SAR reduction for mobile phones based on analysis of EM absorbing material characteristics

With the recent explosive increase of the use of mobile communication handsets, there has been a growing concern about possible hazard to a human body, especially head part, exposed to the EM fields radiated from handsets. The specific absorption rate (SAR) is normally used for one of the important criteria to evaluate the degree of the hazard. The SAR is influenced by various kinds of parameters such as kind and size of antenna, position of antenna, radiated power, handset structure, distance and angle from human body, area of absorbing material if used, and so on. Most of the studies on this area have been performed to evaluate SAR values based on these parameters. In a previous paper (Minscok Jung and Bomson Lee, IEEE APS, vol. 1, pp. 444-448, 2002), after defining SRF (SAR reduction factor) for a quantitative discussion of effective SAR reduction methods, we analyzed the effects of the ferrite sheet attached to the handset based on power conservation relation. In this paper, we analyze the SAR data for various shapes of the ferrite structure. After investigating the reflection and transmission characteristics of the absorbing material layer, we also present a method to estimate the complex permittivity and permeability having a maximum absorption. We then evaluate SAR and SRF data for handsets coated with those absorbing layers.