Biological Effects of Microwaves: Thermal and Nonthermal Mechanisms*

For over sixty years, it has been reported that microwave electromagnetic radiation (EMR) had effects on humans which could not be explained by detectible heating of tissue. Auditory responses to radar, called microwave hearing, have been the best known of these phenomena. To account for microwave hearing, many studies in the literature have adopted a rate-of-heating hypothesis advanced by Foster and Finch in 1974. We show here that theoretical and experimental studies supporting this hypothesis are weaker than usually assumed. We develop a simple framework of understanding of EMR that may be used to explain microwave hearing as a nonthermal, nonacoustic effect. We then extend this approach to other contexts, pointing out several fundamental misconceptions confounding the field. EMR, especially wide-band EMR, primarily must have a nonthermal effect on living tissue before conversion to heat. Auditory and tactile sensations, central neurological disability, and blood pressure loss caused by EMR have been documented. Except microwave hearing, parameters of irradiation causing such effects have not been explored adequately and remain unknown. There appears not to be any forensic methodology to prove the cause of harm at nonthermal levels.