RESUMO
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 2-year NTP cancer bioassay study were the tightly-controlled lifetime exposure of rodents (1568 rats and 1512 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 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, efficiency. The achieved homogeneity was 0.59 dB and 0.48 dB at 900 and 1900 MHz respectively. The temporal variation in the electric field strength was optimized to give similar characteristics to that of the power control of a phone in a real network using the two stirrers. Experimental dosimetry was performed to validate the SAR sensitivity and determine the SAR uniformity throughout the exposure volume; SAR uniformities of 0.46 dB and 0.40 dB, respectively, for rats and mice were achieved.
RESUMO
This paper presents the design, optimization, realization and verification of novel whole-body exposure setups for rats. The setups operating at 902 MHz and 1747 MHz provide highly efficient, National Toxicology Program (NTP) compatible and well-characterized exposures. They are compared to existing concepts of exposure setups with respect to efficiency, induced field uniformity, good laboratory practice (GLP) compatibility and cost. The novel exposure setup consists of a circular cascade of 17 sectorial waveguides excited by a novel loop antenna placed in the centre. The 70% overall efficiency of the exposure setup surpasses comparable values of existing setups. A field uniformity inside the phantom of more than 86% for the 1g cubical averaged specific absorption rate (SAR) within +/-5 dB of the whole-body SAR (WB-SAR) was attained. The uniformity of the exposure inside the setup, defined as the variation of the WB-SAR between animals, was better than +/-24%. Using only stainless steel, gold and polycarbonate in the vicinity of the animals ensured full GLP compatibility. The entire exposure system features fully automated computer controlled exposure and data monitoring, data storing and failure handling. Therefore, the proposed exposure system can be used to run blinded large scale, long-term exposure studies.