Ashley F. Emery’s research while affiliated with University of Washington and other places

Rabbits and monkeys were irradiated in the near field of a cavity-backed 2450 MHz resonant slot radiator, to determine the cataractogenic threshold. Rabbits developed cataracts at incident "apparent" power densities of 180 mW/cm2 (E2/120 pi, where E=rms/electric field strength). Monkeys sustained facial burns, but no lens damage, even at incident "apparent" power densities of 500 mW/cm2. These results were substantiated by computer thermal models.

Rabbits and monkeys were irradiated in the near field of a cavity-backed 2450 MHz resonant slot radiator, to determine the cataractogenic threshold. Rabbits developed cataracts at incident “apparent” power densities of 180 mW/cm2 (E2/120 π, where E == rms/electric field strength). Monkeys sustained facial burns, but no lens damage, even at incident “apparent” power densities of 500 mW/cm2. These results were substantiated by computer thermal models.

The human body was modeled by a finite difference numerical procedure to determine the effect of simulating the sweating rate by different analytical models. Six different models were used in which the hypothalamus, muscle, average skin, and local skin temperatures were used as the controlling parameters for the rate of local sweating. These different models were tested by comparing their predictions of local temperatures for an exercising man with measured values. The computer program was then used to compute the thermal response of a man subjected to microwave irradiation of the entire body and the head only. Transient head and body temperatures and sweating rates were computed and compared with the temperature changes due to an equivalent exercise level. Significant differences in the results found by using the different sweat models point out the need for further work in determining accurate analytical descriptions of this major mode of body heat loss.

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The cataractogenic effects of near-zone 2450-MHz radiation in rabbits are presented. The power deposition pattern inside the eyes and head of rabbits has been determined using a thermocouple technique. It was found that a peak absorption of 0.92 W/kg occurred between the lens of the eye and the retina for each milliwatt/square centimeter incident. Time and power-density studies indicated a cataractogenic threshold of a 150-mW/cm2 incident, or 138-W/kg peak absorption behind the lens for 100 min. The threshold time decreased with increasing power density. Agreement between in vivo intraocular temperature measurements and finite-element computer predictions reinforces the suggestion of a thermal mechanism for microwave-induced lens opacities.

Rabbits, irradiated by known cataractogenic levels of 2.45 GHz radiation at 5 cm, did not develop cataracts if kept under general hypothermia. Radiation-induced temperature elevation appears to be essential for the cataractogenic effect of microwaves.

Microwave power deposition patterns and temperature distributions were measured for rabbit eyes exposed to localized near zone 2450 MHz radiation and good agreement was obtained between the measured and predicted transient temperature fields. The lenses were biomicroscopically examined to determine the minimum exposure times necessary to produce posterior lens opacity (cataracts) and these times are correlated with the temperature calculations to suggest that a threshold temperature level exists.

The electromagnetic field and power patterns, both in and outside the rabbit's head and eye were established by special measurement techniques while the animals were exposed to a 2450 MHz diathermy 'C' director. These quantitative measurement techniques were extended to include animals exposed to a broad class of radiation sources such as corner reflectors, slots, cavities and horns.

Studies on the microwave cataractogenic effects have been going on for many years. Despite the multitude of published information on the mechanism and time and power density threshold, very few of these papers present sufficient quantitative results useful for the purpose of extrapolation to man and, subsequently, establishment of safe human exposure guides. The present project was designed to ascertain the conditions and mechanisms of cataract production in laboratory animals by microwave irradiation and to extrapolate quantitatively the animal results to human exposures to provide data for the establishment of realistic safety standards. This report describes incident and absorbed power relationships in animal eyes exposed to near zone 2450 MHz and 918 MHz radiation, threshold of cataracto-genesis, effect of general body hypothermia, chronic subthreshold exposure results, and a study of the induced temperature rises in the eye.