Eddy Current Distribution Research Articles

Simulation and experimental study on ECT of circumferential cracks in small-diameter tubes

Circumferential crack detection of small diameter tubes is a difficult problem to solve in eddy current testing. The three-dimensional simulation model is established through electromagnetic field simulation software to analyze the eddy current field distribution of the traditional bobbin probe and transverse cylindrical probe in small diameter tubes. The results show that the circumferential crack has a more marked disturbance to the eddy current field generated by the latter. Based on the simulation research, a new type of probe based on transverse excitation is designed to detect the artificial circumferential crack of the specimen with the designed probe, which can effectively detect the circumferential crack and has a potentially high sensitivity to the narrower natural circumferential crack.

Effect of Scanning Acceleration on the Leakage Signal in Magnetic Flux Leakage Type of Non-destructive Testing

This work investigates the influence of acceleration on the leakage signal in magnetic flux leakage type of non-destructive testing. The research is addressed through both designed experiments and simulations. The results showed that the leakage signal, represented by using peak to peak value, decreases between 15.1% and 26.6% under acceleration. The simulation results indicated that the main reason for the decrease is due to the difference in the distortion of the magnetic field for cases with and without acceleration, which is the result of the different eddy current distributions in the specimen. The findings will help to allow the optimisation of a magnetic flux leakage system to ensure that main defect features can be measured more accurately during the machine acceleration phase of scanning. It also shows the importance of conducting measurements at constant velocity, wherever possible.

Two-Dimensional Eddy-Current Losses Model and Experimental Validation Through Thermal Measurements

Eddy-currents, generated by a spatio-temporal magnetic field variation, involve volumic losses, and consequently overheating. A two-dimensional (2-D) analytical model is developed to determine precisely the eddy-current distribution as well as losses. An experimental validation by thermal evolution measurements and an overheating of conductive massive parts is performed. Consequently, the eddy-current losses could be determined experimentally. A comparison of the results considering the segmentation influence of conductive massive parts is carried out. The difference between the theoretical and experimental results is less than 5%.

High frequency eddy current inspection of fibre placement in Carbon Fibre Reinforced Polymer Composites

This paper presents experimental and simulation studies of high frequency eddy current non-destructive testing (NDT) methods for inspection of carbon fibre reinforced polymer (CFRP) composites. It is well known that CFRP composite materials are widely used in industry as structural components, and products based on such materials are increasingly developed and introduced to market. In recent years, non-conventional eddy current method operating at high frequencies for NDT of composites begins to attract attention. It provides a non-contact, couplant-free option of inspection when compared with the other NDT methods currently used in industry. As eddy current relies on fibre fabrics in individual plies to form the current pathways, the eddy current paths in composite are unsurprisingly complex due to the structural features of composite laminates when compared with that in homogenous conducting metals for which conventional eddy current NDT is often used in industry. It will be noted that the knowledge is still limited so far about the eddy current distributions in composite laminates due to lack of effective theoretical and numerical models. This paper will focus on the development of a new numerical model that is suitable for use in simulations of high frequency eddy current inspection of fibre placements. An effective model is desirable for understanding the performance dependence of the eddy current testing method on the material properties, composite structural features, and other parameters involved. In this model, the fibre tow layout of individual plies is taken into consideration. The collection of the pickup signals by the sensor probe shows clear images of the fibre placement in different layers. The simulation results are compared with experimental results of fibre placement imaging. The model is useful for understanding the physical process for inspection of composites using high frequency eddy current methods, and for studying the influence of the controllable parameters involved.

Design and Performance Research of a New Dual-Excitation Uniform Eddy Current Probe.

