In this work, we propose a technique to enhance the performance of circular patch antennas using an embedded system of cylindrical impedance surfaces. The technique utilizes a derived analytical model of a circular patch antenna containing an arbitrary number of coaxial impedance surfaces along with nonlinear optimization algorithms. This allows for the calculation of the radius and impedance of each surface to achieve the desired matching frequency band for given antenna dimensions. We demonstrate two applications of adding an optimal set of impedance surfaces into a compact circular patch antenna, i.e., the expansion of the matching frequency band keeping constant antenna dimensions and the miniaturization (height reduction) maintaining the constant bandwidth. Two corresponding versions of a cavity-backed circular patch antenna each having three impedance surfaces are synthesized. Practical implementations for both versions are designed and considered in full-wave numerical verification of analytically predicted properties. A comparison with the conventional method using multi-element microstrip matching circuits shows a benefit in radiation efficiency.

In this paper, an optimized flexible Microstrip Patch Antenna (MPA) for wearable applications is introduced, particularly characterized by its design concepts of scalable design and comprehensive performance evaluation. The proposed antenna leverages the mechanical flexibility of a leather substrate, complemented by polyimide layers on the upper and lower surfaces of the copper patch, enhancing both structural integrity and electromagnetic performance. The design is optimized for the operation at 2.4\,GHz, ensuring durability and stability even under dynamic bending conditions. Various critical performance metrics, such as resonance frequency, bandwidth, return loss, Voltage Standing Wave Ratio (VSWR), Specific Absorption Rate (SAR) and gain, are evaluated experimentally and through simulation across bending angles of 0-90°. Results also show that the antenna can reliably operate in an extreme bending scenario while having a resonant frequency near 2.44 GHz with a return loss (S₁₁) less than -20 dB up to 60° bending. At approximately 31 MHz bandwidth stability is preserved, and the VSWR is less than 1.2, thus the impedance matching is effective. Further gain measurements are also made under deformation, which further confirms the stable performance and thus reliability of the wearable application. Additionally, SAR analysis is conducted to ensure the antenna's compliance with electromagnetic exposure safety limits. The maximum SAR value of 0.516 W/kg remains well within FCC (1.6 W/kg) and ICNIRP (2.0 W/kg) standards, confirming safe radiation levels. Polyimide shielding improves durability, reduces interference, and minimizes backward radiation, making the design ideal for Wireless Body Area Networks (WBANs) and biomedical monitoring.

In order to solve the problems of susceptibility to environmental disturbances, complex installation and low reliability caused by the photoelectric code disks in the permanent magnet assisted bearingless synchronous reluctance motor (PMa-BSynRM) system, an improved BP neural network (BPNN) left-inverse system is proposed to establish the speed self-sensing system of the PMa-BSynRM. Firstly, the mathematical model of the PMa-BSynRM is established, and the left reversibility of the PMa-BSynRM speed subsystem is analyzed. Secondly, the traditional BP neural network is optimized from four aspects, including the number of neurons in the hidden layer, initial weight, connection weight and learning rate. Then, the improved BPNN model is used as the inverse model of the left inverse system to fit the speed subsystem of the PMa-BSynRM. Finally, the simulation results show that accurate estimation of the speed and rotor position is achieved by the proposed speed self-detection system, and the accuracy and feasibility of the proposed speed self-detection system are validated by the experimental results.

This paper describes the low sidelobe pattern synthesis of planar arrays having a distorted triangular or rectangular lattice. This distortion concerns variable row displacements applied to a triangular, skew or rectangular element lattice. The applied low sidelobe pattern synthesis is based on the iterative Fourier transform (IFT) method that makes extensive use of forward and inverse FFTs. Recently this author has developed new forward and inverse 2D FFT formulations. Due to these two new FFT formulations, the application of the IFT method is no longer limited to the pattern synthesis of a planar array having a rectangular lattice but can now also be applied to array apertures with a triangular or skew element lattice and even when such lattice has displaced element rows. The new IFT method is employed in this paper for the low sidelobe pattern synthesis of arrays featuring displaced element rows. The presented synthesized pattern results, which refer to the sum pattern, concern three planar arrays each with displaced element rows applied to a square or triangular lattice. The sum pattern of the considered antennas has to meet peak sidelobe level (PSLL) requirements for two nulling ring sectors, one of ≤-50 dB and the other of ≤-68 dB. The sum pattern of the third example includes a rectangular nulling sector specified by a PSLL of <– 80 dB.

