| 摘要 |
PURPOSE:To achieve higher accuracy and a lower cost by covering a pressure receiving element with a closed member airtight keeping it at a lower pressure. CONSTITUTION:A capacitor microphone 10 is made up of a cylindrical casing 11, a circuit board 12, a FET 13, an insulating cylinder 14 for keeping an interval, an electlet film 15a for receiving pressures, a fixed electrode plate 15b, an insulating film 16 for a ring-shaped spacer, a glass closed member 18 and the like. The member 18 covers the entire outside of the microphone 10 airtight to keep the inside of the microphone 10 at a low pressure. The member 18 has an inner diameter larger than the outer diameter of the microphone 10 and the microphone 10 is inserted into a hollow part to be fixed with an adhesive. Thereafter, a portion near one end opening is heated with a burner to close the opening by melting the glass while the glass near the opening is melted to close the microphone 10 in a vacuum. Even when an ambient temperature rises, the closed member 18 covers the microphone 10 from outside to prevent the generation of a mechanical distortion of the casing 11 and changes in the capacity thereby achieving very better temperature characteristic. |
