GB2326246A

GB2326246A - Permeable reflecting mesh

Info

Publication number: GB2326246A
Application number: GB9712000A
Authority: GB
Inventors: Timothy Michael William Fryer
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-06-11
Filing date: 1997-06-11
Publication date: 1998-12-16
Also published as: GB9712000D0

Abstract

A reflector consists of a reflecting mesh which may be used to reflect infra red, visible and/or ultraviolet radiation whilst permitting the passage of particles. It may also be used as a selective reflector, for instance, permitting the passage of visible light whilst reflecting infra-red light. The reflector may have a substrate e.g. a mesh or a sheet eg. glass, ceramic or polymer. The reflector may be made by a weaving, photoresist or vacuum deposition process. It can be used as heat reflecting glass, or mesh for solar ponds, sodium thermoelectric generator or the thermionic device.

Description

Permeable Reflector The subject of the current invention is a mesh which may be used to reflect infra-red, visible and/or ultra-violet radiation.

Reflectors of radio waves are made either of a solid sheet of metal or of a mesh. However, this is is not the case for reflectors of visible radiation, which hitherto have always consisted of a continuous sheet of reflecting material.

In the present invention, a reflecting mesh is used as an optical filter. It has two principal applications.

1) To transmit light of a particular wavelength or range of wavelengths, whilst reflecting light of a different wavelength or range of wavelengths.

2) To permit passage of particles, whilst reflecting light.

The light may be visible, infra-red or ultraviolet. The particles may be neutral, for instance gas molecules, or they may be charged, electrons for instance. The mesh may have functions other than the reflection of light.

Thus, in a thermionic device it may also function as a grid; in a cell it may also function as an electrode.

CQust;ruction The reflector consists of a reflecting mesh. It may have various geometries, although it is preferred that it has a square or hexagonal configuration. For optimum efficiency it should consist mostly of voids. For optimum performance, the dimensions of the mesh cells should be no more than one tenth the wavelength of the radiation to be reflected, However, larger meshes may be used.

The reflector may consist entirely of reflecting material.

However, for reasons of strength and economy, it preferably consists of a substrate coated with reflecting material.

The substrate may consist of a continuous sheet, whose surface is coated with reflecting material in the form of a grid pattern, or it may consist of a mesh coated with reflecting material.

The sheet has the advantage of ease of manufacture but is usually impermeable to particles. The mesh substrate is permeable to both light and particles but is more difficult to manufacture Materials All the current state of the art reflecting materials may he used to provide a reflecting surface. Thus, Ag, Au, Al, Cu, Or, Pd, Rh and Ir may all be used.Other metals or alloys may be used.

Alternatively, dielectric reflectors may be used.

Various materials may be used for the substrate.

If the substrate is used in the form of a sheet it should be transparent to the radiation that is to be transmitted. Suitable transparent materials are glasses, ceramics and polymeric materials.

Other materials may be used.

However, when the substrate itself is in the form of a mesh it may be opaque so that materials which are not transparent may be used. For instance, carbon fibre may be used.

This could be woven into the mesh or the precursor could be formed into the grid and subsequently converted into high tensile carbon.

Manufacture The mesh may be made by all manufacturing processes up to the current state of the art.

The mesh may be made by made by all the weaving processes that are included in the current state of the art.

Alternatively, it may be made by the photoresist process. Here, an image of the object to be formed is projected onto a photosensitive substance The light transforms the substance so that the exposed substance may be removed whilst the unexposed substance is retained; in an alternative mode, the unexposed substance is removed whilst the exposed substance is retained.

Thus positive or negative images of an object may be manufactured.

In an alternative mode, the mesh is made by vacuum deposition.

In the preferred mode, particles flow through an orifice and are deposited on a surface, which may be later used to form the substrate. The particles may be neutral or they may be charged.

The particles may be deposited by molecular distillation or by sputtering. The particles may form the substrate for the reflector and/or they may form the reflecting material itself.

