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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]

In this work, the design of broadband, wide-angle, direction-independent metamaterial (MM) electromagnetic wave (EM) absorber for K-band frequency application is investigated and validated experimentally. The unit cell of the metamaterial absorber consists of four 90° rotated L-shaped metallic patches imprinted on a dielectric substrate backed by a metallic sheet. The structure yield absorption in the broad frequency ranges from 22.5 to 29.3 GHz for both TE and TM polarized waves with more than 90 % absorptivity having a wide fractional bandwidth of (6.8 GHz) 25.8 %. The structure is four-fold symmetric and hence yields polarization insensitivity for different angles of polarization under both TE and TM polarized waves. The structure is also investigated under oblique incidence where the 80 % absorptivity holds up to 45° incident angles for both TE and TM waves. The absorption mechanism is explained with the help of top and bottom surface current distribution, induced electric field, and parametric analysis. To verify the resonance in the structure, characteristic mode, and equivalent circuit analysis have been carried out and presented. A prototype of the absorber has been fabricated and simulated results are validated with measured results. Measured results are showing good agreement with the simulated responses. The novelty of the proposed absorber lies in its unique metallic pattern on a λ0/8 (concerning the canter frequency of absorption bandwidth) thin FR-4 substrate while showing the wide absorption bandwidth and direction independence to normal and oblique incidence. The compact nature of the absorber and broadband response with good polarization insensitivity at normal and oblique incidence makes it commercially suitable for the reduction of radar cross section (RCS) in stealth applications at the K-band. [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]

Broadband optical absorbers are increasingly in demand in various applications, including solar cells and radiative cooling systems. Among various types of structures, absorbers based on metamaterial structures have attracted much attention. However, they generally suffer from the issues of narrow bandwidth, high-cost fabrication, and high sensitivity to polarization changes. This paper presents a broadband, polarization-independent metamaterial absorber working in both infrared and visible frequency regimes. This structure is composed of a continuous phase-change material film ( Ge 2 Sb 2 Te 5 ) separated between two thin spacer layers of SiO 2 , and an array of amorphous Silicon particles located on the top of the structure. The proposed device was shown to exhibit remarkable absorptivity (more than 90 percent) within a broad range of frequencies starting from 250 to 1050 THz. In addition, thanks to the structural symmetry, the strong absorbance shows a considerable overlap between transverse magnetic (TM) and transverse electric (TE) modes over an extensive range of incident angles. The designing procedure for this absorber can be used as a guideline for designing similar metamaterial absorbers in any desirable frequency band. [ABSTRACT FROM AUTHOR]

A multi-band electromagnetic absorber is proposed for sensing the adulterant concentration in biofuels based on refractive index variations at room temperature (300 K). The proposed absorber structure consists of a gold based metallic resonating geometry and metallic ground plane on the top and bottom layer of the cavity loaded dielectric material. The unit cell has volume of 24 μ m × 24 μ m × 3. 57 μ m (0. 1088 λ L × 0. 1088 λ L × 0. 01618 λ L where λ L is wavelength at lowest operating frequency), five absorption peaks at 1.36, 3.349, 5.338, 5.887 & 9.307 THz with peak absorptivity of 96.15%, 97.55%, 95.63%, 83.60% & 96.13% and Full Width at Half Maxima (FWHM) of 0.098, 0.275, 1.01 & 0.417 THz respectively. For solid substrate, the absorption performance is polarization insensitive and with cavity inside the substrate, the absorption performance is polarization sensitive in normal incidence. The absorber's Refractive Index (RI) and biofuel adulteration sensing performance is also analyzed by loading analyte on its top surface and inside the substrate cavity. Peak sensitivity of ∼ 3 THz/RIU with a maximum Figure of merit (FOM) of ∼ 5. 69 RIU − 1 and maximum ∼ 0.16% error in ethanol based biofuel adulteration estimation are achieved. The proposed absorber has advantages of ultracompact dimensions, very high sensitivity and very less estimation error in adulteration estimation over other absorber based sensors. • Compact unit cell volume of 0. 10724 × 0. 10724 × 0. 015952 λ L 3 , where λ L = λ at 1.36 THz. • %A ≈ 96.15, 97.55, 95.63, 83.6 and 96.13 at 1.36, 3.349, 5.338, 5.887 and 9.307 • Can be used as a Biofuel adulteration sensor with S m a x ∼ 3 THz/RIU and FOM ∼ 6 RIU − 1 • Unknown refractive indices (avg. calc. RI) estimation with max.{% error} ∼ 0.16% • Substrate cavity & container lead to efficient sensing of solid and liquid analytes [Display omitted] [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]

