Improvement of SAR Accuracy by Combining Two SAR Quantification Methods for Small Animals in Reverberation Chamber Above 10 GHz

Jingjing Shi,Osamu Fujiwara,Jerdvisanop Chakarothai,Soichi Watanabe,Kanako Wake,Jianqing Wang

doi:10.1109/access.2020.3011830

Abstract

Two measurement-based methods are presented to quantify the whole-body-averaged specific absorption rate (WBA-SAR) and local SAR for small animals in a medium-size reverberation chamber (RC) for a bio-effect experiment at frequencies above 10 GHz. S-parameter-based method is a totally experimental approach to quantify the WBA-SAR in small animals based on measuring the mean power density and loss power expressed by S-parameters. Two-step method is a measurement-simulation hybrid approach, which links the mean power density to the finite difference time domain (FDTD) calculated WBA-SAR and local SAR in specified organs. However, at a frequency as high as 10 GHz, the RC is usually not ideal because loss on the RC walls is not negligible. In addition, a numerical-only approach is also unrealistic to quantify the SAR because of the heavy calculation burden and difficulty in obtaining converged results. To address this issue, we proposed an improved two-step hybrid method. The method uses the S-parameter-based method to derive the mean power density by matching its WBA-SAR to that of the two-step hybrid method, and then calculate the local SAR in anatomical numerical animal models using the two-step hybrid method under this mean power density. In such a way, in addition to the advantage of obtaining local SAR, the two-step hybrid method has significantly improved its accuracy of SAR quantification.

Highlights

In recent years, reverberation chamber (RC) exposure setup has been used for small animal experiments to investigate possible adverse biological effect of whole-body exposures by radio-frequency (RF) electromagnetic field (EMF) [1]–[5]
In order to comply with the World Health Organization (WHO) suggestions on investigation of possible effects due to emerging RF technologies, some in-vivo researches on local and whole-body exposures of small animals to RF fields above 10 GHz have been planned and conducted recently [7]
For whole-body exposures, an accurate quantification of exposure level of whole-body-averaged specific absorption rate (WBA-SAR) and local SAR at specified organs such as the brain or heart are of critical importance, since the SAR represents amount of energy deposition of EMFs inside the animal bodies, which may cause the body temperature rise

Summary

INTRODUCTION

Reverberation chamber (RC) exposure setup has been used for small animal experiments to investigate possible adverse biological effect of whole-body exposures by radio-frequency (RF) electromagnetic field (EMF) [1]–[5]. It has advantages over S-parameter-based method since it enables us to find how much power is absorbed in individual organs, i.e., brain, which is usually of great importance in finding functional impact in a long-term whole-body exposure experiment. The uncertainties of the two-step hybrid method include the measurement error of the mean electric field or mean power density, loss of RC walls, and convergence of FDTD calculation depending on the number of incident plane waves. The proposal of the improvement method is the main contribution of this study

Q-FACTOR

TEMPORAL ELECTRIC FIELD VARIATION

CONCLUSION