Due to the high electrical conductivity, relative permittivity, and magnetic permeability of seawater, the propagation behavior of electromagnetic fields differs significantly from that in air. The conductive nature of seawater causes strong eddy current loss and magnetic field attenuation, thereby reducing the effective coupling coefficient and resulting in frequency detuning between the transmitter and receiver coils. Moreover, the marine environment introduces parasitic impedance paths and additional energy dissipation due to the conductive medium, which further decreases transmission efficiency. These unique electromagnetic characteristics make the design and optimization of wireless power transfer (WPT) systems in seawater more complex and challenging than in air, motivating this study to develop and analyze a dual-receiver WPT architecture that improves midrange transmission efficiency under underwater conditions. To address this issue, a single-transmitter dual-receiver (1TX-2RX) WPT system operating in the 300-550 kHz frequency range is designed and implemented. Experimental results demonstrate that, under midrange transmission in seawater, the efficiency of the proposed 2RX architecture improves markedly from 12% in the 1RX system to 25%, while maintaining stable output performance under various receiver coil misalignment conditions. In addition, compared with operation in air, the optimal operating frequency of the 2RX system in seawater shifts leftward from approximately 460 kHz to 410 kHz. To better characterize the impact of seawater on transmission performance, complex impedance and mutual inductance parameters are incorporated into the conventional circuit model, enabling effective representation of the additional losses and coupling attenuation induced by the conductive medium. The predicted load voltage is consistent largely with the experimental measurements, validating the accuracy and applicability of the proposed modeling approach. Overall, this study not only verifies experimentally the feasibility of improving midrange transmission efficiency through a dual-receiver architecture but also establishes theoretically a circuit modeling method suited better for seawater environments, providing useful insights for the design and optimization of marine WPT systems.

In this paper, the electromagnetic performances of partitioned stator flux modulation (PSFM) machines with different rotor structures are compared to highlight the advantages of the auxiliary rotor structures. Two novel auxiliary rotors are proposed to suppress electromagnetic vibration in PSFM machine. First, the PSFM machine topology and the analytical models for the outer air-gap permeance of the different rotors are introduced. Furthermore, a comparative analysis of the electromagnetic and vibrational performance between the different auxiliary rotor machines and the conventional rotor machine are conducted to validate the advantages of the proposed designs. Finally, machines with different auxiliary rotors are mounted onto the experimental platform for testing to validate the effectiveness of the theoretical analysis.

To achieve wideband operation while maintaining a small overall footprint (26 mm × 27 mm × 1.6 mm) and electrical size of 0.46λ × 0.47λ × 0.03λ, this paper presents a compact wideband MPA (Microstrip Patch Antenna) that uses a DGS (Defected Ground Structure) and internal slots on a radiating patch and ground plane. The proposed antenna was designed on FR-4 with loss tangent = 0.02, ε_r = 4.4 & h = 1.6 mm, which achieves a wide bandwidth covering key wireless bands (sub-6 GHz 5G, Wi-Fi, WiMAX) with acceptable gain and radiation stability. The upper and lower edges of the band were tuned by the slot geometry and DGS, as demonstrated by parametric analysis. Full-wave electromagnetic simulation results are reported, and the fabrication and measurement procedure is described. The stated antenna achieves a peak radiation efficiency of 95.46%, a fractional bandwidth of 64.39%, a maximum gain of 4.8 dB, and an S₁₁ below -10 dB over the range of frequency 3.57-6.96 GHz, all in a small size similar to a coin. The antenna is particularly suitable for compact wireless devices, IoT modules, and sub-6 GHz applications.

To address the challenges of high computational complexity in linear system solving and slow convergence of the Alternating Direction Method of Multipliers (ADMM) for compressed sensing Synthetic Aperture Radar (SAR) imaging, this study proposes a precomputation strategy based on Cholesky decomposition. Specifically, the system matrix is decomposed once during the initialization phase and reused across subsequent iterations, substantially reducing the computational overhead associated with the primal variable update. Furthermore, a novel dual-momentum coupling mechanism is designed, and building on Nesterov extrapolation, this mechanism integrates cross-momentum interactions between the real and imaginary components of dual variables, along with the historical variation trends of primal variables, thereby effectively accelerating overall convergence. Both simulated and measured data results demonstrate that the proposed method achieves a significant improvement in computational efficiency while ensuring high imaging quality.

