Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed by the human body when exposed to a radio frequency electromagnetic field (EMF) and must be evaluated during the production of smartphones.

This project will provide the methods, software tools and datasets required for traceable calibration and uncertainty analysis of vector probe array systems (array of vector probes that automatically determines the 3D electromagnetic field mapping using amplitude and phase information through a 3D reconstruction algorithm), which are used to measure the SAR of emitting mobile telecommunication devices.

This work will contribute to the international standard IEC 62209-3 and future standardisation of fifth generation (5G) devices within IEC Technical Committee TC 106. This project will enable the full-compliance of mobile telecommunication devices against IEC 62209-3 in terms of EMF exposure limits to be tested with better reliability, and will enable testing times to be reduced, which will benefit the telecommunications industry.

The need

The development of mobile phones is ever-increasing and approximately 1.3 billion smartphones were sold worldwide in 2014. In addition, the number of telecommunication protocols that need to be tested to assess SAR during the production of such smartphones has increased over the last decade.

Therefore the methods included in the international standards IEEE 1528, IEC 62209-1 and IEC 62209-2 now require excessively long testing times to assess compliance with SAR restrictions. For example, a modern smartphone with more than 30 transmission technologies/bands embedded would require five weeks of continuous testing to demonstrate compliance with SAR limits using the diode probe and robot specified in IEEE 1528, IEC 62209-1 and IEC 62209-2.

In addition, not all foreseeable usage configurations are tested, e.g. the display of the phone is not facing towards the user and separation distances are shorter than that specified in the user manual. Furthermore, upcoming and future communications standards, such as Long Term Evolution (LTE) Releases 10 to 12, will incorporate complex multiple-input multiple-output (MIMO) antennas that cannot be efficiently assessed using the systems specified in current published standards, as they do not measure phase. Multi frequency measurement is also a challenge for traditional SAR measurement technologies as none of them have the capability to distinguish between frequency contributions to SAR.

To overcome these problems, new SAR measurement systems have been developed which use arrays of vector probes, also called time-domain sensors, i.e. sensors which measure phase and amplitude to “image” the fields in a sealed phantom, a shell representing the human body, filled with a tissue-simulating liquid. Using this approach, the time required to acquire data for the SAR measurement of a handset is reduced by a factor of at least 100 compared to that using a traditional single probe scanning system.

However, methods for traceable calibration and well quantified uncertainty estimates for these new systems must be established before they can be adopted into documentary standards, and at present these methods cannot be used for full compliance testing against exposure limits for SAR.