FREQUENCY-DEPENDENCE OF MAGNETIC-PERMEABILITY IN INSPECTION WITH SUPERPOSED TRANSDUCERS

The article compares experimental hodographs with hodographs calculate d by known formulas for a superposed transducer situated above a magne tic half-space. It is shown that when the parameter of the hodograph i s varied by changing the frequency of the current supplied to the tran sducer, matching of the calculated and the experimentally recorded hod ographs can be attained on condition that the remagnetized investigate d material is characterized by the actual frequency-dependent complex magnetic permeability. In other words, it is necessary to take into ac count the magnetic hysteresis that determines the complex nature of ma gnetic permeability, and also the magnetic viscosity that determines t he frequency dependence of the components of the complex. For a number of materials, of which the test specimens were made, these components were calculated in dependence on the frequency of the current supplie d to the transducer, and the corresponding graphs were plotted.