Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
INFRARED RADIATION-INTERACTIVE ARTICLE, AND METHOD OF GENERATING A TRANSIENT INFRARED RADIATION RESPONSE
Document Type and Number:
WIPO Patent Application WO/1996/040505
Kind Code:
A1
Abstract:
An infrared radiation-interactive article (10) comprising an oxidizable metal body (18) of a radiation-interactive size and shape, with an oxidation-promoting salt (20) in contact with the metal body (18), arranged so that in exposure to ambient moisture, the metal body (18) is oxidizable to a radiation non-interactive form. The article (10) of the invention may be employed to carry out a method of generating a transient radiation response, e.g., an infrared radiation reflectance signature, or infrared radiation absorption, at a selected locus receiving radiation incident thereon, by disposing at the locus a radiation interactively-effective amount of such radiation-interactive article (10), for positional location determination applications.

Inventors:
STEVENS WARD C
STURM EDWARD A
Application Number:
PCT/US1996/009020
Publication Date:
December 19, 1996
Filing Date:
June 06, 1996
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ADVANCED TECH MATERIALS (US)
International Classes:
F41H3/00; F41J2/00; G01S7/495; H01Q15/14; H01Q17/00; (IPC1-7): B32B7/12
Foreign References:
US5129323A1992-07-14
Download PDF:
Claims:
THE CLAIMS
1. What is claimed is: An infrared radiationinteractive article comprising an unsupported oxidizable metal body of a radiationinteractive size and shape, with an oxidationpromoting salt in contact with the metal body, arranged so that in exposure to ambient moisture, the metal film is oxidizable to a radiation non interactive form.
2. A radiationinteractive article according to claim 1, wherein said size and shape, and the electromagnetic properties of the metal body, render the article infrared radiationreflective in character.
3. A radiationinteractive article according to claim 1, wherein said size and shape, and the electromagnetic properties of the metal body, render the article infrared radiationabsoφtive in character.
4. A radiationinteractive article according to claim 1, wherein said size and shape, and the electromagnetic properties of the metal body, render the article infrared radiationreflective and radiationabsoφtive in character during said exposure.
5. A radiationinteractive article according to claim 1, wherein said metal body is in the form of a flake.
6. A radiationinteractive article according to claim 1, wherein the metal body has a thickness dimension not exceeding 30 microns.
7. A radiationinteractive article according to claim 1, wherein the metal body has a flake conformation including main surfaces defining a thickness therebetween, with a thickness dimension not exceeding 30 microns, and an edgetoedge dimension not exceeding 300 microns.
8. A radiationinteractive article according to claim 1, wherein the metal body has a fiber conformation, with a fiber diameter not exceeding 25 microns, and a fiber length not exceeding 1 centimeter.
9. A radiationinteractive article according to claim 1, wherein the metal body has a particle conformation, with an equivalent spherical diameter not exceeding 30 microns.
10. A radiationinteractive article according to claim 1, wherein the metal body is formed of aluminum.
11. A radiationinteractive article according to claim 1, wherein the metal body has a thickness not exceeding about 1.5 microns.
12. A radiationinteractive article according to claim 1, wherein the salt comprises a cation selected from the group consisting of calcium, potassium, copper, lithium, and iron, and an anion selected from the group consisting of carbonates, sulfates, and halides.
13. An infrared radiationinteractive article comprising an unsupported oxidizable metal body of an infrared radiationinteractive size and shape, wherein the oxidizable metal body has an oxidationpromoting salt in contact therewith, arranged so that in exposure to ambient moisture, the metal body is oxidizable to an infrared radiation noninteractive form.
14. A method of generating a transient radiation response at a selected locus for detection by targeting radiation, for determination of the positional location of the selected locus, comprising dispersing at the locus a radiation interactivelyeffective amount of a radiationinteractive article comprising an oxidizable metal film of a radiationinteractive size and shape, with an oxidationpromoting salt in contact with the metal film, arranged so that in exposure to ambient moisture, the metal film is oxidizable to an infrared radiation non interactive form.
15. A method according to claim 14, wherein said size and shape, and the electromagnetic properties of the metal film, render the article infrared radiationreflective in character.
16. A method according to claim 14, wherein said size and shape, and the electromagnetic properties of the metal film, render the article infrared radiationabsoφtive in character.
17. A method according to claim 14, wherein said size and shape, and the electromagnetic properties of the metal film, render the article infrared radiationreflective and radiationabsoφtive in character during said exposure.
Description:
INFRARED RADIATION-INTERACTIVE ARTICLE, AND

METHOD OF GENERATING A TRANSIENT INFRARED

RADIATION RESPONSE

DESCRIPTION

Field of the Invention

This invention relates to an article with transient infrared radiation

response characteristics, having utility as an electronic warfare

countermeasure, e.g., for anti-detection masking of an offensive attack, as

well as use as a positional locator means for mapping, survey, search and

rescue, and other applications involving positional location determination.

