Dielectric properties of tissue-equivalent liquids for safety evaluation tests of mobile phones

The radio frequency safety of mobile phones has been evaluated in terms of specific absorption rate (SAR). Standard methods for measurement of the specific absorption rate, including recipes for tissue equivalent dielectric liquids, have recently been discussed among international standard organisations. We measured the change of dielectric properties with time and with temperature of tissue-equivalent liquids recommended in the standard documents, and evaluated their effects on SAR. Experimental results proved that dielectric properties are affected by environmental conditions, and that it is inevitably necessary to adjust the dielectric properties regularly, through the addition of ingredients. We measured the SAR values with aged liquids with a cubic shell and a dipole antenna, and also calculated SAR values by using FDTD method. Both of the SAR values are not strongly affected by the change of dielectric properties. Although further precise investigation is needed, a larger tolerance of the dielectric properties may be acceptable in practical SAR tests.