Programmable Controls to Scattering Properties of a Radiation Array

We propose a chiral metasurface (CMS) that exhibits asymmetric transmission (AT) of double circularly and linearly polarized waves at the same frequency band. In order to realize the manipulation of electromagnetic (EM) waves in the whole space, the unit cell of CMS consists of three layers of dielectric substrate and four layers of metal patches. The Z-shaped chiral micro-structure and a grating-like micro-structure are proposed and designed to achieve AT. The simulated results show that the x-polarized wave that is incident along one direction can be transmitted into the right-hand circularly polarized (RHCP) wave and the left-hand circularly polarized (LHCP) wave that is incident along the opposite direction can be reflected as the LHCP wave in the frequency band of 4.69GHz-5.84 GHz. The maximum chirality response can be reflected by AT and circular dichroism (CD) and they can reach up to 0.38 and 0.75, respectively. In addition, we also produced the sample of CMS, and the experimental results are in good agreement with the simulated results.

Asymmetric transmission for dual-circularly and linearly polarized waves based on a chiral metasurface.

In this work, a broadband tunable reflective polarization convertor using a single layer complementary-cross-shaped (CCS) graphene metasurface was proposed and investigated numerically in terahertz (THz) region. The electric property of CCS graphene could be flexibly tuned through the Fermi energy level ( Ef). When Ef  = 0.9 eV, the proposed graphene metasurface can realize a relative high polarization conversion ratio (PCR) of over 80% from 2.15 THz to 4 THz with a relative bandwidth of 60.16%. Furthermore, the PCR peak can reach up to as high as 99%, 99.5% and 91.5% at 2.4 THz, 3.4 THz and 3.96 THz, respectively. The physical origins of this polarization conversion properties are turned out to be supported by field distributions and Fabry-Perot interference theory. Furthermore, the broadband polarization conversion properties will be regulated by varying the Fermi energy level.

Terahertz broadband tunable reflective cross-polarization convertor based on complementary cross-shaped graphene metasurface

Quad-Band Transmissive Metasurface with Linear to Dual-Circular Polarization Conversion Simultaneously

Phase-gradient metasurfaces (PGMs) constitute an efficient platform for deflection of a beam in a desired direction. According to the generalized Snell's law, the direction of the reflected/refracted wave can be tuned by the spatial phase function provided by the PGMs. However, most studies on PGM focus only on a single diffraction order, that is, the incident wave can be reflected or refracted to a single target direction. Even in the case of multiple beams pointing in different directions, the beams are still in the same order mode, and the energy carried by different beams cannot be controlled. In addition, the energy ratio of multiple beams is generally uncontrollable. Here, we propose a general method to perfectly control diffraction patterns based on a multi-beam PGM. An analytical solution for arbitrarily controlling diffraction beams is derived through which the generation and energy distribution in high-order diffraction beams can be achieved. Three metasurfaces with different diffraction orders and energy ratios are designed and fabricated to demonstrate the proposed method. The efficiencies of diffraction for the desired channels are close to 100%. The simulated and measured far-field patterns are in good agreement with theoretical predictions, validating the proposed method that provides a new way to design multi-beam antennas and that has significance in wireless communication applications.

Perfect Control of Diffraction Patterns with Phase-Gradient Metasurfaces.

A Thin Self-Feeding Janus Metasurface for Manipulating Incident Waves and Emitting Radiation Waves Simultaneously

Low‐Profile Electromagnetic Holography by Using Coding Fabry–Perot Type Metasurface with In‐Plane Feeding

Metasurfaces have been developed as a promising approach for manipulating electromagnetic waves. Recently, deep learning algorithms have been introduced to design metasurfaces, but the network can only output one solution for each desired input and suffers from nonunique issue. To overcome the aforementioned challenges, a deep neural network model for inverse designs of anisotropic metasurfaces with full phase properties in ultrawideband is proposed. Given the target reflection spectra as inputs, the candidate metasurface patterns are generated through a generative adversarial network (GAN), and the corresponding predictions are simply achieved by the accurate forward neural network model to match the target spectra in the whole band with high fidelity. By training the generator and discriminator in GAN in an alternating order combined with setting a threshold of discriminator loss to trigger the phase prediction, the proposed method is much more efficient and consumes less time in the training process. Numerical simulations and experimental results demonstrate that the reflection phases of the generated meta‐atoms have excellent agreements with the given targets, providing an efficient way in automatically designing metasurfaces. The most important advantage of this approach over the previous schemes is to improve the design speed significantly with very good accuracy.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/aisy.202000068

Deep Learning Designs of Anisotropic Metasurfaces in Ultrawideband Based on Generative Adversarial Networks

Digital-coding metasurfaces provide a convenient method for designing metasurface-based functional devices. By delicately arranging the coding sequences, electromagnetic fields on the metasurfaces can be modulated for applications like wave-front engineering, amplitude controlling and polarization conversion. Theoretically, to fully realize arbitrary profiles for radiation patterns, both amplitude and phase modulations are needed for the responses of meta-atoms. Here, a method is proposed to generate multiple beams with arbitrary power intensity ratios using 2 bit amplitude and 2 bit phase digital-coding metasurfaces. A detailed process for designing the coding sequences is elaborated, and four-layer conformal square-loop meta-atoms are adopted to achieve 16 combinations of amplitude and phase codes. Two prototypes with dual beams of different radiation angles and power allocations are simulated, fabricated and measured. The experimental results match well with the predesigned expectations, which verifies the feasibility of the proposed method. It suggests that the digital-coding metasurface is a good candidate for multi-beam radiation pattern syntheses and is promising for various multi-functional telecommunication and radar applications.

https://iopscience.iop.org/article/10.1088/1361-6463/abdb0c/pdf

Arbitrary power allocation for multiple beams using amplitude- and phase-coded metasurfaces

We propose an anisotropic digital coding metasurface to realize arbitrarily polarized retro-reflections. With the theoretical support of generalized Snell's laws, the proposed coding metasurface shows excellent performance of retro-reflections through reflection phase design. A modified metallic Jerusalem cross structure is employed to achieve the required phase profile under oblique incidence due to its good performance in polarization isolation. By changing the length of coding particle's arms, the particle can be digitally named as '00', '01', '10' and '11' elements with different phase responses. Through special design of phase gradient, the coding metasurface can reflect incident waves backwards for arbitrary polarizations, which can be decomposed into transverse electric and transverse magnetic polarizations. A prototype was fabricated and measured. Both simulation and experiment results verify the good performance of the arbitrarily polarized retro-reflections by the metasurface.

https://iopscience.iop.org/article/10.1088/1361-6463/ab42b2/pdf

He Li

Papers

A Thin Self-Feeding Janus Metasurface for Manipulating Incident Waves and Emitting Radiation Waves Simultaneously

Low‐Profile Electromagnetic Holography by Using Coding Fabry–Perot Type Metasurface with In‐Plane Feeding

Deep Learning Designs of Anisotropic Metasurfaces in Ultrawideband Based on Generative Adversarial Networks

Arbitrary power allocation for multiple beams using amplitude- and phase-coded metasurfaces

Arbitrarily polarized retro-reflections by anisotropic digital coding metasurface