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In recent years, active metasurfaces have emerged as a reconfigurable nanophotonic platform for the manipulation of light. Here, application of an external stimulus to resonant subwavelength scatterers enables dynamic control over the wavefront of reflected or transmitted light. In principle, active metasurfaces are capable of controlling key characteristic properties of an electromagnetic wave, such as its amplitude, phase, polarization, spectrum, and momentum. A ‘universal’ active metasurface should be able to provide independent and continuous control over all characteristic properties of light for deterministic wavefront shaping. In this article, we discuss strategies for the realization of this goal. Specifically, we describe approaches for high performance active metasurfaces, examine pathways for achieving two-dimensional control architectures, and discuss operating configurations for optical imaging, communication, and computation applications based on a universal active metasurface.

Here, we show that isorefractive spacetime crystals with a travelling-wave modulation may mimic rigorously the response of moving material systems. Unlike generic spacetime crystals, which are characterized by a bi-anisotropic coupling in the co-moving frame, isorefractive crystals exhibit an observer-independent response, resulting in isotropic constitutive relations devoid of any bianisotropy. We show how to take advantage of this property in the calculation of the band diagrams of isorefractive spacetime crystals in the laboratory frame and in the study of the synthetic Fresnel drag. Furthermore, we discuss the impact of considering either a Galilean or a Lorentz transformation in the homogenization of spacetime crystals, showing that the effective response is independent of the considered transformation.

Recently, space‐time modulation has revolutionized the wave engineering technologies, providing unprecedented opportunities beyond traditional static systems. This advancement is crucial across diverse fields, ranging from non‐reciprocal transmission to wireless communication. However, the current approaches to sound modulation require bulky artificial structures and are limited in achieving space‐time‐variable sound‐matter interactions. Here, a prototype of space‐time acoustic metasurface (STAM) is proposed and implemented, consisting of a reflective piezoelectric array controlled by a field‐programmable gate array. Leveraging the spatiotemporally programmable phases of the STAM, this is experimentally achieved Doppler‐like chirp modulation and space‐time modulation with deterministic frequency and momentum shifts of waterborne acoustic waves. Furthermore, based on this flexible and efficient modulation strategy, a stochastic space‐time modulation method is introduced, showcasing its applications in single‐channel direction‐of‐arrival estimation. The proposed STAM extends the frontier of wave control and thereby lays the foundation for versatile space‐time applications involving sound. This article introduces a novel space‐time acoustic metasurface (STAM) to overcome the limitations of bulky structures in sound modulation. Using a programmable piezoelectric array, the STAM precisely controls waterborne acoustic waves through spatiotemporal phase modulation. Doppler‐like chirp modulation and stochastic modulation are demonstrated, with applications shown in single‐channel direction‐of‐arrival estimation, opening new avenues for wave control.

Joint space-time modulation of light fields has recently garnered intense attention for enabling precise control over both spatial and temporal characteristics of light, leading to the creation of space-time beams with unique properties, such as diffraction-free propagation and transverse orbital angular momentum. Here, we theoretically propose and experimentally demonstrate spatiotemporal Moiré lattice light fields by controlling the discrete rotational symmetry of a pulse’s spatiotemporal spectrum. Using a 4 pulse shaper and an − modulation strategy, we generate tunable spatiotemporal Moiré patterns with varying sublattice sizes and confirm their diffraction-free behavior in time-averaged intensities. Additionally, we demonstrate spatiotemporal Moiré lattices carrying transverse orbital angular momentum. These findings provide a novel platform for studying spatiotemporal light–matter interactions and may open new possibilities for applications in other wave-based systems, such as acoustics and electron waves.

Differential unitary space time modulation (USTM) is identified as one of the best non-coherent technique for future 5th generation mobile networks. Two or more nodes with single antennas cooperate with each other to form a cooperative multiple-input–multiple-output network. In, this paper we examine the use of differential cooperative USTM that avoids channel estimation and also prolong the lifetime of wireless sensor network. Aiming at minimizing the energy consumption per bit we form a differential cooperative energy minimization algorithm by optimally selecting the number of cooperative nodes and finding the route that consumes minimum energy.

A moving medium drags light along with it as measured by Fizeau and explained by Einstein’s theory of special relativity. Here we show that the same effect can be obtained in a situation where there is no physical motion of the medium. Modulations of both the permittivity and permeability, phased in space and time in the form of traveling waves, are the basis of our model. Space–time metamaterials are represented by effective bianisotropic parameters, which can in turn be mapped to a moving homogeneous medium. Hence these metamaterials mimic a relativistic effect without the need for any actual material motion. We discuss how both the permittivity and permeability need to be modulated to achieve these effects, and we present an equivalent transmission line model.

