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Conventional electromagnetic acoustic transducers (EMATs) are generally only used to generate and detect guided waves with a single wavelength, which increases their sensitivity at that particular wavelength but limits their application scenarios and the accuracy of defect assessment. This article proposes a design method for multiwavelength EMATs based on spatial-domain harmonic control. First, the EMAT model is analyzed, where it is then outlined that the eddy-current density distribution of the specimen is equivalent to the spatial low-pass filtering of the coil-current density distribution. This shows that the multiwavelength guided waves can be achieved as long as the spatial distribution of the coil-current density contains those multiple harmonics that are desired. It is then proposed that the structure of the EMAT coil is equivalent to the spatial sampled pulse sequences of a spatial signal. The coil parameter design based on pulse modulation technology is proposed. Taking a dual-wavelength EMAT design for Lamb waves as an example, details of the coil parameter design are presented. The simulation and experiment with the dual-wavelength EMAT proved the correctness of the proposed method. Finally, an experiment with a three-wavelength EMAT demonstrated the feasibility of the proposed method in designing multiwavelength EMATs. [ABSTRACT FROM AUTHOR]

Accelerated degradation test (ADT) is generally used to accelerate degradation processes in products to estimate their lifespan and to assess their reliability in a short period of time. How to perform the failure mechanism consistency test is crucial in the application of the ADT method. Existing failure mechanism consistency test methods assume that degradation rates among individual products are the same. However, these methods do not take degradation dispersions caused by manufacturing technologies into consideration. To address this issue, a failure mechanism consistency test method for ADT based on the activation energy invariant method and the likelihood ratio test is proposed. First, a degradation modeling method for ADT is introduced. Then, the logarithmic maximum likelihood function values of the degradation models are estimated based on the two‐step maximum likelihood estimation (MLE) method. Finally, the decision rule is proposed based on the likelihood ratio test. The method mentioned above is, then, used on the real degradation data of carbon‐film resistors and bullet O‐rings, and its effectiveness is verified. Furthermore, based on the failure mechanism change point in RTV5370 siloxane rubbers, the simulated degradation data are degenerated to compare the proposed method with the method not considering individual differences in different ADT programs and degradation dispersions. [ABSTRACT FROM AUTHOR]

• First introduce the transfer learning into the loose particle localization research. • Apply the majority voting strategy to process the predicted labels. • Propose the definition of equipment-level loose particle localization accuracy. • Give specific implementation steps of loose particle localization methods. • Experiments validate the effectiveness and feasibility of the proposed method. The existing supervised-learning-based loose particle localization method requires a lot of resources to create a complete loose particle localization data set, which leads to the problems of long localization testing cycle, large data storage requirement and low resource utilization. In this study, the authors proposed an instance-based transfer learning method for locating loose particles inside aerospace equipment. It used correlations between the localization data sets corresponding to the aerospace equipment with similar structure or size, to complete the knowledge transfer from the source localization data set to the new localization data set. Specifically, based on the existing localization data set containing a large amount of localization data, when facing new aerospace equipment, only a new localization data set containing small amounts of localization data needed to be created. The TrAdaBoost algorithm is used to learn on the new localization data set, the weights of the localization data in the existing localization data set are calculated, the localization data with higher weights are filtered to add to the new localization data set, thus create the transfer training data set and train the loose particle transfer localization (abbr. LPTL) model. This effectively improves the localization efficiency and data resource utilization. In addition, based on engineering application requirements, the authors proposed the definition of equipment-level loose particle localization accuracy. Tests on aerospace power supplies and aerospace electronic single-machines show that, the appropriate weight threshold was set to 0.35, 6004 pieces of localization data were filtered from the existing localization data set. The average classification accuracy of 82.85% and the average localization accuracy of 83.33% were achieved by the LPTL model based on the parameter-optimized XGBoost ensemble classifier. In theory, this method can be extended and applied to the loose particle material identification and weight estimation research, and has high reference value. [ABSTRACT FROM AUTHOR]

Currently, the finite element method (FEM) and analytical calculation are widely employed for the modeling of electromagnetic acoustic transducers (EMATs). However, it takes long time for finite element calculation. Previous analytical models for bulk wave EMATs are generally considered separately and incompletely, and expressions of radiated wave fields contain infinite integrations and multiple singular points, which result in complex numerical computation. A complete model containing the Lorentz force and radiated wave field calculation for the EMAT with a spiral coil and a NdFeB permanent magnet is established. By introducing a current loop instead of the permanent magnet and adopting the truncated region eigenfunction expansion (TREE) method, the distributions of static and dynamic magnetic fields and their generated Lorentz forces are calculated. A series expansion method is proposed for the computation of radiated wave fields, which replaces the integration by series operation and avoids the solutions of singular points effectively. The Lorentz forces and radiated wave fields of a typical transducer are computed. The validity of the model is verified by FEM and experiments. Their good agreements verify the accuracy and validity of the model. [ABSTRACT FROM AUTHOR]

It is usually considered that the wavelength of guided waves propagating in plates is equal to the double spacing interval of the meander-line coil of electromagnetic acoustic transducers (EMATs). However, the actual value of the wavelength might deviate from the double spacing. This paper takes Shear Horizontal (SH) waves for instance to study the relationship between the wavelength deviation and the parameters of EMATs. It is shown that the wavelength deviation occurs when the operating point of EMATs does not locate on the dispersion curves of a certain SH mode. A wavelength measurement method is proposed to evaluate the deviation by the time-frequency analysis of detected wave signals. Experiments are set up to study the phenomenon of wavelength deviation and verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Minimax optimization (MMO), which aims at pursuing the solutions with the best performances in the worst case, is widely used in the robust design. However, there are still fundamental limitations for MMO to converge to the optimum when solving asymmetric problems. Moreover, when MMO is employed in robust design where the objective function is evaluated through costly simulations, the efficiency of the optimization becomes crucial. To address these issues, in this paper, A novel efficient global optimization algorithm based on co‐evolutionary strategy is proposed to solve the asymmetry MMO problem with satisfactory efficiency. Furthermore, the new algorithm is tested on eight analytical benchmark problems and compared with the state‐of‐the‐art methods. Lastly, the methodology has been successfully applied to the robust design of a practical engineering product. [ABSTRACT FROM AUTHOR]

Coal is considered as an abundant energy source in China and coal-to-methanol chain is an essential routing on account of methanol’s irreplaceable status in chemical industries. However, coal-based methanol production aroused controversy due to its intensive energy consumption and high greenhouse gas emission, compared with other processes by oil or natural gas. Carbon footprint is an improved indicator that evaluates both direct and indirect greenhouse gas emissions in the life cycle perspective and guides policymakers for better industry-chain planning. In this study we proposed the idea of hierarchical attribution management (HAM) to provide a classified method for evaluating carbon footprint of coal-to-methanol chain, combined with life cycle assessment (LCA) and the tool of ASPEN Plus. The results show that the life cycle carbon footprint was 2.971 t CO 2,e /t methanol. By the HAM, it’s concluded that methanol production process was the largest emission contributor in the defined life cycle system with a share of 92.86%, followed by coal mining process with 4.34%. Gasification unit and water-gas shift unit were two major greenhouse gas generators, accounting for 21.26% and 52.80% of life cycle emission, respectively, while methanol synthesis unit showed the potential for CO 2 utilization and emission reduction. Additionally, the results of sensitivity analysis showed that electricity emission factor with a sensitivity factor of 189.11 was the most extensive influence factor on life cycle emission due to its widest application. The discuss on effects of CCS on life cycle emission showed that carbon footprint approximately decreased by 64.9% when the methanol plant was retrofitted with CO 2 capture and compression, indicating that CCS is an effective way to alleviate global warming. [ABSTRACT FROM AUTHOR]

