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04/04/2017

A Radio Frequency Radiation Exposure System for Rodents Based on Reverberation Chambers

Myles H. Capstick, Sven Kuehn, Veronica Berdinas-Torres, Yijian Gong, Perry F. Wilson, John M. Ladbury, Galen Koepke, David L. McCormick, James Gauger, Ronald L. Melnick, and Niels Kuster, IEEE Transactions on Electromagnetic Compatibility, Volume 59, Issue 4, pp. 1041–1052. August 2017, online 17 March 2017, doi: 10.1109/TEMC.2017.2649885

The main objective of this paper is to present the novel design features, their technical implementation, and an evaluation of the radiofrequency (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 second and third generation mobile-phone signals. The system requirements for this two-year NTP cancer bioassay study were the tightly controlled uniform lifetime exposure of rodents (1568 rats and 1512 mice) to three power levels plus sham. The signals simulate the typical daily exposures of users of GSM and CDMA (IS95) devices. The reverberation chambers and animal housing were designed to allow extended exposure time per day for free-roaming individually housed animals. The performance of the chamber was characterized in terms of homogeneity, stirred to unstirred energy, and efficiency. The homogeneities achieved were 0.59 and 0.48 dB at 900 and 1900 MHz, respectively. The temporal variation in the electric field strength was optimized with the two stirrers to give characteristics similar to those of the power control of a phone in a real network. Experimental dosimetry was performed to validate the specific absorption rate (SAR) sensitivity and to determine the SAR uniformity throughout the exposure volume; SAR uniformities of 0.46 and 0.40 dB for rats and mice, respectively, were achieved.

The scientific and technical impact of the study can be summarized as:

  • The design, optimization, and remote-control of two types of reverberation chambers for maximized uniform exposures of unconstrained rats and mice for 20 hours per day over two years is described;
  • The modulation due to the periodic rotational motion of the stirrers was used to simulate the low frequency variation of a phone's RF output power due to power control as the phone user moves;
  • The water supply system consists of shielded distribution pipes with choked flanged drinking valves that do not heat the water, significantly alter the field distribution, or overexpose the tongue of the animal during drinking.
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