Binary geometric phase metasurface for ultra-wideband microwave diffuse scatterings with optical transparency

Symbiotic Electromagnetic Shadow for Regional Invisibility and Camouflage

Low detectability and camouflage skills in the electromagnetic wave and light frequency range provide survival advantages for natural creatures and are essential for understanding the operational principles of the biosphere. Taking inspiration from natural mutualistic symbiosis, this paper proposes a symbiotic electromagnetic shadow camouflage mechanism based on a superdispersive surface, aiming to investigate its impact on the observability of specific objects. The design and experimental results indicate that the symbiotic shadow dihedral can significantly reduce overall scattering quantity, which reaches at least 10 dB shrink in the 12-18 GHz frequency range compared to the contrast object. Unlike known camouflage methods, the electromagnetic shadow technology shrinks the overall scattering without any coating and shield metal target while probably offering extensive functional design freedom for the concealed object, creature, or equipment. This also provides a hint to explore symbiosis-related camouflage phenomena in nature.

Antenna array-based metasurface for multi-scenario wide-angle polarization-insensitive radar cross section reduction

In this paper a novel antenna array-based metasurface design method for wide-angle and polarization-insensitive radar cross section (RCS) reduction has been proposed, which can be applied to a variety of RCS reduction scenarios. The proposed metasurface subarray design employs a dual-element antenna array in which the two ports of each element are connected through a Wilkinson power divider, and meanwhile, two power dividers are connected through a microstrip line with a lumped resistor. The use of dual-polarized wide-beam antennas enables the metasurface array to respond to arbitrarily polarized as well as wide-angle obliquely incident electromagnetic waves. A portion of the electromagnetic waves received will be absorbed by the lumped resistor and converted into heat, while the remaining portion will be canceled in the space, achieving the low RCS characteristic. The proof-of-concept experiments have been conducted in several application scenarios for RCS reduction, including a metasurface array integrated with a microstrip antenna, a densely distributed dual-element metasurface array, and a randomly distributed dual-element metasurface array. Simulated and measured results confirm that the proposed method opens up a new avenue for more flexible and versatile RCS reduction devices and systems.

Ultra-Wideband Electromagnetic Composite Absorber Based on Pixelated Metasurface with Optimization Algorithm

An ultra-wideband electromagnetic (EM) absorber is proposed. The proposed absorber consists of two thin metasurfaces, four dielectric layers, a glass fiber reinforced polymer (GFRP), and a carbon fiber reinforced polymer (CFRP) which works as a conductive reflector. The thin metasurfaces are accomplished with 1-bit pixelated patterns and optimized by a genetic algorithm. Composite materials of GFRP and CFRP are incorporated to improve the durability of the proposed absorber. From the full-wave simulation, more than 90% absorption rate bandwidth is computed from 2.2 to 18 GHz such that the fractional bandwidth is about 156% for the incidence angles from 0° to 30°. Absorptivity is measured using the Naval Research Laboratory (NRL) arch method in an EM anechoic environment. It was shown that the measured results correlated with the simulated results. In addition, the proposed absorber underwent high temperature and humidity tests under military environment test conditions in order to investigate its durability.

Conceptual radar trap model realized via polarization conversion metasurface

General metasurfaces (MSs) can realize low observability of radar by manipulating the polarization mode and transmission direction of the electromagnetic (EM) waves. Here, we propose the radar trap model to realize EM wave imprisonment. This three-layer model is composed of the transmission polarization converter, the connected dielectric substrate and the reflection polarization converter. Using Jones calculation as a guide, we optimized the geometric parameters of the upper and lower layers to realize specific polarization conversion functions. The middle layer is regarded as the support and matching layer. On this basis, the combined radar trap model can realize the imprisonment of EM waves between upper and lower layers, which is attributed to the cooperative effect of asymmetric transmission and polarization conversion. We further verified the feasibility and correctness of our investigations through two kinds of model designs based on linear and circular polarization conversion mechanisms. Good agreements are observed between simulation and experiment. Even though the design presents a narrow operating bandwidth, it still provides novel ideas for developing radar stealth technology.

Broadband and wide-angle metamaterial absorber based on the hybrid of spoof surface plasmonic polariton structure and resistive metasurface

Electromagnetic (EM) wave absorber with broad and robust absorption performance over wide incident angle range is persistently desired in specific applications. In this work, we propose and demonstrate a broadband and wide-angle metamaterial absorber (MA) based on a hybrid of stereo spoof surface plasmonic polariton (SSPP) structure and planar resistive metasurface. At first, we design a broadband SSPP absorber by adjusting the dispersion and loss of the artificial plasmonic structure (PS) simultaneously. Furthermore, owing to utilize its spatial phase manipulation ability, we integrate a resistive metasurface on top of the PS to construct a modified circuit analog (CA) absorber with a dispersive metamaterial spacer. The absorption mechanism of the hybrid structure is analyzed theoretically. The results indicate that the hybrid MA is equipped with broad and robust absorption performance over a wide incident angle range due to the synergistic absorption of the PS and metasurface. Finally, a prototype of the hybrid MA is fabricated by silk-printing technic and its absorption performances are measured. The experimental results can verify the theoretic ones and indicate that proposed hybrid MA can achieve 90% absorptivity from 3.9 GHz to 10.6 GHz with thickness of 7.0 mm, which is only 106% times of the ultimate thickness corresponding to the absorption performance of MA. In general, the concept and design offer a distinct approach of utilizing SSPP to design absorbers with excellent performances from radio frequency to optic band, which are promising for extensive applications.