U.S. patent application number 13/093602 was filed with the patent office on 2013-10-17 for shock wave barrier using multidimensional periodic structures.
This patent application is currently assigned to Raytheon Company. The applicant listed for this patent is DELMAR L. BARKER, Kenneth L. Moore, William R. Owens. Invention is credited to DELMAR L. BARKER, Kenneth L. Moore, William R. Owens.
Application Number | 20130269508 13/093602 |
Document ID | / |
Family ID | 49321350 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130269508 |
Kind Code |
A1 |
BARKER; DELMAR L. ; et
al. |
October 17, 2013 |
SHOCK WAVE BARRIER USING MULTIDIMENSIONAL PERIODIC STRUCTURES
Abstract
A shock wave barrier comprises a periodic structure having the
proper symmetry and local contrast modulation of the acoustic index
to divert an incident shock wave by using constructive/destructive
interference phenomena that produce a "band gap" in the
transmission spectrum of the periodic structure. In general, shock
wave energy within the band gap is reflected from the structure.
Defect cavities may be formed in the periodic structure to create
transmission resonances or "windows" in the band gap. A portion of
the incident energy passes through the window and is concentrated
in the defect cavities where it is dissipated by other means. The
band gap can be quite wide, at least 50% of the center wavelength,
and thus can provide an effective barrier from a wide variety of
threats with varying blast pressure and range. The structure may be
periodic in two or three dimensions providing a band gap barrier in
two or three dimensions, respectively.
Inventors: |
BARKER; DELMAR L.; (Tucson,
AZ) ; Moore; Kenneth L.; (Sahuarita, AZ) ;
Owens; William R.; (Tucson, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BARKER; DELMAR L.
Moore; Kenneth L.
Owens; William R. |
Tucson
Sahuarita
Tucson |
AZ
AZ
AZ |
US
US
US |
|
|
Assignee: |
Raytheon Company
|
Family ID: |
49321350 |
Appl. No.: |
13/093602 |
Filed: |
April 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12473275 |
May 28, 2009 |
8082844 |
|
|
13093602 |
|
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Current U.S.
Class: |
89/36.01 |
Current CPC
Class: |
F41H 5/007 20130101;
F41H 5/06 20130101; F42D 5/045 20130101 |
Class at
Publication: |
89/36.01 |
International
Class: |
F41H 5/06 20060101
F41H005/06 |
Claims
1. A shock wave barrier for an asset in a protected area,
comprising: first and second media arranged in a multidimensional
periodic structure having a symmetry, said structure positioned
between the protected area and one or more potential explosive
detonation threats, said first and second media having different
acoustic indices of refraction that provide a local contrast
modulation of the acoustic index that in conjunction with the
symmetry of the structure defines a band gap in a transmission
spectrum of the periodic structure, said first and second media
spaced in the periodic structure to position the band gap
coincident with the dominant wavelength of the shock wave for one
or more potential explosive detonation threats.
2. The shock wave barrier of claim 1, wherein the periodic
structure reflects show shock wave energy at wavelengths within the
band gap.
3. The shock wave barrier of claim 1, wherein the periodic
structure exhibits translational or rotational symmetry.
4. The shock wave barrier of claim 1, wherein the local contrast
modulation of the acoustic index is at least 2:1.
5. The shock wave barrier of claim 1, wherein the periodic
structure comprises at least six layers within which the shock wave
constructively and destructively interferes to form the band
gap.
6. The shock wave barrier of claim 1, wherein the first media
comprises air.
7. The shock wave barrier of claim 6, wherein the local contrast
modulation of the acoustic index is at least 10:1 and the width of
the band gap is at least 50% of the center wavelength of the band
gap.
8. The shock wave barrier of claim 1, wherein said first media
comprises linear elements that provide local contrast modulation in
two dimensions, said linear elements arranged in said second media
in a three-dimensional periodic structure that define the local
contrast modulation and band gap approximately in two
dimensions.
9. The shock wave barrier of claim 8, wherein the linear elements
may be retracted to permit ingress and egress from the protected
area.