The invention also relates to appertaining methods of use of such article.

Description of the Related Art

In modern warfare, a wide variety of weapons systems are employed

which operate across the electromagnetic spectrum, including radio waves,

microwaves, infrared signals, ultraviolet signals, x-rays and gamma rays.

Infrared countermeasures therefore are becoming of greater

importance to the U.S. military, particularly in the context of proliferation

of heat-seeking missiles and infrared guided arms in military arsenals.

Infrared countermeasures fall into two primary groups: decoys and

smokes.

Infrared decoys typically take the form of flares or active metal

compositions which in use yield a thermal response simulating the thermal

signature of an endangered target for some predetermined period of time.

Infrared smoke can be constituted by warm clouds of gases or

clouds of attenuating particles. Both graphite flake and brass flake materials

have been employed as smoke-forming materials which obscure infrared

targets for military operations. This obscuration is accomplished by

absorption and/or diffuse scattering of the incident infrared radiation. Fixed

and slow moving "assets" can thus be protected by deploying a 'smoke'

cloud between the asset and the threat. Unfortunately, the properties of

previously demonstrated graphite and brass infrared radiation obscuration

materials remain unchanged and these materials persist indefinitely in the

environment. Although the enemy cannot see beyond the infrared-

obscuring cloud, neither can friendly forces, thus rendering the friendly

force weaponry and monitoring equipment correspondingly useless.

In addition to such deficiency of graphitic or brass flake smoke

materials, brass is toxic in character, while both graphite and brass have

very stable electrical conductivity and thus can affect the environment in

which they are deployed for long periods of time.

Apart from such military and electronic warfare countermeasure

applications, there is potential use for chaff materials in positional location

applications, involving marking of terrain, mapping, surveying, search and

rescue operations, air-drop delivery of goods in disaster relief or

humanitarian aid missions, and a host of other applications in which the

identification or perception of a terrestrial locus is desired.

Accordingly, there is a need in the art for an infrared radiation

countermeasure, which is able to be deployed readily to provide a transient

radiation response characteristic, which is non-toxic in character, and which

is environmentally benign.

It therefore is an object of the present invention to provide an

infrared radiation countermeasure of such type, having superior radiation

signature characteristics.

It is another object of the invention to provide a method of

providing a transient infrared radiation reflectance signature, having utility

in the obscuration of tactical and strategic military assets in warfare field

operations, or as a positional locator means.

Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

The present invention, in a broad article aspect, relates to a radiation- interactive article comprising a supported or unsupported oxidizable metal film of a radiation-interactive size and shape, with an oxidation-promoting salt in contact with the metal film, so that in exposure to ambient moisture, the metal film is oxidizable to a radiation non-interactive form.

As used herein, the term "radiation-interactive" means that the article of the invention produces a reflection (back-scatter) or attenuation (absoφtion and/or dispersive scattering) of radiation incident thereon. The term "radiation non-interactive" means that the article in exposure to incident radiation has lost its interactive response characteristic, e.g., that the reflection or attenuation characteristic of the article has been substantially, and preferably essentially completely, diminished. The radiation with which the

articles and method of the invention may be practice includes any suitable portion of the electromagnetic spectrum, including radio waves, microwaves, infrared signals, ultraviolet signals, x-rays and gamma rays. Preferably, however, the radiation comprises infrared radiation.

The term "oxidation-promoting salt" means that the salt in contact with the oxidizable metal in the article of the invention, in the presence of moisture, produces a greater extent and/or rate of oxidation of the metal, relative to a corresponding article in which the salt is absent.

In a specific embodiment, the article of the invention comprises a radiation-interactive article, e.g., infrared radiation-reflective article, comprising an oxidizable metal body coated or doped with an oxidation-

promoting salt, so that the oxidizable metal is rapidly oxidized in use to an

oxidized state in the presence of moisture.

