A miniature-sized dual-broadband eight-element Multiple-Input Multiple-Output (MIMO) antenna with R-shaped radiators in the sub-6 GHz band for 5G applications is presented in this research article. The proposed novel MIMO configuration includes 4 × 2 antennas mounted on a 60 × 112 mm² substrate with each radiator measuring 28 × 28 mm². Modified Ground Structure (MGS) is employed to enhance impedance matching and reduce the effect of electromagnetic interaction between closely placed radiators. The MGS and optimal R-shape design enable this MIMO antenna to work at dual frequencies. Two resonances at frequencies of 1.8 GHz (1.67-2.03 GHz) and 4.4 GHz (4.15-4.75 GHz) are observed in both simulations and measurements, and the maximum reflection coefficient is recorded at -28 dB, which implies that excellent impedance matching is achieved for the designed eight-port radiator. This antenna design offers isolation better than 15 dB in both operating frequency bands (1.67-2.03 GHz and 4.15-4.75 GHz), with a maximum isolation of about 40 dB at certain frequencies. Moreover, it is found that the proposed antenna has good diversity parameters with Envelope Correlation Coefficient (ECC) less than 0.01 and Diversity Gain (DG) around 10 dB. The results show that this novel antenna is capable of providing a suitable balance among small size, strong isolation, stability of radiation, and enhanced diversity performance, thereby becoming an excellent choice for sub-6 GHz 4G/LTE cellular communications and 5G applications.

Free Space Optical (FSO) communication is a high-capacity optical wireless technology for terrestrial backhaul, interbuilding connectivity, and rapidly deployable networks, but fog attenuation, turbulence, and beam-divergence-induced spreading degrade link reliability. This paper evaluates an impairment-aware erbium-doped fiber amplifier (EDFA)-assisted 8-channel, wavelength division multiplexing free-space optical (WDM-FSO) system using On-Off Keying (OOK), Differential Phase Shift Keying (DPSK), and Optical Orthogonal Frequency Division Multiplexing (Optical OFDM). The system uses eight C-band wavelengths from 1552 nm to 1566 nm with 2 nm spacing, each carrying 10 Gbps, and employs a fixed 20 dB EDFA gain for attenuation compensation. Beer-Lambert propagation loss, the Kim visibility-based fog model, log-normal and Gamma-Gamma turbulence models, beam-divergence-induced geometric spreading, WDM filter isolation, laser launch-power fluctuation, and receiver-side DSP-assisted normalization are considered. RSoft OptSim simulations are performed over 1-8 km link distances and 50-500 m visibility. Performance is evaluated using bit error rate (BER), Q-factor, and signal-to-noise ratio (SNR). Under the specified simulation assumptions, Optical OFDM achieves the best performance among the compared schemes, with 1.0 × 10^-9 BER at 10 Gbps and 1.2 × 10^-6 BER, 4.72 Q-factor, and 17.0 dB SNR at 8 km.

Reconfigurable Intelligent Surfaces (RISs) have emerged as a disruptive technology with the potential to fundamentally transform 5G and future 6G wireless communication systems. By intelligently controlling electromagnetic (EM) wave propagation through large arrays of reconfigurable meta-atoms, RIS enables dynamic beam shaping, interference mitigation, coverage enhancement, and energy-efficient communication. This paper presents a comprehensive review of RIS technology, focusing on its fundamental principles, classification, architectural design considerations, and diverse reconfiguration mechanisms. Key aspects, including unit cell structures, material advancements, operating modes, spatial resolution, and control strategies, are examined in detail to provide a holistic understanding of RIS functionality. The review further explores RIS performance modelling, electromagnetic simulation techniques, prototyping methods, and measurement approaches used in evaluating real-world deployments. Emerging application scenarios, including mmWave/THz communications, indoor localization, wireless power transfer, UAV-assisted networks, and smart radio environments, are also highlighted to demonstrate RIS's versatility in next-generation networks. Finally, the paper identifies existing challenges, potential limitations, and future research directions that must be addressed to realize RIS-enabled intelligent wireless ecosystems fully. The insights presented herein aim to guide researchers and industry practitioners in advancing RIS technology as a key enabler for the evolution of future 6G communication systems.

