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This work introduces a wideband metamaterial (MM) absorber designed to operate effectively across a wide reception angle and be polarization-insensitive within ISM band (2.4 GHz) applications. The proposed absorber unit cell comprises four copper sectors loaded with lumped resistors and a full copper ground plane hosted onto two FR4 substrates. Furthermore, an air layer suspended between the ground plane and a FR4 substrate is applied to achieve wideband absorption. In addition, the simulation results show that particular design factors, such as lumped resistors and unit cell geometry, can be optimized to improve the efficiency of the absorber. The simulations demonstrate that the proposed absorber achieves a wideband absorption, exceeding 90%, over a broad frequency range from 1.94 GHz to 2.98 GHz. The designed absorber was fabricated and tested, and the simulation and measurement results were agreed well.

In this paper, a broadband, polarization-independent metamaterial absorber for millimeter waves is proposed. Operating across the frequency range of 22.7 GHz to 37.2 GHz, our broadband, polarization-independent absorber demonstrates exceptional efficacy by capturing over 90% of incident wave power. Distinguished by an array of conductive square patches on a dielectric substrate, the proposed structure boasts a remarkably low thickness, measuring less than a quarter of the free space wavelength of the central point within its operational spectrum (excluding the ground layer thickness). Leveraging a combination of circuit modeling and transmission line theory, this paper presents the design of this absorber and also elucidates its underlying operating principles. The combination of broadband operation, low thickness, and systematic design is rarely seen in previous works. To validate the proposed approach, a physical prototype is realized using 3D printing technology, employing conductive polylactic acid (C-PLA) patches on a light polyvinyl chloride (L-PVC) substrate. The proposed absorber has various potential applications in communication, electromagnetic shielding, and satellite technologies. Finally, a comparison with recent works is performed to demonstrate the feasibility of the proposed structure for millimeter-wave applications. [ABSTRACT FROM AUTHOR]

The present study proposes a strong and wide microwave absorption of multilayered metastructure (SWMAMM) capable of achieving an ultra-wideband absorption of −20 dB and 60° oblique incidence. SWMAMM primarily consists of metasurface-Ⅰ (MS-Ⅰ), metasurface-Ⅱ (MS-Ⅱ), and a top absorption-enhanced skin, which are separated by three support dielectric slabs. Based on impedance matching theory and the interference model, MS-Ⅰ serves as the core functional layer for wideband absorption; whereas MS-Ⅱ not only provides ultra-wideband impedance matching but also enhances absorptivity, distinguishing it from most designs. To further improve impedance matching, different hole arrays are incorporated into the substrates of MS-Ⅰ, MS-Ⅱ, and the top absorption-enhanced skin by modifying their equivalent reactance. The measurement results demonstrate that the −10 dB and −20 dB reflection bands are separately in the range of 3.97–23.19 GHz and 5.24–21.81 GHz when the oblique incidence angle reaches 5°; the −10 dB reflection band can cover the range of 5.99–25.00 GHz when the oblique incidence angle reaches 60°. Our approach, which involves impedance matching design of MS-Ⅱ and optimizing impedance matching by incorporating different hole arrays into the substrates of the MS-Ⅰ, MS-Ⅱ, and the top absorption-enhanced skin, can be applied to various unit cells and dielectric materials. This approach offers significantly enhanced convenience and efficiency compared to existing designs, thereby facilitating further optimization and development of Electromagnetic absorbers.

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.

Performance of a microwave absorbing material can be increased by moulding it into a resonator structure. These tuned structures made up of lossy materials like dielectric cavities trapped the electromagnetic waves and dissipate them. However, resonator structures are narrowband, and to make them wideband absorbers, a technique has been proposed here. In the presented work, an array of dielectric cavity resonators has been proposed having cavities of different physical dimensions. Due to change in physical dimensions, all cavities have unique resonating peaks. Arranging these cavities into two-dimensional array leads to overlapping of all the resonating peaks, and accordingly, a broadband dielectric cavity resonator (DCR) array absorber is designed. Proposed array structure has − 22.6 dB reflection coefficient and 8 GHz (6 to 14 GHz) absorption bandwidth makes it a broadband absorber which can be utilized to build an anechoic chamber for testing the electromagnetic devices. [ABSTRACT FROM AUTHOR]

