Acoustic wave manipulation by phased operation of two-dimensionally arrayed nanocrystalline silicon ultrasonic emitters

To confirm the applicability of thermally induced ultrasound emission from nanocrystalline porous silicon (nc-PS) devices to the directional sound emitter, the spatial emission pattern of a two-dimensionally arrayed nc-PS device has been investigated theoretically and experimentally. A 3 x 5 nc-PS device array is fabricated on a p-type Si substrate by conventional electrochemical anodization with the subsequent formation of surface electrodes. It is shown that due to the flat nature of the frequency response of individual emitters, sound wave manipulation is possible in the arrayed device. The directionality of the emission can be controlled by phase-shift driving and by the operating frequency. The arrayed operation enables practical directional and intense ultrasonic emission.