Metasurface Aperture Research Articles

Dynamic near-field and far-field radiation manipulation using a reprogrammable guided-wave-excited metasurface

The dynamic and integrated control of near- and far-field electromagnetic waves is essential for advancing emerging intelligent information technology. Metasurfaces, distinguished by their low-profile design, cost-effectiveness, and ease of fabrication, have successfully revolutionized various electromagnetic functions. However, current research on the dynamic integrated manipulation of near-field and far-field electromagnetic waves using a single metasurface remains relatively constrained, due to the complexity of element-level control, restricted dynamic tuning range, and tuning speed. Herein, we propose an element-level controlled, versatile, compact, and broadband platform allowing for the real-time electronic reconstruction of desired near/far-field electromagnetic wavefronts. This concept is achieved by precisely regulating the 1-bit amplitude coding pattern across a guided-wave-excited metasurface aperture loaded with PIN diodes, following our binary-amplitude holographic theory and modified Gerchberg–Saxton (G–S) algorithm. Consistent findings across calculations, simulations, and experiments highlight the metasurface’s robust performance in 2D beam scanning, frequency scanning, dynamic focusing lens, dynamic holography display, and 3D multiplexing holography, even under 1-bit control. This simplified and innovative metasurface architecture holds the promise of substantially propelling forthcoming investigations and applications of highly integrated, multifunctional, and intelligent platforms.

Blind Focusing for Computational Microwave Imaging With Metasurface Aperture Based on Sparse Bayesian Learning

Blind Focusing for Computational Microwave Imaging With Metasurface Aperture Based on Sparse Bayesian Learning

A Novel Electrophoretic Technique to Improve Metasurface Sensing of Low Concentration Particles in Solution.

A novel electrophoretic technique to improve metasurface sensing capabilities of charged particles in solution is presented. The proposed technique may improve the ability of metasurfaces to sense charged particles in solution in a manner not possible using the current standard of particle deposition (which allows particles to sediment randomly on a metasurface under evaporation) by inducing an external, nonuniform electric field through the metasurface apertures. Such a technique may be useful in various sensing applications, such as in biological, polymer, or environmental sciences, where low concentration particles in solution are of interest. The electrophoretic technique was simulated and experimentally tested using latex nanoparticles in solution. The results suggest that, using this technique, one may theoretically increase the particle density within the metasurface regions of greatest sensitivity by nearly 1900% in comparison to random sedimentation due to evaporation. Such an increase in particle density within the regions of greatest sensitivity may facilitate more precise material property measurements and enhance identification and detection capabilities of metasurfaces to particles in solution which constitute only a few hundred parts per million by mass. It was experimentally determined that the electrophoretic technique enhanced metasurface sensing capabilities of 333 parts per million by mass latex nanoparticle solutions by nearly 1700%.

Multibeam Metasurface Antenna Enabled by Orbital Angular Momentum Demultiplexing Feeding for IoT Communication

Multibeam antenna radiations provide linkages to multiple nodes and can bring enhanced communication quality with reduced power consumption for Internet of Things (IoT) applications. In this paper, a novel method providing a low-cost and flexible multibeam antenna solution is proposed. Multiple orbital angular momentum (OAM) modes are used as internal excitations of the antenna, and the generated multiple beams are pencil beams with no OAM mode, which is convenient for IoT nodes connection. First, aperture phase distributions that convert incident vortex beams with different and orthogonal topological orders into designated directional pencil beams are acquired and superimposed to form a metasurface aperture that, under excitations of vortex beams with multiple orders, produces multibeam each with a predefined direction. The proposed multibeam method is then illustrated with a transmissive metasurface design, with four beams pointing at arbitrary half space directions. Techniques such as OAM modes spacing and aperture partitioning are utilized for reducing sidelobe levels (SLLs). Furthermore, a similar multibeam metasurface antenna with additional linear-to-circular polarization conversion function is demonstrated, which opens the possibility of utilizing different polarizations on top of the OAM based multibeam. This paper successfully explores and achieves a novel antenna system with multiple radiations suited for multiple IoT nodes accessing with low cost and low energy consumption, and also provides a new degree-of-freedom for OAM applications.

