Microwave auditory effect

The microwave auditory effect, also known as the microwave hearing effect or the Frey effect, consists of the human perception of sounds induced by pulsed or modulated radio frequencies. The perceived sounds 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. The cause is thought to be thermoelastic expansion of portions of the auditory apparatus, although competing theories explain the results of holographic interferometry tests differently.

Research in the U.S.

Allan H. Frey was the first American to publish on the microwave auditory effect (MAE). 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.