Specific Absorption Rate assessment using an Electro-Optic Probe

International audienceSince the nineties, the development of wireless telecommunication systems has been greatly enhanced. As a consequence, studies on the potential effects of radiofrequency (RF) electromagnetic fields (EMF) on human body have acquired considerable attention [1]. For the quantification of the absorbed power in the biological media, i.e. the dosimetry, the Specific Absorption Rate (SAR) has become the reference parameter. The SAR can be obtained either from the electric field or from the temperature variation induced by the interaction between the EMF and the biological medium. This study concerns SAR assessment via temperature measurement using a new minimally invasive electro-optic (EO) probe able to simultaneously measure one component of the electric field and temperature variation [2]. Materials and Methods The experimental setup for SAR assessment is presented in Fig. 1. The setup is composed of a continuous-wave (CW) RF signal generator (HP8648C) at 1800 MHz and a power amplifier (RFPA) which are connected to the exposure system, i.e. a transverse electromagnetic (TEM) cell containing a Petri dish. In order to check the good impedance matching of the exposure system within the setup, the incident and reflected powers (Pin and Pref respectively) are real-time monitored. The 16.1-mm-long EO probe is horizontally inserted in the Petri dish filled with 3 ml of buffered salt solution (σ = 1.7 S/m, εr = 80 at 1800 MHz) which is placed in the TEM cell. A Plexiglas holder fixes the optical fiber and the crystal orientation. The 1.8-mm-diameter crystal, which is the sensitive part of the probe, is 7.1 mm long. During the exposure, temperature data measured in the center of the Petri dish are acquired on a PC at eight samples per second, using a LabVIEW® in-house made program. The electric-field measured with the EO probe is isplayed using a spectrum analyzer (R&S FSP) which is connected to the servo control system. The EO probe has been characterized in terms of linearity, dynamics and selectivity [3]. To ensure the solution temperature stabilization before starting the exposure, the RF generator is switched on after 5 minutes of temperature acquisition. After 35 minutes of exposure, the RF generator is switched off. The input power (Pin) is set to 40 dBm. Fig. 1 : Experimental setup; Pinc: incident power, Pref: reflected power, Pout : output power. (Top view