Microwave Auditory Effect or Microwave Hearing Effect: The most generally accepted non-thermal effect of electromagnetic radiation


Microwave Auditory Effect: Why RADAR operators hear electromagnetic radiation as clicks


World authority in Microwave Hearing, Professor James Lin (Dept of Electr. Engineering, University of Illinois at Chicago), presents the Microwave Auditory phenomenon experimentally in this video



Figure 1: Experimental demonstration of microwave hearing by Professor James Lin.


The transcript of the video is provided below:


"Microwaves and other radio frequencies are known to affect the human body. But could they be responsible for voices in people's heads? In Chicago Illinois, a world authority on microwave hearing shows how it could work.


Prof. Lin: “ I am hearing a micropulse, like a click. Now, it sounds like a chirp… with a tonal quality to it." 


Professor James Lin is hearing sounds that aren't there. But he's not crazy. Pulses of microwave energy are being generated and fired at him from behind.


Prof. Lin: “Microwaves can be heard depending on the individual, depending on the hearing acuity of the individual. Individuals with fairly normal hearing can hear microwaves at quite a low-level.”


The energy of the absorbed microwaves causes brain tissue to very slightly heat up and expand causing a pressure wave to be picked up by the hearing mechanism in the inner ear. Professor Lin is far from hearing voices. But it could be possible to send coded signals to an agent this way.


Prof. Lin: “The brain is an electrical organ. It is susceptible to electrical signals since microwave is electrical. Therefore, in principle, one could embed or encode information in the microwave signal such that it could be perceived by the brain.”



Figure 2: Experimental demonstration of microwave hearing by Professor James Lin. Microwaves transmitted from rear. Two microwave pulses shown on the oscilloscope screen.





Discovery of the microwave auditory effect and subsequent study by Alan H. Frey


The phenomenon of RADAR operators hearing electromagnetic radiation as clicks, buzz, hiss, or chirps was first discovered in 1947 and was reported in 1956 by the Airborne Instruments Laboratory (cf. division of Cutler-Hammer), in the periodical Proceedings of the IRE (renamed in 1962 to Proceedings of the IEEE). The publication reference is provided below:


Airborne Instruments Laboratory (1956): An observation on the detection by the ear of microwave signals. Proc. IRE 1956. V. 44, No 10 (Oct). P. 2A.


Alan H. Frey, a biologist working at General Electric’s Advanced Electronics Center at Cornell University studied this effect which was termed Microwave Auditory Effect or Frey Effect. He is said to have interviewed the radar operators that reported it. A frequently cited publication by A.H. Frey is the following:


 1962 Jul;17:689-92.

Human auditory system response to modulated electromagnetic energy.




The publication is available at this link.


As mentioned at this site: "For the next two decades Frey, funded by the Office of Naval Research and the U.S. Army, was the most active researcher on the bioeffects of microwave radiation in the country. Frey caused rats to become docile by exposing them to radiation at an average power level of only 50 microwatts per square centimeter. He altered specific behaviors of rats at 8 microwatts per square centimeter. He altered the heart rate of live frogs at 3 microwatts per square centimeter. At only 0.6 microwatts per square centimeter, he caused isolated frogs’ hearts to stop beating by timing the microwave pulses at a precise point during the heart’s rhythm."





The microwave effect is due to rise in temperature and thermoelastic expansion of tissue followed by generation of pressure waves which travel to the inner ear's cochlea with subsequent auditory nerve activation


Professor James Lin (Dept of Electr. Engineering, University of Illinois at Chicago) who is considered a world authority in the microwave auditory effect, suggested three potential mechanisms for the effect:


1. Electrostriction

2. Radiation pressure

3. Thermoelastic stress


Based on his theoretical studies (Lin, 1976a,b - mentioned below), he concluded that the thermoelastic pressures would be one to three orders of magnitude greater than the other candidate mechanisms.


Lin JC. 1976a. Microwave auditory effect—a comparison of some possible transduction mechanisms. J Microwave Power 11: 77–81 

Lin JC. 1976b. Microwave induced hearing sensation: Some preliminary theoretical observations. J Microwave Power 11:295–298


He then proceeded to experimental studies to measure the thermoelastic pressures using a hydrophone. Similarly to a microphone which processes the pressure exerted by the sound waves of our voice on a membrane and converts pressure to electricity, a hydrophone converts the pressure waves generated in a liquid medium to electricity to provide a measurement value of pressure.  J. Lin and his colleagues used a hydrophone transducer (3 mm in diameter) which they implanted in the brains of cats, rats, and guinea pigs. The results (Olsen and Lin,1981, 1983; Su and Lin, 1987) showed sound/pressure frequencies that were in accordance with their predictions from the thermoelastic transduction theory. Below are their studies:



Olsen RG, Lin JC. 1981. Microwave pulse-induced acoustic resonances in spherical head models. IEEE Trans Microwave Theory Tech 29:1114–1117    Selected information presentation

Olsen RG, Lin JC. 1983. Microwave-induced pressure wave in mammalian brain. IEEE Trans Biomed Eng 30:289–294.

