Transducer
A transducer is a device that converts one form of energy into another, such as electrical signals into motion or sound. Ultrasonic transducers vibrate at frequencies above human hearing, often 20 to 40 kilohertz or higher. Many work in both directions and can also turn vibration back into an electrical signal.
Example: An ultrasonic jewelry cleaner uses transducers glued to the bottom of its tank to shake the water tens of thousands of times a second.