The requirements for SAR levels have remained largely unchanged for many years (requirements depend on the country/region). In fact, the FCC mobile/handset specific regulations are derived from levels determined in the 1960s during early research of radiation hazards.
Meanwhile, mobile phone designs advanced at light speed while the systems and methods made to test the SAR of those devices remained relatively unchanged for twenty years.
Times are changing now, though, and we’d like to look down the road to see how these changes will turn out.
More and more wearables will include cellular technologies
Currently, most wearables use WiFi or Bluetooth technologies that operate on low power transmission modes and do not require SAR testing. However, wearable devices in the near future are likely to use cellular technologies, emit more electromagnetic radiation, and require SAR testing to ensure compliance.
New technologies will mean more SAR testing
Recent and new technologies that are meant to increase datarates will also mean more SAR testing. With phones against the SAR limits, R&D stage testing is already increasing.
Fast SAR technology makes it possible to do serious line testing
Any piece of equipment that is mass produced has a margin of error in the production, resulting in physical variations from unit to unit. These variations can and do produce variations in SAR levels. With regulatory bodies testing devices across a statistical sample of units to determine the maximum SAR level, manufacturers also must perform random tests over a number of units to statistically ensure SAR compliance.
Fast SAR technologies are capable of performing instant line tests to further increase the statistical accuracy of SAR measurements.
Powerful chipsets that support more bands
The proliferation of chipsets like the Qualcomm RF 360 that support 40 bands mean that thousands of tests must be performed, rather than just hundreds. As chipsets become more powerful and band combinations to support LTE Advanced become more numerous, the amount of SAR testing required to launch a handset or mobile device will only increase.
LTE Carrier Aggregation
LTE Carrier Aggregation combines carriers at the device, using more frequency bands to get more bandwidth. This results in faster downloads and better performance. “Bursty” applications that require sudden bursts of bandwidth will perform much better.
However, all of this affects SAR and will require additional SAR testing, especially as LTE Advanced becomes more common, and more and more combinations of bands are used across the spectrum to deliver content. The exact SAR testing requirements are uncertain, at least according to the FCC.
LTE will likely make obsolete SAR testing technologies that cannot discriminate between different frequency combinations. With SAR values already on the edge of non-compliance at the moment, manufacturers are turning to Fast SAR technologies that can discriminate between frequency bands and also perform the tests faster. These next generation technologies are much faster, which is important because the number of tests to perform is greatly multiplied with LTE, due to the need to test all the band combinations.
Dynamic Antenna Tuning
Dynamic antenna tuning, for example the Qualcomm GFE15, improves antenna performance as the environment interacts with (gets in the way of!) antennas in handsets and other wireless devices. If you cover the antenna with your hand, for example, dynamic antenna matching adjusts the frequency to ensure the best possible reception.
This does, however, affect SAR. The FCC is still currently in the process of deciding exactly what needs to change in terms of taking SAR measurements to ensure that dynamic antenna tuning does not put SAR out of limits.
What it likely means is a whole new set of tests designed to account for and trigger Dynamic Antenna Tuning.
Designers will continue to come up with new tricks
Staying within the SAR certification limits is becoming more and more difficult for designers. With screens becoming larger while phones become lighter and thinner, antenna designers have less and less room, literally, to design their antennas and meet SAR regulations.
What’s more, people are increasingly dependent on their mobile phones, and their expectations are to have reception at all times, even when they are far from the nearest tower.
Thus, you have tricks of the trade like dynamic antenna tuning or proximity sensors that are meant to keep SAR within limits. MIMO is another tricky subject; check how these engineers dealt with MIMO designs. With phones consuming more and more power, we anticipate designers will innovate a few more tricks in the coming years, because they must.
SAR testing will only get faster
Fast SAR Testing technologies already exist. These technologies use a vector-based system that greatly reduces the time it takes to perform testing on handsets, as well as other innovations that can reduce the time-to-market for some handsets by a couple of weeks – a boon for competitors in the race to release new products.
–ART-Fi contributed this blog post