A tri-band terahertz (THz) absorber for sensing the adulteration percentage in mustard oil is proposed in this paper. It consists of a gold based metallic resonating geometry and metallic ground plane on the top and bottom layers of the dielectric material respectively. It has three absorption peaks with peak absorptivity of 99.74%, 99.96% & 99.94% and Full Width at Half Maxima (FWHM) of 0.57, 0.862 & 1.112 THz at 4.6296, 8.295 & 12.6309 THz respectively. The proposed absorber's unit cell volume has an overall volume of 10 μ m × 10 μ m × 1. 61 μ m (0.15432 λ L × 0. 15432 λ L × 0. 024846 λ L where λ L is wavelength at lowest operating frequency i.e. 4.6296 THz). It has polarization insensitive absorption performance under normal incidence and incident angle (θ ∘) stability up to 50° for A ≥ 90%. The proposed structure is simulated through by using CST & HFSS. The results are validated by developing an equivalent circuit model (ECM). The results of CST, HFSS and ECM are found to be in good agreement. A sensitivity varying from ∼ 0.23 THz/RIU to ∼ 1.62 THz/RIU is achieved for Refractive Index (RI) sensing case, whereas a high sensitivity in the range of ∼ 0.4 THz/RIU to ∼ 2 THz/RIU is achieved for mustard oil adulteration sensing case by mounting the absorber's top surface with a polyimide based container filled with an analyte (either refractive index material or mustard oil). During the validation, a maximum ∼ 0.16% error in mustard oil adulteration estimation is achieved. The proposed sensor has advantages of simple & ultra compact dimensions, high sensitivity and minimal error in impurity concentration estimation with respect to other absorber-based sensors. • Unit cell volume 0.15432 λ L × 0. 15432 λ L × 0. 024846 λ L where λ L = λ at 4.6296 THz • Peak absorption of ∼ 99.9% at 4.6296, 8.295 and 12.6309 THz • Polarization independent and Incident angle (θ °) stability up to 50°for A ⩾ 90% • Used as Mustard oil adulteration sensor with maximum sensitivity of ∼ 2 THz/RIU. • Maximum 0.16% error in estimation of unknown refractive indices (avg. calc. RI) [Display omitted] [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

This paper presents a new compact ultra‐thin triple‐band absorber which shows near‐unity absorption in C, X and Ku‐bands. It consists of an inductive stub loaded circular ring resonator and a flower‐shaped resonating patch on top of 0.8 mm thin FR‐4 grounded dielectric substrate. A transmission line equivalent is proposed, and circuit simulation response is in good agreement with the full‐wave analysis. The unit‐cell architect's 4fold symmetry makes it polarisation‐insensitive for different polarisation angles in the azimuthal plane (𝜃 = 0°) under normal incidence. Its good shows angular stability up to 45° under TE (75° under TM) incidences for all three frequencies. Surface current patterns are analysed at resonant frequencies to illustrate the mechanism behind the electromagnetic absorption. This design's novelty lies in the centre patch's dual‐resonating behaviour, making this design compacted one. The absorber has low‐profile nature with cell periodicity of 0.163λL and thickness 0.013λL, where λL is the lowest resonating peak wavelength. An X‐band conventional MSA is fabricated on a thin FR‐4 substrate. In‐band RCS reduction (nearly 18 dBsm) of the antenna is verified after loading with the proposed absorber. The absorptivity peaks are optimised such that the same structure would be used in different applications like RF energy harvesting, RCS reduction and sensor applications. [ABSTRACT FROM AUTHOR]

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]

Recently, the exploration of a new strategy to create pores on carbon frameworks has received great interest. Herein, the selectively tailoring of the covalent bonding method has been shown to be one of the effective methods to generate pores based on graphitic hollow carbon frameworks (HGC). The mechanism of porous structure formation is due to directional clipping of sp2 C–C- and C O covalent bonds into C–O bonds. Due to the effectively ability for selective tailoring of covalent bonds, the resulting porous HGC has dielectric transition behavior from conductive loss to dipole polarization dependent type, which is greatly beneficial to electromagnetic absorption. The results show that the porous HGC developed by this method has exceptionally EM absorption capacity, and the maximum qualified absorption bandwidth (f E) is 7.7 GHz at the thickness of 2.2 mm. Therefore, this work opens up a potential method for the design and synthesis of high-performance EM absorbers. Selectively tailoring of covalent-bonds towards the porous structure, which possessing wideband electromagnetic absorption performance. Image 1 [ABSTRACT FROM AUTHOR]

