Search Results (554)

A compliant parallel multi-directional piezoelectric vibration energy harvester (C-MVEH) is proposed based on a 3-RRR compliant parallel mechanism. The energy harvester structure consists of three identical L-shaped beams, whose bending deformation can be equivalent to the rotations of the three joints. In order to achieve greater bending deformation for composite beams, motion flexibility optimization of the mechanism theory is applied to structure the synthesis of the C-MVEH. Meanwhile, to reduce the natural frequencies corresponding to the working modes, the length of the elastic beam is optimized with the maximum natural frequency among the first three modes. In order to verify the excellent performance of the C-MVEH, an electromechanical model, finite element simulations, and experimental studies are carried out. Analysis of the studies reveals that the C-MVEH has three resonance peaks of output voltage within a bandwidth of 7–13 Hz and can output a total voltage of at least 20 V under a small excitation of 0.2 g. The energy harvester can achieve multiple peak output voltages under small excitations in different directions and a wide frequency range. With its outstanding stability, the proposed C-MVEH demonstrates considerable application value in the supplying of power to microenergy electronic devices, such as smart sensors and microactuators. Full article

This paper proposes a small-signal model of a DC–DC parallel resonant converter operating in continuous conduction mode based on asymmetric pulse-width modulation (APWM) under light-load conditions. The parallel resonant converter enables soft switching and no-load control over a wide load range because the resonant capacitor is connected in parallel with the load. However, the resonant energy required for soft switching is already sufficient, and the current flowing through the resonant tank is independent of the load magnitude; therefore, as the load decreases, the energy that is not delivered to the load and instead circulates meaninglessly inside the resonant tank increases. This results in conduction loss and reduced efficiency. To address this issue, APWM with a fixed switching frequency is required, which reduces circulating energy and improves efficiency under light-load conditions. Precise small-signal modeling is required to optimize the APWM controller. Unlike PFM or PSFB, APWM includes not only sine components but also DC and cosine components in the control signal due to its asymmetric switching characteristics, and this study proposes a small-signal model that can relatively accurately reflect these multi-harmonic characteristics. The proposed model is derived based on the Extended Describing Function (EDF) concept, and the derived transfer function is useful for systematically analyzing the dynamic characteristics of the APWM-based parallel resonant converter. In addition, it provides information that can systematically analyze the dynamic characteristics of various APWM-based resonant converters and control signals that reflect various harmonic characteristics, and it can be widely applied to future control design and analysis studies. The validity of the model is verified through MATLAB (R2025b) and PLECS (4.7.5) switching-model simulations and experimental results, confirming its high accuracy and practicality. Full article

Dynamic Wireless Power Transfer (DWPT) systems require analytical models capable of capturing time-varying coupling and multi-transmitter interactions. However, most existing formulations address only static Wireless Power Transfer (WPT) or single-transmitter configurations, offering limited applicability to realistic DWPT scenarios. This paper addresses this gap by developing a comprehensive analytical framework for Series–Series (SS) compensated DWPT systems, supporting general n-transmitter/m-receiver architectures. The model is derived from coupled RLC circuit equations and expressed in normalized time- and frequency-domain forms, enabling analysis of resonance behavior, transient dynamics, and mutual-inductance variations during vehicle motion. To represent the continuous receiver motion, we establish a coupling-coefficient distribution covering the operating range of $k=0.11$ to $k=0.581$. The framework is then applied to three representative cases: a dynamic $1\times 1$ baseline, sequential transmitter activation, and simultaneous multi-transmitter activation. The study investigates system performance across varying operating frequencies and receiver positions to evaluate efficiency characteristics for $1\times 1$, $n\times 1$, and $n\times m$ wireless power transfer configurations. The proposed analytical framework provides a scalable basis for control development, transmitter coordination, and future real-time DWPT implementation. Full article

