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 address output current over-limit issues, power oscillations, and degraded transient stability in virtual synchronous generators (VSGs) under asymmetric faults, this paper proposes a variable-weight virtual-impedance-based current balancing control strategy for quasi-Z-source inverter-based VSG (qZSI-VSG) systems. First, a detailed mathematical model of the qZSI-VSG is established to analyze the influence of key parameters on the system's dynamic behavior. By leveraging the VSG operating characteristics in the dq reference frame, a negative-sequence current reference generation method is subsequently developed to effectively suppress negative-sequence components under various unbalanced grid conditions. In addition, a PI controller is introduced to regulate active and reactive power deviations, enabling online calculation of adaptive weighting factors for real-time adjustment of the virtual impedance. This mechanism improves both current balancing performance and transient response. Experimental results verify that the proposed strategy can significantly reduce negative-sequence currents and power oscillations, thereby enhancing the transient stability of the system during asymmetric faults and demonstrating its feasibility and effectiveness.

To address the inherent significant average torque degradation in conventional Axial Flux Permanent Magnet (AFPM) machines when the pole-shift method is employed for cogging torque suppression, this paper proposes a novel Elliptical-Cut Rotating Compensated Halbach Pole Axial Flux Permanent Magnet (EC-RCHP AFPM) machine. The proposed machine suppresses cogging torque via elliptically cut rotating poles and compensates for the induced torque loss by introducing dedicated compensating Halbach auxiliary poles. First, the rotor topology of the proposed machine is presented, and an equivalent surface current model is established to elucidate its operating mechanism. Second, sensitivity analysis and response surface methodology are adopted to investigate the correlation between design parameters and performance responses, and the optimal parameter combination is obtained under given constraints. Finally, the electromagnetic characteristics of the proposed machine are comprehensively analyzed through three-dimensional finite element analysis (3D-FEA). The results demonstrate that compared with the conventional machine, the EC-RCHP AFPM machine reduces cogging torque by 54.9%, increases average output torque by 1.8%, and lowers torque ripple to 6.12%, effectively resolving the fundamental trade-off between cogging torque suppression and torque output retention.

CubeSats deployed into Low-Earth Orbit (LEO) are continuously subjected to cyclic thermal loads and power-system degradation. Replicating these stresses through traditional space qualification is resource-intensive, placing it beyond the reach of most academic teams. Stratospheric High-Altitude Balloon (HAB) platforms offer a cost-effective pre-qualification pathway; however, no previous work has provided a rigorous, analytical method for mapping the stress accumulated during a balloon flight to an equivalent fraction of LEO stress. This gap prevents defensible claims of environmental fidelity. This paper introduces the High Altitude to Low Earth Orbit Correlation Index - Thermal and Power (HLCI-TP), a physics-based composite metric comprising three independently computed sub-indices: thermal fatigue (Coffin-Manson model), electrochemical battery degradation (Arrhenius model), and Ultraviolet (UV) fluence (Beer-Lambert model). Each sub-index quantifies the fraction of a 30-day LEO reference stress budget reproduced during a balloon mission, and the three are combined via a weighted linear sum. The UV sub-index is grounded in the Beer-Lambert electromagnetic attenuation law, directly connecting the framework to the quantification of solar ultraviolet irradiance - a component of the electromagnetic spectrum - at stratospheric altitudes. For a 24-hour reference mission at 35 km, the computed sub-index values are R_T ≈ 1.63 × 10^-4 (thermal), R_P ≈ 2.0 × 10^-6 (electrochemical), and R_U ≈ 9.92 × 10^-3 (UV), yielding a composite HLCI-TP score of 2.07 × 10^-3, which falls within the ``minimal screening'' band. This result is robust across three distinct weighting configurations (factor-of-three spread), a 10,000-sample Monte Carlo uncertainty analysis, and across the full practical range of mission durations (6-48 hours). The framework is further corroborated by applying Rainflow cycle counting to real GPS altitude data from the PMC-Turbo stratospheric balloon mission (35.7-39.5 km, 134.8 hours), which confirms the minimal-screening classification across all tested durations. These results quantify, for the first time through an analytical framework, that a 24-hour stratospheric flight reproduces approximately 0.016% of the LEO thermal fatigue budget and approximately 1% of the LEO UV-A/UV-B fluence budget. The cost savings relative to full Thermal Vacuum Chamber (TVAC) testing are one to two orders of magnitude. Future work will target orbital calibration, a vibration sub-index, and an open-source web calculator.

