GB2394361A

GB2394361A - Energy absorbing compositions

Info

Publication number: GB2394361A
Application number: GB8824695A
Authority: GB
Inventors: Robert Fraser Sims
Original assignee: Marconi Electronic Devices Ltd; Plessey Semiconductors Ltd
Current assignee: Marconi Electronic Devices Ltd; Plessey Semiconductors Ltd
Priority date: 1988-10-21
Filing date: 1988-10-21
Publication date: 2004-04-21
Anticipated expiration: 2008-10-21
Also published as: GB2394361B; GB8824695D0

Abstract

A high frequency electromagnetic energy absorbing composition which is particularly suitable for absorbing energy at radar frequencies, comprises a plurality of hollow spheres 1 of sintered ferrite distributed in a resinous liquid binder 2. Apertures 3 in the spheres 1 expose their interior surfaces to incident radiation. Alternatively, spheres of a refractory material not absorbing radiation are added to an energy absorbing material, eg. ferrite, and the composition sintered to form a wholly ceramic body.

Description

- 1 - ENERGY ABSORBING COMPOSITIONS

This invention relates to energy absorbing compositions and more particularly to compositions which are suitable for absorbing high frequency electromagnetic 5 radiation such as radar energy.

Radar absorbing compositions are known in which particles of energy absorbing material, such as ferrite, having diameters of between about 1 and 10 microns are distributed in a liquid binder. The composition may be 10 used to coat surfaces so that they present a low radar cross-section. It has been found that such compositions are more effective at absorbing radar energy than the use of radar absorbing material alone.

The present invention arose in an attempt to provide 15 an improved energy absorbing composition.

According to a first aspect of the invention there is provided an energy absorbing composition comprising a plurality of hollow elements, distributed in a binder, only one of the binder material and the material of the 20 elements being of high frequency electromagnetic energy absorbing material. The use of hollow elements results in a composition of relatively light weight compared to conventional compositions. It is preferred that, where the elements are of energy absorbing material, each 25 element includes at least one aperture from its exterior to its interior surface. Both the interior and exterior

surfaces are then available for the absorption of incident energy, thus improving performance.

It is preferred that the hollow elements are substantially spherical or part-spherical in formulas such 5 shapes are relatively easy to fabricate, although more complicated shapes could be used in which even greater surface areas are presented by the elements.

In one advantageous embodiment of the invention, the energy absorbing material is a ferrite. It is preferred 10 that the energy absorbing material has been sistered.

In one embodiment of the invention the binder is a liquid. In an alternative embodiment, which is particularly convenient where the elements are of absorbing material, the binder is a solid. Thus, for 15 example, alumina elements may be combined with ferrite which is then sintered to give a whollly ceramic composition. According to a second aspect of the invention an energy absorbing composition comprises a binder of high 20 frequency electromagnetic energy absorbing material throughout which particles of material not absorbing such energy are distributed. The particles thus dilute the absorbing material, defining surfaces at which energy absorption can take place. The particles may be hollow 25 to give a lightweight composition and preferably are spherical or part-spherical in form.

Some ways In which the Invention may be performed are

now described by way of example with reference to the accompanying drawing, in which: Figures 1 and 2 schematically illustrate respective energy absorbing compositions in accordance with the 5 invention.

With reference to Figure 1, a composition which is intended, in use, to absorb radiation at radar frequencies includes a plurality of hollow spheres 1 distributed in a resinous liquid binder 2. Each sphere is approximately 10 0.25 mm in diameter and consists of sintered ferrite.

Apertures 3 in the spheres expose the interior surfaces of the spheres 1 to incident radiation so that absorption of radar energy occurs at both interior and exterior surfaces. 15 With reference to Figure 2, another composition comprises solid spheres 4,of about 0.25 mm in diameter, of a refractory material which are added to an energy absorbing material 5, which in this case is ferrite. The composition is then wintered to give a wholly ceramic 20 body. Energy absorption occurs at the boundaries 6 between particles 4 and absorbing material 5. Although in this embodiment, the particles are solid they could be hollow.