Due to the effects of manufacturing tolerances and environmental conditions, component parameters vary and degrade with time. This may cause performance measures of electronic circuits to deviate from design specifications. Therefore, a tolerance design method based on performance degradation is proposed for electronic circuits, so as to improve the robustness of output characteristics. First, sensitive components causing output fluctuation are determined via orthogonal experiment and PSpice simulation. Then, degradation path models are established to describe the degradation process of sensitive components. The predicted values worked out by the degradation path models are substituted into the simulation model for Monte Carlo analysis. Besides, output characteristics and performance reliability are evaluated according to Monte Carlo simulation. Finally, optimum allocation is carried out for component tolerances as per minimum life cycle cost. The proposed method is illustrated by a case study of light-emitting diode (LED) driver. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presented a revised particle impact noise detection (PIND) system to detect loose particles in the sealed electronic devices. The type of particle material is the valuable information to trace the particle’ origins and assess the potential harmfulness. The most traditional classification model cannot effectively recognize the types of material due to particle impact acoustic signals with characteristics such as non-stationary, poor repeatability and reproducibility. To address this problem, a new method of pattern recognition for material identification is proposed based on modified Mel frequency cepstral coefficient (MFCC) and hidden Markov model (HMM). First, to be more suitable for target identification of different material of particle acoustic signals, the relationship between the MFCC features and the Mel filter bank is derived, and the modified filter bank is proposed. The modified MFCC features are then mapped into HMMs, where the model number with the maximum probability is chosen as the identified class. Finally, experiments have been carried out with different features and classifiers. The results show that the proposed method can effectively distinguish the four types of materials including wire, chip, aluminum and tin. [ABSTRACT FROM AUTHOR]

The existence of loose particles left inside the sealed electronic devices is one of the main factors affecting the reliability of the whole system. It is important to identify the particle material for analyzing their source. The conventional material identification algorithms mainly rely on time, frequency and wavelet domain features. However, these features are usually overlapped and redundant, resulting in unsatisfactory material identification accuracy. The main objective of this paper is to improve the accuracy of material identification. First, the principal component analysis (PCA) is employed to reselect the nine features extracted from time and frequency domains, leading to six less correlated principal components. And then the reselected principal components are used for material identification using a support vector machine (SVM). Finally, the experimental results show that this new method can effectively distinguish the type of materials including wire, aluminum and tin particles. [ABSTRACT FROM AUTHOR]

Highlights: [•] We develop a spatial transversal filter model for meander-line coil EMATs. [•] The generated wavelengths have to belong to the wavelength spectrum of the EMAT. [•] The characteristics of multiple wavelengths will cause the multi-modes phenomenon. [•] Developing a new meander-line coil with special geometric pattern. [•] Proposing a method for removing the effect of multiple wavelengths. [Copyright &y& Elsevier]

The non-contact nature of electromagnetic acoustic transducers (EMATs) allows a continuous operation at high temperatures without physical coupling. The existing high-temperature EMATs are mainly shear-wave EMATs, and there are few reports on shear-longitudinal wave or longitudinal-wave EMATs due to the low intensity of the horizontal magnetic field. However, a desirable EMAT design characteristic is the possibility of selecting to generate different acoustic wave modes for various engineering applications. In this paper, a high-temperature EMAT with a double-coil configuration on waveform generation in paramagnetic steel was studied. By adjusting the configuration relationship between the electromagnetic coil and the EMAT eddy-current coil, the selective generation of shear-wave, longitudinal-wave, and shear-longitudinal wave modes was realized. According to quantitative analysis of shear and longitudinal waves generated by the double-coil EMAT, the amplitude ratio of shear and longitudinal waves was about 1 when the diameter of the EMAT eddy-current coil was equal to the inner diameter of the electromagnetic coil. Furthermore, shear-wave mode and shear-longitudinal wave mode high-temperature EMATs were designed and fabricated. The EMAT was placed in a high-temperature environment to continuously measure the paramagnetic steel SUS304. The amplitudes of the shear wave and longitudinal wave at 500 °C decreased by 10.2 times and 3.8 times, respectively, compared with that at 25 °C. The designed EMAT can selectively generate and receive different bulk acoustic wave modes at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Plated copper alloys are widely used in electron industry. The plating lay caused the farther decreasing of the welding property of copper alloys, whose intrinsic weldability was poor. In this paper, the bronze and brass specimens with nickel–tin double plating layer were joined by resistance spot welding method. The microstructure and peel strength of the joints were investigated. The experiment results show that a sandwich-like structure was obtained in the faying surface after welding, and the nickel plating layer thickness had severe effect on the reliability of the joints. [Copyright &y& Elsevier]

In this study, a new moving amplification matching algorithm was proposed, and then the temporal and spatial differences and correlation were analysed and evaluated by comparing the FengYun-4A Lightning Mapping Imager (FY-4A LMI) data and the China Meteorological Administration Lightning Detection Network Advanced TOA and Direction (CMA-LDN ADTD) system data of southwest China in July 2018. The results are as follows. Firstly, the new moving amplification matching algorithm could effectively reduce the number of invalid operations and save the operation time in comparison to the conventional ergodic algorithms. Secondly, LMI has less detection efficiency during the daytime, using ADTD as a reference. The lightning number detected by ADTD increased from 5:00 AM UTC (13:00 PM BJT, Beijing Time) and almost lasted for a whole day. Thirdly, the trends of lightning data change of LMI and ADTD were the same as the whole. The average daily lightning matching rate of the LMI in July was 63.23%. The average hourly lightning matching rate of the LMI in July was 75.08%. Lastly, the mean value of the spherical surface distance in the matched array was 35.49 km, and roughly 80% of the matched distance was within 57 km, indicating that the spatial threshold limit was relatively stable. The correlation between LMI lightning radiation intensity and ADTD lighting current intensity was low. [ABSTRACT FROM AUTHOR]

