To address the rotor vibration induced by rotor unbalance in a permanent magnet assisted bearingless synchronous reluctance motor (PMa-BSynRM), a feedforward compensation control method based on the Least Mean Squares (LMS) adaptive filtering algorithm, optimized by a Back Propagation Neural Network (BPNN), is proposed. Firstly, the operating principle of the PMa-BSynRM is introduced, and the mechanism of rotor unbalance vibration is analyzed. Secondly, a feedforward compensation controller is developed to extract the vibration signal and suppress rotor vibration. The BPNN is employed to adaptively adjust the LMS step size, thereby enhancing convergence speed, accuracy, and anti-interference capability. Furthermore, to overcome the inherent limitations of the BPNN, a hybrid optimization strategy that integrates particle swarm optimization (PSO) with an improved genetic algorithm (IGA) is adopted to optimize the initial weights and thresholds of the BPNN. Finally, a rotor unbalance vibration compensation control system for the PMa-BSynRM is established. Simulation and experimental results verify that the proposed control algorithm effectively reduces radial displacement and suppresses unbalanced vibration, while also exhibiting strong anti-interference performance and robustness.

A compact four-port multiple-input multiple-output (MIMO) antenna operating on the N79 band (4.4-5.0 GHz) is designed for use in 5G wireless communication systems. The suggested antenna is synthesized over an FR4 epoxy substrate with a relative permittivity of ε_r = 4.4, and a standard height of 1.2 mm. The overall dimensions of the antenna are 45 × 45 × 1.2 mm³, making it suitable for insertion into miniature 5G-enabled portable devices. A novel defected ground structure (DGS) is proposed, employing the strategic placement of two stubs of unequal lengths within the shared ground plane to effectively mitigate surface-wave propagation and thereby suppress mutual coupling among antenna elements. Thus, the design achieves considerable isolation, with a level below -20 dB across the targeted operational band. The suggested antenna operates at 4.67 GHz with a peak gain of 2.83 dBi and a radiation efficiency of 92%. The performance of the MIMO antenna was comprehensively assessed using standard diversity metrics, achieving an 0.01 envelope correlation coefficient (ECC), a diversity gain (DG) of 9.99 dB, a channel capacity loss (CCL) of 0.36 bits/s/Hz, and a mean effective gain (MEG) consistently below -3 dB. A strong correlation between experimental and simulated findings points towards the robustness of the suggested design. With its compact size, high isolation, and excellent MIMO performance, the antenna demonstrates strong potential for integration into sub-6 GHz 5G MIMO wireless communication systems.

A methodology for estimating the complex permittivity of liquid dielectrics is presented in a rectangular waveguide using the Ku-band (10-15 GHz, WR75). A two-dimensional finite difference time-domain (FDTD) model with perfectly matched layers (PMLs) serves as the forward solver, and TE₁₀ modal projection provides the simulated scattering parameters. Subsequently, a gradient-free Nelder-Mead inversion extracts the real and imaginary parts of the permittivity from the measured S₁₁ and S₂₁ parameters. This approach is implemented in a multilayer fixture, which enables leak-tight loading while remaining analytically simple. Validation on air and water shows good agreement between simulation and measurement across 10-15 GHz, and results at 12 GHz are consistent with independent X-band extractions. This approach is computationally efficient, practical for experimentation, and can be extended to other liquids and multilayers.

Liquid metals possess significant application value in key sectors such as new energy, nuclear energy, and metallurgy due to their excellent fluidity, high electrical and thermal conductivity, and remarkable high-temperature stability. Accurate flow measurement during their application is crucial for ensuring system safety. However, conventional flow measurement techniques struggle to guarantee long-term stability under high-temperature conditions. To address this challenge, this paper proposes a non-contact alternating current excitation electromagnetic flowmeter. The design generates a stable alternating magnetic field via an excitation coil and employs externally mounted, differentially connected induction coils as the sensing element. This configuration enables non-contact measurement of liquid metal flow within metal pipes, fundamentally overcoming the reliability degradation issues associated with direct sensor contact with the measured medium. Experimental results demonstrate that the system has the potential to operate stably at a high temperature of 600°C and has achieved a high measurement accuracy of 3%.

In the design and fabrication of ceramic filters, the quality of metallization is crucial to minimize resistive losses and ensure optimal resonator performance. This work presents the design and fabrication of a monoblock dual-mode filter with two distinct types of couplings, based on barium titanate (BaTiO₃) ceramics, operating at S-band frequencies. Sputtering deposition was used to create a 5 nm gold seed layer, on which a 30 μm copper metallization was grown through electroplating. This method guarantees high conductivity in the resonator coating, and test results demonstrated that the fabricated device offers very good filtering performance with a minimal insertion loss of 0.57 dB.

