U.S. patent application number 12/473275 was filed with the patent office on 2012-01-12 for acoustic crystal explosives.
This patent application is currently assigned to Raytheon Company. Invention is credited to Delmar L. Barker, Kenneth L. Moore, William R. Owens.
Application Number | 20120006216 12/473275 |
Document ID | / |
Family ID | 45349741 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120006216 |
Kind Code |
A1 |
Barker; Delmar L. ; et
al. |
January 12, 2012 |
ACOUSTIC CRYSTAL EXPLOSIVES
Abstract
An acoustic crystal explosive, which gains its properties from
both its periodic structure and its composition, may be configured
to suppress or enhance the sensitivity of detonation of the
explosive in response to an acoustic wave. An explosive material
and a medium (explosive or inactive) are arranged in a periodic
array that provides local contrast modulation of the acoustic index
to define a band gap in the acoustic transmission spectrum of the
explosive materials. At least one defect cavity in the periodic
array creates a resonance in the band gap. The defect cavity
concentrates energy from an incident acoustic (shock) wave to
detonate the explosive. Multiple defect cavities may be configured
to provide a desired shaped charge or volumetric detonations. Means
may be provided to reprogram the defect cavity(ies) to reconfigure
the explosive.
Inventors: |
Barker; Delmar L.; (Tucson,
AZ) ; Moore; Kenneth L.; (Sahuarita, AZ) ;
Owens; William R.; (Tucson, AZ) |
Assignee: |
Raytheon Company
|
Family ID: |
45349741 |
Appl. No.: |
12/473275 |
Filed: |
May 28, 2009 |
Current U.S.
Class: |
102/200 ;
149/2 |
Current CPC
Class: |
F42B 39/14 20130101;
F42D 5/04 20130101; C06B 45/00 20130101; C06C 7/00 20130101; F42B
12/207 20130101 |
Class at
Publication: |
102/200 ;
149/2 |
International
Class: |
F42D 1/04 20060101
F42D001/04; C06B 45/00 20060101 C06B045/00 |
Claims
1. An explosive configured to suppress accidental or malicious
detonation in response to an external acoustic wave, comprising: an
explosive material having a first acoustic index; and a medium
having a second acoustic index different than said first acoustic
index, said explosive material and said medium arranged in a
periodic array that provides local contrast modulation of the
acoustic index of the explosive in at least one dimension that
defines a band gap in the acoustic transmission spectrum of the
explosive material that overlaps the frequency content of the
external acoustic wave so that energy in the external acoustic wave
is suppressed in the band gap and in a suppression mode does not
detonate the explosive material.
2. The explosive of claim 1, wherein the contrast modulation is at
least 1.5.
3. The explosive of claim 1, wherein the medium comprises a
non-explosive material.
4. The explosive of claim 1, wherein the medium comprises a
different explosive material.
5. The explosive of claim 1, wherein the explosive material is a
secondary explosive.
6. The explosive of claim 1, wherein the spacing of the periodic
array is no greater than 1 cm.
7. The explosive of claim 1, wherein the spacing of the periodic
array is equal to a major wavelength of a dominant frequency of the
external acoustic wave operatively coupled to the periodic array,
said dominant frequency approximately centered in the band gap so
that energy in the external acoustic wave is suppressed in the band
gap.
8. The explosive of claim 6, wherein the medium is non-explosive
material, further comprising a second non-explosive material that
forms at least the first two external rows around the periodic
array in place of the explosive material.
9. The explosive of claim 1, further comprising: means to
reconfigure the periodic array to introduce at least one defect
cavity in the periodic array that creates a resonance in the band
gap to switch from the suppression mode to an enhancement mode in
which said defect cavity operatively couples and concentrates
energy of the external acoustic wave to detonate the explosive
material.
10. The explosive of claim 9, wherein said means to reconfigure the
periodic array comprises an ignition circuit configured to
selectively remove material from the periodic array to introduce
said at least one defect cavity.
