SAR investigations on the exposure compliance of wearable wireless devices using infrared thermography

Wearable electronics have become the norm over the last few years. Extensive use of wearable wireless devices (WWD) in greater proximity to the body has increased concern about potential biological effects due to the interaction of human tissues with electromagnetic (EM) fields. Human tissues absorb radiofrequency (RF) waves that are capable of affecting energy states at a molecular level, leading to unsafe effects. Remarkably, thermal effect due to the absorption of RF waves is a better biological manifestation than traditional specific absorption rate (SAR) values. In this study, we investigated the application of infrared thermography (IRT) to obtain temperature dynamics and reconstructed average SAR to evaluate the exposure compliance of WWDs. A microstrip-based monopole antenna was used to determine the biological effects of the interaction of EM waves with the body. SAR was obtained using EM field simulations and through reconstruction from thermal measurements with the use of bio-heat equations. The maximum average SAR on the skin was 50 mWkg^-1 for the simulations and 54 mWkg^-1 from reconstruction after IRT experiments. The maximum temperature change in both cases was observed to be less than 1 °C. The difference between the average SAR obtained through IRT and simulation tools was 8.9% on average. SAR determination from the information acquired using IR temperature dynamics can assess bio-compliance of modern wearable devices for various wireless applications. Bioelectromagnetics. 39:451-459, 2018. © 2018 Wiley Periodicals, Inc.