A compact, fractal-shaped, triple-band multiple-input multiple-output (MIMO) antenna integrated with a frequency-selective surface (FSS) to improve radiation characteristics is presented in this work. The proposed design employs a fractal-based radiating element to achieve multiband characteristics while minimizing the size. The four-port MIMO configuration is developed from a single-port radiator using an orthogonal arrangement to improve the port isolation. A central square slot is introduced to suppress mutual coupling by interrupting surface current paths, thereby improving inter-element isolation across all operating bands. To enhance the gain, a multi-resonant uniplanar frequency selective surface (FSS) is designed and positioned to act as a partially reflective surface. The FSS unit cell, modelled using an equivalent circuit approach, exhibits three distinct stopbands corresponding to the desired operating frequencies of 2.7-3.5 GHz, 5.5-8.4 GHz and 9.3-10.9 GHz. The combined antenna-FSS configuration, with the overall electrical size of (0.5×0.5×0.235)λ, demonstrates a gain improvement of 3-4 dBi in all bands, without compromising bandwidth. With three frequency bands of 2.5-3.875 GHz, 5.25-6.05 GHz and 8.6-10.6 GHz, the proposed MIMO antenna achieves good MIMO characteristics, making it suitable for modern high-speed wireless technologies including sub-6-GHz 5G (WiMAX), WLAN, and ISM bands.

This paper presents a high-gain substrate-integrated waveguide antenna featuring a narrowly-focused radiation beam with enhanced cross-polarization characteristics, specially designed for precision millimeter-wave radar systems and n-257 band point-to-point 5G wireless applications. The antenna incorporates a novel design with dual radiator slots arranged both vertically and horizontally on the broadside wall of the substrate-integrated waveguide, forming a Non-Intersecting Asymmetrical T-shaped unit cell. This unit cell is periodically distributed to create an eight-element radiator array, thereby improving the antenna's gain and bandwidth. The antenna operates in the frequency range from 27 GHz to 28.54 GHz, thereby covering the n-257 5G frequency band. Moreover, it exhibits a half-power beamwidth of 8.1°, low side-lobe level of -13.3 dB, and cross-polarization discrimination level of 25 dB, making it suitable for high-precision millimeter-wave radar sensing applications. The proposed design provides a peak gain of 10.51 dBi with a radiation efficiency of 84.82%. Moreover, the integration of a dome-shaped polytetrafluoroethylene dielectric lens achieves a peak gain of 12.50 dBi with an enhanced radiation efficiency of 86.35%. The antenna design and simulation were performed using CST Studio Suite, followed by an experimental validation. Owing to its high gain, low side-lobe levels, and a sharply focused main-lobe beam with excellent cross-polarization discrimination, the antenna is well-suited for millimeter-wave radar sensing and point-to-point 5G communication systems.

In optical communications, symbol error rate (SER) is a key indicator of system performance when data is transmitted over optical channels. Improving this rate is a major goal in the design of advanced optical systems, as many factors affect performance, including noise and optical impairments. One mathematical method proven effective for improving performance is the use of Laguerre polynomials. This study investigates the impact of variations in the polynomial parameters regarding Laguerre-Gaussian vortex beam (LGVB) on symbol error rate (SER) under weak, moderate, and strong turbulence conditions. The research uses numerical simulations to analyze the beam's intensity profiles and SER for various parameter combinations. Key findings show that specific parameter pairs yield superior SER performance, reducing error rates. The lowest SER under high turbulence is observed at (3,0) and (2,0) due to their spatially dispersed intensity profiles. Optimizing LGVB's polynomial parameters enhances SER robustness in turbulent FSO systems, offering a practical, non-hardware-based mitigation strategy. Simulation results for (n = 3, m = 0) show that the proposed beam configuration reduces SER to the minimum value compared to other Laguerre Gaussian Vortex beams with different values of radial index (n), and topological charge (m) under identical turbulence conditions (Cn² = 10^-12 m^-2/3). This work provides actionable insights for designing turbulence-resilient optical links, particularly in satellite-to-ground and long-range terrestrial communications.

