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METHOD FOR DETERMINING ELECTRICAL CONDUCTIVITIES IN SAMPLES BY MEANS OF AN EDDY CURRENT SENSOR
 DE 102013004990 A1: 20130319 

 German 
 Patent, Electronic Publication 
 Fraunhofer IKTS () 
Abstract
An eddy current sensor is used to excite an electrical alternating field with a known measurement frequency f, [omega] inside a sample, and an electromagnetic alternating field is thereby formed, which is detected with a detector and the complex impedance Z = R + jX is determined. This procedure is carried out at different measurement frequencies f, [omega] once in air and once with the same measurement frequencies f, [omega] on a calibration body having a known electrical conductivity [sigma]. Then the differences between real and imaginary part [Delta] [R] and [Delta][X] of the values in air and on the calibration body are divided by the respective measurement frequency f, [omega], each pair of values [Delta][R]/[omega] and [Delta][X]/[omega] = [Delta] [L] being assigned a product [omega][sigma] in accordance with the associated measurement frequency [omega] and the known conductivity [sigma] of the calibration body, and said value pairs are used to plot an [omega][sigma] locus curve in a Nyquist diagram.