Low-emissivity glass, commonly employed in building curtain walls strongly reflects and weakly transmits millimeter-wave signals, thereby hindering signal propagation. To address this issue, this paper introduces a novel method that leverages the low-emissivity film itself to design a metasurface for enhanced signal transmission. Two specific metasurface designs are presented. The simulation results validate the proposed method. For the design targeting linearly polarized waves, a 23 dB enhancement in the transmitted electric field is achieved compared to that of uncoated glass. The design for circularly polarized waves achieves a 22 dB enhancement. Both metasurfaces exhibit excellent wide-angle performance, maintaining single-point focusing up to a 30° incidence angle with an electric field enhancement exceeding 15 dB. The proposed millimeter-wave transparent metasurface features a simple structure, supports wide-angle incidence, and can be deployed over large areas with adjustable focal points to meet communication requirements. This work provides a reliable solution for mitigating millimeter-wave transmission loss through low-emissivity glass.

Conventional full-wave methods face prohibitive computational costs for far-field scattering optimization of metasurface-integrated cavity structures. To address this limitation, a lightweight residual neural network is introduced within a two-stage scattering prediction framework. This framework effectively mitigates model degradation. The first stage employs shallow convolutional networks to extract local phase-coupling features. The second stage integrates residual layers with fully connected layers to refine cross-scale scattering responses. A compact CNN-ResNet surrogate model is developed for rapid cavity scattering prediction. With only 2.5×10⁴ parameters and training on 500 full-wave samples spanning 6.0-16.0 GHz, the model achieves high computational efficiency. The proposed approach directly maps binary phase-coded matrices to far-field electromagnetic characteristics. Extensive validation on a cavity structure across 6.0-16.0 GHz demonstrates excellent accuracy. The per-sample runtime is reduced from hours to milliseconds while maintaining prediction errors below 3 dB. These results confirm the effectiveness of the approach in enabling fast and accurate electromagnetic scattering prediction for complex cavity environments. The approach provides a practical solution for metasurface-integrated cavity optimization.

In this paper, a novel wideband coaxial-to-rectangular waveguide transition integrated with a septum horn antenna is proposed for C-band satellite communication applications. The design employs a modified supershape excitation probe, derived from an extended superformula, to achieve smooth impedance transformation and broadband performance. Initially, the probe geometry is optimized through parametric simulations to validate its effectiveness within a rectangular waveguide structure. The transition is then effectively incorporated into a stepped septum horn antenna that facilitates dual circular polarization through a compact dual-feed mechanism. The septum structure ensures efficient conversion of linearly polarized modes into left-hand and right-hand circularly polarized waves, while maintaining high isolation and low axial ratio. An equivalent circuit model is developed to provide analytical insight into the impedance behavior. A prototype antenna is fabricated, and its performance is validated through measurements. The measured results confirm reflection coefficients below -10 dB across 4.6-8.6 GHz, peak gain of 15.8 dBi, and inter-port isolation exceeding 20 dB. Furthermore, the antenna achieves a 3 dB axial ratio bandwidth of 76.9%. A comparison with state-of-the-art designs demonstrates the superior performance and design efficiency of the proposed antenna architecture.

We investigate the thermal and relativistic effects produced when an electrically conductive object is moving in tandem with a source of a variable electromagnetic field. First, we derive an energy–frequency relation to quantify the temperature rise induced by such a field. This relation is then combined with the Lorentz-Fitzgerald contraction and time dilation from special relativity to identify a force, F_c, required to reconcile energy conservation between stationary and moving observers. We further relate F_c to the relativistic energy of a moving mass, extending the analysis to objects without electrical conductivity. This connection leads to the prediction of an inertial force F_cf generated by the frequency sweep of an electromagnetic wave (whether caused by relative motion or by internal modulation) that interacts with mass regardless of its electrical properties.

In response to the demand for broadband antennas in satellite communications, this paper sets out the proposal of a broadband circularly polarised metasurface antenna. Based on the theory of characteristic mode analysis of super surface, a pair of characteristic modes with the potential to realize circular polarization broadband are obtained and used as the modes to be excited. At the same time, the metasurface current is analyzed; the position of the floor gap is determined according to the results; and the shape of the floor gap is designed to better stimulate the characteristic mode. Subsequently, the power is transmitted through the microstrip line gap coupling feeding structure to excite the selected mode. Finally, an MTS antenna with dimensions of 0.9λ₀ × 0.9λ₀ × 0.076λ₀ at a centre frequency of 5 GHz was determined. The antenna was modeled using CST, a 3D electromagnetic simulation software, and then physically tested for verification. The experimental findings indicate that the impedance bandwidth of the antenna in question is 4.20-5.83 GHz (relative bandwidth of 32.6%). Furthermore, the 3 dB axial ratio bandwidth is 4.38-5.97 GHz (relative bandwidth of 30.7%).