• First conduct loose particle detection research based on overlapping signals. • First combine the signal detection research with the material identification research. • Newly propose the definition of confidence coefficient. • Newly propose the definition of two types of identification accuracy. • Verify the proposed method in the latest real application scenarios. Loose particle is an important factor affecting the reliability of aerospace relays. Particle Impact Noise Detection method is a commonly used loose particle detection method, but it can generate interference signals. Accurately identifying loose particle signals and component signals becomes the key to accurately detecting loose particles. Meanwhile, deeply exploring the properties of loose particle signals and further provide material information can provide guidance for manufacturing processes. However, the existing loose particle signal and component signal identification research, as well as the loose particle material identification research, has problems such as limited research objects to pure signals, independent identification results, and failure to refer to the detection requirements in real application scenarios. It is difficult to apply and its practicality is not high. Based on this, the authors proposed a signal detection and material identification method for loose particles based on overlapping signals. Specifically, referring to the latest loose particle detection information, aerospace relay samples were made, and the component identification model and material identification model based on parameter-optimized random forest were trained, respectively. They can achieve good classification effects on data sets created from pure loose particle signals, pure component signals, and pure loose particle signals corresponding to different materials, respectively. On this basis, confidence coefficient was proposed to quantify the degradation degree of the classification effects of the two models on the data set created from overlapping signals, thus the component confidence coefficient and the loose particle confidence coefficient were obtained, respectively. They can be used to determine valid pulses from pure loose particle signals, pure component signals, and mixed signals in overlapping signals, completing loose particle detection. Valid pulses from pure loose particle signals were screened for material identification. In this way, for the aerospace relay to be tested, first, the loose particle detection results can be obtained by a comprehensive judgment of the component identification model, component confidence coefficient, and loose particle confidence coefficient. Second, the material identification results can be obtained by combining the material identification model with the majority voting processing. In addition, the definition of identification accuracy applicable to the loose particle detection was proposed to meet the engineering application requirements in real application scenarios. Multiple experiments verified the feasibility, practicality, and stability of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, the authors combined the research on loose particle signal and component signal identification with the research on loose particle material identification for the first time, providing comprehensive and reliable loose particle detection results. Based on this, a signal detection and material identification method for loose particles inside sealed relays based on fusion classification model is proposed. Due to the limitations of technical means and confidentiality management, the authors made a real sealed relay sample, and took it as the research object. Through the steps of data acquisition, signal processing, feature engineering, and model training, the dedicated component identification feature library and material identification feature library was constructed, respectively, the component identification model and material identification model based on parameter-optimized SVM with linear kernel and XGBoost was trained, respectively. For the seal relay to be tested, through the steps of data acquisition, signal processing and feature engineering, the data set to be tested was created. The component identification model was used to identify component signals with loose particle signals, and the material identification model was used to identify the materials of loose particles. The majority voting process was used to convert the classification results into identification results, resulting in loose particle detection and material identification results. In addition, the general procedure steps of the proposed method for physical testing were given, and the identification accuracy for device-level loose particle detection was newly proposed. The loose particle testing event containing thirty-seven identification tasks shows that, the achieved identification accuracy was 97.30%, and 92.16% of the average classification accuracy was achieved by the component identification model, 80.41% of the average classification accuracy was achieved by the material identification model. This effectively demonstrates the feasibility and practicality of the proposed method in this paper. It is an important supplement to the loose particle detection research, and provides references for signal detection in similar fields. • First combine the loose particle signal detection and material identification study. • First construct the dedicated feature library and perform feature optimization. • Train the optimal component identification model and material identification model. • Newly add majority voting steps to obtain the identification results. • Newly propose the identification accuracy for device-level loose particle detection. [ABSTRACT FROM AUTHOR]

The complex internal structure and heterogeneous composition material of aerospace equipment make it difficult to apply traditional acoustic emission source localization methods to the loose particle localization research. In previous studies, the authors transformed the loose particle localization problem into the multi-classification problem in machine learning, trained the loose particle localization model, but there were problems of low classification accuracy and low practicality. In this paper, the authors first introduced the ensemble learning idea into the loose particle detection field, designed a complete loose particle localization scheme, analyzed the above problems from multiple perspectives, and proposed new algorithms or strategies to enhance the superiority and practicability of the loose particle localization model. Specifically, in view of the low classification accuracy, the authors carried out the research on pulse preprocessing, feature engineering and model training from the four perspectives of signal, feature, data set and classifier, respectively. The zero-pulse-filling pulse matching algorithm and the channel-weighting-based feature selection method was newly proposed, Mel-Frequency Cepstral Coefficients features was newly extracted, feature optimization scheme was designed, and XGBoost ensemble classifier was trained. Thus, high-quality loose particle signals, high-quality localization data sets and high-performance loose particle localization models were obtained, respectively. Test results show that, the classification accuracy achieved by the new loose particle localization model was 96.80%, which was a significant improvement compared to the 83.53% achieved in previous studies. In view of the low practicality, the authors built the loose particle localization experimental system, gave the specific implementation steps of the loose particle localization method, as well as the general procedures for applying the loose particle localization model for physical testing. Meanwhile, taking into account the requirements of aerospace engineering applications, the authors added the majority voting strategy to convert classification results into localization results, thus newly proposed the definition of equipment-level loose particle localization accuracy. Several physical testing results show that, the loose particle localization model achieved a localization accuracy of 90.91%, which effectively verified the feasibility and stability of the proposed method. This study is an important supplement to the loose particle detection research, and of great significance in improving the reliability of aerospace systems. [ABSTRACT FROM AUTHOR]

The component with variable width (such as railway turnout) is one of the most critical configurations in infrastructure. Guided waves have already been employed for flat plates, however, the influence of cross-section width change for guided waves can’t be ignored. In this study, the theoretical cut-off frequency of shear-horizontal (SH)-like guided waves in rectangular plate was analysed. The dispersion curves of rectangular plate with different widths were calculated by the periodic finite element (FE) method. Theoretical calculations and dispersion curves both show that the cut-off frequency of SH-like guided waves decreases when the width of rectangular plate increases. A periodic-permanent-magnet (PPM) electromagnetic-acoustic-transducer (EMAT) at the excitation frequency of 200 kHz was constructed and used in the experiments to generate SH-like guided waves on rectangular plates with the widths of 12 mm and 20 mm, respectively. Experimental results show that multiple wave modes of SH-like guided waves appear as the width of the rectangular plate increases. When the SH-like guided waves propagates in a rectangular plate with variable width, the high-order modes will be cut-off and reflected as the width decreases. [ABSTRACT FROM AUTHOR]

In windy weather, overhead lines swing and collide with each other, often resulting in short-circuits and arc faults. The line is partially molten and produces numerous hot metal particles, which fall and may ignite the fuels on the ground. This paper developed an experimental system to obtain hot particle dimensions at different short-circuit current levels. Based on the results of this experiment, an ignition prediction method was developed. The particle parameters from the experiments were used as a bridge that to complete the prediction from short-circuit current to ignition risk. A neural network was trained according to the experimental and calculated results, then used to predict the risk of ignition. The overhead lines in a forest were used as an example application to perform thte investigation. The results show that copper lines in a forest with needles on the ground create a high risk of ignition hazard. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motors (PMSMs) have a scale of applications linking to the industrial machines. As these machines often work in a wide temperature range, the PMSM quality consistency is threatened by the temperature fluctuate. In fact, at the start of the production of the PMSMs, the quality consistency distribution already exist due to the manufacturing dispersion. However, traditional experiment‐based consistency analysis method is inadequate for the PMSM, due to its inevitable destructive measurement for the magnetic properties. To deal with the problem, this paper proposed a model‐based quality consistency analysis method. In this paper, mechanism analysis of the temperature influence on PMSMs is carried out by the finite element analysis and the digital modeling method, so that the impact of dispersion can be depicted by model rather than destructive measurement. The relationship between the temperature and PMSM cogging torque as well as other features is quantitatively revealed. To obtain the NdFeB temperature coefficient, magnetic samples were prepared and measured. Then, the temperature characteristics of the sensitive components of PMSM are established, and the PMSM temperature characteristics can be simulated by integrating temperature coefficients into the PMSM digital model. The qualitative and quantitative temperature characteristics of cogging torque are verified by experiments with a batch of PMSMs. [ABSTRACT FROM AUTHOR]

