A Radio Frequency Radiation Reverberation Chamber Exposure System for Rodents
Perry F. Wilson, John M. Ladbury, Galen H. Koepke, Capstick Myles, Niels Kuster, Sven Kuhn, Veronica Berdinas-Torres, Yijian Gong, David McCormick, James Gauger, Ronald Melnick
In this paper we present the novel design features, their technical implementation, and an evaluation of the radio frequency (RF) exposure systems developed for the National Toxicology Program (NTP) of the National Institute of Environmental Health Sciences (NIEHS) studies on the potential toxicity and carcinogenicity of 2nd and 3rd generation mobile phone signals. The system requirements for this large 2-year NTP cancer bioassay study were the tightly controlled lifetime exposure of rodents (1568 rats and 1568 mice) to three power levels plus sham simulating typical daily, and higher, exposures of users of GSM and CDMA (IS95) signals. Reverberation chambers and animal housing were designed allowing extended exposure time per day for free roaming individually housed animals. The novel use of the reverberation chamber as a cavity power combiner facilitates the provision of high SAR levels. The performance of the chamber was characterized in terms of homogeneity, stirred to unstirred energy, efficiency, and signal statistics with different loads. The paper also outlines the design and validation of a water system that allows provision of water during exposure without either absorption of power in the water or over exposure during drinking. The achieved homogeneity was 0.59 dB and 0.48 dB at 900 and 1900 MHz respectively. The temporal variation in the field strength was determined and optimized to give similar characteristics to that of the power control of a phone in a real network using the absolute and relative speeds of the two stirrers. Experimental dosimetry was performed to validate the SAR sensitivity and determine the SAR homogeneity throughout the exposure volume; SAR homogeneities of 0.46 dB and 0.40 dB, respectively, for rats and mice were achieved. The control and monitoring system is outlined.
IEEE Transactions on Electromagnetic Compatibility