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.

scholarly journals Imaging the Electro-Kinetic Response of Biological Tissues with Optical Coherence Tomography

2021 ◽  
Author(s):  
Valentin Demidov
Keyword(s):  
Optical Coherence Tomography ◽  
Soft Tissues ◽  
Low Frequency ◽  
Depth Resolution ◽  
Biological Tissues ◽  
Phase Changes ◽  
Optical Coherence ◽  
Ac Electric Field ◽  
Novel Approach ◽  
Phase Images

This thesis reports on developing a novel approach to imaging the electro-kinetic response of biological tissues with optical coherence tomography (OCT). The changes of backscattered OCT signal from tissues were investigated with a low frequency AC electric field being applied to the tissues. Advanced processing algorithms were developed to analyze the amplitude and phase changes of OCT signal. Two-dimensional electrically induced optical changes (EIOC) amplitude and phase images related to the electro-kinetic response of soft tissues were obtained with depth resolution and compared with structural OCT images. The procedure for removing the background noise from EIOC images was introduced.

scholarly journals Imaging the Electro-Kinetic Response of Biological Tissues with Optical Coherence Tomography

2021 ◽  
Author(s):  
Valentin Demidov
Keyword(s):  
Optical Coherence Tomography ◽  
Soft Tissues ◽  
Low Frequency ◽  
Depth Resolution ◽  
Biological Tissues ◽  
Phase Changes ◽  
Optical Coherence ◽  
Ac Electric Field ◽  
Novel Approach ◽  
Phase Images

This thesis reports on developing a novel approach to imaging the electro-kinetic response of biological tissues with optical coherence tomography (OCT). The changes of backscattered OCT signal from tissues were investigated with a low frequency AC electric field being applied to the tissues. Advanced processing algorithms were developed to analyze the amplitude and phase changes of OCT signal. Two-dimensional electrically induced optical changes (EIOC) amplitude and phase images related to the electro-kinetic response of soft tissues were obtained with depth resolution and compared with structural OCT images. The procedure for removing the background noise from EIOC images was introduced.

Eddy Current Flows Around Cracks in Thin Plates for Nondestructive Testing

1982 ◽  
Vol 49 (2) ◽  
pp. 389-395 ◽  
Author(s):  
S. Mukherjee ◽  
M. A. Morjaria ◽  
F. C. Moon
Keyword(s):  
Current Density ◽  
Eddy Current ◽  
Eddy Currents ◽  
Low Frequency ◽  
Numerical Results ◽  
Thin Plates ◽  
Line Integral ◽  
Faraday’S Law ◽  
Induced Currents ◽  
Current Flows

The boundary element method is used to calculate the induced electric current flow around cracks in thin conducting plates. A low frequency approximation leads to a Poisson equation for the current density potential or stream function. A kernel is used which produces the correct singularity at the crack tip. The boundary condition on the crack, derived from Faraday’s law, requires the line integral of the current density around the crack to be zero. Numerical results for induced currents due to a circular induction coil ore given. These results show that hot spots, due to Joule heating, can occur at the tips of the crack. Comparison of numerical results with infrared scanning experiments of eddy currents in a cracked plate are given. It is hoped that the numerical method presented here will provide a tool to simulate both new and conventional nondestructive eddy current testing techniques.

Eddy Current Distribution and Lift Force for Finite Maglev Strips

1974 ◽  
Vol 52 (13) ◽  
pp. 1203-1208 ◽  
Author(s):  
D. L. Atherton ◽  
A. R. Eastham ◽  
C. Fombrun ◽  
M. Chong
Keyword(s):  
Current Distribution ◽  
Eddy Current ◽  
Lift Force ◽  
Eddy Currents ◽  
Vertical Component ◽  
Surface Current ◽  
Strip Width ◽  
Finite Width ◽  
Surface Current Density ◽  
Lock In

The transverse distribution of induced eddy currents across a flat conducting strip of finite width, due to a rectangular d.c. magnet moving above it, has been modelled experimentally, and has been compared with that calculated for an infinite sheet. The electrodynamic suspension was simulated by means of a stationary a.c.-excited copper magnet suspended above an aluminum strip, and the induced surface current density was measured by a voltage pickup probe connected to a lock-in amplifier. Good agreement is obtained between the eddy current profiles for a wide sheet and those calculated by determining the current distribution required to cancel the vertical component of the magnet field at the surface of the sheet. The effect of reducing strip width is examined and shown to produce high current densities close to the edges. These results are related to the variation of lift force with strip width, determined by impedance modelling. A slight enhancement of lift is evident for intermediate strip widths.

