Compact Metasurface Research Articles

Compact metasurface antenna for Sub-6 GHz applications with isolated n77/n78 bands using CSRR

Abstract A compact (0.35 λ0× 0.35 λ0 where λ0 is free space wavelength at the lower resonance frequency 3.50 GHz) bio-inspired tulip flower-shaped antenna (TFSA) is proposed. A double negative (DNG) metamaterial complementary split ring resonator (CSRR) is introduced near the feed in the hybrid triangular-circular patch which inserts a notch-band (4.20-4.38 GHz) in the wide bandwidth (3.15-7.05 GHz) and makes the antenna response dual-band. Consequently, this results in in-band interference reduction in 5G-Sub-6 GHz applications. A slotted FSS is placed at a distance of 28.507 mm beneath the monopole-reduced ground of the antenna to enhance the reduced gain from 4.39 dBi to 7.22 dBi. A further gain is improved to 12.84 dBi by placing a full copper surface (0.35 λ0× 0.35 λ0) as the reflector layer is placed below FSS at 1.6 mm. Finally, prototyped TFSA with FSS and reflector model achieve a dual bands reflection coefficient response (3.15-4.20 GHz): n77/n78, and (4.38-7.03 GHz): n46/n47/n96/n102/n79. The antenna reflection coefficient is tested using Keysight 14 GHz FieldFox Microwave Analyzer N9916A, and radiation patterns in the E-plane and H-plane are measured using an 18 GHz anechoic chamber. The comparison of simulated results with measured results is found an excellent match in bandwidth and with shapes of gain radiation patterns. The reflector and FSS jointly make the radiation pattern strong in the E-plane above the TFSA radiator. The antenna is well suited for n77/n78 (3.30-4.20 GHz), n79(4.40-4.99 GHz), n46 (5150-5925MHz), n47 (5855 – 5925MHz), n96/n102 (5925-6425MHz), 5.8 GHz HiperLAN, WiMAX 3.5GHz applications. An electrical equivalent circuit model of the proposed TFSA antenna is presented and validated using ADS software.

Development of a compact metasurface antenna with reconfigurable pattern through mode combination technique for 5G mm‐wave applications

Development of a compact metasurface antenna with reconfigurable pattern through mode combination technique for 5G mm‐wave applications

Metasurface Enabled Multi‐Target and Multi‐Wavelength Diffraction Neural Networks

AbstractBenefiting from low power consumption and high processing speed, there is a growing interest in diffraction neural networks (DNNs), which are typically showcased with 3D printing devices, leading to large volumes, high costs, and low levels of integration. Metasurfaces can desirably manipulate wavefronts of electromagnetic waves, providing a compact platform for mimicking DNNs with novel functions. Although multi‐wavelength and multi‐target recognition provides a richer and more detailed understanding of complex environments, existing architectures are primarily trained to classify a single target at a specific wavelength. A metasurface approach is proposed to design multiplexed DNNs that can classify multiple targets and spatial sequences across various wavelengths in multiple channels. To realize multi‐task processing, the dielectric metasurface is designed based on phase and wavelength multiplexing, which can integrate multi‐target DNNs with different tasks such as operating at distinct wavelengths and classifying diverse targets. The efficacy of this method is exemplified through the numerical simulation and experimental demonstration of recognizing a single target with two wavelengths, two targets at a single wavelength, and two targets at dual wavelengths. This compact metasurface approach enables the design of multi‐target and multi‐wavelength DNNs, opening a new window to develop massively parallel processing and versatile artificial intelligence systems.

Metasurface array for single-shot spectroscopic ellipsometry

Spectroscopic ellipsometry is a potent method that is widely adopted for the measurement of thin film thickness and refractive index. Most conventional ellipsometers utilize mechanically rotating polarizers and grating-based spectrometers for spectropolarimetric detection. Here, we demonstrated a compact metasurface array-based spectroscopic ellipsometry system that allows single-shot spectropolarimetric detection and accurate determination of thin film properties without any mechanical movement. The silicon-based metasurface array with a highly anisotropic and diverse spectral response is combined with iterative optimization to reconstruct the full Stokes polarization spectrum of the light reflected by the thin film with high fidelity. Subsequently, the film thickness and refractive index can be determined by fitting the measurement results to a proper material model with high accuracy. Our approach opens up a new pathway towards a compact and robust spectroscopic ellipsometry system for the high throughput measurement of thin film properties.

