Programmable metasurfaces (PMs) have significantly advanced electromagnetic (EM) wave manipulation by enabling real-time and digital reconfigurability. However, the current PM designs encounter challenges in achieving independent multi-band controls while keeping structural simplicity. Here, we propose a novel single-layer, dual-band PM based on staggered subwavelength structures. The design enables simultaneous and independent 1-bit phase controls in both the X- and Ku-bands within a simplified single-layer architecture. Both simulations and experimental results verify that the proposed PM exhibits minimal inter-band coupling. A prototype of PM is fabricated, demonstrating dual-band EM wave manipulation in both spatial and temporal domains through space-coding and space-time-coding strategies. We construct a space-frequency multiplexing wireless communication system using the proposed PM. This system is capable of establishing concurrent dual-band wireless links between distributed transceivers. The system enables selective disconnection of one frequency band while maintaining reliable connectivity on the other, as validated by the indoor experiments. The proposed design offers promising potential for next-generation reconfigurable wireless communication and radar systems that require simultaneous multi-frequency operations.
Today, the electromobility sector is increasingly dominated by electric kick-scooters (EKSs), valued for their convenience, affordability, and ease of use. Integrating wireless power transfer (WPT) technology with EKS operations is crucial for developing scalable charging infrastructure in both urban and rural areas. This paper presents a novel WPT system for EKSs charging that operates at 6.78 MHz and uses a metasurface-based resonator (MBR) as the transmitter and a shielded rectangular spiral coil as the receiver, separated by a 100 mm air gap. Through the full-wave numerical simulations, the system’s electromagnetic compatibility and compliance with international safety standards regarding human exposure to electromagnetic fields are assessed. A prototype is fabricated and experimentally validated, demonstrating RF-RF power transfer efficiency of 78% under perfect alignment of the transmitter and receiver. The robustness of the WPT system is tested against lateral and angular misalignment, revealing a graceful degradation in performance; for instance, a 10% reduction in efficiency was observed for misalignment of 120 mm along the x-axis and 60 mm along the y-axis. These findings confirm the high efficiency, misalignment robustness, and exposure safety of the proposed WPT system, underscoring its strong potential for real-world EKSs charging applications.
Recently, quasi-bound states in the continuum (quasi-BICs) of localized spoof surface plasmons (LSSPs) have been developed on several metasurfaces with broken symmetry, which have high quality factors ($Q$-factors) because of low radiation loss. They are transverse electric (TE) modes. In this paper, the quasi-BICs of LSSPs transverse magnetic (TM) modes are realized on a nonparallel circular grating metasurface with a linearly polarized plane wave. When the circular gratings are placed in parallel, the LSSPs TM modes on the metasurface cannot be excited by the plane wave, because they are true-BICs protected by rotational symmetry; when the circular gratings are mechanically reconfigured to be nonparallel, owing to the asymmetry of the structure, the LSSPs TM modes turn into quasi-BICs from the true-BICs and can be excited. Owing to the strong coupling between the circular gratings in the vertical coupling configuration, the quasi-BICs of the LSSPs TM modes have higher $Q$-factors compared with the quasi-BICs of the LSSPs TE modes. An experiment was conducted and the $Q$-factor of $\text{TM}_{2.1}$ was measured to be 305.0. This study provides a new idea for developing LSSPs with low radiation loss. It also extends the LSSPs from two-dimensional to three-dimensional, and brings new potential of transformation.
Fractional charge, a hallmark of modern electric polarization theory, provides a topological framework for understanding quantized polarization. It has only recently been recognized that real-space topological defects, such as disclinations, can further modify charge fractionalization, as an interplay between momentum-space and real-space topologies. So far, all the demonstrated mechanisms that lead to fractional disclination charges have been limited to Hermitian or energy-conserved systems. Although the non-Hermiticity has theoretically been predicted as a new route to modifying fractional disclination charge, experimental evidence remains lacking, mainly because of the challenges in measuring biorthogonal bases and precisely controlling gain/loss. Here, on a circuit metamaterial platform, we experimentally demonstrate the fractional disclination charge modification solely by manipulating the gain/loss. In experiments, negative resistors are employed as on-site gain, while positive ones as on-site loss. By measuring admittance and calculating the local density of states, we observe the topological disclination states and the associated fractionalized disclination charge. Moreover, by precisely tuning the spatial distribution of gain and loss, we observe a transition in disclination charge from fractional to integer values, which coincided with the vanishing of localized disclination states and a topological phase transition from nontrivial to trivial. Our experimental observations demonstrate a distinctive interplay between non-Hermiticity and real-space topological defects.
