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.

Conventional ferrite-based permanent magnet-assisted synchronous reluctance motors (PMaSynRMs) suffer from low torque density and are vulnerable to irreversible demagnetization under heavy-load conditions due to the reverse armature field. To address this, this paper proposes a hybrid-magnet rotor topology in which ferrite and NdFeB magnets are arranged in series along the flux path within each U-type flux barrier (NdFeB on the airgap side, ferrite on the inner side), while the three radially layered U-type branches are connected magnetically in parallel. Within each barrier, the magnetomotive forces of the two magnet types superpose to enhance the excitation flux; meanwhile, a dual synergistic mechanism - outer NdFeB shielding and flux shunting via parallel rotor bridges - suppresses the demagnetizing field. To tackle the 15-dimensional optimization problem, a Kriging-NSGA-III framework incorporating Pearson sensitivity screening is established. Finite-element results show that, compared to the benchmark all-ferrite machine, the optimized motor achieves a 20.78% increase in average torque, torque ripple reduction from 18.80% to 8.07%, and 89.49% efficiency. The benchmark exhibits local irreversible demagnetization at 3 times rated d-axis current, whereas the proposed topology shows no observable demagnetization even at 6 times rated current, validating the effectiveness of the proposed hybrid topology and optimization strategy.

Slow-light photonic crystals with group indices exceeding 100 typically require complex defect engineering - line-defect waveguides, coupled resonator optical waveguides (CROWs), or carefully designed heterostructures. These approaches, while effective, introduce fabrication complexity, optical losses, and bandwidth limitations. Recent advances achieving group indices of 50-100 in engineered structures still fall short of theoretical predictions for bulk photonic crystals operating in higher-order bands. However, a critical knowledge gap persists: most higher bands (3-8) largely unexplored. Here, we demonstrate that bulk square lattice photonic crystals operating in higher-order TM bands achieve ultra-slow light (group index 226.5) and extreme anisotropic dispersion (ratio 58.36) - performance comparable to state-of-the-art defect-engineered waveguide structures, achieved in a bulk crystal without any line defects, coupled resonators, or heterostructures, thereby maintaining fabrication simplicity. Through systematic equifrequency contour (EFC) analysis of bands 1-8 using high-density k-space sampling, we establish a quantitative framework revealing that higher bands offer superior slow-light characteristics unattainable in conventionally studied lower bands. Our GaAs/organic semiconductor system achieves this performance with moderate dielectric contrast (ε_r = 6.86), compatible with standard electron-beam lithography fabrication. A systematic parametric sweep of the rod radius (R/a = 0.30-0.50) further reveals that this slow-light performance is structurally robust and tunable by geometry: the Band 4 group index varies by less than 25% across the full sweep; Band 3 sustains a high normalized delay–bandwidth product (NDBP = 0.40-0.48) over a wide fabrication-tolerant range; Band 4 reaches an NDBP optimum of 0.403 at R/a = 0.38; Band 7 uniquely combines NDBP > 0.1 with an anisotropy ratio above 200; Band 8 exhibits extreme anisotropy (ratio up to 1369).

Owing to glass's excellent electrical properties and stability, Through-Glass Via (TGV) technology is regarded as a key technology for next-generation three-dimensional integration. Research on TGV-based transmission structures and Substrate-Integrated-Waveguide (SIW) structures has been relatively extensive. However, the investigated frequency range remains limited, rarely exceeding 100 GHz, and studies focusing on the intrinsic characteristics of the vias are still lacking. To address this issue, this study designs a set of TGV calibration standards operating in the D-band to extract the S-parameters and electrical parameters of the vias and to analyze their performance, thereby providing useful insights for the subsequent design of TGV devices in the terahertz band.

