U.S. patent application number 13/009837 was filed with the patent office on 2011-12-29 for solid solution-based nanocomposite optical ceramic materials.
Invention is credited to Richard Gentilman, Thomas M. Hartnett, Christopher Scott Nordahl, Brian J. Zelinski.
Application Number | 20110315808 13/009837 |
Document ID | / |
Family ID | 46516009 |
Filed Date | 2011-12-29 |
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United States Patent
Application |
20110315808 |
Kind Code |
A1 |
Zelinski; Brian J. ; et
al. |
December 29, 2011 |
SOLID SOLUTION-BASED NANOCOMPOSITE OPTICAL CERAMIC MATERIALS
Abstract
A solid solution-based optical material capable of transmitting
infrared light, the solid solution-based optical material
comprising at least two nano-sized phases intermixed in one
another, wherein at least one of the at least two nano-sized phases
is a solid solution containing a dissolved dopant, the dissolved
dopant present in an amount sufficient to reduce a refractive index
difference between the at least two nano-sized phases to about 0.2
or less when infrared light is being transmitted. Various
embodiments are directed to related systems and methods. In one
embodiment, the infrared light is visible infrared light,
short-wave infrared light, eye safe infrared light, medium wave
infrared light, long wave infrared red light, or combinations
thereof.
Inventors: |
Zelinski; Brian J.; (Tucson,
AZ) ; Gentilman; Richard; (Acton, MA) ;
Nordahl; Christopher Scott; (Littleton, MA) ;
Hartnett; Thomas M.; (Nashua, NH) |
Family ID: |
46516009 |
Appl. No.: |
13/009837 |
Filed: |
January 19, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12821876 |
Jun 23, 2010 |
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13009837 |
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Current U.S.
Class: |
244/3.16 ; 501/1;
501/152; 501/153; 501/87; 977/831; 977/834 |
Current CPC
Class: |
B82Y 20/00 20130101;
F42B 10/46 20130101; C04B 2235/80 20130101; C04B 2235/3279
20130101; G02B 1/002 20130101; C04B 2235/3225 20130101; F42B 15/34
20130101; C04B 35/01 20130101; C04B 35/505 20130101; C04B 2235/9653
20130101; B82Y 30/00 20130101; C04B 2235/781 20130101; C04B 35/6455
20130101; C04B 2235/3206 20130101; C04B 35/053 20130101 |
Class at
Publication: |
244/3.16 ; 501/1;
501/152; 501/153; 501/87; 977/834; 977/831 |
International
Class: |
F42B 15/01 20060101
F42B015/01; C04B 35/505 20060101 C04B035/505; C04B 35/10 20060101
C04B035/10; C04B 35/58 20060101 C04B035/58; C04B 35/547 20060101
C04B035/547; C04B 35/622 20060101 C04B035/622; C04B 35/00 20060101
C04B035/00; C04B 35/56 20060101 C04B035/56 |
Claims
1. A nano-structure comprising: a solid solution-based optical
material capable of transmitting infrared light, the solid
solution-based optical material comprising at least two nano-sized
phases intermixed in one another, wherein at least one of the at
least two nano-sized phases is a solid solution containing a
dissolved dopant, the dissolved dopant present in an amount
sufficient to reduce a refractive index difference between the at
least two nano-sized phases to about 0.2 or less when infrared
light is being transmitted.
2. The nano-structure of claim 1 wherein the solid solution-based
optical material is a solid solution-based optical ceramic
material.
3. The nano-structure of claim 1 wherein the solid solution-based
optical material is capable of transmitting light within a
long-wave infrared light range, a medium wave infrared light range,
an eye safe infrared light range, a short wave infrared light
range, a visible infrared light range, or combinations thereof.
4. The nano-structure of claim 1 wherein the solid solution-based
optical material is capable of achieving transparency and
functioning in the mid-wave infrared light range and the maximum
refractive index difference between the first and second nano-sized
phases lies between about 0.15% and about 0.6%.
5. The nano-structure of claim 1 wherein the solid solution-based
optical material is capable of achieving transparency and
functioning in the eye-safe infrared light range and the maximum
refractive index difference between the first and second nano-sized
phases lies between about 0.5% and about 1.5%.
6. The nano-structure of claim 1 wherein the solid solution-based
optical material is capable of achieving transparency and
functioning in the short wave infrared light range and the maximum
refractive index difference between the first and second nano-sized
phases lies between about 0.15% and about 0.6%.
7. The nano-structure of claim 1 wherein the solid solution-based
optical material is capable of achieving transparency and
functioning in the visible infrared light range and the maximum
refractive index difference between the first and second nano-sized
phases lies between about 0.05% and about 0.15%.
8. The nano-structure of claim 1 wherein the at least two
nano-sized phases are selected from yttria (Y.sub.2O.sub.3),
magnesia (MgO), aluminum oxide (Al.sub.2O.sub.3), magnesium
aluminum oxide (MgAl.sub.2O.sub.4), carbides, oxycarbides,
nitrides, oxynitrides, borides, oxyborides, sulfides, selenides,
sulfo-selenides and semiconductors and the dopant is a metal
oxide.
9. The nano-structure of claim 1 comprising first and second
nano-sized phases, wherein the dopant decreases the refractive
index of the first phase.
10. The nano-structure of claim 1 comprising first and second
nano-sized phases, wherein the dopant increases the refractive
index of the first phase.
11. The nano-structure of claim 10 wherein the first nano-sized
phase is MgO, the second nano-sized phase is Y.sub.2O.sub.3 and the
dopant is NiO.
12. The nano-structure of claim 11 wherein the solid solution
containing a dissolved dopant comprises
Ni.sub.0.455Mg.sub.0.545O.
13. The nano-structure of claim 1 capable of transmitting infrared
light in a lens, dome or window.
14. A system comprising: an airborne platform; and an electro-optic
sensor system located on the airborne platform, wherein the
electro-optic sensor system includes a nano-structure comprising a
solid solution-based optical material capable of transmitting
infrared light, the solid solution-based optical material
comprising at least two nano-sized phases intermixed in one
another, wherein at least one of the at least two nano-sized phases
contains a dopant in an amount sufficient to reduce a refractive
index difference between the at least two nano-sized phases to
about 0.2 or less when infrared light is being transmitted.
15. The system of claim 14 wherein the airborne platform is located
on a guided projectile.
16. The system of claim 15 wherein the electro-optic sensor is part
of a dome, window or lens.
17. A method of reducing a refractive index mismatch comprising:
intermixing a first nano-sized phase and a second nano-sized phase
into one another, wherein the first nano-sized phase has a first
refractive index and the second nano-sized phase has a second
refractive index; and adding a dopant to the first phase to form a
solid solution, wherein the first refractive index is increased or
decreased to substantially match the second refractive index.
18. The method of claim 17 wherein the first nano-sized phase is
magnesia having a refractive index of about 1.649.
19. The method of claim 18 wherein the second nano-sized phase
comprises yttria having a refractive index of about 1.847.
20. The method of claim 19 wherein the dopant is NiO is added in an
amount sufficient to increase the refractive index of MgO to about
1.844 up to about 1.850.
21. The method of claim 19 wherein the dopant is NiO is added in an
amount sufficient to increase the refractive index of MgO to about
1.846 up to about 1.848.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 12/821,876 filed on Jun. 23, 2010, which is
hereby incorporated by reference in its entirety.
