An on-site dosimetry system for safety assessment of wireless base stations using spatial harmonic components

Abstract

Most of the recently revised safety limits worldwide are set in terms of the limits of rates of internal energy deposition [specific absorption rates (SARs)] for radio/microwave frequencies. Since procedures to ascertain compliance with the SAR limits are cumbersome, requiring complex computer modeling or bulky, mostly homogenous experimental phantoms, they are ignored in favor of easy-to-measure incident fields. Radio-frequency (RF)/microwave installations are thus erroneously declared safety compliant or not based solely on the measured incident fields. A rapid real-time SAR determination system is also needed to define the safety zone for RF/microwave installations such as wireless base stations. We describe an approach where the measured incident electric (E) fields (both vertical and horizontal components) for an imaginary vertical plane of dimension 0.96/spl times/2.28 m in the immediate vicinity of the intended location of the human may be used to obtain whole-body-average and peak 1- or 10-g SARs using a portable PC in less than one minute of compute time. The method relies on describing the measured E fields in terms of space harmonic components and using the prestored solutions for the internal E-fields (E/sub x/,E/sub y/,E/sub z/) for the various voxels of the human body model for six to ten strongest harmonic components. This approach has been validated using examples of commercial base-station antennas both at 835 and 1900 MHz, elevated or not, for varying distances (1-10 m) of the human model from such antennas. The whole-body-average and peak 1-g SARs are less than 5-10% different than those obtained using the computationally intensive full finite-difference time-domain (FDTD) simulations.