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.

This paper presents a novel key-shaped miniaturized four-port MIMO antenna designed for ultra-wideband (UWB) applications. The proposed antenna consists of four orthogonally and symmetrically arranged key-shaped radiating elements. By integrating semi-circular patches at the edges of rectangular radiators, multiple resonance modes are excited to significantly broaden the impedance bandwidth and optimize matching. To suppress mutual coupling within a compact footprint, an enhanced cross-shaped defected ground structure (DGS) is implemented, which effectively blocks surface wave propagation by utilizing narrow rectangular stubs. Experimental results demonstrate that the antenna achieves a continuous impedance bandwidth from 4.4 to 26 GHz, corresponding to a fractional bandwidth of 141.5%. Throughout the operating band, the port isolation remains better than 28 dB, while the envelope correlation coefficient (ECC) is lower than 0.00013, ensuring excellent diversity performance. Furthermore, the antenna, fabricated on an FR4 substrate with a compact size of 47 × 47 × 1.6 mm³, maintains a radiation efficiency between 67.4% and 92.6%. With its superior bandwidth, high isolation, and exceptionally low correlation, the proposed design offers a robust solution for high-performance UWB communication systems.

A novel flexible hybrid rectenna for simultaneous RF energy harvesting (RF-EH) and dedicated wireless power transfer (WPT) is proposed. The rectenna comprises a notched broadband omnidirectional microstrip antenna (2.8-6.3 GHz with a 4.7 GHz notch) and a 4.7 GHz directional dielectric resonator antenna (DRA) located on the microstrip antenna. At the 4.7 GHz notch band, electromagnetic energy is confined around an L-shaped strip and a split-ring slot of the microstrip antenna, exciting a TM₂₀₁^z resonant mode in the DRA that produces a narrow radiation beam at 4.7 GHz. This enables a frequency-domain complementary operation: ambient energy is harvested across the broadband region for low-power applications, while dedicated power is efficiently received at 4.7 GHz for high-power operation. A broadband rectifier employing a dual-channel impedance matching architecture is further proposed, in which two parallel branches cooperatively extend the rectification bandwidth. Measurements demonstrate that the rectenna achieves efficiencies above 45% across 2.8-6.3 GHz, with a peak efficiency of 57.9%. In addition, the use of Polydimethylsiloxane (PDMS) as the substrate provides high flexibility and excellent conformability. These features make the proposed rectenna well-suited for powering electronics on curved surfaces, compact devices, and curved-surface Internet-of-Things (IoT) nodes, such as robots, drones, in-vehicle applications and industrial robotic arm units, enabling reliable conformal deployment on non-planar equipment and distributed IoT systems.

The second-order small-slope approximation (SSA2) is an analytical approximation method applied to electromagnetic scattering simulations on rough surfaces. However, the conventional serial SSA2 method involves a quadruple integral, and each integration requires a fast Fourier transform (FFT). As a result, the method demands very high memory and suffers from very low computational efficiency. In this paper, a parallel SSA2 method is proposed by combining region decomposition with Message Passing Interface (MPI) programming. The OpenMP technique also adopted to further improve the algorithm's performance. To avoid the frequent communication overhead caused by spectral shifting in traditional parallel FFT methods, the matrix data is carefully allocated, which effectively removes the related communication bottleneck. In addition, by using the separability of the two-dimensional (2-D) FFT, each 2-D FFT is implemented using two sequential one-dimensional (1-D) FFTs. This design limits inter-node communication to a constant upper bound. Numerical results show that when the number of computer nodes reaches 10, the parallel efficiency of the proposed method exceeds 80%, which confirms the effectiveness of the proposed method.