Manufacturing tolerances introduce unavoidable dimensional deviations in electrical machine components. In the case of switched reluctance linear synchronous motors (SRLSMs), the manufacturing tolerance, Δx, may significantly affect the thrust characteristics. Therefore, a systematic investigation of the impact of manufacturing tolerance, Δx, on the thrust characteristics of a cylindrical SRLSM through finite element analysis and experimental validation is presented. Two mover shafts with different tolerance control strategies, denoted as S45C-01 and S45C-02 were fabricated. Based on the finding, the accumulated tolerances of -562.3 μm and -20 μm for S45C-01 and S45C-02, respectively, were acquired using a vision measuring system. Then, the model that incorporated the accumulating manufacturing tolerance, Δx, was created and simulated. Thrust characteristics were evaluated under both ideal and tolerance inclusive conditions and experimentally measured over a current range of 0.1-1.0 A. The results indicate that neglecting manufacturing tolerance leads to substantial discrepancies between simulated and measured thrust, particularly at low excitation currents, with thrust errors exceeding 200%. When measured manufacturing tolerances are included in the simulation, the thrust error is significantly reduced to below 8.4% for S45C-01 and below 4% for S45C-02, demonstrating close agreement with experimental results. The findings confirm that manufacturing tolerance is a critical factor in accurately predicting SRLSM thrust performance and that tolerance-inclusive modeling substantially improves the reliability of simulation-based performance evaluation.

This research proposes a microwave sensor based on a dual-split-ring-resonator (DSRR) structure designed for the detection of the permittivity of solid samples and defective materials. The DSRR structure was chosen because it has a high-quality factor Q, is highly sensitive to changes in permittivity, and is easy to integrate into a planar substrate. The designed sensor is fabricated using a Rogers RO5880 substrate having a dielectric constant ε_r of 2.2, tanδ of 0.0009, and a substrate thickness h of 1.58; the sensor operates in the frequency range of 1 GHz-2 GHz and adopts a dual-port configuration by observing changes in the transmission parameter S₂₁. The measurements used the perturbation theory method, where the resonance frequency shift occurs when a material is inserted into the sensor area. This sensor area is defined as the location of maximum electric field concentration within the resonator. Polynomial equations are derived for measurements on dielectric materials with known permittivity values ranging from 1 to 9.8. The proposed sensor demonstrates high performance, with a measured accuracy of 99.6%, a normalized sensitivity of 2.6%, and a frequency detection resolution (FDR) of 0.026 GHz. These results indicate that the sensor using the DSRR method with hole integration offers reliable and precise permittivity detection, particularly for detecting defects in materials.

This paper presents a novel multi-tooth flux-switching permanent magnet (MT-FSPM) machine that incorporates HTS bulks and radially magnetized PMs within the stator teeth. The alternating arrangement of PMs produces a synergistic effect between the flux-reversal mechanism and flux-switching mechanism. Additionally, the magnetic flux shielding effect of HTS materials effectively reduces flux leakage from the stator teeth, thereby enhancing the output torque. Subsequently, parameterized finite element models of the conventional and proposed models were established, and the key design parameters were systematically stratified based on sensitivity analysis. The optimal values for the high-sensitivity parameters were then obtained using the response surface method (RSM) and multi-objective genetic algorithm (MOGA). Finally, compared with the conventional model, the results demonstrate that the proposed model achieves a significant enhancement in torque performance, with the output torque increased by 49.69{\%} and torque ripple reduced by 16.90{\%}. Furthermore, the proposed model exhibits superior overload capability and improved power factor.

This article presents an improved power quality (IPQ) soft-switched diode-driven capacitor (DDC) cell converter for high-gain DC-DC conversion applications. The modified sixth-order DDC cell converter offers several advantages over conventional designs, including common ground configuration, reduced pulsating source current, non-inverted output voltage, and a high voltage gain of (1+D)/(1-D)). A single-capacitor auxiliary circuit is employed to facilitate soft-switching operation by reducing switching stress and minimizing switching losses. The proposed converter achieves zero-voltage switching (ZVS) and zero-current switching (ZCS) conditions without significantly increasing circuit complexity or auxiliary component count. Comprehensive steady-state and small-signal analyses are carried out and validated through MATLAB/Simulink simulations and a 600 W experimental prototype. Experimental results demonstrate improved efficiency, reduced voltage stress, and enhanced input-side power quality with input current THD limited to 3% under rated operating conditions. Owing to its simple structure, reduced switching losses, and high voltage gain capability, the proposed converter is suitable for high-performance DC-DC power conversion applications.

