THERMALLY-EMISSIVE, WEAPONRY TARGET, TRAINING AID OR ARC DESIGNATOR STRUCTURE

Abstract: A thermally-emissive structure which can be a weaponry target, training aid or arc designator structure, the structure having a high heat emissivity material, such as matt black paint, applied in areas which are to define a thermally-emissive target. The mark/space ratio of the image so produced is varied over the area where the high heat emissivity material is applied to achieve the desired thermal image. The structure is electrically-heated and includes a heating element (1) in the form of a plastics film having an electrically-conductive metallic coating. The plastics film is joined to a carrier member (2) which in turn is joined to a rigid backing member (3) of a material with good thermal insulating properties. The high heat emissivity material is applied to the plastics film and when the electrically-conductive coating is heated, thermal emission is markedly greater where the high heat emissivity material has been applied. The front of the plastics film is covered with an insulating material which allows transmission of thermal radiation through it.

Description: THERMALLY-EMISSIVE. WEAPONRY TARGET. TRAINING AID OR ARC DESIGNATOR STRUCTURE This invention relates to a thermally-emissive, weaponry target, training aid or arc designator structure. An electrically operated military target is known from WO 83/01105 which includes a plurality of modules mounted adjacent to one another on a support frame. Each module carries an electrically-conductive laminate for emitting infra-red radiation when a current is passed through it. The laminate in fact includes electrically-insulating top and bottom layers, between which an electrically-conductive layer is sandwiched. This electrically-conductive layer includes at least two areas having different effective electrical resistance to emit differing infra-red signals when an electrical current is passed therethrough for infra-red detection. According to one aspect of the present invention, there is provided a thermally-emissive structure including a surface, the surface being, in a region or regions intended to define an area to be detected by a thermal i ager, darkened relatively to other regions thereof by high heat emissivity material and, in use, being heated above ambient temperature, characterised in that said area is formed by an image, the mark/space ratio of which image being varied over said area to achieve the desired thermal image. The image may be applied as a matrix of dots, bars or similar patterns. The high heat emissivity material may comprise matt black paint. According to another aspect of the present invention, there is provided an electrically heated, thermally-emissive structure including a heating element in the form of a plastics film having an electrically-conductive metallic coating, characterised in that said electrically-conductive metallic coating is of substantially uniform electrical resistance and, in a region or regions intended to define an area to be detected by a thermal imager, one surface of said film and/or said coating is darkened relative to other regions thereof by a high heat emissivity material, said area being produced by passing an electrical current through said coating. The metallic coating can be of aluminium or an aluminium alloy. The aluminium can be vacuum deposited on the plastics film. The plastics film may be a polyester film. The plastics film with its coating may be joined to a carrier member such as a flexible, non-absorbent backing material which in turn can be joined to a rigid backing member of, for example, foamed plastics material or other material with good thermal insulating properties. The high heat emissivity material can be applied to the surface of the coating facing away from the plastics film. The surface of the coating which faces away from the plastics film may be covered by a material having good thermal insulation properties whilst having good transparency in the thermal range to allow transmission of thermal radiation therethrough. Such a material can be a plastics material such as a layer of polyethylene with air bubbles formed in it. The structure can be in the form of a weaponry target structure and the whole structure can be mounted as a panel, with others if required, onto target panels of two-dimensional or three-dimensional targets. The structure in a smaller version could be used as a classroom training aid. The structure can also be formed as an arc designator which would give a thermal indication to those in the field of the boundary of a safety area. Presently, arc designators are formed as panels about 20 m high with a letter or numeral painted on them. According to a third aspect of the present invention, there is provided a method of producing a thermal image to be detected by a thermal i ager, the method comprising providing a surface of a structure with, in a region or regions intended to define an area to be detected by a thermal imager, regions which are darker relatively to other regions thereof, the darkening being by high heat emissivity material and, in use, being heated above ambient temperature, characterised in that said area is formed by an image, the mark/space ratio of which image being varied over said area to achieve the desired thermal image. For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a schematic side view of an electrically-heated, thermally-emissive, structure which can be used as a weaponry target, training aid or arc designator structure, Figure 2 is a schematic front view of a heating element shown in Figure 1 , Figure 3 is a diagrammatic front view of a thermally-emissive structure which can be used as a weaponry target, training aid or arc designator structure, Figure 4 is a photographic reproduction of a thermal image as detected by a thermal imager which was directed onto a structure according to the present invention, and Figure 5 is another photographic reproduction of a thermal image detected. The structure described hereinafter is a weaponry target structure and is arranged to provide a thermal emissivity which is varied to provide a thermal image of a target capable of being detected on a thermal imager and any weapon system that the imager is used to aim. The structure could also be formed as a training aid or