Measurement of multilayered conductive discs using eddy current method

This paper presents an analytical solution that was derived for eddy current testing of multilayer discs. The final formulas, obtained by using the truncated region eigenfunction expansion (TREE) method, have been presented in a closed form, therefore they can be implemented in any programming language or computer algebra system. The developed solution makes it possible to model discs of any thickness and diameter, and its form is independent of the parameters of the employed sensor. The calculation results obtained for three-layer discs made of brass, copper and bronze were verified by experiments. The measurements of the impedance components were carried out for air-core, I-core and pot-core type E sensors. A very good agreement was achieved within the whole analysed frequency range from 1 kHz to 50 kHz. The difference between the results of the calculations and measurements for both the resistance and reactance of each of the sensors was less than 3 %.