10. The shock wave barrier of claim 1, wherein said first media
comprises a three-dimensional geometric objects that provide local
contrast modulation in three dimensions, said three-dimensional
objects arranged in said second media in a three-dimensional
periodic structure that defines the local contrast modulation and
band gap in three dimensions.
11. The shock wave barrier of claim 1, further comprising: one or
more defect cavities in the periodic structure that create a
transmission resonance with the band gap that allows energy from
the shock wave to pass into the structure where it is concentrated
within the one or more defect cavities.
12. The shock wave barrier of claim 11, wherein the one or more
defect cavities are filled with a third media that is ejected from
the cavity to dissipate the energy.
13. The shock wave barrier of claim 11, wherein a plurality of said
defect cavities forms a waveguide that routes the energy away from
the protected area.
14. A shock wave barrier for an asset in a protected area,
comprising: linear elements arranged in air around a protected area
in a three-dimensional periodic structure that exhibits
translational or rotational symmetry, said linear elements having
an acoustic index of refraction of at most one-tenth that of air to
provide a local contrast modulation of the acoustic index in
two-dimensions of at least 10:1 that in conjunction with the
symmetry of the structure defines a band gap in a transmission
spectrum of the periodic structure, said linear elements spaced in
the periodic structure to position the band gap coincident with the
dominant wavelength of the shock wave for one or more potential
explosive detonation threats, said band gap having a width of at
least 50% of its center wavelength.
15. The shock wave barrier of claim 14, wherein the periodic
structure reflects shock wave energy at wavelengths within the band
gap.
16. The shock wave barrier of claim 14, further comprising: one or
more defect cavities in the periodic structure that create a
transmission resonance within the band gap that allows energy from
the shock wave to pass into the structure where it is concentrated
within the one or more defect cavities; and means for dissipating
the energy in the one or more defect cavities.
17. The shock wave barrier of claim 14, wherein the linear elements
may be retracted to permit ingress and egress from the protected
area.
18. A shock wave barrier for an asset in a protected area,
comprising: first and second media arranged in a multidimensional
periodic structure having a symmetry, said structure positioned
between the protected area and a one or more potential explosive
detonation threats, said first and second media having different
acoustic indices of refraction that provide a local contrast
modulation of the acoustic index that in conjunction with the
symmetry of the structure defines a band gap in a transmission
spectrum of the periodic structure, said first and second media
spaced in the periodic structure to position the band gap
coincident with the dominant wavelength of the shock wave for one
or more potential explosive detonation threats; one or more defect
cavities in the periodic structure that create a transmission
resonance with the band gap that allows energy from the shock wave
to pass into the structure where the energy is concentrated within
the one or more defect cavities; and means for dissipating the
energy in the one or more defect cavities.
19. The shock wave barrier of claim 18, wherein the means for
dissipating the energy comprises a third media in the one or more
defect cavities that is ejected from the cavity to dissipate the
energy.
20. The shock wave barrier of claim 18, wherein the means for
dissipating the energy comprises a waveguide formed by a plurality
of said defect cavities that routes the energy away from the
protected area.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of priority under 35 U.S.C.
120 as a continuation-in-part of co-pending U.S. application Ser.
No. 12/473,275 entitled "Acoustic Crystal Explosives" and filed on
May 28, 2009, the entire contents of which are incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to protection of assets in protected
areas from shock waves such as produced by explosive
detonation.
[0004] 2. Description of the Related Art
[0005] Explosive detonation may produce a shock wave that
propagates outwardly from the point of detonation through a media
such as air, liquid or a solid. The shock wave is a pressure wave
that travels at supersonic speed in the media. The shock wave is
characterized by an abrupt, nearly discontinuous change in the
characteristics of the medium. Across the shock there is an
extremely rapid rise in pressure, temperature and density of the
flow. The shock wave carries a large amount of energy in a small
volume that can be very destructive. However, the energy of the
shock wave dissipates relatively quickly with distance.
Furthermore, the accompanying expansion wave approaches and
eventually merges with the shock wave, partially cancelling it out.
In many explosives, the expansive wave expels metal fragments that
provide additional destructive capability.