This paper proposes a polarization-orthogonal self-decoupling wideband shared-radiator Multiple-Input Multiple-Output (MIMO) antenna for 5G mobile terminals. The antenna is fabricated on an FR4 dielectric substrate with a relative permittivity of 4.4 and a loss tangent of 0.02, and integrates a cross-shaped radiation patch, L-shaped slots and metallized shorting vias into a 27 mm × 27 mm standard-sized substrate, and generates polarization-orthogonal modes through dual-port excitation, with an electrical size of 0.35λ₀ × 0.35λ₀ × 0.021λ₀ at the center frequency of 3.9 GHz, which effectively suppresses the mutual coupling between ports. To fully demonstrate the wideband characteristics and self-decoupling advantages of this shared radiator, four identical antenna element pairs are arranged at the four corners of the smartphone rear cover, constructing an 8×8 MIMO antenna system operating in the 3.5-4.3 GHz frequency band. Simulated and measured results show that the proposed 8 × 8 MIMO system achieves an isolation better than 15 dB and an envelope correlation coefficient (ECC) less than 0.06. Featuring wideband operation and a passive self-decoupling structure, this antenna provides a promising design solution for 5G smartphone antennas.

A low-complexity first-order model was developed and verified to account for a single reflected propagation path in the complex transmission-coefficient matrix used for electromagnetic-field focusing by an antenna array. Electrodynamic and mathematical modeling was performed for a system comprising a transmitter, a receiving point, and an ideal specular reflector represented as a scattering point. The reflected-path contribution was incorporated directly into the transmission coefficients used to calculate the complex excitations of antenna-array radiators. The approach was evaluated using a three-element antenna array by comparing field focusing without a reflector, with an uncompensated reflector, and with reflector-aware excitation parameters. Changes in reflector position altered phase difference between direct and reflected waves, resulting in constructive or destructive interference at the receiving point. Taking the reflected path into account modified the calculated amplitudes and initial phases of the array excitations and partially compensated for reflector-induced field distortion. In the considered case, the normalized field amplitude after compensation differed by approximately 3% from the no-reflector case and increased by about 49% relative to the uncompensated case. The mathematical and electrodynamic results were in qualitative agreement. These findings demonstrate that including a reflected path in a transmission-coefficient matrix can improve near-field focusing accuracy in the presence of a reflector.

Terahertz Time-Domain Spectroscopy (THz-TDS) enables noninvasive skin hydration monitoring, but existing techniques rely on one-dimensional fitting, which cannot resolve lateral heterogeneity. This paper presents a physics-informed twodimensional finite-difference time-domain (2D-FDTD) forward modeling framework coupled with an adjoint-based optimization algorithm to reconstruct spatially resolved permittivity maps of hydrated skin. The forward model employs a Dual-Debye dielectric dispersion formulation with relaxation times τ₁ = 8.3 ps (free water) and τ₂ = 0.3 ps (bound water), capturing the frequency-dependent response in the range ε_r = 6.34-8.71 corresponding to physiological hydration fractions φ = 0.20-0.70. An adjointbased gradient descent algorithm with total variation (TV) regularization recovers the 2D permittivity distribution from reflected THz-TDS signals, achieving 0.03% root-mean-square (RMS) reconstruction error at the 30th iteration. Frequencydomain decomposition of the absorption coefficient is validated against synthetic hydrogel phantom data, confirming that bound water contributes 82 ± 4% of total absorption at 0.5 THz. The framework distinguishes healthy skin, psoriasis, and chronic wound edema with p < 10^-17 statistical significance. To the best of the authors' knowledge, this constitutes an early demonstration of a 2D physics-informed inverse imaging framework demonstrated on both depth-resolved gradient phantoms and laterally heterogeneous pore phantoms of the 6-9 permittivity band with sub-percent accuracy in the THz biomedical domain; experimental validation of in-vivo tissue remains a critical next step.

This study presents a novel three-degree-of-freedom (3-DOF) axial-enhanced hybrid magnetic bearing (AEHMB), which introduces an axial auxiliary electric excitation to break the inherent proportional constraint between radial and axial maximum suspension forces in conventional 3-DOF HMBs. This configuration enables independent design of radial and axial bearing performance, satisfying diverse application demands of transmission systems while effectively enhancing the axial load-bearing capability. This study first elaborates the structural topology of the proposed 3-DOF AEHMB, along with its primary bias magnetic circuit and axial compensation bias magnetic circuit. Mathematical models for the axial and radial suspension forces are subsequently established based on equivalent magnetic circuit analysis. Based on the maximum design requirements of the radial and axial suspension forces, key structural parameters were optimized and determined. Finally, the finite element method was adopted to validate the rationality of the magnetic circuit configuration and suspension working mechanism through systematic calculations of the air-gap bias flux density, control flux density, force-current characteristics, and force-displacement characteristics. Simulation results verified the feasibility of the proposed structure, accuracy of the magnetic circuit design method and mathematical models, and reliability of the overall design scheme for the 3-DOF AEHMB.

