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.

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.

To realize a compact and low-profile Ka-band SIW antenna with continuous wideband operation, a wideband SIW slot antenna based on split Magnetic-electric dipole multi-mode coupling is proposed. The central design idea is to transfer electromagnetic energy from the lower SIW cavity to the upper radiating layer through aperture coupling and to merge two adjacent resonant modes generated by the electric- and magnetic-dipole components. The antenna employs a dual-layer configuration. The lower layer consists of an SIW feeding cavity and a coupling slot, and the upper layer incorporates split arc-shaped patches, a central coupling patch, metallized vias, and a cross-shaped perturbation structure. The split patches mainly generate the high-frequency electric-dipole mode, while the central coupling patch and metallized vias introduce an adjacent lower-frequency magnetic-dipole mode. The cross-shaped perturbation structure further optimizes the impedance transition between the two modes. The simulated results show that the antenna achieves an impedance bandwidth of 26.35-29.20 GHz for |S₁₁| < -10 dB and a peak realized gain of approximately 8.15 dBi at 28 GHz. The fabricated prototype exhibits a measured impedance bandwidth of approximately 26.8-29.1 GHz. In addition, the simulated multifrequency radiation patterns and efficiency results demonstrate relatively stable broadside radiation characteristics within the operating band. The proposed antenna provides a compact and readily integrated solution for Ka-band millimeter-wave communication systems.

A novel finite-gap lumped-port model is presented to improve the accuracy of the volume surface integral equation (VSIE) solver for electromagnetic (EM) radiation from composite metallic-dielectric structures. This port model is implemented by modifying the traditional method of moments (MoM) solution to use a novel divergence-conforming testing function at the gap as well as half-basis functions connected across the gap, where a small gap region in the domain of analysis is linked to the lumped-circuit voltage/current source. Then, a hybrid multilevel fast multipole algorithm with multilevel accelerated Cartesian expansion algorithm (MLFMA-MLACEA) is adopted to enhance the capability of this VSIE-based finite-gap lumped-port model for electrically large and multi-scale EM radiation problems. Numerical results are provided to demonstrate the accuracy and efficiency of this VSIE method.

To address the problems of low speed control accuracy and performance degradation caused by time-varying disturbances in conventional control methods for high-precision speed regulation of permanent magnet synchronous motors (PMSMs), an improved full-order model-free sliding mode control (IFOMFSMC) method based on full-order sliding mode control (FOSMC) is proposed. First, a novel ultra-local model under parameter perturbations is established. Based on this model, the IFOMFSMC is designed by combining a second-order full-order sliding mode surface with an improved double-power reaching law, which improves the speed control accuracy of the PMSM. Subsequently, a full-order extended sliding mode disturbance observer (FOESMDO) is developed by incorporating FOSMC into the extended disturbance observer. The FOESMDO estimates unknown disturbances more accurately, thereby compensating the IFOMFSMC and enhancing system robustness under complex time-varying disturbances. Finally, simulation results confirm accurate speed tracking with the proposed method. Under complex time-varying disturbance conditions, compared with the conventional control method, the IFOMFSMC improves speed response and tracking performance by 57.6% and 88.2%, respectively, while reducing steady-state speed error and torque ripple by 71.8% and 29.2%. The proposed method effectively enhances steady-state and dynamic performance as well as disturbance-rejection capability.

The open-circuit fault diagnosis of switches in quasi-Z-source inverters (qZSI) is challenging. Existing methods struggle to simultaneously achieve high robustness and low computational complexity without additional sensors. In this study, an open-circuit fault diagnosis method based on an improved super-twisting non-singular fast terminal sliding-mode observer (IST-NFTSMO) and hybrid features is proposed. The stator currents were estimated in real time by the IST-NFTSMO, and residuals were generated accordingly. By analyzing differences in the statistical distributions of residuals between healthy and faulty conditions, two features were extracted: average log-likelihood ratio (ALLR) and signed cumulative ratio (SCR). The ALLR is used for rapid fault detection, whereas the SCR is used for accurate localization of faulty switches. The proposed method was implemented entirely based on existing current sensors. No additional voltage sensors were required. Moreover, the diagnostic thresholds are adaptively adjusted according to variations in speed and load. The experimental results demonstrate that both single-switch and dual-switch open-circuit faults can be diagnosed rapidly and accurately. Compared with conventional methods, higher robustness and lower computational complexity were achieved.

