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Patent No. 5864517  Pulsed combustion acoustic wave generator (Hinkey, et al., Jan 26, 1999)

Abstract

A pulsed combustion acoustic wave generator includes a tubular barrel having an inlet end and an open outlet end, a fuel controller for metering a controlled quantity of fuel into the inlet end of the barrel, an oxidant controller for metering a controlled quantity of oxidant into the inlet end of the barrel and an igniter extending into the inlet end of the barrel that is controllable by an operator to ignite a mixture of fuel and oxidant in the inlet end.

Notes:

FIELD OF THE INVENTION

The subject invention pertains to a compact device designed to generate repetitive high amplitude acoustic pulses or pressure waves which may be utilized in a variety of applications.

BACKGROUND OF THE INVENTION

A device to produce high amplitude impulsive pressure waves may be based on several different schemes. Electrical energy may be utilized to produce sound waves through loudspeakers or piezoelectric devices, but high power requirements may result in energy storage difficulties as well as problems with the large physical dimensions necessary to produce high acoustic intensities (low power densities). Mechanical devices may be used to produce repetitive loud sounds, but would be inefficient and unwieldy. Methods which convert chemical energy to acoustical energy are ideal because of the high power densities which may be achieved. Solid explosives have very high energy densities and are capable of producing extremely high peak pressure levels (i.e., blast waves from bombs), but are dangerous to work with and are not practical to use if a repetitive impulse is required. Gaseous and liquid chemicals can be easily stored, are typically quite safe when fuels and oxidizers are separately stored, and can be mixed and combusted in a very rapid manner. Although not as high in energy density as solid explosives, gaseous or liquid combustible mixtures provide reasonable energy densities which may be quickly converted to pressure or acoustical energy. Repetitive release of stored chemical energy (via an energetic chemical reaction) to produce high amplitude pressure/acoustic waves can be achieved through pulsed combustion technology. Pulse combustion includes two different modes of burning: detonation and deflagration. Detonative combustion is characterized by an extremely fast flame speed (2,000 to 4,000 m/s) and very high amplitude pressure waves, while deflagrative combustion typically exhibits a much slower flame speed (generally less than about 200 m/s) and significantly lower amplitude pressure waves.

Repetitive, high amplitude pressure or acoustic waves can be utilized as a non-lethal effects device. The detrimental effects on humans of continuous exposure to high levels of "noise" (broad band and discrete frequency) are well studied and have been known for many years. These detrimental effects are usually long term in nature and consist of symptoms such as permanent hearing loss, general fatigue, elevated stress levels, and other physiological effects. The sound pressure and corresponding sound pressure levels (SPLs) of continuous exposure with which the average person is familiar are shown in Table 1.

TABLE 1 ______________________________________ Examples of typical sound pressure levels (SPLs) and sound pressures for common environments. Sound Sound Pressure Pressure Level dB Pa(N/m.sup.2) (2 .times. 10.sup.-5 Pa ref.) Typical Environment ______________________________________ 0.000020 0 Threshold of Hearing 0.000063 10 Rustle of Leaves 0.00020 20 Broadcast Studio 0.00063 30 Bedroom at Night 0.0020 40 Library 0.0063 50 Quiet Office 0.02 60 Conversational Speech 0.063 70 Average Radio 0.1 74 Light Traffic Noise 0.2 80 Typical Factory 0.63 90 Subway Train 2.0 100 Symphony Orchestra 6.3 110 Rock Band 20. 120 Aircraft Takeoff 200 140 Threshold of pain ______________________________________

Sensations of feeling or tickle commence at approximately 130 dB (0.009 psi rms) while significant discomfort occurs at approximately 120 dB (0.003 psi rms). Thus a pressure rise as small as 0.003 psi may cause considerable discomfort.

Non-continuous tone (impulsive noises) may have different effects on an individual, especially if the impulses are unexpected. An impulsive noise is one which has a high peak pressure acting over a short duration. The form of the impulses can be high amplitude sound waves suddenly switched on which then rapidly decay in amplitude or discrete pressure pulses which may contain many frequencies.

The physiological effects of low amplitude impulsive noise consists mainly of the startle response if the peak amplitude is not excessive. At higher peak amplitudes, in addition to the startle response, temporary threshold shift (TTS) occurs. TTS is the temporary increase in the threshold of hearing (the minimum sound level which evokes an auditory response) as a result of exposure to noise. TTS generally occurs at a minimum sound pressure level of 140 dB for gunfire and 130 dB for impact noise in an enclosed space (TTS is reported to increase when exposure occurs in an enclosed space). In general the amount of TTS increases with peak sound pressure level, but as the duration of the impulse decreases below 5 milliseconds, the effect is lessened for a given peak amplitude. In addition, the amount of TTS increases approximately linearly with exposure time, resulting in an increase in TTS with the total number of repetitive pulses one is exposed to (not the total exposure time). Upon cessation of exposure to repetitive impulsive noise. the threshold shift immediately begins a rapid recovery and reaches a minimum after approximately 1 minute, but then rebounds to a maximum at approximately 2 min. This is known as the bounce effect and may be useful in attempts at incapacitation/impairment using repetitive impulsive noise.