A dual-excitation uniform eddy current probe, composed of two excitation coils placed tangentially and one detection coil placed horizontally, is developed to solve the difficulties of detection rate and direction recognition of crack defect. Firstly, a probe simulation model is established using COMSOL Multiphysics, and the differences of eddy current distribution between the dual-excitation probe and the traditional probe are investigated. Then, the influence of the distance between excitation coils on sensitivity and the test capability for crack defects with different depths and directions are investigated. Besides, the sensitivity of the dual-excitation probe is compared to that of the traditional probe made of the same coils. Finally, a physical probe and an experimental system are developed, and the performance of the dual-excitation probe is tested. The experimental results show that the probe developed in this paper exhibits a slightly higher sensitivity than the traditional probe for crack defects with different depths in the range of 0.5 mm-4.0 mm; the measurement accuracy of crack length is about 3.0 mm and can avoid missing detection of crack defects with different directions. In testing, the detection signal can be compensated to achieve precision measurement by identifying the angle of crack defects. This dual-excitation uniform eddy current probe can be used for precise quantification and direction identification of crack defect in eddy current testing.

Determination of Eddy-Current Distribution in Electrically Isolated Vessel Sections of ADITYA-U Tokamak

The time-varying magnetic field induces eddy current in the conducting structure of a tokamak device. The characteristics of eddy currents in the discontinuous vacuum vessel are more complex than those found in a tokamak with a continuous vacuum vessel. Even with multiple electrically isolated sections of the vacuum vessel, there is evidence of a noticeable fast decaying current that flows along the inboard and outboard vessel surfaces and their analysis is not straightforward. It is necessary to detect and investigate the eddy-current effect due to the close vicinity of the vessel surface with the plasma column as they seriously affect the in-vessel magnetic diagnostics, the penetration of equilibrium fields, and the displacement of the plasma column. The induced eddy currents in vacuum-vessel sections are estimated using magnetic probes during the in situ calibration experiments in ADITYA-U tokamak. The filament model is utilized for estimating the spatial and temporal eddy-current profiles generated in the ADITYA-U vacuum vessel. The number of current filaments in the vessel section is optimized using the various combinations of available Mirnov sensors (magnetic probes) located over the poloidal periphery inside the vessel. In this article, the eddy-current measurement under different experimental conditions in the ADITYA-U is presented. This study also serves as an illustration of the usefulness of the filament model for the parameterization of eddy-current paths and magnitude to describe the induced vessel current during ADITYA-U plasma discharges.

Effects of particle size on the separation efficiency in a rotary-drum eddy current separator

Eddy current separation is a technology for recovering non-ferrous metals. The influence of particle size on the separation is of significant importance due to the variety of materials. It was investigated by combining simulations and physical experiments. A strong correlation between the simulation and the experiment was found by Pearson correlation analysis. Then the interaction effects between the particle size and the material type, rotational speed, magnetic pole arrangement were investigated. It shows that an optimal particle size exists for a specific condition, and the separation efficiency of fine particles can be improved by increasing rotational speed, magnetic pole number, and the electrical conductivity/density of material, as well as utilizing torque of Lorentz force. The underlying mechanism of particle size affecting separation was discovered by analyzing eddy current distribution and field gradient. These results provide insight into the design and optimization of eddy current separation for particles of various sizes. • The correlation between simulation and physical experiment was established. • There is an optimal particle size for separation under a specific condition. • The rotation of the particles increases with the decrease of the particle size. • The magnitude and distribution of eddy current is related to the particle size. • Some optimization principles of the eddy current separator were proposed.

3-D Hybrid Analytical Prediction Model for Air-Cored Linear-Rotary Induction Machine

This article presents a 3-D hybrid analytical prediction model for an air-cored linear-rotary induction machine (LRIM) in which its columnar movable armature surfaced with the conductor. The analytical magnetic distributions in the conductor and air gap of the LRIM are predicted by employing a group of H-formulations in the conductor and the Laplacian equations with magnetic scalar potential (MSP) in the others in the Cartesian coordinate. The correctness of the magnetic field distributions and the eddy-current distributions is verified by the numerical computational results using the 3-D finite-element method (FEM).

Optimization on pole pitch of magnetic wheels and thickness of metal plate for floating and a propulsion system using permanent magnets

A magnetic-levitation system using a rotating permanent magnet has been developed. Pole pitch of the magnetic wheels and thickness of the metal plates required for levitation were investigated by experiments and computational calculation. To determine the optimum conditions, the levitation force, generated using motors with different torque and rotation speeds, was measured. These measurements clarified differences in the generated levitation force due to the different rotational speed and torque. Parameters, such as skin depth, magnetic density, eddy-current distribution density, the ratio of drag force to levitation force, and levitation force per driving power were numerically calculated from the magnetic field created by the rotating permanent magnet and effective frequency. Magnetic wheels should be designed to be large and the pole pitch of magnets was to be wide, and the levitation force per driving power will be improved in proportion to the root function of the pole pitch between magnets.