11. An explosive configured to enhance detonation in response to an
external acoustic wave, comprising: an explosive material having a
first acoustic index; a medium having a second acoustic index
different than said first acoustic index, said explosive material
and said medium arranged in a periodic array that provides local
contrast modulation of the acoustic index of the explosive in at
least one dimension, said modulation defining a band gap in the
acoustic transmission spectrum of the explosive material that
overlaps the frequency content of the external acoustic wave; and
at least one defect cavity in the periodic array that creates a
resonance in the band gap that overlaps the frequency content of
the external acoustic wave, said periodic array configured to
operatively couple the external acoustic wave into the array, said
defect cavity concentrating energy in the external acoustic wave to
detonate the explosive material.
12. The explosive of claim 1, wherein the contrast modulation is at
least 1.5.
13. The explosive of claim 11, wherein the second medium comprises
a non-explosive material.
14. The explosive of claim 11, wherein the second medium comprises
a different explosive material.
15. The explosive of claim 11, wherein the explosive material is a
secondary explosive.
16. The explosive of claim 11, comprising a plurality of defect
cavities in the periodic array.
17. The explosive of claim 16, wherein the plurality of defect
cavities are arranged to produce a volumetric detonation of the
explosive material.
18. The explosive of claim 16, wherein the plurality of defect
cavities are arranged in a pattern to produce a shaped charge
detonation.
19. The explosive of claim 16, further comprising: means to
reprogram said plurality of defect cavities to control the
direction or shape of the explosive detonation.
20. The explosive of claim 19, wherein in a suppression mode the
periodic array contains no defect cavities and in an enhancement
mode said means reprograms multiple locations in the periodic array
to introduce the plurality of defects.
21. The explosive of claim 11, wherein in an enhancement mode said
periodic array includes said at least one defect cavity and in a
suppression mode the periodic array includes no defect cavity,
further comprising: means to reprogram the periodic array to
introduce the at least one defect cavity to switch the explosive
from suppression to enhancement mode.
22. The explosive of claim 11, further comprising: a source of the
external acoustic wave.
23. The explosive of claim 22, wherein absent the at least one
defect cavity the acoustic wave is not strong enough to detonate
the explosive material.
24. The explosive of claim 22, wherein the dominant frequency is
approximately centered in the band gap.
25. The explosive of claim 22, wherein the dominant frequency is
approximately coincident with the resonance of the defect
cavity.
26. The explosive of claim 22, wherein the acoustic wave generated
by the source is a shock wave.
27. The explosive of claim 11, wherein the spacing of the periodic
array is no greater than 1 cm.
28. The explosive of claim 11, wherein the spacing of the periodic
array is equal to a major wavelength of a dominant frequency of the
external acoustic wave operatively coupled to the periodic array,
said dominant frequency overlapping the band gap and the resonance
of the defect cavity.
29. An explosive, comprising: a source of an external acoustic wave
having a major wavelength of a dominant frequency; and an acoustic
explosive comprising an explosive material having a first acoustic
index and a medium having a second acoustic index different than
said first acoustic index, said explosive material and said medium
spaced in a periodic array with a spacing of no greater than 1 cm
that provides local contrast modulation of the acoustic index of
the explosive in at least one dimension, said local contrast
modulation and spacing of the periodic array defining a band gap in
the acoustic transmission spectrum of the explosive material that
overlaps the dominant frequency of the external acoustic wave, said
acoustic explosive further comprising at least one defect cavity in
the periodic array that creates a transmission resonance in the
band gap that concentrates energy from the external acoustic wave
to detonate the explosive material.
30. The explosive of claim 20, wherein the spacing of the periodic
array is equal to the major wavelength of the dominant frequency of
the external acoustic wave operatively coupled to the periodic
array, said dominant frequency overlapping the band gap and the
resonance of the defect cavity.
31. An explosive, comprising: an explosive material having a first
acoustic index; and a medium having a second acoustic index
different than said first acoustic index, said explosive material
and said medium arranged in a periodic array with a spacing no
greater than 1 cm that provides local contrast modulation of the
acoustic index of the explosive in at least one dimension that
defines a band gap in the acoustic transmission spectrum of the
explosive material that overlaps the frequency content of an
external shock wave operatively coupled into the periodic array.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to explosives, and more particularly
to acoustic crystal explosives.
