Resonant ultrasonic spectroscopy in high-voltage varistor diagnostics

Resonant spectroscopy is an effective nondestructive testing method focused on defects in tested objects. The testing procedure, based on the resonant pattern, allows rejection of the tested samples with defects which do not fit the pattern. A sweeping frequency method has been used to measure the spectrum of resonances in high-voltage varistors. As a result we can observe resonances that depend directly on inhomogeneity of the object. A few hundreds of high-voltage varistors have been measured using resonant ultrasonic spectroscopy. The shift to a lower frequency caused by the defected material has been observed and this can be the basis for rejecting the defective parts during manufacturing process. The parameter Q relating to the homogeneity of the varistor structure has been proposed as a criterion for the ldquogo- no gordquo testing.