W-band investigation of material parameters, SAR distribution, and thermal response in human tissue

There are new applications in the automotive industry that make use of electromagnetic fields in the centimeter/millimeter-wave range, e.g., radar systems for adaptive cruise control. In this frequency range, only few data are available from the point of human safety and dosimetry. This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Afterwards the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm(2). In the third part of this investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a born antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7 degreesC for a power density of 10 mW/cm(2) and less than 0.1 degreesC for 1 mW/cm(2), both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.