The threshold of pain normally associated with continuous exposure (non-impulsive noise) cannot be used to predict the risk of damage due to non-continuous sounds (impulsive noise). In fact intermittent noise has been observed to be less hazardous than steady-state noise for an equivalent amount of sound energy delivered to the ear.

Eye and hand coordination are particularly affected by impulsive noise, with significant impairment lasting from a typical 2 to 3 seconds to as much as 30 seconds in some individuals.

At still higher peak pressures, the physiological effects are centered mainly on damage to the structures of the ear. Peak impulse pressures of a few pounds per square inch can rupture the eardrum with smaller pressures capable of permanently damaging the conducting mechanisms of the inner ear. The ear's greatest mechanical sensitivity lies in the 1,500 to 3,000 Hz range, and thus is particularly vulnerable to short-duration blast waves which may contain many such frequencies at significant amplitudes.

Additional non-lethal effects of high level impulsive pressure waves include the potential ability to physically move or knock down an individual at close range due to the over-pressure associated with an impulse of sufficient strength. Non-auditory damage occurs at impulse peak pressures of approximately 1 atm (14.7 psi) with little physical damage occurring for peak pressures less than 1 atm which last for very short periods of time (milliseconds).

Infrasound (sound frequencies below approximately 16 Hz) may also have a non-lethal effect on the human body. Pulse jets may cause nausea and difficulty breathing due to the large amplitude impulsive waves generated by the devices, which pulse at up to 45 times per second.

SUMMARY OF THE INVENTION

A pulsed combustion acoustic wave generator which includes a tubular barrel having an inlet end and an open outlet end, a fuel controller for metering a controlled quantity of fuel into the inlet end of the barrel, an oxidant controller for metering a controlled quantity of oxidant into the inlet end of the barrel and an igniter extending into the inlet end of the barrel that is controllable by an operator to ignite a mixture of fuel and oxidant in the inlet end.

The pulsed combustion acoustic wave generator of the present invention is based on pulse detonation and pulse jet technology which enables the production of strong acoustic impulses. These impulses are adjustable in peak pressure levels and repetition rates to suit different applications regarding the non-lethal incapacitation, impairment, or immobilization of individuals and material targets, crowd control and dispersal, and self defense capability. The present invention can be adjusted in size and operation to provide different levels of acoustic power which can quickly be changed. In addition, the acoustic energy may be directed to some degree, thereby enhancing effectiveness.

The general configuration of the invention consists of a combustion tube of a predetermined length and diameter. One end of the combustor tube is open to allow the blast/shock wave produced by the combustion to propagate into the atmosphere. A nozzle or device capable of directing the acoustic energy may be attached to the end of the combustion tube. At the closed end, a fuel injection and ignition system meters and ignites the fuel/oxidizer mixture. Variation of the amount of fuel/oxidizer injected into the combustion tube allows adjustment of the impulse peak pressure. The rate at which the fuel/oxidizer is ignited by the ignition system determines the repetition rate.

In the pulsed acoustic wave generators of the invention, a detonation wave is initiated at the closed end of the tube to start the cycle. The wave propagates at a high velocity (2,000 to 4,000 m/s) through the fuel/oxidizer mixture, producing very high pressures due to the rapid combustion. When the detonation wave reaches the open end of the tube, it produces a blast wave of high amplitude. The process of filling the tube with a detonable fuel/oxidizer mixture and then producing a detonation can be repeated in a rapid manner (i.e., "pulsed") to produce a series of acoustic pressure waves. The frequency of the impulses is controlled by the frequency of injection of the fuel/oxidizer mixture. Ignition is typically initiated by a spark device.

In another mode, the invention utilizes pulse jets which operate by deflagrative combustion in which the combustion wave travels at a much slower speed (typically 10 to 100 m/s), thereby producing a much smaller pressure rise compared to pulse detonation. In this mode, the invention includes a tube with a set of reed valves (one-way valves) at one end, while being open at the other end. Operation is achieved by partially filling the tube with a combustible fuel/air mixture near the valved end, with the balance of the tube containing air drawn in from the open end. The combustion of the fuel/air mixture produces a moderate pressure wave which propels the combustion products and remaining air in the tube out of the open end. The pressure in the tube drops slightly below ambient due to over expansion of the flow which then allows air to be drawn in through the one-way valves at the closed end and through the open end. Fuel is injected into the fresh air in the tube and the cycle is repeated. The repetition rate is controlled by the frequency of fuel injection and ignition can be self sustaining once initiated with a spark device.

