On complex permeability in eddy-current flaw detection

This paper critically considers attempts to prove the frequency dependences of the electrical conductivity and magnetic permeability of metals at frequencies lower than 1 MHz. Such attempts were made by certain authors when studying the operation of eddy-current transducers. It is shown that the complex character of the output voltage of an eddy-current transducer is determined by the vector summation of the magnetic fluxes of the primary magnetizing alternating field and the field of eddy currents, which are induced by the primary field, in a tested article. The frequency dependence of the results of this summation is quite sufficient for a physically correct description of the operation of an eddy-current transducer without involving a hypothesis on the frequency dependence of the physical constants of the material of the tested article.