Information Entropy of Angular Spectrum for Quantitatively Evaluating Eddy Current Distribution Varying in Time Domain

Information Entropy of Angular Spectrum for Quantitatively Evaluating Eddy Current Distribution Varying in Time Domain

Comparison of different types of focusing probes in pulsed eddy current testing

Pulsed eddy current (PEC) testing has attracted widespread attention because of its unique advantages in detecting local defects in insulated pipes. In this paper, rectangular, U-shaped, and semicircular PEC focusing probes are designed, the magnetic energy utilization efficiency and focusing properties of the developed probes are simulated and compared, and their detection sensitivities are experimentally compared. The magnetic flux through specific surfaces is calculated to find the utilization of magnetic energy by the different probes, and the eddy current dissipation power is used to quantitatively describe the eddy current field focusing properties of various types of probes. The simulation results show that the magnetic field energy utilization efficiency of the semicircular focusing probe is significantly higher than that of the other two probes, but the eddy current field distributions of the three probes are similar, and the focusing properties are not significantly different. The experimental results show that the three types of PEC probes can effectively detect local defects under a certain lift-off. By calculating the detection sensitivity of different probes to defects under different lift-off conditions, it is determined that the detection sensitivity of the semicircular probe is significantly higher than that of the U-shaped probe and rectangular probe. The experimental results are consistent with the numerical simulation results. The research results are conducive to the optimal design of PEC focusing probes for insulated pipes.

Simplified 3-D Hybrid Analytical Modelling of Magnet Temperature Distribution for Surface-mounted PMSM With Segmented Magnets

In this article, a simplified three-dimensional (3-D) hybrid analytical thermal model for surface-mounted permanent magnet (PM) synchronous machines is proposed and applied to investigate the influence of PM segmenting strategies on the spatial PM temperature distributions and hotspots. The developed 3-D hybrid thermal model synergies the lumped-parameter thermal model and analytical method and is able to estimate 3-D spatial temperature distributions and hotspots for both unsegmented and segmented surface-mounted PMs accounting for the uneven PM eddy current loss distributions. Meanwhile, by utilizing the proposed matrix-based post-processing methods, the developed hybrid analytical thermal model has a simple mathematical expression but persists in high estimation accuracy. Finally, the proposed hybrid analytical modelling method is validated by 3-D electromagnetic-thermal coupled FEA and experiments.

Research on Nondestructive Testing Signal Processing Method for Intermittent Fault of Circuit Structure

In the process of nondestructive testing of circuit structural units, considering that the eddy current intensity and distribution formed under the action of electromagnetic coupling will inevitably cause the change of voltage or impedance of electromagnetic induction testing coil, this kind of phenomenon reflects the signal change information caused by defects such as insulation wear, corrosion, cavitation and so on. In order to fully avoid the sudden faults such as short circuit, open circuit or arc discharge caused by hidden dangers, which force the equipment to stop for maintenance, this paper studies the principle of intermittent fault detection system of circuit structure, designs the circuit structure of typical modules, and establishes the defect prediction model based on Smoothing Technology. It provides a theoretical basis for effectively detecting intermittent fault signals, analyzing the propagation trend of intermittent faults and identifying defect modes, and can be extended to the acquisition and processing of intermittent fault signals of electronic equipment.

Analysis of the RCF crack detection phenomenon based on induction thermography.

Eddy current pulsed thermography (ECPT) is used to detect rolling contact fatigue (RCF) cracks on the rail. It is observed that some of the cracks disappear in the thermal image with the increase of heating time. Based on the finite element method, with double cracks as the basic unit, three different crack models are established, and the mutual disturbance relationship between the double cracks is discussed based on the eddy current distribution and thermal diffusion process. The simulation and experimental results show that different crack models are affected by thermal diffusion in different heating stages to different degrees, and the time of the crack thermal image disappearance is obtained. According to the above conclusions, the RCF cracks are extracted and classified based on the influence of thermal diffusion. The possibility of rail condition assessment and maintenance based on the disappearance time is explained.