BACKGROUND
[0002] Airborne platforms carrying electro-optical (EO) sensors for
such tasks as target acquisition, identification, guidance, and the
like, are generally provided with a transparent dome to protect the
optical system. In particular, projectiles, such as missiles,
interceptors, guided projectiles, bombs, rockets, shells and
sub-munitions, typically have the dome in the front end. Behind
this dome, and within the body of the projectile, an EO seeker is
provided for capturing electro-magnetic radiation (EMR) from the
target, and conveying target information (e.g. bearing or images)
to a guidance system, which, in turn, guides the projectile to an
object or point within the captured images. Aircraft such as planes
or helicopters may be provided with a directed infrared
countermeasures (DIRCM) system to jam a missile seeker. This system
may be mounted on the belly, tail section or elsewhere on the
aircraft behind a protective dome. The dome is generally made of a
transparent material that can sustain the aerodynamic and thermal
stresses it may experience during missile or aircraft flight. In
many conventional applications the dome is made of sapphire.
[0003] The size of the field of regard (FOR) obtainable by the EO
seeker depends on the spanning angle of the dome used. The term
"spanning angle" when used herein refers to the actual angular
portion that the dome spans without vignetting with respect to a
full sphere whose spanning angle is 360.degree.. The angle measured
from the longitudinal axis through the center of the dome to the
edge of the FOR is one-half the spanning angle and is referred to
as the "look angle." Conventional missile domes, such as sapphire
domes, are made of, at most, approximately half a sphere size.
Therefore, when a conventional optical seeker is provided at the
center of dome, and if mounted on one, two, or more axes gimbals,
this optical sensing unit of the prior art can theoretically view a
field of regard of, at most, 180 degrees.
[0004] Attempts to produce domes in which the FOR is greater than
180 degrees include techniques which separately fabricate two
pieces comprising a spherical portion similar to a conventional
dome and an extended portion, which are then joined to form the
dome. However, the attachment process creates an optical interface
along the line of attachment, which produces a discontinuity as the
EO seeker scans the FOR. Such a discontinuity poses a risk the
seeker may lose track on the target.
SUMMARY
[0005] The inventor is the first to recognize the need for improved
nanocomposite optical ceramic materials which can provide
transparency in the visible and SWIR spectrums while maintaining
robust mechanical and thermal properties. Accordingly, in one
embodiment, a nano-structure comprising a solid solution-based
optical material capable of transmitting infrared light, the solid
solution-based optical material comprising at least two nano-sized
phases intermixed in one another, wherein at least one of the at
least two nano-sized phases is a solid solution containing a
dissolved dopant, the dissolved dopant present in an amount
sufficient to reduce a refractive index difference between the at
least two nano-sized phases to about 0.2 or less when infrared
light is being transmitted is provided.
[0006] In one embodiment, a system comprising an airborne platform;
and an electro-optic sensor system located on the airborne
platform, wherein the electro-optic sensor system includes the
aforementioned nano-structure is provided.
[0007] In one embodiment, a method of reducing a refractive index
mismatch comprising intermixing a first nano-sized phase and a
second nano-sized phase into one another, wherein the first
nano-sized phase has a first refractive index and the second
nano-sized phase has a second refractive index; and adding a dopant
to the first phase to increase or decrease the first refractive
index to substantially match the second refractive index is
provided.
[0008] The novel solid solution-based nanocomposite optical ceramic
materials described herein may be useful in a variety of
applications, other than military, such as civilian or medical
applications. Other features and advantages will become apparent
from the following description of the embodiments, which
description should be taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A and 1B show isometric and section views of the nose
of a guided projectile incorporating a one-piece extended dome in
accordance with an illustrative embodiment of the present
invention.
[0010] FIG. 2 shows tracking of a target through a dome with an
optical interface between the spherical and conical sections as
compared to an optical interface between the spherical and conical
sections in accordance with an illustrative embodiment of the
present invention.
[0011] FIGS. 3A and 3B show a nanocomposite optical material at
different magnifications comprising two separate phases of
nanograins in accordance with an illustrative embodiment of the
present invention.
[0012] FIG. 4 shows transmission versus wavelength of an
approximately 50:50 mixture (by vol.) of yttria:magnesia
(Y.sub.2O.sub.3:MgO) nanocomposite optical ceramic material as
compared to sapphire in accordance with an illustrative embodiment
of the present invention.
[0013] FIG. 5 shows transmission versus wavelength of various
alternative solid solution-based nanocomposite optical ceramic
materials in accordance with illustrative embodiments of the
present invention.
[0014] FIG. 6 is a flow diagram for manufacture of a one-piece
extended dome from a nanocomposite optical ceramic material in
accordance with an illustrative embodiment of the present
invention.
[0015] FIG. 7 is a section view of a one-piece extended dome
comprising a seamless transition between the non-complementary
spherical and conical geometries in accordance with an illustrative
embodiment of the present invention.
[0016] FIGS. 8A-8C are section views of different sphero-conical
geometries in accordance with an illustrative embodiment of the
present invention.
[0017] FIG. 9 is a section view of a sphero-ogive geometry in
accordance with an illustrative embodiment of the present
invention.
[0018] FIG. 10 shows model transmittance of optical materials of
varying thicknesses which contain scattering phases with scattering
coefficient, .gamma..
[0019] FIG. 11A shows the modeling results of index difference
versus wavelength in a spectrum which includes MWIR and LWIR
wavelengths.
[0020] FIG. 11B shows the modeling results of index difference
versus wavelength (at .gamma.=0.1 cm.sup.-1) in a spectrum which
includes the visible, SWIR and eye safe wavelengths.
[0021] FIG. 12 provides refractive index data for common
materials.
[0022] FIG. 13 shows a binary phase diagram for NiO and MgO.
[0023] FIG. 14 shows the modeling results of refractive index
versus fractional composition of NiO for various solid
solution-based MgNiO (NiMgOss) materials in accordance with
illustrative embodiments of the present invention.
[0024] FIGS. 15A-15I show models of computational cells, together
with their particular space group, in accordance with illustrative
embodiments of the present invention.
[0025] FIG. 16 shows the modeling results of refractive index
versus fractional composition of NiO for a solid solution-based
MgNiO (NiMgOss) material in accordance with an illustrative
embodiment of the present invention.
[0026] FIG. 17 shows the modeling results of refractive index
versus energy (eV) for various solid solution-based nanocomposite
optical ceramic materials in accordance with illustrative
embodiments of the present invention.
[0027] FIG. 18 shows the modeling results of absorption index (k)
versus energy (eV) for various ceramic materials in accordance with
illustrative embodiments of the present invention.
DETAILED DESCRIPTION
[0028] The following description and the drawings sufficiently
illustrate specific embodiments to enable those skilled in the art
to practice them. Other embodiments may incorporate structural,
logical, electrical, process, and other changes. Portions and
features of some embodiments may be included in, or substituted
for, those of other embodiments. Embodiments set forth in the
claims encompass all available equivalents of those claims.
[0029] The infrared (IR) spectrum generally refers to
electromagnetic radiation having a wavelength between 0.7 and 300
micrometers. The IR spectrum is typically divided into ranges,
which can vary depending on which scheme is used, such as a sensor
response division scheme, an astronomy division scheme, a CIE
scheme or the ISO 20473 scheme.
