Frequency-Selective Surfaces (FSSs) are structures designed to selectively transmit or reflect electromagnetic waves, making them essential for applications requiring precise control over frequency bands and wave propagation characteristics. However, traditional FSS designs face challenges such as fixed geometries, limited scalability, and poor bandwidth efficiency, often requiring compromises between size reduction and performance. To address these limitations, this work introduces the use of Stepped Impedance Resonators (SIRs) to synthesize miniaturized FSS structures with four-legged elements (FLEs). By combining transmission line theory, SIR equations, and parallel coplanar stripline models, an innovative synthesis method is proposed, enabling precise control over spurious frequencies and resulting in a 54% reduction in unit-cell size without sacrificing performance. This approach significantly enhances the feasibility of compact FSS applications. To further improve performance, an arrow-bending technique was introduced to reduce the coupling between adjacent cells, yielding a 30% improvement in isolation. Three distinct surface designs have been fabricated and tested under both normal incidence and oblique angles for TE and TM modes. These designs include the SIR-based FSS cell, an enhanced design featuring arrow bending, and a reverse arrow formation intended to reduce edge effects between adjacent cells. Additionally, measurements demonstrate excellent performance stability, with tolerance maintained for incident angles up to 60°. Experimental validation confirms effective blocking at 10 GHz and highlights the robustness of the design across varying incident angles. Prototypes fabricated from the miniaturized FSS elements show excellent agreement with simulations, underscoring the potential of this method for advanced applications in communications, radar, and electromagnetic shielding.

In RF front-end circuits, the miniaturization and high-performance integration of duplexer remain critical challenges for 5G communication and IoT devices. A microstrip duplexer design scheme is proposed based on electric and magnetic coupling path separation and dual-mode characteristics. Through the collaborative design of second-order uniform impedance resonators and dual-mode T-shaped resonators, the design achieves signal separation for dual frequency bands at 2.4 GHz and 3.6 GHz. The design forms the electric coupling path via edge-gap coupling of rectangular split-ring resonators, and realizes magnetic coupling path through vias. By independently regulating electric and magnetic coupling strengths, eight transmission zeros are introduced on both sides of the dual passbands, significantly enhancing out-of-band suppression and port isolation. The simulation results show that the passband insertion loss is less than or equal to 1.9 dB. Due to machining tolerances, the measured center frequencies shift to 2.04 and 3.48 GHz, while the out-of-band rejection remains better than 39 dB, validating the engineering adaptability of the design. This scheme achieves high-performance integration of RF front-ends in a compact architecture through the coordinated regulation of multiple transmission zeros and coupling path separation technology, providing a solution for wireless communication devices.

The novel amorphous alloy transformer featuring a closed three-dimensional coil core (CTDCC) represents an innovative approach to transformer structure. In contrast to the conventional three-phase five-column transformer equipped with a planar coil core (PCC), the CTDCC configuration displays a completely equal magnetic circuit, leading to improved short-circuit tolerance. Nevertheless, the design and manufacturing process of the core faces a notable engineering obstacle due to the amplified magnetostrictive coefficient of the amorphous alloy, resulting in vibration noise. In order to address this issue, a magnetic-mechanical coupling mathematical model is developed in this research to analyze the magnetostrictive effect of the amorphous alloy CTDCC. Three-dimensional finite element analysis (FEA) is utilized to compute the magnetic flux distribution and quivering dislocation dissipation of the CTDCC. Furthermore, a validation experiment is carried out on a 30 kVA amorphous alloy CTDCC model to confirm the precision of the model. Moreover, the CTDCC structure has been proven to effectively minimize surface vibrations compared to the PCC model. Additionally, it unveils the governing frequency law of vibration movement at various locations within the CTDCC structure. This revelation serves as a fundamental basis for developing strategies to mitigate vibrations and control noise during the CTDCC design.

