Method of making a variable capacitor microphone

• US 5,101,543 A
• Filed: 01/30/1991
• Issued: 04/07/1992
• Est. Priority Date: 07/02/1990
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Cote, Paul L., Sallavanti, Robert A.
• Primary Examiner(s): Hall, Carl E.
• Application Number:
  US07/647,761
• Time in Patent Office: 433 Days
• Field of Search: 29/631.1, 29/592.1, 29/25.41, 29/594, 204/164, 204/165, 204/169, 381/173, 381/174, 381/191
• US Class Current: 29/25.41
• CPC Class Codes: H01G 7/023 of macromolecular compounds
• CPC Class Codes: H04R 19/016 for microphones
• CPC Class Codes: Y10T 29/43 Electric condenser making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49226 Electret making

Abstract

A method of making a variable capacitor microphone in which the fixed capacitor element is formed by first coating the metallized surface of a relatively rigid insulating substrate with a polarizable dielectric material and then placing the substrate on one of a pair of spaced electrodes positioned in an ionizable gas and subjecting the gas to the action of alpha rays to produce ions in the space between the electrodes while applying a potential across the electrodes to cause ions to migrate toward the dielectric material to polarize the same to form an electret. After the fixed capacitor element has thus been formed, it is mounted in spaced relationship to a flexible diaphragm to form a microphone.

Claims

1. A method of making a variable capacitor microphone having a fixed capacitor element comprising a rigid insulating substrate with a metalized surface including the steps of forming the fixed capacitor element by successively coating the metalized surface of said substrate with polarizable dielectric material, placing the substrate on one of a pair of spaced electrodes positioned in an ionizable gas, subjecting said gas to the action of alpha rays to produce ions in the space between said electrodes, applying a potential across the electrodes to cause ions to migrate toward said dielectric material to polarize the same to form an electret thereof, and mounting said insulating substrate carrying said electret in spaced relationship to a flexible diaphragm to form said microphone.

2. A method as in claim 1 in which said coating steps comprises applying to said metalized surface fluorinated ethylene-propylene copolymer in a solvent.

3. A method as in claim 2 in which said solvent is water.

4. A method as in claim 3 including the step of applying an active circuit element of said substrate following the application of said coating.

5. A method of forming a plurality of variable capacitor microphones including the steps of dividing a wafer of relatively rigid insulating material into a plurality of separable circuit boards, simultaneously forming a film of conductive material on said circuit boards, simultaneously coating areas of said film of conductive material with a polarizable dielectric, separating said circuit boards, individually placing said circuit boards on one of a pair of spaced electrodes positioned in an ionizing gas, subjecting said gas to the action of alpha rays to produce ions in the space between said electrodes, applying a potential across said electrodes to cause ions to migrate toward said dielectric material to polarize the same to form fixed electret capacitor elements thereof and mounting said fixed electret capacitor elements in spaced relationship to flexible diaphragms to form said variable capacitor microphones.

6. A method as in claim 5 in which the coating step comprises applying said dielectric to said areas through a mask to leave uncoated regions of said film on said circuit boards.