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.

High-gain reconfigurable antennas have become a crucial component of 5G systems. However, traditional Composite Right-Left-Hand Structure (CRLH) and Artificial Magnetic Conductor (AMC)-based designs suffer from high complexity, via losses, and complex biasing circuits. In this work, a CRLH transmission line integrated with a Hilbert Electromagnetic Band Gap (EBG) structure and a zero-phase AMC reflector is proposed for sub-6 GHz band. The proposed design integrates CRLH minimization, AMC gain enhancement, and Light-Dependent Resistor (LDR) bias-free reconfiguration within a unified low-complex framework. The design consists of 17-unit cells of a CRLH coupled to an EBG of Hilbert inclusions. An AMC reflector with zero phase shift is designed in the interested band to reduce back lobes and increase gain in forward direction. A maximum gain of 16 dBi was achieved at 5.5 GHz, and an increase of 4 dBi was achieved with the introduction of the AMC. An optical switch of LDR controls antenna performance, where different scenarios are investigated to achieve reconfiguration and beam scanning. The antenna gain is highly affected by changing the LDR switching status; for example, at 5 GHz, the antenna gain varies between 9 dBi and 11 dBi. At 5.5 GHz, the gain varies between 18 dBi and 20 dBi. In addition, the antenna achieved a scan of ∓5° with a consistent gain at 5 GHz by changing the LDR states. Therefore, the proposed antenna is an excellent candidate for direct amplitude modulation. Finally, the simulated results were validated through experimental measurements.

This paper presents a high-performance energy-selective structure (ESS) design methodology based on a stacked slotline. By leveraging the unique characteristics of three-dimensional stacked structures, the method efficiently converts spatial waves into guided waves in slotline transmission lines, which can be tailored via lumped-circuit design to achieve precise energy-selective functionality. The proposed design approach systematically extends previous work by providing a clear theoretical foundation for decoupling and independently optimizing multiple ESS performance indicators. This allows the design of structures with flexibly selectable frequency bands and high shielding efficiency. Two prototypes were fabricated to validate the method. Prototype I targets bandwidth expansion, achieving an operational range from 2.2 to 8.2 GHz (115.4% relative bandwidth), with less than 1 dB insertion loss and over 10 dB shielding effectiveness across the band. Prototype II emphasizes shielding performance, reaching a shielding efficiency greater than 33 dB between 3.9 and 6.3 GHz, with a maximum of 40.3 dB. Both prototypes were fabricated and validated through experimental measurements, showing agreement with the simulation results. The performance of the two designed structures far exceeds other existing ESSs in terms of broadband or high shielding efficiency, indicating that the comprehensive design method has great potential to significantly improve the design of targeted technical specifications.

Malignant breast tumors differ greatly from healthy tissue in their electrical properties. The specific absorption rate (SAR), which utilizes dielectric properties, including conductivity and permittivity, is a crucial metric for identifying malignant tissue. The use of narrow-band radar technology has shown promise in this regard. In this study, a mono-static, narrow-band, high-directivity printed patch antenna was designed and fabricated on a Rogers RO4350B substrate (ε_r = 3.48, loss tangent = 0.0037) with dimensions of 70 × 55 × 1.52 mm³ and a 50 Ω feed line, operating at 2 GHz to ensure an optimal balance between penetration depth and spatial resolution. A three-dimensional breast phantom (radius 50 mm) was modeled in CST Microwave Studio to evaluate the SAR distribution under microwave exposure. The results consistently show elevated SAR values in malignant regions, with a direct correlation with tumor size, enabling accurate tumor localization based on the coordinates of the maximum SAR. Crucially, the maximum SAR values (4.3708 W/kg for 1-g and 2.4388 W/kg for 10-g tissue) remain within the IEEE controlled-environment safety limits. Powered by the proposed antenna, this SAR-based approach offers a safe, non-ionizing, and potentially effective technique for detecting small or deeply located breast tumors, confirming that diagnostic capability is achieved without any compromise to patient safety.

This paper presents the design, fabrication, and testing of a compact multiband microstrip patch antenna built on a low-cost FR-4 substrate. The antenna combines a meandered radiating line, a defected ground structure (DGS), and two types of metamaterial resonators - a Square Ring Resonator (SRR) and a Circular Complementary Split Ring Resonator (CCSRR), to achieve multiple operating bands in a small footprint. Full wave simulations in CST Studio Suite predict five resonant bands with reflection coefficient S₁₁ below -10 dB over 2.420-8.216 GHz, with a minimum S₁₁ of -22.24 dB at 3.452 GHz and an overall fractional bandwidth of 108.89 percent. To verify the design, a prototype was fabricated and characterised using a calibrated VNA (Vector Network Analyser). Measurements confirm five resonant bands at 1.871 GHz (S₁₁ = -13.81 dB, 182 MHz bandwidth), 2.573 GHz (-10.10 dB, 52 MHz), 3.704 GHz (-10.27 dB, 65 MHz), 5.095 GHz (-12.11 dB, 676 MHz), and 9.957 GHz (-11.14 dB, 182 MHz). Simulated analysis also indicates stable directivity with a peak realized gain of approximately 2.12 dB at higher operating bands. To accelerate design evaluation, an Artificial Neural Network (ANN) surrogate model was trained on the measured S₁₁ data. The ANN attains a root mean square error of 1.38 dB and a coefficient of determination R² = 0.79, providing near-instantaneous S₁₁ predictions with an approximate 96,500× speedup compared to full-wave electromagnetic simulations. The key contribution of this work is the coordinated use of a meander line for miniaturization, a DGS for bandwidth enhancement, and dual metamaterial loading to realize five distinct operating bands on a single, inexpensive FR-4 board. The proposed antennas operating bands collectively support LTE Band 3, 5G New Radio (NR) sub-6 GHz, IEEE 802.11a/n/acWLAN, and X-band IoT applications.