| 摘要 |
PURPOSE:To make uniform the surface charge density, to protect the electret material and to stabilize the characteristics, by opposing the electret element member to a grounded conductor and laminating a back electrode floated from ground. CONSTITUTION:On a back electrode 21 made of a conductive metal base, an electret member 22 made of macropolymer such as PP, TFE, FEP is coated to form an electret element 23. The side of the electret member 22 of the element 23 is laminated so that it opposes to a grounded conductive metallic plate or foil 24 having equal or larger area shape than the member 22, and the back electrode 21 is floated from ground. Regardless that a nonelectret part is in existing at the center of the electret member 22, charges with different sign and almost equal amount as the charges on the electret element 23 itself are uniformly distributed on the surface of the back electrode 21. Thus, products rich in moisture-proof and stable in the characteristics can be made. |
