The dependence of electromagnetic energy absorption upon human head tissuecomposition in the frequency range of 300-3000 MHz

The requirements for testing compliance of cellular phones with electromagn etic safety limits demand evaluation of the maximum exposure that may occur in the user group under normal operational conditions. Under these conditi ons, the tissues of the ear region are most exposed, the tissue composition of which is complex and varies considerably from user to user. The objecti ve of this paper is to derive head tissue equivalent dielectric parameters that enable the utilization of one generic homogeneous head for testing com pliance for the entire user group, i.e., granting no underestimation, but a lso not greatly overestimating the actual maximum user exposure. As a prima ry study, a simple analytical model of an infinite half-space layered tissu e model exposed to a plane wave was utilized to investigate the impact of i mpedance-matching standing waves, etc. on the spatial-peak specific absorpt ion rate. The tissue layers were varied in composition and thickness, repre senting the anatomical variation of the exposed head region covering the us er group including adults and children (<10% to >90% percentile). Based on the worst-case tissue layer compositions with respect to absorption at each frequency, head tissue equivalent dielectric parameters for homogeneous mo deling were derived, which result in the same spatial-peak absorption. The validity of this approach for near-field exposures was demonstrated by repl acing the plane wave by different near-field sources (dipoles and generic p hones) and the layered structure with magnetic-resonance-image-based nonhom ogeneous human head models.