Search Results (346)

Welded structures are widely used in ships and marine equipment. The ultrasonic longitudinal critically refracted (LCR) wave method is a reliable technique for measuring residual stress in welded structures. Conventional ultrasonic measurement systems have high power consumption and are difficult to operate under the limited power supply conditions of marine environments. Reducing the excitation voltage can lower power consumption, but as the excitation voltage decreases, ultrasonic echo energy weakens and noise interference increases, thereby affecting the accuracy of stress measurement. This paper proposes a complexity-mutation-based adaptive singular spectrum analysis–variational mode decomposition algorithm (CM-SSA-VMD). The algorithm constructs a complexity index using the spectral centroid, waveform roughness, and zero-crossing rate. By identifying abrupt changes in complexity between adjacent singular spectrum analysis (SSA) components, it adaptively determines which components to retain for reconstruction. Then, variational mode decomposition (VMD) is used to further separate the residual high-frequency noise. Finally, the ultrasonic time of flight (TOF) is estimated using the cross-correlation algorithm, and the stress is calculated. The stress measurement accuracy of the proposed algorithm was evaluated at different excitation voltages: 5.2 V, 3.3 V, 1.2 V, and 0.5 V. The results show that when the excitation voltage drops to 0.5 V, after being processed by CM-SSA-VMD, the average relative error of stress measurement remains below 10%, while the average relative errors of a new adaptive denoising method, Grey Wolf Optimization–Variational Mode Decomposition–Wavelet Transform (GWO-VMD-WT), traditional FIR filtering and VMD are approximately 14%, 18% and 16% respectively. Compared with GWO-VMD-WT, FIR filtering and VMD, the measurement accuracy of this method is improved by 33.35%, 46.16% and 41.82% respectively. The CM-SSA-VMD algorithm can effectively suppress noise in ultrasonic signals at low excitation voltages and improve the reliability of stress monitoring. It provides a feasible method for low-power ultrasonic residual stress monitoring in marine engineering. Full article

This paper investigates waveform-level voltage difference features for the early indication of cell-to-cell voltage reversal in two series-connected lithium-ion cells for electric-vehicle battery management systems (BMSs). The key observation is that a local sign reversal of the cell-to-cell voltage difference can appear inside the constant-current (CC) discharge waveform before the cycle-mean voltage difference changes sign. A positive-fraction feature is introduced to quantify this local waveform reversal and is interpreted as a candidate BMS-oriented indication layer rather than as a universal alarm criterion. The analysis combines a Kirchhoff decomposition of the cycle-mean voltage difference with waveform matrix analysis and physical consistency checks based on principal component analysis (PCA), voltage slope behavior, equivalent-circuit-model sensitivity, and auxiliary temperature signals. In the present dataset, the first 5% crossing of the introduced positive-fraction feature occurs 44 cycles before the cycle-mean voltage reversal, and the five-cycle persistent onset precedes it by 39 cycles; this lead stays between 29 and 46 cycles across the persistence and detection threshold settings examined. The onset location is consistent with the low-slope graphite-staging region of the loaded-voltage curve, where the open-circuit voltage (OCV) slope compensation is weak and the resistance-related offset can dominate locally. The reference event used to quantify this lead is the cycle-mean voltage reversal itself, which is an observable benchmark defined on the scalar that a BMS already computes rather than a ground-truth onset of imbalance; the two cells are measurably unequal from the first cycle. The onset is shown to be insensitive to the resampling grid, the interpolation rule, the detection threshold and realistic voltage noise and channel offsets, and to produce no false onset anywhere in the 998-cycle record. The result is a waveform-level diagnostic observable quantity that converts a hidden local sign reversal into an interpretable cycle-level indication for BMS-oriented screening and monitoring. Because this study rests on a single two-cell series connection, it is presented as a proof-of-concept case study, and replication on independent cell pairs is required before the behavior can be regarded as general. Full article