Metasurface modulator of frequency diverse multi-mode OAM beams with equal divergence angle for coincidence imaging

Traditional multi-mode orbital angular momentum (OAM) beams suffer from low energy efficiency in detection since the divergence angle tends to increase with increasing order of the OAM mode. Thus, OAM beams with equal divergence angle are highly desirable. In this paper, a frequency-diverse multi-mode (FDMM) OAM modulator with approximately equal divergence angle is proposed. The modulator is composed of an OAM modulation metasurface and a spatial filter (SF) with narrow passband. Firstly, the OAM modulation metasurface is designed based on multiple ring-like regions with different radii in the metasurface aperture. Each mode of OAM beam is generated at a corresponding frequency point in one region. Thus, the metasurface aperture can generate different modes of OAM beams at different frequencies (i.e., FDMM OAM beams) simultaneously. Then, the SF with narrow passband is proposed through synthesizing multi-layer frequency selective metasurfaces, aiming to reduce interferences between different modes of OAM beams. Finally, the FDMM OAM modulator is realized by superposing the SF on the OAM modulation metasurface. The FDMM OAM modulator can generate six modes of OAM beams (i.e., , and modes) at 12.5 GHz, 13.0 GHz and 13.6 GHz, respectively. A multi-mode OAM coincidence imaging model based on the FDMM OAM modulator is established. The simulation and experiment results show that the proposed FDMM OAM modulator can be used for target reconstruction and the coincidence imaging performance can be improved assisted by an optimization algorithm.

RCS reduction based on double parabolic phased metasurface

This paper presents a novel metasurface design strategy to realize broadband radar cross section (RCS) reduction. The phase distribution across the metasurface aperture can be regarded as applying an additional parabolic phase upon periodically arranged parabolic subarrays. Such a design fully utilizes the diffusive scattering nature of the parabolic phase distribution. Since the proposed metasurface is governed by only two focal lengths, the optimization procedure is quite easy compared to metasurface with random coding sequence. Experimental results show that the proposed metasurface can achieve more than 10 dB RCS reduction from 7.52 GHz to 19.66 GHz with a fractional bandwidth of 89.3% under both linearly and circularly polarized normal incidences, and keeping a performance of more than 7 dB RCS reduction until the incident angle increases to 40° for both x-polarized and y-polarized incidences in the frequency range of 8–19.35 GHz. When the incident angle increases to 60°, 7 dB RCS reduction can still be obtained for x-polarized incidence from 7.9 GHz to 19.35 GHz with a fractional bandwidth of 84%.

Arbitrary aperture synthesis with nonlocal leaky-wave metasurface antennas

The emergence of new technological needs in 5 G/6 G networking and broadband satellite internet access amplifies the demand for innovative wireless communication hardware, including high-performance low-profile transceivers. In this context, antennas based on metasurfaces – artificial surfaces engineered to manipulate electromagnetic waves at will – represent highly promising solutions. In this article, we introduce leaky-wave metasurface antennas operating at micro/millimeter-wave frequencies that are designed using the principles of quasi-bound states in the continuum, exploiting judiciously tailored spatial symmetries that enable fully customized radiation. Specifically, we unveil additional degrees of control over leaky-wave radiation by demonstrating pointwise control of the amplitude, phase and polarization state of the metasurface aperture fields by carefully breaking relevant symmetries with tailored perturbations. We design and experimentally demonstrate metasurface antenna prototypes showcasing a variety of functionalities advancing capabilities in wireless communications, including single-input multi-output and multi-input multi-output near-field focusing, as well as far-field beam shaping.