In this paper, we present a miniaturized design of a microstrip antenna achieved through the Combination of Minkowski-Sierpinski(M-S) fractal structure and meandering technique, enabling the antenna to be integrated into smaller systems. The antenna achieves right-hand circular polarization (RHCP) through chamfering on a square patch. Further miniaturization is accomplished by loading four symmetrically opposed L-shaped slots along with M-S fractal structure. Specifically, the Minkowski structure undergoes a single iteration, while the Sierpinski fractal is iterated twice on the once-iterated Minkowski fractal to optimize performance. The antenna is manufactured on a textile substrate TLX-8 with dimensions of 50 mm × 50 mm × 0.762 mm, representing a 54.3% reduction in size compared to traditional designs. Moreover, the substrate exhibits robust mechanical properties. Experimental results demonstrate that the antenna achieves excellent radiation characteristics within a bandwidth of 1.563 to 1.581 GHz, an axial ratio bandwidth of 1.569 to 1.578 GHz. These performance metrics meet the requirements for modern Global Positioning System (GPS) antenna applications, highlighting the design's suitability for advanced integration in contemporary electronic systems.

Aiming at the problems of adjusting the weighting factor, significant torque ripple, and insufficient robustness against load disturbances in conventional model predictive torque control (MPTC) for PMSM, an improved model predictive torque control (IMPTC) strategy incorporating a decoupled sliding mode disturbance observer (DSMDO) is proposed. Firstly, the cost function is divided into two components, and both of them are evaluated sequentially to eliminate the need for weighting factors. Secondly, the set of candidate voltage vectors (VVs) is expanded by the VVs modulation technique to reduce the torque ripple, and a low-complexity method is introduced to determine the sector. Subsequently, the action time of the optimal VV is further corrected, which enhances the control of flux while reducing computational complexity. Additionally, a novel sliding mode disturbance observer with decoupling capability is introduced, which offers feedforward compensation to the speed loop and improves system robustness against disturbances. Finally, the correctness and effectiveness of the proposed IMPTC strategy with DSMDO are proved by the experimental results.

Aiming at the problem of low robustness of fuzzy adaptive control when it is applied to permanent magnet synchronous motor system (PMSM), the study introduced the sliding film control method to optimize it, so as to enhance the robustness of PMSM. The results demonstrated that the torque error of the adaptive fuzzy sliding mode control(AFSMC) was 1.86 Nm, which is 62.8% and 38% less than the peak torque pulsation of 5 Nm and 3 Nm for the fuzzy adaptive control, respectively, and indicates a better steady-state capability when the motor is operated at 1500 rpm and 30 Nm load. In addition, in the robustness validation experiments, under the initial stage, the two methods have the same rotational speed response, but after the parameter changes, the AFSMC adjusts quickly, while the traditional fuzzy adaptive control responds slowly. Moreover, under the same load inertia, the AFSMC exhibits smaller overshoot and faster regulation, smaller speed fluctuation and faster recovery during load surge. In complex scenarios, AFSMC reduces recovery time by 60% over traditional control methods, which demonstrates that the fuzzy adaptive sliding film control proposed by the study is successful in enhancing the system's stability and capability when the PMSM is applied.

In this paper, a multi-layer decoupling metamaterial unit (ML-DMU) is proposed to reduce the mutual coupling in a Yagi-antenna array. ML-DMU is a three-layer structure which is composed of two types of decoupling unit named top and bottom unit, middle unit, respectively. On this basis, the |S21| of proposed array is reduced to less than -23 dB from 2.36 GHz to 3.02 GHz while the antenna volume is not changed. The maximum gain of antenna element in the proposed antenna is 6.56 dBi at 3GHz, which is greater than the antenna without ML-DMU, but smaller than a single antenna element. Compared with other composite decoupling structures, the decoupling structure proposed in this paper has a more stable radiation performance and is simple and easy to install, which makes it have a good prospect in the field of 5G communication and the field of near-earth ground penetrating radar.