In this paper, a method is proposed for solving the one-hop sky-wave propagation problems of an arbitrarily oriented lowfrequency (LF) electric dipole within a planar layered Earth-ionosphere waveguide. The purpose of this study is to clarify the relationship between the radiation field and the direction of the electric dipole source in a planar-layered Earth-ionosphere waveguide. In deriving the specific formulas, we employed the ideal far-field approximation idea for an arbitrarily oriented electric dipole in free space and the method of images in layered media. The reflection characteristics of different polarized plane waves at the interface were also taken into account. Based on the improved wave-hop theory, the expressions for the one-hop sky-wave field excited by dipole sources with different directions suitable for an irregular surface are further derived. Using the proposed method, we calculated the sky-wave fields of electric dipoles operating at 100 kHz with various orientations at different receiver altitudes. The results show that the proposed method can be conveniently used to analyze the one-hop sky-wave field of the electric dipole sources with various orientations in a planar stratified Earth-ionosphere waveguide and provides an efficient modeling tool for LF communication system design and signal prediction over complex terrain.

A bandwidth tunable, circularly polarized (CP) patch antenna, with complementary split ring resonator (CSRR), embedded on the ground plane is presented in this paper. The antenna is capable of switching between ultra-wide band (UWB) frequency response, spanning through 2.6 GHz to 12 GHz and a narrowband (NB) frequency response at 6 GHz. Excitation of CSRR results in negative permittivity medium, producing notch band response at its designed frequency. This notch band is shifted by varying the arm length of CSRR using PIN diodes. This will result in tuning the bandwidth (BW) of the NB response of antenna, spanning from 1 GHz to 4.4 GHz, by retaining the central frequency at 6 GHz. The fractional bandwidth can be varied in a range of 16% to 73.3%, exhibiting an increase by a factor of 4.58. The antenna also exhibits switchable circular polarization (LHCP/RHCP) at 6 GHz for both UWB as well as narrowband responses. A compact tunable multiband Artificial Magnetic Conductor (AMC) unit cell is also designed and is used to construct a Phase Gradient Metasurface (PGM). The radiating beam of the antenna is steered using the PGM as a reflector to obtain a beam steering angle of +36° for LHCP and -44° for RHCP radiations. The antenna is a promising solution for applications which demand bandwidth switching & beam steering, such as cognitive radio services.

With the ongoing transformation of the global energy structure and the growing demand for environmental sustainability, transportation electrification has been rapidly advancing and is becoming a key pathway toward achieving carbon neutrality. Maritime transportation accounts for a significant share of carbon emissions, where conventional fuel-based propulsion remains dominant. Consequently, marine electrification is experiencing a transformative opportunity driven by both energy and environmental imperatives. As the core component of the propulsion system, the electric motor places increasingly stringent requirements on control performance and reliability. This paper reviews recent advances in marine propulsion motor control technologies, focusing on three major areas: model predictive control (MPC), fault-tolerant control (FTC), and position sensorless control. In MPC, multi-plane modeling and virtual voltage vector regulation for six-phase permanent magnet machines have substantially improved dynamic response and control accuracy. Additionally, multi-objective optimization can be achieved through the design of weight factors, while the introduction of observers or data-driven approaches can enhance robustness against parameter variations. In FTC, the development from optimal current compensation to post-fault subspace reconstruction topologies has provided a theoretical foundation for robust control under complex operating conditions. In position sensorless control, medium- and high-speed sliding-mode observation combined with low-speed high-frequency signal injection enables accurate position estimation over the full speed range. Future research is expected to integrate the feature extraction and modeling capabilities of machine learning to enhance observer design and fault-tolerant strategies, promoting the intelligent and data-driven evolution of marine propulsion motor control technologies.

