32) Do spikes between Fr and Fa indicate a cracked piezoceramic?

FAQ: All five piezoceramics samples we tested show the same spike noise waveform near 50 kHz, between Fr and Fa. Are these ceramics defective?

TRZ Analyzer curve example of a piezoelectric ceramic suspected of internal crack.

TRZ® Analyzer curve example of a piezoelectric ceramic suspected of internal crack.

In our experience, spikes between Fr and Fa do not necessarily indicate a crack. We have found this result; however, we were not able to confirm an internal crack by other means (nondestructive ultrasonic testing by pulso-eco). This disturbance may be related to material properties gradients inside the element or with dimensional issues. Another possible cause may be poor contact between the PiezoHolder's plunger and the piezoceramic. The piezo element resonates in this frequency range (between Fr-Fa) and it may disengage from the plunger (we cannot simply increase the product plunger force because it has the side effect of scratching the element electrode causing other issues). To test if the spike noise is related to poor contact, the user may gently polish the piezo electrodes over ordinary paper and/or slightly increase the plunger force pressing the plunger manually during the test. If the spikes shape shift or is unstable, then it is caused by poor contact. If the spikes are still there and are reproducible, the issue is within the piezo element.

If you confirm the spikes are related to the piezo element, I would recommend testing other brands and alternatives, unless it is not a critical application. For sensors, this defect should not be a problem, for high power, it may cause premature failures.

Learn more about internal cracks the detection in piezoelectric ceramics.