[0003] 2. Description of the Related Art
[0004] An explosive material is a material that either is
chemically or otherwise energetically unstable or produces a sudden
expansion of the material usually accompanied by the production of
heat and large changes in pressure (and typically also a flash
and/or loud noise) upon initiation; this is called the explosion or
detonation.
[0005] A chemical explosive is a compound or mixture which, upon
the application of heat or shock, decomposes or rearranges with
extreme rapidity, yielding much gas and heat. A reaction must be
capable of being initiated by the application of a shock wave or
heat to a small portion of the mass of the explosive material. A
detonation wave is essentially a shock wave supported by a trailing
exothermic reaction. Detonation involves a wave traveling through a
highly combustible or chemically unstable medium, such as an
oxygen-methane mixture or a high explosive. The chemical reaction
of the medium occurs following the shock wave, and the chemical
energy of the reaction drives the wave forward.
[0006] Primary explosives are extremely sensitive to mechanical
shock, friction, and heat, to which they will respond by burning
rapidly or detonating. Examples include mercury fulminate, lead
styphnate and lead azide. Primary explosives are easy to initiate
but inherently less stable. Secondary explosives, also called base
explosives, are relatively insensitive to shock, friction, and
heat. They may burn when exposed to heat or flame in small,
unconfined quantities, but detonation can occur. These are
sometimes added in small amounts to blasting caps to boost their
power. Dynamite, TNT, RDX, PETN, HMX, and others are secondary
explosives. PETN is the benchmark compound; compounds more
sensitive than PETN are classed as primary explosives. Secondary
explosives are inherently more stable but hard to initiate. Often a
primary explosive or "booster" is used to produce a shock wave with
sufficient intensity to detonate the main charge of secondary
explosives. Many customers would like to eliminate the use of
primary explosives and use only secondary explosives.
[0007] Explosive force is released in a direction perpendicular to
the surface of the explosive. If the surface is cut or shaped or
"lensed", the explosive forces can be focused to produce a greater
local effect; this is known as a "shaped charge". Multi-point
initiation may be used to approximate a volumetric detonation.
Achieving a desired shaped charge or a volumetric detonation is
typically very expensive using known techniques.
SUMMARY OF THE INVENTION
[0008] The following is a summary of the invention in order to
provide a basic understanding of some aspects of the invention.
This summary is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. Its
sole purpose is to present some concepts of the invention in a
simplified form as a prelude to the more detailed description and
the defining claims that are presented later.
[0009] The present invention provides an acoustic crystal explosive
that gains its properties from both its periodic structure and its
composition. The explosive may be configured to suppress or enhance
the sensitivity of detonation of the explosive in response to an
acoustic wave. The explosive may be configured to eliminate the
need for primary explosives, using only secondary explosives. The
acoustic crystal explosive may provide a cost-effective solution
for volumetric or shaped-charge detonation. The acoustic crystal
explosive may be reprogrammed to provide a configurable
explosive.
[0010] In an enhancement mode embodiment, an acoustic crystal
explosive comprises an explosive material having a first acoustic
index and a medium having a second acoustic index different than
the first acoustic index. The explosive material and the medium are
arranged in a periodic array that provides local contrast
modulation of the acoustic index of the explosive in at least one
dimension to define a band gap in the acoustic transmission
spectrum of the explosive materials. At least one defect cavity in
the periodic array creates a resonance in the band gap. The defect
cavity concentrates energy from an incident acoustic (shock) wave
to detonate the explosive. Without the periodic structure and
defect cavity to concentrate energy, the acoustic (shock) wave may
be too weak to detonate the explosive. Multiple defect cavities may
be configured to provide a desired shaped charge or volumetric
detonations. Means may be provided to reprogram the defect
cavity(ies) to reconfigure the explosive either offline or in
real-time
[0011] In a suppression mode embodiment, an acoustic crystal
explosive comprises an explosive material having a first acoustic
index and a medium having a second acoustic index different than
the first acoustic index. The explosive material and the medium are
arranged in a periodic array that provides local contrast
modulation of the acoustic index of the explosive in at least one
dimension to define a band gap in the transmission spectrum of the
explosive materials. The band gap reflects energy from an incident
shock wave to suppress detonation of the explosive. Suppression
mode may be useful for preventing accidental or malicious
detonation of the explosive from an external shock wave. An
initiation source could be placed inside the explosive for
controlled detonation. Alternately, means can be provided to
reconfigure the periodic array to introduce one or more defect
cavities to switch from suppression to enhancement modes when
detonation is desired.