an arc designator. The structures illustrated in the drawings include a heating element 1 in the form of a plastics film having an electrically-conductive metallic coating, preferably of aluminium, deposited thereon. The plastics film is joined to a carrier member 2 which can be of a flexible, non-absorbent material, which in turn is joined to a rigid backing member 3 of foamed plastics material or other material with good thermal insulating properties. The electrically-conductive metallic coating can be located between the plastics film and the carrier member 2 in order to inhibit degradation of the metallic coating. Electrodes 4, preferably copper wire electrodes, are attached by means of electrically-conductive contact pads 5 along electrically opposite edges of the coated plastics film of the heating element 1 and are led away via insulated leads to terminals of an electrical power source (not shown) which may be electronically regulated to vary the overall temperature. The shape, aspect ratio and electrical path length may be varied to suit the particular intended application of the structure and, as shown in Figure 2, slots 6 can be provided in the coating to increase the electrical path length. However, the electrical resistance over the path length is substantially uniform. In the embodiment illustrated, it is, the outer surface of the coating facing away from the plastics film which is given an image of a target such as a tank and this can be done by applying a high emissivity matt black paint 7. The black paint is applied as a matrix of dots, bars or similar patterns and the effective relative temperature or strength of heat emissivity is controlled by varying the mark/space ratio of the dots, bars or similar patterns to allow representative thermal images of target vehicles etc. to be created. The electrically conductive metallic coating is of comparatively low heat emissivity. Figure 3 depicts a typical target panel 9 showing an image of the front of a tank. In practice, the image could be applied to a plurality of adjacent panels. Certain areas of a real tank are known to be thermally-emissive, i.e. are above ambient temperature and these areas have been identified as locations such as head lights 10, various ports 11, the tip of an exhaust outlet 12 and even the endless tracks 13. These and other areas so identified in practice as being thermally-emissive, are darkened with high heat-emissivity material and the mark/space ratio of the image is varied as appropriate to give the intended intensity of thermal emission. Figures 4 and 5 are photographic reproductions of what has been achieved in practice using a structure according to the invention. Figure 4 is the result of a thermal image of the side view of a tank depicted on the present structure and Figure 5 is a front view of the tank. In both views, the thermally-emissive areas are clearly depicted by the lightened regions of the image detected. The view illustrated in Figure 5 corresponds to that of Figure 3. In order to reduce power consumption, the structure so far described is insulated from contact with the surrounding air by means of a layer 8 of thermally-insulating material which however has the property of allowing transmission through it of thermal radiation. Such a material can be polyethylene or a similar material with air bubbles in it. In fact, the layer 8 of insulating material should be transparent in the infrared wavebands. It should be borne in mind that thermal imagers will be sensitive even with differences of only 1 or 2°C above ambient temperature. The plastics film of the heating element 1 can be a polyester film and the various components can be joined to one another by adhesive such as a contact adhesive. If desired, the layer 8 of insulating material may surround the whole assembly so that it is effectively encased in a plastics bag only broken at locations where the electrical supply leads for the heating element pass through. In operation, although the whole of the electrically conductive coating is heated, thermal emission is markedly greater where the matrix of dots is applied and since thermal imagers .tend to look at areas rather than the dots or bars etc., then the imagers will not be affected by the "white" spaces between the dots or bars. However, in regions where there are no dots or bars, the thermal imagers will only detect or "see" the ambient temperature. It is envisaged that the invention could be extended to the case where an electronically-controlled image can be produced in place of the image provided by matt black paint. Although the structure has been generally discussed above in conjunction with electrical heating of the structure, in some cases it has been found sufficient that the structure will operate satisfactorily during daylight using the power of the sun rather than electrically heating the structure or using another heating source as may be deemed appropriate. The regions which are darkened relatively to other regions thereof by the high heat emissivity material are in that case heated above ambient temperature by the sun. The structure will also produce the desired effect if it is, for example, tilted skywards at night where advantage is taken of the cold reflection of the sky, the difference in the ambient temperature of the darkened areas being sufficient to be detected by a thermal imager. It will be appreciated that the present structure will be particularly advantageous for use in remote areas where there is no readily available power supply because of the comparatively low power requirement of the structure, or, as just discussed, no power requirement. Indeed, it is envisaged that the structure could be supplied without the electrical heating facility but the image to be detected should preferably be covered by the material which has good thermal insulation properties whilst having good transparency in the thermal range to allow transmission of thermal radiation therethrough. This as suggested earlier could be a plastics sheet with air bubbles in it. The present structure can also be utilised to assist in positive, real vehicle identification. For example, the structure could be applied to an ambulance and a thermal imager could pick up the image of a red cross or red crescent on the structure, thereby indicated that it is not a target for attack.