Rydberg atoms are neutral atoms excited to high principal quantum number states, which endows them with exaggerated properties such as large electric dipole moments, long lifetimes, and extreme sensitivity to external electromagnetic fields. These characteristics form the foundation of Rydberg atom-based sensors, an emerging class of quantum devices capable of optically detecting electric fields across frequencies from DC to the terahertz regime. Rydberg-based electrometry operates through both Autler–Townes (AT) splitting of resonant Rydberg transitions and Stark-shift measurements for high-frequency or far-detuned fields, enabling broadband field sensing from DC to the THz regime. Using ladder-type electromagnetically induced transparency (EIT) and AT splitting, these sensors enable non-invasive, SI-traceable measurements of field amplitude, frequency, phase, and polarization. Recent developments have demonstrated broadband electric field probes, voltage calibration standards, and compact RF receivers based on thermal vapor cells and integrated photonic architectures. Furthermore, innovations in multi-photon EIT, superheterodyne readout, and multi wave mixing have expanded the dynamic range and bandwidth of Rydberg-based electrometry. Despite challenges related to environmental perturbations, linewidth broadening, and laser stabilization, ongoing advances in atomic control, hybrid photonic integration, and EIT-based readout promise scalable, chip-compatible sensors. This review summarizes the physical principles, experimental progress, and emerging applications of Rydberg atom-based sensing, emphasizing their potential for next generation quantum metrology, wireless communication, and precision field mapping. Full article

Marine risers, critical structures connecting underwater production systems and surface floating platforms, stand freely in water and endure extremely complex marine environmental loads. To meet the multi-parameter observation demand for their overall state, a fiber-optic sensing-based marine riser buoy observation system was developed. Unlike traditional point-type and offline monitoring systems, it integrates marine buoys with sensing submarine cables to achieve long-term real-time online monitoring of risers’ overall state via fiber-optic sensing technology. Comprising two main modules (buoy monitoring module and fiber-optic sensing module), the buoy’s stability was verified through theoretical derivation, simulation, and stability curve plotting. Frequency domain analysis of buoy loads and motion responses, along with calculation of motion response amplitude operators (RAOs) at various incident angles, showed the system avoids wave periods in the South China Sea (no resonance), ensuring structural safety for offshore operations. A 7-day marine test of the prototype was conducted in Yazhou Bay, Hainan Province, to monitor real-time temperature and strain data of the riser in the test sea area. The sensing submarine cable accurately responded to temperature changes at different depths with high stability and precision; using the Frenet-based 3D curve reconstruction algorithm, pipeline shape was inverted from the monitored strain data, enabling real-time pipeline monitoring. During the test, the buoy and fiber-optic sensing module operated stably. This marine test confirms the buoy observation system’s reasonable design parameters and feasible scheme, applicable to temperature and deformation monitoring of marine risers. Full article

To broaden the operating bandwidth of the vibration energy harvester at low frequencies, this paper presents a cantilever beam piezoelectric energy harvester (PEH) based on the sloshing of a liquid-filled container. The harvester is designed to recover energy from the multi-order sloshing modes of the liquid in the container. A mathematical model of the coupled system comprising the liquid within the container and the PEH was established. Based on the fluid–structure interaction (FSI) theory, the coupling mechanism between the liquid natural sloshing frequency and the immersed natural frequency of the beam was revealed. Experimental validation shows that the resonance characteristics of the PEH are mainly dominated by the liquid antisymmetric sloshing mode. Through comparative experiments, the effect of liquid-filled container and cantilever beam parameters on the PEH’s peak output voltage and operating bandwidth was systematically analysed. The performance of the PEH was significantly improved when the first-order natural frequency of the partially immersed beam approached the liquid natural sloshing frequency, with the bandwidth coefficient increasing by nearly fourfold under this condition. This research provides new ideas for the design and optimisation of piezoelectric energy harvesters in liquid sloshing environments. Full article

The high-frequency and high-amplitude pyroshock environment during the use of spacecraft will cause damage to the equipment. To simulate this environment, a pyroshock environment simulator based on electromagnetic excitation is presented in this work. A multiphysics finite-element model with electromagnetic–force coupling is established to analyze field distributions during excitation and the acceleration response of a resonant plate under Lorentz loading. Parametric analyses examine coil structural parameters, coil current, and plate thickness and their effects on the SRS. It is suggested that the pyroshock environment excited by electromagnetic force has the characteristics of wide frequency band and high amplitude similar to the explosive-based pyrotechnical event, and compared with the single coil, the multi-coil combination can excite a higher peak acceleration without changing the SRS shape. At the same time, the structural parameters of the planar induction coil and the current in the coil only affect the SRS amplitude of the resonant plate, and the degree of influence of the parameters on the SRS peak amplitude is coil width > coil lift-off distance > coil thickness > coil turn-to-turn distance. Additionally, the experimental results are in good agreement with the simulated SRS, verifying the validity of the above-mentioned analysis. Full article

