ORIENTATIONAL AND FREQUENCY EFFECTS ON WHOLE ANIMAL ABSORPTION OF RF ENERGY

Abstract

A  parallel plate  waveguide (WG)  is used to determine wideband  (285-4000  MHz)  absorption characteristics of prolate spheroidal bodies of aspect ratios (alb) up to  and including 5.75 (the value taken for humans). The measurements are done for  E || a, H || a and K || a orientations, these corresponding to the major length  (2 a)  of  the body,  respectively, along the electric and magnetic fields and the propagation  vector. The validity of the method is checked by comparing the WG measurements  with those of free space irradiation and also from the correlation with Mie theory  of the absorption characteristics of biological-phantom spheres. For  96, 158, 261,  390  gm  rats in k II a orientation, maximum is observed at frequencies of  1217, 1020,  9C0  and  760  MHz, respectively. The frequencies of peak absorption and the values  thereat demonstrate  W ^-1/3  and W ^2/3  dependences, respectively, upon weight  W  of  the animal. Experiments with animals and prolate spheroids demonstrate a considerably   larger absorption in the E || a than in the H || a orientation, with k || a orientation  giving a value only slightly larger than that for H || a configuration. Peak absorption  in the E || a configuration occurs at a frequency such that ka = 0.75  to 1.0.  Maximum absorption for  k || a and H || a orientations occurs  at  successively higher  frequencies with ka for these frequencies on the order of a/2b.  RE absorption larger by an order of magnitude or more is found to occur at resonance for E || a than for  other orientations.