how ultrasound waves are produced
These jiggle about at ultrasonic frequencies, sending their vibrations to a thin, quartz glass plate (3), which transmits waves (4) into a basin filled with fluid (5) into which you place the objects to be cleaned. Ultrasound waves can be produced using magnetism instead of electricity. Just as piezoelectric crystals produce ultrasound waves in response to electricity, so there are other crystals that make ultrasound in response to magnetism.