Window for transmitting radiation such as microwaves

Abstract: A window for transmitting radiation of 20 µm or longer comprises a layer (10) supported around its periphery (12) by a frame (14). The layer (10) comprises a first major surface (16) on one side capable of receiving the radiation and a second major surface (18) on the opposite side to the first major surface (16). The layer (10) comprises a plurality of diamonds (20) and a bonding polymeric resin (22) capable of transmitting the radiation. The diamonds (20) can, in one embodiment, be diamond plates (24) located edge-on relative to neighbouring diamond plates (24).

Description: BACKGROUND TO THE INVENTION This invention relates to a window for transmitting radiation such as microwave radiation. The material which is used at present for making windows for transmitting microwave radiation is phenolic resin. While phenolic resin will transmit microwave radiation it has poor thermo-mechanical properties. To overcome this problem the window may be made in two layers which sandwich a cooling layer therebetween. Windows are difficult to make in this manner and, in any event, are not very efficient. United States Patent 3,895,313 describes a diamond window for transmitting a laser beam. In one form of the window, a plurality of diamond polygons or window panes are held in a network of metallic tubes. SUMMARY OF THE INVENTION According to the present invention there is provided a window, for transmitting radiation of wavelength 20 microns or longer comprising a supported layer presenting a first major surface on one side capable of receiving the radiation, and a second major surface on the opposite side to the first major surface, the layer comprising a plurality of diamonds and a bonding polymeric resin capable of transmitting the radiation. DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of an embodiment of a window of the invention, Figure 2 is a section along the line 2-2 of Figure 1, Figure 3 is a sectional side view of a second embodiment of a layer for a window of the invention, Figure 4 is a plan view of another embodiment of a layer for a window of the invention, Figure 5 is a section along the line 5-5 of Figure 4, and Figure 6 is a sectional side view of another embodiment of a layer for a window of the invention DESCRIPTION OF EMBODIMENTS The polymeric resin must be capable of transmitting the radiation. The presence of the diamond particles sharply increases the thermal conductivity of the resin layer by a factor of at least 3. One consequence of this is that the melt or working temperature of the resin layer is increased. Another consequence is that heat dissipation is improved. The window may thus be used in circumstances where higher temperatures are experienced and for radiation of greater energy than is possible with prior art resin layers. The resin/diamond layer will be a supported layer and will act, in effect, as a window pane in the support. Typically, the support will be provided around at least a part of the periphery of the layer, for example by means of a frame. Other supporting means known in the art may be used. Typically, the resin/diamond layer will have a thickness in the range 20 to 500 microns, preferably 20 to 250 microns. As a general rule, the thickness of the layer will be less than a quarter of the wavelength of the radiation passing through it. The polymeric resin will typically be selected from thermosetting resins, epoxy resins and PTFE (polytetrafluoroethene). Examples of suitable thermosetting resins are phenolics, e.g. phenolformaldehyhe, imides, quinoxalines and imidazoles. Specific examples of suitable resins are those sold under the trade names RUTAPHEN SP 309® and modified PHENOLIC AR1004®. The resin/diamond layer may take any one of a variety of forms. Examples of suitable forms are illustrated by the accompanying drawings. Referring first to Figures 1 and 2, a window for transmitting radiation of wavelenghs 20 microns or longer, i.e. microwave radiation, comprises a layer 10 supported around its periphery 12 by a frame 14. The layer 10 presents major flat surfaces 16 and 18 on opposite sides thereof. In use, the one major surface will receive the microwave energy which will then pass through the layer and exit through the other major surface. The layer 10 comprises a plurality of discrete diamond particles 20 embedded in a polymeric resin 22. The diamond particles will generally be uniformly dispersed through the polymeric resin. The diamond particles will generally have a size in the range 20 to 200 microns. The concentration of the diamonds will vary according to the application to which the window is to be put. In general, the concentration of the diamonds in the layer will not exceed 65 percent by volume. A mixture of diamond particles of varying sizes may be used in the layer. Figure 3 illustrates another example of a resin/diamond layer. In this layer, a plurality of diamond plates 24 are located in a polymeric resin 26. As with the embodiment of Figures 1 and 2, major flat surfaces 28 and 30 are provided on opposite sides thereof. The diamond plates 24 are positioned edge-on relative to their neighbours and form a monolayer of diamonds across the layer. If the resin in the regions 32 and 34 to either side of the upper and lower surfaces 24a and 24b of the diamond plates is thin, e.g. no more than 5 microns in thickness, then the window can be used for transmitting IR radiation as well as microwave radiation. Where these regions are thicker, then the layer is suitable for transmitting microwave radiation only. A third embodiment of the invention is illustrated by Figures 4 and 5. Referring to these figures, the resin/diamond layer comprises a plurality of diamond plates 40 each of which is located edge-on relative to its neighbours. The diamond plates 40 are bonded to each other by means of a bonding polymeric resin 42. The resin 42 thus provides a bonding network between the diamond plates. The top surface 40a and bottom surface 40b of each diamond plate 40 is not covered by resin. The layer, as with the previous two embodiments, provides major flat surfaces 44 and 46 on opposite sides thereof. The layer of this embodiment may be used for transmitting IR or microwave radiation. The resin/diamond layer may comprise two or more sections of differing diamond concentration. Each layer will thus have a different dielectric constant with the one layer acting, in effect, as an anti-reflective coating for the other layer. An example of such a layer is illustrated by Figure 6. Referring to this figure, the layer comprises two sections 60 and 62 bonded to each other along the interface 64. This interface lies intermediate the major surfaces 66 and 68 of the layer. The diamond concentration of layer 60 is higher than that of the layer 62. The resin/diamond layers of the invention may be made in a mould by suitably locating resin and diamond particles in the mould which is heated, typically, to a temperature of 60°C. Thereafter, pressure is applied to the resin and diamond particles and the temperature raised until the melting point of the resin is reached. The pressure is released, the mould removed and the thus produced layer allowed to cool. If diamond plates are used, they will generally be positioned in the mould and the resin thereafter introduced into the mould. If diamond particles are used, they will generally be mixed with the resin prior to introduction into the mould.

