GB2400750A

GB2400750A - Microwave absorbing systems

Info

Publication number: GB2400750A
Application number: GB8823350A
Authority: GB
Inventors: Edward Daley
Original assignee: Colebrand Ltd
Current assignee: Colebrand Ltd
Priority date: 1987-10-09
Filing date: 1988-10-05
Publication date: 2004-10-20
Anticipated expiration: 2008-10-05
Also published as: GB8823350D0; GB2400750B

Abstract

A system which is applicable to a surface, comprising a carrier and means to absorb and/or reflect internally in the system incident microwave energy. The means (low observable materials) (LOM) may be iron carbonyl powder, graphite, conductive rubber etc. and is utilised with an absorber such as glass microspheres. The system may in particular take the form of a coating comprising three layers of iron carbonyl powder, a fourth layer of a material selected from the group consisting of hollow glass spheres and hollow ceramic spheres, and a fifth layer of a material selected from the group consisting of carbon, iron carbonyl, fluoroelastomers and manganese dioxide.

Description

MICROWAVE ABSORBING SYSTEMS

The invention relates to microwave absorbing systems or those relating to low observable materials (LOM).

It is often desirable to be able effectively to "reduce" a profile or silhouette of a structure such as the hull of a vessel or building, to make the structure difficult to attack by microwave controlled strike systems.

According to the invention there is provided a system which is applicable to a surface, comprising a carrier and means to absorb and/or reflect internally in the system incident electromagnetic energy.

Accordingly, the invention also provides a system which is applicable to a surface, the system comprising a carrier and means to absorb and/or reflect internally in the system incident microwave energy.

The system may comprise several layers.

The system may contain five layers.

The carrier may comprise a binder such as a fluorocarbon elastomer or the like.

The system may be a Plowable or spreadable coating which can be applied to a substrate such as a hull of a ship as by "painting", or by spraying.

Alternatively, the system may be a flowable or spreadable coating which may be applied to a substrate such as a projectile as by "painting", or by spraying. - 2 -

Of the five layers of the system, three may contain iron carbonyl powder, the fourth may container hollow glass (ceramic) microspheres, and the fifth layer may contain carbon/iron carbonyl/or fluoroelastomers only or manganese dioxide.

The principle is that microwaves enter into the coating systems and are effectively "lost" by a combination of absorption and reflection within the various layers of the system.

It has been found that when the substrate is non-electrically conducting, such as concrete, improved results are obtained when an electrically conducting sheet is included between the substrate and the absorbent material. When the substrate is itself electrically conducting (e.g. the steel plates of the hull of a vessel), the electrically conducting sheet is not necessary. Reflection of microwaves after passage through the absorbing material will give the absorbing material a second chance to absorb the microwaves so that the level of microwaves reaching the detector of a strike system will be insufficient to trigger a strike.

The system may comprise a substrate such as a sheet and a (microscopically) uniform distribution of LOM carried by the substrate.

The substrate can be of conductive material, in order to assist the operation of the LOM on a non-conducting object.

A conductive backing may improve the infrared shielding properties of the sheet. The sheet may be in the form of a tape (that is elongate in one dimension) and may be coated with adhesive on one or both sides, to assist attachment to the object to be treated. It - 3 is envisaged for example that objects of circular, oval or rectangular shape can be easily treated with the invention, and also that an object can be lined with the material when the escape of radiation from its interior is to be reduced.

The substrate may be of rubber or resin for example, and such material may be filled with LOM such as iron carbonile, with or without absorbers such as glass spheres or air bubbles. The coating of a substrate with LOM is also envisaged.

It has been found that a thin application of LOM gives a narrow absorption band, and that the band widens with increasing thickness of LOM. Control of the width of the absorption band is made easier with the invention, since several layers of tape can be wound on the object until the desired width of the absorption band is reached.

In one example a sponge-like body, e.g. of plastics netting, forms a carrier which is coated with microwave absorbent materials. When the system is subject to wear, for example by passage of tyred vehicles over the substrate, the coated carrier is contained in a fabric envelope. When the substrate is non-electrically conducting, the wall of the envelope intended to be adjacent the substrate is itself coated with an electrically conducting film, for example of aluminium.

As an alternative to providing a sponge-like body as the carrier which is coated with the LOM and contained within a fabric envelope, the material can be manufactured in panels, comprising top and bottom plates with the LOM supported between the plates, spacers being provided to keep the plates at proper separation, as required. Air or gases in the free space between the plates may be controlled to affect the absorption of infrared radiation.

The plates may be of resin, such as polyester, normally chosen for microwave radiation transparency, and may be rigid or flexible. The resin may contain fibres for additional strength, and/or glass spheres or air bubbles for lightness (and to affect the radiation absorption properties of the panelled LOM). They may be cast around the LOM. The panels may be finished with an adhesive, to assist application to an object to be treated.

A conductive backing for the LOM may be provided by a plate of the panel.

As LOM, graphite, conductive rubber or resin may be utilized.

The use of the panels is primarily but not exclusively for the protection of structures and buildings such as shelters, of aircraft, vehicles and ships or simply as a means of encapsulating objects.

In another embodiment, a system embodying the invention comprises a threedimensional netting or other material coated with radar absorbent materials such as graphite, conductive rubber or resin and iron carbonile, or other effective materials.

Radar transparent resins, such as polyester, rigid or flexible, are cast or placed around the netting or other material to form into a particular shape required.

For lightness the resin may contain glass-spheres or similar materials or simply airbubbles. This may produce additional absorption of energy.

The addition of fibres will give the resin additional strength.

