Multiphysics and Thermal Response Models to Improve Accuracy of Local Temperature Estimation in Rat Cortex under Microwave Exposure

Abstract

The rapid development of wireless technology has led to widespread concerns regarding adverse human health effects caused by exposure to electromagnetic fields. Temperature elevation in biological bodies is an important factor that can adversely affect health. A thermophysiological model is desired to quantify microwave (MW) induced temperature elevations. In this study, parameters related to thermophysiological responses for MW exposures were estimated using an electromagnetic-thermodynamics simulation technique. To the authors’ knowledge, this is the first study in which parameters related to regional cerebral blood flow in a rat model were extracted at a high degree of accuracy through experimental measurements for localized MW exposure at frequencies exceeding 6 GHz. The findings indicate that the improved modeling parameters yield computed results that match well with the measured quantities during and after exposure in rats. It is expected that the computational model will be helpful in estimating the temperature elevation in the rat brain at multiple observation points (that are difficult to measure simultaneously) and in explaining the physiological changes in the local cortex region.

Comparison of Thermal Response for RF Exposure in Human and Rat Models

“…We used the vasodilation models of the brain and skin that were based on our rat measurements for local RF exposure [25] and cutaneous veins of a dog with local warming [39], respectively. The thermoregulatory response model for blood perfusion was assumed to be the same for both rat and human because of the lack of specific data.…”

“…The blood perfusion in the brain was given as follows, based on our rat measurements for local RF exposure [7]:$B\left(boldnormalr,t\right)=B_0\left(r\right)\left(1+F_{HS}\Delta T_H\left(t\right)\right)·2^{\Delta T\left(r\right)/F_{BB}},$ where F HB (=0.053 °C −1 ) and F BB (=13.9 °C) denote weighting coefficients in relation to the variations in the core and brain temperature elevations, respectively [25]. …”

“…The thermal parameters of the rat and human models were taken from [25,43], respectively. The heat transfer coefficient H was set to 0.5 W/(m 2 ·°C) between the skin and air, and 8.1 W/(m 2 ·°C) between lung and inner air in the rat model [7].…”

“…The reason for choosing frequencies above 3 GHz is that the whole-body-averaged SAR cannot be neglected at lower frequencies, making it difficult to discuss the local temperature elevation and its time course. The antenna–head separation for the rat model was only chosen at 5 mm to realize local exposures [7,17,25]. The length of the antenna was adjusted to half the wavelength of each frequency in free space.…”

“…In our previous studies, an integrated computational technique, combining electromagnetics and thermodynamics, was developed by incorporating a thermoregulatory response model based on measured values [7,25]. This study aims to clarify the difference of the temperature elevation and its time course between rats and humans exposed to local RF fields, which is important to estimate how conservative the current limits are for local exposure in the international guidelines/standards.…”