount of computation time. Nevertheless, and due to its nature, the solution achieved was unique, while in PSO the results reproducibility was low, possibly due to the high complexity of the objective function., En este artículo se presentan los principales resultados asociados con el diseño óptimo de un absorbedor electromagnético plano multicapa, para el rango de frecuencias de las comunicaciones inalámbricas. Se diseñó mediante dos estrategias de optimización: una metaheurística (el algoritmo de enjambre de partículas) y otra determinística (el análisis de intervalos). A pesar de que se alcanzaron resultados similares, el método de intervalos mostró consistentemente un mayor tiempo de cómputo. Sin embargo y dada su naturaleza, su solución fue única, mientras que el método de enjambre de partículas mostró una limitada reproducibilidad en sus resultados, debido posiblemente al alto grado de complejidad de la función objetivo.

A layered structure of magnetodielectric slabs, backed with a perfectly conducting plane, is illuminated by a Gaussian beam. The permittivities and permeabilities of each layer are selected so that the incident field penetrates smoothly into the subsequent layers and sustains gradually greater losses when reaching the internal ones. The performance of the device as an absorber is estimated through a newly defined indicator and it has been found that the absorbing capacity of the structure could be very high. This qualitative factor is robust and efficient when identifying which of the considered parameters are critical or insignificant as far as the performance of the layered configuration is concerned.

A layered structure of magnetodielectric slabs, backed with a perfectly conducting plane, is illuminated by a Gaussian beam. The permittivities and permeabilities of each layer are selected so that the incident field penetrates smoothly into the subsequent layers and sustains gradually greater losses when reaching the internal ones. The performance of the device as an absorber is estimated through a newly defined indicator and it has been found that the absorbing capacity of the structure could be very high. This qualitative factor is robust and efficient when identifying which of the considered parameters are critical or insignificant as far as the performance of the layered configuration is concerned.

A layered structure of magnetodielectric slabs, backed with a perfectly conducting plane, is illuminated by a Gaussian beam. The permittivities and permeabilities of each layer are selected so that the incident field penetrates smoothly into the subsequent layers and sustains gradually greater losses when reaching the internal ones. The performance of the device as an absorber is estimated through a newly defined indicator and it has been found that the absorbing capacity of the structure could be very high. This qualitative factor is robust and efficient when identifying which of the considered parameters are critical or insignificant as far as the performance of the layered configuration is concerned.

A layered structure of magnetodielectric slabs, backed with a perfectly conducting plane, is illuminated by a Gaussian beam. The permittivities and permeabilities of each layer are selected so that the incident field penetrates smoothly into the subsequent layers and sustains gradually greater losses when reaching the internal ones. The performance of the device as an absorber is estimated through a newly defined indicator and it has been found that the absorbing capacity of the structure could be very high. This qualitative factor is robust and efficient when identifying which of the considered parameters are critical or insignificant as far as the performance of the layered configuration is concerned.