The radiation-interactive article in the practice of the invention is of a

size and shape which renders it radiation-reflective or radiation-attenuative

in character. Such size and shape characteristics may be readily determined

by those skilled in the art without undue experimentation, but generally

involve small-size flake, fiber, or particulate forms in which the main body

of the article has a thickness dimension on the order of 30 microns or less

(the main body being constituted by the oxidizable metal film alone in the

case of an unsupported metal film, and the main body comprising the

oxidizable metal film as well as the substrate element, when the oxidizable

metal film is supported by being coated, laminated, or otherwise disposed

on such substrate).

In the case of a particulate substrate having the oxidizable metal

coating thereon, the thickness dimension of the particle is measured as the

equivalent spherical diameter of the particle (the diameter of a spherical

particle having the same volume as the particle in question). In the case of a

non-particulate article in flake form, the surface of the article (transverse to

its thickness) has an edge-to-edge dimension which desirably does not

exceed 300 microns. In the case of the radiation-interactive article of the

invention having a fiber conformation, the diameter of the fiber desirably

does not exceed about 25 microns, and the length of such fiber desirably

does not exceed 1 centimeter.

The main body of the radiation-interactive article of the present

invention thus may be constituted by a metal particle, flake, or fiber of the

oxidizable metal itself, having suitable dimensions which may be on the

order of those identified above in reference to the substrate dimensions.

The surface of the metal is coated, doped or otherwise treated with a

salt, preferably a hygroscopic salt, which promotes the oxidation of the

metal film in the presence of moisture, e.g., atmospheric relative humidity.

Alternatively, the article may comprise a substrate for supporting

the oxidizable metal film, in which the substrate may for example comprise a

non-conductive body in the desired conformation. The substrate body in

such article is coated with metal, and the metal in turn is coated, doped or

otherwise treated with a suitable salt, so that the metal is in contact with an

oxidation-promoting salt in its subsequent use.

By way of specific example, the article of the invention in a flake

conformation may comprise a substrate of mica or other suitable natural or

synthetic material in the shape of a disk or platelet having a thickness of for

example 0.1 micron, and a maximum edge-to-edge dimension which is on the

order of 10 microns. The surface of such substrate element is coated with a

thin film of an oxidizable metal, and the metal film in turn is coated,

continuously or discontinously, with a salt which is enhancingly effective

for the oxidation of the metal film in the presence of moisture.

The oxidizable metal may be of any suitable species, but preferably

comprises aluminum, although iron, or other metals or metal blends,

composites, and alloys, may advantageously be employed in the general

practice of the invention.

The metal may be coated on the substrate, or alternatively may be

provided as an unsupported metal film (e.g., metal flake), at any appropriate

thickness, and typically does not exceed about 1.5 microns. The metal may

be coated on a substrate by any suitable means and method, e.g., chemical

vapor deposition, electroless plating, evaporative coating, etc.

In one method aspect, the present invention relates to a method of

transiently altering an infrared radiation response, e.g., an infrared radiation

signature, at a selected locus, comprising dispersing at the locus an infrared

radiation interactively-effective amount of the infrared radiation-interactive

article of the invention. The radiation-interactive article may be deployed in

a quantity of such articles which is uniform in its dimensional and

conformational characteristics. Alternatively, the radiation-interactive article

may be provided in a mixture of different sizes and/or conformations of the

article (e.g., the infrared radiation-interactive material may comprise a

mixture of particulate articles of differing size (diameter) characteristics, or a

mixture of two or more forms of flake, powder, and/or fiber infrared

radiation-interactive articles.

In the use of the radiation-interactive article of the invention, the

oxidizable metal article is deployed at the desired locus, where it functions

as an effective reflector, scatterer or absorber of infrared radiation incident

on the article, depending on its shape, size and intended use. Once the metal

film, particle, fiber, etc. of the article has been corroded, e.g., by oxidation of

the metal to form corresponding metal oxides and/or hydroxides, there is no

longer any elemental metal to reflect, scatter, or absorb incident infrared

radiation.

Other aspects and features of the invention will be more fully

apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a flake conformation of an infrared

radiation-interactive article according to one embodiment of the invention.

Figure 2 is a front elevation view, partially broken away, of a

particulate conformation of an infrared radiation-interactive article according

to another embodiment of the invention.

