This paper describes the design methodology of a compact multiband microstrip patch antenna intended for next-generation wireless communication applications. The proposed antenna operates over seven distinct frequency bands: 1.25-1.32 GHz, 2.30-2.44 GHz, 2.50-2.75 GHz, 2.92-3.25 GHz, 3.40-3.65 GHz, 3.70-4.23 GHz, and 4.70-6.0 GHz. These operating bands support a wide range of wireless services, including LTE, 5G communications, Wi-MAX, ISM applications, radar systems, and broadband wireless communications. Multiband performance is achieved through the incorporation of three strategically placed slits in the radiating patch along with a square split-ring resonator (SSRR). By adjusting the dimensions of the slits and the position of the SSRR, the operating frequency bands can be effectively tuned. The proposed antenna occupies a compact footprint of 40 × 40 mm² and consists of a radiating patch, a partial ground plane, and an SSRR structure. Simulation results demonstrate resonant frequencies at 1.3, 2.38, 2.66, 3.0, 3.5, 4.2, 4.9, and 5.7 GHz. Owing to its compact size, multiband capability, and simple structure, the proposed antenna offers advantages in terms of reduced cost, lower system complexity, and miniaturization, making it suitable for modern wireless communication systems.

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.

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.

In this study, a dual-band active antenna integrated with an IoT healthcare monitoring system for measuring body temperature, heart rate, and SpO₂ is presented. A MAX30100 sensor and NodeMCU ESP32-CAM enable data acquisition and cloud-based monitoring through Ubidots. The antenna, fabricated on a Rogers Duroid RO3003^TM substrate (37 × 42 × 1.52 mm³), operates at 2.4 GHz and 5.8 GHz using an inverted U-shaped slot and a PIN diode for frequency reconfiguration. Received Signal Strength Indicator (RSSI) measurements showed improved signal strength from -35 to -40 dBm compared to -40 to -45 dBm for the on-board antenna. Experimental evaluation on three volunteers aged 21, 36, and 55 years demonstrated reliable physiological monitoring, with heart rate values of 84-90 BPM and temperature readings of 30-36°C. The results validate the suitability of the proposed antenna for reliable IoT-based healthcare applications.

In this paper, a compact ultra-wideband (UWB) bandpass filter (BPF) with triple-notch bands (TNBs) is proposed and demonstrated. We present a cross-shaped anti-shorted coupled-line structure employing a single coupled multi-mode resonator (MMR), whose resonant characteristics and intrinsic transmission zeros are investigated by employing the even-odd mode analysis method. In addition, the three notch bands are generated from the resonator's intrinsic transmission zeros without requiring any additional notch circuits. At the same time, their center frequencies can be quasi-independently controlled by properly adjusting the microstrip electrical lengths. For demonstration, the proposed filter is designed, fabricated, and measured. Simulated and measured results are in good agreement. The measured results agree well with theoretical predictions, which exhibit superior performance, such as triple-notch bands, high skirt selectivity, an ultra-wide passband from 2.8 to 12.5 GHz with a fractional bandwidth of 138%, a compact size of only 7.7 mm × 9.2 mm, and effective notched-band suppression levels.

To address the challenges of coordinating local reactive power compensation with cross-station harmonic interaction suppression in hybrid multi-infeed HVDC (HMIDC) systems, this study proposes an optimal AC filter configuration method based on sensitivity analysis. A harmonic impedance equivalent model was established for a hybrid three-infeed HVDC system, and a comprehensive harmonic interaction index was constructed based on harmonic current interaction influence coefficients. Normalized sensitivity analysis was then performed on the AC filter impedance, receiving-end AC system impedance, and tie-line impedance at the 11th and 13th harmonics. The results indicate that the AC filter impedance serves as the dominant adjustable factor. On this basis, a discrete optimization model was developed, with the number of DT11/24 and DT13/36 double-tuned filter groups in service as decision variables. In addition, this model considers equipment limits, minimum filtering requirements, reactive power compensation, and harmonic voltage constraints. Case study results show that the optimized configuration reduces the overall harmonic coupling among HVDC infeed systems; in particular, the interaction strength from the second conventional HVDC link to the modular multilevel converter-based high-voltage direct current (MMC-HVDC) link at the 13th harmonic decreases by approximately 32%. The proposed method provides a practical reference for coordinated AC filter switching in HMIDC.

This study introduces a compact, low-profile ultra-wideband (UWB) wearable antenna designed for wireless body area network (WBAN) applications. The antenna incorporates a rectangular patch on a flexible jeans substrate, incorporating one patch slot, four identical edge slots, and a defected ground structure (DGS) with a compact dimensions of 23 mm × 30 mm × 1.5 mm. These slots and DGS enable the UWB operation with an excellent bandwidth while maintaining a good balance among the key performance parameters such as efficiency, gain, and SAR, which is the main contribution of this study. The antenna performance was analyzed using a four-layer human body phantom model that includes skin, fat, muscle, and bone layers. It operates across the frequency range of 2.82-11.25 GHz, covering the UWB range for wearable devices, and achieves a peak gain of 3.79 dBi, an average gain of 2.36 dBi, a peak efficiency of 63.36%, and an average efficiency of 52.88%. In addition, the obtained SAR values are 0.549 W/kg and 0.391 W/kg at 5 GHz, and 0.0727 W/kg and 1.97 W/kg at 9 GHz for 1 g and 10 g tissue standards, respectively, complying with SAR regulatory standards. Moreover, bending analysis validated its stable performance under various angles and deformation conditions. The fabrication and on-body testing of the proposed antenna exhibited a bandwidth of 1.38-12 GHz, demonstrating compliance with simulations. Finally, a human body temperature monitoring prototype was developed, which validates its suitability for wearable WBAN applications.