Generation of diffraction-free beam with winding trajectory based on metasurface holography

The diffraction-free beams with curved trajectories and shaped wavefronts have wide application prospects in many fields. This paper proposes the generation of diffraction-free beam with winding trajectory and spiral wavefront based on holographic metasurface. The holographic metasurface consists of rotated rectangular nanoholes and the winding trajectory for the generated diffraction-free beam may be in two or three dimensional space under the control of the rotated nanoholes. The multiple diffraction-free beams are exemplified and the performance of holographic metasurfaces are testified by the simulation and experiment results. The utilization of compact metasurface enables the flexible generation of the diffraction-free beams with complex trajectories and tailored wavefronts. It may bring more new applications of diffraction-free beams with on-demand trajectories and customized wavefronts.

Reprogrammable Nonlinear Transmission Controls Using an Information Metasurface

AbstractNonlinearity manipulation based on electromagnetic (EM) metasurfaces has always been a hot topic, which is an important part of communication and radar systems. However, most of the existing transmission metasurfaces are mainly focused on linear processing on the incident EM waves. In this article, a reprogrammable nonlinear transmission metasurface is proposed for spatial waves using active power amplifiers. An ultrathin and compact metasurface is designed, fabricated, and measured, to achieve reprogrammable functions on the nonlinear transmissions. For EM incidence, the metasurface can not only amplify the magnification of small signals, but also control high‐energy signals nonlinearly, whose magnification is determined by different bias voltages. The simulation and experimental results show good consistency, which verifies the feasibility of the proposed method. This work can find potential applications in signal gain compression and construction of nonlinear units of diffractive deep neural networks.

Ultra-thin single-layer compact metasurface based on a meander structure for multifunctional polarization conversion

In this paper, we proposed and investigated an ultra-thin, single-layer and compact metasurface (MS) based on a meander structure that achieves linear-polarization to linear-polarization (LP-to-LP) and linear-polarization to circular-polarization (LP-to-CP) conversion for both transmission and reflection simultaneously in the microwave region. Simulation and experimental results demonstrated that the cross-polarization coefficients of both transmission and reflection are approximately 0.49 for the normal incident LP wave passing through the MS at approximately 7 GHz, indicating a near LP-to-LP conversion in both reflection and transmission modes. Furthermore, the linear-to-circular polarization coefficients for both transmission and reflection are about 0.65 at approximately 8 GHz, indicating a near LP-to-CP conversion when the incident LP wave passes through the designed MS after transmission and reflection. The simulation results are in good agreement with the experiment. This design provides a valuable reference for the practical applications of MSs in full-space multifunctional polarization conversion and wavefront manipulation.

Active 3D positioning and imaging modulated by single fringe projection with compact metasurface device.

Three-dimensional (3D) information is vital for providing detailed features of the physical world, which is used in numerous applications such as industrial inspection, automatic navigation and identity authentication. However, the implementations of 3D imagers always rely on bulky optics. Metasurfaces, as the next-generation optics, shows flexible modulation abilities and excellent performance combined with computer vision algorithm. Here, we demonstrate an active 3D positioning and imaging method with large field of view (FOV) by single fringe projection based on metasurface and solve the accurate and robust calibration problem with the depth uncertainty of 4 μm. With a compact metasurface projector, the demonstrated method can achieve submillimeter positioning accuracy under the FOV of 88°, offering robust and fast 3D reconstruction of the texture-less scene due to the modulation characteristic of the fringe. Such scheme may accelerate prosperous engineering applications with the continued growth of flat-optics manufacturing process by using metadevices.

A Compact Metasurface Antenna Array With Diverse Polarizations

In this letter, a compact metasurface antenna array with diverse polarizations is proposed. The array element is a dual-polarized metasurface antenna driven with a square patch. In order to have compact size and low sidelobes for the antenna array, shared radiating elements are applied for both polarizations with a size reduction of 18.8% for a 1 × 4 antenna array. The diverse polarization property is achieved with the method of maximum power transmission efficiency (MMPTE), in which a dual-feed patch antenna connected to an ideal power combiner is chosen as the receiving antenna. With different scattering matrices of the power combiner, it is easy to calculate the excitation distribution for any polarizations with maximum gain. For demonstration, the antenna array with diverse polarizations is designed, fabricated, and measured.

