EM fields are created whenever an electric current flows. In nature, they are created by lightning and also occur in the human nervous system. Light from the sun is a form of EM field. They are also created whenever an electrical appliance is connected to the mains supply, including many in daily use such as refrigerators, hairdryers and computers.
Many electrical appliances don’t just create EM fields – they rely on them to work. Television, radio, cordless phones, remote control handsets, baby monitors and the communication systems used by emergency services all communicate using EM fields. So do wireless technologies such as Wi-Fi, which is commonly used by computer and mobile networks, to connect to the internet and to connect different electronic items.
There are many forms of EM fields operating at different wavelengths – the distance between one EM wave and the next. The closer together the waves, the higher the frequency will be.
All types of EM field fall into two categories – ionising or non-ionising. Ionising fields are extremely high-frequency EM waves that carry so much energy they can cause molecules to change. Examples include the x-rays used for medical diagnosis and radiotherapy treatment. Non-ionising fields are lower-frequency EM waves, such as visible light and the RF fields used by mobile devices and base stations, which do not have enough energy to cause molecules to change.