[0030] As used herein, the term "visible range" refers to radiation
having a wavelength range of about 0.4 to about 0.75 microns
(.mu.m). The term near infrared (NIR) is generally considered to
refer to radiation having a wavelength range of about 0.75 to about
1.4 .mu.m, while the term "short wavelength infrared" (SWIR) is
considered to refer to a wavelength range of about 1.4 to about 3
.mu.m. However, as used herein, except where noted, the term "short
wavelength infrared" (SWIR) is intended to encompass both near
infrared (NIR) and SWIR, and refers to radiation having a
wavelength range from about 0.75 to about three (3) .mu.m, with an
"eye-safe" wavelength range considered to be from about 1.5 to
about 1.8 .mu.m. Mid wavelength infrared (MWIR), also referred to
as "intermediate infrared", is generally considered to include
radiation between about three (3) and about 8 .mu.m, possibly up to
about 8.5 .mu.m. However, in guided missile applications, the about
three (3) to about five (5) .mu.m portion of this band is the
atmospheric window in which the homing heads of passive IR "heat
seeking" missiles are generally designed to work, homing on to the
IR signature of a target. That is, this range is generally
considered to be the range of wavelengths which can come through
the atmosphere. Therefore, although most MWIR applications for the
novel materials described herein may fall within the range of about
three (3) to about five (5) .mu.m, it is to be understood that
embodiments directed to the MWIR spectrum, unless otherwise noted,
are not so limited. Long wavelength infrared (LWIR), which is
considered the "thermal imaging" region, generally refers to
radiation having a wavelength of between about eight (8) (or
possibly about 8.5 .mu.m) up to about 15 .mu.m, although most
applications likely don't exceed 12 to 14 .mu.m. Forward looking
infrared (FLIR) systems use this area of the spectrum, sometimes
also referred to as "far infrared" (FIR).
[0031] Current nanocomposite materials do not transmit light in the
SWIR and visible portions of the spectrum because the difference in
refractive indices of the phases comprising the nanocomposite is
too large. This difference causes scattering of the light at the
shorter wavelengths associated with the visible and SWIR, leading
to opacity. In an effort to overcome the limitations of prior
technologies, attempts have been made to provide domes comprising a
single nanostructure or phase in a continuous "host" macro-matrix
background. However, strength-reducing processing flaws are
commonly associated with use of larger-grained matrix phases, which
can negatively affect a dome's optical properties. Such flaws
remain even if the material is reinforced with nano-dispersoids. As
such, such materials may not possess adequate strength to bear the
aerodynamic forces present during launch and flight of a guided
projectile.
[0032] Accordingly, various solid solution-based embodiments
described herein provide materials which have been adjusted to
reduce or substantially eliminate the difference in indices between
the phases of the nanocomposite, thus eliminating scatter and
extending the rage of transmittance into the SWIR and visible
portions of the spectrum. This is accomplished by adjusting one of
the phases through formation of a solid solution, such that the
refractive index of the adjusted phase equals or nearly equals that
of the remaining phase or phases constituting the nanocomposite
optical ceramic material. A solid solution phase, as is known in
the art, is a single phase region that has at least two different
cations mixed together on the same crystal lattice, making it a
homogeneous mixture or solution at the atomic level. Therefore, in
contrast to mixtures of liquids which form a liquid solution, a
solid solution has a crystal lattice (periodic arrangement of
atoms).
[0033] In one embodiment, the nano-sized optical materials comprise
two or more nanostructures (such as, but not limited to nanograins
or nanoparticles) which are intermixed in one another to form a
nanocomposite, but which maintain their chemical distinctness,
i.e., remain in separate phases. Such nanocomposites, by
definition, are not embedded in a macro background, thus
eliminating the issues inherent when using macro-sized grains, such
as strength-reducing processing flaws. Additionally, use of the
novel materials described herein in applications such as extended
domes, provides a spanning angle greater than 180 degrees from a
single integrated material Essentially, the extended dome comprises
seamless first and second non-complementary geometric shapes, such
as a first spherical geometry and a second conical or ogive
geometry.
[0034] Nanocomposite materials useful herein are capable of
transmitting optical light (i.e., visible light, as compared with
light in other spectrums, such as SWIR and MWIR), such as a
combination of nano-sized covalent materials (e.g., diamond)
together with elements such as germanium or silicon. In one
embodiment, the material is a nanocomposite optical ceramic
material comprising two chemically distinct nanostructures
intermixed in one another sufficiently to allow a single, two-phase
material to form which possesses the desired optical properties, as
well as the desired strength and thermal properties. In one
embodiment, a first nanostructure phase (comprising, e.g.,
nanograins) is selected such that the second nanostructure phase
(comprising, e.g., nanograins) does not chemically combine with,
but remains intermixed with first phase. In one embodiment, the two
phases are two nanograined phases which are mixed sufficiently to
allow formation of material barriers to grain growth between the
various nanograins, thus strengthening the nanocomposite optical
ceramic material by retaining the nanoscale of the nanostructure.
In general, the two phases are intermixed sufficiently to prevent
or minimize nanostructure growth to larger sizes due to lack of
"pinning" or restraint of the nanostructure boundaries by the
second phase. In one embodiment, intermixing of at least five (5) %
by volume (v), may be sufficient. In other embodiment, more than
about five (5) % (v), such as up about 10% (v), such as up to about
15% (v) or higher, such as at least 20% (v) or higher, such as
about to an approximately 50:50 mixture by volume, including all
ranges there between.
[0035] In one embodiment, the nanocomposite material comprises two
nano-sized phases (intermixed as described above), with one of the
phases adjusted through formation of a solid solution such that the
refractive index of the adjusted phase becomes substantially equal
or nearly equal to that of the remaining phase, thus forming a
solid solution nanocomposite material. Essentially, in this
embodiment, one phase is "doped" by a dopant which not only causes
formation of a solid solution, but can further improve the
refractive properties of a nanocomposite material, such as a
nanocomposite optical ceramic material.
[0036] The dopant can comprise atoms mixed on a cation or anion
lattice, i.e., on the atomic scale. In one embodiment, the dopant
is sub-nanometer in size, having a radius on the order of about
less than one (1) nanometer, down to about 0.1 nanometers. In one
embodiment, the dopant comprises atoms mixed on a cation lattice
with the cation having a radius of between about 0.1 and about 0.2
nanometers. In one embodiment, NiO is used as the dopant. In one
embodiment the dopant can also maintain or enhance the thermal and
mechanical properties of the material. As such, the novel solid
solution-based nanocomposite materials described herein may be
useful not only in applications in MWIR and LWIR spectral regions,
but also in the SWIR and even visible spectral regions, as well as
in multi-mode operations (i.e., more than one spectral region).
[0037] FIGS. 1A and 1B show an embodiment of a one-piece extended
dome (hereinafter "dome") 10 mounted on the nose 11 of a guided
projectile 12. In this embodiment, the nose 11 is attached to a
projectile body (not shown) that typically includes a fuse assembly
and warhead and one or more aerodynamic control surfaces. Behind
the dome 10, and within the nose 11 of the guided projectile 12, an
EO seeker 16 is provided for capturing images and conveying them to
a guidance system computer 18 (FIG. 1B), which, in turn, controls
aerodynamic control surfaces (e.g. fins, canards, etc.) to guide
the guided projectile 12 to an object or point within the captured
images. In this embodiment, the EO seeker 16 includes an objective
lens 20 mounted on a gimbal mechanism 22 for movement in three
degrees of freedom and a detector 24 receiving EMR passing through
the objective lens 20 to the detector 24 (FIG. 1B), which, in turn,
conveys target information (e.g. bearing or images) to the guidance
system computer 18 (FIG. 1B).