The evolution of electromagnetic compatibility (EMC) standards demands reverberation chambers (RCs) with superior field uniformity and high spatial efficiency. While metasurface-based stirrers are emerging as compact alternatives to traditional Z-shaped mechanical stirrers, their metal-dielectric-metal architectures suffer from dielectric-induced Q-factor degradation (typically less than $10^{3}$) and inefficient low-frequency mode stirring. Here, we present a paradigm-shifting all-metal coding metasurface stirrer (CMSS) that synergizes Pancharatnam-Berry phase modulation with stochastic coding optimization. This innovation achieves three-fold metrics: reduction of the lowest usable frequency (LUF) through optimized coding sequences; expansion of the working volume (WV) via a low-profile CMSS design; and sustainment of Q-factors with dielectric-free CMSSs. Experimental validation using three CMSS units in a $1.2\ \mathrm{m}\times 0.8\ \mathrm{m}\times 1.2\ \mathrm{m}$ aluminum chamber demonstrates an 11.2% LUF reduction, a 78.9% WV expansion, and the sustainment of Q-factor of $10^{3}-10^{4}$. These breakthroughs position CMSS as a cornerstone technology for 5G New Radio Frequency Range 1 (410–7125 MHz) and automotive EMC testing (ISO 11452–4), enabling more efficient, compact, multi-standard compliant RCs for advanced EMC testing.
The expansion of high-speed wireless networks and increasing reliance on connectivity necessitate advanced security beyond traditional software encryption. Programmable metasurface-assisted secret sharing cryptography offers the opportunity of joint software- and physical-layer encryption but requires all secret fragments for decryption, which compromises system robustness and secure communication continuity in adversarial scenarios. To address these challenges, we introduce a secure multiparty communication architecture integrating threshold secret sharing with dynamic beam manipulation. At the software layer, the secret is divided into shares using a threshold cryptography scheme, with the decryption threshold adjusting dynamically to security needs, allowing reconstruction only with authorized subsets of participants. Simultaneously, the metasurface disperses cryptographic shares spatially via beamforming and spectral control, ensuring intercepted channels provide only non-decryptable fragments. The system enables secret reconstruction without needing all fragments, and decryption occurs when the number of available shares meets a predefined threshold. This fault-tolerant design ensures operational continuity even with partial share loss, enhancing communication reliability and system resilience in adversarial conditions. Experiments demonstrate the system’s superior adaptability, capacity, and fault tolerance. By combining cryptographic protocols with real-time electromagnetic control, this research advances the development of next-generation secure wireless networks, facilitating robust multiparty communications even in hostile environments.
Optical analog image processing technology holds great potential for numerous modern applications due to its advantages of high-throughput parallel processing and ultra-low power consumption. The optical spatial differentiator, as a fundamental component of optical analog image processing, finds extensive applications in edge extraction, biomedical imaging, and feature classification. Unfortunately, most current optical differentiators are restricted by a constant modulation transfer function (MTF) across the working wavelength range, which restricts the application of optical differentiators in the spectral domain. Here, we propose and experimentally demonstrate a hybrid operation differentiator that can perform hybrid operations of the 0th-order and 2nd-order radial differential operations within its operational bandwidth, and convert similar color information, which is indiscernible to the human eye, into intensity information that is easily distinguishable. As a proof of concept, we fabricated an electrically tunable liquid crystals (LCs)-based device, which enables continuous adjustment of the MTF at different wavelengths while preserving its broadband operational characteristics, by leveraging the dispersion and electrically tunable characteristics of LCs. The proposed method extends the application range of optical differentiators, expanding from the traditional edge information recognition function to wavelength information recognition. Our approach may have various applications in metamerism recognition, ore color sorting, and advancing biomedical imaging, among others.
A near-field global-correlation method is proposed for accurate tracking of a larger number of dense characteristic modes in a large bandwidth. By using characteristic near-field patterns instead of conventional eigen-vectors or far-field patterns, the information stored in the rapid change of surface currents and the near-field evanescent waves is fully leveraged, thereby enriching the information of the mode database for accurate mode-tracking at the data level. To make full use of the enriched mode information, a global-correlation algorithm is proposed to correlate both the rows and columns of the correlation matrix, rather than conventional local correlation that concerns only the rows or the columns. The proposed method is validated by four examples of different complexities, including a rectangular plate, a bow-tie plate, a ground-backed fractal patch, and a ground-backed metasurface. As a result, both the bandwidth and accuracy of multi-mode tracking are significantly improved, as characterized by the bandwidth and the number of modes tracked without mode-swapping or mode-missing.