Claims: A window for transmitting radiation of wavelength 20 microns or longer comprising a supported layer (10) presenting a first major surface (16) on one side capable of receiving the radiation and a second major surface (18) on the opposite side to the first major surface (16), the layer (10) comprising a plurality of diamonds (20) and a bonding polymeric resin (22) capable of transmitting the radiation. A window according to claim 1 wherein the layer (10) is supported around at least a part of its periphery (12). A window according to claim 2 wherein the support is a frame (14). A window according to any one of the preceding claims wherein the thickness of the layer (10) is in the range 20 to 500 microns. A window according to any one of claims 1 to 3 wherein the thickness of the layer (10) is in the range 20 to 250 microns. A window according to any one of the preceding claims wherein the layer (10) comprises a plurality of diamonds (40) bonded to each other by a network (42) of the resin located between the diamonds (40). A window according to claim 6 wherein the diamonds (40) are diamond plates, each diamond plate being located edge-on relative to neighbouring diamond plates. A window according to any one of claims 1 to 5 wherein the layer (10) comprises a plurality of diamonds (20) embedded in the resin (22). A window according to claim 8 wherein the diamonds are diamond plates (24), each diamond plate (24) being located edge-on relative to neighbouring diamond plates (24). A window according to claim 8 wherein the diamonds are diamond particles (20) having a size in the range 20 to 200 microns. A window according to claim 10 wherein the diamonds (20) are present in the layer (10) in an amount of up to 65 percent by volume of the layer. A window according to any one of the preceding claims wherein the resin (22) is selected from thermosetting resins, epoxy resins and PTFE 〈= polytetrafluoroethene〉. A window according to claim 12 wherein the thermosetting resin (22) is a phenolic resin. A window according to any one of the preceding claims wherein the layer (10) comprises two or more sections (60, 62) bonded to each other at an interface (64) or interfaces which are located intermediate the major surfaces (66, 68), the sections (60, 62) differing in diamond concentration.

Inventors: JONES BARBARA LYNN, JONES, BARBARA LYNN
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1991
Main classification: H01J23
IPC codes: H01P1, H01J47, E06B5