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.

This study presents the design, simulation, and fabrication of a compact patch antenna with metamaterials, dedicated to biomedical applications. The proposed antenna was implemented on an FR4 substrate and resonated at a center frequency of 2.48 GHz. By the integration of metamaterial (MTM) unit cells as the primary radiating element, the design achieves performance improvements compared with traditional patch antennas. The return loss was reduced from -13.45 to -67.20 dB, which indicates improved impedance matching. In addition, the antenna showed enhanced radiation characteristics, with a gain of 1.96 dB and a directivity of 3.10 dB. As the antenna was designed for biomedical use, specific absorption rate (SAR) analysis was conducted to ensure compliance with safety standards. A prototype of the antenna was fabricated to validate the simulation results, and the measured results matched the simulations, which confirms the reliability of the suggested design. The simulation results were obtained using HFSS and CST. Overall, the results demonstrate that the proposed metamaterials-based antenna is a strong candidate for integration into biomedical devices.

To meet the requirements of antenna miniaturization and wide impedance bandwidth in UWB systems, a novel compact UWB Vivaldi antenna is presented in this work. Based on the conventional planar Vivaldi configuration, the radiating arms are etched with elliptical slots, and the front end of the tapered slot is loaded with concentric arc parasitic patches to regulate the surface current distribution and enhance broadband impedance matching. Simulated and measured results demonstrate that the presented antenna achieves a reflection coefficient below -10 dB over the frequency range of 6.61-21.06 GHz, corresponding to a relative bandwidth of 104.45%, with a compact size of 14.5 × 19.8 × 0.51 mm³, while maintaining a single-layer planar structure without increasing structural complexity. It is also indicated that stable end-fire radiation characteristics and low cross-polarization levels are maintained at several representative frequencies. The presented design simultaneously realizes significant size reduction and ultra-wide impedance bandwidth, providing a simple and practical solution for compact UWB Vivaldi antenna applications.

To achieve the dynamic decoupling of a permanent magnet-assisted bearingless synchronous reluctance motor (PMa-BSynRM), this study proposes an innovative decoupling control strategy. In this method, the inverse system is constructed by improving a genetic algorithm optimized fuzzy neural network to achieve decoupling control. Firstly, this article elucidates the structure and working principle of PMa-BSynRM, establishes a mathematical model, and conducts reversibility analysis. Secondly, by optimizing the fuzzy neural network through improved genetic algorithm, a system inverse is derived to achieve the decoupling of the initial system, transforming it into a linear-like system. Thirdly, the decoupling performance of the proposed control method for a 5-degree-of-freedom (5-DOF) system is validated through simulation. Finally, experimental validation is conducted on both 2-DOF and 3-DOF subsystems. Simulation results for the 5-DOF system and subsystem experiments indicate that the proposed method exhibits excellent control accuracy, rapid convergence, and dynamic anti-interference performance.

A corner-truncated (linear and circular) antenna with a compressed reduced ground and parasitically loaded with a single unit of SRR was successfully designed, fabricated, tested, and investigated for 5G wireless communications. The truncated corner with a full ground shifted the narrow bandwidth and resonating frequency (5.10 GHz) from right to left (2.81 GHz). The ground-reduced length and compressed width enable a transition from a narrow band to a wide band, and the antenna is tuned to approximately 3.5 GHz. The antenna is parasitically loaded with an SRR that provides an additional resonating frequency within a wide bandwidth (2.82-5.21 GHz). The antenna achieves wideband with dual tuning frequencies within the band. The antenna has gains of 3.93 and 4.25 dBi at the tuned frequencies, respectively. The truncated ground enhances the antenna gain (3.33 to 4.25 dBi) and impedance bandwidth from narrow band (5.07-5.17 GHz) to wideband. The truncation of the corner and reduced ground length degrades the radiation efficiencies, while ground and substrate dimension (length and width) compression compensatea for the reduced values of efficiencies. The proposed antenna is best suited for Wi-Fi 5 (IEEE 802.11ac), Wi-Fi 6 (IEEE 802.11ax), n48, n77, n78, and n79 applications. The antenna was measured and compared with the simulated results and radiation patterns. They were found in approximations, which helped confirm the antenna design and investigations.

To reduce the implementation complexity of reconfigurable sparse arrays, this study proposes a low-complexity group-sparse orthogonal matching pursuit (G-OMP) algorithm with a minimum spacing constraint for synthesizing sparse arrays with multiple beam-shared element positions. An off-grid OMP algorithm with a minimum spacing constraint can mitigate the accuracy degradation caused by fixed-grid discretization, thereby ensuring the practical feasibility of engineering implementations. To enable beam reconfigurability, a group-sparse structure is incorporated into the off-grid OMP algorithm, and a multi-beam group-sparse reconstruction algorithm based on a dynamic grouping strategy is proposed, allowing multiple beams to share sparse array element positions. Simulation results show that, under the simulation parameters, the proposed algorithm achieves low computational complexity while maintaining good radiation pattern performance.