ESTIMATION OF EDDY CURRENTS AND POWER LOSSES IN THE ROTOR OF A SCREW ELECTROTHERMOMECHANICAL CONVERTER FOR ADDITIVE MANUFACTURING

3D printing technologies for large-scale structures allow architects and builders to considerably expand the design boundaries of structures and increase the efficiency of their construction. Mobile robotic platforms for 3D printing are increasingly being implemented in the construction sector, as well as in the production of road surfaces, allowing to solve the problem of limited working space. The typical design of the extruder assembly of a robotic platform for 3D printing large-scale structures can be improved by combining an electric motor, an auger extruder, and a heater in one housing. The proposed auger-type electrothermomechanical converter uses an external auger rotor, which simultaneously performs the functions of an asynchronous motor rotor, a heating element, an actuator, and a protective housing. The purpose of this study was to evaluate the efficiency of using an auger converter as part of a mobile robotic platform for additive manufacturing. For converters operating in difficult conditions, the use of field calculation methods is relevant. In this study, a field calculation was performed using the finite element method and the spatial distribution of eddy currents in the section of the hollow ferromagnetic rotor was found. Pictures of the three-dimensional distribution of the z-component, the normal component of the density of eddy currents, as well as the distribution of the dissipated power density, which considers all types of losses in the rotor, were obtained using the Comsol Multiphysics software and computing complex. The practical value of the obtained results lies in the possibility of predicting optimal indicators of the influence of the thermal regime on the material, as well as the speed of rotation of the converter rotor. This will determine the mechanical properties of the material at the output of the device.

Measurement of helicity flux density using the eddy-current diagnostic system in Keda Torus eXperiment device

The flux of magnetic helicity characterizes how the topology of a magnetic field changes and helicity and its transport play essential roles in plasma equilibrium and instabilities in the reversed-field pinch (RFP) device configuration. Used to suppress magnetohydrodynamic instabilities effectively, the stabilizing conducting shell located at the boundary of an RFP device is always characterized by an eddy-current distribution that evolves rapidly with time. After measuring and analyzing the eddy currents on this stabilizing shell during tokamak discharges in the Keda Torus eXperiment device, the distributions of multiple physical quantities on the shell are obtained, including the magnetic fields, eddy currents, and electric fields. An experimental technique for measuring helicity flux density is demonstrated, combined with eddy-current diagnosis and these physical vectors on the boundary. How the magnetic and current helicity flux densities evolve is given by a feasible mathematical analysis, and data suggest that the plasma mediates both the generation and transport of magnetic helicity during the discharge. The experimental results of the distribution of the magnetic helicity flux densities (MHFDs) due to the instability on the boundary are given, and the average of these MHFDs over the whole boundary surface is far less than the maximum value of the MHFDs. In addition, the results of current helicity flux densities on the boundary are also presented.

Research on the Influence of Projectile Width on the Efficiency of Reconnection Electromagnetic Launchers

Reconnection electromagnetic launcher is a kind of electromagnetic launcher, which has excellent performance of launching. The change of projectile width has a great influence on the launching efficiency of reconnection electromagnetic launcher. The influence of the reverse vortex generated on both sides of the projectile on the launch efficiency when the projectile width increases is studied in this article. First, the model and basic principles of the reconnection electromagnetic launcher are introduced, and then the electromagnetic finite-element software is used to carry out a large number of simulations to study the launch model. The results show that when the projectile weight is kept constant by digging out a part of the projectile, and the projectile width increases within a certain range, the launch efficiency will increase as the width of the projectile increases, the increasing trend is smaller and smaller, and finally it will gradually decrease. When the mass of the projectile is determined, there is an optimal width. Finally, the eddy current distribution in the projectile is analyzed, and it is found that when the projectile has a wide width, the eddy current opposite to the eddy current in the middle of the projectile will appear on both sides of the projectile. Through the analysis of electromagnetic force, it can be concluded that the reverse eddy current is beneficial to the launch. Therefore, when keeping the weight of the projectile constant and only increasing the width, the efficiency will gradually increase. When the width of the projectile is highly wide, the excavated part of the projectile is very large, which starts to affect the vortex distribution and reduce the efficiency. This research provides a reference for the design of the projectile of the reconnection electromagnetic launcher.