Situations where a single large amplitude pressure wave or a series of such waves may be useful depend on the intended effect. For general crowd control, a repeated series of moderate, amplitude (110 to 130 dB peak level) impulsive sounds from the present invention with a significant low frequency content may be quite effective and non-lethal; especially at close ranges where other methods, such as rubber bullets or water cannons can be quite dangerous. In addition, the potential large low frequency content of an impulsive wave may be difficult to attenuate effectively with typical ear protection devices. Typically maximum attenuation of 20 to 25 dB of high frequency noise can be attained with concurrent use of good quality ear plugs and earmuffs and thus may still be ineffective at higher sound levels, i.e., 140 to 150 dB and lower frequencies.

For incapacitation or immobilization of an individual or closely spaced group of individuals, the present invention discharged at close range may be enough to momentarily confuse, distract, deafen (temporary threshold shift), or startle (temporary loss of eye and hand coordination) the individual or group, resulting in reduced resistance to capture. The incapacitating effects of high amplitude impulsive noise are enhanced if the device is discharged in an enclosed space due to the reflections of energy from walls and internal objects. This may make the present invention suitable to military and law enforcement officials who wish to utilize the device for surprise raids on large numbers of people in enclosed spaces (i.e., homes used for drug trafficking and manufacture, etc.).

As an aid to immobilizing vehicles at close range, the present invention may be used to shatter windshields and vehicle side windows using the potentially high pressure resulting from a reflected high amplitude impulsive wave. No high-speed projectiles would be utilized, thereby reducing the possibility of accidental death due to high-speed projectile wounds (gunshot wounds). The occupants may also be incapacitated to some degree. In general, the present invention may be suited to rapid destruction of windows, doors, and other similar structures which need to be opened quickly without causing serious injury to occupants due to projectiles.

An advantage that the subject invention has over other techniques such as concussion grenades is the directive nature of the impulse, which may enhance the effects of the blast while reducing the effect on the operator. In addition, rapid, multiple pressure impulses may be utilized, if necessary; a characteristic not found in concussion grenades and other solid explosive-based devices. The amplitude of the impulse generated by the present invention would also be repeatable due to the ability to meter the amount of combustible gas injected into the combustion tube.

The characteristic size of the device of the subject invention may be selected for the intended purpose. Larger, more powerful devices applicable for crowd control situations could be mounted on a vehicle or structure. More mobile devices of less power could be man-portable to allow for more flexible use. Small devices for personal protection designed for discharges at very close range may even be made semi-concealed.

If necessary the present invention could, with appropriate design, be made to transition to a lethal mode by introducing projectile(s) into the combustion tube just prior to igniting the combustible mixture. The resulting high velocity of the combustion products upon expansion from the open end of the combustor tube would effectively propel a projectile(s) to a significant velocity.

The subject invention could be used to startle, intimidate, and disperse a crowd of people. It could be hand carried or mounted on a building, barricade, or vehicle. Acoustic emissions could be scaled over a large range. As a result, the device could be used at a low setting to gain the attention of an unruly group, at a moderate setting to startle and disorient a crowd, or at fall power to clear an area by making the noise level intolerable. Alternately, the present invention could be designed to operate at a single setting, substantially decreasing the possibility of mistaken use of excessive power.

The subject invention would be ideal for defense of a fixed position or barricade against a crowd armed only with typical riot weapons (stones, sticks, etc.) Without injuring people, the device would startle them with the abruptness and force of noise, stunning and disorienting them, and forcing their attention away from their objective and toward personal preservation.

Due to the acoustic nature of the device, using it in an enclosed space would heighten the disorientation and stun effects on individuals. The open end could be inserted into a room through a window or partly open door without exposing the operators to the occupants of the room. After a quick single or multiple pulse burst from the device, the room could be stormed while the occupants are recovering from the effects. This type of situation is also applicable to law-enforcement actions.

The present invention can be employed as a booby-trap, where a proximity sensor or other type of trigger begins operation without the direct control of an operator. The highly directional acoustic emissions would deliver full force effects on the target without undesirable effects on appropriately placed friendly troops. In this way, the subject invention would be similar to a non-lethal Claymore mine.

Current methods for dealing with vehicles or people trying to get past a checkpoint include using a barricade or shooting them. The subject invention gives flexibility to the level of response in such a situation. A device buried beneath the checkpoint or mounted to the checkpoint structure would have the ability to seriously impair the vehicle driver's ability to function. A large buried unit could generate sufficient force to damage or overturn a moving vehicle, while an above-ground unit could break vehicle windows. The vehicle driver would be exposed to the full stunning and disorienting effects of the device, as well as having the windows blow in. Since the device could be reset very quickly (multiple, rapid discharges), it could deal with repeated attempts at passage by multiple vehicles or people.

