GB1605261A

GB1605261A - Camouflage system

Info

Publication number: GB1605261A
Application number: GB5062377A
Authority: GB
Inventors: Timothy J Coutts; Donald J Highgate; Kenneth J Lawson
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1977-12-05
Filing date: 1977-12-05
Publication date: 1986-11-12
Also published as: CA1225239A

Description

(54) CAMOUFLAGE SYSTEM (71) I the SECRETARY of STATE for DEFENCE, London do hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a combined infra-red and visible light camouflage system.

The principles of camouflaging an object to hinder visual observation of it are generally well known and basically involve colouring the surface of the object in some way to match its (normal) background or marking the object in a manner which breaks up its shape as seen by the eye. In either way objects can be made to be visually virtually indistinguishable from their background.

Apart from visual observation of objects, observation at infra-red wavelengths is also extensively used. This is commonly observation of a passive kind, ie where the radiation originating only from the object itself is detected, but active observation involving use of a beam of radiation for detection purposes may also be employed. Observation in the infra-red range is commonly carried out at wavelengths in the 3 to 14 micrometers range and relies upon the object having a characteristic infra-red emission to distinguish it from the background. As the emission of infra-red radiation is related to the temperature of the emitting body, this emission has to be somehow disguised in order to provide an infra-red camouflage for the body. It is an object of this invention to provide such an infra-red disguise without seriously detracting from a visible light camouflage.

Accordingly the present invention provides an infra-red and visible camouflage system which comprises, in combination, two materials, one being a selective absorber of visible light and the other a reflector of infra-red radiation in at least the 3-14 micrometer range, said materials being superposed and so chosen that the material on the observed side of the system is at least substantially transparent in respect of that kind of radiation which interacts with the material on the non-observed side of the system.

Throughout this specification reference to the "observed side" of the system is to be understood as reference to the side of the system which is closer to the observer, whereas reference to the "non-observed side" of the system is to be understood as reference to the side of the system which is further away from the observer, when the camouflage system is in normal use.

By a selective absorber of visible light is meant a material which absorbs only at a certain selected wavelength or wavelengths so as to appear to be coloured to an observer of the system. The absorber material may absorb at different wavelengths in different regions of its surface area, thus giving a variegated effect to an observer of the system. Such an effect is well known in conventional visible camouflage technology.

However in the case of the infra-red regions of the spectrum, the situation is more complex due to the fact that, dependent on the circumstances, at least a proportion of the radiation of this kind emanating from a body is characteristic of the temperature of that body.

To disguise the presence of an object which is relatively warm compared to the surroundings (which is generally the situation to be faced) it is preferred that it have a surface of low emissivity (and high reflectivity) for infra-red light. This is because the low emissivity surface ensures that the object will not be prominent to passive observation by being a strong emitter of radiation. A high reflectivity is useful in all cases of passive observation since it means that any infra-red radiation incident on the material from the surroundings will tend to be reflected without change and thus the material will naturally appear rather like its surroundings, ie be well camouflaged.However in an active observation situation such a reflector might appear rather prominent in the field of vision since it would completely reflect the incident detector beam and lead to ready detection of the reflecting object should the beam be intercepted. If such detection is very likely, then use of a reflector material having different reflectivities over different parts of its area may be advantageous in order to provide camouflage in like manner to the differentially selective absorber material for visual camouflage described previously.

Throughout this specification reference to infra-red absorption, reflection and emission properties is to be understood as reference to such properties in at least the 3-14 micrometer range of radiation.

It will be apparent that the two materials comprising the system may be arranged in either of two ways. Thus the visible absorbing material may be on the observed side of the system with the infra-red reflector material on the non-observed side of the system or the two materials may be disposed in the opposite order. In the former case the visible absorbing material should be transparent or at least substantially transparent to infra-red radiation at least in the 3-14 ,am range, whilst in the latter case the infra-red reflecting material should be at least substantially transparent to visible light. In this way the camouflage effects achieved in each wavelength range may be successfully observed from the outside of the system.