To reveal the impulse behavior of radial grounding electrodes with different geometries, a comparative analysis was performed on three typical types: cross-shaped, Y-shaped, and rectangular ray-shaped electrodes. Existing research often examines only a single lightning waveform or influencing factor without addressing the coupled effects of electrode shape and soil resistivity. In this work, CDEGS simulation software was used to analyze the lightning transient characteristics of the grounding electrodes. Multiple lightning current waveforms and soil resistivity levels were considered to quantitatively compare the power frequency resistance, impulse resistance, ground potential rise, step voltage, and frequency-domain response. The results indicate that the rectangular ray-shaped electrode exhibits better impulse performance in low-resistivity soils (150 Ω·m), whereas the cross- and Y-shaped electrodes performed more effectively in high-resistivity soils (2000 Ω·m). For mountainous regions with high lightning density, a cross-shaped configuration is preferred owing to its smaller footprint and lower inductive effect. In high-resistivity areas with infrequent lightning, a Y-shaped electrode provides a more favorable overall protection

In this paper, the frequency-dependent electromagnetic response of argon, krypton, and xenon plasmas is investigated using a fluid approach, the Drude model and the Transfer Matrix Method (TMM). The key plasma properties, electron density, collision frequency and plasma frequency, of a Capacitively Coupled Plasma (CCP) were obtained using a drift-diffusion fluid model within the COMSOL Multiphysics. These properties were then used to predict how the plasma would react to electromagnetic waves in the 0 to 200 gigahertz band. The obtained results demonstrate that the reflective and transmissive characteristics of each gas depend on its plasma frequency. Argon acts as an efficient reflector below 20 GHz and becomes highly transparent above 30 GHz. In contrast, Krypton maintains strong reflection up to 85 GHz, while xenon remains reflective up to 140 GHz before it becomes transmissive. The observed differences are caused by the variations in each gas's plasma frequency and electron-neutral collision rates. The TMM results show excellent agreement with Finite-Difference Time-Domain (FDTD) simulations. The comparison between the two methods demonstrates that TMM is a faster and equally accurate approach for wideband electromagnetic analysis and for the design of adaptive plasma-based frequency-selective devices, including plasma antennas, plasma reflectors and intelligent reflective surfaces (IRS).

A compact Meta-surface absorber based on a novel combination of concentric split-ring resonators (SRRs) and arc dipoles is presented in this work. The proposed CSAD unit cell is a copper structure consisting of Quad dipoles and SRRs with a substrate with a dielectric constant of 4.3 and the tangent loss will be 0.02. The design resonates,17 GHz with a bandwidth of 300 MHz and 99.9% absorption. The symmetric single-band meta-surface allows for polarization-independent, angle-stable absorption up to 60°. The unit cell size for the proposed design is 10.375 × 10.375 × 1.6 mm³. It can be used for reducing the radar cross-section for stealth applications, such as UAVs that require selective frequency absorption. Simulations closely match observations, verifying the meta-surface's high stability and demonstrating its usefulness for practical electromagnetic validations.

To ensure adequate ventilation, radiosonde temperature sensors are typically mounted on top of the device and directly exposed to solar radiation. However, this configuration makes the sensors highly susceptible to radiation-induced errors, which can significantly compromise temperature measurement accuracy. This study proposes a four-wire structural design for the radiosonde temperature sensor and evaluates its performance through computational fluid dynamics (CFD) simulations. The radiosonde follows a helical ascent trajectory, which causes the incident solar radiation on the sensor to vary continuously. This continuous variation makes the quantification and correction of radiation errors more difficult. The proposed four-wire design achieves favorable radiative thermal balance in three-dimensional space. It also demonstrates low sensitivity to changes in the ascent trajectory. This characteristic allows the correction model to be simplified by neglecting variations in the incident radiation direction. A coupled flow-structure thermal analysis is conducted under varying environmental conditions, including altitude, ascent velocity, and solar radiation intensity, to quantify the radiation error of the four-wire sensor. A neural network algorithm is then trained on the simulation data to develop a radiation error correction model. Experimental validation is performed using a platform comprising a full-spectrum solar simulator and a low-pressure wind tunnel. The experimental results yield a root mean square error (RMSE) of 0.159 K, mean absolute error (MAE) of 0.143 K, and correlation coefficient of 0.962 between simulated and corrected radiation errors, demonstrating the high accuracy of the proposed correction algorithm.} After correction, the average radiation error of the four-wire sensor decreases from 0.446 K to 0.143 K, substantially improving temperature measurement accuracy.

