<P> A formerly popular consumer application of ultrasound was in television remote controls for adjusting volume and changing channels . Introduced by Zenith in the late 1950s, the system used a hand - held remote control containing short rod resonators struck by small hammers, and a microphone on the set . Filters and detectors discriminated between the various operations . The principal advantages were that no battery was needed in the hand - held control box, and unlike radio waves, the ultrasound was unlikely to affect neighboring sets . Ultrasound remained in use until displaced by infrared systems starting in the late 1980s . </P> <P> Occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss . Exposure in excess of 155 dB may produce heating effects that are harmful to the human body, and it has been calculated that exposures above 180 dB may lead to death . The UK's independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). </P>

When were sound waves first introduced in medicine