Load materials for use in microwave lenses

Abstract: The load material comprise carbonyl iron powder and a mix of resin/hardener mix. The resin has a low glass transition temperature which together with the ratio of carbonyl iron powder to resin/hardener mix gives a load material that is flexible over the temperature range + 85° C to - 30° C. The carbonyl iron powder may be in the grades E, TH or SF. The resin may be resin CY1300 and the hardener may be hardener HY1308.

Description: The present invention relates to materials, commonly known as load materials which are for use in the manufacture of microwave lenses. Hitherto, load materials used in microwave systems are hard and have a low glass transition temperature which normally causes their insulation properties to drop in high temperature environments. This drop in insulation makes the materials more conductive and often causes disruption in the microwave system. An article in the IEEE Transactions on Magnetics, Vol 10, No 1, March 1974, pages 96 to 97, entitled 'Method of Forming Ferrite Impregnated Resins for Microwave Measurements', by William L Wade Jr, and Aubrey Raffalovich, discloses the use of ferrite and carbonyl iron impregnated polyethylene for fabricating microwave absorbing elements. However, hardness of known materials make them particularly vulnerable to fracture, particularly when the materials were moulded to shapes having 'knife-edges'. It is an object of the present invention to provide a flexible insulative material for use in microwave systems which operate over a wide temperature range. A further object of the invention is to provide a flexible insulative material which may be moulded to shapes having 'knife-edges'. According to the present invention there is provided load materials for use in microwave lenses comprising carbonyl iron powder and resin with which resin said carbonyl iron powder is mixed, characterised in that a mix of resin and hardener is in a ratio of 3:1 carbonyl iron powder to resin/hardener mix, said resin having a low glass transition temperature, which together with the ratio of carbonyl iron powder to resin/hardener gives a load material that is flexible over a predetermined temperature range. It will be appreciated that various grades of material may be used, and that the choice of materials and their quantities provide the desired flexibility in the temperature range of +85° C to -30° C. The load materials may be moulded into shapes having 'knife-edges'. An embodiment of the present invention and a method of manufacturing the load materials will now be described. The flexible insulative material comprises carbonyl iron powder manufactured to the grades of E, TH or SF. This powder is mixed together with an epoxy resin which consists of a resin which may be resin Cy1300 and a hardener which may be a hardener Hy1308. These materials are well known in the art and are obtainable from known suppliers. The resin has a low glass transition temperature Tg (°C). This is the temperature at which on heating, the polymer chains are caused to vibrate in a coordinated manner (ie become plastic) and the polymer chains become rigid and glassy. The mix is made in a ratio of 3:1 of carbonyl iron powder to resin/hardener. The combination of the mix ratio and the resin having a low Tg temperature gives a very flexible material. A method of manufacturing the mix will now be described. A suitable mould is used which corresponds to the size and shape of microwave lens required. The mould is cleaned with industrial alcohol and sprayed with a release agent over the relevant parts of the mould. The mould is assembled ensuring that respective parts mate correctly. The carbonyl iron powder is pre-dried in an oven at 45 to 55° C. In the example that follows, the weights are determined by the size of the microwave lens required and will vary accordingly, however, the mix ratio is in the order of 3:1. In the present example, 300 gm of carbonyl iron powder are used together with 50 gm of resin Cy1300 and 50 gm of hardener Hy1308. The resin and the hardener are mixed together and the carbonyl iron powder is added and mixing continues until a smooth consistent paste is obtained. The mixture is then de-aerated in a vacuum encapsulation plant down to a vacuum of 5 Torr, and is subjected to a dwell period of 5 minutes before the vacuum is released. The mixture is then poured into the mould until the mould is full, and the mould is placed in encapsulation unit, and operated down to a vacuum of 5 Torr and allowed to dwell for 5 minutes before the vacuum is released. The load mix is then allowed to stand for a period of 24 hours at room temperature. The mould is then demounted from the encapsulation unit and the load is carefully extracted. The load may then be affixed to a backing strip for transport. The material is aptly suitable for moulding into shapes having 'knife-edges' and because of its flexibility does not have a tendency to fracture. The flexible material produced by the above method is aptly suitable for use in microwave components which are placed in a temperature environment ranging from + 85° C to - 30° C. It will be readily appreciated by those skilled in the art that the use of other types of ingredients for the mix may be used which give the same flexibility.

Claims: Load materials for use in microwave lenses comprising carbonyl iron powder and resin with which resin said carbonyl iron powder is mixed, characterised in that a mix of resin and hardener is in a ratio of 3:1 carbonyl iron powder to resin/hardener mix, said resin having a low glass transition temperature, which together with the ratio of carbonyl iron powder to resin/hardener gives a load material that is flexible over a predetermined temperature range. Load materials as claimed in Claim 1, which remain flexible in the temperature range of + 85° to - 30° C. Load materials as claimed in Claim 1 or Claim 2, wherein the carbonyl iron powder may be in the grades E, TH or SF. Load materials as claimed in any preceding Claim, wherein the resin is resin Cy1300 and the hardener is hardener Hy1308. Load materials as claimed in any preceding Claim, wherein the material may be moulded into shapes including 'knife-edges'.

Inventors: POYNER JACK ALAN, POYNER, JACK ALAN
Applicants: SIEMENS PLESSEY ELECTRONIC, SIEMENS PLESSEY ELECTRONIC SYSTEMS LIMITED
Application year: 1993
Main classification: H01Q15
IPC codes: H01Q15