[0012] These and other features and advantages of the invention
will be apparent to those skilled in the art from the following
detailed description of preferred embodiments, taken together with
the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a plan view of an acoustic crystal explosive;
[0014] FIG. 2 is a plot of the transmission response including a
band gap;
[0015] FIG. 3 is a plan view of an acoustic crystal explosive
including a defect cavity;
[0016] FIG. 4 is a plot of a resonant peak in the band gap of
transmission response associated with the presence of the defect
cavity;
[0017] FIG. 5 is an embodiment of an enhancement-mode acoustic
crystal explosive;
[0018] FIGS. 6a and 6b are plots of a shockwave and the frequency
response of the shockwave overlaid on the band gap and defect
cavity resonance;
[0019] FIG. 7 is an embodiment of an acoustic crystal explosive
including a waveguide for routing the source wave to the defect
cavity;
[0020] FIG. 8 is an embodiment of an acoustic crystal explosive
including multiple defect cavities for volumetric detonation;
[0021] FIG. 9 is an embodiment of an acoustic crystal explosive
including multiple defect cavities to produce a shaped charge
detonation;
[0022] FIGS. 10a-10b are plan and side views of a programmable
acoustic crystal explosive; and
[0023] FIGS. 11a through 11c are plan views of the programmed
acoustic crystal explosive for volumetric detonation and different
shaped-charge detonations.
DETAILED DESCRIPTION OF THE INVENTION
[0024] As described above, explosive detonation can be initiated by
the application of a shock wave to the explosive. The transmission
properties of most explosives are such that shock waves propagate
through the explosive and if sufficiently intense initiate
detonation. The intensity of the shock wave required to initiate
detonation can be both a plus and minus. Primary explosives are
easy to intentionally detonate (plus) but are also susceptible to
unintentional (environmental, accidental or malicious) detonations
and provide less explosive power (minus). Secondary explosives are
more difficult to intentionally detonate (minus) but less
susceptible to unintentional detonations and provide more explosive
power (plus). The use of a primary explosive to initiate detonation
of the secondary explosive is a common technique to address some of
these issues. However, primary explosives are less stable and
customers would like to eliminate their use in many applications.
To effect a volumetric or space-charge detonation requires
multi-point initiation or explosive lenses, which are expensive and
limited in effectiveness.
[0025] The `acoustic crystal explosive`, which gains its properties
from both its periodic structure and its composition, may overcome
these challenges in a cost-effective manner. The acoustic crystal
explosive may be configured to initiate secondary explosives
directly, eliminating the need for primary explosives. The acoustic
crystal explosive can be programmed, and potentially reprogrammed,
to provide volumetric detonation or a desired shaped-charge
detonation. Essentially the `acoustic crystal explosive` is a
periodic array that provides local contrast modulation of the
acoustic index of an explosive in at least one dimension. This
modulation defines a band gap in the transmission spectrum of the
explosive material. The periodic structures are of similar size to
the central wavelength of the band gap. By itself the band gap
reflects energy from an acoustic or shock wave and tends to
suppress detonation. The creation of one or more defect cavities in
the periodic array creates a resonance in the band gap that tends
to concentrate energy from the acoustic or shock wave to initiate
detonation of the explosive. This `enhancement` allows for the
elimination of the primary explosives if so desired. Furthermore,
the defect cavities can be configured (or reprogrammed) for
volumetric or shaped-charge detonation.