Claims

- 4 - CLAIMS

1. An energy absorbing composition comprising a plurality of hollow elements distributed in a binder, only one of the binder material and the material of the 5 elements being of high frequency electromagnetic energy absorbing material.

2. A composition as claimed in claim 1 wherein the hollow elements are substantially spherical or part spherical in form.

10 3. A composition as claimed in claim 1 or 2 wherein, where the elements are of energy absorbing material, each element includes at least one aperture extensive from its exterior to its interior surface.

4. A composition as claimed in claim 1, 2 or 3 wherein 15 the energy absorbing material is a ferrite.

5. A composition as claimed in any preceding claim wherein the energy absorbing material has been sistered.

6. A composition as claimed in any preceding claim wherein, where the elements are of energy absorbing 20 material, the binder is a liquid.

7. A composition as claimed in any of claims 1 to 5 wherein, where the elements are not of absorbing material, the binder is a solid.

8. A composition as claimed in any preceding claim 25 wherein the elements are spheres of approximately 0.25 mm in diameter.

9. An energy absorbing composition comprising a binder

of high frequency electromagnetic energy absorbing material throughout which particles of material not absorbing such energy are distributed.

10. A composition as claimed in claim 9 wherein the S particles are hollow elements, 11. A composition as claimed in claim 9 or 10 wherein the particles are substantially spherical or part-spherical in form.

12. A composition as claimed in claim 9, 10 or 11 wherein 10 the energy absorbing material has been wintered such that, together with the particles, the composition comprises a ceramic body.

13. A composition as claimed in any of claims 9 to 12 wherein the energy absorbing material is ferrite.

15 14. A composition as claimed in any of claims 9 to 13 wherein the particles are of alumina.

15. A composition as claimed in any of claims 9 to 14 wherein the particles have a diameter of approximately 0.25 mm diameter.

20 16. An energy absorbing composition substantially as illustrated in and described with reference to Figure 1 or 2 of the accompanying drawing.

Amendments to the claims have been filed as follows 1. An energy absorbing composition comprising a plurality of hollow elements distributed in a binder, only one of the binder material and the material of the 5 elements being of high frequency electromagnetic energy absorbing material.

2. A composition as claimed in claim 1 wherein the hollow elements are substantially spherical or part spherical in form.

10 3. A composition as claimed in claim 1 or 2 wherein, where the elements are of energy absorbing material, each element includes at least one aperture extensive from its exterior to its interior surface.

4. A composition as claimed in claim 1, 2 or 3 wherein 15 the energy absorbing material is a ferrite.

5. A composition as claimed in any preceding claim wherein the energy absorbing material has been wintered.

6. A composition as claimed in any preceding claim wherein the elements are of energy absorbing material and the 20 binder is a liquid.

7. A composition as claimed in any of claims 1 to 5 wherein the elements are not of absorbing material and the binder is a solid.

8. A composition as claimed in any preceding claim 25 wherein the elements are spheres of approximately 0.25 mm in diameter.

9. An energy absorbing composition comprising a binder of high frequency electromagnetic energy absorbing material throughout which particles of material not absorbing such energy are distributed.

10. A composition as claimed in claim 9 wherein the 5 particles are hollow elements.

11. A composition as claimed in claim 9 or 10 wherein the particles are substantially spherical or part-spherical in form.

12. A composition as claimed in claim 9, 10 or 11 10 wherein the energy absorbing material has been sintered such that, together with the particles, the composition comprises a ceramic body.

13. A composition as claimed in any of claims 9 to 12 wherein the energy absorbing material is ferrite.

15 14. A composition as claimed in any of claims 9 to 13 wherein the particles are of alumina.

15. A composition as claimed in any of claims 9 to 14 wherein the particles are spheres having a diameter of approximately 0.25 mm.

20 16. An energy absorbing composition substantially as illustrated in and described with reference to Figure 1 or 2 of the accompanying drawing.