An ultra-thin, multiband, micro-slot based metamaterial absorber is presented in this paper. The proposed unit cell is compact which is in the form of single-layer gold patch-gallium arsenide-ground package, involving four identical micro-slots. Using the micro-slots, the fundamental circular patch gains a multiband resonation skill, and the absorber operates at 1.16, 2.73, and 4.57 THz bands with near-perfect absorptivity. The absorption mechanism is discussed based on the electric and surface current distributions, and all outcomes are also validated by the effective medium approach. The proposed absorber is ultra-thin with a thickness of 2.6 µm, corresponding to ∼λ/100 at its lowest operation frequency. The unit cell indicates polarization-independent, and wide incident angle absorption spectra up to 40°, hence, the proposed absorber is a promising candidate as an absorbing platform for THz band imaging and sensing applications. [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]

Devices designed to dynamically control the transmission, reflection, and absorption of terahertz (THz) radiation are essential for the development of a broad range of THz technologies. A viable approach utilizes materials which undergo an insulator‐to‐metal transition (IMT), switching from transmissive to reflective upon becoming metallic. However, for many applications, it is undesirable to have spurious reflections that can scatter incident light and induce noise to the system. We present an electrically actuated, broadband THz switch which transitions from a transparent state with low reflectivity, to an absorptive state for which both the reflectivity and transmission are strongly suppressed. Our device consists of a patterned high‐resistivity silicon metamaterial layer that provides broadband reflection suppression by matching the impedance of free space. This is integrated with a VO2 ground plane, which undergoes an IMT by means of a DC bias applied to an interdigitated electrode. THz time domain spectroscopy measurements reveal an active bandwidth of 700 GHz with suppressed reflection and more than 90% transmission amplitude modulation with a low insertion loss. We utilize finite‐difference time domain (FDTD) simulations in order to examine the loss mechanisms of the device, as well as the sensitivity to polarization and incident angle. This device validates a general approach toward suppressing unwanted reflections in THz modulators and switches which can be easily adapted to a broad array of applications through straightforward modifications of the structural parameters. [ABSTRACT FROM AUTHOR]

Nanostructured microwave absorbing materials attract researchers because of their ability to combat electromagnetic (EM) pollution generated by high-speed electronic gadgets without interrupting gadget mobility. In the reported work, the nanosized meta copper material C2101 Kopu Tharma Loham also called nano twin crystalline copper metal fabricated as per ancient Indian metallurgical technology is characterized to ensure its microwave absorbing properties. X-ray diffraction analysis reveals that the particle size of meta copper samples is 100 nm. Further, the melting temperature of meta copper material is 1135ºC higher than copper metal (1085ºC as per International copper standards) making the absorber thermally stable. The EM properties have been experimentally measured through different techniques for frequency ranging from 2 to 40 GHz. The loss tangent plots show that the proposed material performs better in X band. The reflection loss graphs are plotted for different sample thickness values and optimal reflection loss dip of −34.4 dB is obtained at 9.5 GHz for thickness of 2.2 mm. Proposed absorbing material can be integrated on an array substrate for sidelobe level reduction or can be incorporated on aircraft surface for radar cross-section reduction. [ABSTRACT FROM AUTHOR]

A dual-band electromagnetic absorber based on double-layer frequency selective surface (FSS) is proposed for broadband applications. The layer I is designed with an absorption performance at higher frequency and a transmission window at lower frequency. Simultaneously, the layer II is designed with an absorption performance at lower frequency and a strong-reflection window at higher frequency. Due to the low-pass property of the layer I, this layer is on the top of the absorption structure, allowing the incident waves to transmit to the layer II at lower frequency and be absorbed. Meanwhile, the incident wave is absorbed at higher frequency by the layer I since the layer II acts as the strong-reflection substrate in the bottom of the absorption structure. The reflectivity of absorber below −10 dB covers a bandwidth of 1.3–4.1 GHz and 7.2–10 GHz at normal incidence. Furthermore, the absorber can still maintain an absorption bandwidth below −10 dB at 1.4–4.1 GHz under the 30° oblique incidence. The good agreement between simulation and measurement validates the proposed absorber. [ABSTRACT FROM AUTHOR]

