FDTD analysis of human head-mobile phone interaction in terms of specific absorption rate calculations and antenna design

In this study, the finite-difference time-domain (FDTD) method is used to model mutual effects of a mobile phone and a human head in terms of both biological effects and antenna design. A discrete human head model and a hand-held receiver with various antennas mounted on top of it, are located within a three dimensional (3D) FDTD algorithm is built in Cartesian coordinates. Near fields are simulated directly in the time domain for both sinusoidal and pulse type antenna excitations. The antenna power, input impedance, absorbed power and the specific absorption rate (SAR) distribution inside the head near the hand-held receiver are calculated for various antenna types and human head/hand-held receiver locations. The simulations are carried out for both European GSM and DECT systems (at 900 and 1800 MHz, respectively). The SAR distributions for various vertical and horizontal slices of the head are calculated and are shown to agree with the available calculation and measurement results. Besides, the effects of the human head on the antenna radiation pattern are calculated where far field simulations are obtained via a time-domain near-to-far-field (NTFF) transformation based on Huygen's principle. Various hand-held receiver antennas, including a quarter-wavelength wire, IFA, PIFA, symmetrical and asymmetrical square or rectangular printed loops, are investigated in terms of their radiation pattern, gain and efficiency. Different antenna mountings are used and their effects to both antenna performance and SAR distribution in the head are shown.