Field strengths and specific absorption rates in automotive environments

Abstract

Both densitometric and dosimetric methods were used to measure human exposure in the near fields inside cars, generated by high-power transceivers with a VHF or UHF antenna mounted on the trunk. A back half and full car were used for the tests. The densitometric readings of apparent power density given by the far-field survey probes, although they cannot be used for dosimetric purposes, show relative field strengths such as standing wave patterns inside the cars and thus are called equivalent plane wave power densities. Mounted on a robot arm was an electric field probe used for dosimetric measurement of specific absorption rate (SAR) in a sitting position liquid human phantom. The range of apparent power densities obtained from the survey probe measurements are compared to those calculated for the power radiated from the antenna through a cylindrical surface at the same distance to the interior of the car, where the far-field probe measurements were performed. Results from these measurements show that the E- and H-field intensities do not meet FCC safety limits. The dosimetric measurements show that even though the apparent power densities measured in the car exceeded FCC limits, actual SAR tests conducted in simulated human tissue under the same conditions do meet FCC basic safety limits.