With the increasing maturity of various computational electromagnetics algorithms, the field has evolved from traditional standalone electromagnetic simulations to a stage in which trustworthy electromagnetic computation methods serve as the core, aimed at meeting the advanced demands of computer-aided engineering. Trustworthy electromagnetic computation consists of three key aspects: trustworthy model, trustworthy mesh, and trustworthy algorithm. This paper focuses on the aspect of trustworthy mesh, aiming to establish a systematic framework and methodology for achieving trustworthy computation under the assumption that the target geometry and associated parameters are determined. The framework starts with high-fidelity geometric meshing. An effective strategy is nonconformal domain decomposition, which facilitates accurate modeling of complex geometries and diverse materials. Subsequently, efficient preconditioning methods are utilized to ensure stable convergence when solving the resulting multi-scale systems associated with high-fidelity meshes. After obtaining the numerical solution, verification procedures are applied to evaluate whether the desired accuracy has been achieved. If the solution fails to meet the specified precision, adaptive mesh refinement techniques are used to automatically redistribute mesh density. The objective is to attain greater accuracy with a minimal increase in degrees of freedom, thereby enhancing computational efficiency. The adaptive refinement process proceeds iteratively until the computed solution satisfies the established accuracy criteria. Within this framework, we propose a novel, fast, physics-based self-reference method, which leverages power conservation laws to assess the accuracy of the solution.
As foldable smartphones typically operate in two primary states-unfolded state and folded state, the structural changes between the two states, which can significantly impact antenna performance, such as frequency shifts and efficiency reduction, are critical for practical applications. This paper proposes to use a quarter-wavelength parasitic branch to mitigate the effect of the structural changes between the two states. With the quarter-wavelength parasitic branch, a high-efficiency deca-band mobile antenna with similar performance in both the unfolded and folded states is achieved. Prototype testing shows negligible frequency shifts (approximately 0 MHz) in the low band (LB) of 0.704–0.960 GHz, middle high band (MHB) of 1.71–2.69 GHz, and new radio (NR) bands of 3.3–3.8 GHz and 4.7–5.0 GHz between the unfolded and folded states. The efficiency reductions are 0.45 dB (from −4.98 dB to −5.43 dB) in the LB band, 0.28 dB (from −2.70 dB to −2.98 dB) in the MHB band, and 0.81 dB (from −2.34 dB to −3.15 dB) in the NR band. The proposed antenna, which demonstrates minimal frequency shifts and slight efficiency degradation in the unfolded and folded states, makes it highly promising for practical applications.
In this article, we propose a novel super-resolution method for ultrawideband radar imaging, to address the problem of degraded range estimation accuracy of off-grid targets. We propose generalized atomic norm minimization (ANM) with modality demixing, dubbed ANM-MD, which effectively harnesses the sparsity of radar targets over a continuous range space. First, we demix the radar echo of targets according to their frequency dependency modalities (FDMs) in the geometrical theory of diffraction model. By modality demixing, we can suppress the influence of multiple FDMs on consequent estimation of target ranges. Then, we estimate the scattering parameters of radar targets separately in each FDM, leading to accurate estimation of target ranges. Experimental results show that our method can improve the accuracy of range estimation of off-grid targets by more than 15% compared with existing methods, leading to improved quality of super-resolution imaging.
The design of nonuniform transmission line impedance transformers is demonstrated by applying a convex optimization method. A constrained convex semidefinite relaxation problem is defined by minimizing the input reflection coefficient magnitude squared at a number of frequency values. Additional constraints on the minimum and maximum transmission line impedance values along the length of the line are imposed. The optimization process is demonstrated for real and complex loads. Such impedance transformers find broad applications in broadband impedance matching and balun design for antenna and amplifier circuits or rectifier circuits, for example in energy harvesting and wireless power transmission applications.