Figure 3 is a perspective view, partially broken away, of a fiber

conformation of an infrared radiation-interactive article according to a further

embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED

MODES OF CARRYING OUT THE SAME

The disclosures of the following United States patent applications hereby are

incorporated herein by reference in their entirety: U.S. application no. 08/273,356

filed July 11, 1994, now allowed; U.S. application no. 07/734,199 filed July 22,

1991, now U.S. Patent 5,328,717; U.S. application No. 07/448,252 filed December

11, 1989, now U.S. Patent 5,034,274; U.S. application No. 07/449,708 filed

December 11, 1989, now U.S. Patent 5,039,990; U.S. application No. 07/450,585

filed December 11, 1989, abandoned; U.S. application No. 07/982,393 filed

November 27, 1992, now U.S. Patent 5,352,519; and U.S. application No.

07/449,695 filed December 11, 1989, now U.S. Patent 5,087,515. Additionally,

the disclosure of Intenational Publication Number WO 96/01012 published January

25, 1996 is hereby incorporated herein by reference in its entirety.

Specifically, the radiation-interactive articles of the invention can be fabricated in

accordance with the teachings of the aforementioned application and patent

disclosures, to provide the articles appropriate to the practice of the method of the

present invention, in a given end use application.

The present invention is based on the discovery that an infrared radiation

signature can be transiently altered for effective use as an electronic warfare

countermeasure, by the provision of articles which may be deployed in a location

of infrared radiation monitoring, or otherwise deployed for positional location

determination, wherein the article comprises an infrared radiation-interactively

sized body, formed of or coated at least in part with an infrared radiation-reflective

metal film which in exposure to ambient (e.g., atmospheric) moisture and ambient

temperature conditions rapidly oxidizes to an infrared radiation non-interactive

state.

Although described hereinafter in primary reference to use as an

electronic warfare countermeasure, the article of the present invention is not

thus limited in its utility, and may advantageously be employed for other

purposes of a non-military, non-warfare character. Examples include the

use of the infrared radiation-interactive article of the invention as: a search

and rescue tool deployed by persons who are lost or otherwise at risk at

sea or in remote terrain; a survey or cartographic tool, for deterrnining

locations, a positional location means for marking of terrain, such as for air-

drop delivery of goods in disaster relief, supply, or humanitarian aid

missions.

The salt usefully employed in the practice of the invention may comprise

any suitable salt which promotes the oxidation of the metal film. Examples include

sodium, calcium, potassium, copper, lithium, and iron salts, etc., whose anions

include carbonates, halides, sulfates, etc.

In general, the salt materials, non-conduciive substrates, and metals

disclosed in prior U.S. application no. 08/273,356 filed July 11, 1994 incoφorated herein by reference, as well as the fabrication, and salt-doping application techniques therein disclosed, may be advantageously employed in the practice of the present invention.

Figure 1 is a perspective view of a flake conformation of an infrared

radiation-reflective article 10 according to one embodiment of the invention. The

article 10 comprises a main body portion having main top face 12 and main bottom

face 14 defining a thickness B therebetween associated with the edge suface 16.

The face 12 of the flake article has a maximum edge-to-edge dimension A. The

dimension A may be for example 10 microns, and the dimension B may be for

example 0.5 micron.

The flake article 10 shown in Figure 1 may comprise a metal flake per se, of

aluminum or other suitable suitable metal material. Alternatively, the article may

comprise a main body portion which constitutes a substrate element which is

separate and distinct in relation to the metal film. Thus, the main body portion of

the article shown in Figure 1 may for example comprise a flake of mica or other

mineralic material, or of a non-mineralic material, e.g., of glass or polymeric (natural

or synthetic) material, on which is coated a film 18 of oxidizable metal.

Regardless of whether the main body portion of the article is a metal film

(flake) itself, or is a supportive element having coated thereon a metal film, the

metal film is in contact with an oxidation-promoting salt 20, which as shown may

be in the form of deposits (e.g, islands) of salt on the surface of the metal film, or

alternatively the salt may be relatively continuous on the surface of the metal film,

or as a still further alternative the salt may be codeposited or co-formed with the

metal film, or otherwise provided so that the salt is in oxidation-promoting

relationship to the metal film, and so that exposure of the metal film to

environmental moisture causes the salt-contacted metal film to oxidize to a non-

interactive state (relative to response to incident infrared radiation on the article).

The specific size, shape and conformation of the metal film article of the

invention may be readily determined without undue experimentation for a given

radiation exposure application, by the simple expedient of varying the size, shape

and/or conformation of the article, and measuring the radar interaction characteristic

of interest (reflectance, absoφtion, scattering) at specific relative humidity

conditions simulative of the end use application of interest.