This work presents an ultrawideband and high-absorption structure (UHAS) obtained by a fast design method. The proposed analytic approach can simply design single-FSS-layer absorber with ideal performance stability under oblique incidence. With this method, a composite material reinforced circuit-analog (CA) absorber is designed, which unit cell of CA sheet is a square ring loaded with chip resistors. At normal incidence, both TE and TM polarization simulation results demonstrate that the reflection coefficient below −10 dB is from 5.8 to 22.2 GHz; meanwhile, the reflection coefficient less than −20 dB covers a bandwidth of 7.4–19.1 GHz; also, there is a −30 dB absorption band in 8.6–17.2 GHz. Furthermore, under TE polarization, experimental results indicate that UHAS can maintain a −20 dB absorption band from 7.4 to 18.0 GHz within 40° oblique angle of incidence; −10 dB absorption is from 6.1 to 18.0 GHz within 50° oblique angle of incidence. The good agreement between simulation and measurement validates the proposed method and UHAS. Finally, the UHAS, with a protective layer, will be more stable in practical applications. [ABSTRACT FROM AUTHOR]

With the effect of technological advances, the use of electrical and electronic devices has increased dramatically in recent years. Wireless technologies and related applications are mostly preferred for the communication of these devices with each other. Thus, people are easily exposed to electromagnetic waves in daily life. The extensive global use of these devices raises the question of their possible biological effects on human health. Also, electromagnetic waves influence the functioning of a nearby device. In this study, an electromagnetic absorber based on boric acid (5, 10, 20, and 30 wt%) added wastepaper was developed. Copper (Cu) and aluminum (Al) were also used as mineral additives for comparison. Three different kinds of wastepaper namely, office paper, newsprint, and cardboard paper were selected for the experimental study. The effect of varying boric acid contents on the electromagnetic absorption of the boards manufactured was evaluated and compared to Cu (30 wt%) and Al (30 wt%) added boards. The results show that newsprint has better absorption effectiveness than office and cardboard paper and absorption up to 40 dB was achieved. The absorption effectiveness of Al, Cu, and boric acid added boards was achieved at approximately 40, 30, and 20 dB, respectively. As a result, the electromagnetic absorption effectiveness of boric acid added the board is acceptable levels. Also, apart from the use of boric acid as a powder, it has been determined that the application of the surface as a layer is effective in absorption. [ABSTRACT FROM AUTHOR]

Highlights The role of electron transport characteristics in electromagnetic (EM) attenuation can be generalized to other EM functional materials. The integrated functions of efficient EM absorption and green shielding open the view of EM multifunctional materials. A novel sensing mechanism based on intrinsic EM attenuation performance and EM resonance coupling effect is revealed. Abstract It is extremely unattainable for a material to simultaneously obtain efficient electromagnetic (EM) absorption and green shielding performance, which has not been reported due to the competition between conduction loss and reflection. Herein, by tailoring the internal structure through nano-micro engineering, a NiCo2O4 nanofiber with integrated EM absorbing and green shielding as well as strain sensing functions is obtained. With the improvement of charge transport capability of the nanofiber, the performance can be converted from EM absorption to shielding, or even coexist. Particularly, as the conductivity rising, the reflection loss declines from − 52.72 to − 10.5 dB, while the EM interference shielding effectiveness increases to 13.4 dB, suggesting the coexistence of the two EM functions. Furthermore, based on the high EM absorption, a strain sensor is designed through the resonance coupling of the patterned NiCo2O4 structure. These strategies for tuning EM performance and constructing devices can be extended to other EM functional materials to promote the development of electromagnetic driven devices. Graphic Abstract

An all-dielectric transparent metamaterial absorber with encapsulated water is demonstrated in this paper. Because the proposed absorber is realized using only water and polydimethylsiloxane (PDMS) without any conductive patterns, optical transparency is achieved. In addition, the high dielectric loss of water renders it a good candidate for an electromagnetic absorber. The absorptivity is increased by encapsulating the water within the PDMS, and the absorptivity of the proposed absorber is numerically compared with that of the PDMS and water with the same size. When the proposed absorber is realized using two layers, 92.5% absorptivity is achieved at 10.8 GHz, and the absorptivity exceeds 90% in the range of 10.45 to 11.20 GHz, which corresponds to 6.9% bandwidth. Therefore, the proposed absorber has advantages of high transparency, low cost, wide absorption bandwidth, and eco-friendly fabrication.