Existing electromagnetic (EM) safety analyses for reconfigurable intelligent surface (RIS) systems rely on the far-field equivalent plane-wave density (EPD) formula, which systematically underestimates tissue exposure when the user equipment (UE) operates in the radiating near-field (NF) zone (d_U ≲ d_R/2, where d_R = 2D²/λ is the Rayleigh distance, and D = (N-1)λ/2 is the aperture length). This paper presents five analytically rigorous contributions to NF-aware power allocation and beamforming for RIS-assisted 5G/6G systems. (1) A conservative Fresnel-envelope correction factor κ(d,N) with a provable non-negative overestimation error ε(d,N) ≥ 0 (Propositions 1-2, Lemma 1). (2) Closed-form NF-corrected SAR power ceiling P^∗_NF and minimum exclusion radius d^NF_min; the 1-D Fresnel bound is conservative for 2-D uniform planar arrays (UPAs) with a separability gap up to 13.2 dB, confirmed by exact 2-D spherical-wave summations (SAR_1D ≥ SAR_FF ≥ SAR_2D). (3) A closed-form NF phase-taper Δϕ_n recovering up to 0.4 bit/s/Hz SAR-constrained spectral efficiency (SCSE) at d_U = 1 m (Proposition 3). (4) A two-stage NF-SAR alternating-optimisation (NF-SAR-AO) algorithm with O(N) per-iteration complexity, hard guard margin (d_eff = 1.1d_U), and proved monotone convergence under line-of-sight (LOS) channels (Algorithm 1, Proposition 4). (5) 2-bit phase quantization incurring < 0.3 bit/s/Hz SCSE loss with 100% ICNIRP 2020 compliance for all d_U ≥ 0.5 m. Validated over 5 × 10³ Monte Carlo (MC) trials at 3.5 GHz (N = 64, P_max = 200 mW): d^NF_min = 0.727 m¹ vs. d^FF_min = 0.498 m - far-field models underestimate the required safety exclusion radius by 46%, risking ICNIRP 2020 non-compliance.

This paper proposes a high-thrust-density linear partitioned primary permanent magnet vernier (LPPPMV) machine based on an asymmetric winding configuration, leveraging the advantages of linear machines to avoid the unbalanced magnetic pull caused by asymmetric slot-pole combinations in rotary machines. Firstly, the winding factor and harmonic distribution of asymmetric slot-pole combinations are revealed from the perspective of armature MMF. Furthermore, a higher modulation ratio design is achieved under the same electromagnetic load and its mechanism is analyzed. Then, to address the insufficient fault tolerance of conventional symmetric winding, a modular asymmetric winding machine is proposed and optimized. Consequently, the results show that the proposed machine exhibits superior characteristics in both thrust density and fault tolerance, and finally, experiments on a linear machine test bench validate the theoretical analysis.

As the need for rapid data transmission and dependable wireless networks grows, so does the need for advanced antenna technology. This has become a major focus of modern communication technologies. This paper describes the design of a 4-port multiple-input multiple-output (MIMO) microstrip patch working at 28 GHz in the Ka-band. This antenna is fabricated on a substrate measuring 21 × 21 × 3.97 mm³, composed of FR4, foam, and RT/Duroid 5880. It uses a microstrip feed. Performance enhancements are achieved by positioning the feeds orthogonally, incorporating a U-shaped slot into the MIMO antennas, and implementing a superstrate made of metamaterial (MTM) elements. Additionally, a single-layer MTM superstrate with rectangular slots is created to improve gain while keeping good impedance matching. The design process systematically improves gain and mutual coupling while keeping the overall size compact. The specific challenge addressed by the design is to improve peak gain and radiation efficiency by employing MTM elements operating at 28 GHz. The 4-port MIMO antenna achieves an impedance bandwidth (IB) of 27.11-29.21 GHz, with a peak gain of 14.05 dB, respectively. This antenna is used in next-generation communication systems, vehicular networks, and 5G systems.

The development of interventional radiotherapy techniques has become one of the most important concerns for antenna designers worldwide. In this study, an efficient optimization approach based on a hybrid algorithm derived from exploiting the quantitative concept, along with the theory of reinforcement convexity, called the quantitative-convex approach (QCA), to produce a high-performance electromagnetic radiation pattern is presented. The novelty of this study lies in shaping patterns that mimic the shape of the targeted human organ in radiotherapy by steering a flat main beam of a square antenna array, along with optimal control of the sidelobe level. The proposed approach works by identifying the diseased organ captured from medical imaging, converting it into a binary image (black and white colors), and then feeding it into the antenna system to form a radiation pattern that accurately mimics the diseased organ. To reduce the systemic and computational complexity of the therapeutic antenna system, a sparsity technique was added to the hybrid algorithm. The computer simulation results showed high efficiency in generating robust patterns with sharp boundary profiles, such as those used for isolating diseased and undiseased tissues and measuring the tissue-specific absorption rate (TSAR), making it suitable for use in radiotherapy.

