Study on SARs in Head Models With Different Shapes by Age Using SAM Model for Mobile Phone Exposure at 835 MHz

Four head models with the outer shapes of different ages were established using the specific anthropomorphic mannequin (SAM) model of IEEE Standard 1528. The criteria of head height, face length, head length, and head breadth by age were applied to build the models. We assumed that the shells of all the head models have the same dielectric properties with the head-equivalent tissue in order to simulate a real pressed ear. The cheek and tilt positions of three bar-type phone models were used, and the positioning processes against each head model were described in detail. Antenna input impedances of the phones under the test positions and specific absorption rate (SAR) distributions in the head models were computed using the finite-difference time-domain (FDTD) technique. Spatial peak SARs averaging over 1 and 10 g were compared for fixed input and radiated powers of all the phones. The effect of the dielectric properties in a younger head model on SAR result was analyzed. First, input resistance of the phone antennas in the cheek position gradually increased when head size grew with age, but those for the tilt position showed a slight decrease. Second, for a fixed input power, the head models by age changed peak 1- and 10-g SARs by approximately 15%. The electromagnetic absorption depths in the head models in the same test position were about the same, but the head-averaged SAR was higher in the younger model because of the smaller head volume. Third, for a fixed radiated power, the peak SARs got relatively lower in the smaller head model and higher in the larger head model, compared with those for the fixed input power since the smaller head model needs lower input power. Fourth, it was shown that simultaneous change in the conductivity and permittivity of head tissue within 20%-30% did not have a significant influence on energy absorption.