[0006] To protect assets such as buildings or large equipment from
the shock waves and fragments resulting from nearby explosive
detonations, mass may be placed around the protected area between
the asset and an explosive detonation. The mass absorbs the energy
in the shock wave through translation of the mass and/or internal
friction due to deformation of the mass. Large amounts of mass are
required to adequately protect the asset from potential threats.
The "mass" may be earth/sand filled plywood walls, earth/sand
filled tire walls or vertical reinforced concrete walls. Water
filled bladders may be used to absorb the energy in the shock wave
and convert it to a vertical spray of water. The mass also provides
a barrier to the expelled fragments.
SUMMARY OF THE INVENTION
[0007] 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.
[0008] A shock wave barrier comprises a periodic structure having
the proper symmetry and local contrast modulation of the acoustic
index to divert an incident shock wave by using
constructive/destructive interference phenomena that produce a
"band gap" in the transmission spectrum of the periodic
structure.
[0009] In an embodiment, the shock wave barrier comprises first and
second media arranged in a periodic structure positioned between a
protected area and a potential threat. The first and second media
have different acoustic indices of refraction that provide a local
contrast modulation of the acoustic index. The symmetry of the
periodic structure and local contrast modulation define a band gap
in a transmission spectrum of the periodic structure. The first and
second media are spaced in the periodic structure to position the
band gap coincident with the dominant wavelength of a shock wave
produced by the potential threat. The periodic structure is
suitably configured such that the band gap spans the dominant
wavelengths incident on the structure for a variety of potential
threats. The dominant wavelength is a function of the blast
pressure of the explosive detonation and the range to the explosive
detonation. Generally speaking, the energy of the incident shock
wave that lies within the band gap is substantially reflected by
the periodic structure.
[0010] In an embodiment, the periodic structure is defined by the
lattice symmetry of a crystal or quasi-crystal that form band gaps.
A crystal lattice exhibits translational symmetry if the structure
may be shifted at a certain period and remains identical. The
quasi-crystal lattice exhibits rotational symmetry if the structure
may be rotated through a certain angle (less than 360 degrees) and
remains identical. Rotational symmetry may also provide the added
benefit of providing no linear path through the structure thereby
enhancing the structure's capability as a fragment barrier.
Translation or rotational symmetry is a necessary but not
sufficient condition to produce a band gap. Certain crystal
lattices exhibit both translational and rotational symmetry.
[0011] In an embodiment, the local contrast modulation of the
acoustic indices is equivalent to a velocity contrast in the shock
wave incident upon the first few layers of the periodic structure
where the wave constructively and destructively interferes. 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
structure. The local contrast modulation largely determines the
width of the band gap; the greater the contrast the greater the
width. A minimum contrast modulation of approximately 2:1 is needed
for a complete band gap. Contrast modulations of 10:1 or greater
may be achieved (e.g. steel rods in air or void spaces in concrete)
that produce a 50% band gap or greater for acoustic applications.
The width of the band gap is typically referenced to its center
wavelength.
[0012] In an embodiment, the periodic structure comprises a
two-dimensional structure that provides local contrast modulation
in a two-dimensions. One example is a two-dimensional array of
linear elements in air positioned adjacent to or surrounding a
protected area. This periodic structure would present a band gap to
shock waves travelling along the ground toward the protected area
or anywhere in the plane but not perpendicular to the plane of the
shock wave. The linear elements could be retracted to provide
ingress or egress to the protected area and then deployed to
provide the shock wave barrier.
[0013] In an embodiment, the periodic structure comprises a
three-dimensional structure that provides local contrast modulation
in three-dimensions. One example is a concrete hemisphere or box
with a periodic array of void three-dimensional objects positioned
over the protected area. This structure would present band gaps to
shock waves travelling along the ground toward the protected area
or shock waves from airborne explosive detonations travelling down
towards the protected area.
[0014] In an embodiment, one or more defect cavities are formed in
the first few layers of the periodic structure in which the
constructive/destructive interference occurs. The defect cavity
(ies) creates a transmission resonance or "window" in the band gap
that allows energy from the shock wave to be collected by the
defect cavities. The defect cavity may be detuned to control the
width of the window. The collected energy may be dissipated in the
defect cavities by, for example, expelling a material such as water
or sand that fills the cavity. The collected energy may be rerouted
through the periodic structure around the protected area via a
waveguide formed by a pattern of defect cavities.
