A 2450 Mhz Slab-Loaded Direct Contact Applicator with Choke
A Teflon-slab-loaded, direct contact microwave diathermy applicator has been developed. It produces minimal leakage radiation during effective heating of simulated planar tissue models. Because of TEM mode excitation, heating patterns are relatively uniform.
A comparative heating‐pattern study of direct‐contact applicators in microwave diathermy
Heating patterns, induced in planar and limb phantoms of simulated fat and muscle tissue by large and by small, direct-contact microwave diathermy applicators operating at 2.45 GHz, were studied. Teflon slab-loaded rectangular waveguides, circularly polarized horns, and other large radiators were investigated as well as the only two low-power direct-contact emitters presently in noninvasive clinical use. The integrity of temperature measurements by a thermographic camera was established and probe thermometry was used to compare polyethelene with a silk screen as the midplane phantom film. The width and depth of penetration of microwave heating were determined to evaluate energy deposition inside simulated muscle tissue. The results of temperature profiles show that a Teflon slab-loaded rectangular waveguide and a circularly polarized horn provide uniform heating in the center of the phantom's midplane and that the focusing effects of limb phantoms enhance depth of penetration. Measurements of the electric field demonstrated that direct-contact applicators can be designed to maintain leakage levels below 5 mW/cm2 per 100 watts of forward power for large applicators, and below 5 mW/cm2 per 10 watts of forward power for small applicators at a distance of 5 cm. Leakage of a circular aperture horn can be minimized with an output flange choke.
CONTRAST OF DOSE DISTRIBUTIONIN PHANTOM HEADS DUE TO APERTURE AND PLANE WAVE SOURCES *
Current microwave biologic effects research uses both aperture and plane wave sources. In this theoretic investigation, the dose rate (time rate of energy absorption per unit mass) patterns are compared between phantom heads irradiated by both microwave sources. Two brain tissue-equivalent spheres with radii of 3.3 and 7 cm are used to simulate monkey and human heads, respectively. In addition, a five-layered tissue-equivalent sphere is employed to simulate more closely the various tissues in a monkey head. Theoretic formulations of dose rate patterns in multi-layered tissue-equivalent spheres due to separate plane wave and aperture source treatments are derived from the summation of spherical harmonics technique. Calculations are made for the dose rate patterns along two cross-sectional planes and three rectangular axes in the spheres. The results of these calculations indicate variations in dose rate patterns for different sources and phantom head sizes. For aperture irradiation, microwave energy penetration into the phantom heads appears weak compared to the "hot spots" prominent in the plane wave exposure situation. It is concluded that for different radiation sources, direct comparison of biologic results by external field measurements as the only common denominator may not be dosimetrically valid. The results also indicate that for the same measured exposure rate (power density), the microwave energy absorption pattern in a human head may vary according to the type of radiation source.