Low Frequency Eddy Currents with Magnetic Saturation for In-Line Detection and Sizing of Stress Corrosion Cracks

1995 ◽  
pp. 323-330
Author(s):  
Richard J. Davis ◽  
Donald T. Hayford
Keyword(s):  
Stress Corrosion ◽  
Eddy Currents ◽  
Low Frequency ◽  
Line Detection ◽  
Magnetic Saturation

scholarly journals Dynamic Model of MR Dampers Based on a Hysteretic Magnetic Circuit

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Pengfei Guo ◽  
Jing Xie ◽  
Xinchun Guan
Keyword(s):  
High Frequency ◽  
Eddy Currents ◽  
Magnetic Circuit ◽  
Fluid Model ◽  
Magnetic Hysteresis ◽  
Low Frequency ◽  
Circuit Model ◽  
Magnetic Saturation ◽  
Damping Force ◽  
Mr Dampers

As a key to understand dynamic performances of MR dampers, a comprehensive dynamic magnetic circuit model is proposed in this work on the basis of Ampere’s and Gauss’s laws. It takes into account not only the magnetic saturation, which many existing studies have focused on, but also the magnetic hysteresis and eddy currents in a MR damper. The hysteresis of steel parts of MR dampers is described by Jiles-Atherton (J-A) models, and the eddy current is included based on the field separation. Compared with the FEM results, the proposed model is validated in low- and high-frequency studies for the predictions of the magnetic saturation, the hysteresis, and the effect of eddy currents. A simple multiphysics model is developed to demonstrate how to combine the proposed magnetic circuit model with the commonly used Bingham fluid model. The damping force in the high-frequency case obviously lags behind the coil current, which exhibits a hysteresis loop in the current-force plane. The lag of damping force even exists in a low-frequency varying magnetic field and becomes more severe in the presence of eddy currents.

scholarly journals The Hybrid FEM-DBCI for the Solution of Open-Boundary Low-Frequency Problems

Mathematics ◽  
2021 ◽  
Vol 9 (16) ◽  
pp. 1968
Author(s):  
Giovanni Aiello ◽  
Salvatore Alfonzetti ◽  
Santi Agatino Rizzo ◽  
Nunzio Salerno
Keyword(s):  
Integral Equation ◽  
Eddy Currents ◽  
Computing Time ◽  
Low Frequency ◽  
Dirichlet Condition ◽  
Open Boundary ◽  
Coordinate Transformations ◽  
External Layer ◽  
Electromagnetic Problems ◽  
Electrostatic Fields

This paper describes a particular use of the hybrid FEM-DBCI, for the computation of low-frequency electromagnetic fields in open-boundary domains. Once the unbounded free space enclosing the system has been truncated, the FEM is applied to the bounded domain thus obtained, assuming an unknown Dirichlet condition on the truncation boundary. An integral equation is used to express this boundary condition in which the integration surface is selected in the middle of the most external layer of finite elements, very close to the truncation boundary, so that the integral equation becomes quasi-singular. The method is described for the computation of electrostatic fields in 3D and of eddy currents in 2D, but it is also applicable to the solution of other kinds of electromagnetic problems. Comparisons are made with other methods, concluding that FEM-DBCI is competitive with the well-known FEM-BEM and coordinate transformations for what concerns accuracy and computing time.

Experimental Research of AE Inspection on Stress Corrosion Crack for Small Pressure Vessel

2013 ◽  
Author(s):  
Zhongzheng Zhang ◽  
Hua Liang ◽  
Cheng Ye ◽  
Wensheng Cai ◽  
Jun Jiang
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Crack ◽  
Pressure Vessel ◽  
Low Frequency ◽  
Reference Value ◽  
Ferric Chloride Solution ◽  
Pressure Vessels ◽  
Flexural Wave ◽  
Small Pressure ◽  
Ae Signals

To study acoustic emission (AE) signals characteristics of stress corrosion crack (SCC) on in-service pressure vessels. The small pressure vessel with a pre-crack, filled 6% ferric chloride solution was monitored by AE technique. Conventional parameter-based approach and signal-based analysis were combined to deal with recorded AE signals, and micromorphologic observation and ray detection were performed for further verification. The results showed that the Kaiser effect of Q345R material is obvious, AE hits rate and amplitude & energy of the first pressure cycling was higher. Signal band is mainly distributed in 40 ∼ 400 KHz, Signal waveform was mainly composed of high -frequency (>100 KHz) expansion wave with larger amplitude & energy and low-frequency (<100 KHz) flexural wave with lesser amplitude & energy. The research results have a certain reference value for AE test on SCC for practical in-service pressure vessel.