The lithium thionyl chloride (Li/SOCl2) battery is widely used as an important long‐life backup power source. Accurate battery life prediction is essential to ensure the reliability of equipment and systems. In this paper, a novel method was proposed for the life prediction of Li/SOCl2 batteries based on the pulse load test and accelerated degradation test (ADT). The proposed pulse load test method can estimate the primary battery capacity accurately and nondestructively, which solves the challenge of quantifying degradation due to unknown initial values. Furthermore, we noticed a new phenomenon that capacity loss was affected by electrolyte fluidity, and unexpected capacity loss was observed for batteries at different discharge angles. By analyzing the mechanism of this phenomenon, we avoided serious capacity measurement errors in the 24‐week ADT. A life prediction model with a satisfactory ability to approximate the measured data was established depending on the exponential influence of time and temperature on capacity degradation. [ABSTRACT FROM AUTHOR]

The importance of high-power relays used to interrupt dc current has been significantly growing recently. In their arc chambers filled with nitrogen or its mixtures, bridge-type contacts with permanent magnets are major measures widely used for arc extinguish. Arc dwelling for a short duration after arc ignition, until its voltage increases rapidly, plays a crucial role in contact erosion. In this paper, arc dwelling time in a nitrogen environment during the entire bridge-type contacts interruption process of a resistive dc circuit is studied both experimentally and numerically. A multiphysics model coupled with the fluid flow, the temperature, the current density, as well as the E- and M-fields was built based on the magnetohydrodynamics theory for the arc chamber. The model was solved in COMSOL. The external resistive electric circuit was connected to the model, and the electric field in the arc was solved by adopting a floating potential. The detailed arc dwelling process is presented and preliminarily discussed according to the calculated temperature and current density distribution sequences. The calculated arc voltage shows good agreement with experimental results. Furthermore, the influence mechanism of breaking velocity on arc dwelling is analyzed by arc voltage. In this sense, the arc dwelling time could be shortened by increasing the breaking velocity within the reasonable extent. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) coaxial switches have the advantages of high transmission frequency and power capacity and are widely used in aerospace, communications, military, science, and medical fields. In accelerated thermal cycle (ATC) test, a permanent deformation or displacement occurs in the contact system of RF coaxial switch caused by creep and the RF performance downgrades with the thermal cycle times. In this paper, a 3-D finite-element model of an RF coaxial switch was first proposed. The power loss in the contact system when the switch transmits high frequency and power signals was divided into the conductor loss and the dielectric loss, which were calculated separately. It was noted that conductor loss was the main part of power loss. Then, the power loss in the contact system was considered as the heat source, and the steady-state temperature field of the whole switch was calculated with Ansoft HFSS and Workbench. The temperature rise in an RF coaxial switch was calculated and verified by experimental testing. In order to predict the reliability and working life of RF coaxial switch in ATC test, a creep constitutive equation based on the Coffin–Mason method that has three undetermined coefficients was built. According to ISO204:2009 (Metallic materials-Uniaxial creep testing in tension), the samples of beryllium bronze for creep testing were produced, and two groups of creep testing in the condition of different temperatures and stresses were carried out to obtain the undetermined coefficients. Finally, the stress–strain deformation of contact system with the thermal cycle times was calculated based on the creep constitutive equation. The model of contact system was rebuilt, and the influence of creep on RF coaxial switch in ATC test was investgated. The analysis methods and conclusions presented in this paper have important theoretical significance and practical value for improving the performance and reliability of RF coaxial switch products. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to present a transition detector (TD)-based radiation hardened flip-flop (TDRH-FF) for single event upset (SEU). Design/methodology/approach: With SEU recovery and single event transient (SET) detector mechanism, the TDRH-FF can tolerate SEU during hold mode and generate a warning signal for architecture-level recovery during transport mode when input signal contains SET. Evaluation results show that the TDRH-FF outperforms comparable comprehensive performance. Findings: Simulation results show that 1) the mean pulse width of the correction glitches (at full width half maximum) of TDRH-FF is less than 10 ps; 2) the area overhead of TDRH-FF is similar to the EVFERST-FF, BISER-FF and DNURHL-FF; 3) TDRH-FF has the same average power consumption as SETTOF, and moderate PDP and Ps values among these compared FFs. Originality/value: In this paper, a TD-based TDRH-FF is proposed to solve the problems in the previous design. And the main contributions of the proposed TDRH-FF are summarized: Minimum size transistors are used in the proposed TD which leads to a considerable decrease in area overheads and propagation delay (resulting in an ignorable correction glitch); and compared with other radiation hardened flip-flop, TDRH-FF outperforms comparable comprehensive performance. [ABSTRACT FROM AUTHOR]

DC power relay is a key electromechanical component widely used in electrical vehicles, photovoltaics, as well as more-electric aircrafts for energy managing, power conversion, and distribution. As the voltage and current increase due to relay switches, arc discharge becomes an unavoidable and significant issue during the operation of the dc high-power relay. Bridge-type contact and external permanent magnets are spontaneously employed in its arc chamber to accelerate the quenching of arc. In this paper, the complicated arc discharge plasma in a dc power relay has been investigated by using both experimental and numerical approaches. Initially, arc dwell and arc restriking characteristics during the arc motion phase are presented by analyzing the voltage and current waveforms and arc images acquired in carefully designed breaking experiments. The arc driven by a transverse magnetic field with a variety of flux densities and the influence of flux densities on arc voltage and dwell are preliminarily discussed based on the experimental results. Then, to reveal the arc physics and to determine the influence of transverse magnetic field on arc motion characteristics, a simplified model based on the magnetohydrodynamic (MHD) theory is built and three cases with different magnetic field are calculated. The simulated arc behaviors including distributions of the temperature and current density are presented. The mechanism underlying the influence of transverse magnetic field on the arc motion is analyzed according to arc root transfer and arc voltage variation. In addition, to understand the formation of the arc restriking, the critical breakdown electric-field strength inside the arc gap is also calculated based on streamer breakdown theory. The parameters in the space occupied by earlier arcs, as predicted by the MHD simulations, are used in the breakdown calculation. Results show that the critical breakdown voltage reduces remarkably along with growth of the operating voltage and breaking current, and the arc dwell time can be reduced by strengthening the external magnetic field within a reasonable extent. [ABSTRACT FROM PUBLISHER]