A new mathematical model for resonant-column measurements including eddy-current effects

2005 ◽  
Vol 42 (1) ◽  
pp. 121-135 ◽  
Author(s):  
Giovanni Cascante ◽  
John Vanderkooy ◽  
Wilson Chung
Keyword(s):  
Mathematical Model ◽  
Wave Velocity ◽  
Eddy Current ◽  
Eddy Currents ◽  
Damping Ratio ◽  
Resonant Column ◽  
Induced Voltage ◽  
Eddy Current Damping ◽  
Dry Sand ◽  
Resonant Column Device

Wave velocity and attenuation are commonly studied in the laboratory with the resonant-column device (American Society for Testing and Materials standard), which is driven by a set of coils and magnets. This paper presents a new and robust mathematical model of the electromechanical resonant-column system. The model is used to compute various transfer functions. Eddy currents, a new source of damping identified in the resonant-column device, introduce damping proportional to the velocity of the magnets. Eddy-current damping is considered in the mathematical model. A testing program is devised to calibrate the resonant column with three aluminum probes. Experimental and theoretical results show an excellent agreement (4% maximum error). Exploratory results are presented for a dry-sand specimen. A resonant-column device is modified to demonstrate the significant effect of the induced voltage (electromotive force (EMF)) on damping ratio if tests are not based on current measurements. Free-vibration tests on aluminum specimens and a dry-sand specimen show a significant effect of the induced EMF (up to 400% increase in damping for the sand specimen). The induced voltage depends on the resonant frequency and damping of the specimen. In the case of aluminum probes, eddy-current damping represents 20–150 times the material damping of the specimen. Preliminary results on dry sand show that eddy-current damping represents up to a 15% increase in damping ratio. However, the magnitude of eddy-current damping depends on the configuration and materials used in the resonant-column device. The smaller the damping ratio of the specimen is, the more important the eddy-current damping becomes.Key words: damping, eddy currents, mechanical waves, resonant-column device, shear modulus, wave velocity.

Determination of eddy current losses and hysteresis losses in magnetic circuits of electrical machines

2020 ◽  
pp. 54-58
Author(s):  
S. M. Plotnikov
Keyword(s):  
Eddy Current ◽  
Magnetization Reversal ◽  
Eddy Currents ◽  
Technical Problem ◽  
Electrical Machines ◽  
Eddy Current Losses ◽  
Hysteresis Losses ◽  
Magnetic Circuits ◽  
Core Losses ◽  
Reversal Frequency

The division of the total core losses in the electrical steel of the magnetic circuit into two components – losses dueto hysteresis and eddy currents – is a serious technical problem, the solution of which will effectively design and construct electrical machines with magnetic circuits having low magnetic losses. In this regard, an important parameter is the exponent α, with which the frequency of magnetization reversal is included in the total losses in steel. Theoretically, this indicator can take values from 1 to 2. Most authors take α equal to 1.3, which corresponds to the special case when the eddy current losses are three times higher than the hysteresis losses. In fact, for modern electrical steels, the opposite is true. To refine the index α, an attempt was made to separate the total core losses on the basis that the hysteresis component is proportional to the first degree of the magnetization reversal frequency, and the eddy current component is proportional to the second degree. In the article, the calculation formulas of these components are obtained, containing the values of the total losses measured in idling experiments at two different frequencies, and the ratio of these frequencies. It is shown that the rational frequency ratio is within 1.2. Presented the graphs and expressions to determine the exponent α depending on the measured no-load losses and the frequency of magnetization reversal.

scholarly journals Effects of administration route on uptake kinetics of 18F-sodium fluoride positron emission tomography in mice

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zaniah N. Gonzalez-Galofre ◽  
Carlos J. Alcaide-Corral ◽  
Adriana A. S. Tavares
Keyword(s):  
Positron Emission Tomography ◽  
Sodium Fluoride ◽  
Soft Tissues ◽  
Small Animal ◽  
Phase Changes ◽  
Emission Tomography ◽  
Pharmacokinetic Data ◽  
Administration Route ◽  
Standardised Uptake Value ◽  
Positron Emission

