Power Absorption and Skin Temperature Rise From Simultaneous Near-Field Exposure at 2 and 28 GHz

In international guidelines and standards for human protection from electromagnetic fields, mass-averaged specific absorption rate (SAR) is used as a metric to prevent excessive temperature rise at frequencies from 100 kHz up to 6 GHz. Above this transition frequency, including the frequency region assigned to fifth-generation (5G) wireless communication systems, area-averaged absorbed power density (APD) or epithelial power density is used as a physical quantity to specify restrictions on human exposure. In 5G wireless systems, frequencies above and below 6 GHz may be used simultaneously. The effect of the superposition of SAR and APD on temperature rise should be considered, especially regarding the prevention of excessive surface temperature. Herein, we considered simultaneous exposure from inverted-F antenna and patch antenna array operating at 2 and 28 GHz, respectively. Computational results showed that the effect of superposition was marginal. This result is attributable to the heat diffusion length in biological tissues (
$\sim 10$
mm). The effect of the superposition was higher than 15% only when the patch antenna array and inverted-F antenna were separated by less than 50 mm for the 5 mm antenna-body separation.