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 . Ultrasonic cleaners , sometimes mistakenly called supersonic cleaners , are used at frequencies from 20 to 40 kHz for jewellery , lenses and other optical parts , watches , dental instruments , surgical instruments , diving regulators and industrial parts .