How is SAR measured?
The determination of the SAR requires the use of a measurement sensor, which makes it impossible to carry out compliance checks on living beings. A dummy is used to simulate the human body. This dummy is head-shaped for the head SAR assessment and is flat for the trunk SAR. It is filled with a homogeneous liquid to simulate human tissue, in particular for heating.
The determination of the SAR requires the use of a measurement sensor, which makes it impossible to carry out compliance checks on living beings. A dummy is used to simulate the human body. This dummy is head-shaped for the head SAR assessment and is flat for the trunk SAR. It is filled with a homogeneous liquid to simulate human tissue, in particular for heating
To uphold trust in the measurement, the measuring system using the dummy is tested before each test using emissions created by laboratory antennas and generators that are subject to metrology monitoring. Laboratory practices are regularly audited by an external body (COFRAC in France), to guarantee high quality levels.
Relative to the dummy, the phone is placed in the positions defined by the standards, in particular at maximum mean power.
The sensors assess the head and trunk exposure by measuring the electric field and seeking the average maximum field for 10 grammes in the dummy volume.
This search phase requires finding the maximum in the entire dummy volume considered for all phone orientations, all technology and operating modes and all frequencies when the phone is emitting at full power. If the phone can operate using several simultaneous emissions, these cases are taken into account when seeking the maximum value. Assessments by excess are authorised by totalling contributions, supposing that the maximum is in the same location.
As part of non-compliance checking, usually the tests are not exhaustive and can be set up to quickly identify the configuration that generates maximum exposure.
SAR is estimated using a mobile phone emitting:
- at its maximum mean power;
- for 100 % of the time;
- for a total duration of 6 minutes.
The laboratory-measured SAR values are therefore not an indication of the most frequent use of the phone:
- for voice communications, statistically, the phone only emits for about half the time as it does not emit when the person is listening; furthermore, the average call time is less than 6 minutes;
- for data-oriented use (internet or video), use times are longer, but the phone rarely emits for more than 10 % of the time;
- finally, for all uses, the phone rarely emits at its maximum power. The SAR measurement configuration (maximum power) is only encountered in very special conditions in real life, in particular when the phone is at the limit of coverage (a single bar on the reception icon).