In this paper, a low‐cost metamaterial (MM) absorber is proposed using 3‐dimensional (3D) printing technology. The unit cell of the proposed MM absorber is motivated from a swastika symbol to minimize the footprint size. For further miniaturization, the unit cell is 3D printed by stacking two blocks. The conductive top patterns are realized by painting with a silver ink. The proposed MM absorber consists of 2 × 4 unit cell array which is loaded in the rectangular waveguide. Its absorptivity is simulated and measured to demonstrate the performance. The simulated and measured absorptivity at 1.91 GHz are 99% and 92%, respectively. [ABSTRACT FROM AUTHOR]

• Composite of Fe 3 O 4 -AC nanoparticle used for EM absorber and photo-catalyst. • The frequency increases up to 6.8 GHz and the bandwidth increases up to 3.3 GHz. • Crystallite size and O H bonds were decrease with increasing the temperature. • The photo catalytic performance determined by Uv–Vis spectroscopy. • The stable temperatures for absorber EM is 900 °C and for photo-catalytic is 500 °C. Structural and bonding characteristics of multifunction nanocomposite Fe 3 O 4 -activated carbon (Fe 3 O 4 -AC) for various annealing temperatures; 500 °C, 700 °C, and 900 °C have been studied by using X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FTIR), respectively. Crystallite size and O H bonds were decreases with increasing the annealing temperature. For electromagnetic (EM) properties from the Vector Network Analyzer (VNA) shows working frequency increases from 6 GHz to 6.8 GHz and the bandwidth widening increase up to 3.3 GHz with increasing the annealing temperature, and the reflection loss (RL) values for all composites in this study shows less than −10 dB indicated suitability for EM absorber. The photocatalytic ability was determined by using ultra violet visible (Uv–Vis) spectroscopy and methylene blue (MB) solution as a liquid waste test model. The stable annealing temperatures for absorber EM is 900 °C and for the photo-catalytic application is 500 °C. In this study shows temperature play an important role in stabilizing the performance of multifunction composite of Fe 3 O 4 -AC nanoparticle for EM absorber and for liquid waste purifying catalyst. [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]

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.

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 letter, we propose an ultrawideband electromagnetic absorber using sandwiched broadband metasurfaces. The proposed absorber consists of three layers. The broadband metasurface for high frequencies is loaded on the upper layer. Another broadband metasurface for low frequencies is loaded on the lower layer. The two broadband metasurfaces form a sandwich with the air space in the middle layer. Each metasurface is realized by a periodic array of circular sector patterns with chip resistors. The fabricated absorber shows higher than 90% absorptivity from 3.87 to 14.84 GHz. Under oblique incidence, the absorber shows higher than 80% absorptivity from 3.78 to 15.63 GHz when the incident angle is less than 40° in the transverse electric mode. In the transverse magnetic mode, the absorber shows higher than 80% absorptivity from 5.11 to 15.13 GHz when the incident angle is less than 50°. [ABSTRACT FROM AUTHOR]

• The sandwich-like structure of rGO/Fe 3 O 4 @mSiO 2 nanocomposites (rGAMS) was synthesized via amidation reaction. • The sandwich-like structure of rGAMS resulted in a nanocomposite with excellent electromagnetic absorbing ability. • It enhanced the internal reflection within the structure of the composite to dissipate microwave radiation. • This work has opened the application of multifunctional porous materials in microwave shielding applications. A hybrid composite with a sandwich-like structure constructed from reduced graphene oxide (rGO) and magnetic Fe 3 O 4 particles coated mesoporous SiO 2 (Fe 3 O 4 @mSiO 2) is reported. For better adhesion of Fe 3 O 4 @mSiO 2 on the rGO sheets, the surface of the Fe 3 O 4 @mSiO 2 was modified with amonopropyltriethoxysilane to form amine-functionalized magnetic mesoporous silica (AMS). The anchoring of AMS particles on the surface of rGO in the resulting reduced graphene oxide/amine-functionalized magnetic mesoporous silica (rGAMS) hybrid greatly improved exfoliation of the rGO sheets. The as-synthesized rGAMS readily absorbed microwave radiation in epoxy composites. An rGAMS absorber with 10 wt% filler loading had an effective absorption bandwidth of 9.8 GHz in the frequency from 8.2 to 18 GHz, and the minimum reflection loss was -49.4 dB at 13.4 GHz. The adhesion of AMS particles not only induced a high specific surface area, but also acted as loci for microwave entrapment due to magnetic loss caused by their intrinsic porosity. [ABSTRACT FROM AUTHOR]

