Nonlinear resonant acoustic detection of cracks in multilayer ceramic capacitors

Measurements of resonant ultrasonic frequencies of multilayer ceramic capacitors (MLCCs) were performed as a function of excitation amplitude to assess the potential of nonlinear acoustic methods for sensing the presence of cracks. The ultimate objective of this work is to establish an approach for nondestructively screeningMLCCs for susceptibility to failure that arises from the evolution of structural flaws into electrical pathways during service. Direct ferroelectric tone-burst transduction and time-domain signal analysis were used to measure the frequency of an extensional mode near 1 MHz in BaTiO₃-based MLCCs with interleaved Ag electrodes. The capacitors were subjected to thermal stress by quenching from 189 °C into ice water, which led to generation of visible surface-breaking cracks in a fraction of the MLCCs. The amplitude dependence of the resonant frequencies was found to be strongly correlated with the presence of visible cracks.