When the speed of sound in PZT is faster, the frequency of sound created by a pulsed wave transducer is ______.

• A. Lower
• B. Unchanged
• C. Higher
• D. Decreasing

Answer: (C)

In a pulsed-wave ultrasound transducer, the emitted frequency is set by the transducer’s resonance, which for a piezoelectric element in thickness mode depends on the speed of sound in the material and the element’s thickness. The relationship is that the resonance frequency increases as the speed of sound increases, for a fixed thickness. So if the speed of sound in PZT becomes faster while the thickness stays the same, the transducer’s center frequency goes up, producing higher-frequency sound. The other options would imply a slower or unchanged frequency, which isn’t consistent with the direct link between material speed and resonance frequency.