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]

This paper specifies a concise review of recent research and development in the context of electromagnetic absorbers. An attempt has been made to justify the need for economical and thin microwave absorbers for achieving good absorption characteristics over a wide range of frequencies within a specified band of electromagnetic spectrum. This paper mainly focuses on the challenges encountered while designing a perfect electromagnetic absorber which can absorb electromagnetic radiations of any polarization that may appear from any direction and may occur over a broader bandwidth. The absorbers which are competent enough to withstand all these challenges are capable to suppress the reflection and transmission of unknown electromagnetic radiations efficiently to the lowest possible level. Several prospects of nanotechnology in flexible absorber design are also described to enhance absorber characteristics. This paper also provides a futuristic glimpse on several applications of such absorbers for commercial and military purposes. [ABSTRACT FROM AUTHOR]

This letter presents multiband absorbers with wide absorption bandwidths based on an impedance matching theory. A wideband absorber with a good absorption performance is served as a matching load for multiband bandpass frequency selective surface (FSS) filters. As a result, the reflection coefficients of the proposed absorbers are in high accordance with the counterparts of the original bandpass FSS filters. For demonstration, a triple-band absorber with wide absorption bandwidths is designed and fabricated by cascading a triple-band bandpass FSS filter and a wideband absorber together. The simulated results reveal that the proposed absorber has wide fractional bandwidths of 5.2%, 8.0%, and 6.4%, which is experimentally validated by the measured results. [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]

Reconfigurable multifunctional electromagnetic absorbers have shown broad application prospects in effectively dealing with a series of problems caused by complex electromagnetic environments due to their dynamic reflection wave control characteristics. In this work, we experimentally propose a multifunctional absorber based on a graphene metasurface. Its absorption mode can be flexibly switched among three modes of dual band, broadband, and single band. The reflection amplitude in each absorption mode can be controlled simultaneously. The measurement results of the prepared graphene metasurface indicate that the absorption modes and amplitudes can be dynamically controlled by changing two independent sets of bias voltages applied to the patterned graphene sandwich structures. The proposed graphene metasurface achieves peak absorption rates above 99.9% in both dual-band and single-band absorption modes. Specifically, in the broadband absorption mode, the bandwidth with an absorption rate greater than 90% reaches 17.8 GHz. In addition, it also integrates many advantages, such as optical transparency, polarization-insensitivity, stability of oblique incidence angles, and conformability to the application targets. Therefore, the proposed graphene metasurface is expected to be applied in platforms with optical windows that require resistance to electromagnetic interference and avoidance of electromagnetic radiation.

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]

In this study, we proposed a wideband frequency tunable metamaterial absorber using a switchable ground plane (SGP). We proposed two fire retardant or flame resistant 4 (FR4) substrate structures for the SGP. An SGP is placed at the middle layer, between the top pattern and the bottom ground plane. The SGP can either be made ground or reactive, by switching the PIN diode ON/OFF. As the frequency is determined by the substrate thickness, the frequency can be switched from the SGP. The proposed absorber is demonstrated by full-wave simulations and measurements. When the SGP is turned on, an absorptivity higher than 90% is achieved from 3.5 GHz to 11 GHz. When the SGP is turned off, an absorptivity higher than 90 % is achieved from 1.7 GHz to 5.2 GHz [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]

In this paper, a polarization-insensitive, metamaterial absorber with more than 91 % absorptivity is investigated numerically and experimentally for radar cross-section reduction at X, Ku, and K bands. The unit cell structure of the absorber is comprised of a symmetrically arranged defective L-shaped patch made of copper metal, which is imprinted on a metal-backed FR-4 lossy dielectric substrate. The proposed absorber yields multiband absorption response at distinct absorption peaks at 11.1, 15.5, and 16.3 GHz along with the broadband response of 4.8 GHz from 18.6 to 23.4 GHz (absorption peaks at 18.9, 20, 21.9, and 23 GHz) in the absorption spectra. The Characteristic mode analysis has been carried out and presented to verify the modes and resonance in the structure. The physical absorption phenomenon is clarified by presenting the induced electric field, top and bottom surface current distribution, and various retrieved constitutive electromagnetic parameters. The structure is studied for various polarization angles for both transverse electric (TE) and transverse magnetic (TM) waves at normal incidence which shows strict insensitivity to the direction of arrival of electromagnetic(EM) signal. The structure is also investigated under oblique incidence for both TE and TM waves where the response holds good up to 50° incident angles in both cases. The novelty of the proposed absorber lies in its multiband response at X, Ku, and K bands through a unique metallic pattern on a thin FR-4 substrate along with characteristics of broadband, polarization insensitiveness, wide incidence angle independence, and compactness incorporated in a single and simple design without using external components. A prototype of the absorber has been fabricated and simulated results are validated with measured results. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction and energy harvesting applications at X, Ku, and K bands. [ABSTRACT FROM AUTHOR]

