We demonstrate a controllable electromagnetic wave reflector/absorber for different polarizations with metamaterial involving electromagnetic resonant structures coupled with diodes. Through biasing at different voltages to turn ON and OFF the diodes, we are able to switch the structure between nearly total reflection and total absorption of a particularly polarized incident wave. By arranging orthogonally orientated resonant cells, the metamaterial can react to different polarized waves by selectively biasing the corresponding diodes. Both numerical simulations and microwave measurements have verified the performance.

Switchable metamaterial reflector/absorber for different polarized electromagnetic waves

High-Efficiency Transmissive Programmable Metasurface for Multimode OAM Generation

A transparent low-profile polarization-insensitive metamaterial absorber with ultrawideband microwave absorption is presented. A fractional bandwidth of 125.2% (4.3–18.7 GHz, absorptance > 90%) is achieved using a simple patterned resistive metasurface. The thickness of the absorber is only ∼0.086 times the upper-cutoff wavelength. The experimental results agree with full-wave simulation results. A Cu-metal-mesh ground plane enhances the shielding efficiency and visible transparency. Radar cross-sections (RCS) are reduced across all reflection angles, over frequencies spanning the C, X, and Ku bands. With its visible-wavelength transparency, low profile, polarization insensitivity, excellent absorption, and wideband RCS reduction, the proposed absorber has wide applicability.

Transparent ultrawideband absorber based on simple patterned resistive metasurface with three resonant modes

Since the electromagnetic (EM) absorbers have wide uses in many military and civilian applications, much effort has been devoted continuously to broadening the absorption bandwidth while making the thickness as thin as possible. In this paper, we present an ultra-wideband metamaterial absorber composed of periodic stepped-structures of magnetic material with a mixture of carbonyl iron powder and resin. The proposed metamaterial absorber features an ultra-thin thickness of only 0.025 wavelength and an ultra-broad operating bandwidth (defined by absorption larger than 90%) from 1.23 to 19 GHz. The ultra-broadband strong absorption is mainly attributed to the giant magnetic loss of the magnetic material, the structure-induced multi-resonances, and the edge diffraction effects of the stepped structures. In addition, good angular performance is observed for all polarizations. Experiments are carried out and are in good agreements with the simulated ones. We also propose a method to further reduce the weight of the structure without affecting much of the overall absorbing performance. The proposed metamaterial absorber has promising prospects in many real-world applications, such as RCS reduction and EM compatibility.

Ultra-broadband microwave absorption by ultra-thin metamaterial with stepped structure induced multi-resonances

A Huygens’ metasurface with unit cells of glide symmetric I-shape metal strips is proposed for a high-efficiency metalens antenna. The proposed unit cell achieves more than 98.6% transmission amplitude with 360° phase shift coverage for dual polarization. The mechanism is presented by analyzing a unit cell with two dislocated I-shape metal strips, where the electric dipole and magnetic dipole resonances are tuned by the dislocation. The analysis implies that glide symmetric I-shape metal strips are preferable for high transmittance Huygens’ unit cell design. With the proposed Huygens’ unit cell, a high-efficiency metalens antenna is realized. The simulated and measured results show that the proposed metalens antenna of a 14-wavelength diameter achieves a maximum gain of 30.7 dBi at 27.2 GHz, which is only 1.1 dB lower than its theoretical limit. The maximum antenna efficiency is 61.5%. The 3-dB bandwidth of achieved gain ranges from 25.9 to 29 GHz, covering the fifth generation (5G) millimeter-wave bands. The proposed metalens remarkably enhances the radiation performance of the metalens antennas.

High-Efficiency Metalens Antenna Using Huygens’ Metasurface With Glide Symmetric I-Shape Metal Strips

Active metasurfaces pave a way for manipulating electromagnetic (EM) waves in real-time by incorporating with tunable materials or components, emerging as an attractive solution to achieve versatile EM functionalities in dynamic fashions. However, most of the active metasurfaces demonstrated so far only support tunable responses for a certain single frequency band, or have obvious frequency cross-talks that cannot provide dual-band independent operations, limiting their further uses in practical applications. Here, we propose a 1-bit high-efficiency programmable metasurface to achieve completely independent functions with real-time reconfigurability controlled by FPGA hardware system in both C-band and X-band. Specifically, the metasurface is designed with abilities of generating multi-beams or twin-beam scanning in the low frequency band while dynamic beam-scanning in high frequency band. As the experimental verifications, a double-layered metasurface has been fabricated and tested, and the measured results agree well with the simulations, demonstrating its abilities of independent, high-efficiency, real-time, and programmable manipulation of EM waves in two discrete frequency bands. The proposed concept may largely enhance the information capacity of the metasurface, bringing new degrees of freedom in achieving versatile tunable functionalities and offering useful applications in the radar and wireless communication systems.