A deadbeat control method based on an improved parameter identification algorithm is proposed to improve the control accuracy and rapidity of permanent magnet synchronous motorized spindle (PMSMS). Firstly, based on the mathematical model of PMSMS and Euler discretization formula, the current prediction equation is established. Secondly, the deadbeat control logic is described; the deadbeat control model is established; and the influence of parameters on the system stability is analyzed. Thirdly, in order to improve the parameter robustness of deadbeat control, an improved adaptive parameter identification algorithm is proposed, which combines the least mean square algorithm and the recursive least square algorithm. Based on the voltage equation, the inductance and flux linkage parameters are identified, and then a more accurate parameter identification effect is achieved. Finally, the proposed algorithm is verified by experiments on the experimental platform. Experimental results show that the proposed algorithm has better control accuracy, faster response speed and stronger stability than vector control method and traditional deadbeat control method.

Accurately identifying and calibrating reinforcement bars in concrete is a significant challenge due to their invisibility. This paper proposes a deep learning-based method using magnetic resonance eddy penetrating imaging (MREPI) to acquire data on steel bars embedded in concrete. The data is processed into images and input into the Skel-Unet neural network to extract angle and position information of the central axis of the steel bars. Based on this information, the steel bar diameters are determined. A novel image reconstruction method is also introduced to integrate rebar dimension variations for precise calibration. Experimental results show that the Skel-Unet model achieves high accuracy, with training and testing loss values below 0.01, and F1 score reaches 0.7436. The reconstructed images clearly delineate the position, dimensions, and orientation of the rebars, enhancing calibration and nondestructive testing in structural health monitoring.

This paper presents a switchable terahertz metamaterial device based on vanadium dioxide (VO₂). By leveraging its phase transition properties, the device achieves broadband absorption and polarization conversion functionality through the insulator-to-metal transition (IMT) induced by temperature modulation. When VO₂ is metallic, the device functions as a broadband absorber. achieving an absorption rate exceeding 90% within the frequency range of 2.2 to 4.4 THz. Conversely, when VO₂ is in its insulating state, the device enables polarization conversion of incident terahertz waves. Simulation results reveal that in this state, the cross-polarized reflection coefficient (Ryx) exceeds 0.8, while the co-polarized reflection coefficient (Rxx) is significantly suppressed, indicating efficient conversion from co-polarization to cross-polarization within the 1.4 to 2.1 THz range. Notably, the polarization conversion rate approaches unity in this frequency band. Additionally, the study investigates the influence of the structure's geometric parameters, incident angle, and polarization angle on its performance. The results highlight the device's robust tolerance to variations in these parameters, as well as its low manufacturing precision requirements. The proposed multifunctional switchable terahertz metamaterial device holds significant potential for applications in terahertz research, polarization filtering, and terahertz invisibility technologies.

Coaxial magnetic gear (CMG) with magnetic field modulation mechanism features high torque density, non-contact transmis-sion, and overload automatic protection, making it an optimal substitute for mechanical gears. Considering the unbalanced mag-netic pull caused by the modulation effect of magnetic field and the component eccentricities, the deformations of the key fer-romagnetic pole-pieces (FPs) are analyzed with and without magnetic-force-structure multi-field coupling. Then, the segmenta-tion and reinforcement ideas based on bionic-bamboo are proposed in order to reduce the deformation of FPs. The functional relationships among FPs structural parameters, the output torque of CMG and the deformation of FPs are established with the orthogonal test method and response surface method. Based on NSGA-Ⅲ, the optimal parameters of FPs are obtained, and the corresponding deformation is greatly reduced. Finally, it is proved that the bionic-bamboo FPs can effectively reduce its defor-mation by the experiment and finite element simulation.