Ocean waves constitute a vast renewable resource, yet most linear generator-based wave energy converters (WECs) rely on single-degree-of-freedom (SDOF) linear oscillators that exhibit narrow resonance bandwidths and utilise sliding components prone to wear. To address these limitations, this paper presents a nonlinear three-degree-of-freedom (3DOF) magnetic spring power-take-off (PTO) system for broadband wave energy harvesting. The device comprises three axially levitated NdFeB permanent magnets, each coupled to an independent copper coil, forming a compact, friction-free generator column. A coupled electromechanical state-space model was developed and experimentally validated on a laboratory-scale test rig. The 3DOF PTO exhibited three distinct resonance modes at approximately 35, 48, and 69 rad s⁻¹, enabling multi-mode energy capture across a broad frequency range. Under identical excitation (6.5 N amplitude and 3.13 Hz excitation force), the 3DOF configuration achieved a 114.5% increase in RMS voltage compared with the SDOF design and a 44.10% improvement over the 2DOF benchmark, confirming the effectiveness of the coupled resonance mechanism. The levitated magnetic architecture eliminates mechanical contact and lubrication, reducing wear and maintenance while improving long-term reliability in marine environments. A preliminary life-cycle assessment estimated a cradle-to-gate carbon intensity of 40–80 g CO₂-eq kWh⁻¹, significantly lower than that of conventional hydraulic PTOs, owing to reduced steel use and recyclable magnet assemblies. The proposed 3DOF magnetic spring PTO thus offers a sustainable, low-maintenance, and high-efficiency solution for next-generation ocean-energy converters. Full article

As the primary interface for integrating renewable energy sources such as wind and solar power into the grid, inverters are prone to inducing sub-/super-synchronous or medium-to-high-frequency oscillations during grid-connected operation under weak grid conditions. Optimizing the control structure of a single wind turbine inverter struggles to address multi-mode resonance issues comprehensively. Therefore, a cooperative control strategy for parallel-coupled inverters is proposed. First, a frequency-domain impedance reconstruction method for parallel wind turbines is proposed based on the phase-neutralizing characteristics and damping variation patterns of parallel-coupled impedances. Second, the damping characteristics of inverters are enhanced through the design of an additional damping controller, while the phase-frequency characteristics of wind turbines are improved using active damping based on notch filters. Finally, simulation models based on 2.5 MW permanent magnet synchronous generator (PMSG) units validate the effectiveness of the control strategy. Research results demonstrate that this cooperative control strategy effectively suppresses sub-/super-synchronous and medium-to-high-frequency oscillations: In the 0~300 Hz key oscillation band, the amplitude suppression rate of oscillating current reaches ≥60%, the total harmonic distortion (THD) of the 5th harmonic at the grid connection point decreases from 4.465% to 3.518%. Full article

The multi-layered and multi-scale refined structure of bamboo gives bamboo musical instruments a unique tonal quality. This study employed heat treatment to enhance the acoustic vibration stability of bamboo materials. The hammering method was subsequently employed for conducting multi-point impact excitation tests on instrument-grade bamboo, and the resulting vibration response was subjected to modal analysis. Next, we investigated the acoustic vibration characteristics of bamboo, including its sound vibration efficiency, timbre, and acoustic stability, in terms of its macroscopic gradient structure, ultra-microstructure, molecular scale, key components, and pore structure. Modal analysis revealed that the first three damping ratios of Xipi were 94.55%, 7.89%, and 26.60% higher than those of Erhuang, respectively. The relative stiffness of Xipi across the first three modes was 1.22, 1.22, and 1.18 times that of Erhuang, indicating a generally higher structural rigidity. The first three natural frequencies of Xipi were approximately 1.20, 1.20, and 1.19 times higher than those of Erhuang, and its fundamental transfer function value was 1.5 times greater, suggesting a lower susceptibility to low-frequency resonance. Modal shapes showed distinct vibration behaviors between the two types: Xipi exhibited a more effective energy transmission path in the second mode and less structural distortion in the third mode, potentially indicating higher structural integrity. This research provides support for developing new technologies to select and process bamboo materials for musical instruments. Full article

Diverse application scenarios demand frequency-selective surfaces (FSSs) with tailored center frequencies and bandwidths. However, their design traditionally relies on iterative full-wave simulations using tools such as the High-Frequency Structure Simulator (HFSS) and Computer Simulation Technology (CST), which are time-consuming and labor-intensive. To overcome these limitations, this work proposes an octagonal fractal frequency-selective surface (OF-FSS) composed of a square ring resonator and an octagonal fractal geometry, where the fractal configuration supports single-band and multi-band resonance. A physics-informed reinforcement learning (PIRL) algorithm is developed, enabling the RL agent to directly interact with CST and autonomously optimize key structural parameters. Using the proposed PIRL framework, the OF-FSS achieves both single-band and dual-band responses with desired frequency responses. Full-wave simulations validate that the integration of OF-FSS and PIRL provides an efficient and physically interpretable strategy for designing advanced multi-band FSSs. Full article