[0038] In one embodiment, the gimbal mechanism 22 moves the object
lens 20 in three degrees of freedom through a spanning angle
greater than 180 degrees (look angle .THETA. greater than 90
degrees) without vignetting. In another embodiment, additional EO
components are positioned behind and adjacent to the extended
portion of the dome 10 to receive or transmit EMR through the
extended portion of the dome 10. In this latter case, the gimbal
mechanism 22 may move the objective lens 20 through a spanning
angle that may be less than or greater than 180 degrees, depending
on the configuration of the EO seeker 16.
[0039] The dome 10 can be integrally-formed of a nanocomposite
optical ceramic material or a solid solution-based nanocomposite
optical ceramic material. In one embodiment, the dome 10 is
substantially transparent over a portion of the IR Band including
near IR (about 0.75 to about 1.4 microns), SWIR (about 1.4 to about
3 microns), MWIR (about 3 to about 8.5 microns), LWIR (about 8 to
about 12 microns), and/or the visible band (about 0.4 to about 0.75
microns).
[0040] In an embodiment using a mixture of yttria (yttrium oxide,
Y.sub.2O.sub.3) and magnesia (magnesium oxide, MgO), the
nanocomposite optical ceramic material comprising the dome 10
transmits from 1.5 to 8.5 microns. The dome 10 comprises seamless
first and second non-complementary geometric shapes 26, 28, such as
a first spherical geometry 26 and a second conical or ogive
geometry 28 (i.e., a geometry comprising a section or a large
radius or arc). In this particular embodiment, the spherical
geometry 26 supports a look angle .THETA..sub.1 of 85.degree. and
the conical geometry 28 supports an additional look angle
.THETA..sub.2 of 30.degree. for a total look angle .THETA. of
115.degree.. The spherical geometry 26 is generally bounded to be
less than 90.degree., typically 87.degree. or less and is typically
greater than 75.degree..
[0041] FIG. 2 plots apparent target position 40 versus look angle
for a conventional two-piece extended dome and one embodiment of a
novel one-piece extended dome. In a typical EO seeker for either a
guided projectile or DIRCM system, the seeker moves within the FOR
to lock-on and track a target. As the seeker swings through the
spherical section of the dome, for either the 2-piece or 1-piece
configuration, the seeker maintains track 42 on the target.
However, for conventional two-piece domes as the seeker swings
across the attachment point it sees a discontinuity due to the
optical interface or blockage, which may produce a discontinuity 44
in apparent target position. The guidance system responds to this
discontinuity, which may cause the projectile or DIRCM system to
break track 46, possibly resulting in mission failure. In contrast,
with use of a novel one-piece dome as described herein, as the
seeker swings from the spherical geometry to the conical geometry,
it sees a seamless transition and maintains target track 48. This
seamless transition between the non-complementary spherical and
conical (or ogive) geometries enables the use of extended domes for
guided projectiles and DIRCM.
[0042] FIGS. 3A and 3B show an embodiment of the nanocomposite
optical ceramic powder material 50 comprising two or more different
chemical phases of nanograins intermixed in one another, each phase
having a substantially uniform submicron grain dimension
(.ltoreq.100 nm) in at least the direction approximately
perpendicular to the direction of propagation of the transmitted
light. In one embodiment, the submicron grain dimension may include
all submicron grain dimensions that are less than approximately
1/10.sup.th of the wavelength of transmitted light. In one
embodiment, the submicron grain dimension may include all submicron
grain dimensions that are less than approximately 1/20.sup.th of
the wavelength of transmitted light. Use of two or more phases of
nanograins allows formation of material barriers to grain growth
between the various nanograins, thus strengthening the
nanocomposite optical ceramic material or the solid solution-based
nanocomposite optical ceramic material.
[0043] In this particular example, powder 50 comprises a mixture of
Y.sub.2O.sub.3 nanograins 52 and MgO nanograins 54, each having a
grain dimension which is sub-micron in all directions and less than
approximately 1/10.sup.th the IR transmission wavelength.
Specifically, all of the constituent elements have sub-micron grain
dimensions, i.e., there is no host (i.e., macro) matrix.
[0044] In general, the two or more different phases of nanograins
in the powder are selected from materials which are sufficiently
transparent in the wavelength range of interest and can be
processed to retain nanograins of submicron size in at least one
direction. These materials include, but are not limited to oxides,
such as Y.sub.2O.sub.3, MgO, alumina, (aluminum oxide
(Al.sub.2O.sub.3), spinel (magnesium aluminum oxide
(MgAl.sub.2O.sub.4)) and non-oxides, such as carbides (e.g. silicon
carbide (SiC)), oxycarbides (e.g. silicon oxycarbide
(SiO.sub.xC.sub.y)), nitrides (e.g. silicon nitride
(Si.sub.3N.sub.4)), oxynitrides (e.g. (SiO.sub.xN.sub.y)), borides
(e.g. zirconium boride (ZrB.sub.2)), oxyborides, (e.g. zirconium
oxyboride (ZO.sub.xB.sub.y), sulfides, (e.g. zinc sulfide (ZnS)),
selenides (e.g. zinc selenide (ZnSe)), sulfo-selenides (e.g.
ZnS.sub.xSe.sub.y)), as well as semiconductors, such as silicon
(Si) and germanium (Ge). In one embodiment, a LWIR application is
desired, and ZnS is selected as a first phase. In one embodiment,
the two phases are Y.sub.2O.sub.3 and calcium oxide (CaO).
[0045] The different phases of nanograins in a given powder are
mutually neutral in that they do not react chemically with each
other. In one embodiment, the nanograins are selected to have
similar refractive indices. In one embodiment, the difference
between refractive indices of nanograins in a given powder is less
than about 0.25. If the disparity in refractive indices is too
large, inter-particle scattering can occur, which will degrade
optical performance.
[0046] The material shown in FIGS. 3A and 3B is a nanocomposite
optical ceramic material comprising approximately 50:50 by volume
of Y.sub.2O.sub.3:MgO, although the invention is not so limited.
The relative percentages of the constituent nanograins in the
powder (the composition of the powder) may be varied to achieve
different optical properties, strength and thermal conduction. The
relative percentages and types of nanograins may be varied between
the spherical and conical portions of the extended dome. The
constituent elements and/or relative percentages are varied across
the seamless transition between the two different geometries.
[0047] Rayleigh scattering affects the ability of certain
nanocomposite optical ceramic materials to function in the lower
spectral regions, such as SWIR and visible regions. Rayleigh
scattering can be reduced by decreasing particle size and improving
refractive index match between phases of the nanocomposite, such as
by adding a dopant. FIG. 4 shows transmission versus wavelength for
the material of FIG. 3 in the midwave IR range (curve 402), as
compared with sapphire (curve 404). As can be seen, the
nanocomposite optical ceramic material performs better than
sapphire in the MWIR, but Rayleigh scattering causes a short wave
cut-on (SWCO) at about one to two microns. As such these
nanocomposite optical ceramic materials are not transparent at 1.5
micrometers, at 1.06 micrometers or in the visible region.
