Intelligence at either the material or metamaterial level is a goal that researchers have been pursuing. From passive to active, metasurfaces have been developed to be programmable to dynamically and arbitrarily manipulate electromagnetic (EM) wavefields. However, the programmable metasurfaces require manual control to switch among different functionalities. Here, we put forth a smart metasurface that has self-adaptively reprogrammable functionalities without human participation. The smart metasurface is capable of sensing ambient environments by integrating an additional sensor(s) and can adaptively adjust its EM operational functionality through an unmanned sensing feedback system. As an illustrative example, we experimentally develop a motion-sensitive smart metasurface integrated with a three-axis gyroscope, which can adjust self-adaptively the EM radiation beams via different rotations of the metasurface. We develop an online feedback algorithm as the control software to make the smart metasurface achieve single-beam and multibeam steering and other dynamic reactions adaptively. The proposed metasurface is extendable to other physical sensors to detect the humidity, temperature, illuminating light, and so on. Our strategy will open up a new avenue for future unmanned devices that are consistent with the ambient environment.

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Smart metasurface with self-adaptively reprogrammable functions

An ultrathin single-layer metasurface manifesting both linear cross-polarization conversion (CPC) and linear-to-circular polarization (LP-to-CP) conversion in X-band is presented in this research. The designed metasurface acts as a multifunctional metasurface achieving CPC over a fractional bandwidth of 31.6% (8–11 GHz) with more than 95% efficiency while linear-to-circular polarization conversion is realized over two frequency bands from 7.5–7.7 GHz and 11.5–11.9 GHz. Moreover, the overall optimized structure of the unit cell results in a stable polarization transformation against changes in the incidence angle up to 45° both for transverse-electric (TE) and transverse-magnetic (TM) polarizations. The proposed metasurface with simple structure, compact size, angular stability and multifunctional capability qualifies for many applications in communication and polarization manipulating devices.

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Linear and circular-polarization conversion in X-band using anisotropic metasurface.

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, an ultra-wideband and high-efficiency reflective linear-to-circular polarization converter based on an anisotropic metasurface is proposed, which is an orthotropic structure with a pair of mutually perpendicular symmetric axes u and v along ±45° directions with respect to the vertical y axis. The simulated and experimental results show that the polarization converter can realize ultra-wideband linear-to-circular polarization conversion at both x - and y-polarized incidences, its 3dB-axial-ratio-band is between 5.8 and 20.4 GHz, which is corresponding to a relative bandwidth of 112%; moreover, the polarization conversion efficiency (PCE) can be kept larger than 99.6% in the frequency range of 6.1-19.8GHz. In addition, to get an insight into the root cause of the LTC polarization conversion, a detailed theoretical analysis is presented, in which the conclusion is reached that in the case of neglecting the little dielectric loss, the axial ratio (AR) of the reflected wave can be completely determined by the phase difference between the two reflection coefficients at u- and v-polarized incidences, and any anisotropic metasurface can be used as an effective LTC polarization converter when the phase difference is close to ±90°.

/pdf/an-ultra-wideband-reflective-linear-to-circular-polarization-51bzjhhozi.pdf

An Ultra-Wideband Reflective Linear-to-Circular Polarization Converter Based on Anisotropic Metasurface

In this work, we present an efficient polarization conversion device via using a hollow graphene metasurface. The platform can simultaneously realize a series of excellent performances, including the broadband x-to-y cross polarization conversion (CPC) function with near unity polarization conversion ratio (PCR), dual-frequency linear-to-circular polarization conversion (LTC-PC) function, and highly sensitive polarization conversion function manipulation under wide oblique incidence angle range. For instance, the proposed device obtains an x-to-y CPC function with the bandwidth up to 1.83 THz (χPCR ≥98.8%). Moreover, the x-to-y CPC function can be switched to LTC-PC function via artificially tuning the Fermi energy of graphene. The maximal frequency shift sensitivity (S) of polarization conversion function reaches 23.09 THz/eV, suggesting a frequency shift of 2.309 THz for the LTC-PC function when the chemical potential is changed by 0.1 eV. Based on these superior performances, the polarization converter can hold potential applications in integrated and compact devices, such as polarization sensor, switches and other optical polarization control components.

Multi-functional polarization conversion manipulation via graphene-based metasurface reflectors.

Metasurfaces offer a convenient means to control the polarization state of light. Converting linear polarization (LP) and maintaining circular polarization (CP) in reflection mode have been widely realized, but these two types of polarization control have not been achieved using a single metasurface. This article reports an anisotropic metasurface that allows both multiband LP conversion and CP-maintaining reflection, due to the anisotropy of the metamaterial's unit cell. This system facilitates ultrawide-band polarization converters for $e.g.$ antennas, wireless communication, and radar technology.

Multiple-Band Linear-Polarization Conversion and Circular Polarization in Reflection Mode Using a Symmetric Anisotropic Metasurface

https://iopscience.iop.org/article/10.1088/1674-1056/27/5/054204/pdf

Wideband linear-to-circular polarization conversion realized by a transmissive anisotropic metasurface*

In the communication, a monopolarized and a dual-polarized polarization-rotating frequency-selective surfaces (PR-FSSs) are designed successively. The two PR-FSSs are both a three-layer aperture-coupled-patch periodic structure. When they are interpreted as an array of antenna-filter-antenna (AFA) modules, because polarization directions of the upper and lower antennas in each AFA module are orthogonal to each other, they can both realize polarization rotation and frequency selection at the same time. The monopolarized PR-FSS is designed first, its relative bandwidth reaches up to 13.58% although there is a maximum insertion loss of 0.8 dB in the band. The final-designed dual-polarized PR-FSS can be regarded as the combination of two orthogonal monopolarized one, so it can work under both $x$ - and $y$ -polarized incidences, its relative bandwidth is still up to 9.81%; moreover, the maximum insertion loss in the passband is very low. The performances of the two PR-FSSs are both verified by simulations and experiments.

Second-Order Polarization Rotating Frequency-Selective Surface

An ultra-wideband linear-to-circular polarization conversion metasurface

In this work, a wide-angle and wide-band transmission-type circular polarizer based on a bi-layer anisotropic metasurface is proposed, in which the unit cell consists of two layers of identical patterned metal films deposited on the two sides of a homogeneous dielectric layer, and the geometric pattern of the metal film is a square aperture surrounding a concentric square-corner-truncated square patch. The simulated results show that the polarizer can realize a linear-to-circular polarization conversion at both xand y-polarized incidences in the frequency range from 7.63 to 11.13 GHz with a relative bandwidth of 37.3%, and it can maintain a stable polarization conversion performance under large-range incidence angles. Moreover, it has no asymmetric transmission effect, and the transmission coefficients at xand y-polarized incidences are completely equal. Finally, one experiment is carried out, and the simulated and measured results are almost in agreement with each other.

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Jianxin Guo

Papers

Multiple-Band Linear-Polarization Conversion and Circular Polarization in Reflection Mode Using a Symmetric Anisotropic Metasurface

Wideband linear-to-circular polarization conversion realized by a transmissive anisotropic metasurface*

Second-Order Polarization Rotating Frequency-Selective Surface

An ultra-wideband linear-to-circular polarization conversion metasurface

A Wide-Angle and Wide-Band Circular Polarizer Using a BI-Layer Metasurface