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.

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.

Single-peak-regulation and wide-angle dual-band metamaterial absorber based on hollow-cross and solid-cross resonators

2020 ◽  
Vol 91 (3) ◽  
pp. 30901
Author(s):  
Yibo Tang ◽  
Longhui He ◽  
Jianming Xu ◽  
Hailang He ◽  
Yuhan Li ◽  
...  
Keyword(s):  
Transverse Electric ◽  
Surface Current ◽  
Dielectric Substrate ◽  
Transverse Magnetic ◽  
Metamaterial Absorber ◽  
Absorption Peak ◽  
Dual Band ◽  
Single Peak ◽  
Wide Angle ◽  
Surface Current Density

A dual-band microwave metamaterial absorber with single-peak regulation and wide-angle absorption has been proposed and illustrated. The designed metamaterial absorber is consisted of hollow-cross resonators, solid-cross resonators, dielectric substrate and metallic background plane. Strong absorption peak coefficients of 99.92% and 99.55% are achieved at 8.42 and 11.31 GHz, respectively, which is basically consistent with the experimental results. Surface current density and changing material properties are employed to illustrate the absorptive mechanism. More importantly, the proposed dual-band metamaterial absorber has the adjustable property of single absorption peak and could operate well at wide incidence angles for both transverse electric (TE) and transverse magnetic (TM) waves. Research results could provide and enrich instructive guidances for realizing a single-peak-regulation and wide-angle dual-band metamaterial absorber.

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.

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.

Geometric Effects on Eddy Current Bearing Performance

1989 ◽  
Vol 111 (2) ◽  
pp. 209-214 ◽  
Author(s):  
J. A. Tichy ◽  
K. A. Connor
Keyword(s):  
Eddy Current ◽  
Eddy Currents ◽  
Load Capacity ◽  
Complex Mixture ◽  
Journal Bearings ◽  
Magnetic Bearings ◽  
Repulsive Forces ◽  
The Magnetic Field ◽  
Geometric Effects ◽  
Current Journal

The properties of magnetic bearings, particularly those based on repulsive forces due to eddy currents, are determined by a complex mixture of electrical and mechanical length and time scales. A perturbation solution for the magnetic field structure based on careful ordering of these parameters has permitted the effects of realistic gap geometries to be analyzed. The load capacity of eddy current journal bearings is found to be somewhat larger than previously predicted in an earlier paper which used magnetic fields based on constant gap size. The present results may be of interest to those concerned with calculating eddy currents in conventional attractive magnetic bearings.

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