Work will be continued on the improvement of dosimetric and exposure techniques in the 100 MHz - 10 GHz frequency range, including small animal, in vitro, partial human body and whole human body exposures. In addition, work on the circular waveguide that uses circular polarized TE11 mode for chronic exposure of small animals and illumination of in vitro cell culture preparations will be completed. The high power exposure system will also be completed and calibrated for exposing both full scale and phantom models of animals and scaled models of man, in order to quantify microwave coupling characteristics to various subjects over a wide frequency band. Once absorption characteristics are determined for the models, birds will be irradiated as described in the overall proposal, in order to show the relationship between the power absorption to thermal stress and other biologic effects as a function of body size and frequency. Research on the evaluation of various diathermy applicators, with the aim of providing more efficient coupling between a given laboratory generator and a region of the biological system where deposited energy is desired will be continued. In this regard, applicators will be developed for improving energy transfer to the CNS or the head of an animal so that studies relating pulsed microwave fields and auditory hearing phenomenon may be conducted at the neurophysiological level of analysis. Specifically, the frequency range at which pulsed microwaves are heard and the nature or mechanics of the transducer for the hearing of pulsed microwaves will be investigated. Finally, a major effort will be made in the coming year to evaluate power absorption patterns in human tissues exposed to current diathermy apparatus, and to relate these findings to current safety standards for human exposure.