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]

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.

In this paper, we propose an ultra-broadband metamaterial absorber optimized by the particle swarm optimization (PSO) algorithm. A unit cell of the absorber is made of TiN/TiO 2 /TiN square disks, offering a metal-insulator-metal (MIM) configuration, surrounded by a TiN square ring resonator which all are located on a thin stack of TiO 2 /TiN films. The optimized structure shows high average absorption of 91.63% over the wavelength range of 200–4500 nm. The over 90% absorption bandwidth is 1590 nm, extended from 200 nm to 1790 nm. Furthermore, the absorber absorbs more than 80% of the incident light with wavelengths from 200 nm to 4480 nm, which covers the ultraviolet, visible, and near-infrared regions. The absorber indicates high absorptivity of over 75% under an oblique incidence up to 60° for both TM and TE polarizations. The effect of the presence of the square ring resonators as well as each layer of the MIM on the absorption of the absorber is also studied. It is shown that the use of square ring resonators combined with square disks significantly enhances the absorption of the absorber at wavelengths longer than 1100 nm. The structure has high thermal and chemical stability due to the use of TiN and TiO 2. Owing to the outstanding features of the proposed absorber, it can be used in different fields such as imaging, thermal emitting, and solar applications. • Having high thermal and chemical stability due to the use of TiN and TiO 2 Materials. • Having an average absorption of 91.63% in the wavelength range of 200-4500 nm. • Having a high bandwidth of 1590 nm, ranging from 200 nm to 1790 nm for over 90% absorption. • Having a high bandwidth of 4280 nm, ranging from 200 nm to 4480 nm for over 80% absorption. • Having polarization-insensitive and angle-independent performance for oblique incident light up to 60° in the wavelength range of 200-4500 nm. [ABSTRACT FROM AUTHOR]

Epoxy nanocomposites with magnetic and dielectric loading are developed and characterized with regard to the microwave absorption performance in the X-band (8–12.4 GHz). Therefore, single-phase nanoscale cobalt ferrite CoFe 2 O 4 and calcium titanate CaTiO 3 with different morphological features were synthesized via hydrothermal method. By studying the composites filled separately with 40 wt% of the as-prepared CoFe 2 O 4 , CaTiO 3 or carbonyl iron powder we deduce the superior performance of magnetic fillers compared to the dielectric one. The former show strong but narrowband absorption up to 40 dB. By combining all filler types, we produced magnetodielectric composites with attenuation still as high as 33 dB and wider bandwidth of operation. Moreover, by varying the material thickness from 2.8 mm to 4 mm, zones of high attenuation values (> 10 dB) can be tuned throughout the X-band range. The combined magnetic and dielectric properties apparently favor the fulfilment of the impedance matching conditions for quarter-wavelength thickness. The improved microwave absorbing performance of the multicomponent composites is verified by characterizations with the waveguide and free-space technique. [ABSTRACT FROM AUTHOR]

The understanding of the effect of cell structure on the electromagnetic absorption properties can help to optimize foam structures for different applications. In this research, foams with different air volume percent, spherical and polygonal cell shapes, cell densities in the range of 10 4 –10 10 cell/cm 3 and cell sizes ranging from 2.8 to 370.3 μm are produced using an automatic and controllable supercritical CO 2 foaming system. The results showed that foaming of PMMA/MWCNT composites resulted in a 60% reduction in electromagnetic reflection and a 96% increase in specific electromagnetic absorption. The percolation threshold of foams with polygonal cell shape is found to occur at higher MWCNT loading than spherical cell shapes. Electromagnetic reflection is independent of cell density and cell size, while absorption was improved for about 34% with increasing cell density and decreasing cell size, indicating an enhancement of the multiple reflection mechanism. [ABSTRACT FROM AUTHOR]