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.

To reduce the cogging torque of a 6-pole 36-slot permanent magnet synchronous motor, a method using a nonuniform air gap is proposed. By establishing the sinusoidal distribution subdomain model of the rotor with a nonuniform air gap and combining the energy method with Fourier decomposition, the analytical expressions of cogging torque under the conditions of uniform and nonuniform air gaps are derived. Electromagnetic and thermal performance simulations of uniform and nonuniform air gap motors were performed using ANSYS software. The influence of the nonuniform air gap on the motor's electromagnetic and thermal performance was analyzed by comparing simulation results. First, the finite element model of the motor was established in ANSYS Maxwell to analyze its electromagnetic performance under no-load and load conditions. The magnetic flux density distribution, no-load back EMF, output torque, cogging torque, core loss, copper loss, and eddy current loss of the permanent magnet were analyzed, and the rationality of using a nonuniform air gap was verified. The loss results obtained by the electromagnetic simulation were used as the heat source. It was imported into the steady-state thermal analysis module of ANSYS Workbench to build a three-dimensional temperature-field simulation model of the motor. Through a comparative analysis of electromagnetic performance and steady-state temperature rise results, it was confirmed that the design of the 6-pole 36-slot permanent magnet synchronous motor met the predetermined performance indicators and thermal safety requirements, and the feasibility of the nonuniform air-gap design scheme was verified.

To improve the dynamic performance and disturbance rejection of a Surface Permanent Magnet Synchronous Motor (SPMSM) speed control system, a speed regulation method based on a continuous adaptive fast terminal sliding mode is proposed in this study. First, a novel adaptive variable-gain reaching law (NVGRL) is introduced. By combining the variable gains of the system states with fuzzy adaptive inference rules, the boundary layer width was adjusted in real time to reduce the convergence time to the equilibrium point and suppress chattering. Second, a novel fast integral terminal sliding mode surface (NFITSMS) is designed to improve the global convergence rate. To maintain an ideal speed even under external disturbances and torque surges, a novel finite-time-based super-twisting sliding mode disturbance observer (NSTDO) is designed. The control strategy proposed in this study employs Lyapunov stability theory to provide a closed-loop stability analysis within a fixed time. Finally, the experimental results confirm that the proposed method enhances the speed response, tracking accuracy, and disturbance rejection capability of the SPMSM control system.

This study presents millimeter-wave propagation measurements at 60 GHz conducted in a reverberation chamber to emulate realistic multipath-rich indoor environments. Both line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios are investigated using commercial off-the-shelf devices. The impact of stirring conditions and lossy environments is evaluated through key performance indicators, including Received Signal Strength Indicator (RSSI), Signal-to-Noise Ratio (SNR), Modulation and Coding Scheme (MCS), and throughput. Results show that mechanical stirring speed and the placement of absorbing materials significantly affect channel characteristics and system performance. In NLOS conditions, multipath propagation dominates, where dynamic beamforming demonstrates improved robustness. In contrast, LOS scenarios are highly sensitive to blockage, leading to notable performance degradation. Overall, the findings confirm that the reverberation chamber is an effective platform for over-the-air testing and characterization of 60 GHz wireless systems, offering valuable insights into system behavior under complex indoor propagation conditions relevant to future 5G and 6G deployments.

For the time-harmonic solution of Maxwell's equations, absorbing boundary conditions (ABCs) are widely used to approximate the Silver-Muller radiation condition at infinity on the boundary Γ terminating the computational domain. An original high-order ABC (HOABC) is proposed that links the tangential components of the electric and magnetic fields on Γ via surface differential operators multiplied by coefficients. These coefficients are determined so as to minimize the reflection of a propagative or evanescent wave incident on a planar or spherical Γ - while taking its radius into account - and guarantee a well-posed Maxwell's problem. Numerical results are presented on a plane and coated spheres that demonstrate its efficiency even when evanescent waves are present. If it is implemented in a finite element formulation its numerical complexity is expected to be low.

An electric drive system is a core component of electric vehicles, and its electromagnetic compatibility (EMC) is critical to vehicle safety. Addressing the difficulty of locating electromagnetic interference (EMI) coupling paths via testing alone, this paper presents a simulation study of conducted EMI in motor drive systems. Parasitic parameters of key components are extracted through impedance testing and 3D electromagnetic simulation. Based on transmission line theory and impedance fitting, high-frequency equivalent models of each unit are developed and integrated into a system-level EMI simulation model. Validation shows that the model predicts conducted interference below 30 MHz accurately, with errors within 6 dB below 1 MHz and less than 10 dB in the 1 MHz-30 MHz band. This model enables rapid EMC troubleshooting and provides reliable simulation support for the forward design of electric vehicle drive systems.