[0048] In contrast, when the refractive index difference (.DELTA.n)
is reduced, i.e., refractive index mismatch improved, Rayleigh
scattering is minimized and the SWCO is shifted to shorter
wavelengths. In the embodiments shown in FIG. 5, various
alternative solid solution-based nanocomposite optical ceramic
materials with various useful levels of transparency within a solid
solution-based target range 502 of about 0.4 to about two (2)
microns are shown. As such, the solid solution-based target range
502 includes the visible range of about 0.4 to about 0.75 .mu.m and
a portion of the SWIR, although the invention is not so limited. In
other embodiments, the solid solution-based target range 502 can
include higher SWIR wavelengths, as well as some or all of the MWIR
spectrum or higher. The solid solution-based target range 502 is
obtainable when delta n (.DELTA.n) is about 0.01 as shown with
curve 504. The solid solution-based target range 502 is also
obtainable even with a .DELTA.n of 0.05 as shown in curve 506,
although the SWCO is shifted to the right as compared with curve
504. Once the .DELTA.n approaches 0.2 as shown in curve 508, the
SWCO shifts further to the right. A .DELTA.n of 0.6, shifts the
SWCO even further to the right as shown in curve 510.
[0049] In one embodiment, the novel solid-solution based
nanocomposite optical ceramic materials are more sensitive to the
percentage difference in refractive index rather than the actual
average index of the entire nanocomposite. In the modeling shown in
Example 1, for example, with Y.sub.2O.sub.3 and MgO, an average
refractive index for the two phases of 1.75 was used. If silicon or
germanium materials are used, an acceptable average refractive
index may be 3 or 4. For other materials which do not absorb in the
visible spectrum, an acceptable average refractive index may be
less than two (2).
[0050] Referring now to FIG. 6, an embodiment for integrally
forming a one-piece extended dome from a nanocomposite optical
ceramic powder comprises the steps of powder fabrication and
preparation (step 60), near net shape forming (step 62) and final
shape finishing (step 64). Fabrication and preparation may use a
Flame Spray Pyrolysis (FSP) to provide a precursor solution of
nano-sized MgO and Y.sub.2O.sub.3 (step 70). Other techniques may
also be employed to provide the precursor solution, which is
de-agglomerated (step 72) e.g., ground and mixed with a mill, to
break up any clumps. The solution is then filtered (step 74) to
remove impurities and any residual large particles from the
solution. The solution is granulated (step 76) to remove the liquid
solution to form a dry powder. Near net shape forming may be
accomplished using a dry press process (step 80) in which the
powder is packed into a mold of the desired extended dome and
pressure is applied to produce a green body of the desired near net
shape. A sintering process (step 82) applies heat to densify the
green body. A hot isostatic press (step 84) applies heat and
pressure to complete densification and eliminate any remaining
voids to make a fully dense dome blank. Final shape finishing
includes precision grinding and polishing (step 90) the surface of
the dome to the finished shape and characterization (step 92) of
the dome's mechanical and optical properties to verify the dome
meets the specifications.
[0051] Referring now to FIG. 7, the transition from the spherical
shape 26 to the conical shape 28 of the extended dome 10 is
seamless, with no attachment points or optical interfaces. The
one-piece extended dome comprises seamless first and second
non-complementary geometric shapes. ("Non-complementary" refers to
sections of different geometries e.g. spherical and conical or
spherical and ogive). Other non-complementary pairings may also be
possible. The typical shape will include a spherical leading shape
and either a conical or ogive trailing shape to flare the dome to
meet the diameter of the platform.
[0052] FIGS. 8A through 8C illustrate different embodiments of a
sphero-conical dome. Referring now to FIG. 8A, a one-piece extended
dome 100 integrally formed of a nanocomposite optical ceramic
material comprises a leading spherical shape 102 and a trailing
conical shape 104 that flares the diameter of the dome from the
diameter of the spherical shape to the diameter of the platform
106. The conical geometric shape has inner and outer surfaces
tangent to inner and outer surfaces respectively of the spherical
shape at the point of seamless transition. In other words, lines
108 tangent to the surfaces of the spherical shape at the
transition are coincident with the conical shape. In this case, the
look angle .THETA.1 of spherical shape 102 is selected to satisfy
this constraint. That angle will depend upon the platform diameter
and any overall length limitation on the dome itself. This approach
ensures a smooth physical transition between the spherical and
conical shapes but may not maximize the look angle of the spherical
shape, which is generally desirable.
[0053] Referring now to FIG. 8B, a one-piece extended dome 120
integrally formed of a nanocomposite optical ceramic material
comprises a leading spherical shape 122 and a trailing conical
shape 124 that flares the diameter of the dome from the diameter of
the spherical shape to the diameter of the platform 126. The
conical shape has inner and outer surfaces that form a non-zero
positive angle .gamma. to surfaces 128 tangent to inner and outer
surfaces respectively of the spherical shape at the point of
seamless transition. In other words, the conical shape forms a
skirt that flares outwards at a larger angle to transition from the
diameter of the spherical shape to the platform diameter. In this
case, the look angle .THETA..sub.1 of spherical shape 122 is
suitably selected to be as close to 90.degree. as practicable. This
maximizes the look angle of the spherical shape.
[0054] Referring now to FIG. 8C, a one-piece extended dome 130
integrally formed of a nanocomposite optical ceramic material
comprises a leading spherical shape 132 and a trailing conical
shape 134 that extends the dome to platform 136. This is a special
case in which the diameter of the spherical section equals the
diameter of the platform. In this special case the apex of the
conical shape is at infinity whereby the conical shape becomes a
cylinder. The surfaces of the cone lie at a non-zero negative angle
with respect to the tangent surfaces of the spherical shape unless
the spherical shape is 90 degrees in which case they are
tangent.
[0055] Referring now to FIG. 9, a one-piece extended dome 200
integrally formed of a nanocomposite optical ceramic material
comprises a leading spherical shape 202 and a trailing ogive shape
204 that flares the diameter of the dome from the diameter of the
spherical shape to the diameter of the platform 206. In the
extremes as the radius gets larger the arc flattens approaching a
cone and as the radius gets smaller the arc gets more pronounced
approaching a hemisphere.
[0056] With respect to nanocomposite optical ceramic materials
(primarily MWIR), and solid solution-based nanocomposite optical
ceramic materials in particular (primarily visible and SWIR),
several of the various embodiments described herein possess
properties which are significantly improved as compared to
conventional sapphire. For example, some embodiments are
transparent to 8.5 micrometers, as compared to sapphire, which cuts
off at six (6) .mu.m. Some embodiments possess an approximately
15-30.times. lower emissivity than sapphire at five (5) .mu.m and
an approximately four (4) times lower emissivity of sapphire at six
(6) .mu.m.
[0057] It is expected that the various materials will also be
harder than sapphire. Additionally, the biaxial strength of the
various materials described herein is expected to be higher than
sapphire. Similarly, the thermal shock resistance is also expected
to improve, as is sand and rain erosion resistance as compared with
sapphire
[0058] The materials may be deliverable in a number of different
configurations, such as disks, hemispherical and ogive domes of
various sizes (e.g., a few cm in diameter up to several cm in
diameter, e.g., between about five (5) and nine (9) cm, such as
about 7.64 cm), although the invention is not so limited. The novel
materials described herein are also expected to be useful in even
larger configurations, including configurations not yet employed
for use in a variety of applications, such as various types and
sizes of domes, lenses, flats and windows. Such improvements in
properties enable the novel material described herein to be useful
in missions which not only experience harsher environmental
conditions, but in missions which are faster (e.g., Mach 6 or
higher), longer and hotter than conditions currently achievable
with conventional materials.