This paper presents a low phase noise positive feedback type Push-Push oscillator employing a balanced bandpass filter (BPF). The BPF consists of an array of split-ring resonators and functions as a frequency selective element in the common feedback loop of the oscillator. Two positive feedback oscillators are coupled to create the 180-degree differential signals required for the implementation of a Push-Push oscillator. The proposed oscillator is analyzed and fabricated. The measured results show that the oscillator works at 15.15 GHz of the second harmonic frequency with an output power of -5.6 dBm. Furthermore, the suppression of fundamental frequency signal is 25.2 dB. Excellent phase noise performance of -100.37 dBc/Hz at 100-kHz offset frequency and -127.13 dBc/Hz at 1-MHz offset frequency is obtained.

This paper presents the design and comprehensive measurements of a high-performance 8-element linear and a compact high-gain 32-element planar antenna array covering the n257 (26.5-29.5 GHz) FR-2 millimeter-wave (mmWave) band. First, an 8-element series-fed linear array is designed offering a fan-shaped pattern for 5G point-to-multipoint connectivity. Then a 4-way corporate-series feed network is designed for a high-gain 32-element compact and directive array for point-to-point mmWave connectivity. Comprehensive over-the-air (OTA) measurements are conducted using a state-of-the-art compact antenna test range (CATR) system, enabling precise characterization of radiation patterns across a 180° span in the azimuth and elevation planes. The planar array achieves a peak measured gain of 18.45 dBi at 28.5 GHz, with half-power beamwidths ranging from 11°-13° (elevation) and 23°-27° (azimuth) across the band of interest. The measured results match closely with the simulation results. The measurement results match well with the simulations. The designed antenna array is versatile, applicable to various emerging 5G and beyond mmWave applications such as outdoor fixed wireless access, mmWave near-field focusing, high-resolution indoor radar systems, 28 GHz Local Multipoint Distribution Service (LMDS) as well as the characterization of mmWave path loss and channel sounding in diverse indoor environments.

Despite the apparent simplicity, the problem of refraction of electromagnetic waves at the planar interface between two media has an incredibly rich spectrum of unusual phenomena. An example is the paradox when an electromagnetic wave impinges on the interface between a hyperbolic medium and an isotropic dielectric. At specific orientations of the optical axis of the hyperbolic medium relative to the interface, the reflected and transmitted waves can can disappear entirely, which contradicts reciprocity. In this paper, we analyze the above mentioned paradox and present its resolution by introducing infinitesimal losses in the hyperbolic medium. We show that the reflected wave exists but becomes ultimately localized at the interface when the losses become vanishing. Consequently, all the energy scattered into the reflected channel is absorbed near the interface. We support our reasoning with analytical calculations, numerical simulations, and an experiment with self-complementary metasurfaces in the microwave range.

The design, fabrication, and measurement of a 70 mm × 60 mm × 1.6 mm high-bandwidth Cantor fractal slotted defected ground surface (DGS) antenna for the microwave C-band (4-8 GHz) are presented in this study. This multiband antenna has the best performance ever because it combines a Cantor-inverted Cantor fractal slot with a microstrip quarter-wave transformer feeding network. With simulated operating bands spanning 3.37-3.48 GHz, 4.22-5.67 GHz, and 6.74-8.25 GHz, this antenna demonstrates exceptional simulated impedance bandwidths of 110 MHz, 1.43 GHz, and 1.51 GHz with simulated reflection coefficients of -27.22 dB, -28.23 dB, and -14.71 dB at resonance frequencies of 3.44 GHz, 5.03 GHz, and 7.17 GHz, respectively. Furthermore, the antenna exhibits simulated high gains of 5.6 dB, at 5.03 GHz resonating frequency. The introduction of a split ring resonator (SRR) at the ground surface unlocks the complete simulated bandwidth of 4.13-8.14 GHz and boosts the simulated gain to 6.1 dB. The design of this SRR at 5.03 GHz shifts one band from 3.44 GHz to 2.97 GHz with simulated bandwidth of 60 MHz. The VSWR value of this design is very close to 1. Consequently, its good impedance matching enhances the antenna's wideband performance. This is beneficial because patch antennas usually have a limited bandwidth. In addition, the antenna simulation displays an exactly symmetrical radiation pattern with current densities of 268 A/m and 155 A/m at 5.03 GHz with and without SRR, respectively.

