Absorption of higher‐frequency RF energy by biological models: Calculations based on geometrical optics

Abstract

Theoretical calculations of absorption of radio‐frequency (RF) energy by appropriate models of man have heretofore failed to yield numerical results much beyond the first absorptive peak of whole‐body resonance. Current efforts are directed toward a better definition of whole‐body absorption at supraresonant frequencies. A method based on geometrical optics has been developed recently, and it was used by us to compute absorptive characteristics of a prolate spheroidal model of man to a high‐frequency limit. The technique approximates the surface of the prolate spheroid by small planar subareas. The energy being transmitted into each subarea is determined and is assumed to be completely absorbed due to the small depth of penetration of electromagnetic waves into lossy biological bodies in the supraresonant region. The total energy absorbed is found by summing over all subareas. Validity testing with Mie theory, in conjunction with consideration of the localization principle of geometrical optics, indicates that this technique is applicable to the model of man at frequencies beyond 6 GHz. Computer‐generated results for a 70‐kg prolate spheroidal model of man indicate that (1) the dependence of energy absorption on the incident wave's polarization and angle of incidence is markedly different from dependencies observed at lower frequencies; (2) the rate of energy absorption increases with frequency within the asymptotic limit; and (3) the use of simple planar models is inadequate to determine energy‐absorption characteristics of biological bodies at high RF frequencies.