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Radio Science

A microwave exposure system for primates

Authors

  • Louis N. Heynick,

  • Peter Polson,

  • Arthur Karp


Abstract

Development of a system for exposing nonhuman primates of sizes to and including stumptail macaques (Macaca arctoides) at 2.45 GHz for long periods without constraining the animals (except for cage confinement) is described. The exposure chamber is a multimode mode-stirred cubical microwave cavity of edge length about 90 cm internally; within the cavity is a dielectric cage sufficiently large to house a 15-kg primate. The cavity is excited by a Type 2M53 magnetron. Radiopaque windows are provided for viewing and ventilation. Forward and reflected powers are measured with calibrated diode detectors in a bidirectional coupler between the magnetron and the cavity. Power values are set by phase-angle selection and are held constant by detector-output feedback to a thyristor control circuit. Containers of saline were used as phantoms, i.e., as first approximations to the RF loads presented by monkeys. Calorimetric measurements were made to determine energy absorption values for various quantities and spatial distributions of saline. The results indicate that the dose rate at any given input power is insensitive to phantom location (indicative of isotropy) and is inversely related to the mass of saline within. After the development of the prototype, 12 units were constructed for concurrent chronic irradiation of two squirrel monkeys in each module. A summary is presented of calorimetric measurements on saline-containing dolls serving as phantoms; these measurements were performed to determine net values of RF input power into a cavity unit that are thermally equivalent to specified power-density values of plane-wave irradiation for the same duration of exposure.

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