Domain decomposition method (DDM) is one of the most efficient and powerful methods for solving extra-large scale and intricate electromagnetic (EM) problems, fully embodying the divide-and-conquer philosophy. It provides the strategy of dealing with a computationally huge task that is not easy to be solved directly-dividing the task into a number of smaller ones, i.e. sub-tasks, each can be readily solved independently and employing appropriate transmission conditions (TCs) accounting for the interactions communication among these sub-tasks. This paper presents a comprehensive overview of DDM, highlighting its fundamental principles and wide-ranging applications in many diverse areas, such as very-large-scale integration circuits, antenna array radiation, and wave scattering. In the evolution of this technology, DDM has gradually manifested its remarkable power of tackling complex EM problems through its merging with Laplace, wave, Maxwell equations, as well as surface integral equations and volume integral equations. The further evolved advanced algorithms such as overlapped DDM and non-overlapped DDM are also reviewed. The efficiency of the DDMs depends strongly on the TCs of EM fields at the interface among adjacent sub-domains. The diversity of TCs in differential and integral equations generates a variety of DDMs. Due to the independence of sub-domains, the DDMs are inherently well-suited for parallel processing with high flexibility, making them particularly effective for EM full-wave simulations on distributed computers. Finally, a list of remaining challenging technical issues and future perspective on the fast-evolving field will be provided.
Massive multiple-input multiple-output (MIMO) and intelligent reflecting surface (IRS) technologies have become a research focus for non-stationary vehicle-to-vehicle (V2V) wireless communications due to their capability to control radio propagation environment. In this paper, a non-stationary irregular geometry-based stochastic model (I-GBSM) for V2V massive MIMO systems using three-dimensional uniform linear arrays and discrete IRS at millimetre-wave operating frequencies is proposed. A new approach for determining IRS elements phase-shift using the Doppler effect and channel impulse response is introduced to mitigate channel non-stationarity and enhance propagation conditions. Unlike traditional models, it takes into account practical spherical wavefronts instead of plane wavefronts. The proposed model categorizes clusters into moving and static clusters to examine traffic density and its effects on channel characteristics in V2V environments. It employs a novel birth-death process to ensure consistency in cluster evolution. The non-stationary stochastic channel characteristics are comprehensively analyzed through simulations. These characteristics include space-time-frequency correlation functions, Doppler power spectral density, path loss, delay spread, root mean square error of the correlation function, and achievable rate across different operating frequencies. The analysis demonstrates notable performance improvements. The proposed I-GBSM is also validated by a good agreement with the results from existing models and measurements under reduced scenarios.
In this article, the ultra-efficient transfer matrix method (U-TMM) is developed to detecting the propagation coefficients of ultra-multilayered anisotropic media (UMAM) in the terahertz region. Starting from the curl Maxwell’s equations and combined with the constitutive relation, the governing equation can be described in matrix form from which the four eigenvalues are derived, so that each component of the electromagnetic field can be uniquely represented by the fixed formula. The core thought with U-TMM is to maintain tangential continuity of electromagnetic fields between different media, thereby constructing transfer matrix between various regions and achieving the calculation of propagation coefficients in UMAM. After successfully validating U-TMM through two numerical examples, we find that U-TMM compensates for the shortcomings of COMSOL software in dealing with the UMAM problems, and in addition, the computational efficiency is significantly improved compared to the conventional transfer matrix method. Finally, to verify the energy change process in UMAM, we generate color images of the propagation coefficients by U-TMM in transverse electric/transverse magnetic mode, which can be applied to the analysis for materials and devices in the terahertz region.
The rapid proliferation of Internet of things (IoT) devices has driven an unprecedented demand for efficient multi-user communication solutions. Traditional methods for multiplexing, such as frequency-division and code-division multiplexing, are struggling to accommodate the increasing number of users and the limited spectrum resources available. To address these challenges, this paper presents an innovative wireless communication system that leverages reconfigurable intelligent surface (RIS) and orbital angular momentum (OAM) technologies to enhance spectral efficiency, reduce interference, and meet the high data rate requirements of modern IoT applications. The proposed system integrates a multi-mode OAM transmitter to generate signals carrying multiplexed data streams, which are subsequently directed to a metasurface-based RIS. The RIS is designed to receive the incident OAM beams, demultiplex the data, and focus it in real-time to distinct spatial regions, achieving a high signal-to-noise ratio (SNR) and minimizing interference for efficient multi-user transmission. A practical 2-bit transmissive RIS design is employed, which enables dynamic control over OAM modes, focusing energy at different user locations in the near-field, thereby realizing flexible and independent control of each unit. To generate the multi-mode OAM beams, a simplified microstrip antenna working at 10 GHz is utilized, incorporating a multi-layer printed circuit board (PCB) isolation design to minimize coupling interference between modes, ensuring reliable and efficient mode generation. To validate the effectiveness of the proposed system, we conduct full-wave simulation experiments, and build a complete communication testing environment, covering the entire communication process from the multi-mode OAM transmitter to the RIS-based communication link. Experimental results demonstrate that the proposed solution can effectively achieve near-field spot-beam focusing through the RIS and enable multi-user, same-frequency data separation at each focal point. This provides a novel and efficient solution for high-spectral-efficiency, low-interference multi-user data interaction in IoT networks, offering new insights for enhancing multi-user access and data transmission efficiency in various IoT scenarios, including smart factories, logistics centers, and in-vehicle communications.