Urinary Bladder Volume Monitoring Using Magnetic Induction Tomography: A Rotational Simulation Model for Anatomical Slices Within the Pelvic Region.

Urinary bladder volume monitoring can benefit from contactless measurements, as alternative to the traditional medical methods of transurethral catheterization or ultrasound examination. The emerging modality of Magnetic Induction Tomography (MIT) offers the possibility for estimation of the intravesical volume in the physiological and pathological states using conductivity map reconstructions of the tissues present in the pelvic region. Within MIT, eddy currents originating from the conductive urine can produce their own magnetic field in response to an external magnetic source that is susceptible of being detected outside the body by means of a static ring of sensing coils. However, the ill-conditioned and ill-posed nature of the MIT Inverse Problem make the numerical implementation and conductivity estimation highly laborious. In this paper, we present a rotational frame model based on the MIT principles with application in urodynamic studies, which allows to extend the number of contactless measurements without increasing the overall dimension of the simulation domain, at the expense of solving multiple MIT Forward Problems. On the inversion process, the single-step Gauss-Newton method with Laplacian regularizer is recruited to estimate the bladder volume non-invasively and remotely (estimation error of 19%) using a simplified (quasi 2D) approximation to the distribution of eddy currents in the examined region, therefore paving the way for this technique to surpass the current limitations found in intravesical volume monitoring.

Jensen-Shannon Divergence of Two Eddy Current Distributions Induced by Circular and Fractal Koch Excitation Coils

Eddy current distribution is important to the performance of planar eddy current probes. In this paper, the Jensen-Shannon divergences of tangential intersection angle spectrum and radial direction energy spectrum were proposed to evaluate the difference between eddy current distributions generated by circular and fractal Koch excitation coils. By the simulation for the circular and Koch shape excitation coils, it works out that the difference of the eddy current distributions between the two kinds of coils becomes larger and larger with an increase in the values of the two Jensen-Shannon divergences. At the same time, the correlation between the change of Jensen-Shannon divergence and the detectability of the short crack in the special direction was discussed through simulation and experiment results. It is found that, relative to the crack in 0° direction, the detectability of the Koch and circular differential pickup probes to the crack in 90° direction has a correlation with the Jensen-Shannon divergence of tangential intersection angle spectrum. The width of each signal generated by the two probes has a correlation with the Jensen-Shannon divergence of radial direction energy spectrum.

Computationally Efficient Stator AC Winding Loss Analysis Model for Traction Motors Used in High-Speed Railway Electric Multiple Unit

The aim of this proposed work is to develop a computationally efficient and accurate AC winding loss analysis model for the traction motors for use in high-speed railways (HSRs). The goal of the model is to be able to study AC winding loss under both sinusoidal and pulse width modulated (PWM) inverter voltage sources. The traction motor model considered for the proposed study is a form wound winding permanent magnet (PM) assisted synchronous reluctance motor (PMaSynRM). The traction motor uses an open slot with two-layer winding. First, a flux linkage table is built using finite element analysis (FEA) with sinusoidal current as the input. The machine model then includes the effect of the PWM inverter voltage source with the current controller. For the AC winding loss analysis, the fundamental component and the harmonics due to PWM are considered separately. To find the loss due to the fundamental component only, the vector potential of the slot region is mapped to the subconductors of the form wound winding and the eddy current distribution and the AC winding loss are calculated. The effect of the harmonics due to the PWM switching is then added in the post-processing stage by analytically evaluating the individual harmonic effect. The whole AC loss analysis model proposed in this work is computationally more efficient than the conventional FEA because the transient state of the system is removed. Moroover, the PWM voltage source effect is divided into the effects of the fundamental component and switching harmonics by combining the vector potentia mapping and post-processing analytical calculation.