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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]

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]

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]

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]

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]

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]

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]

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]

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]

We derive periodic multilayer absorbers with effective uniaxial properties similar to perfectly matched layers (PML). This approximate representation of PML is based on the effective medium theory and we call it an effective medium PML. We compare the spatial reflection spectrum of the layered absorbers to that of a PML material and demonstrate that after neglecting gain and magnetic properties, the absorber remains functional. This opens a route to create electromagnetic absorbers for real and not only numerical applications and as an example we introduce a layered absorber for the wavelength of 8 $$\upmu \hbox {m}$$ made of $$\hbox {SiO}_2$$ and NaCl. We also show that similar cylindrical core-shell nanostructures derived from flat multilayers also exhibit very good absorptive and reflective properties despite the different geometry. [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]