The relative value of the stored energy in the dielectric and that in the surroundings for a cylindrical dielectric resonator in a closed metal cavity was studied using a simple electromagnetic field theory model. The influence of this factor on the measurements of the loss tangents of dielectric samples with different dielectric properties and dimensions at their microwave resonant frequencies was discussed. In addition to the traditional calculation method, a perturbation method with a much simpler computation procedure was also adopted for the energy factor calculation, and its accuracy was compared with that of the traditional method.

A low-profile, dual-band, shared-aperture antenna with a large frequency ratio is presented, based on a meshed patch and an AMC-backed Fabry-Perot (F-P) cavity. By taking advantage of the weak frequency sensitivity of grid slotting in meshed patches, the upper meshed patch is utilized as both the parasitic patch for the low-frequency antenna and the partially reflective surface (PRS) for the high-frequency F-P cavity, thereby simplifying the overall structure. Meanwhile, the AMC ground is employed to control the reflection phase and reduce the cavity height to λ/4, which enables both antennas to share the same aperture within an 8-mm profile. A prototype is fabricated and tested at 1.6 GHz and 15.14-15.46 GHz. Measured results demonstrate a frequency ratio of 1:9.6, a peak gain of 6.2 dBi at 1.6 GHz, a peak gain of 11.8 dBi in the high-frequency band, and a port isolation better than 17 dB. The proposed antenna features compact size, low profile, and efficient structural reuse, making it attractive for integrated multi-band communication systems.

We present a review of homogenization models of microwave wire media with different geometries. We begin with a simple (uniaxial) wire medium and then consider more complex types of wire media - double, triple, and interlaced wire media - which remain underexplored. We discuss boundary problems with wire media and the most important physical effects revealed using the reviewed homogenization models.

This study presents a method for generating multiple electromagnetic field minima in specified spatial regions. The relationship between the complex amplitudes of signals at receiving points and those of radiated signals is described using an S-parameter matrix. It is shown that the determination of the complex amplitudes of the radiated signals can be reduced to solving an underdetermined system of linear algebraic equations, which may be unstable because such a system can admit either infinitely many solutions or no solution. To address this issue, an optimization problem is formulated based on minimizing the squared error between the required and obtained electric field distributions. Its solution leads to a new system of linear algebraic equations, to which Tikhonov regularization is applied to ensure the stability and uniqueness of the solution. The proposed approach is validated by mathematical modeling for three electric field configurations, with the complex amplitudes of the radiated signals determined for each configuration. The modeling results confirm the correctness of the theoretical conclusions.

This work presents deep neural networks for the inverse design of an ITO-film angular-selective metasurface absorber. A tandem deep neural network (T-DNN) framework is developed for the inverse design of electromagnetic metasurfaces. A forward network is first trained independently to learn the complex physical mapping between metasurface structures and their electromagnetic responses. An inverse network is then trained in tandem with the pre-trained forward network, eliminating conventional parameter-by-parameter tuning and establishing a performance-driven pipeline that directly maps target electromagnetic responses to structural parameters. Using the trained network, several metasurface absorbers with distinct angular sensitivities are rapidly designed, and their angle-dependent applications are preliminarily investigated. Results show that deep learning enables the fast design of metasurface absorbers customized to realistic incident angle distributions, yielding efficient omnidirectional radar cross-section (RCS) reduction at sensitive angles. This work offers a new strategy for the fast design of omnidirectional scattering suppression.

This research presents the design and evaluation of a high-performance Ku-band microstrip patch antenna for satellite communications. The antenna incorporates a Defected Ground Structure (DGS) and a Defected Microstrip Structure (DMS) to achieve a wide impedance bandwidth and stable radiation characteristics. Etching slots into both the radiating element and ground plane enables the precise control of current distribution, thereby enhancing operational bandwidth. The antenna was modeled and optimized in CST Microwave Studio and HFSS to ensure consistent simulation results. Experimental results demonstrate effective operation from 15 to 18 GHz, with a return loss (S₁₁) below -10 dB. The strong agreement between simulation and measurement results confirms the reliability of the design. The antenna's compact form factor and wideband performance make it suitable for satellite-on-the-move (SOTM) and low-Earth-orbit (LEO) terminal applications.

This reply addresses the comment by Yun [1] regarding the sign errors in the Ω matrix terms for our recent paper on the transfer matrix method for general bianisotropic layers. The comment correctly identifies sign errors, which does lead to non-physical results. In this reply, we present an alternative construction method for Ω that has fewer opportunities for transcription errors over the original formulation. These corrections do not affect the remainder of the formulation and correction. However, it does affect the results of the second example in the original paper, which is corrected here.

