Mobile communications devices include handsets, wireless data cards for laptop computers and other specialised low powered radio transmitters. Handset powers are continuously adjusted to operate at the lowest level possible by taking account of the type of service (voice or data) and the quality of the radio link between the handset and nearby antenna sites.
Connection: When the connection is good, such as close to a base station, a mobile phone will operate on the lowest power level needed for call quality.
Signal: When distance increases between a base station and a mobile phone it must increase transmit power to maintain signal quality. This reduces battery life.
Handover: The process of transferring a call is termed handover and as the mobile phone moves closer to another base station the required power level will be reduced.
Press the labels to see this process in action.
On the left of the mobile phone display is the battery level and on the right the received signal strength. Note the change in the transmitted signal power represented by the circular arcs and the effect on the battery level.
Wireless devices are designed to comply with international safety guidelines.The measure of human exposure is the Specific Absorption Rate (SAR) with units of Watts per kilogram (W/kg). The SAR is determined at the highest certified power level in laboratory conditions, however, the actual SAR level of the phone while operating can be well below this value.
The WHO states that:
‘A large number of studies have been performed over the last two decades to assess whether mobile phones pose a potential health risk. To date, no adverse health effects have been established for mobile phone use.’
A 2005 report for AFSSE (France) reported on exposure measurements of 186 mobile phones with and without a personal handsfree kit. They concluded that substantial reductions of about 10 were typical. This means that exposure to the head is reduced by 90% when using a hands-free kit due to the increased separation.
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