This article presents a compact highly isolated two-port ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with triple band suppression features. The antenna measures 25 × 39 mm² and comprises two orthogonally arranged microstrip-fed square radiators to achieve high inter-element isolation. A T-shaped and L-shaped stubs were incorporated into the ground plane to enhance isolation and broaden the impedance bandwidth. Triple band notches targeting Satellite C-band downlink (3.6-4.6 GHz), WLAN (4.9-5.5 GHz), and Wi-Fi 6E (6.1-6.7 GHz) are realized using three U-shaped slots introduced on each radiating element. The antenna's operation is analyzed through Characteristic Mode Analysis (CMA) by evaluating modal significance, characteristic angle, modal currents and mode patterns. MIMO performance is validated using key diversity metrics, including envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), channel capacity loss (CCL), multiplexing efficiency (ME), and group delay. Results demonstrate an impedance bandwidth exceeding 2.9-10.6 GHz UWB range, with 90% radiation efficiency, peak gain of 6.2 dBi, ECC below 0.02, and mutual coupling under -20 dB. These outcomes confirm the efficacy of the proposed antenna in achieving compactness and high performance for UWB MIMO applications.

In this paper, the dielectric constant distribution of concrete was determined, which is consistent with the experimental values, and the complex dielectric constants obtained were evaluated. Numerical results are given by resulting complex dielectric constant distributions of four types, the time response waveforms and frequency spectra of a composite dispersive medium consisting of concrete using these dielectric constant distributions, and the time response waveforms and frequency spectra separated by each reflection component. A fast inversion of the Laplace transform method was used for the numerical analysis. Consequently, we were able to clarify the dielectric constant distribution suitable for the analysis by using these time response waveforms and frequency spectra.

Long-time coherent integration (LTCI) is an effective method for maneuvering target detection, as it accumulates signal energy over a long observation period, thereby enhancing the signal-to-noise ratio (SNR). However, as the observation duration increases, range migration (RM) and Doppler frequency migration (DFM) occur, which degrade the integration performance. To this end, a scaling factor is first introduced into the parameterized centroid frequency–chirp rate distribution (PCFCRD) algorithm, thereby yielding the scaled PCFCRD (SPCFCRD), which enables flexible adjustment of the chirp rate estimation range and resolution. Furthermore, SPCFCRD is combined with the keystone transform (KT) to form the proposed KT-SPCFCRD algorithm. The RM caused by unambiguous velocity is first corrected by KT, after which the residual RM and DFM are further compensated by SPCFCRD to achieve coherent integration. The effectiveness of the proposed algorithm is validated through simulations and real-data analysis. Compared with several representative algorithms, KT-SPCFCRD achieves superior detection performance while maintaining a balanced computational cost.

This paper presents a newly developed rod-electrode-type microwave plasma source (MPS), which is mainly composed of a panel mount coaxial connector, a self-made metal adapter with an inlet and outlet of working gas, a quartz tube as a flow path of working gas, and a metal rod-electrode. Microwave energy can be then supplied directly to the working gas from the sharp tip of the metal rod-electrode through the panel mount coaxial connector. To verify the validity of the rod-electrode-type MPS, a reasonable microwave power supply system is built to transmit the microwave power from a magnetron to the panel mount coaxial connector. The experiments demonstrate that the rod-electrode-type MPS can convert by autoignition argon (Ar) into plasma at atmospheric pressure. Moreover, the Ar plasma can be changed to dry air (Air) plasma or nitrogen (N₂) plasma by gradually replacing Ar with Air or N₂. The experimental results show that the rod-electrode-type MPS is potentially an available tool for gas processing at atmospheric pressure.

In this paper, a novel monopole broadband dual-band antenna design for wireless communication systems is proposed, with its fabrication and experimental validation presented. To significantly enhance impedance matching performance, the antenna employs a T-shaped feed slot resonant structure integrated with symmetric L-shaped radiating patches. It covers critical Sub-6 GHz bands (N41/N77/N78/N79) along with Wi-Fi 5 and Wi-Fi 6 spectrums. Notably, the N41 band, as a core 5G frequency band, possesses advantages such as wide bandwidth, strong penetration capability, and flexible deployment, rendering it ideal for urban coverage and high-speed transmission. Experimental results demonstrate that the antenna achieves a -10 dB impedance bandwidth spanning 2.43-2.72 GHz and 3.31-7.32 GHz, with a peak gain of 5.48 dB under omnidirectional radiation characteristics. Its compact design is suitable for miniaturized terminal devices, exhibiting high practical value in 5G Sub-6 GHz and multi-band wireless communication applications.

