Transparent and broadband absorption-diffusion-integrated low-scattering metamaterial by standing-up lattice

Extremely wideband low-RCS polarization conversion metasurface based on multivariate phase destructive interference

In this paper, a polarization modulated metasurface to improve the magnitude and expand the bandwidth of radar cross section (RCS) reduction is presented. Two physical mechanisms are responsible for the reflection diffusion of the proposed metasurface. One is the functionality of controlling the spatial distribution of polarization response, and the other is the capability of spanning the entire 2π phase range by making full use of the variable sizes and height difference of unit cells to achieve superwideband phase cancellation. A 10 dB monostatic RCS reduction is obtained from 3.87 to 92.89 GHz (a ratio bandwidth of 24:1) for both polarizations under normal incidence by simulation, which is identical to experimental results and theoretical analysis. The proposed method for suppressing vector fields in an extremely wide band may hold promising potentials for suppression of acoustic, electromagnetic, optical and other elastic waves.

RCS reduction of composite transparent flexible coding metasurface combined phase cancellation and absorption

A wideband low-scattering metasurface with optical transparency and flexibility is proposed by using the combination of phase cancellation and absorption mechanisms. Electromagnetic (EM) diffusion is achieved through the random phase distribution design of the two coding elements. The enhanced energy absorption can be obtained in a wide spectrum by using indium tin oxide (ITO) with suitable sheet resistance in the supercells. The experimental results show that the radar cross section (RCS) reductions of less than -10 dB under the planar and conformal cases are in 6.65-19.40 GHz and 6.11-17.37 GHz, corresponding relative bandwidth are 97.89% and 95.91%, respectively. Both theoretical analysis and simulated results are good accordance with the experiment. Furthermore, the analyses of the surface current, EM field distribution and power loss density are given to explain the hybrid RCS reduction mechanism. The proposed composite transparent flexible coding metasurface (CTFCM) maintains good angular stability within 0°-60° oblique incidence and has polarization insensitivity. The CTFCM has excellent flexibility and high optical transparency, which provides a way to reduce RCS in a wider band and has important application potential for stealth aircraft cockpit and transparent radome.

Ultra-wideband RCS reduction based on coupling effects between beam diffuse and absorptive structures

A hybrid design method for broadband radar cross section (RCS) reduction is proposed and successfully demonstrated based on the coupling effects between diffuse and absorptive structures. The reflection energy is distributed into more directions away from the source direction by the one-bit diffuse coding metasurface (CM). The two-layer resistive frequency selective surface (RFSS) is employed in the one-bit CM structure, reducing the amplitude of the co- and cross-polarized reflected waves under circularly polarized wave incidence by converting it into ohmic loss. In addition, the bandwidth of RCS reduction is further broadened through the coupling effects between the metallic patterns and the two-layer RFSS. The coupling effect shows that the absorption rate of the composite structure is significantly improved compared to the only RFSS structure. A lightweight CM loaded with RFSS (the area density is 597 g/m²) was fabricated, analyzed, simulated, and measured. The results show that the proposed mechanism can effectively break the bandwidth constraints of traditional diffusion and absorption methods. Furthermore, the proposed mechanism significantly expands the bandwidth of RCS reduction. The proposed metasurface can achieve a 10 dB RCS reduction in an ultra-wideband from 7.3 to 44.2 GHz with about 143.3% fractional bandwidth. Moreover, the metasurface also has good performances under wide-angle oblique incidences. Under the condition of maintaining lightweight, the design provides an idea for broadening the frequency band.

Wideband RCS Reduction Using Coding Diffusion Metasurface

This paper presents a radar cross-section (RCS) reduction technique by using the coding diffusion metasurface, which is optimised through a random optimization algorithm. The design consists of two unit cells, which are elements ‘1’ and ‘0’. The reflection phase between the two-unit cells has a 180° ± 37° phase difference. It has a working frequency band from 8.6 GHz to 22.5 GHz, with more than 9 dB RCS reduction. The monostatic RCS reduction has a wider bandwidth of coding diffusion metasurface as compared to the traditional chessboard metasurface. In addition, the bistatic performance of the designed metasurfaces is observed at 15.4 GHz, which shows obvious RCS reduction when compared to a metallic plate of the same size. The simulated and measured result shows the proficiency of the designed metasurface.

Broadband low-scattering metasurface using a combination of phase cancellation and absorption mechanisms

In this paper, a broadband low-scattering metasurface is proposed by using a combination of phase cancellation and absorption mechanisms. The metasurface is composed of two structural layers. One layer adopts the geometric phase cell that can obtain a different reflection phase by changing its orientation. Through the random phase distribution design, electromagnetic diffusion can be realized to reduce the backward scattering energy. The other layer is made of a resistive frequency selective surface (RFSS) that can absorb the incident wave by converting it into Ohmic loss. The above two physical mechanisms respectively play the great roles at two distinct frequency bands, and finally make our metasurface achieve the RCS reduction over a wide frequency band ranging from 13 to 31.5 GHz. Both simulation and experimental results are in good agreement, which fully demonstrates our design method. The analysis of the scattering patterns, electric-field distribution and power loss density are given to explain the hybrid RCS-reduction mechanism of our metasurface.

Optically transparent metasurface Salisbury screen with wideband microwave absorption

We present an optically transparent broadband microwave absorber based on the concept of metasurface Salisbury screen (MSS). The metasurface with optimized reflection phase profiles is used as the ground plane to excite multi-MSS resonances that are required for achieving continuous wide absorption bandwidth. Meanwhile, by employing indium tin oxide (ITO) film and glass dielectric substrate, high optical transparency and wideband microwave absorption can be obtained simultaneously. Both full-wave electromagnetic simulations and experiments demonstrate that the transparent MSS can perform an efficient absorption over 89% in an ultra-wide frequency band ranging from 4.1 GHz to 17.5 GHz with a sub-wavelength thickness. In addition, good angular performances are observed for all wave polarizations. The proposed MSS may provide a powerful platform for efficiently designing broadband absorption in microwave region with advantages of light weight, thin thickness, and high optical transparency, which could further find potential uses in many real-world applications.