Where the infra-red reflector is on the non-observed side of the system, the selective absorber of visible light as described, must be substantially a non-absorber of infra-red radiation. Materials of this kind may be obtained by using a dispersion of a pigment that absorbs strongly in the visible region in a non-infra-red absorbing matrix material, the concentration of the dispersion being such that, although the material is effective to absorb in the visible range it does not absorb any substantial amount of infra-red radiation.

Pigments which have been found suitable for this purpose include red iron oxide, Prussian Blue, cadmium sulphide, cadmium selenosulphide and chromium oxide. These are conveniently used at a concentration of about 3% by weight when in the medium which is about 50 microns thick. For media of different thickness the pigment concentration must be varied correspondingly in known manner in order that the number of absorbing centres on the path of the light passing through the medium be kept roughly constant. A suitable matrix material is polyethylene which has only a relatively low i.r. absorbance in the 3-14 micron range. Using polyethylene as the matrix, the thickness of the visible absorbing material will typically be of the order of 0.1 mm but thicknesses of up to a few millimetres can be used. The pigments may be incorporated into the matrix material by any of the conventional means.

The sub-surface infra-red reflector may be provided by a reflective metal surface which may belong to the object which is being camouflaged eg the metal surface of a vehicle.

The selective absorber of visible light can in this case be applied to the reflective metal surface by using, for example, an adhesive, though this has to be selected carefully in order to avoid using a material which has a strong i.r.

absorption. In order to avoid such problems and also because it is difficult to polish up a metal surface so that it has a sufficiently high reflectivity, it is preferred to use as the i.r.

reflector, a metal coating on a sheet of the selective absorber of visible light. It is especially preferred that the coating be of aluminium since the process of aluminizing is well known and is already commercially applied.

An aluminized sheet of the kind described can be used either as a loose covering to put over the object to be camouflaged or can be affixed to the object, eg using an adhesive. In this case as the adhesive is on the inside of the reflector material, any adhesive can be used.

Where, in the alternative form of the camouflage system of the invention, the infra-red reflector comprises the material, on the observed side of the system, with the selective absorber of visible light on the non-observed side of the system, the reflector material should be at least substantially transparent to visible light and for this purpose dispersions of, for example, lanthanum hexaboride or stannic oxide or mixed oxides of antimony, cadmium indium and tin, including such compounds as cadmium stannate and indium tin oxide, are suitable. The disperson matrix is conveniently a visible light transparent binder, eg a clear polyurethane, and by suitable formulation the dispersion can be made into a paintable composition.This can then be applied as a surface coat to an object which has already been painted with conventional visible pigments in order to provide a camouflage system according to this invention. In another embodiment the visibly transparent, i.r. - reflective material may comprise a disperson of a suitable substance in sheet form one side of which is painted with a visibly absorbing paint. As with the non-infra-red absorbing material, so in this case the concentration and thickness of the dispersion should be so chosen as to ensure that while remaining at least substantially transparent to visible light, the layer is strongly reflecting as regards infra-red radiation. This apart the thickness of the sheet can be chosen to be appropriate for the use to which the system is to be put; for example the sheet may be so thick as to be mechanically self-supporting.

A preferred embodiment of the camouflage system of the invention comprises two reflective metal surfaces attached to each other and each covered with a selective absorber of visible light. Such a laminated sheet has advantages in that, it is fully reversible and hence there is no need to identify the sides when the sheet is applied under, for example, conditions of darkness. In addition, the metal surfaces are protected from damage from either side and the overall strength of the sheet is increased.

The strength of the laminated sheets of the type described can be increased further by placing a layer of reinforcing material between the two reflective metal surfaces before lamination.

A particularly preferred embodiment of the camouflage system of the invention comprises two sheets of polyethylene, in which a visiblyabsorbing, infra-red non-absorbing pigment is dispersed, each covering an aluminium surface, with either canvas or wire mesh as a reinforcing fabric between the two aluminium surfaces. Where reversibility is not an important or useful feature a sheet of pure polyethylene (which may or may not be aluminium coated) may be substituted for one of the pigmented sheets.

