The finite-difference time-domain method as applied to the dosimetry of mobile telephones.

摘要

Cellular telephones have been introduced into society at a very rapid rate. This has resulted in public concern about the possible health hazards associated with the use of these devices. Several safety guidelines, therefore, have been proposed for compliance testing of induced electromagnetic fields in the human body in terms, usually, of specific absorption rates of power or SARs. In this dissertation we have used the Finite-Difference Time-Domain (FDTD) method for the analysis of the interaction of hand-held devices and the human head and for compliance testing of cellular telephones. Effects of the variation of the dielectric properties of human tissues and human head size on the SAR distribution have been considered. To simulate realistic positions of a person holding a cellular telephone, a new technique to rotate the model of the human head derived from Magnetic Resonance Imaging (MRI) scans with six degrees of freedom has been developed. This has allowed us to consider the two realistic postures of the head vis a vis the handset which is kept vertical to avoid the staircase approximation in its modeling. The two postures of the head are: tilted forward by 30 degrees, and tilted forward by 30 degrees with a further rotation of 9 degrees toward the mouthpiece of the telephone. In order to reduce the the large amount of computer memory required for these simulations, we have developed a new truncation technique that results in savings of more than 50% of computer memory with less than 1% error for most of the cases.; An accurate modeling of several antennas commonly used for mobile telephones has also been considered. A new technique to model helical antennas and helix-monopole antennas has been developed and tested against near- and far-field measurements of EM fields.; The influence of the new Perfectly Matched Layer (PML) boundary condition on these simulations has been considered. A new approach to optimize the performance of the PML boundary condition has also been developed and used.; Accuracy of the results has been validated by comparing SARs, radiation patterns, and near field computations with measurements performed at the University of Utah or provided by the manufacturer. Lastly, new directions of research toward the development of low SAR, high radiation efficiency, patch antennas are suggested.