This study presents a broadband, switchable, and bi-functional terahertz device based on the phase transition of vanadium dioxide (VO₂). When VO₂ is in the metallic state, the device operates as a linear polarization converter (LPC). When VO₂ transitions to the insulating state, the device functions as a broadband linear-to-circular polarization converter (LTC-PC). Numerical simulations are conducted to verify the device performance. To further optimize metamaterial performance and accelerate the design process, a deep learning framework that integrates convolutional neural networks (CNNs) and the Transformer architecture via an adaptive mechanism is proposed. Numerical simulations indicate that this LPC achieves a polarization conversion ratio (PCR) exceeding 90% across the 1.92-2.93 THz band and maintains angular stability for incidence angles up to 50°. The LTC-PC operates effectively within the 2.40-4.33 THz range. Featuring broadband operation and bi-functional capabilities, the converter holds significant potential for applications in terahertz imaging, sensing, solar energy harvesting, and communications.

The flux reverse machine (FRM) has the advantages of high utilization rate of permanent magnet (PMs) and wide speed range. However, it still suffers from low output torque and large torque ripple. In this study, an FRM with a double-layer dual-PM Halbach array (DLDPMH-FRM) is proposed. The PMs are arranged in a double layer at the stator slot, and a Halbach array is employed at the rotor slot openings. The stator and rotor PMs together form a dual-PM structure. The response surface method (RSM) and multi-objective genetic algorithm (MOGA) were combined for global optimization. Compared with the dual-PM FRM (DPM-FRM), the torque of the DLDPMH-FRM reaches 7.75 N·m, which is 35.72% higher than DPM-FRM, while the torque ripple is reduced by 86.01%. This model provides a feasible solution for the design and optimization of high-performance FRM.

The proposed prototype miniaturizes a two-port wideband multi-input multi-output (MIMO) antenna structure to operate over a specified frequency spectrum from 2.6 to 5.1 GHz and exhibits an impedance bandwidth of 64.93% to support 5G mid-band (n77/n78/n79) applications. The antenna design incorporates a pair of spoon-shaped radiating units configured orthogonally to achieve polarization diversity. To improve inter-port isolation (S₂₁), T-shaped slots along with a diagonally oriented rectangular slot are employed in the ground plane, while the isolation value remains better than −15 dB within the prescribed limit. The developed MIMO antenna was implemented in a compact configuration on an FR4 substrate, with physical dimensions of 30 × 30 mm². The antenna exhibits a gain ranging from 3.5 to 3.9 dB with radiation efficiency varying from 94% to 96% and a stable radiation pattern within the targeted frequency band. The diversity performance metrics across the operating frequency range were validated by the envelope correlation coefficient (ECC < 0.01), diversity gain (DG < 9.99 dB), and mean effective gain (MEG) close to −3 dB. Experimental findings show close correlation with simulated data, confirming the effectiveness of the developed MIMO antenna structure for 5G New Radio (NR) mid-band operation.

To address the trade-off between increasing output torque and reducing torque ripple and cogging torque in interior permanent magnet synchronous motors (IPMSMs), this study proposes a structure incorporating stator-rotor auxiliary slots and rotor damping holes. Additionally, a hybrid permanent magnet configuration combining N35 and N30 grades was adopted to maintain high performance while further reducing costs. First, an analytical expression for the cogging torque was derived, and a finite element model of the motor was established. Subsequently, a parametric sweep and optimization of the stator and rotor auxiliary slots were conducted to obtain the optimal combination of auxiliary slot dimensions. Furthermore, a multi-objective optimization algorithm was proposed to optimize the motor parameters. Finally, radial electromagnetic force analysis was performed on the optimized motor model. The results demonstrate that the proposed structure effectively suppresses the torque ripple, cogging torque, and amplitude of the radial electromagnetic force, thereby reducing motor vibration amplitude while ensuring that the electromagnetic torque remains unaffected. The proposed design achieves a favorable balance between output torque enhancement and torque ripple/cogging torque reduction, with cost control through hybrid permanent magnets, demonstrating comprehensive performance improvements for IPMSMs.