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.

With increasing demand for renewable energy, perovskite solar cells (PSCs) have emerged as a promising alternative due to their high efficiency and solution-based manufacturing processes. However, the fabrication of PSCs in ambient conditions, as opposed to inert environments, remains challenging due to environmental factors such as moisture and oxygen that degrade perovskite materials. Developing air-processed PSCs is therefore critical for reducing fabrication cost, simplifying manufacturing infrastructure, and enabling scalable production compatible with industrial processes. Moreover, air processing represents a key step toward realistic deployment, bridging the gap between laboratory demonstrations and commercial applications. This perspective discusses the progress of air-processed PSCs, highlights the environmental challenges related to stability and performance, and outlines potential strategies for future research, including precursor chemistry, solvent and additive engineering, and interface optimization. In addition, emerging scalable deposition techniques, automated platforms, and machine learning-assisted control are expected to accelerate device optimization and reproducibility. Despite remaining challenges, commercializing air-processed PSCs is increasingly viable, promising a sustainable and efficient approach for solar energy technology.

This work presents a compact coplanar waveguide (CPW) fed super wideband (SWB) antenna realized on a low-cost FR4 substrate (ε_r = 4.4, thickness = 1.6 mm). The 20 × 20 mm² radiator integrates a multi-slotted patch within a hexagonal ground plane aperture and a carefully optimized tuning stub that excites and merges multiple resonances into a continuous broadband response. The antenna achieves a measured |S₁₁| ≤ -10 dB impedance bandwidth from 2 to 34 GHz (177.7%), encompassing sub-6 GHz 5G, WLAN/WiMAX, and millimeter wave (Ku/Ka) allocations. Radiation measurements reveal quasi-omnidirectional patterns with a peak gain of 6.60 dB and maximum radiation efficiency of 82.68%. Time-domain analysis demonstrates an almost constant group delay (approximately 0.1 to 0.5 ns, mean 0.19 ns) with a single localized deviation near 24.4 GHz, confirming low dispersion and excellent phase linearity, which are desirable for IR-UWB and high data rate communication systems. Parametric optimization and equivalent RLC circuit modeling validate the broadband mechanism, while simulation studies performed using CST Microwave Studio exhibit excellent agreement with experimental results. The proposed design therefore offers a cost-effective, compact, and high-performance antenna solution suitable for 5G/6G front ends, radar imaging, and broadband sensing applications.

The purpose of this study is to experimentally investigate the applicability of a rod-electrode-type microwave plasma source (MPS) for pure carbon dioxide (CO₂) splitting at atmospheric pressure. This paper demonstrates that the rod-electrode-type MPS can convert pure CO₂ gas into plasma. The CO₂ splitting by the CO₂ plasma is investigated in terms of the pure CO₂ flow rate into the rod-electrode-type MPS and the average transmission power to the rod-electrode-type MPS. In the investigations, the emission spectrum of the CO₂ plasma is measured using a spectrometer to observe the dissociation reaction of the CO₂ gas, and the exhaust gas after the CO₂ plasma generation is analyzed using a mass spectrometer to evaluate the CO₂ conversion. As a result, the CO₂ conversion decreases with an increase in either the average transmission power to the rod-electrode-type MPS or the CO2 flow rate into the rod-electrode-type MPS. Under the experimental conditions, the highest CO₂ conversion and energy efficiency are 6.3% and 3.7% at a specific energy input of 4.9 eV/molecule (equivalent to approximately 19.6 kJ/L), respectively.

In this paper, the design of a mechanically tunable band-pass filter in waveguide technology operating in the C-band tunability range [4.4-5] GHz, for satellite communications (SATCOM), is presented. The resonance frequency tunability has been obtained by mechanically inserting movable dielectric cylinders within the waveguide filter. The impedance matching has been achieved by using two movable dielectric ridges, working as quarter-wave transformers. They have been placed at input and output filter ports and can move jointly with the dielectric tuning elements. Filter design has been carried out by adopting a suitable theoretical model, whereas the optimization has been achieved by numerical simulations. The proposed design approach provides key advantages in terms of simplicity, design effectiveness and reproducibility, rendering it particularly suitable for industrial applications. A prototype of high-selectivity tunable filter has been fabricated and characterized within the whole tunability range. The measurements show excellent agreement with simulated results.

