USPTO 6052336: Apparatus and Method of Broadcasting Audible Sound using Ultrasonic Sound as a Carrier

Microwaves and Behavior Dr. Don R. Justesen Laboratories of Experimental Neuropsychology Veterans Administration Hospital Kansas City, Missouri as published in The American Psychologist
Journal of the American Psychological Association
Volume 30, March 1975, Number 3

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Lowrey A. Patent # 6052336 "Apparatus and method of broadcasting audible sound using ultrasonic sound as a carrier" USPTO granted 4/18/00

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2. Description of the Related Art

Over the past few years, several situations have arisen in military and civil areas where crowds, with or without leaders, have posed a serious problem to Government forces.

For example, in Somalia, leader General Aideed would almost never remain outside unless surrounded by a crowd of sympathizers. Troops attempting to seize or capture the leader would have to engage the crowd, probably killing or injuring some, in order to get close enough to capture him. Hence, forces were not likely to attempt to capture the leader.

Another example is the U.S. invasion of Haiti, where a ship with troops was sent to perform various actions that would have been helpful to the population living there. The landing of these troops was, however, opposed by a crowd on the dock. Hence, in order to land, the crowd on the dock must first be disposed of. Again, crowd members would likely be hurt, resulting in the troops deciding not to act.

Still another example is any situation where an angry crowd gathers. In this situation, the crowd frequently turns to looting and destruction of property. It is a constant challenge for, for example, police to disperse such a crowd without causing casualties, perhaps fatal ones.

All of these examples have a common theme, namely a crowd or leader that one would like to influence such that they leave or stop their hostile activities.

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QUALITATIVE DESCRIPTION

PRELIMINARY CONSIDERATIONS

The use of sound controlling groups or crowds in both civil and military situations was considered at least as far back as World War II. Psychological studies on sounds that produce an aversive effect, or a pleasant effect, have been reported since the early decades of this century. Work in the nineteenth century by Helmholtz and Lord Rayleigh (detailed below) show an understanding of the effect that combination tones, or beats, with low frequencies (less than about one hundred Hertz) have on the pleasant or unpleasant quality of a sound.

Crowds can largely be divided into two kinds; those with leaders, and those without. A crowd with a leader can be affected either by limiting the communication between the leader and the crowd, or by directly affecting the crowd. A crowd without a leader (such as a looting mob) can only be affected by something that influences everyone in the crowd. Thus, it is necessary to develop physical methods to either impair communication, or to produce a physical or psychological effect in all persons exposed to the system.

Some of the methods suggested for affecting an entire crowd involve very high intensity sound (120 dB or more above the standard level of 2.times.10.sup.-5 N/m.sup.2). Sirens or very low frequency vibrations (less than 100 Hertz) are frequently spoken of.

Studies indicate several classes of sound to be of interest in crowd control. One class of sounds includes those which are aversive in themselves. Examples of these are: (1) scraping noises, such as that of chalk on a blackboard, (2) the crying of a baby, and (3) screams of pain. These sounds almost involuntarily cause a person to avert his/her attention from what he/she is doing, at least momentarily. Repeated exposure to this class of sounds, if the occurrence is not predictable, tends to produce jumpiness and sometimes leads to irrational behavior.

Secondly, there are a class of sounds which will cause a person to be startled and divert his/her attention from the task that he/she is doing because they indicate a possible imminent danger to him/her. Examples are: (1) gunfire, and (2) automobile crash noises.

Both of these classes of sound will likely produce a "startle" reaction in a crowd the first time that they are used. If the crowd, however, identifies the source as, for example, a loudspeaker, they will likely adapt to and ignore the noise. If the crowd mills around for a longer time, the sounds could cause headaches and other symptoms of stress. The crowd may disperse, but this is not at all certain.

If, on the other hand, one is trying to stop a fleeing person, a sudden noise, such as the screech of brakes, would undoubtedly cause the person to be startled and try to see whether the noise indicated impeding danger to him/her. He/She will clearly be disoriented for a few seconds, although the average time will vary from person to person. The sound of a gunshot may, for example, cause the same effect, or it may simply cause the person to run faster or run in a weaving manner.

A third class of sound includes low frequency vibrations either slightly above or below 20 Hertz; the lower audible limit. Vibrations in this frequency range produce several effects on a person's body.

Resonances of several internal organs lie in this frequency range. It has been shown that exposure to vibrations at an organ resonance cause nausea and a general feeling of malaise. Vibrational amplitudes that are too high will cause physical damage to the organs, whereas vibrations at a constant frequency or starting very low an rising through the range appear to cause a feeling of unease and tend to increase the suggestibility of a crowd.

The effects on a person's mood appear to be caused by hitting frequencies close to the alpha frequency of the brain waves. A phenomenon called "entrainment" occurs when the brain is stimulated at frequencies close to 10 Hz. This means that the brain's natural frequency is pulled close to, and sometime equal to, the stimulating frequency. A normal brain displays a prominent "alpha" pattern (8 to 12 Hz) at a time of relaxed alertness. Tense alertness, such as caused by freeway driving, leads to a "beta" pattern with a frequency of 13 Hz or higher. A relaxed, dreamlike state causes a "theta" pattern of frequencies from 4 to 8 Hz.

