Dielectric properties of tissue equivalent liquids at ratio frequency

The radio frequency safety of mobile phones has been evaluated in terms of specific absorption rate. Standard methods for measurement of the specific absorption rate, including recipes for tissue-equivalent dielectric liquids, have recently been the subject of discussions among international standard organisations. Standards currently recommend glycol-type liquids as tissue-equivalent liquids for frequencies above 1 GHz. In this study we measured the change of dielectric properties with time and with temperature of tissue-equivalent liquids recommended in the standard documents. The conductivity decreased with increasing temperature in any glycol-type specimen. The permittivity, on the other hand, was almost constant. With the evaporation of water, the permittivity decreased, although the conductivities remained constant. These 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, in order to follow the standards.