[0059] Embodiments of the invention will be further described by
reference to the following examples, which are offered to further
illustrate various embodiments of the present invention. It should
be understood, however, that many variations and modifications may
be made while remaining within the scope of the present
invention.
Example 1
[0060] The ability of a nanocomposite optical ceramic material to
be doped with another material to form a solid solution-based
nanocomposite optical ceramic material having a reduced refractive
index difference was explored. In this testing, the doping of MgO
with a material to cause its refractive index to substantially
match that of Y.sub.2O.sub.3 was examined with computer modeling.
Complications unique to transition metals with localized d shell
electrons were also considered.
[0061] MedeA software (Materials Design, Inc.) was used to
determine index differences between the selected end member pairs
for multimode nanocomposites, i.e., components for each phase.
Specifically, the MedA software platform was used for calculating
the refractive index of the (substantially) pure reference
compounds MgO and Y.sub.2O.sub.3 at a wavelength of one (1) micron.
As such it was determined that the refractive index (RI) of MgO is
about 1.649 and the RI of Y.sub.2O.sub.3 is about 1.847.
[0062] From resources such as the Table 2 from Gladstone and Dale
list (Table 2), it is possible to calculate the specific refractive
energy of the chief constituents of a material to determine if it
will likely going to increase or decrease the RI of another
material. As such, the choice was either to select an oxide capable
of increasing the RI of MgO or decreasing the RI of Y.sub.2O.sub.3.
Specifically, it was determined that with a specific refractive
energy of NiO, for example, of 0.184, such a material would,
itself, have an RI of about 2.227, and so would likely increase the
RI of a material such as MgO. Thereafter, phase diagrams of various
materials were reviewed to provide a rough approximation as to
whether the "right" phase relationships would hold. That is, to be
sure that each material can remain in its own phase, even when
intermixed in another material. Thereafter, the MedeA software was
used to generate a model to determine doping needs of MgO to match
NiMgOss index to Y.sub.2O.sub.3.
[0063] FIG. 10 shows model transmittance of optical materials of
varying thicknesses which contain scattering phases with scattering
coefficient, .gamma.. For optical materials which are about one (1)
to about eight (8) mm in thickness, .gamma.=0.1 cm.sup.-1 gives a
transmittance of greater than 90%. From this information, design
constraints which define tolerances were developed.
[0064] Modeling was performed using the Rayleigh model with some
modifications according to the following equation for the
scattering coefficient:
.gamma. = 32 9 .pi. 4 a 3 .lamda. 0 4 ( n A 2 - n B 2 ) 2 f A ( 1 -
f A ) 2 ##EQU00001##
n.sub.A and n.sub.B are the RIs for two different phases, A and B,
present in the nanocomposite as nanograins, a is the average radius
of the nanograins, f.sub.A is the volume fraction of the A phase,
and .lamda..sub.0 is the wavelength of the mode of operation. For
purposes of this experiment, it was assumed that the scattering was
occurring as independent, single scattering, although it is
understood this may not be the case over the entire range.
(Additional modeling may take other factors into account, such as
dependent or correlated and multiple scattering effects.)
[0065] FIGS. 11A and 11B show the absolute magnitude of the index
difference. Specifically, at (.gamma.)=0.1 cm.sup.-1, FIG. 11A
shows the modeling results of index difference versus wavelength
for nanostructures (curve 1102) compared to conventional larger
structures (200 nm) (curve 1104) in a spectrum which includes a
portion of the MWIR (area 1106) and a portion of the LWIR (area
1108). As can be seen, the smaller the structure, the larger the
difference in index that allows the next lower wavelength mode to
be picked up. FIG. 11B shows the modeling results of index
difference versus wavelength (at .gamma.=0.1 cm.sup.-1) for
nanostructures (curve 1110) compared to conventional larger
structures (200 nm) (curve 1112) in a spectrum which includes the
visible (area 1114), a portion of the SWIR (curve 1116) and a
portion of the eye-safe spectrum (area 1118). For FIGS. 11A and
11B, the volume fraction of the second phase (f.sub.A), i.e., the
non-doped phase, is assumed to be 0.5, with n.sub.ave equal to
1.75).
[0066] With this information, it is possible to provide tolerances
around the dopant amount which represent a substantially perfect
match. See Table 1:
TABLE-US-00001 TABLE 1 Likely Ranges for Maximum .DELTA.n Tolerable
for various wavelengths (for nanograin sizes ranging from 100 to
200 nm) Wavelength Visible SWIR Eye Safe MWIR LWIR .DELTA.n range
0.001-0.003 >0.003 up to 0.012, 0.01-0.03 >0.03 up to 0.2,
>0.2, such as such as .004-0.012 such as 0.07-0.2 >0.43 up to
2 % difference 0.05-0.15 >0.15 up to 0.6, 0.5-1.5 >1.5 up to
10, >10, such as such as 0.2-0.6 such as 3.5-10 >21.5 up to
115%
[0067] As Table 1 shows, .DELTA.n is closely related to wavelength.
Essentially, Table 1 shows the acceptable tolerances for a solid
solution-based nanocomposite optical ceramic material capable of
transmitting in the visible range up through LWIR. The various
ranges for .DELTA.n are estimates. Additionally, the index
differences shown are not intended to represent a range which must
be met, rather the .DELTA.n need to be equal to or less than some
value that lies in this range. As such, it is likely that index
differences on the order of magnitude shown and lower will work in
the range indicated. A smaller index difference will allow
additional mode(s) to be picked up.
[0068] For example, with SWIR, the maximum value of the difference
in index that the two phases (for nanograins ranging in size from
100 to 200 nm) can have and still transmit in the SWIR spectrum
lies somewhere in the range of about 0.003 to about 0.012. As can
be seen in FIG. 11B, if the grain size is smaller, the "dashed"
line shifts to higher values and a larger difference in index can
be tolerated and still pass the region 1116.
[0069] If too little dopant is added, the requisite .DELTA.n cannot
be achieved. For example, in embodiments in which a .DELTA.n of
zero is desired, sufficient dopant needs to be added to first
achieve .DELTA.n=0. If an additional phase forms prior to reaching
.DELTA.n=0, further additions will only increase the amount of the
additional phase, and not the refractive index of the solid
solution phase. With this testing, if too little dopant is added to
the MgO the index of the solid state phase will be too low as
compared with Y.sub.2O.sub.3. If too much is added the index of the
solid state phase will be too high, such as higher than
Y.sub.2O.sub.3. In either case, scattering results and SWCO is
shifted to longer wavelengths. Deviation from a perfect match in
refractive indices in either direction will cause transparency to
be lost. In this example, with NiO added to MgO, as the perfect
composition is approached (from below) by adding NiO, the SWCO
shifts to lower and lower wavelengths. At the perfect matching
composition (.DELTA. n=0), there is no scatter and the material is
transparent at all wavelengths where there is no absorption. If
additional NiO is added, the index for the solid solution phase
will begin to depart from the perfect matching value, eventually
becoming larger than Y.sub.2O.sub.3 and scattering will again
occur. Adding even more NiO at this point will only cause the SWCO
to shift to longer wavelengths and additional modes will be
lost.