The panels can also be manufactured from thin, top and bottom layers, of resin with or without fibres or other materials such as polyethelene and other radar transparent materials with a spacer to - 5 connect the two sheets. The netting or other absorbent material is held in between the two layers. This 'gap' may also act for air or gases to be introduced to aid IR deception.

The panels may have a metallic or conductive backing to make the system effective on non-metallic or insulated surfaces. It may also help IR shielding. For ease of application the panels may be finished with a selfadhesive.

Good attenuation can be achieved over a very wide band.

Me absorbing material (LOM) in all embodiments is selected to have maximum absorbing properties at the frequencies of operation of the expected strike system.

Signature reduction, or low reflectability of microwaves, is shown using a system of the invention in the accompanying drawing where the graphs in each case show at different incident microwave energy levels (in GHz) the "signature" 1 of an uncoated surface, structure or object and the signature 2 of a substrate with a coating according to the invention. The graphs show that the object virtually disappears when coated with a system embodying the invention. - 6

Claims

1. A system which is applicable to a surface, comprising a carrier and means to absorb and/or reflect internally in the system incident electromagnetic energy.

2. A system which is applicable to a surface, comprising a carrier and means to absorb and/or reflect internally in the system incident microwave energy.

3. A system according to Claim 1 or Claim 2, comprising several layers.

4. A system according to Claim 3, comprising five layers.

5. A system according to Claim 3 or Claim 4, comprising a Plowable or spreadable coating which can be applied to a substrate as by painting.

6. A system according to Claim 3 or Claim 4, comprising a coating which can be applied to a substrate by spraying.

7. A system according to any of Claims 4 to 6, there being respectively three layers comprising iron carbonyl powder, a fourth layer comprising hollow glass and/or ceramic spheres and the fifth layer comprising carbon/iron carbonyl/or fluoroelastomers and/or manganese dioxide.

8. A system according to Claim 1 or Claim 2, the carrier comprising a sheet which has a uniform distribution of said means over a surface thereof.

9. A system according to Claim 8, the sheet being electrically conductive. - 7 -

10. A system according to Claim 8 or Claim 9, the carrier comprising a tape.

11. A system according to any of Claims 8 to 10, the carrier being coated with adhesive on one or both sides.

12. A system according to any of Claims 8 to 11, the carrier I comprising a rubber material. I

13. A system according to any of Claims 8 to 11, the carrier comprising a synthetic resin material.

14. A system according to Claim 12 or Claim 13, the material being filled with said means comprising iron carbonite. I

15. A system according to Claim 14, including an absorber comprising glass spheres and/or air bubbles.

16. A system according to any of Claims 8 to 11, the carrier comprising a sponge-like body coated with said means and contained in a fabric envelope.

17. A system according to any of Claims 8 to 11, the carrier comprising a plurality of panels.

18. A system according to Claim 17, the panels comprising l spaced plates with said means supported therebetween.

19. A system according to Claim 18, including spacers connecting the plates.

20. A system according to Claim 18 or Claim 19, the plates comprising resin.

21. A system according to Claim 20, the resin being cast round - 8 - the means.

22. A system according to Claim 21, the panel or a plate thereof having a conductive backing.

23. A surface protected by a system according to any preceding Claim.

23. A system according to Claim 21 or Claim 22, the resin including strengthening means. I

24. A system according to any of Claims 8 to 11, the carrier comprising a netting or like material.

25. A system according to Claim 24, a microwave transparent resin being formed round the netting or like material to form into a particular shape.

26. A system, substantially as hereinbefore described with reference to the accompanying drawings.

27. A surface protected by a system according to any preceding claim.

Amendments to the claims have been filed as follows 1. A system for losing incident electromagnetic energy, comprising a coating comprising three layers of iron carbonyl powder, a fourth layer of a material selected from the group consisting of hollow glass spheres and hollow ceramic spheres, and a fifth layer of a material selected from the group consisting of carbon, iron carbonyl, fluoroelastomers and manganese dioxide.

2. A system according to Claim 1, the coating comprising a Plowable or spreadable layer which can be applied to a substrate.

3. A system according to Claim 1, the coating comprising a layer which can be applied to a substrate by spraying.

4. A system according to any preceding Claim, comprising a sheet which has a uniform distribution of the coating over a surface thereof.

5. A system according to Claim 4, the sheet being electrically conductive.

6. A system according to Claim 4 or Claim 5. the sheet compris- ing a tape.

7. A system according to any Claims 4 to 6, the sheet being coated with adhesive on at least one or both side.

8. A system according to Claim 4, the sheet comprising a rubber material.

9. A system according to Claim 4, the sheet comprising a syn- thetic resin material. 1

10. A system according to Claim 8, the material being filled with iron carbonyl.

11. A system according to Claim 10, including an absorber com- prising glass spheres and/or air bubbles.

12. A system according to Claim 4, the sheet comprising a sponge -like body coated with said coating and contained in a fabric envelope.

13. A system according to Claim 4, the sheet comprising a plurality of panels.

14. A system according to Claim 13, the panels comprising spaced plates with the coating supported therebetween.

15. A system according to Claim 14, including spacers connecting the plates.

16. A system according to Claim 14 or Claim 15, the plates com prising resin.

17. A system according to Claim 16, the resin being cast round the coating.

18. A system according to Claim 17, the panel or a plate thereof having a conductive backing.

19. A system according to Claim 17 or Claim 18, the resin includ- ing strengthening means.

20. A system according to any of Claims 4 to 7, the sheet com- prising a netting or like material.

21. A system according to Claim 20, a microwave transparent resin being formed round the netting or like material to form into a particular shape. /1

22. A system substantially as hereinbefore described with refer- ence to the accompanying drawings.