Plasmonic designs for mid-infrared extraordinary optical transmission (EOT), a direct route to tailored filtering with broadband out-of-band rejection, have long been constrained by a fundamental trade-off between high transmission efficiency and narrow linewidths, a challenge rooted in the material properties of noble metals. Here, we theoretically propose and numerically demonstrate a versatile design paradigm that resolves this challenge by functionally decoupling the tasks of light coupling and resonant filtering. Our approach uses a dual-stacked noble metal-dielectric grating architecture to surpass the intrinsic limitations of single-layer structures. This paradigm provides the flexibility to engineer devices for ultra-high spectral selectivity and transmission efficiency. We demonstrate this with distinct designs: one at 10 μm with a quality factor (Q-factor) >2000 and >91% transmission; a high-Q design at 4 μm and >80% transmission; and a high-efficiency design at 4 μm with >92% transmission over a uniquely broad spectral-angular range. These generic designs produce solitary, narrow EOT peaks originating from a ``triple-coupling'' mechanism that mitigates reflection and absorption losses, with symmetry-broken configurations capable of exceeding Q-factors of 16,000 while maintaining a peak transmission efficiency > 60%. Crucially, these compact two-layer designs exhibit exceptional robustness against fabrication variations, offering a broadly applicable route to ultra-compact, low-cost infrared components, enabling advanced architectures such as angular sensing, spectro-polarimetric imaging, and isotope-resolved gas diagnostics.

This work introduces a small cycle-shaped antenna for multiband applications. The design combines three main ideas, concentric circular rings on the patch, spoke-like arms to excite higher frequencies, and a hexagonal slot in the ground to extend bandwidth. The antenna is built on a 40 × 42 × 1.6 mm³ FR-4 substrate and works across three frequency bands within 3.04-3.62 GHz and 5.07-8.08 GHz, suitable for sub-6 GHz, ISM, WLAN applications. The structure is easy to tune, and increasing rings and the length of the spokes shifts the resonance to lower frequencies. Smaller gaps between rings may increase coupling and bandwidth. A bigger hexagonal slot etched on the ground widens the range but may slightly shift the frequency. With these features, the antenna achieves strong resonances and good return loss at 3.31, 5.75, and 7.58 GHz, achieving S₁₁ of -19.4 dB, -34.9 dB, -21.4 dB showing that it can support wireless applications.

To address the issues of step loss, control lag, and low precision in open-loop hybrid stepper motors applied in economical CNC machine tools, a deadbeat predictive current field oriented control method (DPCFOC) is proposed. First, the research progress of hybrid stepper motor vector control is systematically reviewed, analyzing the advantages and limitations of existing schemes in error compensation, model construction, and algorithm implementation. Subsequently, the continuous mathematical model of the hybrid stepper motor in the rotating coordinate system is established, and the discrete deadbeat predictive model and current prediction equation are derived using the first-order forward Euler method. On this basis, a deadbeat vector control algorithm is proposed. Compared with the traditional dual-closed-loop vector control with PI regulators, the algorithm predicts the next-step current through the motor model and calculates the optimal reference voltage vector in advance to eliminate current error, thereby improving dynamic response speed. Stability analysis via Z-transformation reveals that the system remains stable when the model inductance parameter is within 0-2 times the actual inductance. For the two-phase hybrid stepper motor, a space vector pulse width modulation (SVPWM) strategy based on a dual H-bridge inverter is designed, using 4 non-zero vectors and 2 zero vectors to synthesize the desired voltage vector. Finally, an experimental platform is built with a TMS320F28335 controller and a 57CME22A closed-loop stepper motor to verify the algorithm. This study provides a feasible solution for improving the control precision and dynamic performance of hybrid stepper motors in economical CNC machine tools.

Rare-earth permanent magnet motors are widely used in industrial and civil applications due to their advantages of high efficiency, energy saving, simple structure, etc. However, its development is hindered by escalating raw material costs. The current research focuses on developing high-performance and cost-effective permanent magnet motors with less rare earth. To reduce the large cogging torque of the integer slot 4-pole 36-slot less rare earth combined magnetic poles permanent magnetic synchronous motor (LREH-PMSM), a fractional slot 4-pole 30-slot LREH-PMSM is proposed and optimized. The motor and its parameters are designed, simulated, and analyzed by the finite element method. The effects of these parameters are analyzed on motor torque, torque ripple, efficiency, and material cost. The fractional slot 4-pole 30-slot LREH-PMSM can effectively reduce the cogging torque compared with the integer slot 4-pole 36-slot LREH-PMSM, and its value decreased by 88.28%. Compared with traditional rare-earth permanent magnet synchronous motor (PMSM), it not only has small cogging torque, but also lowers the reliance on rare-earth permanent magnet materials, which in turn lowers the material cost of the motor.