Su JL, Lin JC. 1987. Thermoelastic signatures of tissue phantom absorption and thermal expansion. IEEE Trans Biomed Eng



They also measured the speed of thermoelastic pressure wave propagation in the brains of cats irradiated with pulsed microwaves and they found a value of 1523 m/s (Lin et al., 1988).


Lin JC, Su JL, Wang YJ. 1988. Microwave-induced thermoelastic pressure wave propagation in the cat brain. Bioelectromagnetics 9:141–147.


The measured sound pressure in the brain corresponds to the loudness by which the sound is perceived by the subject. Interestingly, the greater the pulse width, the more increased the loudness up to a certain point, after which it decreases (Lin, 1977a,b,c cited in Lin JC, 2004. Studies on Microwaves in Medicine and Biology: From Snails to Humans Bioelectromagnetics 25:146-159).





FDTD Analysis of the Microwave Auditory Effect



The mechanism of the microwave auditory effect consists of the absorption of microwave energy and the subsequent small but rapid temperature rise which induces tissue expansion and generates a thermoelastic/pressure wave that propagates to the cochlea of the inner ear with subsequent activation of the auditory nerve.


In order to quantitatively study the phenomenon and calculate the pressure exerted on the cochlea, a two-step process is followed:


(a) Calculation of the specific absorption rate (SAR) of the incident microwave energy by solving the Maxwell's equations using the finite-difference time-domain (FDTD) algorithm. The Maxwell's equations allows us to calculate the magnetic and electric fields at different space points as time evolves and subsequently to determine the specific absorption rate (SAR) distribution. The SAR produces temperature rise corresponding to thermal energy which exerts stress (physical quantity σ) on tissues.


(b) Calculation of the elastic/pressure waves generated by the thermal stress by solving the thermoelastic equation of motion using the FDTD algorithm.

Initially, scientists had used a spherical homogeneous model of the head for calculations of SAR and thermoelastic waves. Subsequent studies introduced an anatomical model of the human head (MRI-based) composed of different tissues (brain tissue etc.) with distinct dielectric and mechanical properties.


The SAR is provided by the equation:

SAR=σ * Ε^2 /2 ρ

where E is the electric field amplitude, σ is the conductivity and ρ is the mass density of the tissue.


The SAR distribution is calculated by solving the Maxwell’s equations using the FDTD algorithm.

As mentioned by Wikipedia, "Maxwell's equations describe how electric and magnetic fields are generated by charges, currents, and changes of the fields. An important consequence of the equations is that they demonstrate how fluctuating electric and magnetic fields propagate at a constant speed (c) in a vacuum."


As mentioned by this reference:

"Maxwell didn't invent all these equations, but rather he combined the four equations made by Gauss (also Coulomb), Faraday, and Ampere.

"But Maxwell added one piece of information into Ampere's law (the 4th equation)", the "Displacement Current, which makes the equation complete."


Maxwell's equations:

1.  “Gauss's law for static electric fields”

2. “Gauss's law for static magnetic fields”

3. “Faraday's law which says that a changing magnetic field (changing with time) produces an electric field”

4. “Ampere-Maxwell's law which says that a changing electric field (changing with time) produces a magnetic field”


The FDTD algorithm is used for physical systems that are governed by time-dependent partial differential equations (PDE). The derivatives are approximated as finite-differences. The FDTD algorithm consists of the generation of a grid of points over the domain to be considered computationally. The electric field (E) vectors of all points are solved at a given instance in time; then the magnetic field (H) vectors of all points are solved at the next instance in time (update equation step). The process is repeated over and over until the electromagnetic field behavior is evolved. It is said that the system “leapfrogs” between the E field and the H field or that the E and H equations are solved in a "leapfrog" manner (Wikipedia, ref.).


The calculated SAR distribution is used to compute the thermoelastic waves that are generated by the absorption of electromagnetic radiation.


In continuum mechanics, we refer to stress (σ) as a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other (https://en.wikipedia.org/wiki/Stress_(mechanics). Any strain (deformation) on a material generates an internal elastic stress, analogous to the reaction force of a spring, which tends to restore the material in its initial non-deformed state. These are described by Hook's law in a linear elasticity context.


In order to compute the thermoelastic waves that are generated, we solve another set of equations, the thermoelastic equations of motion and specifically, the Hook's law and the equations of motion for the particles.


