Ultrasonic cleaners are sometimes mistakenly called supersonic cleaners. They are used at frequencies from 20-40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments and industrial parts. An ultrasonic cleaner works by the energy released from the collapse of millions of tiny (microscopic) bubbles near the dirty surface. The bubbles are formed by cavitation and collapse, forming small jets directed at the surface.