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Currently, standards for the compliance testing of wireless devices are being extended to cover a wider frequency band and different usage patterns of mobile phones as well as of novel body-worn and handheld devices. As a consequence, not only the head but also strongly varying tissue distributions of the body are exposed to electromagnetic radiation. Several authors have reported changes in the SAR absorption of body tissue due to the presence of a low permittivity fat layer. This paper identifies two different effects which can lead to increased SAR in layered tissue in comparison to the SAR assessed using homogeneous tissue simulating liquid: (1) for larger distances between the tissue and the antenna, standing wave effects occur depending on the frequency and fat layer thickness. (2) In the very close near-field (distances approximately lambda/40), reactive E-field components lead to high local absorption in the skin. The latter effect occurs at lower frequencies and depends on the antenna type. Modification of the parameters of the homogeneous liquids cannot compensate for these effects. However, a conservative exposure estimate can be obtained by applying a multiplication factor between 1 and 3 to the values assessed using current experimental dosimetric techniques.

This paper investigates the temperature rise in a 1-D layered tissue model, which is irradiated with nonionizing radiation. Of the numerous tissue configurations that correspond to realistic body trunk and limb representations, only those are examined which maximize the averaged specific absorption rate (SAR). The results show that the old IEEE standard on safety was more conservative in terms of temperature rise than the Non-Ionizing Radiation Protection guidelines. They also indicate that the removal of heat exchange from the skin surface can induce a significant temperature rise in it, which is, however, mostly due to imposing the adiabatic conditions themselves, rather than the electromagnetic energy absorption.

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