This paper systematically analyzes the electromagnetic coupling characteristics between microstrip resonators and proposes a novel structure that enables mutual cancellation of electromagnetic coupling, effectively reducing the spacing between resonators. Based on this approach, a 14th-order compact high-temperature superconducting (HTS) microstrip bandpass filter is designed and implemented. By constructing a folded symmetric resonator structure to minimize the total electromagnetic coupling energy, and by optimizing the non-uniform coupling gaps in conjunction with the coupling characteristics, precise control of the coupling paths is achieved, leading to a significantly enhanced compactness. The filter is fabricated using double-sided YBCO HTS thin films and tested at liquid nitrogen temperature (77 K). Both simulation and measurement results show that the filter operates within the 0.96~1.06 GHz frequency band, exhibits an insertion loss below 0.4 dB, an out-of-band rejection better than 78 dB, and a passband edge roll-off rate exceeding 60 dB/MHz, demonstrating excellent performance in terms of low loss, wide bandwidth, and high suppression.

Generalized sidelobe canceller (GSC) based adaptive beamformer possesses a main advantage of superior interference rejection due to its capability in tracking the interference characteristics. However, its performance is very sensitive to even a small mismatch in array scenarios. For example, the mismatch due to mutual coupling between array sensors is a common phenomenon in practical environments. Two common problems considered are as follows. (1) The existing adaptive array beamformers are very sensitive to MCE. (2) The existing robust methods inevitably suffer from the problems, including additional computational complexity and estimate accuracy. In this paper, we present an efficient method to deal with the performance degradation induced by the MCE to achieve robust beamforming. The proposed method simply utilizes a well-known scheme, namely the zero-forcing (ZF) equalizer. The ZF equalizer simply preprocesses the data vector received by the antenna array and then inputs the processed data vector into a GSC based adaptive array processor. The combination of a ZF equalizer and a GSC based adaptive array processor results in an adaptive array beamformer providing satisfactory beamforming performance in the presence of the MCE. The performance analysis regarding the proposed method is analyzed. Simulation results are also presented for confirmation and comparison. The simulation results show that the ZF equalizer alleviates the MCE and the GSC based adaptive beamformer can subdue the background noise enhanced by ZF equalizer.

This paper investigates the circuit theory of elementary passive topology exhibiting reconfigurable positive/negative delay (RPND) effect. This novel evaluated framework enables identification of the first-order L-topology constituted by RC-network operating under RPND effect. The investigated passive L-cell can operate in both negative and positive group delay (NGD or PGD) mode depending on the RC-network parameter. After establishing the NGD existence condition, the design equations versus the RPND effect including the target parameter values are formulated. To validate the theory, an RC-circuit representing a RPND Proof-of-Concept (PoC) was designed, implemented and tested especially in the time-domain by verifying the time-advance signature corresponding to the NGD operation mode. By tuning a PoC resistor, experimentation of pulse and arbitrary waveform signals confirm the feasibility to observe RPND reconfigurability. In the NGD mode, it is observed that outputs in time-advance of their own inputs about -3 ms. The RPND circuit is particularly useful for adjusting delay effect and signal synchronization in the communication system.

The history of science is filled with legendary ``happy accidents", from penicillin to the microwave oven. These breakthroughs are often attributed to luck. But Prof. Keisuke Goda (University of Tokyo) and his team argues in a recent paper in Progress In Electromagnetics Research (Vol. 184, 14--23, 2025: doi:10.2528/PIER25100702) [1], entitled ``Serendipity Engineering with Photonics: Harnessing the Unexpected in Biology and Medicine," that such accidental discoveries can be systematically cultivated. It introduces ``serendipity engineering" --- the intentional design of tools and research cultures to make unexpected, yet meaningful findings more likely.

A compact wideband antenna with a multi-slot configuration is proposed for radar, military, and modern wireless communication systems. The antenna is fabricated on an FR-4 substrate with overall dimensions of 14 × 16 × 1.5 mm³, corresponding to a miniaturized electrical size of 0.163λ × 0.187λ × 0.017λ₀ at 3.5 GHz. To achieve broad impedance bandwidth and improved matching, multiple slots are etched on both the patch and ground surfaces. Experimental validation shows that the antenna effectively covers the 3.5-14 GHz frequency range, offering nearly 120% fractional bandwidth. Within this spectrum, it delivers a peak gain of 5.1 dB and a maximum radiation efficiency of about 89%, ensuring stable and low-loss performance. The compact structure maintains consistent radiation characteristics, making it suitable for portable and defense-oriented devices. Its ability to support Sub-6 GHz and 5G bands further enhances its applicability in next-generation communication platforms.