Current mine detonation methods involve the use of high explosives, which must be stored, carried into position, and exploded properly. However, it is not always clear that the mine has been detonated; the high explosives can mask the mine's explosion. The present invention could reduce that risk and decrease uncertainty associated with this operation. The pressure waves produced by the subject invention may be sufficient to trigger pressure-fused mines. Some mines are designed to do the most damage by going off only after repeated triggering. The subject invention could be cycled several times a second to ensure that these types of mines would be triggered. A mine-clearing device could be deployed on a boom from an armored vehicle, on a remotely controlled self-propelled platform, or suspended below a helicopter. Other airborne or ground-based installations are possible.

In addition to use as a mine disposal device, the subject invention has the potential to be used as a non-lethal mine. A buried device would, upon being triggered, fire its blast upwards at the target. While a very large device could inflict mortal injury in this manner, a small one almost certainly would not. It would stun and disorient the target, as well as giving loud notice to all concerned that the mine had been triggered. The present invention could also be designed to create a fuel-oxidizer cloud above ground before detonating, resulting in a much larger, omni-directional blast (similar to a fuel-air explosive). This type of free explosion could affect targets some distance away.

The subject invention produces high amplitude pressure waves which propagate through the air in an expanding shock wave. Depending on the size of the device and the distance involved, these pressure waves could be used to exert pressure force at a distance to, for example, break windows, knock down doors, and other types of use where a non-projectile force needs to be delivered without seriously harming the occupants. Multiple units could be synchronized to produce constructively interfering pressure waves, resulting in traveling force loci or nodes with higher pressures than could be achieved with a single device.

Recent use of loud music for psychological warfare in Panama and Waco, Tex., demonstrates the potential of using acoustics for disrupting sleep, disturbing thought patterns, and causing disorientation. The present invention would be ideal for this role, as its acoustic power and speed of pulsing could be varied drastically depending on need, it could run in repeating mode indefinitely as long as fuel is available, and its impulsive noise is very difficult to shut out. A device could be set to steadily increase noise levels with a random time between pulses until the target of its emissions surrenders or leaves. Steady-state high frequency noise could be reduced and canceled through electronic means, but high amplitude low frequency transient noise cannot be effectively attenuated in this manner. In addition, sound suppressers (i.e. headphones, earplugs) are probably not capable of reducing the noise level enough to render it ineffective.

The subject invention could be designed to propagate its pulsed acoustic emissions into water where the wave will travel very quickly for long distances. The ability to generate, repetitive high amplitude underwater acoustic pulses at any rate desired could be useful for decoys or to drown out noises which could otherwise be detected and identified, such as submarines or surface ships. Another important application in this area is that of civilian or military rescues where a device could produce discrete, high amplitude underwater acoustic waves which could be detected at large distances, thereby aiding in location in maritime emergencies.

The present invention may be capable of setting off contact and pressure triggered underwater mines in the same manner as land mines. High amplitude sound waves, like those created by this invention, propagate very well under water. As the waves strike the mine surface and reflect, sharp impulses would be delivered to the triggering mechanism. As with land mines, the present invention may trigger the mine without the use of conventional explosives which could mask the explosion and are dangerous to carry and place near the mine.

In mountain passes, recoilless howitzers and explosive charges placed on the slopes are used to trigger avalanches in a controlled manner. The sound pressure delivered by this invention may be enough to trigger avalanches without having to resort to expensive and dangerous solid explosives. By varying the frequency of pulses across a wide range, the device could create a harmonic vibration in the snow pack, increasing the likelihood of forcing the snow pack to avalanche.

This invention can function as an acoustic cleaner in power generation facilities. Deposits on the interior heat-transfer and structural surfaces can decrease the efficiency of a heat exchanger and increase the rate of corrosion. By producing low frequency, high amplitude acoustic waves, the subject invention would cause particulate and slag deposits to resonate and dislodge from the surface without having to resort to expensive steam cleaning.

The subject invention could be used in much the same manner for animal control purposes as it could for crowd control. A fixed or mobile unit could be used to scare wildlife or birds away from an airport runway and units suspended from helicopters could be used to herd wild animals without resorting to gunfire.

By introducing sound waves into the ground and recording their reflections, scientists can determine the composition of the earth's sublayers, without drilling for samples. Explosives and large "thumper" trucks are currently used to generate sound waves, but the invention could generate precise sound waves at exact intervals to increase the amount of information that could be gained from these studies. Such a device may be significantly less expensive than a "thumper," and is easier and safer to work with than conventional explosives.

The invention's ability to generate precise high amplitude pressure waves in air could be utilized to create these waves in any gas, liquid, or solid material at exact intervals and at significant amplitudes. This ability translates to an inexpensive and precise acoustic emitter for use in acoustic research such as mechanical and electronic noise attenuation and shock wave propagation.

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While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.