The rapid and accurate identification of biological tissue types in resected specimens is critical to ensure complete tumor excision during surgery. By leveraging inherent electromagnetic property variations among tissues, this study presents a novel dual-port electromagnetic method that employs two-port S-parameters for quantitative tissue discrimination. The proposed technology leverages differences in the broadband electromagnetic properties among biological tissues, which are manifested as distinct attenuation characteristics during signal transmission. This approach allows for the successful differentiation of various tissue types, such as skin, muscle, fat, and tumor tissues, in ex vivo tumor-bearing mouse models. Specifically designed for biological tissue detection, this dual-port framework is the first to achieve a calibration-free operation and facilitate the detection of tumors with a size as small as 0.1 mm. Experimental validation in tumor-bearing mouse models demonstrated robust differentiation among skin, fat, muscle, and tumor tissues. Consistent measurements across multiple orientations were achieved, with a specific absorption rate below 0.0091 W/kg confirming operational safety. The transmission characteristics reveal significant bioelectromagnetic interactions, providing physical insights into tissue dielectric properties. This method provides a promising platform for clinical diagnostics and precision surgical guidance.
This work introduces and investigates a highly efficient eye diagram model, called the periodic eye diagram (PED), for assessing the performance of ultra-broadband transmission lines from the perspective of signal integrity. The PED model is based on the theory of periodic sequence, a novel approach for representing the propagation of time-periodic electromagnetic (EM) waves. Leveraging the parallel nature of EM periodic sequences, the full-wave response of high-speed channels can be rapidly obtained using one-batch multiprocessing. The computational scale remains small due to the inherent frequency-independent property of periodic sequences. Consequently, the PED and its corresponding eye parameters can be derived with both high speed and accuracy. This proposed method holds significant potential for enhancing the analysis and design of emerging ultra-broadband transmission lines with matched loads and manageable discontinuity.
For engineering electromagnetism, one of a typical case is that a medium/object rotates possibly with a deformable time-dependent shape. The electrodynamic behavior of such a system is governed by the Maxwell’s equations for a mechano-driven media system (MEs-f-MDMS). Here, by defining the effective electric and magnetic fields, the MEs-f-MDMS reduces to the standard form of the Maxwell’s equations (MEs) in some engineering scenarios. This means that the accelerated motion of a medium is a source for generating electromagnetic wave, while the propagation of the waves in the system follows the classical MEs. Therefore, the standard methods for solving the MEs can be adequately applied. We first present the theoretical derivation, then we will present the solutions of the MEs-f-MDMS in both time- and frequency-space. Second, the shortcomings in classical approach regarding to the calculation of electromagnetic radiation from a rotating medium is analyzed. Third, the theory about the impact of medium rotation on reflection and transmission of a plane wave at an interface is considered. Fourth, the theory for quantifying the output of triboelectric nanogenerator is given. Fifth, since the effective fields warrant the covariance of the MEs, the Lorentz transformation can be introduced for extrapolating the effective field theory to a case there is a translation motion of the system with considering relativistic effect. Finally, recent progresses about the experimental proofs in supporting the MEs-f-MDMS are covered.
Flexible electromagnetics, as an emerging and interdisciplinary field, integrates traditional electromagnetic functions such as the transmission, radiation, receiving, and processing of electromagnetic waves with advanced flexible electronic technologies. This integration overcomes the inherent limitations of traditional rigid electromagnetic devices, thereby significantly expanding the applicability of electromagnetic technology in complex environments. It provides new research avenues and directions for the application of electromagnetic technology in cutting-edge fields such as smart healthcare, artificial intelligence, and aerospace. This paper provides a comprehensive overview of recent advancements in flexible electromagnetics from four key aspects: materials, devices, integration, and applications. Firstly, we provide a succinct introduction to flexible electromagnetic materials including metallic materials, inorganic nonmetallic materials, polymer materials, and composite materials. Then, we explore the development status of flexible electromagnetic devices such as antennas, radio frequency resonators, and electromagnetic shielding devices. Furthermore, we survey the advancements and applications of flexible electromagnetic integrated system in the fields of intelligent medical treatment and intelligent information perception. Finally, we summarize the current challenges in the field of flexible electromagnetics and provide a preliminary outlook on future development trends.
