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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.
---------------------------------------------
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.