SAR stands for Specific Absorption Rate : which is the unit
of measurement for the amount of RF energy absorbed by the body when using a
mobile phone. 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. This is because the
phone is designed to use the minimum power required to reach the network.
Therefore, the closer you are to a base station, the more likely it is that the
actual SAR level will be lower. To communicate with the network, mobile phones emit low
levels of radio waves (also known as radio frequency or 'RF' energy) when being
used. Governments around the world have adopted comprehensive international
safety guidelines, developed by independent scientific organizations, governing
the exposure to RF energy. Mobile phones are designed to operate within these
stringent limits.
How is SAR measured for mobile phones?
Specialized laboratory test equipment is used for conducting SAR measurements. The equipment consists of a ‘phantom’ (human or box), precision robot, RF field sensors, and mobile phone holder. The phantom is filled with a liquid that represents the electrical properties of human tissue
Head
Measurements - SAR test inside a head phantom:
- The mobile phone is positioned against the phantom head and switched on to full power.
- The precision robot moves the RF probe throughout the phantom head measuring the radio signal level in the head phantom.
- The computer analyzing the data converts the radio signal levels into SAR (W/kg).
- The full test is conducted at all operating frequencies and using different phone positions.
- The maximum level measured is recorded as the SAR value against the head.
Body
Measurements - SAR test inside a body (box) phantom:
- The mobile phone is positioned against the phantom body and switched on to full power.
- The precision robot moves the RF probe throughout the phantom body measuring the radio signal level in the body near the phone.
- The computer analyzing the data converts the radio signal levels into SAR (W/kg).
- The maximum level measured is recorded as the SAR value against the body.
Is there a separation distance from the body required for mobile phones?
Mobile phones generally get better reception when used away from the main part of the body. Some mobile phones are designed to have a small minimum separation from the body when in use, typically 15 – 25mm depending on the phone. The minimum separation often represents the spacing created by a phone holder or clothing. This is to ensure the phone operates more efficiently and also meets the SAR requirements.
If a minimum separation is specified, the SAR test against the body will be conducted at that distance.
A mobile phone can always be used up against the head without separation. This is because the antenna in the phone is designed to be far enough away from the head to meet SAR requirements and operate most efficiently.
Do the SAR limits apply to children?
Yes. The EMF exposure guidelines are designed to offer protection for all persons including children with a large built-in safety margin.
How is SAR measured for base station antennas?
EMF exposure guidelines for radio communications transmitting antennas (like base stations) specify the maximum level of radio frequency energy (SAR) that can be safely absorbed by the whole body. This is because exposure from a radio communications transmitting antenna is typically over the whole body, for example a technician working on a rooftop near base station antennas.
SAR due to exposure to small base station antennas can also be tested using a similar procedure to the SAR test for wireless devices. The base station antenna is placed up against a human phantom and the precision robot scans the entire body and measures the absorbed radio signals. The computer analyzing the data converts the radio signal levels into SAR (W/kg).
The SAR test procedures are specified in international standards.
