Computation of SAR levels in SAM's head model located inside an automobile via the parallel FDTD Algorithm

Abstract

In recent years, ever-increasing proliferation of handheld terminals has served to enhance the level of concern for possible deleterious biological effects of electromagnetic waves absorbed by the human body. Generally speaking, when the cellular mobile radio system is functioning, and the transmitting terminal is located in close proximity of the human head — say less than 7 mm — a large fraction of the power radiated by the mobile radio is absorbed by the user. During the last 10 years, the Specific Absorption Rate (SAR) value has been used as the standard dosimetric parameter in defining the energy absorbed by the human body exposed to electromagnetic radiation. In particular, in the RF and microwave frequency bands, the absorbed Elctromagnetic (EM) energy mainly contributes to the heating of the tissues[1]. The value of 4W/kg is accepted worldwide as the threshold for the induction of biological thermal effects[2]. In this paper, we evaluate the effects of near-field exposure, specifically the SAR values induced by the cellular Multi-Input Multi-Output (MIMO) antenna. Towards this end, we employ the Specific Anthropomorphic Mannequin (SAM) Head Model, comprised of a low-loss dielectric material, whose shape and dimension parameters are selected from the 90th-percentile anthropometic data corresponding to the adult male head, as tabulated by the US Army[3]. The model is made of two parts: the phantom shell and flat phantom. The phantom shell thickness is approximately 2mm and the dimensions of the flat phantom are about 22.5 cm × 15 cm in the major and minor axes, respectively[4]. We evaluate the SAR values at two frequencies in the industrial, scientific and medical (ISM) band, namely 2.255 GHz and 2.4 GHz that are the operating frequencies of WiFi, Bluetooth and ZigBee. It is well known that computing and measuring the SAR values in different electromagnetic environments is a highly complex problem. In this work we employ the parallel FDTD Algorithm, specifically the generalpurpose electromagnetic solver GEMS, to calculate the SAR values of SAM head models located within an automobile, then compare with the values we obtain with the corresponding results in free-space environment.