Devices such as drones and low Earth orbit satellites demand antennas that are lightweight, thin, and sufficiently flexible to conform to curved surfaces. At millimetre wave frequencies, however, closely placing multiple antennas inevitably introduces mutual coupling, which degrades communication quality. This paper presents a four element antenna array fabricated on a flexible polyethylene ter-ephthalate (PET) substrate, operating in the 26.21-29.64 GHz band. Unlike conventional approaches that rely on additional decoupling components, our design eliminates interference solely through a centrosymmetric four quadrant layout of the radiating elements, without any auxiliary structures. Measurements show that isolation among all four ports exceeds 46.95 dB; the envelope correlation coefficient (ECC) reaches as low as 0.0000312; and the diversity gain approaches the theoretical limit of 10 dB. The antenna maintains a radiation efficiency above 90% and a gain of 2.40-3.20 dBi, with stable coverage patterns across the entire band. With a thickness of only 0.12 mm, this flexible antenna offers a simple, low cost, high performance solution for conformal ap-plications. The work demonstrates that careful layout design can replace complex decoupling networks, providing a new pathway for lightweight, flexible, large scale antenna arrays in future 5G/6G communication systems.

Rotor mass eccentricity in an outer-rotor coreless bearingless permanent magnet synchronous motor (ORC-BPMSM) causes synchronous unbalance vibration, which degrades suspension stability and limits high-speed operation. To suppress this vibration, an optimized secondary-path estimation variable-step-size filtered-x least mean square (OSPE-VSS-FxLMS) feedforward compensation method is proposed. First, the rotor unbalance vibration mechanism is derived from the suspension force model. Then, a hyperbolic tangent-exponential (tanh-exp) function is introduced to adaptively regulate the FxLMS step size, improving the trade-off between convergence speed and steady-state error. Meanwhile, a normalized least mean square (NLMS)-based online secondary-path estimation strategy is developed to reduce gradient deviation caused by secondary-path mismatch. Simulations and experiments are conducted under constant-speed and acceleration conditions. Compared with the uncompensated condition at 3000 r/min, the displacement vibration amplitudes in the x- and y-direction are both reduced to 11 μm, corresponding to a reduction of about 69.4%. The effectiveness of the proposed unbalance vibration compensation method is confirmed by both simulated and experimental results.

This manuscript presents a novel compact reflective frequency selective surface (FSS) for wideband polarization conversion, enabling efficient polarization manipulation over the frequency range of 8.2 GHz to 9.5 GHz, which is the X-band spectrum for electromagnetic applications. The proposed FSS consists of a metallic pattern printed on an FR4 substrate with a relative permittivity of ε_r = 4.4, loss tangent of tanδ = 0.02, and thickness of 1.6 mm, backed by a ground plane. This configuration enables reflective-mode operation with a tunable frequency range typically spanning X-band, achieved by optimizing the unit cell's geometrical parameters. The proposed structure provides efficient linear-to-orthogonal polarization conversion over 8.2-9.5 GHz (1.3 GHz bandwidth, center frequency of 8.85 GHz), with a polarization conversion ratio (PCR) exceeding 98%. This frequency range lies within the X-band and provides a fractional bandwidth of approximately 14.69. Under oblique incidence, the proposed FSS maintains a PCR above 90% up to 40°, with only a slight bandwidth reduction, and shows good agreement between simulated and measured results. Owing to its compact nature, excellent angular stability and wide operating bandwidth, the proposed FSS is suitable for radar and wireless communication applications.

Electromagnetic harvesters based on magnetic levitation have emerged as particularly attractive systems owing to their contactless suspension, low mechanical damping, and inherently nonlinear stiffness behavior, which are suited to low-frequency ambient excitation. The investigated harvester consists of a levitating magnet suspended between two fixed outer magnets via repulsive magnetic forces, with a pickup coil converting oscillatory motion into electrical energy under base excitation. The primary source of difficulty in this system is the nonlinear magnetic restoring force F_mag and the electromechanical transduction coefficient γ, which must be pre-characterized via semi-analytical or finite element methods before any solution can be attempted. Therefore, the accurate pre-characterization of both F_mag and γ is the essential foundation of the entire modelling process. A Fourier space semi-analytical approach is proposed and developed, transforming a three-dimensional magnetostatic problem into a computationally efficient one-dimensional spectral calculation without remeshing. The semi-analytical predictions were validated against COMSOL finite element simulations, and their strong mutual agreement confirmed the accuracy of the proposed method before embedding it into the motion's coupled nonlinear equations.

