GB2226704A - Deflection of radiation by particulate matter - Google Patents

Abstract

Material for the deflection of radiation, eg light or radio waves, comprises small particles of a relatively light carrier material, e.g. glass or basalt flake, at least partially coated with a metal or metal alloy eg aluminium or copper, having radiation deflecting properties. There is also provided a method of protecting a target against attack by a missile making use of the material and a method of making the material.

Description

DEFLECTION OF RADIATION BY PARTICULATE PATTER This invention relates to materials and methods for deflecting radiation, for instance, light or radio waves.

According to the present invention there is provided material for the deflection of radiation comprising small particles of a relatively light carrier material, these particles being at least partially coated with a metal or metal alloy having appropriate radiation deflecting properties.

The carrying material may be any suitable material such as glass or basalt flake. It should be strong and light and preferably should not interact with the metal or metal alloy but be capable of acting as a stable base or carrier for the metal or metal alloy.

Material in accordance with the present invention may be used in the form of a dry composition in which the size ofthe individual particles are sufficiently small and thin that the particles can be discharged into the air and remain suspended there for a significant time under normal conditions. A significant period of time would be a period of, say, 15 minutes or perhaps less than this. By depositing a sufficient quantity of such particles into the air to form a cloud of such particles, high frequency radio beams and laser beams can be deflected. The individual particles or flakes deflect the signals in random directions. This effect can be utilised to confuse, for instance, the radar signals of an attacking missile. The target may be, for instance, a ship or a ground installation.By discharging into the air in the path of the anticipated attack a cloud of material of the invention, the radar beams will not penetrate through to the target in sufficient strength and order to enable the missile to continue to recognize" its target and guide itself towards the target.

The present invention also provides a method of protecting a target against attack by a missile making use of radiation to guide itself to the target, the method including discharging into the air between the target and the likely direction of attack a cloud of material of the invention so as to deflect at least some of the guide radiation.

The guiding radiation may be emitted and received by the missile itself. Alternatively a separate emitter and/or receptor of radiation may be used. The missile may be an air or water borne missile. The cloud of material may be formed by putting the material into a container and filing the container into an appropriate position, the container including means for ejecting the material. The container may, for instance, be provided with explosives which cause the container to eject its contents in the appropriate position. The container may be in the form of, for instance, a cardboard tube capable of being fired out of a gun located either-ojihe-targetor4at some other appropriate position.

In another embodiment the material may be dropped or scattered out of an aeroplane.

For best results, the particles of the material should have a high ratio of surface area to thickness, this ratio, termed the aspect ratio, should preferably be at least 100:1 and more preferably 1000:1. The thickness of the particles should be such that they are capable of remaining suspended in the air for a significant amount of time.

Preferably the thickness is between 0.5 and 1 micron, including the carrier material and the metal or metal alloy coating.

Preferably the coating is of aluminium or copper or some other metal with a low melting point.

In one embodiment in accordance with the present invention the material is in the form of glass particles or flakes coated with aluminium. The aspect ratio is of the order of 1000:1, the thickness of the glass carrier particles is of the order of 0.75 microns, and the thickness of the aluminium deposit on the glass particles is of the order of 0.2 microns.

The particles of material of the invention comprise a light carrier material coated with a heavier but radiation deflecting (including reflecting) metal. Taking into account the particular materials, the size and thickness of the particles are such that they will tend to hang in the air and float on convection currents. They will twist and turn in the air thereby presenting multiple facets to impinging radiation. They will deflect, reflect and absorb both high frequency radio waves and laser beams. The whole cloud of particles will co-act in order to absorb between them the impinging radiation. As a result, the radiation beam, being relied upon to obtain information about the position of the target, will not reach and be reflected back from the target in sufficient strength to be useful to guide the missile to the target.

The material of the present invention may be used in other applications. For instance, the material may be included in paint which may be applied to, for instance, a ship in order to break up its radar image. The paint is applied according to a camouflage pattern in much the same way as is camouflage paint intended to break up a light image. In this application the size of the particles is not so important, although preferably the particles should have a high aspect ratio. Preferably the particles will be small enough to form an appropriate paint pigment and typically would be the order of 1 mm or less.

The present invention also provides a method of making the material of the present invention, the method comprising forming flakes of the carrier material to an f appropriate size and coating said flakes by means of a vacuum deposition method with a metal or metal alloy.

In the case where the particles or flakes are made of glass and the coating is of aluminium, a preferred method involves the use of apparatus in which a heated stream of molten material is fed downwardly into a rotating cup. The cup is arranged with its mouth facing upwardly so that molten material entering the cup is caused to flow over the upper edge of the cup and then radially outwardly due to centrifugal force. The apparatus includes a pair of spaced-apart substantially parallel plates arranged about the cup with the space between the plates adjacent the upper edge of the cup. The material leaving the cup passes into the space between the plates.The plates are mounted within a cyclone vacuum chamber arranged so that a vacuum is applied to the space between the plates to draw air between the plates in a radial direction to prevent the molten material from touching the sides of the plate. As the material moves within the space it solidifies into a flat film and ultimately breaks into small platelets.

