Phased array operation of nanocrystalline porous silicon ultrasonic emitters

To confirm the applicability of thermally induced ultrasound emission from nanocrystalline porous silicon (nc-PS) devices as directional sound emitter, the radiation pattern of one-dimensionally arrayed nc-PS device have been investigated. The nc-PS emitter is fabricated on a p-type Si substrate by conventional electrochemical anodization with subsequent formation of the surface electrode. It is shown that the emission pattern of arrayed devices can be controlled due to flat nature of the frequency response of the individual nc-PS devices. Furthermore we report a technique for wave control by phase-shift operation. This PS array enables the development of a directional sound emitter and intense sound source. (c) 2005 WrLEY-VCH Verlag GmbH & Co. KGaA, Weinheim.