Ultrasonic pulse-echo testing exploits the converse and direct piezoelectric effects in ferroelectric lead zirconate titanate (PZT) ceramic elements. An electrical excitation spike excites high-frequency mechanical thickness vibrations, sending an ultrasonic acoustic pulse through the test specimen. Internal material boundaries or structural crack defects reflect acoustic echoes back to the transducer, where acoustic pressures are reconverted into voltage signals for time-of-flight flaw sizing.