The microwave auditory effect, also known as the microwave hearing effect or the Frey effect, consists of audible clicks induced by pulsed/modulated microwave frequencies. The clicks are generated directly inside the human head without the need of any receiving electronic device. The effect was first reported by persons working in the vicinity of radar transponders during World War II. In 1961, the American neuroscientist Allan H. Frey studied this phenomenon and was the first to publish information on the nature of the microwave auditory effect.
Pulsed microwave radiation can be heard by some workers; the irradiated personnel perceive auditory sensations of clicking or buzzing. The cause is thought to be thermoelastic expansion of portions of the auditory apparatus. Competing theories explain the results of interferometric holography tests differently.
The first American to publish on the microwave auditory effect (MAE) was Allan H. Frey. Frey's Human auditory system response to modulated electromagnetic energy appeared in the Journal of Applied Physiology in 1961. In his experiments, the subjects were discovered to be able to hear appropriately pulsed microwave radiation, from a distance of a few inches to hundreds of feet from the transmitter. In Frey's tests, a repetition rate of 50 Hz was used, with pulse width between 10–70 microseconds. The perceived loudness was found to be linked to the peak power density instead of average power density. At 1.245 GHz, the peak power density for perception was below 80 mW/cm2. According to Frey, the induced sounds were described as "a buzz, clicking, hiss, or knocking, depending on several transmitter parameters, i.e., pulse width and pulse-repetition rate". By changing transmitter parameters, Frey was able to induce the "perception of severe buffeting of the head, without such apparent vestibular symptoms as dizziness or nausea". Other transmitter parameters induced a pins and needles sensation. Frey experimented with nerve-deaf subjects, and speculated that the human detecting mechanism was in the cochlea, but at the time of the experiment the results were inconclusive due to factors such as tinnitus.
Auditory sensations of clicking or buzzing have been reported by some workers at modern day microwave transmitting sites that emit pulsed microwave radiation. Auditory response to transmitted frequencies from approximately 200 MHz to at least 3 GHz has been reported. The cause is thought to be thermoelastic expansion of portions of auditory apparatus, and the generally accepted mechanism is rapid (but minuscule, in the range of 10−5 °C) heating of brain by each pulse, and the resulting pressure wave traveling through skull to cochlea.
In 1975, an article by neuropsychologist Don Justesen discussing radiation impacts on human perceptions referred to an experiment by Joseph Sharp and Mark Grove at the Walter Reed Army Institute of Research during which Sharp and Grove reportedly were able to recognize 9 out of 10 words transmitted by "voice modulated microwaves". Since the radiation levels approached the (then current) 10mW/cm² limit of safe exposure, critics have observed that under such conditions brain damage from thermal effects of high power microwave radiation would occur, and there was "no conclusive evidence for MAE at lower energy densities".
In 2003–04, the WaveBand Corp. had a contract from the U.S. Navy for the design of a MAE system they called MEDUSA (Mob Excess Deterrent Using Silent Audio) intended to remotely, temporarily incapacitate personnel. Sierra Nevada Corp. reportedly took over the contract from Waveband. Experts, such as Kenneth Foster, a University of Pennsylvania bioengineering professor who published research on the microwave auditory effect in 1974, have discounted the effectiveness of the proposed device. Foster said that because of human biophysics, the device "would kill you well before you were bothered by the noise". According to former professor at the University of Washington Bill Guy, ”There’s a misunderstanding by the public and even some scientists about this auditory effect," and "there couldn’t possibly be a hazard from the sound, because the heat would get you first".
Numerous individuals suffering from auditory hallucinations, delusional disorders or other mental illness have claimed that government agents use forms of mind control technologies based on microwave signals to transmit sounds and thoughts into their heads as a form of electronic harassment, referring to the technology as "voice to skull" or "V2K".
There are extensive online support networks and numerous websites maintained by people fearing mind control. California psychiatrist Alan Drucker has identified evidence of delusional disorders on many of these websites and other psychologists are divided over whether such sites reinforce mental troubles or act as a form of group social support.
Psychologists have identified many examples of people reporting 'mind control experiences' (MCEs) on self-published web pages that are "highly likely to be influenced by delusional beliefs". Common themes include "Bad Guys" using "psychotronics" and "microwaves", frequent mention of the CIA's MKULTRA project and frequent citing of a scientific paper entitled "Human auditory system response to modulated electromagnetic energy