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Electromagnetic Testing

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Analytical Approach (Pc & f g )<br />

Analytical approaches for probe design involve analyzing the eddy current<br />

testing phenomenon and calculating the coil impedance and examining the<br />

operating point on the impedance plane as well as the effect of variations in<br />

coil radius r, shape, material conductivity, thickness t and test frequency f.<br />

Two popular impedance plane diagram based methods are<br />

1) calculation of characteristic parameter, Pc introduced by Deeds and Doods for<br />

planar geometries and<br />

2) calculation of characteristic frequency ratio f/f g<br />

, where fg is the characteristic<br />

frequency introduced by Förster for tubular geometries.<br />

(f g<br />

= 5066/ (μ r<br />

∙ σ∙ d 2 )<br />

Using these two methods, coils are designed such that the operating point is<br />

in the “knee” region on the normalized impedance plane diagrams.<br />

Charlie Chong/ Fion Zhang<br />

http://www.geocities.ws/raobpc/Probes.html

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