There is increasing public concern that adverse health effects may arise from exposure to radiofrequency (RF) sources, particularly due to the increasing use of mobile and wearable devices with growing radio-communication capabilities such as GSM, Wi-Fi, and Bluetooth. This is particularly true with wearables, which are usually worn on the body and sometimes in direct contact with the. The primary concern is that the RF electromagnetic fields can be absorbed by tissues of the human body and could potentially lead to carcinogenic or adverse health effects .
Since then, dozens of studies have been done to investigate the possible adverse effects of radio-communication devices near the human body with various review articles published. Specific absorption rate (SAR) is a measure of energy absorption by the body from the source being measured when exposed to a transmitting source [2, 3], is defined as the power absorbed per mass of tissue. It has units of watts per kilogram (W/kg) and the value is averaged either over the whole body or over stated volume or mass (typically 10g of tissue). SAR provides a straightforward means for measuring the RF exposure characteristics of devices, which in most studies are usually mobile phones, due to the increasing prevalence of mobile smartphones.
Studies in 1998 hypothesize possible effects when the transmitter is in close proximity to the head (brain) . However new studies done with Bluetooth transmission at 2.45Ghz with a 100mW normalized radiation power showed SAR values averaging at 0.4W/Kg , and 10µW/kg over 24hours  – all well below ICNIRP limits of 2W/Kg  and FCC limits of 1.6W/Kg . The results of epidemiological studies on mobile phones or broadcasting stations are inconclusive or to have no known direct ill health effects on humans [1, 4-6, 9-24].
Noting public concerns and understanding of academic studies investigating health effects by radiating devices thus far, the Federal Communications Commission (FCC)’s 47 C.F.R. 1.1307(b), 1.1310, 2.1091, 2.1093 guidelines require that smart phones sold have an SAR level at or below 1.6W/kg taken over the volume containing a mass of 1g of tissue that is absorbing the most signal [8, 12]. The European Union’s CENELEC specifies SAR limits within the region, following IEC 62209-1  standards. For mobile phones and other such handheld devices, the SAR limit is 2 W/kg averaged over the 10g of tissue absorbing the most signal.
The SARs for the iPhone 6 models can be found here, whilst future mobile and wearable devices complying with the emission power and SAR value not exceeding 1.6W/Kg would be a suitable design guideline . A new generation of tracking and wearable technologies are designed with SAR values of <1W/Kg and will be suitable for long-term deployment in close proximity with humans.
With the explosive growth of IoT and WSNs and as the number of radio-communication devices around us increases with the increased use of wearables and reliance on smartphones, it’s important to note that safety needs to be part of a new technology of device design considerations, and over extended periods of time, and keeping RF emissions from these communication devices within acceptable limits will enable quicker regulatory approval, is socially responsible for engineers introducing new devices into the market.
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