Date of Award

Spring 2005

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Computational Analysis and Modeling

First Advisor

Weizhong Dai

Abstract

Short duration, fast rise time ultra-wide-band (UWB) electromagnetic pulses (“nanopulses”) are generated by numerous electronic devices in use today. Moreover, many novel technologies involving nanopulses are under development and expected to become widely used soon. Study of nanopulse bioeffects is needed to probe their useful range in possible biomedical and biotechnological applications, and to ensure human safety.

Based on the well-known dispersive properties of biological matter and their expression as a summation of terms corresponding to the main polarization mechanisms, the Cole-Cole expression is commonly employed to describe the frequency dependence of the dielectric properties of a tissue. Solving the Maxwell's equations coupled with the Cole-Cole expression, however, is difficult because it is not easy to convert the equations from the frequency domain to the time domain.

In this work we develop a computational approach to investigating electromagnetic fields in biological matter exposed to nanopulses, where the relative dielectric constant is given by the Cole-Cole expression for the frequency dependence of the dielectric properties of tissues. The Cole-Cole expression is first transformed to the z-domain using the z-transform method and then approximated by a second-order Taylor series of variable z. After converting the result from the frequency domain to the time domain, the finite-difference time-domain method (FDTD) is used to solve Maxwell's equations coupled with the Cole-Cole expression, and a perfectly matched layer is applied to eliminate reflections from the boundary.

The method is then applied to investigating the penetration of a short electromagnetic pulse into biological matter, where the relative dielectric constant is given by the Cole-Cole expression. Transmission, reflection, and absorption are calculated as a function of pulse width. It is found that these properties depend substantially on pulse characteristics.

Future work in this direction could be examining the relevance of pulse rise time and pulse shape to tissue penetration. Such study could help to elucidate non-thermal mechanisms of nanopulse bioeffects.

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