| 摘要 |
1493518 Electrets PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 21 March 1975 [25 March 1974] 11904/75 Heading H1M In a method of making a homopolar electret, a foil of non-polar polymeric material is heated to a temperature between the glass transition temperature and the melting point of the material, an electret forming voltage is applied across the foil of such magnitude that the homocharge is greater than the desired value, the foil is removed from the forming field before it has cooled to the glass transition temperature, whereby the surplus, less strongly bound, charge is drained off. Charge removal may be accelerated by raising the temperature further, or holding it constant for a time, after the field has been removed. The electret forming material may be a fluorine polymer metallized with vapour deposited nickel-chromium alloy on one side and separated on the other side from the preferably negative forming electrode by porous material such as glass cloth. |
