GB2237862A

GB2237862A - Radiation absorbers

Info

Publication number: GB2237862A
Application number: GB9023195A
Authority: GB
Inventors: Klaus Norbert Tusch
Original assignee: Colebrand Ltd
Current assignee: Colebrand Ltd
Priority date: 1989-10-30
Filing date: 1990-10-24
Publication date: 1991-05-15
Anticipated expiration: 2010-10-24
Also published as: GB2237862B; GB9023195D0

Abstract

An absorber of incident electromagnetic radiation in the non-visible range comprises a paint in which is distributed a plurality of discrete absorbers of incident electromagnetic radiation (e.g. silver coated magnetic ceramic microballoons or spheres of diameter 4-100 microns) or carbon fibre or powder. The paint may comprise butyl rubber or fluorocarbon material, and is applied with a squeegee blade to a substrate. Where the substrate is a woven fabric, the paint is applied under pressure to integrate the material into the weave.

Description

ABSORBERS The invention relates to absorbers1 particularly to absorbers of incident electromagnetic radiation in the non-visible range.

It is often necessary or desirable that camouflaging material be provided, particularly for military use. Such material, usually woven, is generally required to be flexible so that it can be draped over an object, or made into clothing to be worn by personnel. The material is often dyed, painted or otherwise treated to provide a visual camouflaging effect on an in use outer surface.

Infrared camouflaging has become increasingly important with the use of heat-seeking missiles and infrared sensitive gun-sights. The camouflaging material must therefore blend not only the visual appearance of the object into the surroundings, but also the infrared appearance. The object should radiate no more, but just as important no less, heat than its surroundings.

Materials for visual and infrared camouflaging have often been combined with a backing sheet of absorber material such as aluminium which is designed to absorb incident electromagnetic radiation incident on it from in front, and reflect infrared radiation incident on it from the rear. However, the material is cumbersome to use, being heavy and not readily manipulable.

It is accordingly an object of the invention to seek to mitigate these disadvantages.

According to a first aspect of the invention there is provided a flowable settable material containing a component adapted to absorb a controlled proportion of incident electromagnetic radiation in the non-visible range.

Any flowable settable material may be used, including paints. If a single layer of material is used, it avoids the exposure of a non-absorbing backing layer when damage occurs, as might happen in a multi-layer camouflaging material described above. When laser gun-sights are used, a damaged camouflaging material may cause injury to the gun-sight operator if its exposed highly reflecting layer reflects the laser beam back to the operator's eye.

The material may be a colourant such as a dye or a paint as mentioned above, suitably a camouflaging dye or paint. This provides that the material can be applied to a carrier to provide visible camouflaging effects.

The component may comprise a plurality of discrete absorbers of electromagnetic radiation in the non-visible range distributed in the flowable settable material. Controlling the proportion of discrete absorbers in the material controls the emissivity/reflectance of the filled material.

The discrete absorbers may comprise particles coated with reflecting material, such as silver-coated spheres. The spheres may be magnetic ceramic microballoons.

The spheres may each have a diameter in the range of 4-100 microns, or 10-100 microns, averaging preferably 40 microns. This small size enables a vast number of the spheres to be distributed in the material, which may be a colour-fast dye or paint, and paste-like so providing a flowable settable material which provides controllable properties of absorption of incident electromagnetic radiation in the non-visible range.

The flowable settable material may comprise butyl rubber in the form of vulcanised latex, which is largely resistant to attack by chemicals, and may also be readily cleansed of chemicals by hosing down with water and/or other media.

The flowable settable material may in addition or alternatively comprise a fluorocarbon material, which may be resistant to radiation, particularly heat radiation.

According to a second aspect of the invention, there is provided an absorber of incident electromagnetic radiation comprising a substrate to which a material as hereinbefore defined is applied.

The substrate may be a flexible fabric. This allows the substrate to be draped over an object to be concealed, or formed into clothing for use as wearing apparel for personnel.

The fabric may be canvas, cloth, silk or any other suitable substrate. Where the substrate is silk, there is provided a particularly light-weight substrate which may be readily folded and unfolded, stored, and transported.

Where the substrate is a fabric which necessarily has nonhomogeneous surface layer provided by the weave, the discrete absorbers may penetrate into the substrate to provide an integrated absorber of incident electromagnetic radiation.

