Time-domain analysis of resonant acoustic nonlinearity arising from cracks in multilayer ceramic capacitors

Acoustic nonlinearity of cracked and uncracked multilayer ceramic capacitors (MLCCs) was characterized through time-domain analysis of resonant waveforms following tone-burst excitation. A phase-sensitive receiver was employed to measure the phase, relative to a reference sinusoid, of decaying oscillations of a resonant mode near 1 MHz that was excited through ferroelectric coupling within the barium-titanate-based ceramic of the MLCC. Amplitude dependence of the resonant frequency during decay of the oscillations was characterized through measurements of changes in the resonant phase versus time. Waveforms were analyzed by fitting the recorded RF amplitude versus time to a decaying exponential and inserting the parameters of this fit into a second function to fit the time-dependent phase, with amplitude dependence of the resonant frequency incorporated in the second function. The measurements and analyses were performed on unmounted type-1210 MLCCs before and after quenching in ice water from elevated temperatures. This thermal treatment generated surface-breaking cracks in a fraction of the specimens. Measurements of a nonlinear parameter B of the capacitors before quenching were used to set a range corresponding to plus and minus three standard deviations (±3σ) relative to the mean of a Gaussian fit to the distribution of this parameter. 93 % of the values of B determined for heat-treated MLCCs with cracks were outside of this ±3σ range of the as-received MLCCs, while only 10 % of the values of B for heat-treated MLCCs without visible cracks were outside this range. These results indicate that time-domain nonlinear measurements with tone-burst excitation are a promising approach for rapid nondestructive detection of cracks that have no significant initial effect on the electrical characteristics of an MLCC but can evolve into conductive pathways during service and lead to electrical-device failure. They also illustrate the potential of this approach for nonlinear acoustic detection of structural flaws in other materials.