Electric and electronic systems have become so pervasive that it is now difficult to imagine life without them. While they contribute to our quality of life in many ways, they also create electromagnetic fields (non-ionising radiation) which, when emitted at sufficient levels, may warm biological tissues (as they do in microwave ovens).
Electromagnetic fields have different frequencies - expressed in Hertz (Hz), or oscillations per second - suited to different uses, for example:
- strong static fields (0 Hz) are used in medical MRI scanning
- low frequencies (50 Hz) are used by the standard alternating electric current (AC) feeding our homes and offices
- high frequencies are used by mobile phones (900 MHz).
Until about 20 years ago, the main manmade sources of electromagnetic fields were radio and television broadcasting stations and high voltage power lines. The rapid development of mobile telecommunications and other electronic appliances since the 1990's has substantially increased the number of sources and types of electromagnetic fields we are exposed to. This has raised concerns about their possible adverse health effects.