This paper presents a passive UHF RFID dipole antenna designed for object identification in supply chain applications. The antenna features a simple structure measuring 75 × 28 × 1.6 mm³ (2.17 × 0.81 × 0.046λ₀), with a copper radiating element printed on Taconic RF-35A2 substrate. It is matched to a Monza R6 chip with an impedance of 13 - j125 Ω at 868 MHz through a T-matching circuit. The prototype was tested on various complex surfaces, including plastic bottles, foam, cardboard, plastic boxes, and wood. Its performance evaluation involved measuring the reading distances in these environments. Simulation and measurement results demonstrate effective impedance matching between the antenna and chip. The read distances vary with the surface type, with the maximum distance reaching up to 14 meters on a plastic bottle within the European UHF RFID band ((865.5-869.5) MHz) and the shortest distance around 6 meters on wood. Overall, the tag exhibits strong adaptability to different surfaces. Simulations were conducted using CST Studio microwave software.

In this study, we describe a compact two-port MIMO dielectric resonator antenna (DRA) system made from biodegradable polylactic acid (PLA) using additive manufacturing techniques. Performance goals were achieved through a systematic performance study on the pin height, pin position, cavity width, and cavity length. The simulated results showed a wide range of bandwidth from 5.0 to 7.4 GHz with return loss (|S₁₁|) lower than -10 dB corresponding to a fractional bandwidth of approximately 36.8%. Excellent port isolation is achieved with |S₂₁| < -20 dB consistent across the entire band. The antenna provides more than 10 dBi gain with a high directivity making it useful for high-performance wireless applications. Furthermore, diversity MIMO performance confirms exceptional diversity performance with the Envelope correlation coefficient (ECC) remaining below 0.015 and ideal Diversity Gain (DG) of 10 dB. Another important feature is the electronic beam steering capability of this antenna, enabled by adjusting the phase difference between the two ports. With excitation phase shifts of 0°, 90°, 180°, and 270°, the antenna's main beam can be steered between broadside and unidirectional directions, providing flexible spatial coverage through dynamic phase control, rather than switching among fundamentally different radiation patterns. The employment of environmentally friendly PLA materials paired with 3D printing technology fosters sustainable practices for antenna development while simultaneously permitting inexpensive prototype creation and swift adaptability in the design changes. This MIMO DRA system can be extensively employed in C-band applications like the 5G communication systems, satellite downlink services, radar systems, and high-speed wireless data links where it is crucial to have wide bandwidth, high isolation, and compact size.

In this paper, for millimeter wave (mmWave) vehicle-to-infrastructure communication, a reconfigurable intelligent surface (RIS) is introduced for assisted beam tracking in order to overcome the problem that the line-of-sight (LOS) transmission characteristics of mmWave are highly susceptible to communication disconnection caused by large vehicles or obstacles in a highly mobile scenario like Internet of Vehicles (IoV). In this paper, we study the case of switching to the RIS-assisted virtual-line-of-sight (VLOS) path for temporary beam tracking when the direct connection LOS path is disconnected. The cascading channel model for the VLOS path used for tracking after the introduction of RIS is investigated. Combining the new state model of position and velocity, a three-dimensional beam tracking model of the VLOS path is derived based on the extended Kalman filter algorithm. The beam tracking process is designed, and the beam tracking performance is analyzed for different cases under this scheme. Simulation results show that the scheme in this paper has lower tracking error than the scheme of the conventional state model, and the introduction of RIS can overcome the problem that mmWave IoV communication is vulnerable to occlusion.