Frequency-diverse MIMO metasurface antenna for computational imaging with aperture rotation technique

Metasurface antennas have been proposed for computational imaging (CI) systems, which can reconstruct images without using mechanical scanning or large antenna arrays. In a CI system based on metasurface antennas, a variety of different radiation fields, which can be applied to sample the objects, are generated by exciting different frequency points in broadband. According to the compressed sensing theory, the imaging performance of the system is mainly limited by frequency-diversity radiation modes. In general, it is difficult to achieve rich radiation modes; therefore, a special design of metasurface aperture is required. In this paper, we propose a frequency-diversity MIMO metasurface antenna that consists of 2 × 2 sub-apertures with randomly distributed surface impedance. By employing the aperture rotation technique (ART) which rotates the MIMO metasurface antenna around the panel axis, the pseudo-randomness of the radiation fields is utilized. The diversity of the radiation field is improved on the premise of ensuring the relatively low complexity of the system. The ART significantly improves the measurement richness at the cost of increasing the measurement time. The performance of the proposed method is evaluated through simulations and experiments, suggesting that the proposed 2 × 2 MIMO metasurface antenna and the ART are effective to reconstruct high-quality images.

Two-Dimensional Off-Grid DOA Estimation With Metasurface Aperture Based on MMV Sparse Bayesian Learning

Two-Dimensional Off-Grid DOA Estimation With Metasurface Aperture Based on MMV Sparse Bayesian Learning

Non‐Interleaved Polarization‐Frequency Multiplexing Metasurface for Multichannel Holography

AbstractIn order to enhance channel capacity in modern wireless communications, diverse multiplexing techniques, such as polarization, frequency, and spatial multiplexing, are proposed and implemented. Here, a non‐interleaved polarization‐frequency multiplexing metasurface is proposed, which can realize independent controls of orthogonal linearly polarized or circularly polarized waves in two frequency bands to achieve four independent information channels. As a proof of concept, the metasurfaces that can independently realize four different polarized holographic images in two frequency bands are designed, simulated, and measured. The results show that two orthogonally polarized holographic images are achieved in each frequency band, respectively, which can be either linear or circular polarization. Benefitting from the advantages of non‐interleaved design, the proposed metasurfaces can reach not only high information capacity but also high information density by taking full use of the metasurface apertures.

Design Methods for Dual Polarized Metasurface Antennas: Three Simple Approaches

Metasurface (MTS) antennas are based on the transformation of a cylindrical-wavefront surface wave (SW) into a general wavefront leaky wave (LW). The MTS aperture is constituted by a grounded dielectric slab printed with an electrically dense distribution of subwavelength patches realizing space-variable, homogenized tensor impedance boundary conditions (IBCs). One of the challenges in this type of antenna is related to obtaining dual polarization operations by using the same impedance modulation. In this article, we explore and compare three simple approaches to obtain two beams with orthogonal polarizations by feeding two ports. A first known method is based on exciting both a transverse electric (TE) and a transverse magnetic (TM) SW mode on the same modulated impedance. A second method exploits the concept of impedance modulation sharing, according to which two distinct modulations, designed to radiate different polarizations when properly illuminated by distinct offset feeding points, are superimposed on the same aperture. A third method consists in duplexing an outward (radially diverging) and an inward (converging to the center) SW. Simple analytical formulas are presented for the synthesis of the impedance that allows for the control of the inward/outward waves to ensure balanced radiation performances in terms of aperture efficiency for the two polarizations. A comparison in terms of performances between the latter two approaches is presented.

Suspended Metasurface for Broadband High-Efficiency Vortex Beam Generation

Electromagnetic (EM) waves carrying orbital angular momentum (OAM) exhibit phase vortex and amplitude singularity. Broadband OAM generation with high efficiency is highly desired with suggested applications such as broadband imaging and communications. In this paper, suspended metasurface structure achieving low-Q factor is proposed to realize broadband phase control and excellent reflection efficiency. Broadband vortex beam generation with OAM order of 1 and 2 are realized using the proposed suspended structure. Furthermore, by analyzing different metasurface aperture phase distribution schemes, the efficiency of the OAM generator is maximally achieved. The designs are validated by simulation and measurement. The proposed OAM generators work across 4–10 GHz with efficiency higher than 82%. This design provides a route to broadband metasurface realization and high efficiency OAM generation.

