Pressure wave generator and process for manufacturing the same

Abstract

Even when compression stress is generated because a volume of a thermal insulation layeris expanded due to oxidized by oxygen in the air, occurrence of cracks and fractures of the thermal insulation layer and a heating conductorcaused by the cracks are prevented by dispersing the compression stress. A pressure wave generator comprises a substrate, the thermal insulation layerof porous material which is formed on a surface of the substratein thickness direction, and the heating conductorof thin film formed on the thermal insulation layer, and generates pressure waves by heat exchange between the heating conductorand a medium. When a thickness at the center of the thermal insulation layerin width direction W is used as a reference thickness, and it is assumed that distribution of thickness of thermal insulation layer in the width direction is averaged with the reference thickness, porosity in an outer peripheral portion of the thermal insulation layer is made smaller than porosity in the center portion. By making the porosity in the outer peripheral portion of the thermal insulation layersmaller, a number of immovable points on the outer periphery of the thermal insulation layerrestricted by the substrateis increased and the positions of them are dispersed, so that the compression stress compressed in the outer peripheral portion of the thermal insulation layercan be dispersed.