Electromagnetic fields (EMF) are part and parcel of man’s environment. The most well-known naturally-occurring fields are those generated by the earth and sun. Manmade fields are, among others, the radio frequency fields of mobile telephones and the low-frequency fields generated by the use of mains power. When a television, hair drier, or other domestic household appliance is plugged in, there is an electric field in and around the appliance. When the appliance is switched on and powered up, also a magnetic field is generated around the appliance. The strength of both the electric and magnetic fields diminishes rapidly further away from the surface of the appliance. The electric field is generated from the differences in voltage and its strength is measured in volts per metre (V/m). A higher voltage causes a stronger electric field. Electric fields are at their strongest in the close vicinity of high voltage power distribution systems and high-powered industrial equipment. The electric fields generated by domestic house-hold appliances are insignificantly small. Appliances and cables which carry electric current produce magnetic fields. The strength of a magnetic field is described as the density of a magnetic flux which is measured in teslas (T). Magnetic field sources are generally more significant to health than electric field sources. A television picture or computer monitor can be disturbed by magnetic fields. The cause of a field can be a nearby indoor transformer substation or a main distribution board. A radio frequency (RF) electromagnetic wave can transfer data over long distances. RF fields are generated by, among others, mobile (tele)phones and base stations, television and radio transmitters, and radar systems. The strength of radio frequency fields is presented as a power density which is measured in watts per square meter (W/m2). When an RF source - such as a mobile phone - is near the body, a SAR value is used instead. The unit of SAR is watts per kilogram (W/kg). See Mobile phones and base stations
Page updated 29/10/2009 |
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