Abstract: A vibrating electrode plate that senses a sound pressure faces a counter electrode plate to constitute a capacitance type acoustic sensor. In the counter electrode plate, acoustic perforations are opened in order to pass vibration, and plural projections are provided on a surface facing the vibrating electrode plate. An interval between the projections is decreased in a region where the vibrating electrode plate has high flexibility to easily generate local sticking with the counter electrode plate. The interval between the projections is increased in a region where the vibrating electrode plate has low flexibility to hardly generate local sticking with the counter electrode plate. The projections thus arranged prevent firm fixing of the vibrating electrode plate to the counter electrode plate and interruption of vibration of the vibrating electrode plate.

Abstract: A vibrating electrode plate 24 that senses a sound pressure faces a counter electrode plate 25 to constitute a capacitance type acoustic sensor. In the counter electrode plate 25, acoustic perforations 31 are opened in order to pass vibration, and plural projections 36 are provided on a surface facing the vibrating electrode plate 24. An interval between the projections 36 is decreased in a region where the vibrating electrode plate 24 has high flexibility to easily generate local sticking with the counter electrode plate 25. The interval between the projections 36 is increased in a region where the vibrating electrode plate 24 has low flexibility to hardly generate local sticking with the counter electrode plate 25. The projections thus arranged prevent firm fixing of the vibrating electrode plate to the counter electrode plate and interruption of vibration of the vibrating electrode plate.