Off-Grid Error and Amplitude–Phase Drift Calibration for Computational Microwave Imaging With Metasurface Aperture Based on Sparse Bayesian Learning

Computational microwave imaging (CMI) based on the frequency diversity metasurface apertures (FDMAs) is an emerging technology and has attracted wide attention. FDMA based CMI (FDMA-CMI) can be considered as microwave compressive sensing imaging with the frequency diversity pattern of the FDMA being the sensing matrix and solved by sparse signal reconstruction algorithms. However, the imaging quality is affected by the sensing matrix error and off-grid error seriously. In this paper, we propose a novel algorithm for FDMA-CMI, referred to as OGSISBL, by taking both the off-grid error and sensing matrix error into account. Firstly, we establish the measurement model with both the off-grid error and sensing matrix error. Specifically, the off-grid error is represented as a set of parameters to be estimated in the measurement model and the sensing matrix error is represented as the amplitude-phase drift of the transceiver channels of the imaging system due to the principle of the FDMA. Then, under the framework of the sparse Bayesian learning, a robust imaging algorithm OGSISBL is developed via the variational Bayesian expectation maximization (VBEM), which can not only recover the amplitude and position of the return of the scattered, but also simultaneously calibrate the amplitude-phase drift of the transceiver channels and the off-grid error. The performance of the proposed algorithm is evaluated by both the simulation data and the measured data collected by the self-designed experimental FDMA-CMI system, and the results validate the effectiveness and robustness of the proposed method.

Enhancement of Metasurface Aperture Microwave Imaging via Information-Theoretic Waveform Optimization

Computational microwave imaging with frequency-diverse metasurface (FDM) apertures is an emerging technology. In this article, we establish an experimental FDM microwave imaging system and address the waveform design problem based on the information theory, aiming to enhance the advantages of the FDM imaging. Two waveform design methods based on the different criteria are proposed for the FDM imaging system. The first waveform is designed by maximizing the mutual information between the object and the measured data with the constant transmitted energy, and the second one is designed by minimizing the transmitted energy while the mutual information is not less than a threshold. The performance of the proposed waveform design methods is evaluated by the data gathered by the self-established experimental FDM imaging system. The results show that the proposed waveform design methods are capable of improving the imaging quality or the imaging efficiency of the FDM imaging system.

Frequency Selective Computational Through Wall Imaging Using a Dynamically Reconfigurable Metasurface Aperture

A two-dimensional (2D) dynamically reconfigurable metasurface aperture is presented to perform frequency selective through wall imaging (TWI) with an unknown structure of the wall. Generally, in TWI, the medium properties and thickness of the wall need to be known in advance, which is not always possible. Moreover, compensating for these effects can significantly increase the computational complexity. We propose a two-stage method that leverages the concept of a dynamically reconfigurable metasurface antenna (DMA) in a narrow frequency band in which the effects of the wall are minimum to perform TWI. First, two simple probe antennas are used to evaluate the reflection response of the wall by means of a simple backscatter measurement. Based on these characteristics, a narrow band frequency selective window is identified. Second, a DMA consisting of an array of tunable metamaterial elements is used for TWI in the identified frequency selective window. The DMA aperture enables the scene information to be sampled through a set of spatio-temporally varying quasi-random modes using a single-channel transmit and receive architecture. This physical-layer compression scheme can significantly simplify the data acquisition while the quasi-random sampling of the scene information eliminates the need for conventional raster-scan based modalities.

Implementation of Resonant Electric Based Metamaterials for Electromagnetic Wave Manipulation at Microwave Frequencies.

In this paper, we present the application of a resonant electric based metamaterial element and its two-dimensional metasurface implementation for a variety of emerging wireless applications. Metasurface apertures developed in this work are synthesized using sub-wavelength sampled resonant electric-based unit-cell structures and can achieve electromagnetic wave manipulation at microwave frequencies. The presented surfaces are implemented in a variety of forms, from absorption surfaces for energy harvesting and wireless power transfer to wave-chaotic surfaces for compressive sensing based single-pixel direction of arrival estimation and reflecting surfaces. It is shown that the resonant electric-synthesized metasurface concept offers a significant potential for these applications with high fidelity absorption, transmission and reflection characteristics within the microwave frequency spectrum.

