A multi-grid finite-difference time-domain (FDTD) method was applied for numerical dosimetry analysis in the human head for 5 GHz band portable terminals. By applying fine FDTD grids to the volumes in the human head where the highest electromagnetic (EM) absorption occurs and coarse grids to the remaining volumes of the head, the spatial peak specific absorption rate (SAR) assessment was achieved with a less computation memory and time. The accuracy of applying the multi-grid FDTD method to the spatial peak SAR assessment was checked in comparison with the results obtained from the usual uniform-grid method, and then the spatial peak SARs for three typical situations of a person using a 5.2 GHz band portable terminal were calculated in conjunction with an anatomically based human head model.

This paper presents a dosimetric analysis in an anatomically realistic human head model for a helical antenna portable telephone by using the finite-difference time-domain (FDTD) method. The head model, developed from magnetic resonance imaging (MRI) data of a Japanese adult head, consists of 530 thousand voxels, of 2 mm dimensions, segmented into 15 tissue types. The helical antenna was modeled as a stack of dipoles and loops with an adequate relative weight, whose validity was confirmed by comparing the calculated near magnetic fields with published measured data. SARs are given both for the spatial peak value in the whole head and the averages in various major organs.

Analysis of the specific absorption rate (SAR) of a realistic head model generated with a 1.5-tesla MRI antenna is described. It is found that the SAR of the eyeball is strongly affected by the position of the feeding point, whereas the sensitivity of the antenna is virtually independent of the feeding point.

A method is described for approximately estimating the surface specific-absorption-rate (SAR) in an anatomically realistic model of the human 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 spatial pattern tracking between the one-gram averaged surface-SAR and external magnetic near-field is demonstrated on the horizontal cross sectional perimeter of the head model. The regression coefficients between them are also obtained on the fifty-five horizontal cross sectional perimeters, which could give an approximate value of the surface-SAR in an acutual head, if the external magnetic near-field would be measured. This is validated by the theoretical results in a semi-infinite homogeneous flat model for normal incidence microwave exposure.

Correlation between the surface-SAR and external magnetic near-field in a realistic head model for 1.5GHz microwave far-field exposure is described. The regression relation is shown between the one gram averaged SAR and squared external magnetic field on the cross sectional perimeter of the head model.