[0026] As used herein an `acoustic wave` refers to a pressure
fluctuation that travels through a medium (solid, liquid or gas) at
or near the speed of sound. A `shock wave` is an acoustic wave that
is traveling faster than the speed of sound in the medium. Shock
waves are typically characterized by an abrupt, nearly
discontinuous change in the characteristics of the medium. Across a
shock there is an extremely rapid rise in pressure, temperature and
density of the flow. A `detonation wave` is a shock wave that is
supported by a trailing exothermic reaction in a combustible or
chemically unstable medium that drives the wave forward.
[0027] As shown in FIG. 1, an acoustic crystal explosive 10
includes an explosive material 12 having a first acoustic index and
a medium 14 having a second acoustic index different than said
first acoustic index. The explosive material may be a solid, liquid
or gas. The medium may be a solid, liquid or gas and may be either
a different explosive material or a non-explosive (inactive)
material. In this example, the medium is a `slab` and the explosive
materials are `rods` spaced in a periodic arrangement in the slab.
Alternately, the explosive material may be the slab and the medium
the rods. The explosive material may be a Primary, Secondary or
other explosive. If both the explosive material and the medium are
explosives, they may both be Primary explosives, Secondary
explosives or a Primary and Secondary explosive or other.
[0028] The explosive material 12 and medium 14 are arranged in a
periodic array 16 that provides local contrast modulation of the
acoustic index of the explosive in at least one dimension. A 2-D
array as shown provides modulation in 1-D. A 3-D array would
provide modulation in 2-D. A local contrast modulation of at least
1.5 for a 2-D array and 2.0 for a 3-D array creates a `band gap` 18
in the acoustic transmission spectrum 20 of the explosive material
as shown in FIG. 2. The wavelength at the center of the band gap is
approximately equal to or at least on the order of the spacing `d`
in the periodic array. The material can be actively controlled to
open or close the band gap, or shift the edges of the band gap.
This can be accomplished by modulating the contrast of the acoustic
indices, changing the geometric arrangement or altering the
symmetry of the scattering objects. Outside the band gap the energy
in an acoustic wave operationally coupled to the periodic array
will be transmitted through and partially absorbed by the explosive
material. Inside the band gap the energy in the acoustic wave will
constructively interfere and be largely reflected. The more rows or
layers to the periodic array the better defined the band gap 18 in
the acoustic transmission spectrum 20.
[0029] The `acoustic index` is defined as the ratio of the speed of
sound in a control medium to the speed of sound in the material of
interest. We have selected diamond as the control medium although
any medium can be used. When computing the contrast or local
modulation of the acoustic index the control medium cancels out
leaving only the properties of the explosive materials and medium.
Table 1 lists a number of explosive materials, the speed of sound
in the material and acoustic indices.
TABLE-US-00001 TABLE 1 Material m/sec Acoustic Index Diamond 12000
1.00 Air (20 C.) 1,125 10.67 Aluminum 4877 2.46 Brass 3475 3.45
Copper 3901 3.08 Iron 5130 3.08 Lead 1158 10.36 Steel 6100 1.97
Water 1433 8.37 Nitroglycerine 2200 5.45 PETN 1450 8.28 Cyclonite
2300 5.22 Tetryl 1500 8.00 PBXW 115 5642 2.13 PBXN 111 5760 2.08
Composition H-6 7368 1.63 Composition B 7879 1.52
[0030] As depicted there are many combinations of materials
explosive-explosive or explosive-inactive that provide a local
contrast modulation (index1/index2) of greater than 1.5 or greater
than 2.0. For example, an array formed of PETN and aluminum
provides a local contrast modulation of 8.28/2.46=3.45. An array
formed of two different explosive compounds PETN and PBXN111
provides a local contrast modulation of 8.28/2.08=3.98.
[0031] The acoustic crystal explosive 10 may be useful for
preventing accidental or malicious detonation of the explosive from
an external shock wave. On account of the availability of materials
with large differences in acoustic index, the width of the band gap
is fairly large, approximately 20% to 70% of the center wavelength.