This paper presents a compact wideband eight-antenna array for sub-7 GHz 5G smartphone applications with a low-profile metal frame. By employing a multi-near-circular open-slot configuration integrated into the system ground and metal frame, the proposed design achieves wideband operation from 3.3 to 7.125 GHz, covering 5G NR bands n77/n78/n79 and NR-U bands n46/n96, without requiring additional decoupling structures. The antenna element occupies a compact volume of 8 × 3.5 × 4 mm³, enabling a low-profile implementation compatible with modern smartphone form factors. Measured results demonstrate a 6-dB impedance bandwidth, fully covering the target bands, with inter-element isolation higher than 10 dB and an envelope correlation coefficient (ECC) below 0.1. The measured total efficiency ranges from 40% to 86% across the operating band. Furthermore, the antenna array maintains stable performance under practical conditions, including hand and battery effects. The proposed design offers a simple and effective solution for achieving wideband, low-profile, and low-correlation MIMO performance in metal-frame smartphones.

Oil-immersed transformer bushings are critical power system components, whose internal defects can cause electric-field distortion and insulation breakdown. In this study, a three-dimensional finite element model of a transformer bushing is established via COMSOL Multiphysics using actual structural parameters. The baseline electric field and voltage distributions under defect-free conditions are analyzed, and systematic simulations and quantitative evaluations are conducted to explore electric-field distortion and corresponding insulation risks under four typical defects: capacitor core metal particle contamination, insulating oil gas bubbles, capacitor final screen grounding loss, and capacitor screen damage. The results demonstrate that all defects break the inherent electric-field uniformity and induce local field intensification. Metal particle contamination and capacitor screen damage pose the greatest risks of distortion and insulation breakdown, while grounding loss causes the most extensive overall electric-field disturbance. This study clarifies the defect-induced electric-field response mechanisms, providing theoretical support for fault early identification, risk warning, and optimized operation of oil-immersed transformer bushings.

RGB LED luminaires often exhibit nonlinear luminous-flux variation and chromaticity-coordinate drift during high-to-low brightness switching, reducing color stability at low brightness levels. To address this problem, this paper proposes a color-stability-oriented RGB LED color-mixing optimization algorithm. Nonlinear fitting is first used to compensate for temperature-induced luminous-flux variation and chromaticity shift. Then, a spectral reconstruction method based on Bounded-Variable Least Squares (BVLS)-constrained parameter mapping is developed to predict RGB-channel spectra and correct single-channel chromaticity coordinates under different duty cycles. Furthermore, a two-dimensional affine chromaticity-point mapping method is introduced to adaptively correct the target chromaticity point according to the variation of RGB primary chromaticity coordinates at different brightness levels. The proposed method is evaluated using chromaticity tolerance, CAM16, and CAM16-UCS. Experimental results show that the chromaticity tolerance can be maintained within four SDCM steps in the 1%-10% low-brightness range, while color appearance differences are reduced under different brightness conditions. These results demonstrate that the proposed method improves the color stability and visual consistency of RGB LED luminaires.

This paper presents a wideband circularly polarized (CP) antenna featuring a significantly enhanced front-to-back ratio (FBR). The proposed design employs a composite structure that integrates a dipole with a loop resonator and is fabricated using a multilayer architecture. The top layer is a dielectric substrate loaded with a cyclic zigzag patch. The middle layer contains an L-shaped radiating patch with etched rectangular grooves, and the bottom layer comprises a metal ground plane and surrounding vertically tilted-slot fences. Circular polarization is achieved by exciting orthogonal degenerate modes via strategic rectangular-groove perturbations that work in concert with the loop resonator's inherent asymmetric current path. The tilted-slot fences, in conjunction with the zigzag patch layer, function collectively to suppress backward radiation and improve the FBR. Measured results demonstrate that the antenna achieves a 3 dB axial ratio (AR) bandwidth of 54% from 2.45 to 4.3 GHz, a stable FBR of more than 27.5 dB with 2.5 dB variation, and a peak gain of 9.3 dBic. This design offers a high-performance, planar antenna solution well-suited for satellite communication and radar systems.

