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
Cellular frequencies in the US Cellular frequencies in the US The usage of frequencies within the United States is regulated by the Federal Communications Commission (FCC). When distributing initial spectrum licenses in a band the FCC divides the US geographically into a number of areas. A mobile operator (or other interested party) must bid on each area individually. A license owner can use any technology within the licensed area and frequency range subject only to the band rules defining various analog limits. A license owner can also partition the license (split geographically) or disaggregate it (split the whole licensed frequency range into two sub-ranges). Whole,