Feature: Software & Tools
SAR testing is mandatory for mobile phones and smartphones. Given the proximity of these devices to the user's body, especially during calls, SAR testing ensures that the emitted RF energy is within safe limits
data services. Tese technologies can be classed as an un-attended service, meaning that the device can be placed anywhere about the body with the user (in most cases) being unaware of the transmit status of the device. For example, the device could be
doing an update, sending a large file, or being used by a third party as a Wi-Fi hotspot. Following the introduction of this technology the amount of regulatory testing that is required increased significantly, and the allowable separation distance between the device and the body reduced significantly. Tese changes made the SAR testing of mobile handsets much more demanding.
Wireless consumer products Devices like tablets, smartwatches and other wireless communication devices that are used in close proximity to the body, are also subject to SAR testing. Tis includes devices with Wi-Fi, Bluetooth and cellular connectivity. As some of the devices in this category can be used in the hands or on limbs, a slightly relaxed SAR test limit might be allowed as these extremities do not contain any major organs and are primarily made up of skin, bone and muscles. Once again, it’s important to consider
all of the use cases. For the example, a smartwatch could be classed as limb use only. But, if you can speak into the smartwatch then you must consider the proximity of the user’s face to the device when speaking into it. Tis front of face condition could result in a head SAR use case condition with a separation distance of 10mm, which would need to be tested to the more stringent head and body SAR limits, as well as testing the limb conditions.
Wireless infrastructure In addition to individual devices, SAR testing is sometimes applicable to wireless infrastructure components, such as antennas and base stations, to ensure that the overall RF exposure levels are within acceptable limits. As the use of small (pico-cell)
office-based base station infrastructure technologies is becoming more widespread, how they are installed in the workplace must be considered. In the case of a base station, it’s often the device's compliance distance which is important. If the minimum distance a user can get to a device and still meet the regulatory requirements is known, then the placement of that device in the workplace can be easily assessed. For example, if the base station is
compliant at 0mm separation distance, then it can effectively be placed anywhere. Alternatively, if the separation distance is relatively large then this could be mitigated by specifying a minimum height at which the base station could be mounted on an office wall. Certain medical devices that use
wireless technology, such as wearable health monitors or implantable devices, may also require SAR testing to national regulatory requirements. As can be seen from the various descriptions above, it’s vitally important to understand and define how a product will be used to understand when and how SAR tests will be applied. Another key requirement is to
understand and apply all ‘reasonably foreseeable use’ conditions. Examples of this would be for something like a mobile phone, where a manufacturer has stated that it’s used in a body condition at a separation distance of
15mm, when in reality most users are placing the device in their pocket. In this case it is the pocket use case at 0mm to 5mm that must be assessed. Similarly, if a device is classified as only for use in the hands when it can be placed in a coat or hoodie type garment pocket while it is transmitting, then body conditions would also need to be applied. The other conditions that are important
to consider is whether the device under test is for public use or for occupational use. If a device is for occupational use, the SAR limits are less stringent. The reason behind this is that professional users can be given training on the operation of their equipment and on how to limit their exposure to the RF radiation from those devices. This would result in an awareness of the equipment with regards to what it is doing and how to use it. If a device is classed as occupational
use, it may have been designed to the limits associated with occupational use, and manufacturers must be certain that the device cannot be easily obtained by the general public. If this is not the case, then the device must be tested to the general public limits. Such an issue would be particularly
difficult to deal with as SAR testing is a physical test that must be carried out on hardware that is representative of that being placed on the market. Any issues that need to be fixed at the end of a product development cycle would be far more costly to rectify than if they were found earlier in the development cycle. In most cases a fix for SAR compliance issues is to turn down the output power of a product but this will negatively affect device performance when a device is being developed. It is therefore important to fully understand SAR testing requirements from the start. Tis will ensure that a practical and realistic SAR test programme is thought out and carried out as soon as possible in a product’s development cycle, to minimise the likelihood of design reworks which can be costly and cause time-to-market delays.
https://www.tuvsud.com/en-gb/ industries/manufacturing
www.electronicsworld.co.uk September 2024 21
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