A permanent magnet synchronous motor (PMSM) is a crucial device for power conversion in an energy system. The cogging torque of the PMSM is a crucial output characteristic, the robustness of which affects the operational reliability of the energy system. Therefore, the robust design optimization (RDO) of cogging torque has aroused widespread concern. There are several challenges in designing a robust cogging torque PMSM. In particular, some design parameters contain repetitive units, and the finite element analysis (FEA) method is time-consuming. State-of-the-art RDO methods usually treat these uncertainties from repetitive units as the same parameter, which neglects the fluctuation of the manufacturing process and cannot obtain a robust solution for the cogging torque of the motor efficiently and accurately. In order to solve this issue, an approximate modeling method based on manufacturing uncertainties analysis for RDO is proposed in this paper. First, the peak-to-peak value of cogging torque (Tcpp) is used to characterize the cogging torque, which is decoupled to an ideal component and fluctuation component produced by the center values and manufacturing tolerances of design parameters. The design of experiments (DoE) and simulation of the two components are carried out. Then, these two components are approximated separately, and the approximate model of Tcpp is obtained by adding the two components. Finally, the proposed approximate model is embedded into the RDO algorithm, and the PMSM design scheme for good Tcpp robustness is obtained. The effectiveness of the proposed method is verified through a case study of the PMSM. [ABSTRACT FROM AUTHOR]

Electromagnetic ultrasonic (EMU) Lamb waves excited by electromagnetic acoustic transducers (EMATs) possess many advantages in NDT. However, their characteristic multi-modes and dispersion are disadvantageous for inspection and restrict further improvements in their real applications. By deducing the excitation equation of EMU Lamb waves, the primary design parameters of EMATs and the characteristic equation of Lamb waves are combined, and excitation curves based on the excitation equation are plotted to aid the design of EMATs. The excitation characteristic of EMU Lamb waves on different thickness of plates is analyzed according to the excitation curves. The influence of multi-modes of EMU Lamb waves is minimized by choosing reasonable operating points and operating zones to excite a single-mode Lamb wave or multi-mode Lamb waves with identical or approximate propagation velocities. The influence of dispersion is minimized by searching corresponding points whose slope of group velocity tends to zero. The validity of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

Contact bounce is a common phenomenon in the closing process of electromagnetic relays, which seriously affects the electrical contact reliability of the system. The whole closing process of flexible spring components consists of the free movement stage and the contact bounce stage, which increases the complexity of analyzing the electrical contact behaviors of electromagnetic relays. In this study, a novel nonlinear dynamic model of the flexible spring components in electromagnetic relays is established to analyze the physical mechanism of the electrical contact bounce. Considering the electromagnetic effect, flexible deformation, contact collision, and welding force, the proposed mathematical model can capture the dynamic closing process accurately and collect bounce parameters efficiently. The Kelvin–Voigt viscoelastic contact model is employed to evaluate the nonlinear contact force between the static and movable contacts. Based on the Galerkin method, the nonlinear equations of motion for the movable spring within electromagnetic relays are formulated. A series of experimental work are designed to measure the typical waveforms of displacements of the movable contact and currents in the coil during the closing process of the movable spring. Furthermore, the theoretical results are validated by comparing with the experimental data. The dependences of some key factors, including the structural, material, and electrical contact parameters on the contact bounce characteristics, are investigated explicitly. The theoretical results attest that the proposed model can accurately predict the dynamic behaviors of the movable spring, and the contact bounce can be effectively suppressed by adjusting the parameters of the flexible spring component. [ABSTRACT FROM AUTHOR]

• Dynamic characteristics testing and evaluation of electromagnetic devices. • A digital modeling approach to evaluate dynamic characterization is proposed. • Multiphysics modeling approach for FEM description of the electromagnetic devices. • The nonlinear effects of temperature on the dynamic characteristics are considered. • Transmission line parallel algorithm improves the efficiency of solving FEM models. Electromagnetic systems of Electromagnetic devices involve multiphysics coupling of electromagnetic fields, electrical circuits, mechanical motion, and temperature fields. When the digital prototype model has a large number of meshes, the commercial finite element software also has the disadvantage of long computation time in the simulation of dynamic characteristics of electrical apparatus. This paper proposes a transmission line method (TLM) based digital modeling method for the electromagnetic-thermal-force coupling to test and evaluate the static and dynamic characteristics of electromagnetic devices more accurately and efficiently. The case study is developed on a direct current (DC) contactor, and the dynamic characteristics testing and modeling in the electromagnetic-thermal-force coupling of the contactor are investigated. The numerical results of the finite element method (FEM) model for the electromagnetic system of the contactor are compared with the commercial FEM software Altair Flux and the experimental results, which demonstrate the exceptional accuracy of the proposed digital modeling method for the multiphysics coupling of the DC contactor. Meanwhile, the dynamic characteristics of the DC contactor at different ambient temperatures are measured and evaluated, and the comparison with the experimental measurements shows the applicability of the proposed digital prototype model at different ambient temperatures. Compared with the conventional Newton-Raphson (NR) iteration, when dividing fine mesh and extremely fine mesh, the TLM parallel computing significantly improves the efficiency of solving the dynamic characteristics of multiphysics coupling by about 35 % and 44 % with the same computational accuracy, respectively. The dynamic characteristics evaluation method combined with digital modeling technology and experimental measurements proposed in this paper demonstrates high accuracy and solving efficiency, making a notable contribution to the field of design and optimization of electromagnetic devices. [ABSTRACT FROM AUTHOR]

Traditional method evaluates operating reliability by counting life-test results of a small number of samples, which ignores variability between individuals and cannot accurately reflect the true state. This paper proposes a model for predicting operational reliability of mechanism in a batch of micro-switches based on manufacturing parameters, in view of complex structure and diverse manufacturing parameters. A multi-body kinetic model based on manufacturing parameters and principle of action considering contact fatigue and wear was established, and the operating characteristics in the degradation process with sliding wear of joints were obtained. Finally, the linkage with revolute clearance in miniature circuit breaker (MCB) was used as numerical example application to perform investigation. Prediction results are consistent with batch experiments, which verifies accuracy of model. In addition, the optimal combination of clearances was obtained by using genetic algorithm based on predicted model, which increases locking reliability to 99.3% after 10000 operation cycles. [ABSTRACT FROM AUTHOR]

There are various challenges in designing a life-cycle robust permanent magnet actuator (PMA) to satisfy the application-oriented requirements of quality consistency. In particular, ubiquitous uncertainties from manufacturing and operating process that cause unstable or even infeasible solutions significantly increase the difficulty of the life-cycle robust design of PMA. Conventional methods usually treated these uncertainties as fixed design constraints, which neglect the nonlinear characteristic of time-dependent degradations, cannot reflect authentic impacts on the life-cycle robustness of PMA. To address this issue, this study propose a method of life-cycle dynamic robust design optimization for batch production PMA. An innovative time-dependent global sensitivity analysis-based classification method is first proposed to divide design variables into three categories: nonlinear, degradation insensitive, and degradation sensitive variables. Then, a modified Spatiotemporal Kriging model with Karhunen-Loeve expansion is applied to establish the life-cycle robustness model of PMA with consideration of uncertainties. This model can valid describe the nonlinear fluctuation of the life-cycle robustness. Furthermore, on the basis of the three categories of design variables and life-cycle robustness model, a multistage dynamic robust design optimization strategy is derived, which realizes the synchronous control of life-cycle robustness deterioration rate (mean value) and fluctuation (standard deviation). Finally, taking a case of rotary PMA, the effectiveness of the proposed method is verified. [ABSTRACT FROM AUTHOR]

