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Abstract Flexible frequency controls are crucial in many photonic and electronic applications, ranging from communications systems, spectroscopy, and metrology to quantum information processing. However, the state-of-the-art solutions based on nonlinear bulk media, electro-optic effect, and nonlinear metasurfaces incur very limited spectral controllability, and merely a couple of harmonic orders can be independently manipulated. Here, we theoretically propose and experimentally demonstrate synthetic moving-envelope metasurface antennas capable of simultaneously generating arbitrary harmonic orders and independently manipulating their wave properties in a software-defined manner. As proof-of-principle examples, we demonstrate unidirectional frequency transition, frequency comb generation, arbitrary harmonic orders independent control, and their applications in frequency-division multiplexing communications. All these complicated functionalities are achieved by the 1-bit spatiotemporally ON-OFF switching of meta-atoms of the waveguide-integrated metasurface antenna. Our proposed synthetic metasurface antenna solution greatly expands the frontiers of wave engineering and information manipulation, showing promising potential in wireless communications, spectroscopy, metrology, and quantum science.

Abstract All-optical diffractive neural networks, as analog artificial intelligence accelerators, leverage parallelism and analog computation for complex data processing. However, their low space transmission efficiency or large spatial dimensions hinder miniaturization and broader application. Here, we propose a terahertz spoof plasmonic neural network on a planar diffractive platform for direct multi-target recognition. Our approach employs a spoof surface plasmon polariton coupler array to construct a diffractive network layer, resulting in a compact, efficient, and easily integrable architecture. We designed three schemes: basis vector classification, multi-user recognition, and MNIST handwritten digit classification. Experimental results reveal that the terahertz spoof plasmonic neural network successfully classifies basis vectors, recognizes multi-user orientation information, and directly processes handwritten digits using a designed input framework comprising a metal grating array, transmitters, and receivers. This work broadens the application of terahertz plasmonic metamaterials, paving the way for terahertz on-chip integration, intelligent communication, and advanced computing systems.

Reconfigurable intelligent surface (RIS) as a smart reflector is revolutionizing research for next-generation wireless communications. In contrast to this is a concept of using RIS as an efficient propagation medium for superiorly low path loss characteristics and excellent flexibility. Motivated by the recent porous surface architecture that facilitates reconfigurable pathways with cavities filled with fluid metal by the mean of microfluidic systems.This paper comprehensively studies the propagation characteristics of different pathway configurations in different lossy dielectric materials on the reconfigurable surface wave platform by utilizing Computer Simulation Technology, a commercial full electromagnetic simulation software package, and then conducts S-parameters experimental verification. By using a porous surface model with dense uniformly cylindrical cavities, this paper also examines the optimal scheme for transitioning between a straight pathway and a 90° bend, while attempting to quantify the additional path loss incurred during the 90° bend. The experimental results confirm the simulation results, showing the effectiveness of the proposed reconfigurable surface wave platform for wideband, low-path-loss, and highly programmable communications. The results provide useful references for researchers in the areas.

Beyond 5G and 6G technologies mark a pivotal evolution in the telecommunications landscape. They are not only anticipated to deliver unprecedented speed and capacity but also to serve as critical enablers for a host of emerging technologies and applications, including joint communications and sensing, autonomous driving, augmented reality (AR), virtual reality (VR), and the burgeoning Internet of Things (IoT) [1], [2], [3]. As we transition into this new era, the expectations for system performance, reliability, and versatility are higher than ever before.

Abstract Metasurfaces have promising potential to revolutionize a variety of photonic and electronic device technologies. However, metasurfaces that can simultaneously and independently control all electromagnetics (EM) waves’ properties, including amplitude, phase, frequency, polarization, and momentum, with high integrability and programmability, are challenging and have not been successfully attempted. Here, we propose and demonstrate a microwave universal metasurface antenna (UMA) capable of dynamically, simultaneously, independently, and precisely manipulating all the constitutive properties of EM waves in a software-defined manner. Our UMA further facilitates the spatial- and time-varying wave properties, leading to more complicated waveform generation, beamforming, and direct information manipulations. In particular, the UMA can directly generate the modulated waveforms carrying digital information that can fundamentally simplify the architecture of information transmitter systems. The proposed UMA with unparalleled EM wave and information manipulation capabilities will spark a surge of applications from next-generation wireless systems, cognitive sensing, and imaging to quantum optics and quantum information science.