As such, the band gap may effectively suppress initiation of the
explosive from an external shock wave. Because an external shock
wave may penetrate 1 or 2 rows before being reflected, if
suppression is desired the explosive material in the outer couple
rows may be replaced with an inactive material of the same or
similar acoustic index to avoid initiating detonation around the
periphery. An initiation source (shock or temperature) could be
placed inside the explosive for controlled detonation. Alternately,
means can be provided to reconfigure the periodic array to
introduce one or more defect cavities to switch from suppression to
enhancement modes when detonation is desired.
[0032] As shown in FIG. 3, an acoustic crystal explosive 30
includes an explosive material 32 having a first acoustic index and
a medium 34 having a second acoustic index different than said
first acoustic index. The explosive material 32 and medium 34 are
arranged in a periodic array 36 that provides local contrast
modulation of the acoustic index of the explosive in at least one
dimension. A local contrast modulation of at least 1.5 for a 2-D
array and 2.0 for a 3-D array creates a `band gap` 38 in the
acoustic transmission spectrum 40 of the explosive material as
shown in FIG. 4. A defect cavity 42 in the periodic array creates a
transmission resonance 44 within band gap 38. The defect cavity may
be any significant disturbance or "defect" in the periodic
structure e.g. the absence of explosive material 34, different
geometry of the same explosive material 34 or a different explosive
or non-explosive material. Techniques to construct high-Q defect
cavities are well-known. The "Q" indicates how well the defect
cavity resonates over many cycles of the acoustic wave to
concentrate and reach a non-linear effect to initiate detonation.
Graded cavities are known to provide high Q.
[0033] If an acoustic (shock) wave is operatively coupled to the
explosive with frequency content that overlaps the band gap and
particularly the resonance, the defect cavity will concentrate
energy from the wave at the defect for some number of cycles. The
effect may be to create a hot or high-pressure spot sufficient to
initiate detonation of the explosive material near the spot. As
will be detailed below, this phenomenon can be useful to initiate
detonation of the explosive material using a relatively weak
acoustic or shock wave, to directly initiate secondary explosive
material without the use of primaries, to control the location of
initiation within the explosive, to achieve volumetric detonation,
to produce a shape-charged detonation and to reprogram the one or
more defect cavities for some or all of the above.
[0034] As shown in FIG. 5, an embodiment of an explosive 50
includes a source 52 of an acoustic wave 54 (in this case a shock
wave), an acoustic explosive material 56 including an explosive 58
and a medium 60 configured in a periodic array to produce a local
modulation of the acoustic index and at least one defect cavity 62
in the array and an impedance-matched medium 64 to operatively
couple the acoustic wave 66 to the acoustic explosive material.
Defect cavity 63 concentrates and resonates energy 63 to trigger
the surrounding explosive 58. The impedance-matching medium may not
be required but is useful to limit coupling losses. Source 52 may
be a primary explosive or another shock producing phenomenon like a
laser pulse, a bursting diaphragm, a mechanical transducer and
shock tube etc. to produce wave 54 as shown in FIG. 6a. Shock wave
54 is characterized by an abrupt, nearly discontinuous change in
the characteristics of the medium. Across a shock there is an
extremely rapid rise in pressure, temperature and density of the
flow.
[0035] As shown in FIG. 6b, the frequency content 68 of wave 54 in
the medium overlaps the band gap 70 and particularly the resonance
72 created by the acoustic crystal explosive. In this embodiment,
dominant frequency 74 of the acoustic wave 54 is aligned with both
the center of the band gap and the resonance. Although this may be
preferred it is not required. In general, all that is required is
for the overlap between the acoustic wave and the resonance to
concentrate enough energy to initiate detonation. Either the
dominant frequency or the resonance may be positioned elsewhere
within the band gap.
[0036] The center of the band gap is approximately the spacing `d`
of the periodic array. This spacing may range from as small as
approximately 1 micron to as large as approximately 1 cm depending
upon the materials in the periodic array. The material will produce
a shock velocity with a certain band of excited modes. The major
modes will determine the dominant frequency of the wave. The
spacing of the periodic array is set at approximately the major
wavelength (or at least on the order of) to center the dominant
frequency of the acoustic wave in the band gap. The advantage of a
large spacing "d" is that the periodic structures are simpler to
fabricate.