In this paper we report a cascaded circular ring antenna with semicircular C-shaped radiating slots for multiband applications. The novelty of this paper lies with three techniques as follows: cascading circular rings, semicircular C-shaped slots and complimentary split ring resonators embedded on the ground are included in the paper. The dimensions with optimised values are 35 × 35 × 1.61 mm³. The antenna operates from 2.124 GHz to 8.284 GHz, and it is deposited on a 1.6 mm thick FR-4 substrate. The radiating patch is built on the substrate; it is made by developing multiple circular ring structures to develop a cascaded ring-like pattern that provides the wideband response. The antenna successfully resonated with a wide bandwidth of 6.16 GHz in the span of 2.124 GHz to 8.284 GHz. The ground features a half hexagonal slot that is embedded within the larger etched rectangular slot. An equivalent circuit with R-L-C elements is developed. The resonating bands are obtained at 3.0 GHz, 5.89 GHz, and 7.07 GHz with reflection coefficients of -21.3 dB, -19.7 dB, and -26.7 dB, respectively. The optimised design operates at UWB, WLAN, WiMAX, and 5G midband applications.

This paper proposes a reconfigurable 3-dB coupler with tunable phase and frequency characteristics based on triple-line loaded varactor diodes. The core structure employs a four-line coupling configuration to ensure strong coupling characteristics and stability. Through integrated theoretical analysis and experimental verification, the coupler demonstrates a center frequency tuning range of 1.8-2.4 GHz with continuous phase difference adjustment from 40° to 140°. Measured results indicate that high isolation (> 20 dB) and low return loss (< -20 dB) can be obtained.

In the manuscript a novel design of microstrip patch antenna with moderate degree of complexity is proposed in terms of metamaterial based unit cells as radiating patch on the top as well as metamaterial based periodic structure as defected ground structure at the bottom (MRPMGS) for Intelligent Transportation System (ITS) applications. The novel design of patch antenna exhibited multibands with broad-band transmission patterns, improved high gain and compact structure. The MRPMGS has a three layered structure with overall dimensions of 32 mm × 28 mm × 1.6 mm. The top layer with radiating patch has unit cell(s) with dimensions of 3.6 mm × 3.6 mm, and at the bottom the defective ground structure (DGS) has unit cell(s) with dimensions of 4 mm × 4 mm. The middle layer is of FR4 substrate with 1.6 mm thickness. The MRPMGS has experimental (simulated) transmission frequencies at 11.54 GHz (11.24 GHz), 12.91 GHz (12. 98 GHz), and 13.20 GHz (13.48 GHz) with reflection coefficients of -20.91 dB (-25.16 dB), -26.19 dB (-29.36 dB), and -18.94 dB (-26.02 dB) respectively. The VSWR varies between 1 and 3. The radiation efficiency reaches 80%, and high gain varying between 2.35 and 5.5 is achieved at the desired frequencies.

A compact microstrip dual-band filter using stepped-impedance resonators (SIRs) is proposed. The ring-type structure is used to minimize the size of the filter, and the location of the input/output excitation port is used to adjust the filter's performance. A dual-band filter has been fabricated and measured to verify the performance of the proposed configuration. The results show that the filter exhibits two passbands, centered at 30.5 GHz and 35.9 GHz, with fractional bandwidths of 7.2% and 5.6%, respectively. The corresponding insertion losses at the center frequencies are 2.7 dB and 3.3 dB. The proposed filter configuration shows great potential for applications in next-generation 5G and satellite communication systems requiring compact and high-performance multi-band filters.

This study investigates the electrical characteristics of grounding electrodes in seasonal frozen soil through experimental and simulation approaches. Experimental measurements reveal the variation patterns of soil resistivity and dielectric constant within the frequency range of 100 Hz-10 MHz at different temperatures. The results indicate that decreasing temperature leads to increased resistivity and decreased dielectric constant, with both parameters tending to stabilize at high frequencies. Computations based on the method of moments demonstrate that accounting for the frequency dependence of frozen soil reduces the impedance magnitude by 20%-40% in the high-frequency range and results in more complex resonant behavior. When the length of the grounding electrode is less than the freezing depth, the high-frequency capacitive effect is significantly enhanced. Time-domain analysis shows that under lightning impulse conditions, the potential reduction is approximately 22% during the first return stroke and can reach up to 42% in subsequent return strokes. The study concludes that the frequency dependence of the electrical parameters of frozen soil has a considerable influence on the response of grounding electrodes and should be considered in modeling and lightning protection design.