Conventional multi loop control of diode clamped active power filters suffers from response conflicts and slow regulation due to strong coupling among DC voltage, neutral point potential, and reactive power. This paper proposes a single agent deep deterministic policy gradient (DDPG) framework for multi objective cooperative control. Unlike generic DRL applications, our design retains the current PI inner loop for hardware safety. At the same time, a single agent replaces the three outer loops (voltage, neutral point, and reactive power) to eliminate cascade coupling. A composite reward function based on the L2 norm - rather than linear weighting - quadratically penalizes large errors, forcing the agent to prioritize the most severe deviations and resolve multi objective conflicts optimally. Simulations show that the proposed strategy reduces grid side current THD from 6.7% to 1.09%, cuts midpoint balancing and DC bus settling times by 50% and 66.67% respectively, achieves zero overshoot and zero steady state error, and exhibits strong robustness under voltage sags and load surges. This work offers a customized, low tuning effort intelligent solution for power quality control in complex grids.

In this manuscript, a well-designed multiband cavity-backed X-shaped slot antenna is presented using substrate-integrated waveguide (SIW) technology. Its performance is optimized for the K and Ku bands to suit various advanced communication scenarios. Including an X-shaped slot in this design leads to significant advantages, such as better impedance matching, broadside radiation pattern, and multiband operation. In addition, it shows decent gain values of 6.89 dB at 15.02 GHz, 6.91 dB at 15.90 GHz, and 7.12 dB at frequency 19.58 GHz. This is accomplished by the innovative application of X slots on the substrate integrated waveguide (SIW) cavity. Simulated and experimental results validate multiband antenna operation and exceptional performance, highlighting its potentially high suitability for state-of-the-art millimeter-wave applications, such as satellite communications and radar systems. This compact structure, along with the proposed antenna performance metrics, confirms its feasibility for future wireless communication systems. This progress enables further developments in SIW-based antenna technology.

Receiver nonlinearity degrades signal quality in modern wireless systems. This paper proposes an adaptive post-distorter using Chebyshev polynomials as basis functions to improve numerical stability and convergence speed. Unlike conventional or distributionmatched bases, the Chebyshev basis ensures a well-conditioned input correlation matrix regardless of signal distribution. This property, together with the minimax approximation, enables the RLS algorithm to converge within a few pilot symbols - an order of magnitude faster than the power-series basis. Experiments on a real wideband receiver with OFDM and WCDMA signals show significant ACPR improvements over the power-series and Legendre bases. The proposed approach exhibits robust performance, fast convergence, and broad applicability.

This letter presents a cross-coupled SIW filter with a quasi-elliptic response and improved stopband suppression. For cross-coupled SIW filters, suppressing spurious modes often requires rearranging feeding ports, but this rearrangement tends to increase port-to-port crosstalk and limit achievable out-of-band rejection. To address this inherent issue, we keep port positions unchanged and change the port configuration from conventional microstrip lines to an opposite-face GCPW feeding structure. The input and output ports are placed on opposite metal layers, with their ground planes separated by the dielectric substrate. Simulation results show that the port-to-port crosstalk is reduced from -25 to -40 dB to below -100 dB. Measured results show that the proposed filter maintains a similar stopband width as the previous design, while the suppression of the first spurious passband is improved by about 20 dB, reaching better than -50 dB. The improvement is achieved without hybrid structures or extra fabrication steps.