Single-pixel polarimetric direction of arrival estimation using programmable coding metasurface aperture

This paper presents a single-pixel polarimetric compressive sensing (CS)-based direction of arrival (DoA) estimation technique using a cavity backed programmable coding metasurface aperture. The single-pixel DoA retrieval technique relies on a dynamically modulated waveform diversity, enabling spatially incoherent radiation masks to encode the incoming plane waves on the radar aperture using a single channel. The polarimetric nature of the wave-chaotic coded metasurface ensures that the DOA estimation is sensitive to the polarization state of the incoming waves. We show that the polarimetric single-pixel DoA concept can be realized by encoding the polarization information of the incoming waves at the physical layer level within the antenna. A dynamically reconfigurable wave-chaotic metasurface, which possesses a structured sparsity of dual-polarized coded metamaterial elements, is proposed for the proof of concept. It is shown that by encoding and compressing the source generated far-field incident waves into a single channel, we can retrieve high fidelity polarimetric DoA information from compressed measurements.

Efficient Holographic Focusing Metasurface

We present the design and experimental demonstration of an efficient holographic metasurface aperture that focuses microwaves in the Fresnel zone. The proposed circular structure consists of two stacked plates with their periphery terminated in a conductive layer. Microwaves are injected into the bottom plate, which forms the feed layer, and are coupled to the top holographic metasurface layer via an annular ring. This coupling results in an inward traveling cylindrical wave in the top layer, which serves as the reference wave for a hologram. The radiating elements consist of a slot pair with their orientations designed to couple efficiently with the cylindrical reference wave while maintaining a linearly polarized focused beam. A general condition on the slot pairs radiated power is proposed to ensure low sidelobe level (SLL) and is validated with full-wave simulation. An aperture that is 20 cm in diameter, operates at 20 GHz in the K-band frequency, and forms a diffraction-limited focal spot at a distance of 10 cm is experimentally demonstrated. The proposed near-field focusing metasurface has high antenna efficiency and can find application as a compact source for Fresnel-zone wireless power transfer and remote sensing schemes.

User Tracking and Wireless Digital Transmission through a Programmable Metasurface

AbstractUser tracking has been an important aspect in wireless communications. Commonly, distributed apertures such as array antennas or multiple sensors are needed in wireless communication systems to achieve spatial resolutions for user tracking. Here it is proposed to realize the user tracking and wireless digital transmission simultaneously by using a single metasurface aperture. The reflection‐type metasurface consists of many subwavelength binary reconfigurable units. By programming these binary units, the metasurface can steer waves radiated from a horn antenna to a specified direction with different digital radiation phases. With this function, the metasurface can track the users by steering directional beams and transmit phase‐modulated digital signals through the directional beams. A prototype based on a programmable metasurface is developed and experiments in terms of cyclic redundancy check (CRC) and constellation diagrams are performed. The measured results prove that the user tracking and wireless digital transmission can be integrated through the programmable metasurface. Considering the simple architecture and flexible controlling features, the proposed methodology has great application prospect in integrated radar‐communication systems and cognitive electronic systems.

Nature-inspired orbital angular momentum beam generator using aperiodic metasurface

This article presents the design of reflective nature-inspired metasurfaces for generation of wideband and high purity circularly polarized (CP) orbital angular momentum (OAM) waves. It has been shown in this article that the breaking of the transitional periodicity and the combination of aperiodic nature-inspired distribution of sub-wavelength sized meta-atoms based on Pancharatnam–Berry (PB) phase theory can lead to OAM beams of high purity with improved bandwidth. The distribution of the PB anisotropic meta-atoms across the proposed metasurface aperture is non-uniform and distributed along logarithmic spirals similar to sunflower seeds, i.e. outwardly logarithmic spiral lattices of no transitional periodicity. The proposed reflective CP-OAM beam generator metasurface diameter is 140 mm, thickness ≈ 0.11λ 17GHz and has 600 anisotropic spatially rotated PB meta-atoms of sub-wavelength size of 5 mm ≈ 0.28λ 17GHz. Four OAM metasurface generators have been designed to produce OAM waves of various modes from 1 to 4. Both simulation and experimental results have demonstrated that the proposed metasurfaces can efficiently generate CP-OAM beams from 13.1 GHz to 20.5 GHz (BW = 44%) with high mode purity >90%.