Advances in Radio Science www.adv-radio-sci.net 1684-9965 1684-9973 5 Kleinheubacher Berichte 2006 2007 10.5194/ars-5-189-2007 http://www.adv-radio-sci.net/5/189/2007/ http://www.adv-radio-sci.net/5/189/2007/ars-5-189-2007.html http://www.adv-radio-sci.net/5/189/2007/ars-5-189-2007.pdf 189 195 2007-06-13 Radiation characteristics of a coaxial waveguide with eccentric inner conductor for application in hyperthermia and microwave reflex therapy R. Herschmann herschmann@hft.uni-hannover.de O. Büchel Leibniz Universität Hannover, Institute of Radiofrequency and Microwave Engineering, Appelstraße 9a, 30167 Hannover, Germany Smart Devices GmbH & Co. KG, Schönebecker Allee 2, 30823 Garbsen, Germany Fuba Automotive GmbH & Co. KG, Tec Center, 31162 Bad Salzdetfurth, Germany This paper examines the radiation characteristics of a contact emitter conceived for application in hyperthermia and microwave reflex therapy. It is important to analyse the distribution of power density in the near field area, as the radiator's therapeutic sphere of activity is localized here. The contact emitter is a coaxial radiator with an eccentric course of the inner conductor. According to Huygens principle, a theoretical view of the near field radiation characteristics is made by determining the equivalent current densities in the emitter aperture. It is shown that by an eccentric shift of the inner conductor, an almost isotropic near field radiation pattern and power density can be achieved. For this, the electromagnetic field in the emitter aperture is determined by using a Bipolar coordinate system. This calculation considers only the fundamental TEM mode of the contact emitter. Besides the theoretical results near and far fields are simulated using the programme system Ansoft HFSS. Bakhtiari, S., Ganchev, S. I., and Zoughi, R.: Analysis of radiation from open-ended coaxial line into stratified dielectrics, IEEE Transaction on Microwave Theory and Techniques, 42, 1261–1267, 1994. Kalantaewskaja, K. A.: Morphologie und Physiologie des Hautgewebes, Moskau, Medizin-Verlag, 1972. Maloney, J. G., Smith, G. S., and Scott, W. R.: Accurate computation of the radiation from simple antennas using the finite-difference time-domain method, IEEE Transactions on Antennas and Propagation, 38, 1059–1068, 1990. Mosig, J. R., Besson, J. C. E., Gex-Fabry, M., and Gardiol, F. E.: Reflektion of an open-ended coaxial line and applikation to nondestruktive measurement of materials, IEEE Transactions on Instrumentation and Measurement, 30, 46–51, 1981. Murray, R.: Handbuch für Mathematik, New York, McGraw - Hill, 1979. Nevels, R. D., and Wheeler, J. E.: Radiation from a dielectric coated hemispherical conductor fed by a coaxial transmission line, IEEE Transactions on Electromagnetic Compatibility, 31, 16–20, 1989. Rossetto, F., Diederich, C. J., and Stauffer, P.: Thermal an SAR characterization of multielement dual concentric conductor microwave applicators for hyperthermia, a theoretical investigation, Medical Physics, 27, 4, 2000. Stauffer, P., Rossetto, F., Leoncini, M., and Gentilli, G. B.: Radiation Patterns of Dual Concentric Conductor Microstrip Antennas for Superficial Hyperthermia, IEEE Transaction on Biomedical Engineering, 45, 5, 1998. Stuchly, M. A. and Stuchly, S. S.: Coaxial line reflection methods for measuring dielectric properties of biological substances at radio and microwave frequencies – a review, IEEE Transactions on Instru-mentation and Measurement, 29, 176–183, 1980. Stuchly, M. A., Brady, M. B., Stuchly, S. S., and Gajda, G. B.: Equivalent circuit of open-ended coaxial line in a lossy dielectric, IEEE Transactions on Instrumentation and Measurement, 31, 116–119, 1982. Sumbar, E., Chute, F. S., and Vermeulen, F. E.: Implementation of radiation boundary conditions in the finite element analysis of eletromagnetic wave propagation, IEEE Transactions on Microwave Theory and Techniques, 39, 267–273, 1991.