Background: Two international guidelines/standards for human protection from\nelectromagnetic fields define the specific absorption rate (SAR) averaged over 10 g of\ntissue as a metric for protection against localized radio frequency field exposure due to\nportable devices operating below 3ââ?¬â??10 GHz. Temperature elevation is suggested to be\na dominant effect for exposure at frequencies higher than 100 kHz. No previous studies\nhave evaluated temperature elevation in the human head for local exposure considering\nthermoregulation. This study aims to discuss the temperature elevation in a human\nhead model considering vasodilation, to discuss the conservativeness of the current\nlimit.\nMethods: This study computes the temperature elevations in an anatomical human\nhead model exposed to radiation from a dipole antenna and truncated plane waves\nat 300 MHzââ?¬â??10GHz. The SARs in the human model are first computed using a finitedifference\ntime-domain method. The temperature elevation is calculated by solving\nthe bioheat transfer equation by considering the thermoregulation that simulates the\nvasodilation.\nResults: The maximum temperature elevation in the brain appeared around its\nperiphery. At exposures with higher intensity, the temperature elevation became larger\nand reached around 40 Ã?°C at the peak SAR of 100 W/kg, and became lower at higher\nfrequencies. The temperature elevation in the brain at the current limit of 10 W/kg is at\nmost 0.93 Ã?°C. The effect of vasodilation became notable for tissue temperature elevations\nhigher than 1ââ?¬â??2 Ã?°C and for an SAR of 10 W/kg. The temperature at the periphery\nwas below the basal brain temperature (37 Ã?°C).\nConclusions: The temperature elevation under the current guideline for occupational\nexposure is within the ranges of brain temperature variability for environmental\nchanges in daily life. The effect of vasodilation is significant, especially at higher\nfrequencies where skin temperature elevation is dominant.
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