Multiple loss mechanisms involving multiple scattering and reflection, conductive loss, interface polarization, dipolar polarization as well as magnetic loss caused by exchange resonance, natural resonance and eddy current loss contribute to effective electromagnetic wave absorption behavior. • rGO/N-C/FeNi hybrids were synthesized via an environmentally friendly process. • Nitrogen was doped in the carbon matrix through exploiting pyrrole. • The hierarchical structure provides absorbers with favorable EM properties. A unique reduced graphene oxide (rGO)/nitrogen doped carbon (N-C)/FeNi hybrid was successfully synthesized via a green and environmentally friendly process by means of one pot method. The morphology, phase structure, composition and electromagnetic (EM) wave absorption behavior of all hybrids were studied in detail. All rGO/N-C/FeNi hybrids are composed of rGO sheets on which there are nitrogen doped carbon and FeNi nanoparticles, and the novel structure endows the absorber with multiple scattering and reflection, interfacial polarization, dipole polarization and so on, further bringing remarkable EM wave absorption behavior. Moreover, the complex permittivity of rGO/N-C/FeNi hybrids is able to be controlled through changing the amount of GO. All results show that the rGO/N-C/FeNi-3 hybrid displays a substantial improvement in EM wave absorption performance compared with other hybrids. The minimum reflection loss (RL min) value is −68.87 dB at 12.08 GHz with the thickness of 2.5 mm and the largest effective absorption bandwidth (EAB) achieves 6.88 GHz at 2.2 mm with RL min value of −14.73 dB at 12.16 GHz. Our research proves that the unique structure and composition have the potential to elevate EM wave absorption performance. [ABSTRACT FROM AUTHOR]

This article deals with a controversial topic in the field of reverberation chambers which is the potential efficiency of inserting diffracting metallic objects in order to improve the performance of these so-called “chaotic” chambers at low frequency. Taking advantage of the accuracy of the “well-stirred condition” method, an extensive campaign of measurements helps to conclude on the absence of any undeniable effect of such diffracting objects. It is also demonstrated that the insertion of these objects modifies (slightly) the quality factor of the chamber. Therefore, the performance of a chamber having different chaoticity degree has to be compared with and without these objects for the same $Q$ -factor, which requires small amount of absorbers to be inserted in the chamber having a lower chaoticity degree in order to compensate the metallic losses of these diffractors. Otherwise, a bias is introduced which can lead to draw erroneous conclusions on their effects. [ABSTRACT FROM AUTHOR]

Highlights: The role of electron transport characteristics in electromagnetic (EM) attenuation can be generalized to other EM functional materials. The integrated functions of efficient EM absorption and green shielding open the view of EM multifunctional materials. A novel sensing mechanism based on intrinsic EM attenuation performance and EM resonance coupling effect is revealed. It is extremely unattainable for a material to simultaneously obtain efficient electromagnetic (EM) absorption and green shielding performance, which has not been reported due to the competition between conduction loss and reflection. Herein, by tailoring the internal structure through nano-micro engineering, a NiCo2O4 nanofiber with integrated EM absorbing and green shielding as well as strain sensing functions is obtained. With the improvement of charge transport capability of the nanofiber, the performance can be converted from EM absorption to shielding, or even coexist. Particularly, as the conductivity rising, the reflection loss declines from − 52.72 to − 10.5 dB, while the EM interference shielding effectiveness increases to 13.4 dB, suggesting the coexistence of the two EM functions. Furthermore, based on the high EM absorption, a strain sensor is designed through the resonance coupling of the patterned NiCo2O4 structure. These strategies for tuning EM performance and constructing devices can be extended to other EM functional materials to promote the development of electromagnetic driven devices. [ABSTRACT FROM AUTHOR]

In this article, a novel slot-array defected ground structure (DGS) for decoupling microstrip antenna array is proposed. The slot-array DGS is etched surrounding each antenna element on the ground plane and parallel to the radiating edges of each antenna element. The decoupling mechanism is elucidated via an equivalent circuit model and the coupled current field analysis, which reveals slot-array DGS has the spatial band-stop characteristic and changes the direction of the partially coupled current, respectively. Both characteristics of the slot-array DGS contribute to mutual coupling reduction. Three practical design examples of applying slot-array DGS to single-linearly polarized (LP), dual-LP, and compact circularly polarized (CP) antenna array are given to illustrate the design process and considerations. The simulated and measured results show that about 50 dB isolation enhancement is obtained by using the slot-array DGS when the edge-to-edge spacing between CP antenna elements is 0.057 wavelength. Additionally, a wheel-shaped absorber based on the electromagnetic loss material is designed and fabricated to reduce the backward radiation caused by slot-array DGS. The absorber has an absorptivity of more than 95% in the frequency range of 1.2–1.35 GHz and suppresses the backward radiation over 12.5 dB in the plane phi = 0° and 16.1 dB in the plane phi = 90° without deteriorating other antenna performances. [ABSTRACT FROM AUTHOR]