Particular embodiments of the camouflage system according to this invention will now be described by way of example only, with reference to the drawings filed with the provisional specification in which: Figure 1 shows an arrangement of the system where the selective absorber of visible light is on the observed side of the system whilst the infra-red reflecting material is on the non-observed side of the system; and Figure 2 shows an arrangement of the system where the infra-red reflector is on the observed side of the system whilst the selective absorber of visible light is on the non-observed side of the system.

In Figure 1 a laminated sheet comprises two sheets of visibly pigmented polyethylene (1,2), each of which has a metal coating (3,4), eg of aluminium. The sheets are typically 50 to 100 ,um thick and the metal coating 2 to 3 CL thick. The sheets are joined on their metallized faces with a layer of a fabric material 5 between the faces to provide added strength. The fabric may be a material such as canvas or a wire mesh and the sheets may be joined by any suitable adhesive. Exemplary of the pigments which may be present in the polyethylene sheets is synthetic red iron oxide pigment supplied by Morris Ashby as Deanox 1,70.

In Figure 2, a body to be camouflaged is shown generally at 10. Applied to the surface of the body is a layer 11 of a visibly absorbing pigment or of different pigments as the case may be, painted on to the body surface. A further layer 12 consisting of a visibly nonabsorbing, infra-red reflecting pigment/binder composition is deposited on the visible pigment layer 11. The pigment/binder composition may conveniently be in paintable form and so can be painted on the first (visible) pigment layer once this has dried. The composition may comprise stannic oxide or lanthanum hexaboride or mixed oxides of antimony, cadmium, indium and tin in a polyurethane carrier.

WHAT WE CLAIM IS: 1. An infra-red and visible camouflage system which comprises, in combination, two materials, one being a selective absorber of visible light and the other a reflector of infra-red radiation in at least the 3 to 14 micro-meter range, said materials being superposed and so chosen that the material on the observed side of the system is at least substantially transparent in respect of that kind of radiation which interacts with the material on the non-onserved side of the system.

2. An infra-red and visible camouflage system according to Claim I wherein the reflector of infra-red radiation has different reflectivities over different parts of its area.

3. An infra-red and visible camouflage system according to either Claim 1 or Claim 2 wherein the reflector of infra-red radiation is on the observed side of the system and the selective absorber of visible light is on the non-observed side of the system.

4. An infra-red and visible camouflage system according to Claim 3 wherein the reflector of infra-red radiation comprises either lanthanum hexaboride or stannic oxide in a dispersion matrix.

5. An infra-red and visible camouflage system according to Claim 3 wherein the reflector and infra-red radiation comprises mixed oxides of antimony, cadmium, indium and tin.

6. An infra-red and visible camouflage system according to Claim 4 wherein the disperson matrix comprises a polyurethane which is transparent to visible light.

7. An infra-red and visible camouflage system according to either Claim 1 or Claim 2 wherein the selective absorber of visible light is on the observed side of the system and the reflector of infra-red radiation is on the non-observed side of the system.

8. An infra-red and visible camouflage system according to Claim 6 wherein the reflector of infra-red radiation is a reflective metal surface.

9. An infra-red and visible camouflage system according to Claim 7 wherein the reflective metal surface is the surface of the object that is being camouflaged.

10. An infra-red and visible camouflage system according to Claim 7 wherein the reflective metal surface is a metal coating attached to a sheet of the selective absorber of visible light.

11. An infra-red and visible camouflage system according to Claim 9 wherein the metal coating is of aluminium.

12. An infra-red and visible camouflage system according to Claim 9 wherein the metal coated sheet is affixed to the object to be camouflaged.

13. An infra-red and visible camouflage system according to any one of Claims 7 to 11 comprising two reflective metal surfaces attached to each other and each covered with a selective absorber of visible light.

