An electromagnetic decoupling method in eddy current testing

Eddy current testing is an efficient nondestructive testing tool, which has been applied in pipeline transportation, aerospace, chemical industry, and so on. In fact, the response signal of eddy current testing contains both conductivity and permeability information of samples. Therefore, it is difficult to accurately measure the conductivity and permeability due to the electromagnetic coupling. In this paper, the analytical solution is established for multi-layer metal plate, and the permeability invariance phenomenon(PIP) has been found. Moreover, the numerical solution, i.e. finite element method, is also applied to verify the PIP. According to the PIP, the electromagnetic parameters decoupling (conductivity and permeability) can be realized. Based on the characteristic of PIP, the conductivity measurement method is investigated, which is not affect by permeability. Related experiments are also carried out to estimate the conductivity. The results show the error is only 5.1%, and the maximum error is 8.8%.