Analysis of specific absorption rate in humans for wearable wireless devices in underground mines

Abstract

In the last decades, the use of wireless communication has proliferated, which has mushroomed the amount of electromagnetic radiation (EMR) in the environment. Human body interacts directly or indirectly with these EMR, which may cause adverse health impact. The exposure of EMR is regulated by the guidelines anticipated by the standardisation bodies. Specific absorption rate (SAR) determines the amount of electromagnetic energy absorbed in human tissues and is used as an index to regulate EMR exposure to humans by standard regulatory authorities. Underground mining is an important industry and especially vital for the South African economy. Underground mining processes can be made more productive and reliable by deploying different systems for monitoring, tracking and controlling different activities in the underground mines. Different tracking systems are deployed in the underground mines to track the exact location and vitals of the miner, particularly after a disaster. Most of these devices are wearable and mounted on the head or torso of the miners. Due to the proximity of these devices to human organs in a confined environment of underground mines and continuous operations for extended hours, the public concern for the use of these devices has arisen in recent years. This study evaluates the SAR variations for wearable wireless devices used in underground mines using frequencies of relevant ISM bands i.e. 433 MHz, 868 MHz and 2400 MHz. The SAR variations are evaluated by numerical simulations using two high resolution (1x1x1 mm3) human anatomical models and by modelling different underground mine scenarios. The SAR results of two human models on head without helmet, torso and head with helmet are compared for open space and underground mine scenarios for all frequencies. The results show that the SAR values are higher in all underground mine scenarios than the open space scenarios, and the SAR values are also higher for higher frequencies than the lower frequencies. It is observed that in terms of SAR, the torso is a suitable location to mount these devices on the body of the miner compared to the head. Recommendations based on the SAR guidelines are provided on head for maximum transmit power level of 1 W, 0.5 W and 0.12 W can be used at 433 MHz, 868 MHz and2400 MHz, respectively, for short duration of time in case of a disaster to aid the rescue operation in underground mines. Finally, the SAR was investigated with variation of distance between human model and underground mine structure. It was concluded that the SAR values are higher than the open space scenario when the distance between the boundaries of the underground mine and miner is less than 200 mm