Field and Temperature Gradients from Short Conductors in a Dissipative Medium

Abstract

This paper considers the specific absorption rate (SAR) in tissue of radiofrequency (RF) energy and temperature increases produced by RF currents on short conductors (0.03–0.1λ). We consider a cylindrical model in which a center-feeds, insulated antenna is embedded in tissue. We introduce a new method for the analytic evaluation of the fields in the cylindrical phantom taking advantage of the axial symmetry of the antenna and the tissue. Results of the analytical model are compared to results of numerical (finite difference time domain) simulations; in addition, the thermal response of the exposed material is calculated by finite element solution of the heat conduction equation. For model antennas of 1 to 3 cm total length with a feedpoint current of 10mA RMS at 900MHz, the maximum SAR (in tissue next to the antenna) is less than ∼2.5W/kg. SAR decays rapidly with radial distance from the antenna (∼r−4 for the 1cm antenna) and creates a steady-state temperature rise less than 0.05K at the location of SARmax. Heat conduction causes the temperature to decline steeply with radius (depth into tissue).