Peak SAR reduction in human head for handset applications with resistive sheets (R-cards)

Abstract

The rapid growth in the use of cellular phones has increased public concerns on the exposure of human head to electromagnetic radiation. The specific absorption rate (SAR) is a defined figure of merit to evaluate the power absorbed by biological tissue. For mobile phone compliance, the SAR value must not exceed the exposure limits [1, 2]. For example, the SAR limit specified in IEEE C95.1:1999 is 1.6 W/kg in a 1g averaging mass while that specified in ICNIRP guidelines is 2 W/kg in a 10g averaging mass [3]. In general, the SAR value is influenced by various parameters such as antenna positions relative to the human body, radiation patterns of the antenna, radiated power, and antenna types. Over the years, lots of attentions have been paid to the analysis of SAR in human head due to the complexity and large scale involved in such kind of problems. Recently research efforts have been devoted to the reduction of peak SAR in human head for handset applications. A ferrite sheet was adopted as protection attachment between the antenna and the head. A reduction over 13% for the spatial peak SAR over 1g averaging was achieved. Experimental study on the effects of attaching conductive materials for SAR reduction was presented. It was concluded that the position of shielding played an important role in the reduction effectiveness. With proper design and arrangement, stop bands at desired cellular frequencies could be obtained to notch out the radiated power. Highly directive antennas were also utilized for SAR reduction.