In continuous-wave transducers, the emitted sound frequency is determined by the machine's electrical frequency.

• A. True
• B. False
• C. It is determined by crystal thickness
• D. It is determined by tissue properties

Answer: (A)

In continuous-wave ultrasound, the tone of the sound is set by the oscillator that drives the transducer. The piezoelectric crystal responds to the applied electrical signal by vibrating at the same frequency as that signal, so the emitted sound frequency equals the electrical drive frequency. The crystal’s thickness matters for how efficiently the transducer converts energy and for its resonant properties, but it does not set the emitted frequency in this mode—the drive frequency does. Tissue properties affect how the wave propagates (speed and attenuation), not the frequency produced at the transducer.