The permanent magnet brushed DC motor (PMDCM) features a simple structure and reliable performance, making it widely used in home appliances and automotive applications. To further optimize the output torque quality of the PMDCM, this paper proposes a concave-slot Halbach array magnet ring (CSHAMR) structure. First, a finite element model was established to analyze the electromagnetic characteristics of the motor. By comparing with the traditional Halbach array magnetic ring (THAMR), the superiority of the proposed structure for application in brushed motors was verified. Secondly, by defining the magnitude of the no-load back electromotive force (EMF) generated by a single-sided conductor within the interval ``γ'' , the optimization level of the CSHAMR structure for commutation performance was evaluated. The influence of concave slot parameters on motor commutation performance under different values was analyzed. Finally, a parametric model of the CSHAMR was established, and multi-objective optimization of the motor was performed based on the particle swarm optimization (PSO) algorithm. The results demonstrate that CSHAMR can effectively reduce torque ripple and cogging torque in PMDCM motors while improving motor commutation performance.

Highly-miniaturized MIMO antennas are very much desired for 5G-and-beyond hand-held devices as well as miniaturized stationary devices for WSN and IoT applications. In this paper, two compact two-port printed MIMO arrays, measuring 28 × 14 × 0.8 mm³ each, with and without isolation enhancement, are proposed. These arrays have nearly omni-directional radiation patterns over an extended operational bandwidth. The proposed designs feature an extended set of control parameters by which the desired performance could be achieved without compromising space and weight requirements or accuracy. They were fine tuned to provide an operational bandwidth about 4 GHz with relatively low starting frequencies of 2.7 and 3.3 GHz, respectively, allowing simultaneous WiFi, WiMax, 5G operation with a moderate gain and very high efficiency. Prototypes are manufactured and examined for impedance bandwidth, isolation, diversity, and radiation properties showing very good agreement with simulation results.

This study presents a structure design methodology to analyze the operational efficiency of a flux switching permanent magnet machine utilizing non-oriented electrical steel materials. First, iron losses of non-oriented electrical steel materials assembled by bonding and welding stacking methods ware tested, and the comparison results demonstrated that the bonded stator core exhibited lower iron losses than the welded stator counterpart. Then, the proposed non-oriented electrical steel material 35SW360 was implemented in the straighted-rotor core of flux switching permanent magnet machine, and the simulation results shown that both the amplitudes and harmonics of induced electromotive force with 35SW360 was almost identical to the standard non-oriented electrical steel material DW360_50. Finally, prototype flux switching permanent magnet machine with straighted-rotor and skewed-rotor including above two non-oriented electrical steel materials was manufactured and tested. Both the simulation analysis and hardware test results revealed that the flux switching permanent magnet machine with skewed-rotor achieved higher efficiency than the straighted-rotor design. Consequently, the proposed non-oriented electrical steel material 35SW360 and skewed-rotor design illustrate a potential solution for efficiency improvement of flux switching permanent magnet machine.

The burgeoning reliance on electronic devices in sectors such as aerospace systems and consumer electronics necessitates robust electromagnetic interference (EMI) shielding. Current challenges often involve balancing material performance with sustainability and cost-effectiveness. This study addresses these needs by exploring the use of recycled carbon fiber (rCF) in acrylonitrile butadiene styrene (ABS) composites for enhanced EMI shielding, contributing to more sustainable material development. We investigated the impact of different rCF treatments (untreated, chemically treated, and chemically-mechanically treated) on the mechanical properties (tensile strength, stiffness, flexibility) and EMI shielding effectiveness of these composites. Furthermore, the role of electron beam (EB) irradiation at 200 kGy in creating cross-linked structures to boost conductivity and shielding performance was thoroughly examined. Fabricated via melt compounding, the composites' electrical conductivity and EMI shielding capabilities were the main focus. Results show that the EB-irradiated composite with 30 wt.% chemically treated rCF achieved a peak electrical conductivity of 1.34 × 10^-8 S/m and an impressive shielding effectiveness of 46.13 dB. These findings offer crucial insights for developing high-performance, cost-efficient, and potentially sustainable rCF-filled ABS composites for advanced EMI shielding applications.