[0015] 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
[0016] FIGS. 1a and 1b are planar and perspective views of an
embodiment of a shock wave barrier comprising a periodic structure
of metal rods in air surrounding a protected area;
[0017] FIG. 2 is a plot of the barrier's transmission profile
exhibiting a band gap;
[0018] FIGS. 3a and 3b are plots of a shock wave and its response
at the barrier coincident with the band gap;
[0019] FIGS. 4a and 4b are planar and perspective views of the
shock wave barrier illustrating the constructive/destructive
interference that occurs in the first few layers of the periodic
structure to form the band gap and reflect the energy of the shock
wave;
[0020] FIG. 5 is a planar view of an embodiment of a shock wave
barrier comprising defect cavities formed in the periodic structure
that form a resonance in the band gap to collect energy from the
shock wave;
[0021] FIG. 6 is a plot of the barrier's transmission profile
exhibiting a defect resonance within the band gap;
[0022] FIG. 7 is a diagram of a water filled defect cavity
configured to dissipate the collected energy by expelling the water
from the cavity;
[0023] FIG. 8 is a plan view of a periodic structure including
multiple defect cavities that form a waveguide to collect and
reroute the transmitted energy away from the protected area;
[0024] FIGS. 9a and 9b are diagrams of a periodic structure that
exhibits rotational symmetry;
[0025] FIG. 10 is a diagram of an embodiment of a three-dimensional
periodic structure comprising void spheres arranged in a concrete
hemisphere; and
[0026] FIG. 11 is a diagram of an embodiment of a three-dimensional
periodic structure comprising concentric hemispheric mesh
structures arranged in air.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present invention describes a shock wave barrier. This
is accomplished with a periodic structure having the proper
symmetry and local contrast modulation of the acoustic index to
divert an incident shock wave by using the constructive/destructive
interference phenomena that produces a "band gap" in the
transmission spectrum of the periodic structure. In general, shock
wave energy at wavelengths within the band gap is reflected from
the structure. Defect cavities may be formed in the periodic
structure to create transmission resonances or "windows" in the
band gap. A portion of the incident energy passes through the
window and is concentrated in the defect cavities where it is
dissipated by other means. The band gap can be quite wide, at least
50% of the center wavelength, and thus can provide an effective
barrier from a wide variety of threats with varying blast pressure
and range. The structure may be periodic in two or three dimensions
providing a band gap barrier in two or three dimensions,
respectively.
[0028] Referring now to FIGS. 1a-1b and 2, in an embodiment a shock
wave barrier 10 comprises a first media of linear elements (e.g.
rods) 12 and a second media of air 14 arranged in a periodic
structure 16 of multiple layers 18 around a protected area 20 and
asset 22. The first and second media have different acoustic
indices of refraction that provide a local contrast modulation of
the acoustic index orthogonal to the linear elements and the
periodic structure. The symmetry of the periodic structure and
local contrast modulation define a band gap 24 in a transmission
spectrum 26 of the periodic structure. Incident energy that falls
within the band gap 24 is reflected from the periodic structure.
The periodic structure is suitably configured such that the band
gap 24 spans the dominant wavelengths incident on the structure for
a variety of potential threats (e.g. varying blast pressures at
varying distances to the protected area). In some embodiments, the
rods 12 may be retractable to allow ingress or egress to the
protected asset or of the protected asset.
[0029] Periodic structure 16 is configured to produce
constructive/destructive interference of an incident shock wave to
define band gap 24. The symmetry, local contrast modulation, number
of layers and spacing of the periodic structure form band gap 24
and determine its center wavelength, width and definition.
[0030] Periodic structure 16 exhibits a symmetry that will form a
band gap. There are many crystal and quasi-crystal lattices that
are known to form band gaps in crystalline periodic structures. To
form periodic structure 16 the first media (rods) 12 are arranged
in a pattern corresponding to the vertices of the crystal or
quasi-crystal lattice within the second media (air) 14. In this
particular embodiment, the periodic structure is based on a square
crystal lattice. Other patterns based on, for example, a triangular
or honeycomb crystal lattice may be used.