The absorber may function to absorb a controlled incident proportion of incident electromagnetic radiation by the discrete absorbers deflecting and reflecting internally that radiation at the absorber so that the radiation is reflected back to source at the same level as radiation incident on the surroundings. Therefore, where the radiation is in the radar frequency range, the absorber is effectively concealed from the source and therefore in turn a substrate such as a vehicle or personnel is also concealed.

Moreover, as the discrete absorbers also reflect infrared radiation, the emissivity of the camouflaging material can be controlled such that heat emanating from a substrate over which the absorber is placed is reflected back to the substrate so that any detector of infrared will not function to detect the substrate in relation to its surroundings. Therefore the heat from an engine or exhaust of a vehicle, or body heat of personnel wearing clothing comprised of an absorber according to the invention is concealed both from an infrared detector and radar surveillance.

The emissivity of an absorber may be controlled in the range of 0.2 to 0.8, depending on the environment in which it is to be used. In cold surroundings a low value should be used, the value rising with temperature of the surroundings. Reflectance values in the region of 30% are provided by the filled material.

According to a third aspect of the invention there is provided a method of providing an absorber, comprising the steps of providing a substrate, providing a flowable settable material as hereinbefore defined1 and applying the material to the substrate.

The material may be applied under pressure.

The material may preferably be in the form of a paste, and the application step may comprise passing a squeegee blade over the substrate with the paste material between the substrate and blade.

However any suitable application method can be used for the flowable settable material in general.

The substrate may be a woven fabric, and the application step may comprise forcing the paste material into the weave whereby to integrate the material, particularly the discrete absorbers, into the weave.

The material is allowed to dry, so providing an absorber that is light in weight, flexible and foldable. The flowable material may be a dye or paint which may be colour-fast. The dye or paint may be a camouflage colour dye or paint to confer on a substrate visual camouflaging effects.

The substrate may be wood, metal, rubber or any other suitable material to which the absorber material may be applied.

Carbon powder or fibre may be used, not necessarily silver-coated, as the component by which the emissivity/reflectance of the material is controlled.

Claims

1. An absorber of incident electromagnetic radiation, comprising a flowable, settable material, a component adapted to absorb incident electromagnetic radiation and the component being distributed in the flowable settable material whereby to provide an absorber which can be applied as desired to a substrate.

2. An absorber according to Claim 1, the flowable, settable material comprising a colourant.

3. An absorber according to Claim 2, the colourant comprising a paint or dye.

4. An absorber according to any preceding Claim, the component comprising a plurality of discrete aborbers of electromagnetic radiation distributed in the flowable, settable material.

5. An absorber according to Claim 4, the component comprising a plurality of discrete particles coated with a reflecting material.

6. An absorber according to Claim 5, the component comprising a plurality of discrete spheres each coated externally with a reflective silver coating.

7. An absorber according to Claim 6, wherein the spheres comprise magnetic ceramic microballoons.

8. An absorber according to Claim 7, the ceramic microballoons having a diameter in the range 4-100 microns.

9. An absorber according to Claim 7, each sphere having a diameter in the range 10-100 microns.

10. An absorber according to Claim 1 or Claim 2, the flowable settable material comprising a butyl rubber.

11. An absorber according to Claim 10, the rubber comprising a vulcanised latex butyl rubber.

12. An absorber according to Claim 1 or Claim 2, the flowable, settable material comprising a fluorocarbon material.

13. An absorber according to Claim 12, the flowable, settable material comprising a butyl rubber material and a fluorocarbon material.

14. An absorber as defined in Claim 3, the component comprising carbon.

15. An absorber of incident electromagnetic radiation, comprising a substrate1 a flowable settable material, a component adapted to absorb incident electromagnetic radiation, the component being distributed in the settable flowable material to provide a settable flowable mixture, and the mixture being applied to substrate.

16. An absorber according to Claim 15, the substrate comprising a fabric.

17. An absorber according to Claim 16, the fabric being a woven fabric and the material being applied to the fabric under pressure whereby to integrate the material into the weave.

18. An absorber according to Claim 15, the substrate comprising wood.

19. A method of providing an absorber according to Claim 15, comprising the steps of providing a substrate, providing a mixture consisting of a flowable settable material and a component adapted to absorb incident electromagnetic radiation, and applying the mixture to the substrate when flowable whereby to provide a coating on the substrate.

19. A method according to Claim 19, the application step comprising spreading the mixture over the substrate with a squeegee.

20. An absorber and a method of making same, substantially as hereinbefore described.