The development of 5G telecommunication technology has seen a high demand for effective electromagnetic (EM) wave absorbers in the millimeter wave (mmWave) band. Because hexagonal M‐type ferrite is known to have high ferromagnetic resonance (FMR) in the 5G band frequency, it has attracted significant attention as a mmWave absorber. However, study of the relationship between magnetocrystalline anisotropy, FMR frequency, and EM wave absorption performance in the mmWave band remains insufficient. In this study, Ni–Ti‐substituted M‐type barium ferrite (Ba–M ferrite) was synthesized using the citrate sol–gel method, and the change in the magnetic properties caused by Ni–Ti substitution was analyzed. The complex permittivity, permeability, and reflection loss (RL) of the Ni–Ti‐substituted Ba–M ferrite composites in the 8.2–75 GHz broadband frequency range were also studied. The EM wave absorption frequency, which is governed by the FMR frequency, could be tuned by controlling the amount of substituted Ni–Ti ions in the Ba–M ferrite. The prepared EM wave absorber exhibited excellent EM wave absorption properties with an RL of −52 dB at 29.5 GHz and a matching thickness of 0.95 mm. This study provides insights into a frequency‐tunable EM wave absorber with enhanced absorption properties, attained by changing the magnetic properties of Ni–Ti‐substituted M‐type hexaferrites in the mmWave frequency band. [Display omitted] • A single-phase Ni–Ti-substituted Ba–M ferrites were synthesized by citrate sol-gel method. • The electromagnetic properties were studied in a wide frequency range from 8.2 GHz to 75 GHz. • Electromagnetic wave absorption frequency was tuned by controlling the ferromagnetic resonance frequency. • Optimum reflection loss of −52 dB at 29.5 GHz and an EAB of 10.05 GHz were obtained at 0.95 mm thickness. [ABSTRACT FROM AUTHOR]

This paper proposes a switchable metasurface for broadband and polarization-insensitive absorption, whose absorption spectrum can be fluidically switched using liquid metal. The proposed metasurface consists of a top metallic pattern, a flexible printed circuit board substrate, a polydimethylsiloxane substrate, and a bottom metallic ground plane. The proposed unitcell is inspired by a four-circular-sector structure. To maintain the symmetrical geometry and increase the switching range, a symmetrical microfluidic channel is designed with a circular ring capillary and four isolated patches. To measure the absorptivity of the proposed metasurface, 10 × 10 unitcells are fabricated with 20 inlets and 20 outlets. When the microfluidic channels of the metasurface are empty, the fabricated metasurface achieves an absorptivity of higher than 90%, from 6.23 to 12.14 GHz. When eutectic gallium-indium alloy is injected into the microfluidic channels, the fabricated metasurface achieves higher than 90% absorptivity, from 5.44 to 6.12 GHz. Thus, for both cases, the absorptivity is constant at different incident polarization angles.

In this paper, we propose a metamaterial absorber using 3-D printing technology. To miniaturize the footprint size of a unit cell, we introduce a 3-D printed stair-like Jerusalem cross (JC) structure. It is demonstrated that the absorption frequency can be decreased by building up one and two stairs from the planar JC. In this paper, the unit cell footprint size of the three-stair JC is reduced by 41% compared with the unit cell footprint size of the planar JC. The proposed metamaterial absorber with 9×9 unit cells is fabricated using a 3-D printer. Poly lactic acid is used as a dielectric material for 3-D printing, and a conductive pattern is realized by applying the silver paste to the 3-D printed dielectric structure. The simulated and measured absorptivity are 99.9% and 99.8%, respectively, at 5.18 GHz. Due to the symmetric unit cell structure, the absorptivity does not change, although the incident polarization gets rotated.