Abstract18F-sodium fluoride (18F-NaF) is a positron emission tomography (PET) radiotracer widely used in skeletal imaging and has also been proposed as a biomarker of active calcification in atherosclerosis. Like most PET radiotracers, 18F-NaF is typically administered intravenously. However in small animal research intravenous administrations can be challenging, because partial paravenous injection is common due to the small calibre of the superficial tail veins and repeat administrations via tail veins can lead to tissue injury therefore limiting the total number of longitudinal scanning points. In this paper, the feasibility of using intra-peritoneal route of injection of 8F-NaF to study calcification in mice was studied by looking at the kinetic and uptake profiles of normal soft tissues and bones versus intra-vascular injections. Dynamic PET was performed for 60 min on nineteen isoflurane-anesthetized male Swiss mice after femoral artery (n = 7), femoral vein (n = 6) or intraperitoneal (n = 6) injection of 8F-NaF. PET data were reconstructed and the standardised uptake value (SUV) and standardised uptake value ratio (SUVr) were estimated from the last three frames between 45- and 60-min and 8F-NaF uptake constant (Ki) was derived by Patlak graphical analysis. In soft tissue, the 18F-NaF perfusion phase changes depending on the type on injection route, whereas the uptake phase is similar regardless of the administration route. In bone tissue SUV, SUVr and Ki measures were not significantly different between the three administration routes. Comparison between PET and CT measures showed that bones that had the highest CT density displayed the lowest PET activity and conversely, bones where CT units were low had high 8F-NaF uptake. Intraperitoneal injection is a valid and practical alternative to the intra-vascular injections in small-animal 18F-NaF PET imaging providing equivalent pharmacokinetic data. CT outcome measures report on sites of stablished calcification whereas PET measures sites of higher complexity and active calcification.

Analysis of Eddy-Current Measurement System for Residual Stress Assessment in Stainless Steel Grade 304

2015 ◽  
Vol 659 ◽  
pp. 623-627 ◽  
Author(s):  
Cherdpong Jomdecha ◽  
Isaratat Phung-On
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Eddy Current ◽  
Measurement System ◽  
System Analysis ◽  
Stress Measurement ◽  
Steel Grade ◽  
Current Measurement ◽  
Residual Stress Measurement ◽  
Stress Assessment

The objective of this paper is an analysis of statistical discreteness and measurement capability of an eddy-current measurement system for residual stress assessment in stainless steel Grade 304 (SS304). Cylindrical specimens with 50 mm in diameter and 12 mm thickness were prepared to generate residual stress by Resistance Spot Welding at which the welding currents were set at 12, 14, and 16 kA. The eddy-current measurement system was including a probe with frequency range of 0.1 to 3 MHz and an eddy current flaw detector. They were performed by contacting the probe on the specimen. The measurements were performed particularly in the vicinity of heat affected zone (HAZ). In order to determine the results of the residual stress measurement, the calibration curves between static tensile stress and eddy current impedance at various frequencies were accomplished. The Measurement System Analysis (MSA) was utilized to evaluate the changed eddy-current probe impedance from residual stress. The results showed that using eddy current technique at 1 MHz for residual stress measurement was the most efficient. It can be achieved the Gauge Repeatability & Reproducibility %GR&R at 16.61479 and Number of Distinct Categories (NDC) at 8. As applied on actual butt welded joint, it could yield the uncertainty of ± 58 MPa at 95 % (UISO).

Analysis and Experiments of Eddy Current Brakes with Moving Magnets

2008 ◽  
Vol 575-578 ◽  
pp. 1299-1304 ◽  
Author(s):  
Jaw Kuen Shiau ◽  
Der Ming Ma ◽  
Min Jou
Keyword(s):  
Drag Force ◽  
Relative Motion ◽  
Eddy Current ◽  
Eddy Currents ◽  
Test System ◽  
Image Method ◽  
Electromagnetic Interactions ◽  
Finite Dimensional ◽  
Conducting Plate ◽  
Lorentz Force Law

This paper discusses the magnetic drag force resulting from the relative motion of a permanent magnet moving along a finite dimensional conducting plate. The image method with imaginary eddy currents is investigated. Boundary conditions are established to ensure that the eddy currents vanished at the boundaries of the conducting plate. Magnetic drag force is computed based on the eddy current distributions using Lorentz force law. A test system is built to demonstrate the magnetic brakes arose from the electromagnetic interactions.

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