This study presents a compact and tunable microstrip of a dual-path wideband filter that employs coupled-lines and varactors to address the needs of 4G/sub-6 GHz 5G communication systems. This work integrates tunable methods inspired by wideband parallel coupled line-based topologies to realize a reconfigurable solution achieving a 34% frequency tuning range (1.13-1.51 GHz) while maintaining a low insertion loss of approximately below 1 dB. Specifically, the proposed microstrip-based filter, which is designed, uses parallel coupled-line resonators with a quarter-wavelength length, enabling a broad tuning range between 1.27 and 1.54 GHz. Adjusting the coupling strengths of both adjacent and non-adjacent resonators, the filter can be shifted within this frequency band without compromising performance. Therefore, to achieve the desired level of control, two identical varactor diodes and biasing circuitry are meticulously selected for their stable and repeatable capacitance-voltage characteristics to adjust the filter's resonant frequency. The optimal positions for these tuning circuits are determined based on the resulting capacitance, which is crucial for achieving a wide tuning range. Simulation and measurement confirm that this reconfigurable microstrip filter, implemented on a 60.7 x 35.4 mm² footprint, benefits not only from a reduced footprint but also from the ability to target multiple frequency bands with minimal hardware modifications, delivering the intended performance for modern wireless front ends.

In this letter, a novel, compact bandpass filter architecture that leverages a quadruple-mode stepped impedance resonator (SIR) is introduced. This design is predicated on the principles of odd-even-mode analysis, which has been meticulously applied twice to elucidate the resonator's operational dynamics. The distinct boundary conditions inherent to the odd-odd and even-odd degenerate modes result in their splitting, a phenomenon that is pivotal to the filter's performance characteristics. The equivalent circuits representing the quadruple modes function as quarter-wavelength SIRs, a design choice that inherently confers a compact form factor upon the resonator. This is achieved without compromising the filter's functionality, as each mode contributes to the overall filtering response in a manner that is both efficient and space-saving. Furthermore, the filter is characterized by a 20-dB stopband rejection that extends up to 6.9 GHz, which corresponds to 3.8 times of the fundamental frequency (f₀). This outstanding stopband performance is a testament to the design's effectiveness in attenuating unwanted signals while maintaining a compact footprint.

The work presented in this paper has great significance in improving electromagnetic models based on the strong coupling between the magnetic and electric fields transient equations while considering a realistic random multi-turn stranded winding where eddy currents, proximity and skin effects occur. The space-time partial differential equations of electromagnetic field expressed in terms of magnetic vector potential under nonlinear (B-H) magnetic materials curves handled by the iterative Newton-Raphson (NR) algorithm are simultaneously coupled with the voltage fed multi-turns electric circuits equations based on Kirchhoff's voltage law for each turn coil current loop. The magnetic field-multi-turn electric circuit coupled model solved using the time-stepping finite element method (FEM) formulation is dedicated to highly accurate computation of electromagnetic-mechanical devices. The developed FEM tools implemented under Matlab software are used to the modeling of the permanent magnet synchronous motor (PMSM) behavior through the physical quantities such as magnetic flux density, electric current, electromagnetic torque, and angular velocity.

Emerging technologies in future 6G mobile systems are expected to achieve unprecedented access rates and network capacity, but are hindered by high hardware cost and complexity, especially in terms of RF chain requirements. The wireless communication paradigm enabled by programmable metasurfaces, which leverages their ability to precisely manipulate electromagnetic waves, facilitates RF chain-free transmitters and spatial down-conversion receivers, revolutionizing wireless transceiver architectures by simplifying hardware complexity and reducing costs. In this review, we provide the recent advances of intelligent metasurfaces in the applications of wireless communication. We firstly summarize the mainstream realizations of reconfigurable metasurfaces at microwave and then focus on the advances of intelligent metasurfaces with spatial/spatiotemporal modulations. We conclude by analysing the challenges in this research area and surveying new possible directions.