We present an energy harvesting surface (EHS) designed for electromagnetic energy harvesting and wireless power transfer consisting of an array of cross-dipole metallic elements. The EHS unit cell of the proposed harvester is based on two cross-dipoles that enable capturing the energy from various angles of illuminations at an operating frequency of 3 GHz. The simulation results yielded a radiation to ac efficiency of 94% at multiple angles of polarization. As a proof of concept, a finite array of $7\times 7$ unit cells was fabricated and tested experimentally. The experimental results of the EHS energy harvesting array show an overall radiation to dc harvesting efficiency of 74% at various polarization angles. A critical design feature of the proposed cross-dipole EHS array is that it allows direct matching to a rectifying circuitry at the dipoles plane. The design also enhances the available power per diode, thus, maximizing the rectifying diodes’ turn-on time. [ABSTRACT FROM AUTHOR]

• The impedance design of metasurfaces is important for this absorber's exceptional electromagnetic absorption capability. • The utilization of a dielectric hole array as an impedance matching layer can significantly enhance absorptivity. • By employing hole-dielectric arrays as substrates for metasurfaces, the impedance matching can be enhanced. The present study proposes a strong and wide microwave absorption of multilayered metastructure (SWMAMM) capable of achieving an ultra-wideband absorption of −20 dB and 60° oblique incidence. SWMAMM primarily consists of metasurface-Ⅰ (MS-Ⅰ), metasurface-Ⅱ (MS-Ⅱ), and a top absorption-enhanced skin, which are separated by three support dielectric slabs. Based on impedance matching theory and the interference model, MS-Ⅰ serves as the core functional layer for wideband absorption; whereas MS-Ⅱ not only provides ultra-wideband impedance matching but also enhances absorptivity, distinguishing it from most designs. To further improve impedance matching, different hole arrays are incorporated into the substrates of MS-Ⅰ, MS-Ⅱ, and the top absorption-enhanced skin by modifying their equivalent reactance. The measurement results demonstrate that the −10 dB and −20 dB reflection bands are separately in the range of 3.97–23.19 GHz and 5.24–21.81 GHz when the oblique incidence angle reaches 5°; the −10 dB reflection band can cover the range of 5.99–25.00 GHz when the oblique incidence angle reaches 60°. Our approach, which involves impedance matching design of MS-Ⅱ and optimizing impedance matching by incorporating different hole arrays into the substrates of the MS-Ⅰ, MS-Ⅱ, and the top absorption-enhanced skin, can be applied to various unit cells and dielectric materials. This approach offers significantly enhanced convenience and efficiency compared to existing designs, thereby facilitating further optimization and development of Electromagnetic absorbers. [ABSTRACT FROM AUTHOR]

Abstract Special materials for electromagnetic absorber (EMA) and stealth camouflage techniques are desired due to their widespread applications in the military field. In this paper, BaTiO 3 /reduced graphene oxide (RGO) composites via hydrothermal process were prepared. BaTiO 3 nanotube has unique features: single crystalline, high aspect ratio and uniform distribution on RGO nanosheet. Compared with pure BaTiO 3 nanowire, BaTiO 3 /RGO composites exhibited good absorption properties. The maximum reflection loss (RL) of BaTiO3/reduced graphene oxide (RGO) composites is about of −44.9 dB, and they exhibited an effective electromagnetic absorption bandwidth of 5.4 GHz with the thickness of 2.5 mm BaTiO 3 /RGO composites could be used as promising materials for EMA and broad absorption properties. Highlights • BaTiO 3 /reduced graphene oxide (RGO) composites via hydrothermal process were prepared. • BaTiO 3 nanotubes were distributed on the surface of RGO nano sheets. • BaTiO 3 /RGO composites exhibit a remarkable absorption properties. • BaTiO 3 /RGO composites have a good electromagnetic absorption properties. [ABSTRACT FROM AUTHOR]