The water-blocking buffer layer of high-voltage cross-linked polyethylene (XLPE) power cables is prone to degradation during long-term operation due to factors such as moisture and ablation. The degradation may cause an increase in leakage current, which is affected by frequency. However, the correlation between buffer layer status and leakage current under various frequencies needs further investigation. Accordingly, this paper investigates leakage current characteristics of cable water-blocking buffer layers with different statuses under multi-frequency excitation. Firstly, a multi-frequency leakage current test platform was established. Afterwards, composite specimens consisting of XLPE insulation and a water-blocking buffer layer were prepared in four different states: normal, moisture-affected, slightly ablated, and severely ablated. The leakage current responses of different specimens under various voltage frequencies were systematically examined. The results show that, under moisture-affected conditions, the leakage current increases by 15–30% compared with the normal state. The voltage–current phase difference decreases significantly in the low-frequency range by 9–64°. The total harmonic content increases markedly as the frequency decreases, with the 3rd, 5th, and 7th harmonics exhibiting the highest sensitivity. Ablated samples have limited influence on the leakage current. But localized spikes appear in the waveform. Under normal conditions, the leakage current waveform follows the applied sinusoidal voltage, forming a natural symmetry in both frequency and time domains. However, moisture ingress and ablation defects break this symmetry by introducing harmonic distortion in the frequency domain and pulse-shaped spikes in the time domain, respectively. The method utilizes low-frequency leakage-current harmonics and harmonic–residual spikes to identify buffer layer moisture and ablation defects. The proposed method enables the effective identification of different buffer layer states and provides a technical approach for the defect diagnosis of water-blocking buffer layers in high-voltage cables. Full article

Piezoelectric acoustic logging transmitters are commonly evaluated using low-voltage small-signal impedance measurements, whereas their practical operation involves high-voltage, high-current, finite-cycle short-burst excitation. This difference makes it difficult to predict the actual loaded electrical input state and directional acoustic response from conventional impedance spectra alone. In this study, a high-voltage short-burst electroacoustic measurement method is developed for piezoelectric acoustic logging transmitters. Unlike conventional small-signal impedance analysis, the proposed method synchronously measures the terminal voltage, terminal current, and 1 m hydrophone response under the same high-voltage short-burst excitation condition. A three-cycle sinusoidal burst was amplified and applied to a water-loaded PZT-5A tube transducer over an 8–100 kHz frequency sweep. For the finite-cycle non-steady-state waveforms, adaptive time-window extraction and single-frequency projection were used to obtain the dynamic apparent impedance, instantaneous power, single-burst input energy, effective short-burst transmitting voltage response, and hydrophone direct-wave voltage energy. The results show that small-signal impedance spectra measured in air and water can identify modal characteristics and candidate frequency bands, but they cannot directly represent the actual high-voltage short-burst operating state. The single-burst input energy shows a stronger frequency-dependent association with the hydrophone direct-wave voltage energy than the impedance magnitude or current amplitude alone. To further evaluate practical applicability, eight nominally identical acoustic logging transmitters were characterized using both conventional small-signal impedance analysis and the proposed high-voltage short-burst method, and their transmitting performances were independently evaluated in a natural-rock model well. The high-voltage dynamic conductance and, in particular, the single-burst input energy showed substantially stronger correspondence with the received P-wave voltage energy than the conventional small-signal conductance. The proposed method provides a practical measurement basis for evaluating acoustic logging transmitters under realistic short-burst excitation conditions, while the eight-transmitter model-well experiment provides preliminary support for its potential use in transmitter screening. Full article

