GB2360569A

GB2360569A - Camouflage material

Info

Publication number: GB2360569A
Application number: GB8009266A
Authority: GB
Inventors: Alan Harold Lettington
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1979-03-26
Filing date: 1980-03-24
Publication date: 2001-09-26
Anticipated expiration: 2000-03-24
Also published as: GB8009266D0; DE3123754C1; GB7910479D0; GB2360569B

Abstract

Infra red camouflage material comprises a material having a highly reflecting surface 4 coated with a layer 5 of an infra red transparent material such as hard carbon or a semiconductor material eg germanium or silicon in the form of particles in a plastic material matrix. The reflecting surface may be foil eg aluminium foil, or a sprayed coating or the polished surface of a base material 3.

Description

2360569 CAMOUFLAGE This inve.-rLion concerns camouflage particularly the

prevention of detection by visible or infra red imaging system.

Camouflage a7ainst visible detection is usually obtained by colouring an object with a random array of slightly differently coloured patch-.whic,In bland in visibly with adjacent' objects. Paint applied to e.-. vehicles or patches on netting- are examples of mi,14-'Vary C1 camouflage. All rely on material that is selectively absorbing at visible -wavelengths.

Camouflage against infra red detection is most difficult since all objects emit infra red energy and man made objects such as tanks emit considerable infra red radiation from local hot spots e.g. exhaust p ipes. Humans also are emitters and can be detected uD to considerable ran ge- s. Wher, observed through thermal imagin- systems hot objects show up against a background of the cooler surroundings. The larger the temperature dif---"erence bezween hot objects and its surrounding the greater the white-black contrast. For example an engine exhaust pipe 0 0 may be at over 100C in a 20 background and this shows clearly on current thermal imagers for many kilometers of range.

t Preferably camcuf."'Lage for military purposes should be effective against infra red and visible detection.

According to this invention camouflage material includes a material having a surface Anich is highly reflecting to infra red radiation coated with a layer of infra red transparent material.

The highly reflecting surface may be a separate layer that is attached to a base mate--j.al, either solid or flexible, e.g. slabs of metal or plastic, or thin layers of fabric etc. The highly reflecting layer may be coated e.g. by spraying or electro-deposition onto the base material or may be a thin sheet e.g. of highly reflecting aluminium glued onto the base material. Alternatively the base material may have its surface polished.

The highly reflecting layer may be in the form of a layer broken up into numerous islands of dimension small comnared to the wavelength of radar (e.g. 4mm to 10m) to reduce radar reflections.

1 The infra red transparent layer is preferably absorbent to visible radiation and may be a thin layer of glassy carbon or a semiconductor having a 2 to 5 electron volt band gap. The semiconductor may be in the forr- of particles held in a matrix of polypropolene or p'yethylene or other suitable plastic.

oi.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 shows a tank having sheets of camouflage over its engine compartment; Figure 2 shows a sectional view of camouflage material; Figure 3 shows apparatus for applying a layer of amorphus 25 carbon to a highly reflecting layer.

As seen in Figure 1 a tank. 1 bas its engine compartment at the rear of the tank covered with camouflage plates 2. These plates 2 are shown in more detail in Figure 2 and comprise a base material such as steel or plastic 3 covered on one side with a highly reflecting layer of aluminium foil 4 itself coated with an amorphous carbon layer 5, 0.5 to 10m thick, typically about 1. /,um thick.

The ca;ucuj'lage is effeictive for the fc;l"Lowir,,,- reasons: the layer 4 is I highly reflecting at infra red (as well as visible) wavelengths and therefore emits, from the base material 3, little infra red radiation. Also, because the layer 5 is substantially transparent to infra red radiation, any infra red detector systems imaged onto the camouflage 2, will see reflected from the reflective layer 4 infra red frcm nearby objects e.g. trees and the sky. Thus the camouflage 2 appears to be at the same tem-Derature as its surroundings and is not easily distinguished on an infra red detector kthermal imaging systems) screen.

As deposited the amorphous carbon layer is absorbent to visible light. As a result the camouflage is not readily visible.

Since the camouflage -Properties are provided by the two layers 4, 5 the exact nature of the base material is not inDortant. Thus instead of separate sheets of camouflage being fixed to a tank, the layers 4, 5 -ly to any desired part of the tank -including, could be applied direct wrapping round exhaust Dipes. The layers 4, 5 may be anDlied to plastic sheets e.g. humand body armour, to fabric or netting. When applied to fabric the resultant material may be used to provide clothing to soldiers to tents or mobile workshops for vehicles or aircraft.