This paper presents the design, fabrication, and characterization of a novel optical fiber temperature sensor based on a single-mode-multimode-single-mode (SMS) structure for real-time monitoring of transformer oil temperature in high-voltage environments, addressing the limitations of conventional electronic sensors such as electromagnetic interference, electrical safety hazards, and restricted spatial coverage. The sensor, fabricated with corning single mode fiber (SMF)-28e+ single-mode and Thorlabs FG050UGA multimode fibers (5 cm active section), operates on the Mach-Zehnder interferometer principle, where temperature-induced refractive index changes in transformer oil modulate light propagation. Systematic experiments over a 30-90 °C range using a 1550 nm tunable laser, temperature‑controlled oil bath, Pt100 reference, and optical spectrum analyzer yielded a wavelength sensitivity of 4.17 × 10^-3 nm/°C with excellent linearity (R² = 0.9646), a standard error of 4.45 °C, repeatability better than 0.5 % coefficient of variation, and progressive OSNR improvement from 0 dBm at 30°C to 2.26 dBm at 90 °C. The wavelength-based calibration method significantly outperformed the power-based approach, offering 1.36× lower error (4.45 °C vs. 6.04 °C) and higher correlation, with expanded uncertainty (95 % confidence, k = 2) calculated as 6.14°C. Compared to fiber Bragg grating and fiber-loop mirror sensors, the proposed SMS sensor provides electromagnetic immunity, cost-effective fabrication, high stability, and a simple all-fiber configuration, making it a reliable and practical solution for continuous thermal monitoring in power transformers and laying the foundation for comprehensive fiber-optic sensing networks in high-voltage power systems.

To address vibration and noise issues in outer-rotor flux-switching permanent-magnet (OR-FSPM) machines for high-precision applications, radially magnetized PMs are placed between regular tangentially magnetized PMs, forming a U-shaped structure. An air-gap magnetic barrier is introduced between the two types of PMs to achieve magnetic isolation. Then, the spatiotemporal distribution of radial electromagnetic force density (EFD) waves is derived based on the magnetomotive force permeance model. Modal and harmonic response analyses are then conducted for both the conventional and proposed U-shaped machine topologies using electromagnetic-structural field simulations to reveal vibrational characteristics. The results demonstrate that the proposed U-shaped topology effectively suppresses second-order resonance while maintaining superior electromagnetic performance.

In fixed switching frequency pulse-width modulation (PWM) drive systems for switched reluctance motors (SRMs), the duty cycle directly affects current-tracking precision and torque output performance. To address the slow dynamic response of conventional PI control and the model dependence and limited robustness of conventional model predictive duty-cycle control (MPDCC), this study proposes a robust duty-cycle control strategy based on double-power sliding mode compensation. This strategy constructs a duty-cycle generation mechanism by combining model predictive feedforward with sliding-mode compensation. It utilizes MPDCC to generate a base duty cycle, whereas a double-power sliding mode generates a compensation duty cycle to correct deviations. Simulated and experimental results demonstrate that the proposed strategy generates accurate PWM duty cycles, keeps the current tracking error bounded within a small quasi-sliding-mode band, and improves current-tracking accuracy and torque-ripple suppression under parameter-mismatch conditions, validating the robustness of the system against parameter mismatches.

The design of ultra-wideband (UWB) band-notched antennas is highly sensitive to geometric dimensions. Consequently, traditional metaheuristic algorithms incur prohibitive computational costs from massive full-wave electromagnetic (EM) simulations. An efficient co-design framework, termed the Surrogate-Assisted Nutcracker Optimization Algorithm with Gaussian Process (SANOA-GP), is proposed. By leveraging a GP surrogate for epistemic uncertainty quantification with a lower confidence bound (LCB) prescreening strategy, SANOA-GP balances exploration and exploitation, overcoming high-dimensional multimodal traps. Moreover, intelligent early stopping is achieved through a performance-driven dual-termination criterion with a progressive reward mechanism. Sobol global sensitivity analysis is incorporated to quantitatively evaluate geometric influences, enhancing black-box interpretability and verifying the independent tunability of the dual notches. Measurement results confirm that the optimized antenna achieves precise and deep notches (S₁₁ > -5 dB) at the 5G N79 and X-band frequencies. Remarkably, SANOA-GP converges with an average of only 69.3 full-wave EM simulations. Compared to surrogate-free algorithms, it reduces computational time by over 50%, while still ensuring high optimization accuracy and physical reliability. The proposed framework offers an efficient and reliable paradigm for the automated design of complex radio frequency (RF) and microwave components.

The conventional optimization of permanent magnet synchronous motors (PMSMs) for hybrid electric vehicles (HEVs) often neglects the dynamic nature of real-world driving cycles, resulting in suboptimal overall energy efficiency. To address this issue, this study proposes a multi-region efficiency optimization strategy that fully integrates actual driving cycles. First, motor operating points were extracted from the WLTC and CLTC standard driving cycles and identified as key operating regions via cluster analysis. A variance-based sensitivity analysis is then employed to quantify the contribution of each rotor parameter, thereby reducing the optimization dimension. The NSGA-III algorithm, coupled with finite element analysis (FEA), performs multi-objective optimization, targeting average efficiency and permanent magnet cost. A new method that comprehensively considers the average efficiency of both the cluster centers and boundaries of the operating points was proposed as an optimization objective. The results show that the optimal candidate improves the average efficiency to 96.77\%. Depending on the practical requirements, different candidate points are ultimately selected by balancing efficiency, cost, and driving comfort.