A method of making aluminium coated glass flakes will now be described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic section through apparatus for making the glass flakes; and Figure 2 shows apparatus in which the flakes are coated with aluminium.

Referring to Figure 1 of the accompanying drawings, apparatus 1 for manufacturing flaked material from a stream of molten material consists of a variable speed electric motor 3 mounted vertically to which is attached a tapered cup 5.

The rim of the cup 7 lies between two annular plates 9, 11, the upper one 9 of which is adjustable. The two plates 9, 11 are mounted within a cyclone vacuum chamber 13 which is connected via the outlet connection 15 to a cyclone precipitator, separator and vacuum pump (not shown).

The method of operation is as follows. The cup 5 is rotated at speed and the stream 17 in this case of glass, is allowed to enter from above. Centrifugal force distributes the glass evenly within the cup and pushes the glass outwards over the cup rim 7.

The vacuum is applied to the cyclone vacuum chamber 13 via the outlet connection 15. Air enters this chamber via the gap 19 between the annular extraction plates 9 and 11 at a point 21 on the lower plate 11 and a corresponding location on the upper plate 9.

The entering air has a dual effect on the process.

The air rapidly cools the centrifuge cup 3 and the glass leaving the cup 3 at the rim 7.

The glass leaving the centrifuge cup 3 at 7 is located within the gap and prevented from touching the sides of the annular plates 9 and 11 by the air flow.

The air flow continues to cool the glass until it reaches a solid state, and due to friction upon the glass, continues to pull in a radial direction, thus preventing the glass from rolling or rucking over, keeping the glass flat and breaking it into small platelets.

The platelets are collected in the cyclone vacuum chamber 13 and exit via connection 15 to a precipitator cyclone and filter section (not shown).

The size and the thickness of flake can be varied through a considerable range by adjusting the flow of glass into the cup 3, adjusting the speed of rotation of the cup 3, adjusting the distance between the annular extraction plates 9 and 11 and varying the vacuum pull or velocity through the gap 19 between the annular extraction plates for any given gap by varying the amount of air flow through the extraction connection 15. Thus, a range of materials can be manufactured on this equipment both in diameter and thickness without recourse to further grading, crushing or grinding operations.

Referring to Fig. 2 of the accompanying drawings apparatus for coating the flakes with aluminium by a vacuum deposition method includes a base tray 31 on which is located a dome-like cover 33. Base tray 31 is provided with a series of small holes 5 which will allow the passage of air into the apparatus. The dome-like cover 33 is provided with outlet 36 which is connected to a vacuum pump. The dome-like cover 33 is also provided with a heating element 37 around which is wrapped aluminium wire 9.

Flaked glass 41 is located in the base tray 31 and the apparatus is evacuated by means of a vacuum pump and air outlet 36. The small holes 35 in the base tray 31 allow air to bleed into the apparatus so fluidizing the glass flakes. The heater is operated to cause the aluminium wire 9 to vaporise and the aluminium deposits on the cooler surfaces of the glass flakes. The fluidisation of the glass flakes ensures that the upper flakes do not mask the lower ones.

The above described method for making coated glass flakes in accordance with the present invention enables flakes to be made of any suitable size and aspect ratio.

Claims (11)

1. Material for the defection of radiation comprising small particles of a relatively light carrier material, the particles being at least partially coated with a metal or metal alloy having appropriate radiation defecting properties.

2. Material according to Claim 1 wherein the material is glass or basalt flake

3. Material according Claim 1 or Claim 2 wherein the particles are at least partially coated with aluminium or copper.

4. Material according to any of the preceding Claims wherein the aspect ratio of the particles is at least 100:1.

5. Material according to Claim 4 wherein the aspect ratio is at least 1000:1.

6. Material according to any of the preceding Claims wherein the thickness of the particles is between 0.5 and 1 micron.

7. A method of protecting a target against attack by a missile which makes use of radiation to guide itself to the target, the method including discharging into the air between the target and the likely direction of attack a cloud of material according to any of the preceding claims so as to deflect some of the guide radiation.

8. A method for making material as claimed in any of Claims 1 to 6, the method comprising forming flakes of the carrier material to an appropriate size and coating said flakes by means of a vacuum deposition method with a metal or light alloy.

9. Material according to Claim 1 and substantially as herein described.

10. A method according to Claim 8 substantially as herein described.

11. A method of making material according to Claim 1, the method being substantially as described herein with reference to the accompanying drawings.