In general, the dimensions of the article of the invention are selected so that

the main body of the article (either the metal film itself in the case of an

unsupported metal film, or the substrate element in the case in a supported metal

film) has a thickness dimension on the order of 30 microns or less, more preferably

on the order of 25 microns or less, and most preferably on the order of 25 microns

or less.

In the case of a particulate substrate, such thickness dimension is the

diameter of the particle. In the case of a non-particulate article in flake form, the

surface of the substrate article (transverse to its thickness) has an edge-to-edge

dimension which desirably does not exceed 200 microns. In the case of a fiber

conformation, the diameter of the article generally does not exceed 100 microns,

more preferably does not exceed about 30 microns, and most preferably does not

exceed about 25 microns, whille the fiber length typically does not exceed 1

centimeter.

The substrate may be a metal particle, flake, or fiber itself, or alternatively,

the substrate may be a non-conductive body in the desired conformation, with such

substrate body being coated with metal, and doped or otherwise treated with a

suitable salt, so that the metal is in contact with an oxidation-promoting salt in its

subsequent use. In a preferred aspect of the present invention, the substrate of the

article is formed of a biodegradeable material, e.g., a water-soluble material, which is

readily broken down in the environment in which the article is deployed.

Figure 2 is a front elevation view, partially broken away, of a particulate

conformation of an infrared radiation-reflective article 22 according to another

embodiment of the invention. The article 22 is spherically shaped, being

symmetrical about axis L-L, with a diameter D, which as indicated may be on the

order of 1.5 microns or less, e.g., 0.2 to 1.0 micron. The article 22 in the

embodiment shown comprises a non-metal spherical support body whose outer

surface 26 has a coating 28 of oxidizable metal thereon, wherein the metal film

comprises or is otherwise in contact with the oxidation-promoting salt, e..g, in the

surface-doped salt deposits 30 shown in Figure 2.

Figure 3 is a perspective view, partially broken away, of a fiber

conformation of an infrared radiation-reflective article 32 according to a further

embodiment of the invention. In this embodiment, the article 32 comprises a fiber

substrate 34 which may for example be formed of a soluble material such as boria

which in the presence of water is dissolvable to dissipate the support element of

the article. The substrate 34 has respective circular-shaped end faces 36 and 38 of

diameter D, with a main cylindrical outer surface 40 defining a length L of the fiber

and having coated thereon the metal film 42 doped with salt deposits 46. The fiber

shown in Figure 3 may alternatively comprise a metal fiber which is wholly formed

of oxidizable metal and appropriately fabricated so that the metal thereof is in

contact with a suitable salt promotor material for the desired oxidation of the metal.

As an illustrative example of radiation-interactive articles of the present

invention, an iron-coated glass fiber (E-glass, Owens-Corning D filament) having a

diameter of 4.8 microns, may be provided with an iron coating on the fiber outer

surface which is 0.075 micron in thickness. The metal coating on such fiber article

may be doped with iron (III) chloride to yield an oxidatively susceptible metal-

coated fiber substrate article. As another example, a glass fiber of the same material

(E-glass, Owens-Corning D filament) may have a diameter of 25 microns, and is

coated with a 0.1-1 micron thickness of an oxidizable metal coating, with the metal

coating being doped with a hygroscopic salt at a concentration of less than 3% by

weight of salt, based on the weight of the metal coating, to facilitate the rapid

oxidation of the metal coating in use of the article.

In a particularly advantageous embodiment of the invention, aluminum

powders aluminum flake materials, and aluminum coated finely divided substrates

are doped with a salt to effect a temporal infrared radiation absorber. Small

amounts of salt applied to the surface of the aluminum causes corrosion of the

metal surface in exposure to ambient moisture which converts the metal to an oxide

or hydroxide. Prior to such corrosion, finely divided aluminum and aluminum

coated finely divided substrates may be deployed to advantageously function as

good scatterers or effective attenuators of IR radiation. Once the aluminum film

has been corroded, there is no longer any metal to reflect incident radiation, nor to

carry electrical current if the article subsequently contacts electrical components or

assemblies.

While the invention has been described herein with reference to specific

embodiments and features, it will be appreciated that the utility of the invention is

not thus limited, but encompasses other variations, modifications, and alternative

embodiments, and accordingly the invention therefore is to be broadly construed as

comprehending all such alternative variations, modifications, and other

embodiments within its spirit and scope.