An enhanced Vivaldi antenna operating in the ultra-wideband (UWB) region - featuring circular slots and a trapezium-shaped parasitic patch Vivaldi antenna (CSTPP-VA) - is presented in this article. The uniformly arranged slots contribute to a wide bandwidth, while the trapezoidal parasitic patch, located in the end-fire region, enhances impedance bandwidth and improves overall antenna gain. The CSTPP-VA operates over the 3.2-11 GHz frequency range with a peak gain of 9 dB. Compared to the conventional coplanar Vivaldi antenna, it exhibits a 3.6 dB gain improvement, demonstrating enhanced radiation performance.

This paper proposes a novel equivalent thermal network (ETN) model for permanent magnet vernier (PMV) machines, featuring a detailed in-slot mesh to address the challenges in analyzing the temperature distribution within the slot. The key innovation is the equivalent analytical mesh, which is the equivalent mesh derived through analytical methods. Firstly, a systematic in-slot mesh partitioning method is presented to solve the temperature distribution in the slot. The method includes detailed mathematical derivation and implementation processes. The novel mesh provides high computational accuracy while maintaining uniform modeling requirements. Secondly, an accelerated solution framework combining a lumped parameter thermal network (LPTN) with the ETN topology is introduced. This hybrid approach significantly reduces both computational time and modeling complexity for temperature field analysis. Finally, thermal testing was conducted on the PMV machine prototype. The accuracy of the proposed ETN model is validated compared to both computational fluid dynamics (CFD) simulations and experimental measurements.

Bearingless interior permanent magnet synchronous motors (BIPMSMs) have a simpler and more compact structure and incur a lower cost than motors supported by magnetic bearings. BIPMSMs offer the advantages of both magnetic bearings and conventional interior permanent magnet synchronous motors. However, rotor vibrations can severely degrade the performance and limit the application of BIPMSMs. Therefore, vibration suppression in BIPMSMs is investigated in this study. First, the factors causing rotor vibrations are analyzed, and the mathematical model of the unbalanced force that causes rotor vibrations is derived in terms of the rotor mass unbalance and inverter dead-time effect. Second, a vibration suppression strategy based on a variable sampling frequency repetitive controller is proposed to enable stable motor operation over a wide frequency range. The sampling frequency is dynamically adjusted according to the change in the vibration frequency to maintain a constant order of the repetitive controller. Finally, simulations and experiments are conducted to verify the effectiveness of the proposed vibration suppression strategy.

Position encoders for motors are susceptible to electromagnetic interference (EMI) in industrial environments, which distorts position signals and degrades motor control accuracy. This paper focuses on two prevalent types of EMI: the coupling interference of switching frequency from motor drives and wideband electromagnetic background noise. To analyze their impact, a simulation platform for a permanent magnet synchronous motor (PMSM) control system is established, examining the distortion of the encoder's electrical angle signal under varying coupling voltages. A filtering suppression strategy for the position angle, based on a phase-locked loop (PLL), is proposed and its effectiveness is thoroughly analyzed. Simulation results indicate that the coupling interference of switching frequency induces periodic spike pulses in the encoder's electrical angle waveform, whereas wideband background noise causes continuous, random fluctuations. The proposed suppression strategy demonstrates significant efficacy, achieving maximum reduction rates in electrical angle signal distortion of 80% and 80.8% for the two interference types, respectively. This method effectively mitigates the impact of electromagnetic interference on encoder signal integrity.

This study addresses the synthesis of shaped beams for linear antenna arrays under dynamic range ratio constraints on excitation amplitudes. When hardware limitations restrict excitation freedom, conventional methods suffer significant sidelobe degradation. The proposed approach jointly optimizes the element positions and excitations through iterative second-order cone programming. A distinguishing feature is the error-aware constraint formulation, which incorporates linearization error bounds, ensuring actual pattern compliance with the beam mask at each iteration. Adaptive trust-region control based on actual-to-predicted improvement ratios ensures robust convergence. Numerical experiments with flat-top and cosecant-squared beams demonstrated 7-12 dB sidelobe improvement over excitation-only methods under strict amplitude constraints. Compared with particle swarm optimization, the proposed method achieves superior sidelobe suppression while being orders of magnitude faster.

In this paper, we present a Microstrip feed slot ring resonator with a central circular disc antenna that operates at triple bands. The suggested antenna covers 5G, military, radar, and UWB applications. It resonates within 2.71 GHz-12 GHz at center frequencies of 4.13 GHz (S₁₁ = -17.9 dB), 8.53 GHz (S₁₁ = -38 dB), and 9.09 GHz (S₁₁ = -20 dB). Simulations of the ultrawideband antenna matched the manufactured devices. The proposed antenna has dimensions of 40 × 42 × 1.6 mm³ and is constructed on a cost-effective FR4 substrate. It achieves an operating impedance of less than -10 dB. The circular ring slot antenna shows remarkable capabilities, achieving multiband frequencies at 4.13 GHz, 8.53 GHz, and 9.09 GHz. The unique ultra-wideband design has a positive impact on gain and yields stable radiation characteristics, with surface currents contributing to a promising design. The design achieves a gain of about 5 dBi and a fractional bandwidth of roughly 128.7%.