In this work, a delamination model for millimeter-wave inspections of glass fiber reinforced polymer (GFRP) is proposed that replicates the scattering characteristics of a real delamination. The model can be used not only for the performance assessment of conventional non-destructive testing (NDT) approaches, but also for structural health monitoring (SHM) applications with permanently installed radar sensors in the frequency band from 57 to 65 GHz. Parametric numerical and experimental investigations were carried out for three different cases: (a) delamination represented by two GFRP plates with a defined air gap between the plates, (b) erosion protection tape above a GFRP plate separated by an air gap, and (c) erosion protection tape on top of a rigid foam that has similar dielectric properties to air. All signals have been processed using a damage indicator approach (DI). The numerical and experimental results show a high degree of similarity in the DI curve as a function of the delamination thickness. The differences between simulation and experiment are between 0 and 0.3 mm in delamination thickness. Hence, the proposed model can be used for the qualification of radar-based NDT and SHM systems for various practical applications, e.g. wind turbine blades, eliminating the need for expensive, destructive testing.

To achieve accurate characterization of a dielectric sample, an improved approach to the cylindrical cavity perturbation technique is proposed, with particular emphasis on the depolarization factor. The problem arises from the depolarized field within the sample when its height is smaller than that of the cavity, and it depends on the sample's geometry and the orientation of the applied field lines. Two models are examined: the proposed model, based on the resolution of Maxwell's equations, and the ellipsoidal model refined through image theory. The objective is to enhance the accuracy of complex permittivity extraction for lossy dielectric materials. Standard low-loss and high-loss materials (Al2O3, Teflon, and SiC) with various shapes (rod, needle, disk and sphere) are analyzed using HFSS simulations and MATLAB computations. The maximum sample volume is also evaluated for different geometries and material types to ensure accurate permittivity estimation. Low-loss materials generally allow a larger sample volume than high-loss ones, and provide more consistent results for permittivity extraction. Experimental measurements were further performed on disk-shaped polyamide and ceramic samples, demonstrating that the proposed approach provides improved permittivity estimation, particularly for high-loss and disk-shaped dielectric materials.

This manuscript presents the design of a nanopatterned H-shaped photoconductive antenna on an LT-GaAs substrate for terahertz applications. The use of gold nanoparticles and Si lens in the gap between two electrodes improves the photoconductive conductive antenna's low efficiency. It is noticed that the proposed PCA resonates at 1.35 THz with -24.2 dB, 1.65 THz with -22.1 dB, and 2.4 THz with -21.32 dB reflection coefficient. Further, with the Si lens, PCA resonates at 2.15 THz with a -30.2 dB reflection coefficient. Moreover, the nanopatterned H-shaped photoconductive antenna resonates at 1.7 THz with the minimum reflection level of -40 dB. These results indicate that the reflection in the photoconductive antenna can be reduced using the nanopatterning technique. This further increases the efficiency of the photoconductive antenna. The proposed H-shaped photoconductive antenna is designed and optimised using the COMSOL Multiphysics platform.

With the development of smart grids and the high proportion of new energy integration, traditional electromagnetic power metering technology is gradually facing bottlenecks in terms of accuracy, anti-interference ability and frequency response range. This paper proposes a new ultra-high-precision power measurement method based on diamond nitrogen-vacancy (NV color center) quantum sensing. By establishing an electromagnetic field-spin quantum state coupling model, it achieves microtesla-level magnetic induction intensity measurement, and then reconstructs current, voltage and power parameters. At the theoretical level, the response function of the multi-pulse quantum manipulation sequence (XY8-K) to the power frequency alternating magnetic field was derived, and an adaptive quantum state locking algorithm was proposed to suppress environmental noise. At the device level, a multi-layer heterogeneous integrated miniaturized quantum sensing chip was designed, combining silicon-based photonic waveguides and microwave resonant structures. Its size was controlled at 8×8×2 mm³, and its power consumption was less than 200 mW. Experiments show that this system has a remarkable effect and provides technical support for the next generation of intelligent metering equipment.

This letter presents a compact electromagnetic vector antenna (EMVA) operating across the 3–30 MHz high-frequency (HF) band and capable of simultaneously sensing all six Cartesian components of the electromagnetic field. The design integrates three orthogonal dipoles and three orthogonal loops co-located at a common phase center (CPC), enabling full vector-field reconstruction for polarization analysis and direction finding. A transformer-assisted broadband passive matching network ensures impedance compatibility across the HF band, with measured insertion loss and inter-port isolation appropriate for electrically small HF elements. Field experiments using an ionospheric sounding configuration validate the antenna's effectiveness, achieving RMS direction-of-arrival errors of 10.02° (azimuth) and 8.42° (elevation) for O-mode signals, and 14.77°/26.09° for X-mode signals, respectively. These results demonstrate the suitability of the proposed CPC EMVA for compact, polarization-diverse sensing in mobile and space-constrained HF platforms.

