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 details the design and analysis of a tri-arm-shaped microstrip patch antenna with a partial ground plane, intended for wearable applications. The proposed antenna is designed on a flexible jeans substrate and operates within the Industrial, Scientific, and Medical (ISM) band (2.40-2.48 GHz). It features a low-profile structure with overall dimensions of 40×20×1.2 mm³, impedance bandwidth of 580 MHz, and radiation efficiency of 82%. Impedance matching and miniaturization were achieved in the design through the use of the stub loading technique. Furthermore, on-body measurements, such as bending and crumpling analyses, demonstrated its robust performance with good return loss values. The Specific Absorption Rate complies with the safety limits, and the proposed conformal antenna is reliable for wearable applications.

This paper presents a wideband four-port microstrip antenna operating from 2.75 GHz to 6.75 GHz with frequency reconfigurability and controllable notch characteristics. The antenna employs an asymmetric radiating structure to realize circular polarization around 5.5 GHz, while multilayer graphene(MLG) pads are introduced to enable bias-controlled frequency tuning and adjustable band rejection. The four-port configuration, implemented on an RT/Duroid 5880 substrate (ε_r = 2.2, thickness = 1.6 mm), achieves inter-element isolation better than 20 dB without additional decoupling structures. The proposed design also exhibits strong diversity performance with an envelope correlation coefficient below 0.02 and diversity gain above 9.97 dB. The results demonstrate that the proposed antenna provides a compact and low-complexity solution for wideband and reconfigurable sub-6 GHz wireless communication applications.

An innovative analysis of a negative group delay (NGD) circuit exhibiting a dual bandpass (BP) characteristic is presented. The passive BP-NGD topology consists, essentially, of parallel RLC resonant networks. The BP-NGD topology is characterized by the NGD value, the NGD center frequency, and the attenuation, as functions of the constituent RLC resonant networks. The dual BP-NGD topology is designed using series impedances, which are composed of two distinct parallel RLC networks. After considering the reduced-order model of the passive cell within the NGD frequency range, which enables the determination of component values for the dual BP-NGD circuit, the circuit is formulated as a function of the desired NGD values and center frequencies. The feasibility of the design theory is verified through a proof-of-concept (PoC), designed to operate with the following specifications (1 MHz, -20 μs, -8 dB) and (2 MHz, -20 μs, -8 dB). First, a frequency-domain analysis of the PoC demonstrates the dual BP-NGD behavior, exhibiting an attenuation of approximately 8 dB. Subsequently, time-domain analyses were conducted using input signals with amplitude modulation on sinusoidal carriers at frequencies of 1 MHz, 1.5 MHz, and 2 MHz. The obtained results highlight the possibility of generating output signal envelopes that exhibit a temporal advancement relative to the input ones, provided that the input signal spectrum falls within the NGD bandwidth. However, the output envelope exhibits a positive delay when the input signal spectrum lies outside the NGD frequency band. A potential application principle for the dual BP-NGD circuit is discussed, specifically for the compensation of delay dispersion in electronic and communication systems.

This paper presents a compact, low-profile, single-layer filtering antenna. The antenna features a simple structure, consisting of a substrate, two pairs of U-shaped defected ground structures, a symmetric dumbbell-shaped radiating patch, and a microstrip cross-feed line with asymmetric branches. The symmetric dumbbell-shaped patch and the asymmetric branch feedline collaboratively introduce additional high-frequency resonances, thereby broadening the impedance bandwidth. Furthermore, two pairs of U-shaped slots are etched into the bottom layer to introduce two radiation nulls on both sides of the passband, enhancing the frequency selectivity at the band edges and optimizing the antenna's radiation and filtering performance. To validate the proposed design, a prototype of the antenna was fabricated and measured. The measured and simulated results are in good agreement. The design achieves a wide impedance bandwidth of 48.6% from 3.7 to 6.18 GHz (centered at 5 GHz), a peak realized gain of 4.5 dBi, and a compact overall size of 35 mm × 29 mm × 0.8 mm. Moreover, the antenna structure is simple and easy to fabricate. Benefiting from its superior radiation performance and filtering characteristics, the proposed antenna is well-suited for wireless communication applications in the 5G Sub-6 GHz and WiFi-6E bands.

To address the shortcomings of conventional permanent magnet synchronous motors (CPMSMs), such as the inability to adjust the permanent magnet field and a narrow speed control range, this paper proposes a variable leakage flux permanent magnet synchronous motor (HPM-VLFM) based on a hybrid series-parallel permanent magnet configuration. This motor achieves a variable leakage flux permanent magnet motor (VLFM) by designing a magnetic barrier on the q-axis, and further realizes the HPM-VLFM by designing ferrite permanent magnets with a series-parallel magnetic circuit. First, this paper introduces a rotor topology of the proposed motor and establishes its equivalent magnetic circuit to elucidate its operating principle. Second, sensitivity analysis and response surface analysis are employed to investigate the relationship between parameters and response variables, and an optimal solution is obtained based on the given constraints. Finally, based on two-dimensional finite element analysis (FEA), the electromagnetic characteristics of the proposed motor were analyzed in detail, including variable flux leakage characteristics, no-load characteristics, inductance characteristics, and torque efficiency characteristics. The results indicate that the HPM-VLFM has a wider speed control range and higher efficiency.

