APPROXIMATION OF SURFACE-SAR IN A REALISTIC HEAD MODEL FOR MICROWAVE EXPOSURE USING EXTERNAL MAGNETIC NEAR-FIELD

A method is described for approximately estimating the surface specifi c-absorption-rate (SAR) in an anatomically realistic model of the huma n head for microwave exposure using the external magnetic near-field. The finite-difference time-domain (FD-TD) technique is used to compute the electromagnetic fields in the head model for 750-MHz and 1.5-GHz far-field exposures with the 1991 ANSI specified safety level. The spa tial pattern tracking between the one-gram averaged surface-SAR and ex ternal magnetic near-field is demonstrated on the horizontal cross sec tional perimeter of the head model. The regression coefficients betwee n them are also obtained on the fifty-five horizontal cross sectional perimeters, which could,give an approximate value of the surface-SAR i n an acutual head, if the external magnetic near-field would be measur ed. This is validated by the theoretical results in a semi-infinite ho mogeneous flat model for normal incidence microwave exposure.