Technical focus: what is SAR and to measure it?

The ANFR has published this week the results of a SAR measurement report carried out on 95 mobile phones in 2020. But what is exactly the SAR? To answer this question, the AFNUM "Waves and Health" working group members share their expertise on the subject.

What is SAR?

The SAR (Specific Absorption Rate) measurement quantifies the amount of energy carried by electromagnetic waves absorbed by the human body when using a radio equipment, such as a mobile phone, a smartwatch… . This measurement is expressed in watts per kilogram.

Since the 1990s, radio equipment used near the human body must comply with maximum SAR values, defined in French and European regulations.

 ANFR SAR banner (FR)

SAR normative limits

SAR is taken into account in three different places in the human body:

- “Head SAR”, measured at the head, measures the SAR when using a device near the head, such as a phone during a talk.

 - The "trunk SAR", “corresponding to the waves absorbed by the trunk when the device is in a jacket pocket, a backpack, etc.

 - Finally, the "limb SAR", measured when the device is located near a limb, in an armband or in a trouser pocket.

The maximum SAR level authorised in France is 2W/kg for the head and trunk, and 4W / kg for the limb.

History

Since the 1830s, when electromagnetic fields were discovered, many innovations using radio broadcasts have appeared such as microwaves and television broadcasting.

It is from the middle of the 20^th century that their impact on health started to be monitored. Thus, from the 1950s, standards emerged to study and limit the effects of some of these waves on nature and human beings. The standards gradually arose, first imposed on the head, then on the body.

In France, the National Frequencies Agency (ANFR) was created in 1997 to manage in particular the good use of the waves and to control independent radio networks. The Agency also monitors compliance with SAR limits on radio equipment such as mobile phones.

How to measure the SAR?

Current methods consist in evaluating the maximum quantity of electromagnetic waves absorbed in an anthropomorphic model of the human body and head. The mobile phone has to transmits at its maximum power in all the radio configurations of the transmission protocols (3G, 4G, 5G). These traditional SAR systems are all made up of mannequins in the shape of a human head and trunk. They are filled with biological fluids which mimic the behavior of the body and the head in terms of wave propagation.

Performing tests on those systems take between 20 to 90 minutes for each measurement, bringing the entire certification process for a single device to around 5 weeks. Verification and calibration of measurements is an incompressible part of measurement time with these techniques. This current practice corresponds to the measurement technologies authorized by the international standards of 2005 (IEC 62209-1) and 2010 (IEC 62209-2).

Video: traditional way of measuring SAR in a test laboratory

Who controls the SAR?

The ANFR is responsible for carrying out SAR measurements controls on phones launched on the French market. The ANFR ensures that wireless devices are compliant with the French regulations. Each year, the ANFR publishes the results of its measurements in open data. Devices displaying results over the limits are ordered to make corrections under penalty of a market withdrawn. 

The 5G impacts

With the 5G arrival and new smartphones compatible with this latest mobile network generation, SAR measurement issues are crucial and the need for a rapid, precise and efficient measurement technology is becoming central. Indeed, the new 5G functions in terms of wave management make the tests more complex. Also, manufacturers are looking for solutions that allow reliable and rapid results, while remaining economically sustainable.

More precisely, this new generation of mobile networks allows for the first time a mobile phone to transmit on several frequencies at the same time: one speaks about multi-frequency emission, compared to the single-frequency emissions of the older generations (2G, 3G, 4G).

The test methods have therefore evolved to take into account the measurements compatible with a multi-frequency emission, as it is the case with the 2019 IEC 62209-3 standard. This makes it possible to have SAR measurements more consistent with use of 5G mobile phones.

Discover the new SAR measurement method