Journal of Microwave Power and Electromagnetic Energy (JMPEE)
TITLE	Biological Effects of Microwave Exposure – An Overview [PDF]
AUTHORS	S. M. Michaelson 1971 6 3 259-268
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Abstract In October, 1968 the U.S. Congress passed, and former President Johnson signed, Public Law 90-602, The Electronic Products Control Law. To carry out the provisions of this law the Bureau of Radiological Health (BRH) of the United States Public Health Service was given the responsibility of setting standards and maintaining surveillance over all electronic products that may emit hazardous levels of electromagnetic radiation. In addition to the problem of ionizing radiation, a very large area of concern involves exposure to microwaves. The exact nature of the biologic effects of microwaves is not completely understood. Although most of the experimental data support the concept that the effects of microwave exposure are primarily a response to local or general hyperthermia, there are large areas of confusion, uncertainty and actual misinformation. This paper reviews the present state of knowledge on biologic effects of microwaves and attempts to (1) differentiate between the known and substantiated from the speculative and unsubstantiated effects and (2) provide a realistic perspective on the nature of microwaves and the possible effects of exposure to this form of energy. Unless this is done, the tremendous potential of electromagnetic energy in the microwave range for Radar, communications, biomedical, industrial, and consumer use and applications will be hampered. According to the best evidence available, the most important effect of microwave absorption is the conversion of the absorbed energy into heat. Exposure of various species of animals to whole body microwave radiation at levels of 100 mW/cm² or more is characterized by a temperature rise which is a function of the thermal regulatory processes and active adaptation of the animal. The end result is either reversible or irreversible change depending on the conditions of the irradiation and the physiologic state of the animal. The thermal response induced by microwave exposure in an animal with thermal regulatory capability comparable to that of man (such as the dog) is characterized by three phases (a) initial thermal response, (b) period of thermal equilibrium and (c) period of thermal breakdown. In areas in which relatively little blood circulates, the temperature will rise considerably since there is little means for the interchange of heat. Consequently, tissue damage is more likely to occur in those areas where proportionately a greater rise in temperature can occur. Thus the lens of the eye and testes are readily susceptible to thermal damage, since these organs do not posses an adequate vascular system for the exchange of heat. The greatest need today in the assessment of Biological Effects of Microwave exposure is to maintain a realistic perspective on the nature of microwave fields and the possible effects from exposure. The mechanisms by which cell damage is produced, the biological tolerance of the most susceptible tissues and safe levels of intensity must be established in an organized fashion. Ultimately, a clear differentiation between hazard and biologic effect must be made.