This paper presents the design of an absorptive metasurface suitable for complex-shaped targets, achieving precise control over electromagnetic waves, which has been experimentally validated. The metasurface, with a design thickness of only 0.27 mm, maintains sufficient absorption properties under appropriate curvature conditions to ensure the stealth characteristics of the coated target. Through simulation and experimental validation, this study demonstrates the metasurface's strong resonance characteristics near 11.26 GHz and a reduction of approximately 3 dB in far-field radar cross section (RCS) simulation. The experimental test results are almost consistent with the simulation results, confirming the metasurface's effectiveness in reducing the RCS of actual complex models. The research findings provide strong technical support for the radar stealth research of targets.

Quadrature 3-dB impedance-transforming transdirectional (TRD) couplers based on double-shielded coupled lines are analyzed and synthesized; design relationships are also presented. To verify proposed concept two couplers implemented with high-permittivity (higher than 10) dielectrics are designed, fabricated, and measured. The first TRD coupler features a suspended ceramic bar, and the second one features a meandering layout of the upper line on a high-permittivity dielectric overlay. Comparison of the proposed solutions with known ones shows that novel coupler designs have advantages in small dimensions and an extended bandwidth of operating frequency (about 1.5-2 times). The simulated results are in good agreement with the measurement data.

Spherical harmonics are classical analysis tools in many science and engineering domains. For analyzing the electromagnetic fields of antennas in the frequency domain, the mostly used formulation is the one proposed by Hansen. This article proposes an alternative solution, relying on spin spherical harmonics. On a sphere, the tangential components of the electric and magnetic fields are represented by means of harmonics of spin ±1. Then new closed-form relations are established between the spin spherical harmonics and the ones formulated by Hansen. A sampling theorem and fast transforms that are consistent with spin spherical harmonics are used. The radiations of spin spherical harmonics of order 1 are related to elementary dipoles and Huygens sources in circular polarization. Finally, numerical experiments are performed with a horn antenna and a GNSS antenna installed on an aircraft. They show that a very large radiating system with a band-limit of 2048 can be efficiently analyzed by means of fast spin spherical harmonic transforms, with a computation time of 2 minutes, approximately.

The misalignment between the transmitter and receiver coils in the wireless power transfer WPT systems causes a reduction in the power transfer efficiency (PTE). This manuscript presents a numerical and experimental study of a WPT with different sequences that compensate for the misalignment effects of WPT systems. Circular loops were used for the transmitter's source coil and the receiver's load coil. Then, a magnetic resonator coil has been added to the transmitter and receiver circular loops. The transmitter coil (Tx) has 4 turns and is connected to a 67 pF capacitor, and the receiver coil (Rx) has 14 turns and is connected to a 9 pF capacitor, which resonates at 13 MHz. The planner 5 × 5 spiral rings array of the metamaterial (MTM) was designed. The MTM unit cell has 5 turns and is loaded with an external 100 pF capacitor. Four scenarios are studied. The first one is the Tx and Rx coils in misalignment without MTMs, and the second one is by inserting the MTM plate in the middle space. Then, double plates are used in the middle, and finally, MTM plates are located behind the coils directly. The transmission coefficient S₂₁ is enhanced by -7 dB when the MTM plate is placed in the middle space between coils. Adding another layer of MTM results in an increase in coupling between coils and enhances the S₂₁ by -1 dB from the previous value. The PTE is improved from 32% to 63% in the instance of misalignment when MTM plates are behind coils. Finally, measurements are achieved and show acceptable agreement with the simulated results. This work could be helpful in biomedical implants where the locations of Tx and Rx coils are frequently changed.