This paper presents a fault diagnosis approach for a five-level Cascaded H-Bridge Multilevel Inverter (CHBMI) supplying an Interior Permanent Magnet Synchronous Motor (IPMSM). The method is based on a two-dimensional Convolutional Neural Network (2D CNN) designed to process voltage signals converted into image representations. In particular, the inverter voltage waveforms are transformed into grayscale images through a time-series reshaping procedure. This allows for the model to capture spatial patterns associated with different fault conditions, including both open-circuit and short-circuit faults. A multi-branch CNN architecture is adopted to simultaneously process multiple voltage signals, improving the ability to distinguish between fault types and locations. The proposed framework is evaluated on a dataset including 17 operating conditions under different speed and load profiles. The results confirm that the proposed approach provides accurate and reliable fault detection and is suitable for real-time diagnostic applications in multilevel inverter-based drive systems. Full article

Low-noise front-end amplifiers are essential for the acquisition of weak biopotential signals, such as electrocardiograms (ECGs), where the noise introduced by the first amplification stage directly limits the overall signal quality. While correlated noise-cancellation techniques have been extensively investigated for radio-frequency (RF) low-noise amplifiers, their application to low-frequency biomedical interfaces remains largely unexplored because of the different dominant noise mechanisms. This work investigates the applicability of an RF-inspired correlated noise-cancellation methodology to a low-frequency CMOS biomedical preamplifier core intended for ECG front-end applications. The proposed architecture extends a conventional resistive-feedback common-source amplifier by introducing an auxiliary feedforward path designed to attenuate the internally generated correlated noise components without significantly affecting the useful signal. The amplifier was designed in a 150 nm CMOS process and evaluated through AC, noise, Monte Carlo, PVT and time-domain analyses. Compared with the reference single-stage implementation, the proposed architecture achieves approximately a 20% reduction in integrated input-referred noise and a 14% reduction in integrated output-referred noise while marginally improving the voltage gain. Statistical analyses confirm that the proposed technique maintains its effectiveness under process, voltage, temperature, and mismatch variations. Time-domain evaluations with representative ECG waveforms further validate the methodology at the amplifier-core level and indicate its potential integration into complete low-noise biomedical analog front-ends. Full article

Latent faults in electromagnetic transient (EMT) components can alter initialization, switching-event, and history-state semantics while producing sparse or small waveform discrepancies. This study formulates a reference-model-based verification as a closed-set, waveform-guided diagnosis and constrained source-repair problem. Global, local-window, and event-level evidence rank fault mechanisms or trigger abstention. Repairs must pass compile-feasibility, behavioral-conformance, and applicability-aware physics-and-discretization audit gates. A multi-agent workflow implements this process. InvSqrt and single-phase-breaker faults were corrected to exported-waveform precision; the breaker record contained only two nonzero differences among 20,000 samples. The VARRL correction yielded 0.1% residual node-voltage RMS differences. A within-case VARRL extension across four matched conditions and three source variants exposed condition-dependent activation, a weakly separated effect of 0.018% RMS relative difference, a smaller inseparable effect routed to expert review, and a mixed-snapshot variant that reduced reference error but violated a discretization contract. An author-constructed ten-candidate challenge set spanning three component structures compiled in RSCAD FX 2.3 CBuilder; the deterministic audit returned Pass for three designed semantics-preserving refactorings, Reject for six isolated rule violations, and Expert review for one underspecified temporal convention. These results provide mechanism-level and preliminary audit-coverage evidence rather than population-level fault frequency, independent classification accuracy, general rule sufficiency, or formal verification. Full article

This contribution presents a methodology for optimal placement (OP) of meters in power systems, using the state-space reference frame. The goal is to minimize the state estimation error, specifically, the mean squared error (MSE), through OP of a limited number of measurement devices and keep the total observability of the system. The measurement set is applied to the time-domain state estimation based on the Kalman filter (KF) to obtain voltage and current waveforms in real time, and the harmonic content is evaluated through the application of the Fast Fourier Transform (FFT). The effectiveness of harmonic state estimation (HSE) is demonstrated in case studies considering different operating points in a test electrical network, particularly in estimating the dynamic behavior of nonlinear electrical loads. The HSE method is implemented in physical tests using Lab-Volt^® equipment to monitor the system in real time using MATLAB/Simulink^® software through the RL-LAB^® platform; the real-time experimental tests (RTE) allow validation of the real-time digital simulation (RTS). Full article

