Patent ID: 8379887

Claim:
An acoustic sensor comprising: a substrate; a vibrating electrode plate that is fixed to the substrate to sense a sound pressure; and a counter electrode plate that is fixed to the substrate to face the vibrating electrode plate with an air gap interposed therebetween, wherein a plurality of projections are provided on a surface on the air gap side of one of the vibrating electrode plate and the counter electrode plate, and wherein, in a perpendicular section in a diagonal direction of one of the vibrating electrode plate and the counter electrode plate, each projection comprises a leading end surface and two side surfaces, wherein the two side surfaces are perpendicular to the leading end surface and are connected to a same one of the vibrating electrode plate and the counter electrode plate, wherein an interval between the adjacent projections is changed according to a projection forming region in one of the vibrating electrode plate and the counter electrode plate, and wherein, in one of the vibrating electrode plate and the counter electrode plate on which the projections are provided, the interval between the adjacent projections in a high-flexibility region of the vibrating electrode plate or a counter region of the counter electrode plate facing the high-flexibility region is smaller than the interval between the adjacent projections in a low-flexibility region of the vibrating electrode plate or a counter region of the counter electrode plate facing the low-flexibility region.