Electrically switchable metallic polymer metasurface device with gel polymer electrolyte.

We present an electrically switchable, compact metasurface device based on the metallic polymer PEDOT:PSS in combination with a gel polymer electrolyte. Applying square-wave voltages, we can reversibly switch the PEDOT:PSS from dielectric to metallic. Using this concept, we demonstrate a compact, standalone, and CMOS compatible metadevice. It allows for electrically controlled ON and OFF switching of plasmonic resonances in the 2-3 µm wavelength range, as well as electrically controlled beam switching at angles up to 10°. Furthermore, switching frequencies of up to 10Hz, with oxidation times as fast as 42ms and reduction times of 57ms, are demonstrated. Our work provides the basis towards solid state switchable metasurfaces, ultimately leading to submicrometer-pixel spatial light modulators and hence switchable holographic devices.

Two-Dimensional Beam Steering Based on Compact Programmable Coding Metasurface

A programmable coding metasurface provides unprecedented flexibility to manipulate electromagnetic waves dynamically. By controlling the peculiarity of subwavelength artificial atoms, devices with metasurfaces perform various functionalities. In this paper, a compact programmable coding metasurface with PIN diodes is proposed to realize the beam steering in the Ka band. The phase distribution on the metasurface can be actively controlled by switching the states of each meta-atom. By tuning the phase gradient along the metasurface plane, the reflective beam can scan all directions in the upper half-plane. In addition, the compact metasurface is easier to integrate, which could expand the fields of applications. The full-wave simulation results show that the radiation direction of the main lobe is consistent with the theoretical calculation results, and the maximum steering angle of simulation is 60°. As experimental verification, a prototype was processed and the functionality of beam steering in the xoz plane and in the yoz plane was tested. Experimental results show that the designed metasurface can achieve beam steering in both planes, and the maximum scan angle is 45° in the xoz plane. The proposed metasurface opens a new way of beam steering in half space, which may have potential applications in sensing and wireless communications in millimeter waves.

Compact low‐profile metasurface antenna via non‐uniform fractional meta‐cells with an e ‐TM 30 mode for Wi‐Fi applications

A compact metasurface (MTS) antenna with a dimension of 20 mm × 20 mm consisting of non-uniform fractional meta-unit (n-MTS) cells has been proposed in this article. The n-MTS shows distinctive electromagnetic characteristics compared to conventional MTS, that is, the E-field surface waves on the n-MTS are singularly co-extending in nature, exhibiting an e-TM30 mode (e—extraordinary). The higher order modes with n-MTS significantly improves the antenna resonant properties at (5–6) GHz Wi-Fi band. The potential improvement in antenna modal parameters are showcased with numerical approach for validations in proximity to the theoretical quantitative metrics. A MTS antenna array configuration of dimension 40 mm × 40 mm with a RF power-divider feeding arrangement has been proposed, operating at dual-bands (5.45, 6.4 GHz) with radiation gain >8 dBi and radiation efficiency >80% (at dual-bands). The unit cell n-MTS configuration has sharp resonances and unique meta-parameters are achieved at operating frequency, enabling existence of higher-order mode in a low-profile and proliferates for compact antenna design embodiment. The prototype antennas are fabricated and measured, which shows good correlation between simulation and test results, to be implemented in Wi-Fi applications.

Single/Dual/Triple Broadband Metasurface Based Polarisation Converter with High Angular Stability for Terahertz Applications.

This paper presents design and characterisation of a new compact metasurface based linear polarisation converter for terahertz applications. The metasurface unit cell with periodicity of 0.292 consists of an asymmetrically oriented planar double semicircular goblet-shaped resonators. It is printed on a polydimethylsiloxane (PDMS) dielectric substrate backed by a gold layer that acts as a ground plane. This metasurface structure exhibits a broadband cross-polarisation conversion in the frequency range of 0.72–0.99 THz with a polarisation conversion ratio (PCR) > 95% and angular stability > for both TE and TM modes. However, the PCR for the single band is >99% at resonant frequencies of 0.755 and 0.94 THz, while the optimised design shows 100% PCR over a BW of 95 GHz. Furthermore, slight modification and optimisation of the broadband design results in quad-ring and slotted DSGRs that produce dual and triple broadband polarisation conversion, respectively. The quad-ring DSGR performs polarisation conversion for frequency range of 0.70–1.08 and 1.61–1.76 THz while the slotted DSGR shows the triple broadband cross-conversion for frequency range of 0.67–0.85, 1.04–1.11, and 1.62–1.76 THz with PCR > 95%. This design is simple, easy to modify to implement single and multi broadband polarisation conversion with high PCR at terahertz regime. In addition to that, it is easy to fabricate and integrate with other components like multiple-input multiple-output terahertz antennas for mutual coupling reduction.