scholarly journals The EM response due to a plane sheet of arbitrary shape and conductivity profile

1995 ◽  
Vol 37 (2) ◽  
pp. 267-278
Author(s):  
D. G. Hurley ◽  
P. F. Siew
Keyword(s):  
Eddy Currents ◽  
Thin Sheet ◽  
Low Frequency ◽  
Depth Of Penetration ◽  
Frequency Limit ◽  
Planar Shape ◽  
Method Of Solution ◽  
Conductivity Profile ◽  
Plane Sheet ◽  
Variable Conductivity

AbstractThe eddy currents induced in a thin sheet of variable conductivity by a sinusoidally varying primary magnetic field are investigated in the low frequency limit when the depth of penetration of the primary field is much greater than the thickness of the sheet. The problem is formulated in terms of a set of integro-differential equations. The method of solution is applicable to bodies with arbitrary planar shape and the result is particularly useful in inverse problems involving bodies with conductivity inhomogeneities.

Eddy Current Measurement for Characterizing Soft Tissues

2012 ◽  
Author(s):  
Emily K. Sequin ◽  
Joseph West ◽  
Vish V. Subramaniam
Keyword(s):  
Eddy Current ◽  
Eddy Currents ◽  
Soft Tissues ◽  
Low Frequency ◽  
Morphological Structure ◽  
Current Measurement ◽  
Phase Changes ◽  
Induced Voltage ◽  
Porcine Muscle ◽  
Lock In

Real-time and non-invasive imaging of tissues and detection of diseases on millimeter to centimeter scales can be useful in some clinical applications such as determination of margins during cancer surgery and image-guided pathology. In this paper, we describe an eddy current measurement method for characterizing soft tissues. The device consists of a pair of concentrically wound coils, a primary coil excited by a low frequency (<100 kHz) sinusoidal voltage, inducing a voltage and current in the secondary detecting coil. When a conducting sample is present, eddy currents develop in the sample and alter the induced voltage and phase on the detecting coil. The output voltage and phase of the detecting coil are then monitored using lock-in amplification. Experimental measurements on porcine muscle tissue examine the effects of varying tissue macrostructure and conductivity on the eddy current detector. Three sets of experiments are presented. First, muscle samples cut into different sized grids simulating the restriction of eddy current domains show that morphological structure has a strong influence on the detector signal. Second, eddy current measurements made on porcine muscle samples at varying degrees of dehydration show that as conductivity decreases, eddy current signals also decrease. Finally, measurements on porcine muscle samples soaked overnight in deionized water complement the dehydration experiments and confirm detector voltage and phase changes decrease with decreasing conductivity.

Low-Frequency Magnetic Localization of Capsule Endoscopes with an Integrated Coil

2021 ◽  
Vol 6 (1) ◽  
pp. 38
Author(s):  
Samuel Zeising ◽  
Rebecca Seidl ◽  
Angelika Thalmayer ◽  
Georg Fischer ◽  
Jens Kirchner
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Density ◽  
Eddy Currents ◽  
Low Frequency ◽  
Magnetic Sensors ◽  
Video Frame ◽  
Magnetic Flux Density ◽  
Field Source ◽  
Localization Method

Wireless capsule endoscopy is a promising and less invasive alternative to conventional endoscopy. A patient swallows a small capsule with an integrated camera to capture a video of the gastrointestinal tract. For accurate diagnosis and therapy, the capsule position in terms of the travelled distance must be known for each video frame. However, to date, there is no reliable localization method for endoscopy capsules. In this paper, a novel magnetic localization method is proposed. A coil as a magnetic field source is integrated into a capsule and fed with a low-frequency alternating current to prevent static geomagnetic field interference. This alternating magnetic field is measured by twelve magnetic sensors arranged in rings around the abdomen. The coil and the capsule batteries were designed based on the geometry and power supply of a commercially available endoscopy capsule and simulated by COMSOL Multiphysics software. In this way, the coil position and orientation were determined with an accuracy below 1 mm and 1°, respectively. As an analytic model for the magnetic flux density of the coil in that setup, a modified dipole model was derived. It was used to show that the batteries help to increase the amplitude of the magnetic flux density. The model is valid when signals below 100 Hz are applied, and no eddy currents are generated within the batteries. It is concluded that the magnetic flux density generated by the developed coil would be measurable with state-of-the-art magnetic sensors.

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