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A previously unreported oscillatory temperature response has been observed in canine thigh muscle subjected to an abrupt application of a constant specific energy absorption rate (SAR). The power was applied to anesthetized dogs (stage 3 plane of anesthesia) using 2,450-MHz microwaves. Five types of responses have been identified that have occurrences depending on the maximal temperature produced by the applied power. In particular, for SAR values resulting in sufficiently high initial temperatures, self-sustaining temperature oscillations lasting over 4 h have been observed with amplitudes up to 7 degrees C. The temperature oscillations are believed to be caused by oscillations in the local blood perfusion rate.

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The current sheet applicator is an electromagnetic heating device whose size may be chosen virtually independent of frequency even though practical limitations may restrict it to VHF and UHF bands. In this paper we investigate absorbed power distributions in muscle tissue from current sheet applicators when used as elements of a planar array intended for superficial hyperthermic treatment of tumours. Advantages offered by current sheet applicators for tissue heating include compact size, a linear polarization of the induced electric field and relatively large heating area. It is shown that the effective field produced by a pair of these elements is continuous regardless of whether the common edges of the elements are perpendicular or parallel to the direction of impressed current. The feasibility of customizing the shape and size of the field is also illustrated. The absorbed power distribution patterns due to a coherently driven array operating around 434 MHz is relatively insensitive to phase variations of about 20 degrees but is sensitive to relative power level variations as low as 10%. Mutual coupling between array elements may be reduced to acceptable levels by incorporating suitable spacing between them. It is also demonstrated that there is good agreement between measurements of absorbed power distributions and predictions using the Gaussian beam model.