[0070] With respect to the visible range, Table 1 indicates that
sufficient dopant needs to be added to modify a first phase of a
nanocomposite optical ceramic material to provide a maximum index
difference between the first phase and a second phase that lies in
the range between about 0.001 and about 0.003 and still achieve
transparency as modeled (at (.gamma.)=0.1 cm.sup.-1). In other
words, in order for the material to function in the visible range
with sufficient transparency, there can be a maximum difference in
refractive index between the two phases lying in the range between
about 0.05% and about 0.15%.
[0071] With respect to the SWIR range, as noted above, Table 1
indicates that sufficient dopant needs to be added to modify a
first phase of a nanocomposite optical ceramic material to provide
maximum index difference between the first phase and a second phase
that lines in the range between about 0.003 up to about 0.12, such
as between about 0.004 and about 0.012 and still achieve
transparency as modeled (at (.gamma.)=0.1 cm.sup.-1). In other
words, in order for the material to function in the SWIR range with
sufficient transparency, there can be a maximum difference in
refractive index between the two phases lying in the range between
about 0.15% and about 0.6%.
[0072] With respect to the eye safe range, Table 1 indicates that
sufficient dopant needs to be added to modify a first phase of a
nanocomposite optical ceramic material to provide a maximum index
difference between the first phase and a second phase that lies in
the range between about 0.01 and about 0.03 and still achieve
transparency as modeled (at (.gamma.)=0.1 cm.sup.-1). In other
words, in order for the material to function in the eye safe range
with sufficient transparency, there can be a maximum difference
between the two phases lying in the range between about 0.5% and
about 1.5%.
[0073] With respect to the MWIR range, Table 1 indicates that
sufficient dopant needs to be added to modify a first phase of a
nanocomposite optical ceramic material to provide maximum index
difference between the first phase and a second phase that lies in
the range between about 0.03 and about 0.2, such as between 0.07
and about 0.2, and still achieve transparency as modeled (at
(.gamma.)=0.1 cm.sup.-1). In other words, in order for the material
to function in the MWIR range with sufficient transparency, there
can be a maximum difference between the two phases lying in the
range between about 0.5% and about 1.5%, such as lying in the range
between about 3.5% and about 10%.
[0074] With respect to the LWIR range, Table 1 indicates that
sufficient dopant needs to be added to modify a first phase of a
nanocomposite optical ceramic material to provide maximum index
difference between the first phase and a second phase that lies
above about 0.2, such as in the range between about 0.43 and about
2, and still achieve transparency as modeled (at (.gamma.)=0.1
cm.sup.-1). In other words, in order for the material to function
in the LWIR range with sufficient transparency, there can be a
maximum difference between the two phases of greater than about 10%
such as lying in the range between about 21.5% and 115%.
[0075] The literature was reviewed in an effort to identify
suitable nanocomposite end-member pairs based on .DELTA.n. The
information available, however, such as the index dispersion of
common dome and window materials from "Materials for Infrared
Windows and Domes: Properties and Performance", Daniel C. Harris,
SPIE Optical Engineering Press, p. 17, (1999) and shown in FIG. 12
only provides refractive index data for common materials So-called
"uncommon" materials are shown in Table 2 (from Gladstone and Dale
(1864)). However, these materials are only known by additive
combination of constants accurate to 5% at best and at a single
wavelength.
TABLE-US-00002 TABLE 2 Specific refractive energies ( n - 1 d = k )
##EQU00002## of the chief constituents of minerals. Molecular
weight. k. H.sub.2O 18 .sup.a0.335 , .sup.b.340, .sup.c.354
Li.sub.2O 30 .31 (NH.sub.4).sub.2O 52 .503 Na.sub.2O 62 .181
K.sub.2O 94 .189 Cu.sub.2O 143 .250 Rb.sub.2O 187 .129 Ag.sub.2O
232 .154 Cs.sub.2O 282 .124 Hg.sub.2O 416 .169.sub.Li Tl.sub.2O 424
.120 C1O 28 .238 MgO 40.4 .200 CaO 56 .225 MnO 71 .sup.d.191,
.sup.e.224 FeO 72 .187 NiO 75 .184 CoO 75 .184 CuO 79.6 .sup.d.191,
.sup.e.253.sub.Li ZnO 81.4 .sup.d.153, .sup.e.183 SrO 103.6 .143
CdO 128.4 .134 BaO 153.4 .127 HgO 216 .18 PbO 223 .sup.d.137,
.sup.e.175.sub.Li B.sub.2O.sub.3 70 .sup.g.220 C.sub.2O.sub.3 72
.265 Al.sub.2O.sub.3 102 .193, .sup.f.214 Cr.sub.2O.sub.3 152 .27
Mn.sub.2O.sub.3 158 .sup.d.300, .sup.e.304.sub.Li Fe.sub.2O.sub.3
160 .sup.d.308, .sup.e.36.sub.Li As.sub.2O.sub.3 198 .sup.g0.202,
.sup.h0.225 Yt.sub.2O.sub.3 226 .144 Sb.sub.2O.sub.3 285.4
.sup.g.209, .sup.i.232 La.sub.2O.sub.3 326 .149 Ce.sub.2O.sub.3
328.3 .16 Hf.sub.2O.sub.3 464 .163 CO.sub.2 44 .217 SiO.sub.2 60
.207 TiO.sub.2 80 .397 SeO.sub.2 111 .147 ZrO.sub.2 122.5 .201
SnO.sub.2 151 .145 SbO.sub.2 152 .198 TeO.sub.2 159.5
.sup.e.200.sub.Li ThO.sub.2 264.5 .12 N.sub.2O.sub.5 108 .240
P.sub.2O.sub.5 142 .100 Cl.sub.2O.sub.5 151 .218 V.sub.2O.sub.5
182.4 .43 As.sub.2O.sub.5 230 .169 Br.sub.2O.sub.5 240 .183
Cb.sub.2O.sub.5 268 .295 Sb.sub.2O.sub.5 320.4 .152, .222(?)
I.sub.2O.sub.5 334 .177 Ta.sub.2O.sub.5 445 .133 SO.sub.3 80 .177
CrO.sub.3 100 .36 SeO.sub.3 127 .165 MoO.sub.3 144 .241.sub.Li
TeO.sub.3 175.6 .607 WO.sub.3 235 .133 UO.sub.3 286.5 .134
.sup.aWater and ice. .sup.bAverage. .sup.cAlums, etc.
.sup.dCalculated from compounds containing the oxide.
.sup.eCalculated from the oxide. .sup.fCalculated from feldspar,
feldspathoids, etc. .sup.gIsometric oxide. .sup.hMonoclinic oxide.
.sup.iOrthorhombic oxide. indicates data missing or illegible when
filed
[0076] As such, the inventor is the first to provide a solid
solution-based nanocomposite optical ceramic material comprising
components which allow only the doped phase to be impacted by a
dopant, but not the other phase or phases, as confirmed with
computer modeling.
[0077] As will be shown herein, surprisingly, the two phase
nanocomposite material of MgO and Y.sub.2O.sub.3 discussed above,
in combination with a specific amount of NiO as the dopant in MgO,
exhibits transmittance not only in the SWIR, but also in the
visible spectrum (while retaining excellent mechanical properties),
by reducing the difference in the refractive index between MgO and
Y.sub.2O.sub.3, thereby minimizing Rayleigh scatter. It is expected
that other combinations of nanostructures may be combined to
convert a nanocomposite optical ceramic material into a solid
solution-based nanocomposite optical ceramic material having the
desired properties for a particular application or
applications.