We assume that the temperature rise T is provided by T=SAR/C where C is the specific heat of the tissue at a specific point.


By solving the equations, we calculate the distribution of the pressure waves and the pressure waveform at the cochlea.


The simulation by Watanabe et al (2000) shows that a 915 MHz microwave at 20 μs pulses generates mostly 7-9 KHz mechanical waves for the given human head template. This dominant mechanical frequency corresponds to the fundamental acoustic resonance frequency of the human head (cf. head as an acoustic resonator - sound generation in the human head).
As a 9 KHz mechanical wave is a wave of 9000 cycles per one second, one cycle of this wave has a duration of 1/9000 or 110 μs. It is found that if the duration of the pulse corresponds to half the acoustic resonance frequency/period i.e is approximately 50 μs then constructive interference occurs as the arriving energy is integrated and thermoelastic waves are excited more efficiently. If it is longer, then phase cancellation occurs.

The frequency distribution of the waves at the cochlea (Fig. 4) demonstrates a peak at 7-9 KHz corresponding to the resonance frequency for the human head.





Figure 3: SAR distribution (Fig.11) and pressure waveform at the cochlea (Fig.13) from Watanabe et al 2000.




Figure 4: Power spectrum of wave in cochlea (Fig.14) from Watanabe et al 2000. Dominant frequency of 7-9 KHz corresponds to resonance frequency of pressure waves in the head.



Yitzhak N. et al (2014) (ref.) (a study that has been cited by Professor Igor Goychuk) mention a mathematical relationship - derived by simple homogeneous spherical models - between the induced pressure amplitude P and the pulse width τ for a given point of the head and an acoustic angular frequency ω:

P(τ)= A | sin (ωτ/2) |
where A is an amplitude factor independent of the pulse width.
They mention that this holds to a good approximation even for complicated models using head and body templates.
Yitzhak N. et al (2014) conduct simulations for a head model as well as a body model. They mention:
"In all models, the strongest acoustic response occurs at the frequency of about 8 kHz, which represents the fundamental resonance frequency of sound generation in the human head [Lin, 1977a,b; Watanabe et al., 2000; Lin and Wang, 2010]. The occurrence of a peak in the acoustic power spectrum near 8 kHz persists also for other electromagnetic frequencies, irradiation directions, polarizations and pulse widths, although secondary peaks, in the range between 1 kHz and about 30 kHz also appear."
They also test the effect of horizontal and vertical polarization:
"For the vertical polarization there occurs a peak at about 60MHz, which corresponds to the well known whole body resonance [Dimbylow, 1997, 2002]. For both polarizations there occurs a peak at around 200MHz, and another broader one around 750MHz."


Figure 5: Calculated power spectra of the pressure waves at the cochlea for different models from Yitzhak N. et al (2014)




Microwave auditory effect: from clicks to sound modulation and intelligible speech

Microwave effect and the military - the military term "V2K"


Patent US 6470214 B1 [http://www.google.com/patents/US6470214] held by the U.S. Air Force and entitled “Method and device for implementing the radio frequency hearing effect” describes how it is possible to modulate sound information for transmission in a way that can be heard by an individual through the mechanism of thermoelastic expansion of the head.


The military is said to have coined a term based on the above mechanism, the term “Voice-to-Skull” abbreviated "V2K", which refers to a non-lethal weapon that performs microwave transmission of sound, either voice or audio subliminal messages, into the head of a person or animal. 





"V2K" webpage by the U.S. Army referring to weapon implementation of the microwave auditory effect was "permanently deleted" by its webmaster



Article published in 2008 by Sharon Weinberg, journalist and author of "Imaginary Weapons" and "The Imagineers of War: The Untold Story of DARPA, the Pentagon Agency That Changed the World"


Excerpt from the article:


"The entry, still available on the Federation of American Scientists' website reads: 

"Nonlethal weapon which includes (1) a neuro-electromagnetic device which uses microwave transmission of sound into the skull of persons or animals by way of pulse-modulated microwave radiation; and (2) a silent sound device which can transmit sound into the skull of person or animals. NOTE: The sound modulation may be voice or audio subliminal messages. One application of V2K is use as an electronic scarecrow to frighten birds in the vicinity of airports."


Acronym: V2K
Broader Terms: nonlethal weapons



"The U.K.-based group Christians Against Mental Slavery first noted the change (they also have a permanent screenshot of the page. A representative of the group tells me they contacted the Webmaster, who would only tell them the entry was "permanently removed."



Sharon Weinberg has also reported on the “Voice of God weapons” in the article https://www.wired.com/2007/12/the-voice-of-go/ (and cited hyperlinked reference) which consist of the implementation of the microwave auditory effect with low-power microwaves to transmit religious content.