To overcome bandwidth-accuracy trade-offs in sensorless surface-mounted permanent magnet synchronous motor (SPMSM) drives, this study addresses the limitations of traditional observers. Conventional first-order sliding-mode observer (SMO) inherently exhibits high-frequency chattering due to discontinuous switching functions. To smooth the estimated back-EMF, a low-pass filter (LPF) is typically appended as a remedy; however, this filtering induces speed-dependent phase lag during medium- and high-speed operations, whereas its impact at low speeds is negligible. Although conventional higher-order model-based SMO (HOSMO) can better attenuate chattering, a lower cutoff frequency inherently compromises dynamic tracking precision due to increased phase lag. To overcome these challenges, the proposed scheme substitutes filter-dependent laws with a second-order super-twisting algorithm (STA), ensuring continuity of the control signal and zero phase lag. Furthermore, a state-dependent adaptive tuning mechanism based on a continuous nonlinear barrier function was developed. This adaptive law dynamically boosts observer gains to suppress transient perturbations and contracts them at a steady state to minimize chattering. Comprehensive simulations and experimental verifications demonstrated that the proposed gain-adaptive super-twisting higher-order SMO (GAST-HOTSMO) significantly reduced harmonic distortion, restricted estimation errors, and accelerated dynamic recovery compared to conventional methods.

This paper presents a low-profile, flexible, and wideband conformal wearable antenna for biomedical and wireless applications, including Internet of Things (IoT). The proposed antenna is based on an edge-truncated and slotted rectangular patch structure (ETSRP) developed on a jeans textile substrate, with compact overall dimensions of 0.163×0.269×0.006³. The antenna offers peak gain of 6.3 dBi with an impedance bandwidth of 2.32 GHz to 8.84 GHz, corresponding to a fractional bandwidth of 116.5%, with a reflection coefficient (S₁₁) of -42.4 dB in the ISM bands. The antenna's performance was evaluated using a human phantom and showed minor frequency detuning across different placement conditions. The specific absorption rate (SAR) was evaluated at 2.45 GHz and 5.8 GHz, with values of 0.7 W/kg and 0.8 W/kg, respectively, which are within accepted safety limits. The measured results were in good agreement with the simulated results in terms of impedance bandwidth, gain, and resonance characteristics. The proposed textile antenna offers wideband operation, low SAR, and compact size, making it suitable for wearable biomedical devices and IoT-based on-body communication systems.

To reduce the cost and improve the accuracy of position estimation for switched reluctance motors (SRMs) at medium to-high speeds, this study proposes a sensorless control strategy based on a dual-stage resonant filter (DSRF) and a feedforward phase-locked loop (FPLL). First, to address issues of weak dc-offset suppression and high-frequency harmonics in the second-order generalized integrator (SOGI) when processing nonlinear flux linkage, a DSRF with ideal band-pass characteristics is proposed. This filter effectively suppresses the dc-offset and higher-order harmonics. Second, the proposed FPLL introduces a feedforward compensation path related to the speed derivative. By adding zeros to broaden the system bandwidth, the dynamic response is accelerated. The tracking accuracy and response speed of the position observer are also enhanced under variable-speed and sudden-load conditions. Finally, the effectiveness of the proposed strategy was verified on a six-phase 12/10 SRM experimental platform. The experimental results show that the proposed sensorless control strategy achieves a fast and highly accurate estimation of the rotor position and speed at medium to-high speeds, particularly during dynamic processes, thereby enhancing system reliability and dynamic performance.

To address the requirements for compact size and low cost of RF signal sources, a novel design method for high-efficiency Class-F power oscillators is proposed. The key contribution of this method is the integrated design of the harmonic-tuning and impedance-matching networks. An asymmetric π-type harmonic tuning network is proposed to simultaneously realize harmonic termination for high-efficiency Class-F operation and fundamental load impedance matching, thereby significantly reducing circuit footprint. The amplifier's output was coupled to a feedback network via a capacitor and returned to the amplifier through a frequency-selective network, enabling a stable self-excited oscillation. To verify the design, a power oscillator is implemented using a low-cost LDMOS transistor and an FR4 substrate. The experimental results show that the fabricated oscillator operates at 918\,MHz with a direct current-to-radio-frequency (DC-RF) efficiency of 68.20% and a maximum output power of 42.90 dBm. Additionally, a low phase noise of -130 dBc/Hz at 1 MHz offset is achieved, robustly validating the effectiveness of this approach.