[0078] As discussed herein, NiO and MgO are mutually soluble in
each other in the solid solution-based. See FIG. 13, for example
which shows a binary phase diagram for NiO and MgO. The constraints
as shown in Table 1 apply, such that if too much NiO is added, the
two phases would not be preserved, resulting in ternary phases.
[0079] FIG. 14 shows the modeling results for refractive index
versus fractional composition of NiO in solid solution-based MgNiO
(NiMgOss) in curves A, B, C and D, with the selected target area
1402 showing the target level 1404 of 1.902 for nY.sub.2O.sub.3.
Target compositions of NiO were initially selected at values of
0.15, 0.3 and 0.45 as shown. The various curves show the linear
average refractive index, the Clausious Methodxy Expression, (CM-1
and CM-2) and the Bruggerman effective medium approximation (EMA).
As is known in the art, the CM Expression predicts the refractive
index as a function of weighted combinations of atomic
polarizability of the atoms in the structure. As FIG. 14 shows, it
is theoretically possible to use a range of possible
polarizabilities for the nickel.
[0080] Complications unique to transition metals with localized d
shell electrons were also considered. As such, the CME software was
further optimized with respect to this property, with use of
electron density functional and hybrid functional providing the
best results, Ni--Ni ordering and electron spin orientation. A very
slight preference for Ni--Ni spacing of 0.42 nm with opposite spins
was shown. The algorithm showed that the efficiency of hybrid
functional calculations was greatly increased.
[0081] FIGS. 15A-15I show models of computational cells used in
this study, together with their particular space group (or
crystallographic group, or Fedorov group), which is a description
of the symmetry of the crystal build unit cells of a crystal. The
CME software was allowed to "relax" the structure such that a
steady state equilibrium configuration was reached. From that, the
CME software was able to calculate both the refractive index was
calculated and the polarization matrix
[0082] FIG. 16 shows the modeling results for the refractive index
versus fractional composition of NiO for a solid solution-based
MgNiO (NiMgOss) material with the original "selected target area"
1402 identified. Surprisingly, the composition predicted to
substantially match the refractive index of Y.sub.2O.sub.3 has a
much higher NiO content than the prior art would suggest. The
Ni.sub.0.455Mg.sub.0.545O composition is also higher than any
compositions in the selected target area 1402. However, the
computer modeling confirms that a solid solution nanocomposite
material having a doped nano-sized solid solution-based phase of
Ni.sub.0.455Mg.sub.0.545O and a non-doped nano-sized phase of
Y.sub.2O.sub.3 will minimize Rayleigh Scatter and be capable of
transmitting infrared light in the visible spectrum.
[0083] FIG. 17 shows the modeling results for the refractive index
versus energy (eV) for various nanocomposite ceramic materials, as
modeled by the software, with the area within oval 1702
approximately representing the energy of interest, which
corresponds with a spectrum which includes the visible wavelength
of 1.06 .mu.m. As can be seen, the refractive index of solid
solution-based NiOMgO increases systematically with increasing NiO
(See curves A-I).
[0084] Additional considerations include whether or not doping of
one phase to cause it to become solid introduces absorption or
adsorption bands into the undoped phase. FIG. 18 shows the modeling
results for absorption index (k) versus energy (eV) for various
nanocomposite ceramic materials. As shown, no absorption peaks area
present in the area of interest 1702 which corresponds with a
spectrum which includes the visible wavelength of 1.06 .mu.m.
Additionally, modeled phonon dispersion curves (not shown) further
indicated the absence of any absorption bands.
[0085] These modeling results demonstrate that combining of NiO and
MgO can be combined accomplished, with the resulting solid solution
phases having substantially uniform composition. The modeling
further showed that a proper phase relationship can exist when
solid solution-based NiOMgO is combined with Y.sub.2O.sub.3.
Example 2
[0086] Various dense samples of MgO:Y.sub.2O.sub.3, i.e., salt
solutions were prepared as described above to verify the modeling
work performed with these materials with respect to refractive
index. To date, the nanocomposite optical ceramic materials made
include: 85:15 mol % MgO:NiO; 70:30 mol % MgO:NiO; and 55:45 mol %
MgO:NiO.
[0087] Rough approximations of solid solution-based
NiMgO:Y.sub.2O.sub.3 nanocomposite (two-phase) optical ceramic
materials were fabricated by adding large scale (non-nano-sized)
NiO. Although these materials were not transparent, this experiment
was useful to ensure that the expected chemical interactions exist
between these phases (e.g., when heated to above 1200.degree. C.)
in order to ensure phase relationships are maintained, e.g., to
ensure that a ternary phase is not being produced with the addition
of NiO.
Example 3 (Prophetic)
[0088] The prototypes fabricated in Example 2, as well as
additional prototypes will be optically characterized, including
prototypes with varying amounts of Y.sub.2O.sub.3 to achieve the
desired goal, which, includes transparency. These materials will be
compared against the computer modeling results obtained in Example
1. Various mechanical properties, including those noted herein,
will also be determined.
CONCLUSION
[0089] Embodiments described herein provide a cost-effective
extended dome having a spanning angle greater than 180 degrees for
EO sensors without the optical interface and discontinuity created
along the line of attachment of the first and second
non-complementary geometries. The extended dome is an enabling
technology that addresses a long felt need in the industry to
provide a cost-effective design for a seamless extended dome having
a spanning angle greater than 180 degrees. The extended dome may be
used, for example, with guided projectiles or DIRCM systems, and
the like.
[0090] In various embodiments, both phases of these novel optical
materials comprise grains with sizes in the submicron range
(.ltoreq.100 nm), which, in effect, eliminates any distinction
between a "host" matrix and a "submicron-grained" phase as in the
prior art. Instead, use of two or more phases of nanograins allows
formation of material barriers to grain growth between the various
nanograins, while enhancing both mechanical and optical properties
of the nanocomposite optical ceramic material or solid
solution-based nanocomposite optical ceramic material. These
materials also exhibit an enhancement to their mechanical
properties as compared with conventional optical materials
comprising less than one phase, while mitigating optical scatter.
Additional benefits of this technology include their near-net shape
forming capabilities as well as the ability to tailor properties of
the composite by varying constituent selection according to a
particular application.
[0091] With respect to the solid solution-based embodiments,
positive benefits of increased strength, hardness and thermal shock
resistance that derive from the sub-micron composite structure can
be realized, along with extension of the spectral band of
applicability beyond the MWIR to the SWIR and visible portions of
the spectrum, thus facilitating multi-mode applications.
[0092] 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. For example,
although the material has been described herein as a ceramic, any
material capable of transmitting optical light can be used, such as
a suitable combination of covalent materials, such as diamond,
silicon and/or geranium. However, such materials may not be useful
in applications requiring wavelengths shorter than MWIR, such as
SWIR or visible. However, 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.
[0093] The Abstract is provided to comply with 37 C.F.R. Section
1.72(b) requiring an abstract that will allow the reader to
ascertain the nature and gist of the technical disclosure. It is
submitted with the understanding that it will not be used to limit
or interpret the scope or meaning of the claims. The following
claims are hereby incorporated into the detailed description, with
each claim standing on its own as a separate embodiment.
* * * * *