This research is aimed towards the development of improved methods for time-domain simulations of EM propagation through inhomogeneous media such as human body tissue. A new time-domain method has been developed and implemented. The advantages of which include: 1) high accuracy, 2) high efficiency, 3) isotropic numerical dispersion error, 4) increased stability allowing larger time steps, and 5) straightforward implementation of PML absorbing boundary conditions.

Excitation of a Hertzian dipole field

This is novel because it allows a dipole excitation for an arbitrarily oriented dipole without incurring errors due to staircasing. Also, any number of dipoles may be excited via superposition.

SAR distributions

SAR distributions for the sagittal slice (scale is in dB)

SAR distributions for the frontal slice (scale is in dB)

SAR distributions for the coronal slice (scale is in dB)

A method of moments code was used to solve for the currents on a center-fed half wavelength wire antenna operating at 900 MHz. The resulting current elements are treated as a string of dipoles and were excited into the FDTD region using the Hertzian dipole excitation of the first Figure (excitation of a Hertzian dipole field). The above figures are specific absorption rate (SAR) distributions for the center-fed half-wavelength antenna next to a human head.


FDTD numerical dispersion error

The Figures show the comparison of the numerical dispersion error 1-w/kc as a function of propagation direction at 10 cells/wavelength for the Yee algorithm and the present algorithm.

Yee algorithm dispersion error

Present algorithm dispersion error

These figures come from a novel time-domain method that was developed in Eric Forgy's M.S. thesis. The title is "A Time-Domain Method for Computational Electromagnetics with Isotropic Numerical Dispersion on an Overlapped Lattice."


Total field/scattered fields for a plane wave

The following Figures show the total and scattered fields for a plane wave at 10 cells/wavelength with the optimized algorithm, the combined algorithm, and the Yee algorithm.

Total and scattered fields for the optimized algorithm

Total and scattered fields for the combined algorithm

Total and scattered fields for the Yee algorithm

The optimized and combined algorithms are from Eric Forgy's thesis. The bleeding of the fields from the total-field to the scattered-field region is a result of phase error as the wave propagates from front to back. The optimized algorithm has essentially no error, the combined algorithm has phase error but is a great improvement over the Yee algorithm.

The above work is a collaboration between Eric Forgy and Prof. Weng Cho Chew. Please send suggestions, comments, and inquiries to: forgy@students.uiuc.edu.