Abstract The terahertz frequency range is gaining popularity in security, stealth technology, and the future 6G network communication. For the control of severe terahertz electromagnetic interference (EMI) pollution, frequency‐selective stealth‐capable shielding materials are being explored to mask terahertz signals. For the realization of masking terahertz signals, the robustness, lightweight, and shape‐conformable materials with excellent terahertz EMI shielding/absorption are crucial. Here, the study reports the fabrication of 3D symmetric pyramidal architectural MXene composite films with frequency‐selective stealth performance characteristics via the facile drop casting method. With the high absorption capability of 2D MXene layers, the MXene composite films exhibit substantial terahertz stealth performance. 3D pyramidal microstructure design leads to frequency selective surface‐assisted reflection resonance in the frequency range of 0.6–1.1 THz. The MXene composite film demonstrates an outstanding maximum terahertz shielding effectiveness (SE) of up to 70.4 dB and a specific SE of 0.55 dB µm−1. These terahertz SE values exceed all of those for MX‐based shielding material designs reported in the literature. The investigation will open a new direction toward developing terahertz EMI shielding thin films with easy integration into any surface for stealth capabilities.

Lens antennas, which can transform the incident spherical wavefronts to planar above the radiating aperture, have attracted increasing attention due to their simple structure and high gain performance. Nevertheless, conventional lens antennas face with the problem of dispersion effects, which hinders their applications in large bandwidth and multi-channel communications. In this article, we propose a millimeter-wave achromatic metalens antenna using three-dimensional (3D) printing technology to reduce the dispersion effect and enlarge its bandwidth. The proposed ultra-wideband achromatic metalens antenna consists of a convex-liked metalens (VLM) and a concave-liked metalens (CLM) integrated as a metalens group. The VLM is designed on the basis of dielectric posts with different heights. The calculated transmission phase (from 0 to $2\pi$ ) of VLM can be realized by changing the height of dielectric posts. The CLM consists of discrete variable-width dielectric posts with two different heights to achieve desired transmission phase. Measured results demonstrate that the maximum realized gain is 23.27 dBi, and the return loss is smaller than −15 dB within the whole operating bandwidth. More importantly, a broad 3-dB gain bandwidth of more than 68.4% has been achieved to cover nearly the entire V and W bands, ranging from 50 to 102 GHz.

Leaky-wave antenna (LWA), as a special kind of waveguiding structure simultaneously characterized by both the guidance and radiation of electromagnetic waves along it, has received much attention and has been in the spotlight of both academia and industry since its inception in the 1940s. This is mainly because LWAs possess many appealing properties such as the highly directive beam, easy feeding mechanism, simple configuration, and particular frequency-driven beam-scanning, which enable them to hold promise in the development of a unique front-end antenna solution than others (e.g., reflector antenna and phased array). In addition to these inherent features, the exploitation of LWAs featuring multifarious sophisticated electrical functionalities (i.e., functional LWAs), with resort to engineering relevant radiating discontinuities and waveguiding structures, constitutes one mainstream research in the communities and increasingly prevails in the research & development of modern multifunctional wireless RF/microwave systems recently. This article is structured under this background, which is mainly dedicated to reviewing and investigating several enabling concepts, structures, and techniques that are specifically applied to the design of functional LWAs characterized by, for example, simultaneously low side-lobe and cross-polarization behaviors, rapid beam-scanning, stable radiation, frequency-selectivity, and open-stopband suppression. To make the technical discussions much more self-contained and systematic, this article begins with leaky-wave basics as well as general geometrical and electrical characteristics of LWAs. In addition, some representative system-level applications enabled by LWAs are briefly described, together with several promising research directions that can be further explored and galvanized, from the authors’ perspective.

This paper introduces a novel transparent proximity-coupled-fed patch antenna with enhanced impedance bandwidth and good filtering response. The proposed antenna consists of a ground plane, a specific feeding structure and a slotted patch. All the conducting surfaces are realized with metal meshes printed on glass substrates. Optical transparency of the antenna depends on the mesh density. The feed line of a traditional proximity-coupled-fed patch antenna is terminated with a driven stub etched with a half-wavelength U-shaped slot. This modification introduces an additional resonant mode but also a radiating null. By further etching a pair of quarter-wavelength open slots on the radiating patch, another resonant mode accompanied with an extra radiation null is generated. Finally, three resonant modes within the operating band along with two radiation nulls near the two edges of the passband are achieved. The proposed antenna is implemented to demonstrate an impedance bandwidth of 7.6% from 3.41 to 3.68 GHz and a maximum gain of 4.6 dBi.

This paper will present a novel design of optically transparent multiple-input multiple-output (MIMO) antenna made by indium tin oxide (ITO) films. The MIMO antenna involves patch and monopole antenna elements at 4.9 GHz and 26 GHz respectively. The upper and lower surface of the MIMO antenna are covered by a thin film of glass substrate with conductive ITO coatings, while top layer is radiating elements and the bottom layers is ground planes. Both patch and monopole antennas are fed by transparent 50Ω transmission lines. The prototypes were fabricated by an in-house photolithography process. Measurements are carried out to confirm the simulation. The characteristics showed that the proposed MIMO antenna can be considered as a potential antenna for 5G smartphone communications applications.

