Ultrasound 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). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
Medium frequency A major use of these frequencies is AM broadcasting; AM radio stations are allocated frequencies in the medium wave broadcast band from 526.5 kHz to 1606.5 kHz in Europe; in North America this extends from 525 kHz to 1705 kHz Some countries also allow broadcasting in the 120-meter band from 2300 to 2495 kHz; these frequencies are mostly used in tropical areas. Although these are medium frequencies, 120 meters is generally treated as one of the shortwave bands. There are a number of coast guard and other ship-to-shore frequencies in use between 1600 and 2850 kHz. These include, as examples,