Exposure to radio frequency (RF) fields from mobile phones is measured using the specific absorption rate (SAR) – the amount of energy from an RF field absorbed by the human body. SAR values are given in watts per kilogram (W/kg).
The International Commission for Non-Ionizing Radiation Protection (ICNIRP) guidelines set a maximum SAR value of 2W/kg for a mobile.
SAR is the accepted international measure of exposure to electromagnetic fields. The SAR value for a particular mobile phone is provided when the handset is bought. Many manufacturers also make this information available on the Mobile Manufacturers Forum website.
However, the values provided are based on the maximum possible exposure from a mobile phone. The actual exposure when using a mobile phone is much harder to measure. Mobile phones always use the minimum amount of energy to provide a service, and this depends on a range of factors:
The distance between the person and the mobile phone
RF fields are much weaker even a short distance from a mobile phone. Keeping the mobile phone away from the body by using an earpiece or loudspeaker function will significantly reduce exposure.
The distance from the base station
The signal from a base station becomes weaker the further away the mobile phone is, meaning the RF field strength from the mobile phone must increase so it can still communicate with the base station.
The landscape between the user and the base station
If there is a building, hill or other obstruction between the mobile phone and the base station, the signal from the base station may also be weaker.
The service being used
Making a call from a mobile phone leads to greater exposure to RF fields than texts, emails, pictures, web, TV and downloads. This is because calls are generally made with the mobile phone next to the head, while it is held away from the body when sending texts and emails and watching TV. Calls also take longer than sending texts and emails, again increasing exposure.
All these factors affect the RF field strength from the mobile phone, and consequently the person’s exposure. This means that buying a mobile phone with a lower maximum SAR value does not guarantee reduced exposure.
We are working with the International Electrotechnical Commission (IEC), a standard-setting organisation, to develop and gain agreement for a new global protocol for testing mobile phones and other wireless devices worn close to the body.