Analysis of focusing of pulsed baseband signals inside a layered tissue medium

The derivation and application of a method designed to investigate the focu sing properties of pulsed baseband signals of short pulsewidth (similar to 1 ns) in biological tissue media are reported. To this end, sources fed fro m TEM waveguides, concentrically placed at the periphery of a three-layer c ylindrical lossy model, are assumed. A Fourier-series-based methodology, ap propriate for a useful class of pulse train incident signals, is presented and utilized to study the dynamics of pulse propagation inside the tissue m edium. The propagation of each spectral component of the incident field wit hin the tissue medium is analyzed by applying an integral-equation techniqu e and a Fourier-series representation is used in order to obtain the time d ependence of the electromagnetic fields produced at any point within tissue due to the pulsed excitation of the array elements. Numerical results are computed and presented at several points in a three-layer geometry, 20 cm i n diameter, irradiated by an eight-element waveguide array, Focusing at a s pecific point of interest within tissue is achieved by properly adjusting t he time delay of the signals injected to the individual applicators of the array.