The compact and wideband patch antennas applied to WiFi 7 multiple-input multiple-output (MIMO) antenna systems are presented. The MIMO antenna structure consists of four multi-branch radiating patches fed by coupled microstrip lines, which occupies a size of $32\times 32\times 1 {\mathrm{m}\mathrm{m}}^3$. By exploiting multiple resonant modes, an impedance bandwidth of 37% (5.07–7.37 GHz) achieves a reflection coefficient of less than −10 dB and fully encompasses both WiFi 7 high-frequency ranges. To alleviate mutual coupling, two decoupling structures, named complementary split-ring resonators (CSRRs), are employed between the MIMO elements to interact with the undesirable surface current; furthermore, the proposed orthogonal placement of four elements further minimizes radiation coupling. Consequently, the proposed array achieves measured isolations greater than 14.5 dB and 11 dB at 5 GHz and 6 GHz bands, respectively. The prototype of the proposed MIMO antenna has been manufactured. It has also been measured and the results show similarity with the simulations. The measured radiation pattern and the diversity performance, including the envelope correlation coefficient (ECC), diversity gain (DG), and multiplexing efficiency, are calculated, and they verify the outstanding diversity characteristics of the proposed MIMO antenna. This makes it a promising solution for emerging WiFi 7 wideband applications. Full article

This paper investigates a dual-active-bridge (DAB) converter topology based on a voltage-doubler rectifier and series resonant network. By integrating phasor-domain analysis with time-domain modeling, a comprehensive mathematical model of the output voltage and instantaneous inductor current is established. The voltage gain expression is further refined by accounting for the effects of dead-time and power switch output capacitance. Based on this model, a multi-objective global optimization is performed, aiming to minimize reactive power, RMS current, and switch conduction losses, while simultaneously satisfying zero-voltage switching (ZVS) conditions and voltage gain requirements. Leveraging the optimization results, an extended phase-shift control strategy incorporating phase-shift feedforward and frequency closed-loop regulation is proposed. Experimental results demonstrate that the proposed topology achieves high efficiency across the entire operating range, with a peak efficiency of 96.92%. The results validate the effectiveness and engineering practicability of both the topology and the control scheme. Full article

This paper introduces a theoretical framework for designing and tuning band-pass filters with a highly extended periodicity using cascaded Mach-Zehnder Interferometer (MZI) networks. We show that a filter centered at frequency f₀ with a bandwidth of FSR₀ and an arbitrarily large free spectral range (FSR) can be built with a minimal number of MZIs by using stages with FSRs that are prime multiples of FSR₀. Due to the inherent multi-spectral transparency of materials, this design ensures that only a single narrow passband is transparent. We derive the total power transmission for such a cascaded system and show that the filter’s overall periodicity is the product of the individual MZI transfer functions. Furthermore, we deduce the linear relationship between the applied differential voltage and the resulting frequency shift, offering a precise method for continuous spectral tuning without altering the filter’s intrinsic FSR. We propose a new, simplified electronic circuit that uses a single input current and series impedances for continuous resonant peak tuning and analyze the feasibility of such a design. This circuit improves practical implementation and allows for compensation of fabrication errors. This work offers crucial analytical tools and insights for developing advanced reconfigurable photonic integrated filters, essential for future optical communication and sensing systems. Full article

High-Intensity Radiated Fields (HIRFs) can cause severe interference to airborne GNSS equipment. This paper builds a CST model based on the real structure and evaluates shielding effectiveness (SE) with respect to frequency, material, polarization, angle of incidence, and aperture; anechoic-chamber tests combined with the DO-160G compliance method (Section 20, Class G) are then conducted, and this integrated scheme: (1) validates the simulation’s effectiveness and confirms the HIRF coupling risk; (2) reveals the GNSS failure mechanism—C/N₀ decrease → DOP increase → loss of lock. Subsequently, an equation-based mechanism framework (cavity modes, slot/aperture coupling, waveguide-below-cutoff, thickness attenuation) is proposed, together with an effective-dimension correction, by which a single-point calibration can predict the remaining resonances. Accordingly, mechanism-aligned design strategies are provided (aperture control and honeycomb windows, geometric detuning and local absorbers, high-permeability inserts, multi-polarization and multi-directional protection), achieving predictable, verifiable, and quantifiable improvements in SE. Full article