We have developed a carbon nanotube organic silicone rubber (CNT-OSR) composite medium, composed of methyl trifluoropropyl silicone rubber as the matrix, with different mass fractions of carbon nanotubes added and formed through vulcanization using a bis (cyclopentadiene) vulcanizing agent. The CNT-OSR composite media with carbon nanotube contents of 2wt%, 5wt%, and 8wt% were tested, and the maximum absorption and shielding efficiencies of the media for terahertz waves in the 0.5-1.0 THz frequency range were found to be 69.77 dB, 76.28 dB, and 63.69 dB, respectively. Through impedance matching theory analysis, the absorption and shielding effectiveness of the medium for terahertz waves were confirmed. Additionally, the composite medium exhibits excellent hydrophobic properties. It provides a simple and feasible approach for developing lightweight, efficient, and multifunctional terahertz wave absorbing and shielding materials for the next generation of terahertz wireless communication.

Eddy current effects in underwater wireless power transfer (UWPT) systems introduced additional losses and shifted circuit parameters, severely undermining precision of conventional primary-side identification. To address this issue, this study investigated the mechanism of eddy current loss and established an improved mutual inductance model by introducing an equivalent eddy current resistance. Based on this, a primary-side sensing identification method was proposed to achieve the decoupled identification of mutual inductance, load resistance, and eddy current resistance by measuring the input impedance Z_in at multiple frequencies. Experimental results confirmed that at a resonant frequency of 85 kHz, the identification errors for eddy current resistance, mutual inductance, and load resistance were within 4%, 3%, and 5%, respectively. Furthermore, the average error remained below 3.5% across various salinities, lateral misalignments, and load conditions. This study provided a reliable technical foundation for optimizing the performance and ensuring stable operation of UWPT systems in complex underwater environments.

The existing research on axial magnetic field (AMF) contacts in vacuum interrupters mostly focuses on power frequency or low current conditions and lacks in-depth optimization of magnetic field characteristics and contact structure parameters under short-circuit current impact. Therefore, the AMF characteristics of the vacuum interrupter under short-circuit current excitation are studied, and the contact structure parameters are optimized. Firstly, a three-dimensional transient electromagnetic field model of the vacuum interrupter, excited by the measured short-circuit current, is constructed, and the effects of four key geometric parameters - contact slotting angle, cup finger angle, slotting length, and slotting width - on the peak AMF are quantified. Secondly, the orthogonal test method is used to screen significant factors, and it is concluded that cup finger angle is the most critical parameter among the four. Finally, a quadratic regression model is constructed by combining the response surface model (RSM) to explore parameter interactions. The theoretical optimum is obtained and further refined through boundary verification to yield the actual optimal parameter combination. This study guides the design of AMF contacts in vacuum circuit breakers under short-circuit conditions.

This paper presents a design methodology for a concurrent dual-band integrated filtering high-efficiency power amplifier (PA) through the coordinated use of a dual-band harmonic control network (DB-HCN) realized with an adjustable-transmission-zero dualband filtering matching network (ATZ-DB-FMN). To improve the efficiency under dual-band operation, the proposed DB-HCN enables simultaneous impedance control up to the third harmonic at both operating frequencies. To realize a compact integrated structure, the proposed ATZ-DB-FMN provides dual-band impedance matching,and introduces transmission zeros (TZs) on both sides of the passbands and in the inter-band region. In particular, the inter-band TZ is adjustable and can be used to suppress interference at a desired frequency between the two passbands. To validate the proposed method, a prototype operating at 2.4 and 3.6 GHz was designed and fabricated, with the adjustable TZ set at 3.1 GHz. The measured results show drain efficiencies of 78.6% and 75.3% and output powers of 40.05 dBm and 40.2 dBm at 2.4 and 3.6 GHz, respectively. The effective tuning range of the TZ is 2.6-3.4 GHz, and the measured power gain at 3.1 GHz is -26.5 dB, confirming effective inter-band suppression. These results demonstrate that the proposed design method can simultaneously achieve dual-band high efficiency, integrated filtering, and adjustable inter-band suppression.

