Proximity sensing for mobile phones SAR requirements
Research in to the long term health effects from exposure to radio frequency energy has been ongoing over the past two decades. As a result of this research the FCC and other telecommunications agencies have adopted limits for safe exposure to radio frequency (RF) energy. These limits are referred to as the Specific Absorption Rate (SAR), which is the measure of the amount of radio frequency energy absorbed by the body when using a mobile phone or other wireless device. The FCC and other agencies require that manufacturers of wireless devices comply with these limits for safe exposure.
Proximity sensing for SAR
In order to meet SAR limits many designers implement circuitry to reduce the power output of a device’s radio frequency circuits when the device is in close proximity or in contact with the user. This application note from ATMEL describes a capacitive proximity circuit which can be used to detect when a device is in contact or close proximity with the user.