Abstract
Due to a strong quantum confinement effect, the thermal conductivity and heat capacity per unit volume of a nanocrystalline silicon (nc-Si) layer prepared by electrochemical anodization are extremely low when compared to those of single crystal silicon (c-Si). These large differences in the thermal properties between nc-Si and c-Si make it possible to produce an efficient ultrasound emitter device based on thermo-acoustic conversion without any mechanical vibration. In this paper, the fundamental ultrasound characteristics of a fabricated thermally induced nc-Si ultrasound emitter are explained with regard to an application as an ultrasound speaker. Ultrasound generated at the same frequency as the input signal exhibits a flat frequency response over a wide range and is non-directional. This behavior is totally different from that of conventional airborne ultrasound devices such as piezoceramic transducers.