Microwave acoustic effect

The microwave acoustic effect may be defined as the auditory perception of microwave radiation which is a form of electromagnetic energy which occupies the part of spectrum between ordinary radio waves and infrared and optical waves. This definition may... 

There are three widely accepted routes by which bone-conducted sound stimulates the cochlea. These are the compres-sional, inertial and osseotympanic theories of bone conduction (12). Compressional bone conduction implies that the cochlear shell is compressed slightly in response of the pressure variation caused by a sound. Inertial bone conduction alludes to a relative motion between the ossicular chain and the temporal bone for low frequency vibrations. The osseotympanic theory denotes a mechanism by which relative movement of the skull, with respect to the mandible, sets up pressure variation in the air present in the auditory meatus. Since perception of microwave pulses are correlated with the capacity to hear high-frequency sound, it rules out inertial or osseotympanic bone conduction as potential mechanisms for microwave acoustic effect. 

A vast amount of electrophysiological evidence has accumulated over the past several years demonstrating that auditory responses to microwave pulses are similar to those evoked by conventional acoustic pulses (6,7, U, 13,1 A, 15). Furthermore, they show that microwave acoustic effect is mediated by an electromechanical interaction which is initiated outside or at the cochlea. An alternative hypothesis involves direct stimulation of the cochlear nerve or neurons at higher levels along the auditory pathway. This latter mechanism is probably not at work as I shall presently demonstrate. 

The results presented demonstrate that auditory systems of animals and humans respond to pulsed microwaves. However, there is little likelihood of the microwave acoustic effect arising from direct interaction of microwave pulses with the cochlear nerve or neurons at higher structures along the auditory pathway. The pulsed microwave energy, instead, initiates a thermoelastic wave of pressure in the head that travels to the cochlea and activates the hair cells in the inner ear. This theory covers many experimental observations, but it may be incomplete and thus require further extension to account for certain additional experimental findings. Tyazhelov, et al. (1 1) found in their beat frequency experiment that matching of microwave pulses (10 ps, 8000 pps) to a phase-shifted 8 kHz sinusoidal sound input... 

One strength of the theory is that it stimulates new questions and permits a more precise statement of new problems. The thermoelastic mechanism is apparently adequate to characterize the acoustic effect occurring in heads of humans and animals exposed to pulsed microwaves. The precise location in the head (scalp, skull or brain) microwave pulses are transformed into the acoustic wave of pressure however is at present not specifiable. Several speculations can be advanced, but there is little direct physiological data that would identify the possible gross tissue structures involved. Clearly, this is an area still requiring study. 

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