Intelligent metasurfaces have gained significant importance in recent years due to their ability to dynamically manipulate electromagnetic (EM) waves. Their multifunctional characteristics, realized by incorporating active elements into the metasurface designs, have huge potential in numerous novel devices and exciting applications. In this article, recent progress in the field of intelligent metasurfaces are reviewed, focusing particularly on tuning mechanisms, hardware designs, and applications. Reconfigurable and programmable metasurfaces, classified as space gradient, time modulated, and space–time modulated metasurfaces, are discussed. Then, reconfigurable intelligent surfaces (RISs) that can alter their wireless environments, and are considered as a promising technology for sixth‐generation communication networks, are explored. Next, the recent progress made in simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR‐RISs) that can achieve full‐space EM wave control are summarized. Finally, the perspective on the challenges and future directions of intelligent metasurfaces are presented. This review presents the recent progress of intelligent metasurfaces, focusing on tuning mechanisms, hardware designs, and applications. The authors discuss the reconfigurable and programmable metasurfaces, classified as space‐gradient, time‐modulated, and space–time modulated metasurfaces. Furthermore, the emerging research direction of reconfigurable intelligent surfaces are demonstrated. Finally, the challenges and future directions of intelligent metasurfaces are presented.

This paper presents a high-precision angle demodulation method for magnetic encoders by integrating orthogonal-signal correction with space–time modulation (STM). The proposed approach specifically addresses a critical vulnerability of STM-based high-frequency pulse interpolation: its interpolation accuracy is highly sensitive to zero-crossing timing jitter of the quadrature signals. In practical magnetic encoders, non-idealities such as DC offsets, amplitude mismatch, and phase non-orthogonality in the sine/cosine outputs induce jitter and shift in the zero-crossing points. This directly leads to fluctuations in high-frequency counts and amplifies the final angle error. To mitigate this issue, an online orthogonal-signal correction module is first developed. This module sequentially performs offset estimation, amplitude normalization, and real-time phase orthogonalization, thereby enhancing the orthogonality and zero-crossing stability of the quadrature signals at the source. This preprocessing significantly reduces the sensitivity of the subsequent interpolation counting to noise and signal imperfections. Based on the corrected signals, an STM pulse-counting interpolator is adopted to convert angle information into a time-domain phase (time) difference, and high-frequency counting is used for fine subdivision. A Kalman-filter-based predictor is employed to estimate angular velocity and compensate the intrinsic latency of counting-based demodulation in dynamic conditions. Experimental results demonstrate that the proposed phase orthogonalization correction markedly suppresses zero-crossing timing jitter and enhances the stability of high-frequency pulse interpolation. Consequently, the overall demodulation error is reduced by more than 30 percent compared with existing methods, and the final angle error is maintained within 0.033°.

This paper investigates a space-time modulated digital metamaterial array (DMA) based on reconfigurable plasma ionization. The DMA consists of 8 × 8 unit-cell elements with total dimensions of 120 × 120 × 3.2 mm 3 . Each unit-cell consists of a ring container filled with argon gas and is backed with a grounded dielectric substrate. The argon gas is ionized into a plasma state through metallic electrodes. The logic state of the unit cell is controlled via the changing of the plasma frequency, ω p . The value of ω p = 6 × 10 11 rad / sec represents logic “0”, and ω p = 8 × 10 11 rad / sec represents logic “bit 1”. The periodic time switching of the plasma ionization controls the radiation at the fundamental and harmonic frequencies. The on-time instants and on-time durations control the number of radiated beams, their directions, amplitudes, and side-lobe levels. Different time-switching sequences are investigated for beam steering, dual-sum beams, broadside beams, end-fire beams, multi-beams, and fan-shaped beams for wireless communications applications. The DMA was investigated under different switching sequences for phase-modulation and amplitude-modulation schemes. A full-wave simulation CST Microwave Studio simulator is used to analyze the proposed DMA and the results are compared with ideal point sources array excited with the same switching sequences.

Sub-Nyquist sampling technology can ease the conflict between high resolution and wide swath in a synthetic aperture radar (SAR) system. However, the existing sub-Nyquist SAR imposes a constraint on the type of the observed scene and can only reconstruct the scene with small sparsity (i.e., number of significant coefficients). The information channel model of microwave imaging radar based on information theory, in which scene, echo, and the mapping relation between the two correspond to information source, sink, and channel, is built, and noisy-channel coding theorem explains the reason for the aforementioned under this model. To allow the wider application of sub-Nyquist SAR, this paper proposes sub-Nyquist SAR based on pseudo-random space-time modulation. This modulation is the spatial and temporal phase modulation to the traditional SAR raw data and can increase the mutual information of information source and sink so that the scenes with large sparsity can be reconstructed. Simulations of scenes with different sparsity, e.g., an ocean with several ships and urban scenes, were run to verify the validity of our proposed method, and the results show that the scenes with large sparsity can be successfully reconstructed.