The dielectric constant, which is the real part of the complex permittivity, of composite materials at microwave frequencies was investigated in this study. Ceramics of titanium dioxide, calcium titanate, and strontium titanate with high dielectric constants of 100, 170, and 300, respectively, were selected. Ceramic powders were spread in the polyethylene matrix to form composite samples. The dielectric constants of the composite samples were measured to determine their matching conditions with the mathematical curves of five well-known mixture equations. These five mixture rules were then applied to estimate the dielectric constants of the three selected ceramics from the measured dielectric properties of the composite samples with various volume percentages of ceramic fillers. The mathematical equations of the potential theory errors of the five mixture rules for the dielectric constant estimation were derived and discussed. One of the five rules was selected and modified to obtain a new empirical mixture equation. This proposed empirical equation can significantly improve the accuracy of dielectric constant measurements for the selected ceramic materials. An empirical mathematical relation of the new mixing rule with the dielectric constant of the ceramic is then concluded.

The design of large-scale coding metasurfaces poses significant computational challenges, often limited by the prohibitive time required for full-wave simulations necessary for optimization. This paper proposes an efficient design strategy based on a Hybrid Genetic Algorithm, validated through the design, fabrication, and characterization of an X-band metasurface for Radar Cross Section reduction. The proposed design strategy relies on a two-stage optimization process: a fast pre-optimization phase, based on the analytical Huygens-Fresnel principle, generates a preliminary solution which is subsequently refined by a second optimization stage utilizing full-wave simulations. Specifically, the optimization targets a 1-bit coding scheme, where meta-atoms switch between two distinct states with a phase difference of 180 ± 37°. This hybrid approach demonstrates optimal convergence, reducing computational time by 25% compared to traditional full-wave-only techniques. Furthermore, a novel ``spiralling cross'' unit cell topology is introduced. Owing to its delay-line geometry, this structure provides additional degrees of freedom for spectral tuning and supports intermediate phase shifts, thus enabling encoding schemes beyond traditional 1-bit configurations. Experimental results confirm the validity of the proposed approach, demonstrating how the combination of versatile geometry and hybrid optimization effectively overcomes the trade-offs between numerical accuracy and computational efficiency.

To address the need to differentiate between dielectric and perfect electric conductor (PEC) conformal methods in the finite-difference time-domain (FDTD), this study proposes a conformal approach based on the harmonic mean to achieve a unified formulation. In this approach, the relevant electromagnetic parameters are weighted using harmonic mean weighting, enabling a conformal implementation within the FDTD framework. Both dielectric and PEC conformality are incorporated into a single mathematical framework, allowing for a unified treatment in the FDTD. The proposed method provides a consistent formulation that can be seamlessly integrated with standard FDTD procedures while ensuring high compatibility and accuracy of the results. The conformal method based on harmonic mean requires only 60% of the computational time and 36% of the memory compared to the CST method, indicating its high computational efficiency. Furthermore, it demonstrates strong applicability to complex biological models, such as specific absorption rate (SAR) calculations in the human head. This approach is particularly well suited for RF device design and biomedical applications, offering improved modeling efficiency and reliability.

When designing the parameters of electromagnetic interference filters in BUCK rectifiers using a particle swarm optimization algorithm, the resulting solution set tends to fall into local optima, resulting in a lower cost-performance ratio for the filters. Therefore, an optimization scheme for the parameter design is proposed. First, a multi-objective optimization model is established, with common-mode capacitance and inductance, as well as differential-mode capacitance as decision variables, conducted noise and cost as the objective function, and conducted noise limits and leakage current as constraints. Next, three improvements are made to the conventional algorithm, classifying initialization for the particle population, dividing the total number of iterations into stages with differentiated handling, and implementing an adaptive early termination for iterations, thereby an improved algorithm is obtained. Finally, both the improved and conventional algorithms are applied to solve the optimization model, yielding two types of optimal solutions: performance-prioritized and cost-prioritized solutions. The comparison results show that, between the two optimal solutions, the performance of the improved algorithm is similar to that of the conventional algorithm, but its cost is reduced by 28.37% and 53.14%, respectively. Meanwhile, the Pareto solution set obtained by the improved algorithm is more widely distributed, avoiding local optima, and the iterative convergence efficiency of the improved algorithm was improved by 81%.

A high-performance Two-Dimensional Photonic Crystal (2DPC) demultiplexer is proposed for application in Dense Wavelength Division Multiplexing (DWDM). Simultaneous high-field confinement and higher modal coupling are achieved using a new hybrid cavity geometry design, which consists of a square cavity with an inner rod radius (r = 110 nm) and a circular cavity with an outer rod radius (r = 100 nm). It is an operating silicon platform featuring a square lattice, bus waveguide, and four drop ports. Plane Wave Expansion (PWE) and Finite Difference Time Domain (FDTD) simulation methods reveal a large photonic bandgap (0.27-0.37a/λ) and excellent spectral performance, including a 98.75% average transmission efficiency, a high Q-factor of 7281, and precise 0.8 nm channel separation. System-level verification, Lumerical INTERCONNECT, and eye diagram and BER analyses were used to test signal integrity. The hybrid geometry also has a smaller footprint and improved integration, making it a suitable design for next-generation optical communication systems.