Programmable Coding Metasurface for Dual-Band Independent Real-Time Beam Control

In this article, we theoretically and experimentally demonstrate a single-layered spin-decoupled metasurface and its application to a dual-circularly polarized reflector antenna. A developed method is first analyzed to guide the design of broadband spin-decoupled metasurface. Then, a quasi-I-shaped meta-atom, which exhibits a phase coverage of $2\pi $ and high cross-polarization conversion efficiency within 12–21 GHz, is accordingly designed to actualize spin-decoupled phase change by simultaneously tuning the structural parameters and self-rotation of the element. To illustrate the independent phase control of orthogonal spins, a dual-circularly polarized multiplexing reflector antenna is designed with offset configuration. The experimentally measured results of the assembled reflector antenna are in good agreement with the simulated ones, showing a peak gain of 29.5 and 29.6 dBic, peak aperture efficiency (AE) of 53% and 54%, 3 dB gain bandwidth (BW) of 13.2–20.2 GHz (41.9%) and 13.4–20.2 GHz (40.5%), and 3 dB axial ratio (AR) BW of 11.8–21 GHz (56.1%) and 11.5–22 GHz (62.7%) for left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) radiations, respectively. The design strategy and the well-performed multiplexing reflector antenna may have promising perspective in many practical applications, for example, satellite communication system and long-distance wireless communication system.

Broadband Spin-Decoupled Metasurface for Dual-Circularly Polarized Reflector Antenna Design

We present the analysis and design of a multi-octave broadband microwave absorber with simultaneous high optical transparency. Assisted by the semi-analytical method, the proposed metamaterial absorber, composed of transparent dielectric substrates and patterned indium–tin–oxide, can achieve an excellent electromagnetic wave absorption in a wide frequency band from 6.21 GHz to 19.31 GHz within a total thickness of only about 0.075λ. The experiment results are in agreement with full-wave simulations, demonstrating high-efficient and broadband absorption in a wide angular range from 0° to 45° for all polarizations. In addition, by substituting the middle layers with flexible dielectric layer, we successfully design a flexible metamaterial absorber for conformal applications. The performance of conformal absorber is also verified by simulation and experiment, both of which validate an excellent backward scattering suppression for cylinder object with wavelength-comparable radius. With advantages of excellent absorption, polarization-insensitivity, thin-thickness and especially high transmittance and flexibility, the proposed absorber may have potential uses in many real-world applications.

https://iopscience.iop.org/article/10.1088/1361-6463/ab2365/pdf

Multi-octave microwave absorption via conformal metamaterial absorber with optical transparency

Metasurface retroreflectors, which scatter the incident electromagnetic wave back to incoming direction, have received significant attention due to their compelling advantages of low profile and light weight compared with conventional bulky retroreflection devices. However, the current metasurface retroreflectors still have limitations in wide-angle and omnidirectional operations. This work proposes a high-efficiency, wide-angle, reconfigurable, and omnidirectional retroreflector composed of spin-locked phase gradient metasurface with a thickness of only 5.2 mm or 0.07 operating wavelength. The reflection phase of constituent meta-atoms can be controlled dynamically and continuously by altering their orientation states through individually addressing each mechanically rotational meta-atom, whereas the reflection handedness is kept the same as incidence. Therefore, adaptive and arbitrary momentum can be imparted to the incident wave, providing high-efficiency retroreflection over a wide continuous range from -47° to 47°. Moreover, such high-performance retroreflection is extended to omnidirectional level, enabling great degrees of freedom that are unavailable by previous researches. As a proof of concept, a retroreflective metasurface is fabricated and experimentally demonstrated at microwave frequencies. The proposed thin thickness, high efficiency, and reconfigurable metasurface retroreflector can be extended to other frequencies that may offer an untapped platform toward reconfigurable spin-based retroreflection devices for electromagnetic signal processing.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202100885

Yilin Zheng

Papers

Programmable Coding Metasurface for Dual-Band Independent Real-Time Beam Control

Broadband Spin-Decoupled Metasurface for Dual-Circularly Polarized Reflector Antenna Design

Multi-octave microwave absorption via conformal metamaterial absorber with optical transparency

Angular-Adaptive Reconfigurable Spin-Locked Metasurface Retroreflector.

Kirigami Reconfigurable Gradient Metasurface