In reconfigurable array transmissions, a phased-array transmitter changes its characteristics, yet must still be able to control its transmission while optimizing its performance. To enable full reconfiguration while transmitting predictably, performing accurate, real-time measurements within the transmit chain is useful. This recently developed in-situ measurement approach, shown in multiple previous contributions, is summarized in this paper. It serves two purposes: (1) informing the real-time optimization algorithm whether changes in transmitter characteristics improve or worsen performance, and (2) updating the array calibration to obtain the desired transmit array pattern. This will enable real-time, “on the fly” optimizations of transmitters to coexist with other wireless devices in an increasingly congested spectral environment. A four-port coupler, with two monitoring outputs, is used to monitor the total voltage and current between a reconfigurable impedance tuner and the antenna in each element of a transmit array chain. Experimental work from the different prior contributions shows the overall trajectory, reliability, and proposed applications of this in-situ measurement technique. Less than 1 mV of error vector magnitude is shown in vector network analyzer methods compared with simulations using the in-situ coupler approach. The integration and calibration of a software-defined radio to perform antenna input current in-situ measurements has been implemented, with an average current error vector magnitude of 258 µA when comparing the software-defined radio measurements with simulations. Simulation results have shown that in-situ measurements can successfully correct input voltage waveforms for accurate directionally modulated transmissions, lessening reliance on fixed transmitter array pre-calibrations. Full article

Large-capacity lithium iron phosphate (LFP) batteries dominate energy storage systems, but their degradation characteristics differ from small-capacity cells. Most existing life prediction methods require complete voltage–current time-series data, which is hard to obtain in practical operation. This paper proposes two life prediction methods: a data-driven method and an empirical-data hybrid method. The data-driven method adopts Summed Voltage Falloff (SVF) extracted from partial voltage segments as the health indicator, which removes the dependence on full charge–discharge waveform data and enhances engineering practicability. It uses a unified numerical fitting framework with Gaussian process regression (GPR) residual correction, with tailored fitting strategies for 320 Ah and 298 Ah battery datasets. The hybrid method integrates the Arrhenius model with Kalman filtering for closed-loop online prediction correction. Both methods are validated using 281 cycles of 320 Ah battery data, and the data-driven method is further verified with 150 cycles of 298 Ah battery data. Results show that the data-driven method performs better with limited data, suitable for offline one-time inspection scenarios; the hybrid model achieves higher accuracy with sufficient data, applicable to long-term online remaining useful life monitoring. The data-driven method yields a worst-case cycle life of 3304 cycles at 2σ confidence level, and the hybrid model maintains error below 5% when forecasting 1000 cycles with 200 cycles of training data. Full article

Air circuit breakers are critical protective devices in low-voltage distribution systems, and their reliability is considered to have significant influence on the operation of such systems. With respect to the electrical performance degradation of air circuit breakers, the relationship between the change in over-travel and the contact mass loss is analyzed, and a mechanical parameter method for the degree of contact erosion is proposed. The relationship between contact over-travel and the rotation angle of the pole shaft is investigated, and the monitoring of over-travel variation is achieved by measuring the pole shaft rotation angle. An electrical performance degradation model for air circuit breakers is established based on a univariate linear Wiener process with drift. The variation characteristics of the model parameters under different current stresses are analyzed, and a residual electrical life prediction method based on over-travel variation is developed. Electrical performance degradation experiments are conducted on air circuit breakers, from which the degradation model parameters are obtained. The residual electrical life is predicted using the over-travel variation data, and the relative prediction error is shown to be less than 5%. Real-time monitoring of the interrupting current and voltage waveforms of the air circuit breaker is not required by this method, which makes it convenient for practical engineering applications. Full article