Multi-span composite lattice sandwich beams have wide application prospects in the aerospace, high-speed trains and civil engineering fields because of the low specific weight, high specific strength and multifunctional potential. Moreover, the span number and the subspan length have a great influence on the vibration and thermal buckling properties of multi-span beams. Therefore, a simple and effective method is presented to investigate the vibration and thermal buckling behaviors of different multi-span sandwich beams with pyramidal truss core in this study. The first-order shear deformation theory is used to evaluate the strain–displacement relations in the structural modeling. The mode shapes modified by the interpolation function are used to evaluate the vibration modes of the multi-span lattice sandwich beam. The differential equation of motion is formulated by Hamilton's principle. The natural frequencies of the multi-span sandwich beam with pyramidal truss core are validated through comparing the finite element method results. The parametrical investigations with respect to the ply angle of the composite laminated face sheets and the radius of trusses are conducted. Furthermore, the influences of the span number and subspan length on the vibration and thermal buckling behaviors of the composite lattice sandwich beams are also performed and discussed. [ABSTRACT FROM AUTHOR]

Contact bounce is a common phenomenon in the closing process of the electromagnetic relay under capacitive loads. The investigations on the contact characteristics are mainly conducted by experimental methods. However, the experimental method is extremely complicated and time-consuming in structural design, and it cannot clearly reveal the mechanism of contact bounce. Therefore, a new theoretical model is proposed to investigate the dynamic characteristics of the electromagnetic relay under capacitive loads. The model allows for simulating dynamic process and collecting bounce parameters in a simple and effective way compared with conventional simulation and experimental methods. The physical mechanism of contact bounce for the electromagnetic relay is presented. The nonlinear contact force between the fixed and moving contacts is evaluated according to the Kelvin–Voigt viscoelastic contact model. The equations of motion considering the coupling of electromagnetic and mechanical fields are established. The theoretical results obtained in this study are validated by comparison with experimental data. The influences of the structural parameters, coil current, surge current, and contact resistance on the contact bounce are analyzed. The numerical results well demonstrate that the contact bounce can be effectively weakened by adjusting the parameters of contact spring and the mass of the moving contact. [ABSTRACT FROM AUTHOR]

Power transmission and protection of power electronics–electromagnetic actuators are crucial parts in renewable energy systems (energy management of photovoltaic, wind power, hybrid and electric vehicles). Consistency optimization of electromagnetic actuators has attracted extensive attention from corporations in competitive markets. Robust design has been widely applied for reducing the influence of uncertainties in the manufacturing process to improve the consistency of product quality. However, the cost factors of the actual manufacturing process are not fully considered in state-of-art methods. Although the consistency has been improved, the optimization scheme may not be optimal from the perspective of engineering applications, because unnecessary cost increments may be produced. In this paper, an application-oriented robust design method for consistency optimization is proposed. The impact of tolerance values on quality loss and manufacturing cost can be considered simultaneously to guide the tolerance optimization process. Thus, the optimal solution of total loss is obtained by optimizing the quality fluctuation to the design objective with the minimum increment of manufacturing cost. An example of the consistency optimization of an electromagnetic actuator used in the photovoltaic system is presented to illustrate the procedure and verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The magnetostrictive Fe 3 O 4 -film electromagnetic acoustic transducer (EMAT) consists of a magnet, a coil, and a magnetostrictive Fe 3 O 4 -film bonded to a sample, which can be implemented on parts that are complex shaped, or have uneven or rough surfaces. In this short communication, high transduction efficiency of the proposed EMAT is demonstrated, with a signal-to-noise ratio of up to 50.3 dB, which is beneficial for industrial ultrasonic testing. The proposed EMAT is studied under varying bias magnetic fields and dynamic alternating magnetic fields, to improve transduction efficiency by optimizing the transducer design. The experimental results show a significant nonlinear relationship between the amplitude of the received signal and the strength of the bias magnetic field strength. The horizontal and vertical bias magnetic fields corresponding to the maximum amplitude of the received signal are approximately 0.1 T and 0.14 T, respectively. The amplitude of the received signal varies linearly with the strength of the dynamic magnetic field provided by the EMAT. This investigation represents a further development of magnetostrictive film EMATs, and widens the potential for industrial applications. [Display omitted] • A magnetostrictive Fe3O4-film electromagnetic acoustic transducer (EMAT) is developed. • The Fe3O4-film EMAT can apply to parts that have rough surfaces, or complex shapes. • The ultrasonic response behavior has been quantified in experimental measurements. • The Fe3O4-film EMAT provides a potential alternative to other existing approaches. [ABSTRACT FROM AUTHOR]

Contactors are typical electromagnetic devices whose optimization is multi-objective optimization problems. Contactors’ static and dynamic characteristics obtained by the finite-element method (FEM) are typical objectives. Due to the low efficiency of FEM, the intelligent optimization algorithms that require multiple computations cannot be applied well here. In this paper, a fast algorithm for characteristics of contactors based on radial basis function neural network approximate model is proposed. The orthogonal least squares, data pre-processing and subsection modeling methods are adopted here to make the model more accurate. Meanwhile, a hybrid multi-objective optimization algorithm which combines the differential evolution and the particle swarm optimization is also proposed to speed up convergence and obtain the limit optimal solutions. The feasibility of the above-mentioned methods has been verified by solving a multi-objective optimization problem of the contactor with solenoid structure. [ABSTRACT FROM AUTHOR]

At present, finite element method (FEM) is still the mainstream tool in a range of complex science and engineering applications, including the analysis of structures, heat, fluid, and electromagnetics. However, FEM becomes computationally very intensive when the number of physics equations grows and the mesh is refined. In this paper, we investigated the parallel computing techniques in the nonlinear magnetostatic field solution of an axisymmetrical actuator with permanent magnet by proposing a generalized black-box transmission line method (BB-TLM). A novel black-box circuit model was built to represent complex FEM element data. By means of the transmission line model, each element is isolated and then a series of parallel procedures is considered during the solution stages. The magnetic field distribution and magnetic force of the studied actuator are calculated by the proposed method and the simulation results are compared with COMSOL. Compared with the conventional N-R method, the generalized BB-TLM algorithm greatly reduces the computation time. [ABSTRACT FROM AUTHOR]

Abstract With the voltage increasing in DC power systems, positive bias temperature instability (PBTI) induced gate oxide degradation of commercial n-channel power vertical double diffused MOSFETs (VDMOSFETs) has been greatly enhanced recently. However, it is not mature in some aspects, e.g., parametric models of PBTI and the turn-around phenomenon are rarely studied. Aiming at these disadvantages, the experimental study and the argument are proposed in this paper. First, the simulation was used to identify and verify the threshold voltage as the characteristic parameter and the accelerated experiment test was conducted to collect data for degradation modeling. Then, a Power law-Arrhenius combined model was adopted in the degradation model to take into account the electrical and thermal influence. Besides that, a two-phase PBTI degradation model was presented, which can describe the turn-around phenomenon. Moreover, the comparison of the estimated remaining useful life (RUL) results with the experimental data verified the accuracy of the developed model. Highlights • A two-phase model is developed using threshold voltage to describe the PBTI degradation. • Turn-around appearance point can also be estimated by the falling and rising phase of the model. • A Power law-Arrhenius combined model is adopted in the degradation model to take into account the electrical and thermal influence. • Utilizing the model, a more accurate remaining useful life of power VDMOSFETs can be estimated. [ABSTRACT FROM AUTHOR]