[0031] A crystal lattice exhibits translational symmetry if the
structure can be translated by a certain distance and remains
identical. The quasi-crystal lattice exhibits rotational symmetry
if the structure may be rotated through a certain angle (less than
360 degrees) and remains identical. Rotational symmetry may also
provide the added benefit of providing no linear path through the
structure thereby enhancing the structure's capability as a
fragment barrier. Certain crystal lattices exhibit both
translational and rotational symmetry. Translation or rotational
symmetry is a necessary but not sufficient condition to produce a
band gap. To date, no general solution has been identified to
specify all types of crystals and quasi-crystals that will form
band gaps.
[0032] Periodic structure 16 exhibit a minimum local contrast
modulation of the acoustic index of approximately 2:1 to form a
complete band gap. This modulation produces a velocity contrast in
the shock wave incident upon the first layers of the periodic
structure where the wave constructively and destructively
interferes. Contrast modulations of 10:1 or greater may be achieved
(e.g. steel rods in air or void spaces (air) in concrete) that
produce a 50% band gap or greater. The width of the band gap is
typically referenced to its center wavelength.
[0033] The `acoustic index` of refraction 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 first and second
media. Table 1 lists a number of different media, the speed of
sound in the material and acoustic indices. The Table is not an
exhaustive list of usable media, merely representative. As shown a
combination of metal and air produces modulations in excessive of
10:1.
TABLE-US-00001 TABLE 1 Material m/sec Acoustic Index Diamond 12000
1.00 Air (STP) 343 35 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 Concrete 3200-3600 3.33-3.75 Brick 4176 2.87
[0034] Periodic structure 16 includes multiple layers 18 to
adequately establish and define band gap 24. As shown in FIG. 2,
the definition of band gap 24 improves with additional layers.
Typically, a periodic structure comprising 6-10 layers 18 provide a
well-defined band gap 24 with approximately zero transmission
across the band gap.
[0035] The wavelength at the center of the band gap is
approximately equal to or at least on the order of the spacing `d`
in periodic structure 16. Secondary factors such as element
diameter, element shape and small positional placement of the
elements that are slightly symmetry braking will contribute to the
exact spacing `d` required for a specific center wavelength.
[0036] In an embodiment, periodic structure 18 may be actively
controlled to open or close the band gap, or shift the edges of the
band gap. The periodic structure may be actively controlled by
modulating the contrast of the acoustic indices, changing the
geometric arrangement or altering the symmetry.
[0037] Referring now to FIGS. 3a-3b and 4a-4b, an explosive
detonation 30 produces a shock wave 32. Shock wave 32 travels as a
plane wave at supersonic speed in air towards periodic structure 16
and protected area 20 and asset 22. The shock wave is characterized
by an abrupt, nearly discontinuous change in the air pressure.
Simplifying, the blast pressure produced by the explosive
detonation forms the initial shock wave. The response 34 of the
shock wave as it arrives at the barrier may be characterized by a
dominant wavelength 36. Most of the energy in the shock wave is
centered about the dominant wavelength. This wavelength is to a
large extent determined by the amount and type of explosive. As the
shock wave propagates through air towards the protected area and
decays its dominant wavelength shifts downwards. Consequently, the
dominant wavelength incident on the periodic structure is
determined by the initial blast pressure and the range. Depending
upon the application (protected area and asset) and the potential
threats (initial blast pressures and ranges), the periodic
structure is configured to present a band gap that spans the
dominant wavelengths of the incident shock wave for a variety of
potential threats. The band gap is also positioned to reflect those
wavelengths that most efficiently and destructively couple to the
asset.
[0038] When shock wave 32 reaches periodic structure 16 energy
within band gap 24 will constructively and destructively interfere
and be substantially reflected away from the structure as reflected
energy 37 while energy outside the band gap will be transmitted
through the structure. The incident shock wave interacts with the
rods in the periodic structure to produce secondary waves 38. These
secondary waves intersect and produce destructive interference and
cancellation of a wide band of wavelengths to form the band gap.