For a flexible camouflage material the carbon layer, may be applied on one side of an infra red transmitting.

plastic material, such as polyethylene, and aluminium paint on its other side.

A disadvantage of the layer 4 is that it is also highly reflecting to radar. To avoid radar detection the layer may be broken up into 30 numerous patches small in comparison to a radar wavelength.

As an alternative to t'lie above the base material may be polished and a layer of amorphus carbon deposited thereon. Alternatively a layer of semiconductor material in the form of particles held in a plastic binder matrix may be painted onto the polished base material. Selected 5 parts of a ship could 'thus be camouflaged from heat seeking missiles. The semiconductor mater-ial may be silicon or germanium alone or mixed with boron. The plastic matrix may be polypropolene or polyethylene.

Apparatus for coating the foil 4 or any suitable reflecting surface with carbon is shown in Figure 2. A specimen 20 to be coated is placed in an air tight metal container 21 which is then evacuated by a vacuum pump 22 to about 10-5 Torr. A gas such as methane, or propane is bled into the container 21 and the pressure maintained at about 10 Torr by throttling the pump 22 continuously. The container 21 is connected to earth 23 whilst the suecimen 20 is connected 24 through an insulated connector 25 to a -700 volts D.C. suDply. As a result ionisation of the gas takes place with conseauential dissociation of hydrogen and carbon atoms. Carbon atoms impinge onto the heated specimen 20 to form a layer having a time dependent thickness. For example a 1 v- thic11z!ayer is formed in about 50 minutes.

As an alternative -to D.C. glow discharge RP glow discharge may be used. In this technique the D.C. supply of Pigure 2 is replaced by an RP supply at 13 MHz frequency supplied through a capacitor (26) developing a cathode potential of about -700 volts. Operating conditions are as for D.C. operati6n.

The specimen 20 of Figure 2 ray be a sheet of aluminium foil several metres long mounted. on two spaced rollers in the container 21. The foil is wound from one roller to another whilst submitted to the bombardment of carbon atoms which causes a carbon 'Layer to grow onto the exposed foil between the rollers.

What 1 claiia is:- Camouflage material having a suri.:"ace which is highly reflectin!7 to infra red radiation and a layer of infra red transparent material.

2. The material C!aimed in claim 1 wherein the infra red trans parent material is absorbent at visible wavelengths.

3. The material claimed in claims 1 or 2 wherein the infra red transparent material is a layer of hard glassy carbon.

4. The material claimed, i_n claims 1 or 2 wherein the -;_nfra red transparent material is a layer of a semiconductor having a 2 to 5 electron volt energy gap.

5. The material claimed in claim 4 wherein the semiconductor material is in the form of particles held in a binder matrix.

6. The material claimed in claim 5 wherein the particles are Dartieles of silicon.

7. The material claimed in claim 5 wherein the particles are particles of germanium.

8. The material claimed in any one of claims 1 to 7 wherein the highly reflecting surface is the surface of a thin metallic sheet.

9. The material claimed in any one of claims 1 to 7 wherein the highly reflecting surface is coated onto the surface of a base material.

10. The material claimed in claim 9 wherein the base material is an infrared transparent plastic material arranTed between the reflectinz surface and the layer of infra red transparent material.

11. The material claimed in claim 8 wherein the metallic sheet is arranged into irimerous islands of dimensions small in comparison with the wavelengths of radar.

- 5 12. A camouflage material constructed, arranged and adapted to operate substantially as hereinbefore described reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1 Camouflage material having a surface which is highly reflecting to infra red radiation covered with a layer of hard glassy carbon, -.qh ch is transmitting to infrared radiation and absorbent to visible radiation.

2. The material claimed in claim 1 wherein the highly reflectir-.,.

surface is the surface of a t-hin metallic sheet.

3. The material claimed in claims 1 or 2 wherein the highl.y 10 reflecting surface is coated onto the =face of a base material.

4. The material claimed.in claim 3 wherein the base material is an infra red transparent plastic material arranged between the reflecting surface and the layer of hard glassy carbon. 15 5. The materiall claimed in claim 2 wherein the metallic sheet is arranged into numerous islands of dimensions small in comparison vi.'L-.h the wavelengths of radar.

6. A camouflage material as claimed in claim 1 constructe-1-1, arranged and adapted to Operate substantially as hereJLnbefQre deser-ibed with reference to the accompanying drawin s.

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