This paper explores the characteristics of unidirectional carbon-fiber-reinforced-polymer (CFRP) laminas and their use in electromagnetic absorber design. Unidirectional CFRP composites have been used for decades in structural applications. The electromagnetic properties of unidirectional CFRP composites have been well documented in the open literature. Since many structural applications may also have specific electromagnetic compatibility requirements, it is logical to exploit the useful electromagnetic properties of unidirectional CFRP. Specifically, this paper investigates circuit-analog absorbers (CAAs) made from a unidirectional CFRP lamina, foam spacer, and a ground plane. The unique properties of the unidirectional CFRP sheet provide the necessary resistive and reactive properties for the development of a CAA. To investigate such a CAA, the electromagnetic properties of several off-the-shelf unidirectional CFRP laminas were measured from 4 to 18 GHz using a free-space measurement system. A surface-impedance representation of the unidirectional CFRP lamina was used to build rigorous transmission-line models that provide insights about the properties of the absorbing structure. Transmission line as well as full-wave models were compared to measured absorption performance of fabricated prototypes. Maximum absorption configurations were found to be highly dependent on incident polarization relative to fiber orientation. [ABSTRACT FROM AUTHOR]

We present a design of an electromagnetic energy harvesting surface inspired by an array of printed metallic dipolar elements. The unit cell of the proposed harvester is based on two printed asymmetric off-center fed dipoles. As a proof of concept, a finite array of $9 \times 3$ unit cells was analyzed numerically and experimentally. The array was first analyzed for maximizing radiation to ac absorption where each dipole was terminated by a resistor across its gap. For dc conversion, the resistors were the replaced by Schottky diodes. The simulation results show radiation to ac harvesting efficiency of 99%. An overall radiation to dc harvesting efficiency of 76% was obtained experimentally, which, to the best of the authors’ knowledge, exceeds the performance of all previous energy harvesting surfaces. Another critical feature of the proposed designs is enhancing the power per diode in order to maximize its turn-ON time. [ABSTRACT FROM PUBLISHER]

Carbon microcoils (CMCs) have an interesting 3D-helical/spiral form with a coil diameter of micrometer orders and a coil length of mm orders. Pulverized CMCs are generally embedded into polymer matrix to form CMC/polymer composites for various applications. The CMCs are very interested as a possible candidate for electromagnetic absorbers, remote microwave heating elements, microwave visualization materials, tactile and nearness sensors, chiral catalyst, etc. In this review, the preparation conditions, morphology, some properties and possible applications of the CMCs are briefly introduced.† This report was originally printed in J. Soc. Powder Technology, Japan, 42, 715-720 (2005) in Japanese, before being translated into English by KONA Editorial committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

The recently developed two-dimensional transition metal carbides (such as MXene) have shown amazing electrical properties. MXene and derivative two dimensional (2D) materials are widely used in electron devices, and have large potential application in electromagnetic (EM) absorber. Herein we describe a mild method to prepare an urchin-like ZnO-MXene Ti 3 C 2 T x nanocomposite through a coprecipitation process. The nanocomposite delivers a substantially enhanced EM absorbing performance with an optimum reflection loss of −26.30 dB, which is significantly better than that of primitive Ti 3 C 2 T x (−6.70 dB), owing to the construction of unique semiconductive networks and larger interfaces. The EM absorption performance can be effectively controlled in the range of 14.0–18.0 bands by changing the growth time of ZnO. Considering the large amount of members in MXene, this study demonstrates a new strategy applicable in maximizing their applications in EM absorbing materials. [ABSTRACT FROM AUTHOR]

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.

In this study, we propose a thermal frequency reconfigurable electromagnetic absorber using germanium telluride (GeTe) phase change material. Thermally-induced phase transition of GeTe from an amorphous high-resistive state to a crystalline low-resistive state by heating is used to change the resonant frequency of the absorber. For full-wave simulation, the electromagnetic properties of GeTe at 25 °C and 250 °C are characterized at 10 GHz under normal incidence for electromagnetic waves. The proposed absorber is designed based on the characterized electromagnetic parameters of GeTe. A circular unit cell is designed and GeTe is placed at a gap in the circle to maximize the switching range. The performance of the proposed electromagnetic absorber is numerically and experimentally demonstrated. Measurement results indicate that the absorption frequency changes from 10.23 GHz to 9.6 GHz when the GeTe film is altered from an amorphous state at room temperature to a crystalline state by heating the sample to 250 °C. The absorptivity in these states is determined to be 91% and 92%, respectively.