The rapid evolution of wireless communication networks is driving the rapid development of communication systems toward greater integration, wider bandwidth, and higher efficiency. To satisfy the design requirements of broadband, high-efficiency power amplifiers, this study proposes an implementation scheme that integrates filtering, matching, and harmonic-control technologies. In this innovative method, high-order matching networks are converted into low-order passive networks that integrate the parasitic output capacitance and package inductance of transistors, thereby achieving a more compact area. In addition, a dual-stub microstrip line cascaded topology is introduced to suppress the second harmonic. The test results demonstrate that the power amplifier achieves a gain of more than 16.5 dB in the 100-900 MHz frequency band, maintains a drain efficiency of over 55%, with a peak drain efficiency of up to 75% under saturated operation, delivers a saturated output power of 40.5-42 dBm, achieves a second harmonic suppression of up to 61 dBc, and has a relative bandwidth of 160%. This design realizes high-efficiency power transmission performance and demonstrates excellent potential for engineering applications in communication systems.

To suppress multiple narrowband interferences in ultra-wideband (UWB) communication systems while maintaining a compact size and wide passband response, a quad-notch ultra-wideband filter based on a bowtie T-shaped resonator is proposed and investigated. The proposed filter employs an improved stepped-impedance resonator (SIR) with multi-branch loading and an annular defected ground structure (DGS) to enhance bandwidth extension, passband flatness, and frequency selectivity. A novel quasi-closed-loop C-shaped resonator with an additional coupling path is introduced to generate an extra controllable resonant mode, providing enhanced flexibility for independent notch-band tuning. Combined with an asymmetric open-circuited branch, four independently adjustable notch bands are achieved within the UWB passband. The resonance characteristics of the proposed multimode structure are analyzed using even-odd mode theory, providing an effective approach for mode-frequency control. Experimental results demonstrate that the fabricated filter achieves a wide passband from 2.71 to 11.5 GHz with a fractional bandwidth of 124%, along with four sharp rejection bands centered at 5.91, 6.75, 7.29, and 8.08 GHz. The maximum attenuation reaches 34.55 dB, while the filter maintains a compact size of 23 mm × 29.74 mm with excellent passband flatness and out-of-band suppression. The proposed quad-notch UWB filter provides an effective solution for interference-resistant wireless communication systems.

Visible Light Communication (VLC) combined with Non-Orthogonal Multiple Access (NOMA) is a promising technology for meeting the high-capacity demands of future 6G indoor networks. Most existing VLC-NOMA user pairing schemes rely solely on the direct-link channel gain for user ordering and ignore wall reflections that introduce spatially nonuniform interference, thereby degrading successive interference cancellation (SIC) performance. To overcome these limitations, a user ranking based on the user's effective signal-to-interference-plus-noise ratio (SINR) from both direct and indirect links is proposed, and users are paired into independent pairs with balanced SINR separation through a SINR-based user pairing framework. The proposed framework reduces interference accumulation by isolating users into independent NOMA pairs, thereby improving scalability and throughput. The results of the MATLAB simulation demonstrate that the proposed scheme achieves a throughput of 710 Mbps for eight users, which is 274% higher than the 190 Mbps achieved by conventional NOMA. The proposed framework achieves 320 Mbps under imperfect SIC conditions, whereas conventional NOMA achieves 74 Mbps, demonstrating the robustness of the proposed framework under practical receiver impairments.

To address the issues of weak disturbance-rejection capability and poor parameter robustness in traditional model predictive control, a deadbeat model predictive current-control strategy with an improved disturbance observer is proposed. First, an active disturbance rejec-tion controller is designed to replace the PI control, achieving both fast response and overshoot-free per-formance during speed tracking. Then, the influence of parameter disturbances on motor control performance in conventional model predictive control is analyzed, and a disturbance observer with adaptively adjustable gain is designed. The parameter mismatch disturbances can be compensated. Therefore, the current ripple can be significantly suppressed，and the robustness of the system parameters can be enhanced. Finally, the performance of the proposed method was demonstrated through simulations and experiments.