The energy outside the band gap is naturally attenuated or does not
couple destructively to the asset.
[0039] In certain situations it may not be desirable to reflect all
or even a substantial portion of the shock wave. The reflection may
cause collatoral damage of other nearby assets. As shown in FIG. 5,
defect cavities 40 may be formed in the first few layers of
periodic structure 16. The defect cavity may be any significant
disturbance or "defect" in the periodic structure e.g. the absence
of one or more rods 18 or different geometry of the one or more
rods 18. Defect cavities 40 create a transmission resonance 42 or
"window" in band gap 24 as shown in FIG. 5. The defect cavity may
be detuned to control the width of the transmission resonance. The
defect cavity may be detuned by altering the size of the defect,
the acoustic index of refraction or the lattice constant of the
periodic structure. A portion of the incident energy passes through
the window and is concentrated in the defect cavities where it is
dissipated by other means.
[0040] As shown in FIG. 7, an embodiment to dissipate the energy
concentrated in the defect cavities is to fill the cavities 40 with
another media 50 such as water or sand. The energy is dissipating
by ejecting media 50 from the defect cavity.
[0041] As shown in FIG. 8, another embodiment to dissipate the
energy is to configure the defect cavities 40 to form a waveguide
52 to reroute the energy around and away from a protected area 53.
The energy from an incident plane wave 54 is collected by the
defect cavities 40 and routed through waveguide 52 around protected
area 53.
[0042] As shown in FIG. 9, rods 18 may be positioned at the
vertices 60 of a quasi-crystal lattice 62 around a protected area
64 and asset 66. The pattern of rods 18 exhibits a rotational
symmetry that forms a band gap. A benefit of this pattern is that
it provides no clear linear path from the outside through the
periodic structure to the protected area. This increases the
periodic structure's viability as a fragment barrier in addition to
being a shock wave barrier.
[0043] The periodic structure may comprise a three-dimensional
structure that provides local contrast modulation in two
dimensions. This structure comprises three-dimensional objects
(spheres, cubes, rods, etc.) arranged with certain symmetry in a
contrasting media that form a band gap.
[0044] Referring now to FIG. 10, in an embodiment of a
three-dimensional shock wave barrier 67 a unit cell 68 of the
periodic structure comprises cubes 70 arranged at the vertices 72
of a cubic lattice 74. Unit cells 68 are repeated in a
three-dimensional periodic structure 76 both around and above a
protected area 78 and asset 80. The structure provides local
contrast modulation in a first dimension 82 orthogonal to its walls
and a second dimension 84 orthogonal to the ceiling. As such, shock
wave energy from either a terrestrial or airborne explosive
detonation may be reflected. In an alternate embodiment, the unit
cells 68 may be repeated in a hemispheric configuration around and
above protected area 78. In one example, cubes 70 are void spaces
of air embedded in a concrete media. Alternately, cubes 70 may be
metal objects suspended in a lattice in air.
[0045] Referring now to FIG. 11, in an embodiment of a
three-dimensional shock wave barrier 89 comprises unit cells 90
constructed from welded circular elements of a suitable material
such as steel. The three-dimensional periodic structure is formed
of concentric hemispheres 91 of unit cells 90 with the appropriate
spacing. The band gap is obtained by arranging smaller concentric
hemisphere structures with the appropriate spacing between
hemisphere radii. A protected asset 92 sits at the center of the
structure that contains at least 6 concentric hemispheres. A door
structure may be provided thru the hemispheres for ingress and
egress.
[0046] As described above, the shock wave barrier may be configured
to protect an area and an asset from shock waves travelling in air.
The barrier may be configured to protect an area and an assets from
shock waved travelling in liquid (e.g. the ocean), in solids (e.g.
tank armor) or through the ground towards an underground area. The
dominant wavelengths of the shock wave will change, hence the
spacing of the periodic structure will change to position a band
gap coincident with the dominant wavelength but the principle
remains the same.
[0047] 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.
* * * * *