Electrical lifespan prediction is one of the key problems for the designers of switching apparatus. It is of great necessity to develop empirical correlations between the design parameters and the electrical lifespan. In this paper, a novel method using the arc erosion mass as the prediction variable is proposed to predict the electrical lifespan of high-voltage direct-current (HVDC) relays. The arc current waveforms are measured, and the arc erosion mass during each breaking operation is calculated based on the relationship between the arc current and the arc erosion rate. The arc erosion mass is accumulated until it reaches a threshold value, which is determined by the electrical lifespan experimental results using HVDC products. It is found that the arc erosion mass linearly accumulates with the lifespan, which is very convenient in the electrical lifespan prediction. Experiments are carried out with a parameter-adjustable device similar to the actual HVDC relay structure. Effects of two key design parameters, the arc-blowing magnetic field flux density and the contact breaking speed, of the electrical lifespan are investigated. The magnetic field flux density is changed in the range from 40 to 80 mT, and the breaking speed is varied from 0.85 to 1.3 m/s. The relationships between the lifespan and the magnetic field flux density as well as the breaking speed are regressively constructed. It is shown that the developed relationships can be used for HVDC relay electrical lifespan prediction. [ABSTRACT FROM PUBLISHER]

The typical adhesive phenomena of gold-coated contact material under cold switching conditions are observed using a micro-adhesion apparatus as a switch simulator. With repeated actuation, the recorded adhesion force results uniformly show a Gaussian-like distribution. Moreover, the effects of curvature radius of contact and contact force on adhesive force are investigated experimentally. For better understanding of the adhesion mechanism, the theoretical analysis model is built by introducing the Hamaker’s discussion about the interaction between a pair of neutral atoms or molecules. Data suggest that the substantial increase of adhesion force is correlated closely with the microscopic contact area. [ABSTRACT FROM AUTHOR]

The consistency of batch electromechanical device is influenced seriously by the uncertainty in manufacturing process. Robust tolerance design (RTD) can reduce the impact of uncertainty on the batch products consistency. However, in the traditional RTD method, the contribution rate coefficients of design parameters remain constant during the tolerance optimisation process, which badly affects the accuracy of optimisation. In the paper, a new RTD method of automatic optimisation is proposed based on the variation of contribution rate coefficients. During the tolerance optimisation process, the contribution rate coefficients will be recalculated for each iteration, the step size of tolerance decrease for each parameter can be automatically adjusted according to the difference between the current consistency index and the optimisation target. Compared with the traditional Taguchi RTD method, the optimisation accuracy can be obviously improved by the new method proposed in the paper. [ABSTRACT FROM AUTHOR]

The condition monitoring problem of power devices is significant for diagnostics and prognostics of a switched-mode power supply (SMPS) system. For power mosfet, the gate oxide degradation often occurs in various applications. However, there is no online condition monitoring method for gate oxide degradation so far. In this paper, a new precursor that can be used for online condition monitoring of power mosfet gate oxide degradation is proposed. Gate oxide degradation mechanisms and effect are summarized, and the mosfet turn-on process is analyzed. Then, a theoretical model is established to describe the relationship between miller platform voltage and two types of gate oxide defects, and miller platform voltage is identified as a new precursor. The precursor can be extracted without impacting system operation, thus online condition monitoring can be accomplished. The accelerated degradation test is carried out for power mosfets with both high electric field and gamma irradiation methods, and the degraded devices injection and in situ monitoring of miller platform voltage are conducted on a BOOST circuit to verify the feasibility of the new precursor. Experimental results demonstrate that the new precursor can be applied to online condition monitoring of power mosfet gate oxide degradation in the SMPS system. [ABSTRACT FROM AUTHOR]

• A finite-element (FE) model of electromagnetic transient of Sen transformer (ST) with field-circuit coupling is proposed, and the proposed model can characterize the effects of core and winding topology on the internal magnetic field distribution. • The proposed FE model can characterize the electromagnetic field changes of the ST device under different conditions, such as short-circuit fault, injected harmonics, and dynamic power flow control in the external power system. • The electromagnetic transient field-circuit co-simulation of the ST device and external power system is realized. The conventional electromagnetic transient model of Sen transformer (ST) is mainly established by the magnetic equivalent circuit method, which can be used for the fast calculation of transient characteristics for ST. Unfortunately, this approach may lead to oversimplification and missing significant information in the modeling process. To accurately calculate the transient electromagnetic field and reveal the internal magnetic field distribution of the ST under different operating conditions, an electromagnetic transient model and field-circuit coupling numerical calculation of ST based on finite-element (FE) method is proposed in this paper. The proposed model can characterize the effects of core and winding topology on the internal magnetic field distribution, as well as the complex nonlinear property of core materials, such as saturation, eddy current, and hysteresis. The field-circuit coupling method enables the FE model to establish a connection with external networks and realize the electromagnetic transient field-circuit co-simulation of the ST device and external power system. The case studies are performed on a FE model of the ST and a two-machine transmission system. The corresponding winding voltage and current variations of the ST in the presence of short-circuit fault, injected harmonics, and dynamic power flow control in the external networks are analyzed. The numerical calculation and co-simulation results of the proposed FE model of the ST and the external networks are compared with the commercial FE software, which demonstrates the effectiveness of the proposed FE model of the ST. Moreover, the co-simulation results of dynamic power flow control show that the ST can adjust the power flow distribution of two transmission lines through changing compensation voltage. [ABSTRACT FROM AUTHOR]

• A new class of multi-stress acceleration models with interaction effects is designed. • A multi-stress accelerated degradation model is further developed by incorporating a generalized Wiener process. • Simulation and a real-world case are performed to validate the effectiveness and practical values of the proposed model. Most products operate under multiple stresses. The influences of multi-stress factors on products are commonly not independent and promote a more violent degradation through interactions, referred to as stress interaction effects. However, few studies consider such effects in multi-stress acceleration models, which may reduce the extrapolation precision and further lead to an inaccurate reliability assessment. In this paper, a new class of multi-stress acceleration models with interaction effects is designed to extrapolate more accurate reliability metrics under multi-stress operating conditions. The main stress effect terms are determined by two criteria: physical stress-based ageing law and statistical correlation. The interaction effects are interpreted as the influences of other stress variables on the main stress effects. In particular, the explicit functions of interaction effects are alternative, which can be identified by adaptive optimization using the maximum likelihood criterion. Furthermore, this multi-stress acceleration model is extended to an accelerated degradation model by integrating a generalized Wiener process with nonlinear time scale functions and random effects. The acceleration factor constant principle is utilized to identify the stress-dependent parameters, facilitating a more appropriate model development. Finally, simulation and a real-world case are performed to validate the effectiveness and practical values of the proposed model. [ABSTRACT FROM AUTHOR]

