Dielectric properties of tissue-equivalent liquids and their effects on electromagnetic power absorption

Mobile phone safety has been evaluated by the specific absorption rate (SAR). The measurement method, including recipes for tissue-equivalent dielectric liquids, have been discussed among international organisations. Standard documents currently recommend glycol-type liquids as tissue-equivalent liquids for frequencies above 1 GHz. Although the relative amounts of the ingredients are specified in the recipes provided, possible difficulties relating to the stability of dielectric properties are not clearly described. In this work we measured the time dependence of the dielectric properties of glycol-based dielectric liquids, and evaluated their effects on SAR. The experimental results suggest that relative permittivities decrease with time and that conductivities remain nearly constant. SAR, however, was not affected significantly by the change in dielectric properties.