FDTD characterization of radiation patterns from flexible microstrip applicators

The FDTD numerical method has been used to calculate the radiation patterns from 915 MHz dual concentric conductor (DCC) applicators which were designed for use in superficial hyperthermia applications. Results are given for radiation from single 2 cm square apertures considering several different electromagnetic feed and tissue coupling configurations, and from multiple element arrays of six adjacent apertures. Radiated electric field distributions are expressed as specific absorption rate (SAR) patterns in a lossy muscle tissue load. The power deposition patterns are illustrated in planes 1 cm deep in tissue (e.g. just under the superficial tumor target) and in a vertical cross section plane cutting through the applicator and layered tissue load. The results demonstrate that when coupled with a 5 mm thick water bolus layer, the thin, flexible and lightweight planar DCC antennas produce effective heating out to the periphery of each aperture to a depth of approximately 1 cm in realistic tissue loads, and may be combined into arrays for relatively uniform heating of larger surface areas with >50% of maximum power deposition extending out to the perimeter of the array.