A double-ended traveling-wave accurate fault location method based on variational mode decomposition (VMD), generalized S-transform (GST), and a symmetric difference energy operator (SDEO) is proposed for single-phase-to-ground faults in small-current grounding distribution networks. The method is designed for fault conditions in which the fault current amplitude is low, the transient duration is short, and the initial traveling-wave wavefront is easily affected by high-frequency oscillation, reflection, refraction, and noise. The three-phase voltage traveling waves measured at both ends of the fault section are first transformed using Clarke modal transformation, and the voltage line-mode component is selected as the input signal. VMD is then used to decompose the nonstationary traveling-wave signal into several finite-bandwidth intrinsic mode functions. The high-frequency mode containing the initial wavefront mutation is processed using the generalized S-transform to enhance local time–frequency features. Finally, the SDEO instantaneous energy spectrum is used to calibrate the initial wavefront arrival time. For distance calculation, an improved double-ended traveling-wave location formula based on the horizontal section length and the absolute propagation time ratio at both line ends is constructed. This formulation reduces the dependence on a fixed empirical wave velocity and weakens the influence of line length deviation caused by practical line geometry. The method is verified using a deterministic PSCAD/EMTDC v5.0.2 and MATLAB R2021b co-simulation model with a fixed distribution network topology and arc-suppression-coil grounding. The tested cases cover selected fault distances, transition resistances, and fault inception angles. The simulation results show that the absolute location error remains within 100 m under all tested deterministic cases. The representative location error is 15 m at the 2.5 km fault point, 45 m under a 500 Ω transition resistance at the 1.5 km fault point, and 11 m under a 90° fault inception angle at the 6.15 km fault point. Compared with EMD-TEO, VMD-TEO, and VMD-GST, the proposed VMD-GST-SDEO method provides more stable wavefront calibration and lower location error in the studied cases. The results indicate the feasibility of the proposed approach within the stated simulation scope; further validation under stochastic noise, synchronization error perturbation, different sampling frequencies, and measured field waveforms is still required for engineering deployment. The fundamental novelty of the study lies in the task-oriented integration of VMD, GST, and the SDEO as a complete wavefront calibration chain and in coupling this chain with a propagation-time-ratio-based double-ended location formula for small-current grounding distribution networks, rather than in treating VMD, GST, or the SDEO as new standalone signal-processing algorithms. Full article

The complex and nonlinear load characteristics of Hall thrusters remain a key challenge in the design of propulsion power-supply output stages. In existing power-supply simulations for electric propulsion systems, the Hall thruster is often simplified as a fixed impedance or a prescribed current source, which makes it difficult to capture the time-synchronized interaction during simulation between the power-supply output stage and the thruster discharge process. To address this issue, this study encapsulates a one-dimensional discharge model as an externally callable thruster slave and proposes a HallThruster.jl–Simulink–Saber co-simulation method. The proposed method enables synchronized bidirectional exchange between the power-port voltage $V_{cmd}$ and the thruster discharge current $I_{out}$. The results show that the discharge current under the co-simulation condition exhibits a sustained low-frequency response at approximately 15.0 kHz. Compared with a fixed-voltage standalone simulation, the co-simulation preserves the same principal oscillation band and overall internal-field structures, while small but observable differences remain in instantaneous phase, local waveform shape, harmonic amplitudes, and high-gradient regions of the internal fields. The proposed method provides a computational framework for investigating dynamically coupled port behavior between a Hall thruster and a representative power-supply output stage. Full article

