What happens to piezoelectric coefficients and resonance when aging or depoling occurs in PZT transducers?

• A. Increase piezoelectric coefficients and widen bandwidth.
• B. Decrease piezoelectric coefficients but strengthen resonance at the same frequency.
• C. Decrease piezoelectric coefficients, shift resonance, and reduce bandwidth.
• D. No change in properties.

Answer: (C)

The main idea is that piezoelectric coefficients determine how efficiently a PZT transducer converts electrical energy into mechanical motion and back. When aging or depoling occurs, the material’s dipoles become less well aligned and domain walls become less responsive, so the piezoelectric coefficients (like d33, d31) decrease. With weaker coupling, the transducer transfers energy less effectively, which dulls the resonance, tends to shift its frequency, and reduces the bandwidth over which the device responds efficiently. In other words, lower piezoelectric coefficients lead to a shifted resonance and a narrower bandwidth, reflecting degraded electromechanical performance. The other options describe improvements or no change, which doesn't match what happens with aging or depoling.