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. These induced sounds are not audible to other people nearby. The microwave auditory effect was later discovered to be inducible with shorter-wavelength portions of the electromagnetic spectrum. During the Cold War era, the AmericanneuroscientistAllan H. Frey studied this phenomenon and was the first to publish (Journal of Applied Physiology, Vol. 17, pages 689-692, 1962) information on the nature of the microwave auditory effect; this effect is therefore also known as the Frey effect.
Research by NASA in the 1970s showed that this effect occurs as a result of thermal expansion of parts of the human ear around the cochlea, even at low power density. Later, signal modulation was found to produce sounds or words that appeared to originate intracranially. It was studied for its possible use in communications but has not been developed due to the possible hazardous biological effects of microwave radiation. Similar research conducted in the USSR studied its use in non-lethal weaponry.
The technology gained further public attention when a company announced in early 2008 that they were close to fielding a device called MEDUSA (Mob Excess Deterrent Using Silent Audio) based on the principle.
Natural sources of electromagnetic perception
For centuries, humans have reported hearing unexplained noises in conjunction with meteors including "thunder-like sounds" at the scene of the Tunguska event on June 30, 1908. Astronomer Edmund Halley collected several such accounts after a widely-observed meteor burned up in the sky over England . The Leonid meteor shower in November 2001 also led to many reports of observers hearing crackling or fizzing noises. Similar observations have been reported by soldiers near the site of nuclear explosions.
Colin Keay, a physicist at the University of Newcastle in Australia, has advanced a hypothesis that purports to explain these phenomena. According to Keay's theory, meteor trails give off very low frequency (VLF) radio signals that the human ear cannot sense directly but are heard because a transducer on the ground must be converting the radio waves into sound waves. He has produced experiments that demonstrate that materials as commonplace as aluminum foil, thin wires, pine needles, and wire-framed glasses can act as suitable transducers.
X-rays can induce visual effects. This was discovered in 1895 as reported by G. Brandes who saw a uniform blue-gray glow that scientists say is likely the result of direct excitation of retinal nerve cells.
Gamma rays were first reported to cause visual perception of flashes of light during the Apollo program. Astronauts en route for the Moon were subject to cosmic rays bombardments, inducing some Cherenkov effect in the fluid of their eyeballs.
The first American to publish on the microwave hearing effect was Allan H. Frey, in 1961. In his experiments, the subjects were discovered to be able to hear appropriately pulsed microwave radiation, from a distance of 100 meters from the transmitter. This was accompanied by side effects such as dizziness, headaches, and a pins and needles sensation.
F.A. Giori and A.R. Winterberger. "Remote Physiological Monitoring Using a Microwave Interferometer", Biomed Sci Instr 3: 291-307, 1967.
A.H. Frey and R. Messenger. "Human Perception of Illumination with Pulsed Ultrahigh-Frequency Electromagnetic Energy", Science 181: 356-8, 1973.
R. Rodwell. "Army tests new riot weapon", New Scientist Sept. 20, p 684, 1973.
A.W. Guy, C.K. Chou, J.C. Lin, and D. Christensen. "Microwave induced acoustic effects in mammalian auditory systems and physical materials", Annals of New York Academy of Sciences, 247:194-218, 1975.
D.R. Justesen. "Microwaves and Behavior", Am Psychologist, 392(Mar): 391-401, 1975.
S.M. Michaelson. "Sensation and Perception of Microwave Energy", In: S.M. Michaelson, M.W. Miller, R. Magin, and E.L. Carstensen (eds.), Fundamental and Applied Aspects of Nonionizing Radiation. Plenum Press, New York, p 213-24, 1975.
E.S. Eichert and A.H. Frey. "Human Auditory System Response to Lower Power Density Pulse Modulated Electromagnetic Energy: A Search for Mechanisms", J Microwave Power 11(2): 141, 1976.
W. Bise. "Low power radio-frequency and microwave effects on human electroencephalogram and behavior”, Physiol Chem Phys 10(5): 387-98, 1978.
J.C. Lin. "Microwave Auditory Effects and Applications", Thomas, Springfield Ill, p 176, 1978.
P.L. Stocklin and B.F. Stocklin. "Possible Microwave Mechanisms of the Mammalian Nervous System", T-I-T J Life Sci 9: 29-51, 1979.
H. Frolich. "The Biological Effects of Microwaves and Related Questions", Adv Electronics Electron Physics 53: 85-152, 1980.
H. Lai. “Neurological Effects of Radiofrequency Electromagnetic Radiation” In: J.C. Lin (ed.), Advances in Electromagnetic Fields in Living Systems vol 1, Plenum, NY & London, p 27-80, 1994.
R.C. Beason and P. Semm. "Responses of neurons to an amplitude modulated microwave stimulus", Neurosci Lett 333: 175-78, 2002.
J.A. Elder and C.K. Chou. "Auditory Responses to Pulsed Radiofrequency Energy", Bioelectromagnetics Suppl 8: S162-73, 2003.