14. An infra-red and visible camouflage system according to Claim 12 wherein the two

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The strength of the laminated sheets of the type described can be increased further by placing a layer of reinforcing material between the two reflective metal surfaces before lamination. A particularly preferred embodiment of the camouflage system of the invention comprises two sheets of polyethylene, in which a visiblyabsorbing, infra-red non-absorbing pigment is dispersed, each covering an aluminium surface, with either canvas or wire mesh as a reinforcing fabric between the two aluminium surfaces. Where reversibility is not an important or useful feature a sheet of pure polyethylene (which may or may not be aluminium coated) may be substituted for one of the pigmented sheets. Particular embodiments of the camouflage system according to this invention will now be described by way of example only, with reference to the drawings filed with the provisional specification in which: Figure 1 shows an arrangement of the system where the selective absorber of visible light is on the observed side of the system whilst the infra-red reflecting material is on the non-observed side of the system; and Figure 2 shows an arrangement of the system where the infra-red reflector is on the observed side of the system whilst the selective absorber of visible light is on the non-observed side of the system. In Figure 1 a laminated sheet comprises two sheets of visibly pigmented polyethylene (1,2), each of which has a metal coating (3,4), eg of aluminium. The sheets are typically 50 to 100 ,um thick and the metal coating 2 to 3 CL thick. The sheets are joined on their metallized faces with a layer of a fabric material 5 between the faces to provide added strength. The fabric may be a material such as canvas or a wire mesh and the sheets may be joined by any suitable adhesive. Exemplary of the pigments which may be present in the polyethylene sheets is synthetic red iron oxide pigment supplied by Morris Ashby as Deanox 1,70. In Figure 2, a body to be camouflaged is shown generally at 10. Applied to the surface of the body is a layer 11 of a visibly absorbing pigment or of different pigments as the case may be, painted on to the body surface. A further layer 12 consisting of a visibly nonabsorbing, infra-red reflecting pigment/binder composition is deposited on the visible pigment layer 11. The pigment/binder composition may conveniently be in paintable form and so can be painted on the first (visible) pigment layer once this has dried. The composition may comprise stannic oxide or lanthanum hexaboride or mixed oxides of antimony, cadmium, indium and tin in a polyurethane carrier. WHAT WE CLAIM IS:

1. An infra-red and visible camouflage system which comprises, in combination, two materials, one being a selective absorber of visible light and the other a reflector of infra-red radiation in at least the 3 to 14 micro-meter range, said materials being superposed and so chosen that the material on the observed side of the system is at least substantially transparent in respect of that kind of radiation which interacts with the material on the non-onserved side of the system.

reflective metal surfaces have a layer of reinforcing material between them.

15. An infra-red and visible camouflage system according to Claim 13 wherein the reinforcing material is either canvas or wire mesh.

16. An infra-red and visible camouflage system according to any of the preceeding Claims wherein the selective absorber of visible light absorbs at different wavelengths in different regions of its surface area.

17. An infra-red and visible camouflage system according to any of the preceeding Claims wherein the selective absorber of visible light comprises a dispersion of a pigment, that absorbs strongly in the visible region, in a non infra-red absorbing matrix material.

18. An infra-red and visible camouflage system according to Claim 16 wherein the pigment is red iron oxide.

19. An infra-red and visible camouflage system according to Claim 16 wherein the pigment is any one of the following, Prussian Blue, cadmium sulphide, cadmium selenosulphide and chromium oxide.

20. An infra-red and visible camouflage system according to any one of Claims 16 to 18 wherein the matrix material is polyethylene.

21. An infra-red and visible camouflage system according to any one of Claims 16 to 19 wherein the thickness of the matrix material is about 0.1 mm.

22. An infra-red and visible camouflage system substantially as herein before described.

23. An infra-red and visible camouflage system substantially as hereinbefore described with reference to either Fig. 1 or Fig. 2 of the drawings filed with the Provisional Specification.