Random effects are ubiquitous in the degradation processes of multiple performance characteristics (PCs) of a complex system, and these PCs are not commonly independent. Neglecting either of the above features will lead to bias in system reliability estimation. Therefore, this study develops a reliability estimation method for the complex systems with multiple PC degradations considering both of the features. First, a Wiener process-based marginal degradation model with random effects (including the random initial PC, unit-to-unit variability, temporal uncertainty, and measurement errors) is proposed to track the degradation path of each PC. A model based on D-vine copulas is put forward to describe the correlation among multiple PCs. Then, a system reliability function is derived based on the two models. Furthermore, a two-step statistical inference is developed to estimate the unknown parameters in the system reliability function. Finally, using a practical case, the effectiveness of the proposed method is illustrated. • A reliability estimation method is proposed for complex systems. • A marginal Wiener process-based degradation model with random effects is proposed. • The correlation among multiple performance characteristics is modeled by D-vine copulas. • A two-step statistical inference is developed to perform the parameter estimation. [ABSTRACT FROM AUTHOR]

As a key component in power electronic systems, the accurate reliability assessment of metallized film capacitors (MFC) is very critical to assure the system reliability and safety. In most operating conditions, the gradual capacitance decrease induced by dielectric film aging and the accumulation of each sudden capacitance loss by random self-healing events under elevated temperature and voltage are the main degradation mechanisms of MFC. However, most investigations tend to directly fit the MFC degradation data by some statistical means, which ignores the specific degradation mechanisms. Such treatments for degradation data often perform a lower modeling accuracy, which may also bring an obvious deviation of reliability assessment result. In this article, we design a degradation mechanisms-based reliability modeling approach for MFC under temperature and voltage stresses. The dielectric film aging is characterized by Wiener process, where the aging rate is dependent with temperature. The compound Poisson process is developed to capture the random self-healing events, where the arrival rate and each sudden capacitance loss are related to the operating voltage as well as the dielectric film aging rate. Finally, an ADT with temperature and voltage acceleration for MFC is conducted to validate the effectiveness of the proposed approach. • A degradation mechanisms-based reliability model for metallized film capacitor is designed. • The dielectric film aging and self-healing process are quantitatively characterized. • An ADT with temperature and voltage acceleration is conducted to validate the proposed model. [ABSTRACT FROM AUTHOR]

• An innovative permanent magnet type broadband SH guided wave MPT is proposed. • The bias magnetic field is enhanced by alternating permanent magnet array. • The diameter of through-hole is exactly quantified by frequency scan detection. T(0,1) guided wave is non-dispersive and has been widely used in the long distance inspection and condition monitoring. Magnetostrictive patch transducer (MPT) is a new type of EMAT with high energy conversion efficiency, which can be used to generate and receive torsional guided waves in pipe samples. In this paper, a permanent magnet broadband torsional guided wave MPT composed of a linear coil EMAT array is proposed. The MPT was experimentally verified to be broadband and the bandwidth is 230.79 kHz when using a 5 mm wide linear coil. The wavelength corresponding to the center frequency of the transducer is about 0.6 times the width of the coil. Base on the design, through-hole defects with diameters of 3–6 mm in the 2-mm-thick aluminum plate were quantified by frequency sweeping detection, and the relative error is less than 7 %. Compared with the single-frequency guided wave signal reflected by through-hole defects, the variation pattern of the quantitative results using frequency sweeping can contribute to a more accurate prediction of the remaining service life of the test specimen. [ABSTRACT FROM AUTHOR]

The existing meander coil type SH guided wave electromagnetic acoustic transducer (EMAT) has a fixed center frequency and narrow bandwidth, which cannot quantify the defect size by continuous frequency scanning. Therefore, this study proposes an array of wideband unidirectional SH guided wave magnetostrictive patch transducer and its control method for excitation of unidirectional SH guided waves at random frequencies over a wide frequency range. A narrow magnetostrictive patch and a linear coil are used for each array element to increase the bandwidth of a single element. By controlling the excitation delay and initial phase of each array element separately, the direction of the SH guided wave can be controlled, and its wavelength can be changed without replacing the coil. In addition, a mathematical model of the array sources of finite width is developed to excite unidirectional SH guided waves at different frequencies. Based on this model, the effects of the number, width and distance of the array element on the frequency response characteristics of the transducer array are analyzed. The experiments show that: The proposed transducer array can excite unidirectional SH guided waves of random frequency over a wide frequency range. The amplitude of the guided wave signal on the suppressed side is almost 0, while the signal on the non-suppressed side is significantly increased, leading to a significant improvement in the energy conversion efficiency. The frequency range can be selected by designing the width and distance of array elements, and the experimentally measured frequency response characteristics of the transducer array are highly consistent with the trend of the mathematical model results. [Display omitted] • A magnetostrictive patch transducer phase array and a theory model for exciting unidirectional SH guide are proposed. • Unidirectional SH guided wave of continuous frequency can be excited within a larger frequency range. • The unidirectional SH guided wave is significantly enhanced in the operating frequency range. • This technology can be employed in defect quantization by continuous frequency scanning detection. [ABSTRACT FROM AUTHOR]

Two mass erosion mechanisms or mass loss modes for electrodes during the repetitive arcing processes should be responsible for the failure of electromagnetic relays, and there are evaporation erosion and sputter erosion. Of these two, the evaporation erosion is believed to be the main failure mechanism for the electrodes used in low-current relays. Unfortunately, there is still no straight-forward model to predict the characteristics of the evaporation process on the electrodes. In this paper, heat transfer and fluid dynamics in the molten pool in silver contacts are coupled with the gas dynamics in the vicinity of arc spot to determine the evaporation rate due to static arc. The influences of input parameters, such as arc current and material properties, on the evaporation rate are analyzed. Of all those parameters, boiling point and thermal conductivity of the electrode are found to be the most significant influences on the evaporation rate. The transfer direction of mass due to electrode evaporation is discussed on the assumption of zero net material loss, and it is found to be directly related to the current and heat flux from the arc to the electrodes. The method used in this paper to evaluate the evaporation erosion characteristics can serve for strategies to alleviate evaporation erosion for relay electrodes. [ABSTRACT FROM AUTHOR]

Composite contacts used for dc relays can help reduce their cost and the amount of precious metals used in their construction. Because of their electrical properties, silver metal oxide-copper (AgMeO–Cu) composite contacts are widely used; however, at heavy loads, the bonding strength of the composite contact will change due to the influence of uneven temperature and stress distributions, which may even cause failure in the form of oxide layer peeling. Here, typical AgSnO2In2O3–Cu composite contacts are studied. A 3-D finite-element simulation model that considers contact making, arcing, and breaking was established to calculate the contact temperature and thermal stress after any operation cycle. The model can be used to determine the variation of the contact temperature and thermal stress distributions versus operation time during an electrical life cycle test. For different AgMeO layer thicknesses (0.25 and 0.38 mm), the temperature and thermal stress distribution of composite contact’s bonding area were calculated under different current load levels: 30, 45, and 60 A, while the load voltage is a constant 17 V. Results show that the thickness of the AgMeO layer has a significant effect on the temperature and stress distribution of the bonding area in the moveable contact and the composite contacts may more easily curl and crack with an increment of the AgMeO layer thickness under the same current condition. The simulation results agree well with the experimental data and the relative error is less than 10%. The validity of the model and method was verified. The numerical model in the paper may be used to analyze a composite contact’s properties and is therefore useful for design optimization and the selection of composite contact materials. [ABSTRACT FROM PUBLISHER]