The Frey Effect

In 1961, Allan Frey was working as a biophysicist at the General Electric Advanced Electronics Center when a technician at a radar installation told him something unusual. The technician said he could hear the radar. Not through the air. Not through vibration in the floor. He could hear it inside his head, as a clicking or buzzing that appeared when the radar was on and stopped when it was off.

Frey investigated. He published his findings in the Journal of Applied Physiology in 1962 under the title "Human Auditory System Response to Modulated Electromagnetic Energy." The paper described a real, reproducible phenomenon: pulsed microwave energy, at power levels that produced no measurable heating of tissue, was being perceived as sound by human subjects. The sound appeared to originate inside the skull. It bypassed the ear entirely.

The military classification of subsequent research on the effect began almost immediately after publication.

The mechanism Frey identified, later confirmed by other researchers, works through thermoelastic expansion. When a pulse of microwave energy is absorbed by tissue, the rapid heating of the water content in that tissue causes a tiny, instantaneous expansion. That expansion produces a pressure wave. The cochlea, which transduces pressure waves into neural signals, detects the wave and sends the corresponding signal to the auditory cortex. The brain interprets it as sound.

The process requires no conventional acoustic pathway. The sound does not travel through air to the ear. It is generated directly within the tissue of the head, at the cochlea or nearby structures, by the electromagnetic pulse itself. A person in a room with no audible sound, in conditions of complete acoustic silence, will hear a sound if a properly configured microwave pulse is directed at their head.

The power levels required to produce the effect are low. Frey documented the effect at power densities well below what safety standards of the period identified as hazardous. The perception threshold for the effect, the minimum power density at which subjects began reporting auditory phenomena, was substantially lower than the thermal safety threshold. The gap between those two numbers is where the effect's practical implications become significant.

Frey's 1962 paper attracted immediate attention from military research programs. He subsequently received funding from the Office of Naval Research and other defense agencies to continue his investigation. Some of the research he conducted under those funding arrangements was published. Some was not.

Frey has stated in interviews that he was approached by government researchers who asked him to keep certain findings out of publication. He has described being told that specific results were classified before he could submit them for peer review. The specific findings that were withheld and the programs that classified them have not been identified in any publicly available document.

What is documented is the trajectory of published research on the effect. Publications on the Frey effect appeared regularly through the 1960s and into the 1970s, then slowed significantly. The slowdown coincides with the period when Project PANDORA, the classified US research program studying the Moscow Signal, was most active. Whether the two research tracks were connected by classified information sharing is not established in any available record.

The basic Frey effect produces clicks, buzzes, and hissing. With pulse modulation, it can produce more complex sounds. Researchers demonstrated in the 1970s that by varying the pulse parameters, recognizable audio content could be transmitted directly into a subject's head without any speaker or acoustic device. The subject would hear words or tones that no one else in the room could detect.

The implications of that capability are specific. A device using the Frey effect could transmit audio content to an individual that no one nearby could hear, detect, or attribute to a physical source. The subject would have no way to determine where the sound was coming from or whether others were hearing the same thing. At higher power levels or with extended exposure, the effect produces headache, disorientation, and the pressure sensations reported by Havana Syndrome patients.

Whether a weaponized Frey effect device has been developed and deployed is not established in any publicly available document. The physics required to build one are straightforward. The effect was documented in 1962. Sixty years of classified military research have occurred since then. What that research produced has not been disclosed.

When the National Academies of Sciences, Engineering, and Medicine assessed Havana Syndrome in 2020, they identified pulsed radio frequency energy as the most plausible explanation for the reported symptoms. The Frey effect is the mechanism by which pulsed radio frequency energy produces the specific symptom profile described by affected personnel: sudden onset of pressure in the head, perception of sound with no identifiable source, and immediate cognitive disruption.

The Havana Syndrome patients described hearing a sound that seemed to come from a specific direction and stopped when they moved away from a particular location. That directionality and location-specificity are consistent with a focused beam source. The Frey effect, produced by a directed beam, would present exactly that way to the person experiencing it.

The National Academies did not identify a specific device or a specific perpetrator. They identified a mechanism that had been documented in peer-reviewed literature since 1962, that had been the subject of classified military research since shortly after that publication, and that matched the symptom profile of over 1,000 US government personnel injured across 90 countries over a period of years.

Allan Frey gave interviews in the years following the Havana Syndrome disclosures in which he described his understanding of how his research had been used. He stated that the effect he documented in 1962 was sufficient to explain the Havana Syndrome symptoms. He stated that the technology required to produce those symptoms had existed for decades. He described his experience of having research results classified before publication and his frustration at not being able to discuss specific findings.

Frey died in 2021. The classified research conducted under the programs he contributed to has not been released. The full scope of what military research on the Frey effect produced between 1962 and the present is not in the public record.

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A biophysicist published a paper in 1962 describing a real, reproducible phenomenon: pulsed microwaves produce sound inside the human head without going through the ear. The military classified subsequent research on the effect almost immediately. Sixty years passed. Over 1,000 US government personnel reported hearing unexplained sounds accompanied by pressure, disorientation, and neurological injury. The National Academies identified the 1962 mechanism as the most plausible explanation. The research conducted on that mechanism in the intervening six decades is not in the public record.