A novel type of a broadband flexible electromagnetic absorbing panel made of a resistive pattern printed on a dielectric spacer backed by a conducting surface is investigated in this paper. It is shown that an appropriate choice of the shape and sheet resistance of the pattern allows extending an absorption spectrum up to an octave and beyond, which is very competitive over alternative solutions. The pattern is made of ink with graphene nano-platelets, which allows achieving expected sheet resistance with decent repeatability, what is confirmed with measurements undertaken with the DC point probe and microwave dielectric resonator techniques. An exemplary sample of the proposed absorber is manufactured and characterized, indicating a very good agreement between theoretical study and experiments. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The complex permittivity and permeability of ferrite-filled polymer composites were studied at 50 MHz to 1 GHz, and their effects on the electromagnetic compatibility (EMC) of an integrated circuit (IC) package mounted on a printed wiring board (PWB) in the far- and near-field modes were investigated. Incorporating the ferrite particles into the polymer increased the real part of the complex permeability to 10-11 at 50 MHz, and the real part exhibited a frequency dependency over the applied frequency range (50 MHz to 1 GHz). The ferrite particle increased the magnetic loss (μ″ = 3-5) as well, which can absorb the magnetic energy of the incident electromagnetic wave. By coating the test IC package with the ferrite-polymer composite materials, the EMC level of the PWB was dramatically improved. This improvement may be due to the high magnetic loss of the ferrite-polymer composite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Controlling the load of Co-CoFe 2 O 4 can receive exceptional impedance matching. • The minimum reflection loss is −65.31 dB at 2.1 mm. • The maximum effective absorption bandwidth is 8.48 GHz at 2.4 mm. Carbon nanomaterials have attracted a great deal of attention in various fields especially in electromagnetic wave absorption due to unique physical and chemical properties. Herein, a novel Co-CoFe 2 O 4 @mesoporous hollow carbon spheres (PCHMs) nanocomposites were prepared by two-facile steps, which included synthesizing three-dimensional mesoporous hollow carbon nanospheres (3D PCHMs) by hard template method, pyrolysis and etching process and in-situ growth of ultra-small Co-CoFe 2 O 4 nanoparticles on PCHMs. The microscopic morphology and electromagnetic wave absorption mechanisms were discussed in depth. The synthesized Co-CoFe 2 O 4 @PCHMs maintained a stable hollow and mesoporous structure and the Co-CoFe 2 O 4 nanoparticles are uniformly distributed on the PCHMs. The complex permittivity and complex permeability could be effortlessly controlled by the content of Co-CoFe 2 O 4 nanoparticles. Benefitting from the remarkable impedance matching under the influence of moderate complex permittivity and complex permeability, the minimum reflection loss (RL min) of S2 exhibited −65.31 dB at 2.1 mm. The maximum effective absorption bandwidth (EAB) reached up to 8.48 GHz. The Co-CoFe 2 O 4 @PCHMs nanocomposites will have great potential application in electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

An optically transparent metamaterial absorber that can be obtained using inkjet printing technology is proposed. In order to make the metamaterial absorber optically transparent, an inkjet printer was used to fabricate a thin conductive loop pattern. The loop pattern had a width of 0.2 mm and was located on the top surface of the metamaterial absorber, and polyethylene terephthalate films were used for fabricating the substrate. An optically transparent conductive indium tin oxide film was introduced in the bottom ground plane. Therefore, the proposed metamaterial absorber was optically transparent. The metamaterial absorber was demonstrated by performing a full-wave electromagnetic simulation and measured in free space. In the simulation, the 90% absorption bandwidth ranged from 26.6 to 28.8 GHz, while the measured 90% absorption bandwidth was 26.8–28.2 GHz. Therefore, it is successfully demonstrated by electromagnetic simulation and measurement results. [ABSTRACT FROM AUTHOR]

In this study, we propose a thermal frequency reconfigurable electromagnetic absorber using germanium telluride (GeTe) phase change material. Thermally-induced phase transition of GeTe from an amorphous high-resistive state to a crystalline low-resistive state by heating is used to change the resonant frequency of the absorber. For full-wave simulation, the electromagnetic properties of GeTe at 25 °C and 250 °C are characterized at 10 GHz under normal incidence for electromagnetic waves. The proposed absorber is designed based on the characterized electromagnetic parameters of GeTe. A circular unit cell is designed and GeTe is placed at a gap in the circle to maximize the switching range. The performance of the proposed electromagnetic absorber is numerically and experimentally demonstrated. Measurement results indicate that the absorption frequency changes from 10.23 GHz to 9.6 GHz when the GeTe film is altered from an amorphous state at room temperature to a crystalline state by heating the sample to 250 °C. The absorptivity in these states is determined to be 91% and 92%, respectively. [ABSTRACT FROM AUTHOR]