Electro ultrasonic spectroscopy of cermet thick films

The electro-ultrasonic spectroscopy is non-destructive testing method for cermet resistors. This method can be used as a diagnostic tool for the quality and reliability assessment. AC current varying with frequency f_E and the ultrasonic signal varying with frequency f_U are applied on the conducting sample and a new intermodulation signal on the frequency f_m given by the superposition or subtraction of exciting frequencies is measured on the sample. The sample resistance is influenced by the ultrasonic signal. The ultrasonic signal changes the contact area between the conducting grains in the sample structure and then resistance is modulated by the frequency of ultrasonic excitation. The electrical charge and also the electrical current flowing through the sample structure are conserved. In case the contact area between the conducting grains is changing then the current density is changed. This leads to the resistivity change of measured structure. We suppose that for the sample with more defects in the structure the influence of the ultrasonic signal is more pronounced and the resistance change is higher.