Patent ID: 7881157

Claim:
A pressure wave generator comprising a substrate, a heat generating layer, and a heat insulating layer formed between said substrate and said heat generating layer, and configured to generate a pressure wave in a surrounding medium by a change in temperature of said heat generating layer, which is caused upon energization of said heat generating layer, wherein said heat insulating layer comprises a porous layer and a barrier layer formed between said porous layer and said heat generating layer, wherein said barrier layer has a structure where porosity and average pore diameter of said barrier layer are smaller than those of said porous layer, wherein said barrier layer has a porous structure, and at least a part of pores of said porous layer are communicated with pores of said barrier layer, and wherein said barrier layer is formed by expanding the volume of a part of said porous layer so that most of the pores in the barrier layer are sealed, thereby preventing diffusion of a component of said medium into said porous layer.