Compact and efficient elastic metasurface based on mass-stiffness relation for manipulation of flexural waves

Metasurfaces are a group of lower dimensional metamaterials. They have shown excellent capacities in precise and efficient manipulation of wavefront at-will. However, most of them suffer from low transmission performances since they only consider the control of phase but ignore the impedance that determines transmission behaviours. To optimize the behaviours of metasurface, we employ the mass-stiffness relation to realize efficient manipulation of flexural waves. We use external mass blocks (pillars) to tune the effective mass and cut grooves in connecting beams to release effective stiffness. The two degrees of freedom are used to control the two design targets: local phase shift and impedance. Based on the theoretical analysis and finite element simulations, a three-unit metasurface with high transmission performances and compact geometry is designed. From the comparisons with currently existed designs, we show that our proposed metasurface is much more efficient and compact. This research may play an important role in guidance of the design of highly efficient and compact metasurfaces for precise engineering of elastic wavefront.

Asymmetric parametric generation of images with nonlinear dielectric metasurfaces

Subwavelength dielectric resonators assembled into metasurfaces have become a versatile tool for miniaturising optical components approaching the nanoscale. An important class of metasurface functionalities is associated with asymmetry in both generation and transmission of light with respect to reversals of the positions of emitters and receivers. Nonlinear light-matter interaction in metasurfaces offers a promising pathway towards miniaturisation of the asymmetric control of light. Here we demonstrate asymmetric parametric generation of light in nonlinear metasurfaces. We assemble dissimilar nonlinear dielectric resonators into translucent metasurfaces that produce images in the visible spectral range being illuminated by infrared radiation. By design, the metasurfaces produce different and completely independent images for the reversed direction of illumination, that is when the positions of the infrared emitter and the visible light receiver are exchanged. Nonlinearity-enabled asymmetric control of light by subwavelength resonators paves the way towards novel nanophotonic components via dense integration of large quantities of nonlinear resonators into compact metasurface designs.

Multichannel Superposition of Grafted Perfect Vortex Beams.

Inspired by plant grafting, grafted vortex beams can be formed through grafting two or more helical phase profiles of optical vortex beams. Recently, grafted perfect vortex beams (GPVBs) have attracted much attention due to their unique optical properties and potential applications. However, the current method to generate and manipulate GPVBs requires a complex and bulky optical system, hindering further investigation and limiting its practical applications. Here, a compact metasurface approach for generating and manipulating GPVBs in multiple channels is proposed and demonstrated, which eliminates the need for such a complex optical setup. A single metasurface is utilized to realize various superpositions of GPVBs with different combinations of topological charges in four channels, leading to asymmetric singularity distributions. The positions of singularities in the superimposed beam can be further modulated by introducing an initial phase difference in the metasurface design. The work demonstrates a compact metasurface platform that performs a sophisticated optical task that is very challenging with conventional optics, opening opportunities for the investigation and applications of GPVBs in a wide range of emerging application areas, such as singular optics and quantum science.

Gain and isolation enhancement of a wideband MIMO antenna using metasurface for 5G sub-6 GHz communication systems