A partition optimization strategy (POS) based on the differential evolution (DE) algorithm is proposed for low sidelobe synthesis of sparse linear arrays (SLAs). The approach starts by dividing the array aperture into a centrally symmetric full zone and several sparse subzones, where elements are fully arranged in the former zone and sparsely populated in other zones. Then, by introducing random parameters, including a full-zone adjustment factor, sparse subzone reduction factors, and sparse subzone filling factors, both the size of the full zone and the array aperture, as well as the total number of elements, could be dynamically adjusted. Next, for each sparse subzone, two random parameters are introduced to generate a nonuniform vector based on the 1D Rastrigin function so that the elements within the current zone are non-uniformly arranged by using the components of the vector. Finally, all the aforementioned parameters were optimized by the DE algorithm to find the SLA with reduced sidelobe level. Numerical simulations demonstrate that this method can reduce the SLAs' sidelobe level by 0.37~4.34 dB along with the decrement of the number of elements by about 0.7%-15.0% compared to the published reports.

This study proposes a high-performance miniaturized wideband circularly polarized (CP) metasurface (MTS) antenna for WLAN and 5 GHz wireless communication systems. The design innovatively utilizes a hybrid embedded structure, where regular octagonal patches are incorporated into the gaps of modified X-shaped primary radiating elements to increase edge capacitance and lower resonant frequency, thereby achieving antenna miniaturization. To effectively excite the orthogonal degenerate modes required for CP radiation, a characteristic mode analysis (CMA) was employed to guide the design of the feed network. A feeding structure consisting of a hook-shaped microstrip line and a symmetrical stepped cross-slot is designed to achieve CP excitation via a 90˚ phase delay introduced by path length differences. Measured results demonstrate that the antenna achieves a -10 dB impedance bandwidth of 34.2% (4.38-6.19 GHz) and a 3 dB axial ratio (AR) bandwidth of 23.9% (4.68-5.95 GHz). Regarding radiation characteristics, the radiation efficiency remained stable above 75%, and the peak realized gain reached 5.26 dBic. The experimental results verified that the proposed design achieved stable CP and radiation performance within a miniaturized footprint.

Manually optimizing the performance of a circularly polarized (CP) patch antenna typically requires numerous iterative adjustments and can be highly time-consuming. To address this challenge, artificial intelligence techniques can be employed to efficiently explore the parameter and solution spaces. In this work, a well-known genetic algorithm (GA) is utilized to design and optimize a novel CP antenna. Specifically, a multi-objective genetic algorithm (MOGA) is adopted as a powerful optimization tool, providing effective exploration of the parameter space to achieve the desired operating bandwidth and CP characteristics. The optimized CP antenna features a compact size of 20 mm × 20 mm × 1.6 mm. The design process is carried out using HFSS and MATLAB, and the results are further validated through simulations in CST and ADS (equivalent circuit modeling). The antenna is fabricated by etching the patch and ground plane on the top and bottom sides of an FR-4 epoxy substrate (ε_r = 4.4), respectively. The simulated reflection coefficient bandwidth (RCBW) and axial ratio bandwidth (ARBW) are significantly enhanced, achieving fractional bandwidths of 25.78% and 16.68%, respectively, while the measured RCBW reaches 24.5%. Furthermore, the proposed antenna provides a peak gain of 5.9 dBi and a radiation efficiency exceeding 67%. The application of MOGA effectively enhances both the operating bandwidth and CP performance, making the proposed antenna a strong candidate for various Ku-band applications.

To improve the accuracy and stability of parameter identification for permanent magnet synchronous motor (PMSM) drives, which are affected by the dead-time nonlinearity of the voltage source inverter (VSI), this study presents an enhanced Blackwinged Kite Algorithm (BKA) integrated with 5th- and 7th-order harmonic voltage compensation. Initially, harmonic compensation targeting the 5th and 7th voltage components is introduced to suppress the detrimental influence of the VSI dead time on both identification precision and operational stability. Subsequently, a Good Point Set-based initialization approach is adopted to distribute the initial population more evenly across the search domain, which contributes to improved population diversity and algorithmic consistency. In addition, the Thinking Innovation Strategy (TIS) is embedded into the exploration stage of the black-winged kite algorithm to strengthen its global optimization capability. Experimental investigations across different operating scenarios demonstrated that the proposed method achieved superior effectiveness and improved performance.

Conventional fiber-optic measurement systems for pulsed electromagnetic fields are limited by power-supply instability due to the temperature sensitivity of photocells. To address this issue, we developed a highly reliable broadband fiber-optic transmission system featuring a hybrid power supply. In our design, a lithium battery serves as the primary power source for the optical transmitter, while a compact photocell provides short-term supplemental power and simultaneously recharges the battery. An additional shunt resistor (5-50 Ω) is added to avoid damping oscillations. Results: The system achieves a -3 dB bandwidth from 5 Hz to 122 MHz. The optical transmitter volume is reduced to one-fifth of a previous design. Ten repeated electric-field measurements show relative errors below 3%. Conclusion: The proposed system offers stable operation, low power consumption, wide dynamic range, and strong anti-interference capability, making it well-suited for harsh electromagnetic environments.