In‎ this ‎paper, ‎ a low-cost, lightweight open ‎transverse electromagnetic (TEM) ‎cell with an operating bandwidth from DC up to around 1.5 GHz is‎ designed ‎and‎ fabricated‎. Initially, a fully metallic open cell is simulated, and associated TEM modes are exhibited by the spatial electric field distributions. The cell length (L_b), width (W_b), and height (H_b) are respectively 398, 200, and 103.93 mm. In the next step, a printed circuit board (PCB) is used as the septum to reduce the device's overall weight. Moreover, longitudinal slots are cut on both sides of the septum to prevent the transverse currents, which results in the excitation of higher-order modes. For further weight reduction, sub-wavelength slots are cut in the metallic sidewalls without affecting the overall performance. The metal filling factor reduction is of great importance for reaching a portable test facility with reduced cost. Finally, the device's input ports are further manipulated to reduce discontinuity by gradually tapering them. The device is realized by the combination of metal sheet, computer numerical control (CNC) water jet, machining, and PCB technologies. The measured scattering parameters confirm the acceptable performance of the fabricated device.

This paper presents the design and experimental validation of a miniaturized Printed Log-Periodic Dipole Array (PLPDA) antenna operating within the 1.3-6.0 GHz frequency range. The objective of this work was to reduce the antenna's overall footprint while preserving its wideband performance. A sequential miniaturization strategy was adopted, employing m-segment fractal geometry for lateral size reduction and Cross-Entropy (CE) optimization for axial compaction. The reference PLPDA, measuring 255 mm × 116 mm, was progressively refined to a final size of 217 mm × 88 mm, achieving an overall footprint reduction of approximately 34%. The simulated and measured results confirmed excellent impedance matching, with S₁₁ remaining below -10 dB across the entire operating band and an average gain exceeding 7 dB. These results validate that the proposed CE-optimized m-segment PLPDA successfully achieves substantial miniaturization without degrading bandwidth or radiation performance. The presented approach offers a practical framework for developing compact, high-performance wideband antennas.

This paper proposes a model-free direct speed control (MFDC) method based on a second-order ultra-local model to address the speed loop bandwidth issue and difficulty of further improving the dynamic response performance in the speed control of a traditional cascaded permanent magnet synchronous motor drive system. The speed control method based on an accurate mathematical model has poor robustness to unknown disturbances, such as parameter uncertainty and inverter nonlinearity. This method eliminates the double closed-loop cascade structure of the traditional speed outer loop and q-axis current inner loop. By establishing a second-order ultra-local model of the surface-mounted permanent magnet synchronous motor ( SMPMSM ) drive system considering parameter uncertainty and inverter nonlinearity, the mechanical speed of the motor was directly related to the inverter's output voltage, and a model-free direct speed controller integrating speed control and torque current control functions was designed. Simultaneously, a model-free current controller based on the first-order current ultra-local model is used to realize the independent adjustment of the d-axis stator current. In addition, a virtual q-axis current ultra-local model torque limitation method for direct speed control is proposed to realize an effective constraint of electromagnetic torque without a cascade structure. Experimental results demonstrate that the proposed method provides enhanced load-disturbance rejection, particularly under medium- and high-speed conditions. At 500 r/min, load-step speed fluctuation is reduced from 3.6152% to 2.0638%, and recovery time is shortened from 0.0288 s to 0.0080 s. Under the rated-speed step condition, the speed overshoot is reduced from 2.8028% to 2.2136%.