Abstract The ability to manipulate the propagation properties of electromagnetic waves, e.g., divergence, focusing, holography or deflection, is very significant in terahertz applications. Metasurfaces with flat structures are attractive for achieving such manipulations in terahertz band, as they feature low profile, lightweight, and ease of design and installation. Several types of terahertz reflective or transmitting metasurfaces with focusing function have been implemented recently, but none of them can provide scanning ability with controllable focus. Here, a flat reflective metasurface featuring controllable focal shift is proposed and experimentally demonstrated. Furthermore, the principle of designing a focus scanning reflective metasurface is presented and the focusing characteristics are discussed, including focus scanning along a line parallel or orthogonal to the metasurface with a large bandwidth. These interesting properties indicate that this flat reflective metasurface could play a key role in many terahertz imaging and detection systems.

An improved full-wave multilevel Green's function interpolation method (MLGFIM) with RBF-QR technique is proposed for the fast evaluation of electromagnetic field. The difficulty in applying the interpolation approach with radial basis functions (RBFs) lies in solving the increasingly singular matrix equation with the increase of the number of interpolation points. The compromise of making the basis functions relatively less smooth was used in the previous RBF implementations to address this problem. In this paper, a new interpolation scheme, the RBF-QR technique is applied to the interpolation of Green's function to resolve the ill-conditioning issue without such a compromise. A better conditioned basis function is generated by the QR-factorization technique, and it also solves the sensitivity of the basis function to the value of shape parameter. Moreover, a new hybrid interpolation pattern is adopted to optimize the grid pattern, e.g., reduce the number of interpolation points required and the boundary interpolation errors. The employment of the proposed RBF-QR technique in conjunction with hybrid interpolation pattern makes the efficiency of the MLGFIM greatly improved. The proposed algorithm is used for the analysis of problems involving objects, such as patch arrays, photonic bandgap structures, metasurface structures, double negative metamaterial and so on. Five numerical examples are given to validate this new algorithm, and show the accuracy and efficiency of the improved MLGFIM.

A circularly polarized patch antenna for future fifth-generation mobile phones is presented in this paper. Miniaturization and beamwidth enhancement of a patch antenna are the two main areas to be discussed. By folding the edge of the radiating patch with loading slots, the size of the patch antenna is 44.8% smaller than a conventional half wavelength patch, which allows it to be accommodated inside handsets easily. Wide beamwidth is obtained by surrounding the patch with a dielectric substrate and supporting the antenna by a metallic block. A measured half power beamwidth of 124° is achieved. The impedance bandwidth of the antenna is over 10%, and the 3-dB axial ratio bandwidth is 3.05%. The proposed antenna covers a wide elevation angle and complete azimuth range. A parametric study of the effect of the metallic block and the surrounding dielectric substrate on the gain at a low elevation angle and the axial ratio of the proposed antenna are presented.

By employing the complementary dipole antenna concept to the normal waveguide fed slot radiator, an improved antenna element with wide impedance bandwidth and symmetrical radiation patterns is developed. This is achieved by mounting two additional metallic cuboids on the top of the slot radiator, which is equivalent to adding an electric dipole on top of the magnetic dipole due to the slot radiator. Then, a high-gain antenna array was designed based on the improved element and fabricated, using 3D printing technology, with stable frequency characteristics operated at around 28 GHz. This was followed by metallization via electroplating. Analytical results agree well with the experimental results. The measured operating frequency range for the reflection coefficient ≤−15 dB is from 25.7 GHz to 29.8 GHz; its corresponding fractional impedance bandwidth is 14.8%. The measured gain is approximately 32 dBi, with the 3 dB beamwidth around 4°.

Bistable morphing structures are widely used as actuation mechanisms in soft actuators, soft robotics, energy absorbers, mechanical computers, optical lenses, meta materials, and flexible electronics. However, untethered actuators, repetitive actuators, and hybrid-assembly (containing in-plane-assembly and out-of-plane-assembly) actuators remain challenging to realize using existing bistable structures, which hinders the novel application of such actuators in research, engineering, and daily life. This problem is solved by fabricating a magnet-driven soft bistable actuator (MSBA) unit. The self-buckling of the circular polydimethylsiloxane (PDMS) sheet ensures the bistability of the actuator and allows it to operate as an independent unit, free of external constraints. The reorientation of neodymium-iron-boron (NdFeB) microparticles embedded in the PDMS sheet enables the dome-shaped actuators to exhibit repetitive snapping under the stimulus of a direction-switching magnetic field. The potential of this MSBA unit in bionics, electronics, and biomechanics applications is demonstrated in systematic studies involving modification of the buckling deflection and magnetic moment density. The MSBA unit exhibits excellent performance in hybrid designs and intelligent systems. [ABSTRACT FROM AUTHOR]