A Radio Frequency Radiation Reverberation Chamber Exposure System for Rodents; BEMS 29th Annual Meeting; ;

Objectives. This paper presents the design and experimental results for a reverberation chamber based exposure setup for individually housed unconstrained rodents suitable for exposure over extended periods. The idea of using reverberation chambers for animalexposure to electromagnetic fields was first suggested by the National Institute of Standards and Technology (NIST) in a special session at BEMS 2001. A preliminary study involving an experimental investigation performed by NIST and a preliminary numerical dosimetry study performed by IT’IS, both funded by the National Institute of Environmental Health Sciences (NIEHS) in the USA. The results of this preliminary study were very encouraging and in January 2006 the main study to evaluate the potential toxicity and carcinogenicity of cell phone RF radiation in laboratory animals was issued by NIEHS under the National Toxicology Program. These results constitute the out come of the chamber prototype development and evaluation phase of the study. Methods. Reverberation chambers are resonant enclosures where the field structure is continuously altered using stirrers such that they provide a statistically homogeneous field distribution within a specific volume in the chamber. In the NTP studies, rats will be chronically exposed at 900MHz and mice at 1.9GHz, different exposure groups will be subjected to either GSM or IS95 signals at one of three SAR levels or sham, over an entire lifespan. The design of the reverberation chamber had to encompass both the electrical design and animal housing issues, this resulted in a fully welded stainless steel design with two mode stirrers. The rodents have to be supplied with drinking water without energy absorption in the water or increased SAR in or RF burns to the animal whilst drinking. The exposure in the chambers is controlled using a closed loop system. This system is based on the measurement of three orthogonal components of both the electric and magnetic field at two locations in each chamber. The required field strength was determined from numerical dosimetry using high resolution animal models based on 4 different size models covering the whole life span. Each model has over one hundred different tissue types differentiated. Using the models the average field strengths required to produce the target SAR in the animals in each exposure group was determined. Results. The important performance metrics for a reverberation chamber used for animal exposure are: the field uniformity, field isotropy, SAR uniformity and efficiency. Using EField probes the measured electric-field uniformity (one standard deviation) in the empty chamber measured on a 300mm 3D grid was 0.6dB and the field isotropy 0.85dB and in the fully loaded chamber, over a reduced number of points, 0.74dB and 1.3dB respectively. Figure 1, shows the E-field uniformity results. The SAR uniformity measured in rat and mouse phantoms, using the temperature method, were 0.46dB and 0.40dB respectively. The design achieves an overall efficiency of ~70% for adult rats and 45% for adult mice. A water system was developed could be installed in the chambers without introducing additional loss. The design for use in a reverberation chamber environment with high RF fields (up to 400 V/m) was developed that avoided or minimized: 1) high local SAR peaks in the animal whilst drinking, 2) variations in whole-body average SAR with respect to the animal not drinking, 3) significant distortions in the fields around the water system. The design uses flanged quarter wave choke tubes integrated into a stainless steel automatic water system. The numerical analysis was performed with SEMCAD using high resolution anatomical models. Figure 2 shows both the flanged choke arrangement and the anatomical model used for the numerical dosimetry. The experimental verification was done using gel animal phantoms and temperature probes. The designed water system provides a safe drinking environment without disturbing the field homogeneity and isotropy within the animal enclosures. Conclusions. Overall, the performance across all the criteria of the reverberation chamber for animal exposure is excellent, with all target performance metrics being met or exceeded. The performance of this exposure environment is comparable to the best exposure setups using constrained animals. Acknowledgements. This work was supported by the National Institute of Environmental Health Sciences (N01-ES-55544).