This article introduces a microwave system operating in the low-frequency band of 1.6-2.8 GHz, specifically designed for biomedical applications. Tumor detection in the human brain was achieved by monitoring variations in antenna S-parameter response. A high-gain antenna was positioned on the skull's surface, whose gain and directivity are enhanced by backing it with a Frequency Selective Surface (FSS) array. This arrangement effectively channels energy toward human tissues, which facilitates tumor detection. The combined Antenna-FSS structure improved the gain and directivity by 5.3 and 5.1 dB, respectively. Simulations were conducted using a multilayered skull model consisting of the skin, skull, and brain. The experimental validation was done by performing measurements using a near-realistic human brain phantom and by inserting a tumor in the brain area of the fabricated phantom. The study revealed that the measured S-parameters vary by approximately 11.38 dB when a 6 mm × 6 mm tumor is introduced into the brain region. Additionally, S-parameters are analysed by varying shapes, sizes, and locations of tumors within the brain. The study's findings indicate that variations in the characteristics of the S-parameter can be potentially utilized for detecting tumors in the human brain.

Lightning electromagnetic fields are essential inputs for protection system design, electromagnetic compatibility analysis, and lightning location system calibration. Although most computational studies rely on a single ``typical'' current waveform, real lightning exhibits significant variation in peak current, rise time, and temporal characteristics. This paper presents a systematic investigation of how return stroke current parameters influence radiated electromagnetic fields using the finite-difference time-domain (FDTD) method. Five representative waveforms are examined: typical subsequent stroke (12 kA, 40 kA/µs), first return stroke (28 kA, 12 kA/µs), severe subsequent stroke (25 kA, 80 kA/µs), fast-rising subsequent stroke (20 kA, 120 kA/µs), and rocket-triggered lightning (16 kA, 20 kA/µs). Simulations are performed over homogeneous ground (σ = 0.001 S/m, ε_r = 10). Electric and magnetic field components are computed at near-field (r = 50 m) and far-field (r = 5 km) distances, both underground (d = 2 m) and above ground (h = 10 m). Results show strongly distance-dependent behavior: at 50 m, current rise rate (di/dt) dominates, with fast-rising 16 kA strokes producing fields comparable to slower 22 kA events. At 5 km, peak current governs all components, with 28 kA first strokes producing fields 1.5-2× higher than subsequent strokes. Field attenuation from 50 m to 5 km varies from 130× to 3000× depending on waveform frequency content. The azimuthal magnetic field exhibits uniform attenuation (225-350×) and ground independence, supporting its use in lightning location systems. Triggered lightning underestimates severe natural strokes by 40-60% at 50 m, narrowing to 20-30% at 5 km. These findings indicate that worst-case protection scenarios must be distance-specific: fast-rising strokes govern buried infrastructure within 100 m, while first strokes dominate overhead systems beyond 1 km.

This paper presents the design, fabrication and experimental validation of a novel compact high-gain decagonal microstrip patch antenna designed for noninvasive soil moisture sensing. The antenna utilizes the strong correlation between its dielectric properties and soil moisture content, which directly influences the antenna's reflection coefficient and resonant frequency. The decagonal geometry using a Taconic TLY-5 substrate achieves a high gain of 7 dBi and an excellent radiation efficiency of 96.5% compared to the FR-4 substrate. The prototype antenna fabricated on Taconic TLY- substrate resonates at 2.445 GHz frequency with a measured reflection coefficient of -34.3 dB, validating the high-performance characteristics predicted by full-wave simulations using CST Studio Suite 2018. The sensing capability of the fabricated antenna is carefully tested across sandy, loamy, and clay soils, demonstrating a predictable downward shift in resonant frequency as moisture content increases. A linear regression analysis is performed on the experimental data from sandy, loamy, and clay soils, yielded a high coefficient of determination (R² ≈ 0.9) for all three soil types, establishing a calibration model to accurately convert the resonant frequency shifts into soil moisture values. The obtained sensitivity values for soil moisture detection are 4.76 MHz/% for sandy soil, 5.15 MHz/% for loamy soil and 4.89 MHz/% for clay soil respectively. The compact size, high gain and consistent performance across different soil samples make this proposed antenna a better solution for precision agriculture and environmental monitoring through integration into wireless sensor networks.