In one form of manufacture, a film is made to flow past an array of small orifices through which metal vapour flows, thereby producing a set of parallel lines. The process is then repeated with the film travelling at right angles to the lines, thereby causing a second set of lines, perpendicular to the first set, to be formed. Thus a square grid is deposited onto a substrate.

To obtain such fine mesh sizes the grid may be deposited on a substrate which is subsequently shrunk. This may be done by depositing the grid onto a substrate consisting of a stretched elastomer. Afterwards the tension is released causing the substrate, and hence the grid, to shrink. Alternatively the grid is deposited onto a substrate consisting a memory alloy or a heat shrinkable polymer. The substrate, and hence the grid, is made to shrink by the application of heat.

B2amnles af uses The present list of applications is not exhaustive and merely illustrates some of the applications of the device.

1) Heat reflecting glass 2) Heat reflecting mesh for solar pounds 3) Heat reflecting mesh for sodium thermoelectric generator.

4) Heat reflecting mesh for thermionic devices.

Heat reflecting glass Conventional windows lose heat through radiation in the far infrared. Coating the panes with a reflecting mesh reduces such losses whilst permitting transmission of visible light. Such a glass may also be used in solar collectors and to to prevent thermal radiation from light sources.

Solar Ponds A solar pond is a pool of water used to collect solar energy.

Ideally it should absorb all incident solar radiation whilst not re-radiating heat back into its environment. If a reflecting mesh were installed above the pond this radiation loss could be reduced.

Such a mesh would also impede the flow of air over the emend and help to prevent heat loss from convection currents.

Thermoelectric generators In the sodium thermoelectric generator, a reservoir of sodium at high temperature and pressure is seyarated from an evacuated chamber by a wall of beta alumina. The sodium passes through the wall, generating an electric current, vaporises and is removed by condensation. The efficiency of the device i8 impaired by radiation of heat from the wall to the condensing surface.

The reflecting grid which could be formed on the wall, would reduce this radiative heat loss whilst permitting flow of the sodium vapour. It could also form part of an electrode system.

A second grid could be installed in the vacuum chamber to reduce the heat loss still further.

Thern;aric devices In a thermionic device, a heated electrode radiates electrons which are then collected by another electrode The reflector could be used to prevent heat loss from the cathode whilst permitting flow of electrons. It could also be used as a control grid.

Claims

Permeable reflector

Claims 1) A reflector consisting of a reflecting mesh which may be used to reflect infra-red, visible and/or ultraviolet light.

2) A reflector as claimed in claim 1 which is permeable to particles 3) A reflector as claimed in claims 1 and 2 which is able to transmit light of a particular wavelength or range of wavelengths whilst reflecting light of a different wavelength or range of wavelengths.

4) A reflector as claimed in claims 1, 2 and 3 in which reflecting material is deposited on a substrate.

5) A reflector as claimed in claim 4 in which the substrate is a mesh.

6) A reflector as claimed in claim 4 in which the substrate is a sheet 7) A reflector as claimed in claims 1, 2, 3, 4, 5 and 6 in which the reflecting material is a metal or a mixture of metals.

8) A reflector as claimed in claim 7 in which the reflecting surface contains or consists of Al, Ag, Au, Cu, Cr, Pd Rh or Ir.

9) A reflector as claimed in claims 1, 2, 3, 4. 5 and 6 in which a dielectric reflector is used.

10) A reflector as claimed in claims 1,2,3,4,5, 6, 7,8 and 9 which is made by a weaving process.

11) A reflector as claimed in claims 1, 2, 3, 4, 5, 6, 7, 8, and 9 which is made by a photoresist process.

12) A reflector as claimed in claims 1, 2, 3, 4, 5 > 6, 7, 8, and 9 which is made by vacuum deposition.

13) A reflector as claimed in claims 1 to 12 used in heat reflecting glass 14) A reflector as claimed in claims 1 to 12 used to prevent heat loss from solar ponds.

15) A reflector as claimed in claims 1 to 12 used to prevent heat loss in thermoelectric generators.

16) A reflector as claimed in claims 1 to 12 used to prevent heat loss from the cathodes of thermionic devices.