This article describes a four-element ultra-wideband (UWB) Multiple-Input Multiple-Output (MIMO) antenna for the Sub-7 GHz. The antenna element is an elliptical patch slot antenna with a coplanar waveguide (CPW) feed. To make the bandwidth wider, we add step-by-step parasitic stubs based on the results of the Characteristic Mode Analysis (CMA) analysis, which can control multiple modes better. The four-element antenna is connected to a common ground structure with a central cross-shaped isolation stub and also inhibit the propagation of surface waves. It can be used in the range from 1.08 GHz to 8.70 GHz (155.8%), which is fabricated on a low-cost FR4 substrate. In this range, the isolation between antenna elements exceeds 20 dB. The performance of the design is very good. The envelope correlation coefficient (ECC) is less than 0.02, and the diversity gain (DG) is greater than 9.96.

Accurate prediction of magnetic interaction forces is important for electromagnetic actuators, inductive coupling systems, and calibration devices. This paper presents a unified analytical and numerical framework for evaluating the axial magnetic force between two finite-dimensional, perfectly coaxial, air-core cylindrical coils under steady currents. The model assumes uniform purely azimuthal current density and neglects radial and axial current components, winding-pitch effects, magnetic materials, misalignment, and transient phenomena. Starting from the Biot-Savart law and Lorentz force formulation, the coil-coil interaction integral is derived and reduced using cylindrical symmetry, leaving only the axial resultant force. Three complementary methods are developed in MATLAB: a semi-analytical elliptic-integral formulation, a direct trapezoidal numerical-integration method, and a filament-based mutual-inductance method. The methods are computationally benchmarked for representative thin-wall, moderate finite-radius, mixed-radius, and large finite-radius coil geometries. The results show consistent force predictions, with relative half-spread values below approximately 4% for the cases considered. Discretization sensitivity and error-source analysis are included to clarify numerical accuracy and convergence. The proposed framework provides a transparent benchmark for axial force evaluation in idealized coaxial air-core coil systems.

The proposed symmetric quad circular radiator antenna with a semicircular etched-slot DGS was designed and fabricated on an FR4 substrate of size 50 × 50 × 1.6 mm³. The antenna provides impedance bandwidths of 2.24-2.94 GHz, 3.84-3.98 GHz, and 4.92-5.06 GHz, with resonant frequencies observed at 2.44 GHz (-40.3 dB), 2.86 GHz (-17.9 dB), 3.92 GHz (-14.9 dB), and 4.98 GHz (-10.6 dB). These operating bands make the antenna suitable for WLAN, ISM, and other sub-6 GHz wireless communication systems. The antenna also achieves a realized gain above 5 dB at the operating frequencies, indicating stable radiation characteristics. The diversity performance was evaluated using standard metrics. The ECC remains below 0.5, which lies within the acceptable range for diversity operation. In addition, the diversity gain varies between 9.88 and 10.02 dB, while the channel capacity loss stays below 0.6 bits/s/Hz across the frequency range. A compact symmetric quad circular radiator antenna incorporating a three-segment semi-circular bridge along with a semicircular etched-slot mdefected ground structure (DGS) is presented for multi-band wireless communication applications. These results confirm that the proposed antenna provides reliable radiation and diversity performance for practical wireless communication applications.

This paper presents a miniaturized implantable antenna with multi-resonances operating at the Medical Implant Communication Service (MICS) band (402-405) and Industrial, and Medical (ISM) band (433.1-434.8 MHz, 868-868.6 MHz, and 902-928 MHz) for advanced biomedical applications. The proposed antenna is notably compact, occupying a volume of 10 × 10 × 1.27 mm³ (equivalent to 127 mm³). Multi-resonance frequencies are generated by incorporating a shorting pin and a meandered resonator structure. The proposed antenna exhibited wideband characteristics, with bandwidth ratios of 39.5% and 28.8% at 402 and 915 MHz, respectively. Moreover, the performance of the implantable antenna was further validated in different organs within a realistic human body model, such as the heart, stomach, small intestine and colon. The practical performance of the fabricated antenna prototype was validated using a tissue-equivalent liquid phantom. Additionally, to evaluate the transmission performance under real-world scenarios, an on-body antenna matched with the implanted antenna was designed for an in-body to on-body transmission setup. Under the maximum safe input power of 25 μW, link budget analysis demonstrates that data can be transmitted at a rate of 10 Mbps over distances of 9.5 and 12 cm in the MICS and ISM bands, respectively. The simulated and experimental results verified the feasibility of substituting a realistic human model with a homogeneous muscle model in the design of an implantable antenna system and demonstrated a strong potential for diverse implantation scenarios and future biotelemetry applications.