In this paper, we propose a triple band polarization-independent metamaterial absorber using square-shaped closed ring resonators over wide angle of incidence. The unit cell consisting of various square loops is designed by using the parametric analysis so that it exhibits a triple band absorption response with two bands lying in C-band and one in X-band for airborne and surveillance radar signal absorption applications. Furthermore, in X-band, the absorber exhibits a broadband response with full width at half maxima bandwidth of 940 MHz (9.43%). The structure exhibits bandwidth enhanced properties for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence up to 60°. The proposed structure is fabricated and experimental results show proper matching with the simulated responses.

A broadband polarisation‐independent circuit analogue absorber comprising multi‐layer resistive frequency selective surfaces (FSS) has been presented in this study. The proposed structure consists of a periodic arrangement of square loops loaded with lumped resistors and these square loops are printed on dielectric substrates separated by an air spacer. The simulated result shows the reflectivity below −10 dB in the frequency range from 4.96 to 18.22 GHz (fractional bandwidth of 114.40%) under normal incidence, covering C, X, and Ku bands. An equivalent circuit analysis has been introduced to characterise the proposed absorber, which shows good matching with the full‐wave analysis. The effects of the individual FSS layers and the air spacer have been studied and several parametric variations have been carried out to examine the sensitivity of the design parameters on the absorption bandwidth. Finally, the designed absorber has been fabricated and measured in anechoic chamber, which shows good agreement between the experimental results and the simulated responses, under different angles of incidence as well as for various polarisation angles.

In this paper, a bandwidth-enhanced polarization-insensitive ultra-thin metamaterial absorber has been presented. A simple equivalent circuit model has been proposed describing the absorption phenomenon to estimate the frequency of absorption of the proposed microwave absorber. The basic structure consists of concentric rings embedded one inside another to enhance bandwidth by incorporating the scalability property of the metamaterials. Simulation results show that the structure has enhanced bandwidth response with full width at half maxima (FWHM) of 1.15 GHz (9.40–10.55 GHz) with two absorption peaks at 9.66 and 10.26 GHz (96% and 92.5% absorptivity, respectively). The structure is symmetric in design giving rise to polarization-insensitivity and can achieve high absorption for oblique incidence up to 40°. The proposed absorber has been fabricated and measured in anechoic chamber, showing that experimental results agree well with the simulated responses.

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Fig. 1. (a) Perspective view, and (b) equivalent circuit of the unit cell of the absorber structure. Abstract-An equivalent circuit model of an ultra-thin metamaterial absorber comprising of square ring shaped frequency selective surface (FSS) is presented. The model can be considered as series R-L-C resonators connected in parallel with coupling capacitance and short circuited transmission line. The even and odd mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated and close matching among the calculated, simulated and measured results have been observed. Index Terms-Metamaterial absorber, equivalent circuit, frequency selective surface, lumped parameter.

In this paper, an optically transparent metamaterial with broadband absorption is presented theoretically and demonstrated experimentally. The design comprises of structures made of resistive films of indium-tin-oxide and the metamaterial exhibits over 10 dB absorption in the frequency range of 6.06–14.66 GHz. The novelty of the structure lies in its large absorption bandwidth along with a reduced thickness and optical transparency compared to broadband absorbers reported earlier. Besides, the proposed design is polarization-insensitive and gives rise to angular independent absorption for both transverse electric and transverse magnetic polarizations. The absorption mechanism in the structure has been studied by deriving an equivalent circuit model as well as analyzing several design parameters. Finally, a prototype of the proposed structure has been fabricated and measured, which shows good agreement with the simulated results.

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