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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]

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]

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 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 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]

This paper focuses on the design and analysis of a polarization-insensitive wide-angle broadband metamaterial absorber for stealth applications at the K band. The unit cell of the metamaterial absorber is comprised of a symmetrically arranged ladder shape geometry made of copper metal, which is imprinted on a metal-backed FR-4 substrate. The structure shows more than 91% absorptivity ranging from 21.2 to 28.2 GHz for both transverse electric (TE) and transverse magnetic (TM) polarized waves under normal incidence. The topology is four-fold symmetric and yields polarization-insensitive responses 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 resonances 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. The novelty of the proposed absorber lies in its unique metallic pattern on a λ 0 /8 thin FR-4 substrate while showing the wide absorption bandwidth to normal and oblique incidence. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction applications at the K band. [ABSTRACT FROM AUTHOR]

• A mechanically actuated frequency reconfigurable metamaterial electromagnetic absorber is proposed. • A linear actuator and microcontroller is used for changing air substrate thickness mechanically. • The absorption frequency changes from 6.96 GHz to 5.78 GHz when the air substrate thickness is changed from 17 mm to 26 mm. • A rate of change for the absorption frequency relative to the air substrate thickness is 0.12 (GHz/mm). • The proposed metamaterial absorber can be potentially used for wireless pressure sensor applications. In this paper, a mechanically actuated frequency reconfigurable metamaterial electromagnetic absorber is proposed. The absorber's metamaterial unit cell is designed to exploit LC resonance from inductive and capacitive coupling. Because this inductance and capacitance determine the absorber's resonant frequency, we propose a mechanical tuning method that changes the resonant frequency by changing the overall thickness of the metamaterial unit cell. The proposed unit cell consists of an FR4 dielectric substrate with fixed thickness and an air substrate with tunable thickness. When the air substrate thickness is varied over the range of 17 mm to 26 mm, the absorber's resonant frequency changes from 6.96 GHz to 5.79 GHz in EM simulation. In order to verify the proposed idea, a metamaterial absorber was fabricated as a 17 × 17 array of unit cells and a linear actuator was used to control the thickness of the air substrate. We experimentally demonstrated that the absorption frequency changes from 6.96 GHz to 5.78 GHz with 0.12 (GHz/mm) sensitivity when the air substrate thickness is mechanically changed from 17 mm to 26 mm. [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]