Beam steering antennas are advanced technologies used for directing radio waves in a specific direction without physically moving the antenna. In this paper, a simple two steering beams antenna is designed based on Fabry-Perot structure. The amplitude and phase control theory is introduced to design the electric field phase and electric field strength in the near field to obtain the far-field radiation pattern required for the Fabry-Perot antenna (FPA). The FPA working at 10 GHz with the aperture of 5λ₀ × 5λ₀ steers to ±30° with the maximum gain of 18 dB for each beam realized by a proper design of the superstrate, which is a key to realizing a beam-steering antenna with a simple structure.

The control of all of light's degrees of freedom and its harnessing for applications is captured by the emergent field of structured light. The modern toolkit includes external modulation of light with devices such as metasurfaces and spatial light modulators, their intra-cavity insertion for structured light directly at the source, and their deployment to engineer quantum structured light at the single photon and entangled state regimes. Historically, this control has involved linear optical elements, with nonlinear optics only recently coming to the fore. This has opened unprecedented functionality while revealing new paradigms for nonlinear optics beyond plane waves. In this review we look at the recent progress in structured light with nonlinear optics, covering the fundamentals and the powerful applications they are facilitating in both the classical and quantum domains.

This work presents the design, characterization, and experimental validation of waveguide-fed metasurface antennas based on complementary electric-LC (CELC) resonators. The magnetic polarizability of individual unit cells was extracted using the Incremental Difference Method, enabling physically grounded complex weighting of each metasurface element without the need for external feeding networks. Two CELC geometries (square and circular) were investigated under identical WR340 waveguide excitation. The circular CELC exhibited a smoother current distribution and a more uniform polarizability profile, as observed in the polarizability-mapping results, whereas the square CELC provided a slightly higher gain owing to its sharper magnetic resonance. Lateral-slot perturbations were introduced as a simple geometric modification to overcome the intrinsic narrowband nature of Lorentz-type resonators. The simulated and measured results confirm a significant improvement in impedance bandwidth, reaching 194 MHz (simulated) and 189 MHz (measured) for the square slot geometry, and 222 MHz (simulated) and 209 MHz (measured) for the circular slot geometry. Radiation-pattern measurements in an indoor antenna chamber showed good agreement with full-wave simulations, validating the polarizability-based weighting mechanism and the overall metasurface antenna model. The results demonstrate that magnetic-polarizability mapping combined with geometry-tailored perturbations provides an effective and experimentally verified approach for compact and bandwidth-enhanced metasurface antenna design.

In this article, the authors propose the design and implementation of a frequency reconfigurable metamaterial-inspired octagon-shaped antenna for multiple wireless standards. The multiband functionality is achieved by incorporating a slotted self-similar octagonal radiating part with two SRR cells. The antenna design incorporates PIN diode switching elements on the slotted radiating patch, along with metamaterial-based SRR cell loading and a modified trapezoid-shaped partial ground plane, enabling its use across multiple wireless standards. The proposed design is resonating across five microwave frequency bands, including S-band WiMAX (3.5 GHz - IEEE 802.16e), 5G NR bands (n48: 3.55-3.70 GHz, n46: 5.15-5.925 GHz, n47: 5.855-5.925 GHz, n77: 3.3-4.2 GHz, n78: 3.3-3.8 GHz, n79: 4.4-5.0 GHz), C-band WLAN (5.0/5.8 GHz - IEEE 802.11a/ac), X-band (satellite communication, radar, terrestrial broadband, space communication), lower Ku-band for radar communication (13.43-14.55 GHz), upper Ku-band for molecular rotational spectroscopy (17.25-18.32 GHz), and lower K-band for astronomical observation services (18.81-19.96 GHz). The multiband antenna is then fabricated and tested, with measured and simulated results for return loss, gain, radiation efficiency, E-plane, and Hplane showing good agreement. The antenna's penta-band operation, compact size, stable radiation characteristics, and good impedance across the entire resonating band make it well-suited for various wireless applications.