Development of a rat head exposure system for simulating human exposure toRF fields from handheld wireless telephones

The aim of this project was to develop an animal exposure system for the bi ological effect studies of radio frequency fields from handheld wireless te lephones, with energy deposition in animal brains comparable to those in hu mans. The finite-difference time-domain (FDTD) method was initially used to compute specific absorption rate (SAR) in an ellipsoidal rat model exposed with various size loop antennas at different distances from the model. A 3 x 1 cm rectangular loop produced acceptable SAR patterns. A numerical rat model based on CT images was developed by curve-fitting Hounsfield Units of CT image pixels to tissue dielectric properties and densities. To design a loop for operating at high power levels, energy coupling and impedance mat ching were optimized using capacitively coupled feed lines embedded in a Te flon rod. Sprague Dawley rats were exposed with the 3 x 1 cm loop antennas, tuned to 837 or 1957 MHz for thermographically determined SAR distribution s. Point SARs in brains of restrained rats were also determined thermometri cally using fiberoptic probes. Calculated and measured SAR patterns and res ults from the various exposure configurations are in general agreement. The FDTD computed average brain SAR and ratio of head to whole body absorption were 23.8 W/kg/W and 62% at 837 MHz, and 22.6 W/kg/W and 89% at 1957 MHz. The average brain to whole body SAR ratio was 20 to 1 for both frequencies. At 837 MHz, the maximum measured SAR in the restrained rat brains was 51 W /kg/W in the cerebellum and 40 W/kg/W at the top of the cerebrum. An exposu re system operating at 837 MHz is ready for in vivo biological effect studi es of radio frequency fields from portable cellular telephones. Two-tenths of a watt input power to the loop antenna will produce 10 W/kg maximum SAR, and an estimated 4.8 W/kg average brain SAR in a 300 g medium size rat. Bi oelectromagnetics 20:75-92, 1999. (C) 1999 Wiley-Liss Inc.