Other experiments, such as the ones cited by Norbert Wiener in "Nonlinear Problems in Random Theory", found that "a decidedly unpleasant sensation" was produced by stimulating the brain at "about 10 Hz." In fact, Helmholtz argues that beats of frequency less than 40 Hz are not perceivable as tones, but rather create a jarring feeling and are responsible for the unpleasant sensation of dissonant combinations of notes in music. As the low notes of the organ are in the range of 30 Hz, it would seem that tones ranging in frequency from about 12 to 40 Hz will produce an unpleasant feeling, or suggestibility. These tones are probably useful in crowd control used either by themselves, or to induce a mood that could then be triggered by another sound.

In producing low frequency vibrations with a conventional loudspeaker, several problems arise. First, at frequencies as low as this, loudspeakers are not very efficient in producing sound. The speaker will have to be quite large. Second, there is very little directivity possible with frequencies this low. Directive arrays would be huge, making it almost impossible to define an area where the effect occurs or to draw a line in the sand where individuals start feeling the effect when they cross it. Finally, the signal would be strongest at the speakers, requiring protective gear for at least the operators, and probably for all of the crowd control personnel.

Methods to impede communication between a speaker and a crowd have also been examined. One of the most interesting is techniques includes playing back to a speaker his/her own voice with a slight delay (less than a second). The speaker stutters and trips on his/her words unless he/she slows down his/her rate of delivery a great deal.

If two moderately loud audible tones of different frequency are received by the ear simultaneously, then, in addition to the two original tones, somewhat weaker tones with frequencies given by the sum and the difference of the original frequencies can be heard. This is called the Beat Frequency phenomenon when the two frequencies are close together, and the Combination Tone phenomenon when they are not. The combination tones are caused by a non-linear response by the ear to somewhat loud sounds. The details of the production of these tones are discussed in more detail herein below.

It is important, and in fact one of the critical physical principles in this invention, that an audible combination tone can be heard even when the two original tones are ultrasonic so that their frequencies lie above 20,000 Hz, the upper limit of audibility. In this case, the combination tone corresponds to the difference of the two original frequencies and is audible if it lies in the 20-20,000 Hz range of audibility.

The present invention shows ways in which, by altering the frequency and amplitude of one of the ultrasonic tones, the difference tone can be made to be a single tone (possibly of very low frequency), a scream or shot, or a voice.

More detailed discussions will be deferred until the "Technical Description" hereinbelow. We will discuss a way of causing a targeted person (or group) to hear whatever pattern of sound, be it speech or anything else, that we wish.

A combination tone is produced in the heads of all individuals exposed to both ultrasonic tones. If you are exposed to only one, you hear nothing, Additionally, these individuals are unable to detect the source of the sound.

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Effects of the System

The primary psychological difference between this system and other proposed systems using sound for crowd control is the property creating the sound within the head of the target individual. The effect on a person who suddenly starts to hear sounds with no apparent source is not known.

Since most cultures attribute inner voices either as signs of madness, or as messages from spirits or demons, both of which will invoke powerful emotional reactions, it is expected that the use of a voice will have an immediate intense effect.

Another effect is the low (less than 100 Hz) frequency sound. There are several reasons for this. First, these low frequency sounds will have a higher amplitude, in general, than the voice frequency sounds. Second, sounds at these low frequencies have been shown to increase the suggestiveness or apprehensiveness of exposed persons.

A system using a barrier array so that a person would feel more and more apprehensive as he/she moved in a given direction, and less if he/she turned around and went out. This may require a "trigger", such as a soft voice suggesting that it is dangerous and one should go back might work, in addition to the low frequency sound.

In addition, interference with the brain's alpha rhythm of a targeted individual or group may be achieved. This may cause temporary incapacitation, intense feelings of discomfort which would cause immediate dispersal of the crowd, or departure of the targeted leader.

Other sound patterns are possible, either alone or in combination. Sounds such as random shots, or screams may be very effective when combined with low frequency sounds producing apprehensiveness.

A leader could be singled out by using highly focused beams projected from one projector system 60, that target only the head region of a single person. The sound patterns described above could be used, or one could use the speaker's own voice, with an appropriate delay. The pattern selected would depend on whether it is desired to disrupt the speaker or his speaking ability.

Return to the Situations Described in the Background Section

Whether to use two projector system 10 or one projector system 60 depends on the applicable situation. For example, in the "Somalia" situation, the best effect could probably be achieved by using projector system 10, wherein one projector focused on the individual and another broad beam device targeting the crowd. A frequency near the alpha frequency would be directed at the individual to disorient him/her and perhaps make him/her collapse.

The crowd could be handled in a different way, for example, with sounds that induce apprehensiveness, without disabling. Ideally, the crowd would disperse, leaving the leader to be apprehended. In fact, certain characteristic sounds may be known to a particular culture that indicate that a person has a dreaded disease, such as the plague. This, together with sounds causing general apprehensiveness, might work.

The crowd on a dock described in the Haiti example, would be handled in roughly the same way. Sounds causing general discomfort would be mixed with other, for example, culturally specific sounds that would incite fear and discomfort. The intensity of the sounds could be increased for a while, then followed by a scream, or some related noise. Since the source of the sounds is not readily obvious, there will probably be general panic and fleeing.

An ultrasonic device may also be used to control looting crowds, instead of the more harmful tear gas after hard to control crowds. Additionally, the difficult task of removing residual tear gas is eliminated. An ultrasonic device would be used to control the crowd by exposing them to disorienting sounds, and sounds inducing fear. 

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