What does the piezoelectric crystal do?

• A. Converts electrical energy into magnetic fields.
• B. Filters electrical signals.
• C. Transforms energy from electricity into sound waves and heat.
• D. Stores energy for later release as heat.

Answer: (C)

The piezoelectric crystal acts as the actuator that turns electrical energy into mechanical energy, producing ultrasound waves. When a high-frequency electrical signal is applied, the crystal rapidly expands and contracts, generating ultrasonic vibrations that propagate into the tissue. As these sound waves travel, some of their energy is absorbed by the tissue and converted into heat, contributing to the therapeutic heating effect. This is the primary role of the crystal in ultrasound therapy—to generate the sound waves—and the heating comes from how the tissue interacts with those waves. It’s not used to create magnetic fields, act as a filter, or store energy.