Claims: CLAIMS: 1. A thermally-emissive structure including a surface, the surface being, in a region or regions intended to define an area to be detected by a thermal imager, darkened relatively to other regions thereof by high heat emissivity material and, in use, being heated above ambient temperature, characterised in that said area is formed by an image, the mark/space ratio of which image being varied over said area to achieve the desired thermal image. 2. A structure according to claim 1, characterised in that the image is applied as a matrix of dots, bars or similar patterns. 3- A structure according to claim 1 or 2, characterised in that said high heat emissivity material comprises matt black paint. 4. A structure according to any one of the preceding claims, characterised by a heating element in the form of a plastics film (1) having an electrically-conductive metallic coating, one surface of said film and/or said coating being darkened relatively to other regions thereof by high heat emissivity material as aforesaid. 5. A structure according to claim 4, characterised in that said metallic coating is of aluminium or an aluminium alloy. 6. A structure according to claim 4 or 5, characterised in that said plastics film (1) is a polyester film. 7. A structure according to claim 4, 5 or 6, characterised in that said plastics film (1) with its coating is joined to a carrier member (2). 8. A structure according to claim 7, characterised in that said carrier member (2) is formed of a flexible, non-absorbent backing material. 9. A structure according to claim 8, characterised in that said backing material is joined to a rigid backing member (3). 10. A structure according to claim 9, characterised in that said rigid backing member (3) is formed of foamed plastics material. 11. A structure according to any one of claims 4 to 10, characterised in that said high heat emissivity material is applied to the surface of said coating facing away from said plastics film (1). 12. A structure according to any one of claims 4 to 11, characterised in that the surface of the coating which faces away from said plastics film (1) is covered by a material (8) having good thermal insulation properties whilst having good transparency in the thermal range to allow transmission of thermal radiation therethrough. 13. A structure according to claim 12, characterised in that said material on the surface of the coating which faces away from the plastics film (1) is comprised by a layer of polyethylene with air bubbles (8) formed in it. 14. A structure according to any one of claims 4 to 13, characterised in that said electrically-conductive metallic coating is connected via electrically-conductive contact pads (5) and electrodes (4) to leads for connection to an electrical power source. 15. A structure according to any one of claims 4 to 14, characterised in that the shape, aspect ratio and electrical path length is varied to suit the particular intended application of the structure. 16. A structure according to claim 15, characterised in that slots (6) are provided in said metallic coating to increase the electrical path length. 17. A structure according to any one of the preceding claims, characterised in that substantially the whole of the structure is surrounded by a layer of insulating material. 18. A structure according to any one of claims 4 to 17, wherein said surface of said film and/or said coating is darkened relatively to other regions thereof by an electronically-controlled image. 19. An electrically heated, thermally-emissive structure including a heating element in the form of a plastics film (1) having an electrically-conductive metallic coating, characterised in that said electrically-conductive metallic coating is of substantially uniform electrical resistance and, in a region or regions intended to define an area to be detected by a thermal imager, one surface of said film and/or said coating is darkened relative to other regions thereof by a high heat emissivity material, said area being produced by passing an electrical current through said coating. 20. A structure according to any one of the preceding claims and being in the form of a weaponry target structure. 21. A structure according to claim 20, wherein said weaponry target structure is mounted as a panel (9) on a two-dimensional or three-dimensional target. 22. A structure according to any one of the preceding claims and being in the form of a classroom training aid. • 23. A structure according to any one of claims 1 to 19 and being in the form of an arc designator. 24. A method of producing a thermal image to be detected by a thermal imager, the method comprising providing a surface of a structure with, in a region or regions intended to define an area to be detected by a thermal imager, regions which are darker relatively to other regions thereof, the darkening being by high heat emissivity material and, in use, being heated above ambient temperature, characterised in that said area is formed by an image, the mark/space ratio of which image being varied over said area to achieve the desired thermal image.

Inventors: DEAN WILLIAM ROBERT, WATERS JOHN HENRY, DEAN, WILLIAM, ROBERT, WATERS, JOHN, HENRY
Applicants: IMVEC LTD, IMVEC LIMITED
Application year: 1989
Main classification: F41J1
IPC codes: F41J2