[0037] In an embodiment, "but for" the periodic structure of the
acoustic crystal explosive and particularly the defect cavity, the
energy and intensity of wave 54 would be insufficient to detonate
the explosive material. This may provide for the use of sources
that generate relatively weak shock waves or even acoustic waves
that are not shock waves. This may also provide for the direct
initiation of secondary explosives. In other embodiments in which
the primary objective is to use the periodic structure and defect
cavities to produce volumetric, shape-charge or safe & arm
detonation, the source may produce a wave 54 with either sufficient
or insufficient energy and intensity to initiate detonation of the
explosive material without the periodic structure and resonance. In
other words, a source that produces a strong shock wave can be
used. The band gap will suppress the strong shock wave from
initiating detonation throughout the explosive material and
concentrate the energy at the defect cavity(ies) for controlled
detonation.
[0038] As shown in FIG. 7, in an embodiment a low-loss waveguide 80
in the periodic array guides acoustic wave 54 to defect cavity 62
to initiate detonation. Waveguides facilitate directing the shock
wave to distant detonation points without triggering the explosive
at points in between. This provides for control of both the
direction and distribution of the detonation. As shown in FIG. 8,
in an embodiment a plurality of defect cavities 62 are arranged
throughout the periodic array. The defect cavities 62 will
concentrate energy from the acoustic wave 54 to initiate detonation
in multiple locations almost simultaneously. This has the benefit
of producing a volumetric detonation. Multiple defect cavities and
waveguides may be combined to produce a sequenced multi-point
detonation.
[0039] As shown in FIG. 9, in an embodiment a plurality of defect
cavities 62 are arranged in the periodic array to produce a
shaped-charge detonation 82. As shown in FIGS. 10a-10b and 11a-11c,
in an embodiment an acoustic crystal explosive 90 may be configured
and provided with the means to reprogram cites of defect cavities
to produce a safe & arm device with single, multi-point,
volumetric or shaped-charged detonation. The explosive could be
reprogrammed prior to deployment, prior to launch, at launch, in
flight or during terminal guidance.
[0040] Acoustic crystal explosive 90 includes an explosive material
92 having a first acoustic index and a medium 94 having a second
acoustic index different than said first acoustic index. The
explosive material 92 and medium 94 are arranged in a periodic
array 96 that provides local contrast modulation of the acoustic
index of the explosive in at least one dimension. A local contrast
modulation creates a `band gap` in the acoustic transmission
spectrum. In this particular embodiment, medium 94 is a slab of
glass formed with a periodic array of holes that form the sites for
the explosive material. Explosive material 92 albeit a solid,
liquid or gas can be removed from these cites thereby forming a
defect cavity 98. The defect may be formed by air in place of the
explosive or by replacing the explosive material with a different
material e.g. a different explosive material, an in active material
with a different acoustic index with rods of index matching glass.
In this particular embodiment, the acoustic crystal explosive is
placed on top of a matching array of compressed air canisters 100
that are individually activated by an ignition circuit 102. The
circuit triggers specific canisters that released compressed gas to
pop the explosive material out of its site in the glass slab. As
shown in FIG. 11a, six sites are activated to form six defect
cavities 98 to effect volumetric detonation. As shown in FIGS. 11b
and 11c, five sites are activated to form eight defect cavities 98
in the form of a shaped-charge oriented in different directions. A
side-benefit to this approach is that until the circuit activates
the defect cavities the acoustic crystal explosive is in
suppression-mode, relatively immune to accidental or malicious
detonation from an external shockwave. Reprogramming in this manner
allows a generic acoustic crystal explosive to be stock-piled and
then configured based on mission needs. The explosive may be
reprogrammed in-flight to produce a desired shaped-charge.
[0041] While several illustrative embodiments of the invention have
been shown and described, numerous variations and alternate
embodiments will occur to those skilled in the art. Such variations
and alternate embodiments are contemplated, and can be made without
departing from the spirit and scope of the invention as defined in
the appended claims.
* * * * *