In conventional permanent magnet-assisted synchronous reluctance motors (PMaSynRMs), the peak current angles of permanent magnet (PM) and reluctance torques are theoretically separated by 45 electrical degrees, which prevents full superposition of the two torque components and limits torque density improvement. This paper proposes a novel asymmetric rotor topology based on the principle of magnetic flux linkage phase-shifting (MFS). The proposed topology reconfigures the rotor magnetic circuit by shifting a bar-shaped PM to the junction center between two adjacent reluctance segments and removing the PMs on one side of the U-shaped flux barriers (so that magnets are only placed on one side of the pole). This forces a controllable shift of the effective electromagnetic d-axis. A unified torque mathematical model incorporating the current angle β and the magnetic axis shift angle γ is established, revealing the regulation mechanism of flux linkage phase shift on the phase characteristics of torque components. Taking a 4 kW, 8-pole ferrite PMaSynRM as the research object, a multi-objective optimization is carried out using the Kriging surrogate model and the Non-dominated Sorting Genetic Algorithm III (NSGA-III). Finite element simulation results show that the effective d-axis of the optimized motor shifts by 45 electrical degrees, achieving nearly full peak alignment of PM torque and reluctance torque at the same current angle. With a 7.8% reduction in ferrite PM usage, the utilized PM torque increases from 13.88 N·m to 16.82 N·m (an increase of 21.2%); the total output torque rises from 38.67 N·m to 40.32 N·m (an increase of 4.27%); torque ripple decreases from 9.15% to 6.09%; and efficiency remains stable. Furthermore, under a direct-axis demagnetization condition with twice the rated current, the proposed asymmetric topology exhibits no local demagnetization, demonstrating better demagnetization resistance than the conventional symmetric motor. This study provides an effective approach for high torque density design of low-cost ferrite electric drive systems.

To cut rare-earth consumption and suppress cogging torque of conventional symmetrical pole permanent magnet generators (PMGs), this paper presents a low-rare-earth composite asymmetric pole topology with hybrid NdFeB-ferrite magnets. The magnetic field modulation of permanent magnet magnetomotive force (MMF) is analyzed, and an energy-method cogging torque formula is derived to elaborate the flux-improving and torque-reducing mechanism of asymmetric poles. Equivalent magnetic circuit and finite element models are built, followed by stratified sensitivity analysis of structural parameters. Taking high induced electromotive force (EMF), low EMF THD, and small cogging torque as targets, magnet arc angle is optimized via an evolutionary algorithm coupled with TOPSIS; magnet width and thickness are further optimized for optimal cost-performance. After optimization, EMF fundamental amplitude rises; EMF THD and cogging torque drop; and NdFeB usage falls by 8.56%. Prototype tests verify the simulation accuracy. The hybrid magnet scheme saves rare-earth materials and enhances overall generator performance.

To address the challenge of limited bandwidth in magnetic induction communication, this study proposes a magnetic induction antenna adopted a gradient-radius structure. The antenna adopts a discretized gradient-radius design, which effectively broadens the system bandwidth by increasing the antenna's resistance-to-inductance ratio. The study integrates theoretical analysis, simulation, and experimental testing to systematically investigate the effects of different taper ratio structures on resistance, inductance, and bandwidth. Experimental results demonstrated that the gradient-radius structure can significantly extend the bandwidth, and the extension effect became stronger as the taper ratio increased. Meanwhile, combined with simulation and experimental data, the attenuation effect of this structure on the near-zone magnetic field was evaluated, verifying that the bandwidth improvement came at the cost of coupling strength. Specifically, when the bandwidth was extended to nearly twice its original value, the received signal strength decreased by approximately 6.4 dBm. This study provides a simple and practical implementation approach for the broadband design of magnetic induction communication systems.

Electromagnetic wave propagation and scattering in materials with time-variant parameters is subject of an active field of research. The theory is usually restricted to transverse-electric or transverse-magnetic modes in one- or two-dimensional settings. Here we discuss the theory of three-dimensional, multi-component electromagnetic waves in a homogeneous, time-variant material. We present 3 × 3 causal and acausal Green's matrices and a 6 × 6 propagator matrix. We derive a number of fundamental properties such as conservation of momentum density for a piecewise continuous, time-variant material, symmetry properties of the propagator matrix, and a relation between the causal and acausal Green's matrices. These properties are used in derivation of a general wave-field representation (the counterpart of the Kirchhoff integral for a time-invariant material) and an expression for Green's function retrieval with space-correlations (the counterpart of Green's function retrieval with time-correlations in a time-invariant material).