Tear analysis plays a crucial role in the early screening and diagnosis of ophthalmic diseases. However, conventional methods are often limited by poor real-time performance, low portability, and insufficient capability for multi-parameter detection. Here, we present a bioinspired triboelectric electronic tongue integrated with a microfluidic chip for multimodal detection of tear pH and disease-related biomarkers. The system combines three triboelectric nanogenerator (TENG) modes, including droplet-based, dual-electrode sliding, and single-electrode sliding configurations. The droplet-based TENG converts gravitational potential energy into electrical energy, generating a maximum output voltage of 65 V. The sliding TENG further expands the sensing dimensions by characterizing droplet flow behavior and viscosity-related properties. Benefiting from the high sensitivity of the dual-electrode mode and the waveform differentiation capability of the single-electrode mode, the platform enables enhanced sample discrimination. After optimizing key parameters, including droplet height and chip inclination angle, the output stability errors for all three TENG modes were maintained within ±10%. Combined with a random forest algorithm, the multimodal sensing system achieved a classification accuracy exceeding 96.6% for artificial tears with different pH values. Moreover, distinct electrical response patterns were observed for ophthalmic disease-related biomarkers, including Lysozyme, Interleukin-6 (IL-6), and Chlamydia, demonstrating excellent type identification and concentration detection capability. This work provides a self-powered and miniaturized strategy for intelligent tear analysis and multiple-parameter sensing, offering significant potential for ophthalmic disease diagnosis. Full article

Geoelectric field observations play a vital role in geophysical exploration, geological disaster early warning, and underground resource detection. Traditional contact non-polarisable electrodes, which require burial and electrolyte coupling, are hindered by several issues, such as limited adaptability to challenging terrain, significant electrode potential drift, and high susceptibility to environmental interference. Existing non-contact electric field sensors often exhibit insufficient coupling capacitance, poor impedance matching for ultra-weak high-impedance signals, and inadequate low-frequency noise suppression, rendering them unsuitable for the precise acquisition of natural microvolt-level geoelectric field signals. To address these challenges, this study introduces an innovative non-contact geoelectric field sensor with a three-layer composite structure. The sensor operates based on the principle of a parallel-plate capacitor, with a conductive silver paste layer at the top acting as the signal acquisition electrode plate, which forms an equivalent parallel-plate capacitance model with the ground to achieve non-contact capacitive coupling for geoelectric field detection. The intermediate layer uses lead zirconate titanate (PZT) piezoelectric ceramics as a support medium with a high dielectric constant. At the bottom is a silicon-based, flexible, sensitive ground-contacting layer with high elasticity, which allows it to adapt to micro-level surface irregularities, eliminating air gaps between the electrode plate and the ground, increasing plate-to-ground coupling capacitance, and ensuring the stability of the capacitance. The three-layer structure was created using a dry-press sintering integration approach, which eliminates interlayer bonding materials while ensuring consistent dielectric performance and efficient charge transfer. Additionally, a specialised signal-conditioning circuit was designed to match the ultra-high-impedance sensitive unit, utilising the ADA4528-2 ultra-low-noise precision operational amplifier, which achieved low-loss conversion and strong noise suppression for ultra-weak high-impedance charge signals. The circuit simulation results demonstrate that the designed circuit achieves an input impedance of no less than 10 TΩ, an effective operating bandwidth from 0.02 Hz to 20 kHz, and a voltage noise density lower than 1.5 μV/√Hz at 10 Hz, fully covering the ultra-low-frequency effective band of natural geoelectric fields. Field experiments comparing artificial and natural field signals revealed that the proposed sensor could be quickly deployed by simply attaching it to the ground without burial. Its time-domain waveform consistency and frequency-domain component matching were nearly identical to those of commercial standard solid non-polarisable electrodes, with a cross-correlation coefficient greater than 0.98, indicating no significant potential drift or power-frequency interference. By structurally eliminating the inherent electrode potential difference, the sensor offers advantages such as ease of deployment, strong environmental adaptability, high precision for weak signal acquisition, and excellent engineering substitutability. It is well suited for long-term geoelectric field observations in complex field scenarios, including deserts, Gobi areas, and frozen soil regions, and provides a high-performance, novel sensing solution for geoelectric field detection in extreme environments. Full article