This work proposes a compact metasurface (MS)-integrated wideband multiple-input multiple-output (MIMO) antenna for fifth generation (5G) sub-6 GHz wireless communication systems. The perceptible novelty of the proposed MIMO system is its wide operating bandwidth, high gain, lower interelement gap, and excellent isolation within the MIMO components. The radiating patch of the antenna is truncated diagonally with a partially ground plane, and a metasurface has been employed for enhancing the antenna performance. The suggested MS integrated single antenna prototype has a miniature dimension of 0.58λ × 0.58λ × 0.02λ. The simulated and measured findings demonstrate a wideband characteristic starting from 3.11 to 7.67 GHz including a high realized gain of 8 dBi. The four-element MIMO system has been designed by rendering each single antenna orthogonally to one another while retaining compact size and wideband properties between 3.2 and 7.6 GHz. The suggested MIMO prototype has been designed and fabricated on a low loss Rogers RT5880 substrate with a miniature dimension of 1.05λ × 1.05λ × 0.02λ and its performance is evaluated using a suggested 10 × 10 array of a square enclosed circular split ring resonators within the same substrate material. The inclusion of the proposed metasurface with a backplane significantly reduces antenna backward radiation and manipulates the electromagnetic field, thus improving the bandwidth, gain and isolation of MIMO components. The suggested 4-port MIMO antenna offers a high realized gain of 8.3 dBi compared to existing MIMO antennas with an excellent average total efficiency of 82% in the 5G sub-6 GHz spectrum and is in good accordance with measured results. Furthermore, the developed MIMO antenna exhibits outstanding diversity characteristics in respect of envelope correlation coefficient (ECC) less than 0.004, diversity gain (DG) close to 10 dB (> 9.98 dB) and high isolation between MIMO components (> 15.5 dB). Therefore, the proposed MS-inspired MIMO antenna substantiates its applicability for 5G sub-6 GHz communication networks.

Generation of vector beams with different polarization singularities based on metasurfaces

In view of wide applications of vector beams and powerful light manipulation ability of metasurfaces, this paper studies the generation of two kinds of vector beams with different polarization singularities based on metasurfaces. One kind of vector beams are the linearly polarized vector beam with uncertain polarization orientation and the other kind of vector beams are the elliptically polarized vector beam with hybrid polarization states with uncertain polarization orientation, ellipticity and handedness. These vector beams can be decomposed into two or more uniform polarization states carrying the spiral phases. The metasurfaces consisting of rotated cross nanoholes are designed to generate vector beams on basis of the decomposition of vector beams and phase modulation of nanoholes. The simulation results verify the availability of the designed metasurfaces and the experiment results validate the generation of two kinds of vector beams. The generation of complex vector beams based on compact metasurfaces can bring more application possibilities of vector beams in classical physics and quantum sciences.

High gain and efficiency dual-band antenna using meta-surface

This article presents a compact meta-surface (MS) based antenna with dual-band operation for 5G applications. The MS-based antenna consists of a layer of MSs on the top of a single-band microstrip patch antenna. The dual-band operation is achieved by adding the MS layer at a height of 0.089λ0, where λ0 is the free space wavelength at the lower resonant frequency. The patch antenna is designed on a 21 mm × 20 mm × 0.508 mm substrate. The MS is comprised of two metallic layers printed on the top and bottom of a 1.575 mm Rogers 5880 substrate. The overall thickness of the proposed antenna is 0.27λ0. The proposed antenna is fabricated and tested. The configuration achieves dual-band features with bandwidth, and gain of 1 GHz, and 10 dBi at 26.4 GHz, 800 MHz, and 9.6 dBi at 27.6 GHz, respectively. Also, a high radiation efficiency of 91.2 % is achieved at the frequency bands.

Improving homogeneity in abdominal imaging at 3 T with light, flexible, and compact metasurface.

Radiofrequency field inhomogeneity is a significant issue in imaging large fields of view in high- and ultrahigh-field MRI. Passive shimming with coupled coils or dielectric pads is the most common approach at 3 T. We introduce and test light and compact metasurface, providing the same homogeneity improvement in clinical abdominal imaging at 3 T as a conventional dielectric pad. The metasurface comprising a periodic structure of copper strips and parallel-plate capacitive elements printed on a flexible polyimide substrate supports propagation of slow electromagnetic waves similar to a high-permittivity slab. We compare the metasurface operating inside a transmit body birdcage coil to the state-of-the-art pad by numerical simulations and in vivo study on healthy volunteers. Numerical simulations with different body models show that the local minimum of causing a dark void in the abdominal domain is removed by the metasurface with comparable resulting homogeneity as for the pad with decreasing maximum and whole-body SAR values. In vivo results confirm similar homogeneity improvement and demonstrate the stability to body mass index. The light, flexible, and inexpensive metasurface can replace a relatively heavy and expensive pad based on the aqueous suspension of barium titanate in abdominal imaging at 3 T.