To address the issues of a narrow speed control range and permanent magnet demagnetization in interior permanent magnet synchronous motors (IPMSMs), this paper proposes a tangentially magnetized reverse-salient permanent magnet synchronous motor structure. The reverse-salient permanent magnet synchronous motor features a wide constant power speed control range, strong overload capacity, and resistance to permanent magnet demagnetization. This design resolves the issues of a narrow speed control range and permanent magnet demagnetization by segmenting the permanent magnets to incorporate magnetic bridges and adding magnetic barriers on the q axis. Through parametric analysis, the effects of parameters such as the permanent magnet thickness, the magnetic bridge length, and the magnetic barrier width on the motor's electromagnetic performance are determined, leading to a more significant structural optimization. Finally, finite element simulation is employed to analyze the motor's electromagnetic and mechanical performance. The constant power speed of the tangentially magnetized reverse-salient permanent magnet synchronous motor reaches 3.6 times the rated speed. The theoretical analysis results are consistent with the simulated ones, verifying the effectiveness and feasibility of the new motor's flux-weakening design, which is particularly suitable for high-speed operating conditions.

A dual-core photonic crystal fiber surface plasmon resonance biosensor employing a hybrid Au-TiO₂ coating is presented for biosensing. The study is formulated as an extension of our earlier Au-only dual-core PCF-SPR design, with the main modification being the introduction of an ultra-thin TiO₂ dielectric overlayer to improve modal coupling and sensing performance. The numerical analysis tracks the resonance behavior for analyte refractive indices from 1.28 to 1.44 and shows a clear redshift of the resonance wavelength as the analyte index increases. The resonance wavelength moves from 400 nm to 650 nm, corresponding to an overall wavelength shift of 250 nm across the investigated range. The confinement-loss spectra also show stronger coupling at higher refractive indices, with the largest loss peaks observed near the upper end of the sensing range. In addition, the amplitude sensitivity reaches a maximum absolute value of about 842 RIU^-1, confirming a strong intensity response around resonance. Compared with the previous Au-only configuration, the hybrid structure provides a measurable improvement in amplitude response and extends the usable lower-end refractive-index range. These results indicate that the proposed hybrid-coated dual-core PCF structure is a promising platform for high-contrast refractive-index detection.

A miniaturized multi-band MIMO antenna for Sub-6 GHz and 5G mmWave is proposed. The antenna is composed of a C-shaped radiating element and coupled ground branches. Tri-band coverage is achieved (4.37-5.88 GHz, 23.5-32.89 GHz, and 36.8-40.1 GHz) through the optimization of the dimensions of the C-shaped antenna and the incorporation of a cross-shaped structure. The low-frequency band fully covers the n79 (4.4-5 GHz) band, as well as the Wi-Fi 5/6 (5.15-5.85 GHz) and 5 GHz ISM (5.725-5.875 GHz) bands. The mid-frequency band completely covers the 5G mmWave n257 (26.5-29.5 GHz), n258 (24.25-27.5 GHz), and n261 (27.5-28.35 GHz) bands, while the high-frequency band fully covers the n260 (37-40 GHz) band. Measured results show gains of approximately 0.95 dBi, 5.89 dBi, and 8.83 dBi in the low-, mid-, and high-frequency bands, respectively. Inter-element isolation is found to be better than -20 dB, and the envelope correlation coefficient (ECC) is < 0.003. The antenna is characterized by a compact size, simple structure, and multi-band coverage, making it suitable for cooperative communication between Sub-6 GHz and 5G mmWave bands.

A novel ceramic waveguide filter using coupled slots and two sets of cascade quadruple (CQ) coupling units is presented in this study. Owing to this CQ structure, there are two pairs of transmission zeros at the edge of the passband to ensure that the filter has good selectivity. First, the effect of cavity dimensions on the resonant frequencies of the intrinsic modes was analyzed. Next, the impact of the coupling structure on the coupling bandwidth and the characteristics of the electric-field distribution was explored, followed by an examination of the relationship between the feeding structure and the quality factor (Qe). Finally, a prototype filter centered at 3.5 GHz with a bandwidth of 200 MHz was designed and fabricated. The insertion loss within the passband was less than 1.9 dB, and the return loss was greater than 20 dB. The out-of-band suppression exceeds 42 dB in the 3.3-3.36 GHz and 3.64-3.7 GHz, and even exceeds 70 dB in the 3.2-3.3 GHz and 3.7-3.8 GHz.