Desktop exposure system and dosimetry for small scale in vivo radiofrequency exposure experiments

Yijian Gong, Myles Capstick, Thomas Tillmann, Clemens Dasenbrock, Theodoros Samaras, and Niels Kuster, Bioelectromagnetics, Volume 37, Issue 1, pp. 49–61, January 2016, online December 18, 2015

In this paper, a new approach to the assessment of risk due to exposure to radiofrequency (RF) fields from wireless network devices is described, including an exposure setup and dosimetric assessment for in vivo studies. A novel desktop reverberation chamber for well-controlled exposure of mice for up to 24 h per day was developed to address the biological impact of human exposure scenarios by wireless networks. The carrier frequency of 2.45 GHz corresponds to one of the major bands used in data communication networks and is modulated by various modulation schemes, including the Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Radio Frequency Identification (RFID), and wireless local area networks, etc. The new system is designed to enable assessment of whole-body averaged specific absorption rate (SAR) of up to 15 W/kg for six mice of an average weight of 25 g or of up to 320 V/m incident time-averaged fields under loaded conditions without distortion of the signal. The dosimetry for whole-body SAR and organ-averaged SAR of the exposed mice, with analysis of uncertainty and variation analysis, is reported. The experimental dosimetry based on temperature measurement agrees well with the numerical dosimetry, with a very good SAR uniformity of 0.4 dB in the chamber. Furthermore, thermal analysis and measurements were performed to provide better understanding of the temperature load and distribution in the mice during exposure.

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

• A desktop reverberation chamber system for in vivo studies – with two chambers, an automatic RF-safe watering system, full computer control, and a monitoring system; the new system has an exposure field homogeneity of 0.3 dB and an overall efficiency at 2.45 GHz of 36%

• The less computationally costly 12-plane-wave numerical approach could be used with an appropriate offset to approximate the more accurate random-plane-wave method to estimate exposure levels in the reverberation chamber

• Whole-body and organ-specific exposure levels of each individual exposed mouse can be predicted, with an overall peak instantaneous SAR of >250 W/kg, an average SAR of 10 W/kg (15dB peak-to-average ratio)

• Temperature measurements demonstrate that, the larger the SAR, the stronger the effect on thermoregulation and the more time is needed for a return to basal temperature

• Thermal response is dependent on the metabolic rate, i.e., the mass and activity level, of the animal, thus, a higher threshold is expected for free-running animals 

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