Ghost surface polaritons (GSPs) in anisotropic materials exhibit an unusual bi-state nature with a complex-valued out-of-plane wavevector, providing unique opportunities for nanoscale light manipulation. However, the exploration and application of GSPs have been limited by the scarcity of natural crystals. Here, we revisit GSPs from the perspective of transformation optics. By introducing a shift parameter, we establish a mapping between material tensors and ghost modes, demonstrating the existence of GSPs at various transformed uniaxial interfaces. It is further shown that the wavefront can be modulated via shift parameters, enabling precise control of GSP propagation. Our study provides new insight into GSPs and establishes a versatile framework for their flexible manipulation.

This paper presents the design, simulation, fabrication, and comprehensive measurement of a compact dual-port multiple-input multiple-output (MIMO) microstrip patch antenna integrating a split-ring resonator (SRR) superstrate with a hybrid defected ground structure (DGS) for multiband C/X-band satellite uplink and radar applications. The antenna is implemented on an FR-4 substrate (ε_r = 4.4, tanδ = 0.02, h = 1.6 mm) with a compact footprint of 40 × 40 mm². A 10 × 8 array of SRR unit cells positioned at 7 mm air gap above the radiating patches serves as a periodic frequency-selective superstrate to enhance gain via Fabry-Perot cavity resonance and suppress surface waves. Hybrid H-shaped and dumbbell-shaped DGS slots etched on the ground plane provide high isolation between ports by disrupting ground current paths and introducing bandstop characteristics. The simulated antenna resonates at 7.20, 8.62, and 10.66 GHz with return loss below -10 dB and isolation better than -15 dB in the operating bands. The fabricated prototype was tested using a vector network analyzer, and the measured $S$-parameters show good agreement with the simulations, with small shifts due to fabrication tolerances, SMA soldering, FR-4 dielectric variation, and air-gap alignment. Radiation patterns and gain are reported from HFSS simulation, whereas S-parameters are experimentally validated.

To address high common-mode voltage (CMV) and neutral-point voltage (NPV) imbalance issues in practical neutral-point-clamped (NPC) three-level inverters, a logic virtual space vector pulse width modulation (LVSVPWM) strategy is proposed. Based on the conventional virtual space vector pulse width modulation (VSVPWM), the proposed method first eliminates vectors with large CMV and redivides small sectors to reduce sector switching, limiting the CMV to ±V_dc/6. Second, it uses a logical judgment for the initial variable duty-cycle distribution to reduce the number of switching actions. Then, it redistributes the duty cycles according to NPV balancing requirements to achieve NPV balance. Finally, experiments validate the accuracy and effectiveness of the proposed strategy.

A compact wideband antenna suitable for RF energy harvesting applications is presented in this paper. The proposed antenna consists of a slotted rectangular radiating patch excited by a coplanar waveguide (CPW) feed and implemented on an FR4 substrate with overall dimensions of 40 × 40 × 1.6 mm³. A wide impedance bandwidth is achieved through the combined use of a hybrid hexagonal defective ground structure (DGS) and multi-slot loading of the radiating patch, where the patch is embedded within the slotted ground plane to achieve size reduction and enhanced impedance matching. The antenna exhibits a measured impedance bandwidth of 3.61 GHz (|S₁₁| ≤ -10 dB) ranging from 2.18 GHz to 5.79 GHz, covering the Wi-Fi and sub-6 GHz 5G frequency bands. Stable radiation characteristics are observed across the operating band, with a figure-of-eight radiation pattern, a peak gain of 3.67 dB at 3 GHz, and a minimum gain of 2.73 dB at 5 GHz. The antenna exhibits radiation efficiency greater than 95% throughout the operating band, with a maximum value approaching 98%. The antenna is designed and optimized using ANSYS HFSS and experimentally validated through Vector Network Analyzer and anechoic chamber measurements, showing good agreement between simulated and measured results. Owing to its wide bandwidth, compact size, and stable radiation performance, the proposed antenna is well-suited for wideband RF energy harvesting, with future integration into a rectenna system.

This manuscript investigates the design and implementation of a Substrate Integrated Waveguide (SIW) bandpass filter using an inset feed as a defect and a rectangular slot defect in the ground plane. In this research, the feed line is also used as a defect by replicating the inset feed line on the ground. The inset-feed structure on both conducting layers improves filter performance and reduces size. To further enhance the filter's passband characteristics, a simple rectangular slot is introduced in the ground plane. This Defected Ground Structure (DGS) modifies the current distribution and improves the impedance bandwidth. The proposed filter operating at a center frequency of 10.5 GHz with a bandwidth of 500 MHz and offering a return loss better than 30 dB is designed, fabricated, and experimentally validated. The measured results show good agreement with simulations. The filter exhibits good performance, featuring appropriateness for single-channel satellite communication applications.