APPLICATION OF FINITE DIFFERECE TIME DOMAIN METHOD IN FREQUENCY DISPERSIVE MEDIA

Abstract

With the rapid increase in the use of portable telephones, public concern regarding potential health hazards due to the absorption of electromagnetic (EM) energy emitted by these telephones has been growing. The main objective of this work is to introduce a detailed analysis regarding the incorporation o f the various dispersive models into the FDTD method. The FDTD method is reliable and common in use in modeling human body. Unfortunately, the electrical properties of the head materials vary significantly with frequency. The FDTD method using the nonnally constant electric properties fails to cover this subject for wide-band signals so that, there is a need to incorporate these variations into the FDTD method. In general the dielectric properties of the dispersive materials can be modeled either by the Debye, the Lorentz or the Cole­ Cole models for dispersive media. These models result in a good fitting with the measured data. However the Cole-Cole model gives a better physical modeling to the measured data than that of the Debye model. The incorporation of the dispersive media into the FDTD method is always a challenging task. Different authors attempt to treat both the D ebye and the Lorentz models within the F DTD codes, but very little attempts were done toward the Cole-Cole model. Most of workers attempt to convert the Cole-Cole model to the Debye model; in order to be able to treat it with the FDTD method. In this work, a development of the FDTD method is introduced for the analysis of the scattering in dispersive media using the Debye, Lorentz and Cole-Cole model for dispersive media. Those analyses are performed for the scattered and the total field formulation. As an application to these analyses, the scattering of an incident plane wave in the presence of a half space dispersive media is calculated for the Debye, Lorentz and the Cole-Cole models. Another application is the scattering due to the human head in the presence of a radiating dipole. The head model is based on the magnetic resonance images (MRI) while its materials are expressed by the Cole-Cole model. The SAR distribution inside the head is examined. This work is important in predicting the SAR levels with the human head due to the electromagnetic field exposure from Mobile phones.