This paper presents a numerical iterative approach to synthesizing multiband filtering functions that can realize equi-ripple in-band responses and enforce the same return loss (RL) level across all passbands. By iteratively updating the reflection zeros (RZs) and some additional transmission zeros (TZs), the multiband filtering function can be constructed to give an equi-ripple characteristic and ensure the same RL levels in all passbands. The advantages of the proposed method include that equal RL level in all passbands can be enforced, and the numerical stability is improved over existing methods. The proposed method can be used to synthesize symmetric or asymmetric multiband filter (MBF) responses with an arbitrary number of passbands. Two synthesis examples are provided. The first example is a tri-band filter (TBF) with an RL level of 23 dB. Its passband frequency ranges are (-1, -0.7), (-0.15, 0.15), (0.7, 1) rad/s, in the normalized frequency domain, and the numbers of poles in the three passbands are 5, 4, and 5, respectively. In the second example, a dual-band waveguide filter (DBF) with four poles in each passband is synthesized and designed. The frequency ranges of the two passbands are (11.8, 11.95), (12.085, 12.2) GHz. Both simulated and measured RL levels of the filter are 22 dB. The measured insertion loss 0.73 dB in the lower passband and 0.75 dB in the upper passband. The simulated and measured results are in excellent agreement with the theoretical response, thus verifying the proposed synthesis method.

Non-embedded uncertainty analysis methods are widely used in the field of electromagnetic compatibility (EMC). Their essence is to construct a surrogate model to simulate the actual electromagnetic simulation process and obtain the desired uncertainty simulation results through exhaustive sampling. However, when performing complex electromagnetic compatibility simulations, non-embedded uncertainty analysis methods face an inherent problem. This problem arises from the excessive number of deterministic simulations, which leads to computational inefficiency. In this paper, an active sampling strategy based on Bayesian optimization is proposed. By selecting the locations of deterministic simulation sampling points in a more reasonable manner, the overall number of sampling points required for the uncertainty simulation can be minimized, thereby improving the computational efficiency. Finally, the effectiveness of the sampling strategy proposed in this paper was verified using a typical parallel cable crosstalk example and a lightning electromagnetic pulse electromagnetic interference simulation example.

This paper presents a numerical approach for solving the magnetic diffusion equation using structure-preserving discretization methods, like Discrete Exterior Calculus (DEC) and Finite Element Exterior Calculus (FEEC). A detailed derivation of the DEC operators is provided, also their geometric foundation and relevance for discretizing differential forms on meshes. Furthermore, the paper includes an explicit introduction to the finite element exterior calculus framework, with a concise overview of the underlying functional spaces. The proposed formulations aim to preserve the topological and metric structure inherent in Maxwell's equation system. Numerical examples illustrate the stability and convergence of both methods, while also comparing their treatment of boundary conditions and discrete Hodge star construction which makes DEC and FEEC solvers spurious free and efficient useful for complex geometries.

In this paper, a highly compact half mode substrate integrated waveguide (HMSIW)-based self-quadplexing antenna is proposed, employing four quarter-mode SIW (QMSIW) radiating elements integrated with longitudinal slots. The antenna operates at four closely spaced resonant frequencies 3.68 GHz, 3.83 GHz, 4.04 GHz, and 4.17 GHz achieved by precisely tuning the slot dimensions. A minimum port isolation of 26 dB is maintained between any two ports, ensuring minimal mutual coupling. The proposed design exhibits a compact footprint of only 0.05λ₀², where λ₀ is the free-space wavelength at the lowest resonant frequency. The simulated and measured gains exceed 5.5 dBi across all four bands, with a radiation efficiency of approximately 85%. Owing to its compact size, high isolation, and efficient radiation performance, the proposed antenna is well-suited for the upper S-band (3.1-3.9 GHz) and lower C-band (4.0-4.2 GHz) which are widely allocated for fixed-satellite service (FSS) communications applications.