Precise eddy current impedance measurement of metal plates
ABSTRACT: Properties of conductive materials can be characterized and validated by electrical conductivity. Multi-frequency AC measurements (compared with only DC or singlefrequency AC measurements) improve significantly the coverage of validation and give more information about the material properties under investigation. Eddy current measurements, have many benefits, as being nondestructive and faster, compared with 4-contact measurements. Furthermore, for eddy current case results are not directly depending on the exact size of the specimen. Challenge for eddy current measurements is carrying out of absolute measurements, without having reference pieces with known conductivity values. Combining theoretical and experimental studies and development works show, that with single planar coil measurement probe, absolute measurements can be carried out, with accuracies, much better than 10%, for non-magnetic materials with conductivities from 2.5 to 15 MS/m, in the frequency ranges up to 500 kHz. Measurement coil, setup (instrumentation) and software for conductivity measurements (and simultaneously lift-off estimation and compensation) and measurement results are given in the paper.