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International Journal of Antennas and Propagation
Volume 2007 (2007), Article ID 57670, 8 pages
doi:10.1155/2007/57670
Research Article

Field and Temperature Gradients from Short Conductors in a Dissipative Medium

Quirino Balzano,1 Kenneth R. Foster,2 and Asher R. Sheppard3,4

1Department of Electrical and Computer Engineering, University of Maryland, College Park, 20742, MD, USA
2Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, 210 S. 33rd Street, Philadelphia 19104-6392, PA, USA
3Asher Sheppard Consulting, 108 Orange Street, Suite 8, Redlands 92373, CA, USA
4Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11021 Campus Street, Loma Linda 92350, CA, USA

Received 31 March 2007; Accepted 28 October 2007

Academic Editor: Charles Bunting

Copyright © 2007 Quirino Balzano et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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).