The environment is crucial to maintaining a healthy lifestyle and ensuring the continued existence of life on Earth. Nonetheless, throughout the past several years, environmental pollution has increased significantly due to the rapid growth of the global population and technological advancement. Consequently, numerous new sensors and techniques have been developed to effectively detect different types of environmental pollutants. Among all the various methods proposed for environmental monitoring, photonic crystal (PhC) devices have demonstrated great potential in sensing applications due to their high sensitivity to refractive index change, visual detectability, room-temperature operability, and easy portability. Recently, integrated mid-infrared (mid-IR) photonics have gained considerable attention because most gases exhibit a characteristic absorption peak in the mid-IR range. As a result, Mid-IR photonic crystals offer enormous potential for novel applications in optical interconnects and sensing. In this work, we propose a novel highly-sensitive mid-infrared photonic crystal-based slotted-waveguide coupled-cavity sensor to behave as a refractive index sensing device at a mid-infrared wavelength of 3.9 µm. The proposed sensor is simulated using Plane Wave Expansion (PWE) method and Finite-Difference Time-Domain (FDTD) algorithm. The high performance and simple design of the proposed sensor make it a promising candidate for environmental monitoring applications.

Complex beams hold significant value in radar and communication systems due to their distinctive propagation characteristics. Digital metasurfaces, which can dynamically control electromagnetic (EM) waves, play an important role in realizing complex beams. Conventional analytic and optimization methods face challenges in synthesizing complex beams of low-bit digital metasurfaces due to the quantization error and the high computational complexity. Here, we propose a statistical method to realize complex beams with phase-only digital metasurfaces. To this end, we introduce tailored quantization probabilities to design the discrete random phase distributions, which approximate the continuous excitation coefficients derived from analytic methods. Based on the proposed method, we analyze the error between the realized and target patterns. These findings offer critical insights into the accuracy of random quantization. Complex patterns with cosecant, prescribed null, flat-top, and dual-beam are designed and validated in combination with a 2-bit phase coding digital metasurface. The experimental results are in good agreement with the theoretical analysis. This work pioneers the application of random phase approximation and statistical synthesis in digital metasurfaces, providing a fast and efficient route for realizing complex beams in modern radar and wireless communication technologies.

This paper proposes a single-layer, low-profile, and compact filtering patch antenna. The antenna requires no additional filtering structures and consists only of a dielectric substrate, a radiating patch etched with both star-shaped slots and L-shaped slots, a feeder line integrated with a quarter-wavelength matching stripline, and a partial ground plane connected to inverted-π branches. Among these components, the radiating patch, feeder line, and inverted-π branches work synergistically to form two radiation nulls on either side of the passband. This not only enhances the frequency selectivity at the band edges but also optimizes the antenna's radiation performance and filtering performance simultaneously. Finally, to verify the validity of the design, a prototype of the antenna is designed, fabricated, and tested, and the measured results are in good agreement with the simulated results. The design achieves a wide impedance bandwidth of 66.5% (2.33-4.65 GHz), a peak realized gain of 4.25 dBi, and an average efficiency of up to 92%. With a size of 35 mm × 29 mm × 0.8 mm, the antenna satisfies the miniaturization requirement and can be applied to various scenarios, including short-range wireless communication and 5G communication.

This research presents a quad-band dipole antenna for use with a surveying drone. The dipole antenna structure design employs the technique of adding I-shaped stubs and V-shaped etching, using aluminum plates with a strong and lightweight structure, with a thickness of 2 mm, a width of 1,325 mm, and a length of 190 mm. The antenna is designed to support frequency bands according to standards (VOR: Very High Frequency Omnidirectional Range) at 118 MHz, (GS: Glide Slope) at 336 MHz, (DME: Distance Measuring Equipment) at 1231 MHz, and WiFi at 2.45 GHz. From the calculations and simulations using the CST program, optimal parameter values were obtained, leading to the fabrication of a prototype antenna and the testing of its antenna properties. The results showed reflection coefficient values of -21.87 dB (108-118 MHz), -12.76 dB (328-336 MHz), -11.99 dB (962-1231 MHz), and -21.79 dB (2400-2480 MHz), which covers the VOR/GS/DME/ IEEE 802.11b/g/n standards. The antenna gain values are 1.12, 2.38, 3.76, and 4.00 dBi, respectively, with an omnidirectional radiation pattern, and the prototype dipole antenna tested with a drone was found to operate normally in the low frequency range of 108-118 MHz, the first mid frequency range of 328-336 MHz, the second mid frequency range of 962-1231 MHz, and the high frequency range of 2400-2480 MHz.

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%.