Microwave Auditory Effect, Laser Auditory Effect and Directional Sound

Microwave auditory effect

Please refer to the following page: https://www.havana-syndrome-infosite.com/home/microwave-auditory-effect

Laser auditory effect

Laser communication using the photoacoustic effect

https://www.ll.mit.edu/news/laser-can-deliver-messages-directly-your-ear-across-room

Researchers from the MIT Lincoln laboratory created in 2019 a laser communication system based on the the photoacoustic effect, which consists of the generation of pressure waves or sound waves in a material, following light absorption. They determined that water vapor, which is found in all environments, absorbs light at the infrared wavelength of 1907 nm thereby generating mechanical/pressure waves which are perceived as sound when they reach a person's ear. The researchers used a laser of the above wavelength as a carrier on which they modulated sound information or messages. In one technique, the message is heard by all persons crossing the beam, whereas in another technique the message is delivered at a specific distance from the transmitter and is heard only by the person found at the specified location.

Corresponding FB post: https://www.facebook.com/MITLincolnLaboratory/posts/2783720194979519

Laser communication using the laser-induced plasma effect

Featured development: Generation of generic sound (and light) 

https://www.defenseone.com/technology/2018/03/us-military-making-lasers-create-voices-out-thin-air/146824/

Researchers from the U.S. military’s Joint Non-Lethal Weapons Program (JNLWD) announced in March 2018 that they created a system that produced sound or light at a distance based on the laser-induced plasma effect. This could be used for deterrence if for instance the sound of a flashbang grenade used for disorientation was generated.

Their efforts consisted of the use of a combination of femtosecond and nanosecond laser excitations in the so-called "igniter-heater" scheme*. Specifically, a femtosecond laser removes electrons from air molecules, thereby generating plasma which corresponds to a field of "electrified gas" which is significantly responsive to electromagnetic manipulation. Then, a nanolaser manipulates the plasma field in order to produce sound (noise) or light.

The distance at which this effect can be mediated depends on the dimensions of the used optics system and is theoretically considered to be at the range of tens of kilometers. The Kerr effect, which refers to the change of the refractive index of a material in response to an electromagnetic field, makes it easier to focus at large distances.

* Reference: https://bit.ly/2sBNYl7

Corresponding FB post: https://www.facebook.com/DefenseOne/posts/905525562951900

Transcript of video (slightly modified): We have whole propagated weakly-focused laser pulses, one of which is a femtosecond 30 mJoule igniter pulse which creates a very dilute plasma. The plasma is subsequently densified by copropagating a nanosecond pulse with about 3 Joules of pulsed energy.

At this point only a nanosecond pulse is propagating. The femtosecond pulse is blocked. As you can see, although the nanosecond pulse has huge energy, it doesn't have any visible effect and does not produce any amount of plasma except for occasional sparks due to the dust in the lab.

You can see that if I insert different objects in the beam like this piece of paper, then immediately on the surface there is dielectric breakdown (electrical breakdown). This is all left-over dust triggering the breakdown.

Depending on the type of materials I put in the beam, dark or light and so forth, the amount of noise that the plasma produces is different, the amount of plasma is different.

This is a blackened foil. Of course immediately the amount of plasma and noise increases.

Now let me turn on the femtosecond pulse. The femtosecond pulse will trigger the plasma formation in the gas and the nanosecond pulse will enhance the plasma, and create another plasma in the air.

Now the igniter and heater pulses propagate together and the level of sound is (...) maybe at about a loud voice level. The plasma is created in the form of a string which expands maybe to a distance of 10 cm.

If I block the igniter femtosecond pulse, the effect disappears even though the Joule pulse is still propagating.

Now I am again opening again the igniter pulse and I see the stable formation of plasma in the air.

Laser communication using the laser-induced plasma effect

Featured developments:

1) Sound modulation and mimicking human speech

2) Discomfort effect for deterrence

https://www.militarytimes.com/news/your-military/2019/07/19/pentagon-scientists-are-making-talking-plasma-laser-balls-for-use-as-non-lethal-weapons/

Researchers from the U.S. military’s Joint Non-Lethal Weapons Program (JNLWD) announced in July 2019 that following their creation of a system that produced sound or light at a distance based on the laser-induced plasma effect, they had implemented sound modulation for audio messages. This included experimentation with algorithms for human speech mimicking by adjusting low and high frequencies.

  The researchers commented that it suffices to create plasma at a location of choice (target) for sound to be then induced at the location through modulation. Additionally, sequential sounds similar to those of flashbang grenades used for disorientation have been developed. Next steps include the extension of the effect range.

Another implementation uses skin heating. The high energy laser with a very short pulse rate removes electrons from air molecules thereby generating plasma. This is used to create microscopic pores in a person's skin even below clothing thereby activating nerve endings and generating discomfort or pain.

Corresponding FB post: https://www.facebook.com/MilitaryTimesOnline/videos/374304256619014

Directional sound: large sources or parametric arrays (loudspeaker arrays), ultrasound heterodyning, audio spotlight, LRAD

Directional sound is a technological principle which consists of the concentration/focusing of sound waves or, in other words, the decrease of their dispersion (spread). The purpose is to generate a beam with increased directivity. For all wave sources, including sound sources, the larger the source compared to the wavelength it generates, the more directional the beam is. Also, sound waves of higher frequency and therefore lower wavelength, like ultrasound, are spreading less. For this reason, ultrasound has been used as a carrier for sound information via modulation or conventional mixing termed heterodyning ("sound from ultrasound") in order to achieve directional audible sound delivery. 

Figure 1: Image from Wikipedia article "Directional sound" presenting an array of point sound sources.

Additionally, using an array of sound sources like loudspeakers, it is possible to create a beam of increased directionality. Researchers have experimented since the 1960s on directional sound using ultrasound heterodyning with parametric arrays. The term "Audio Spotlight" coined for this technology by a theoretical study in the 1980s, in now a trademark. Holosonics, founded by an MIT graduate, is an example of a company specialized in Audio Spotlight speaker systems for corporations and venues like museums. Additionally, a billboard advertisment for A&E's TV show "Paranormal State" used directional sound to generate a message that could be heard only by a person walking by the advertisment. 

In the military and law enforcement, the Long Range Acoustic Device (LRAD) (ref.) is an acoustic hailing device which uses directional sound to send instructions or warnings to disperse crowds (Figure 1). If verbal instructions do not produce a result, the LRAD can generate a loud warning tone that approaches or surpasses the threshold of pain. When used in this deterrence manner, the LRAD is a non-lethal weapon.

Holosonics and A&E's advertisment are cited in this article. Also, this video discusses the article, as well as the technique of voice morphing.

Figure 2: Long Range Acoustic Device (LRAD) used by the U.S. Navy (Wikipedia).