How are ultrasound waves produced in the transducer?

How are ultrasound waves produced in the transducer?

• A. The crystal heats up
• B. Alternating current causes the crystal to compress and expand
• C. The crystal is struck by a hammer
• D. The crystal is irradiated with light

Answer: (B)

The main idea is the inverse piezoelectric effect: when an alternating electrical signal is applied to a piezoelectric crystal, it repeatedly contracts and expands. This rapid mechanical motion at ultrasonic frequencies turns into acoustic waves that propagate into the body. The drive frequency fixes the ultrasound frequency, allowing control over image resolution and depth. Heating the crystal wouldn’t generate a controlled, directional ultrasound wave. Striking with a hammer would produce a rough, broadband impulse rather than a steady ultrasonic signal. Irradiating with light isn’t how standard transducers generate ultrasound, since medical probes rely on the electric-driven vibration of the crystal.

The main idea is the inverse piezoelectric effect: when an alternating electrical signal is applied to a piezoelectric crystal, it repeatedly contracts and expands. This rapid mechanical motion at ultrasonic frequencies turns into acoustic waves that propagate into the body. The drive frequency fixes the ultrasound frequency, allowing control over image resolution and depth.

Heating the crystal wouldn’t generate a controlled, directional ultrasound wave. Striking with a hammer would produce a rough, broadband impulse rather than a steady ultrasonic signal. Irradiating with light isn’t how standard transducers generate ultrasound, since medical probes rely on the electric-driven vibration of the crystal.