Characteristics of Thermally Induced Ultrasonic Emission from Nanocrystalline Porous Silicon Device under Impulse Operation

Abstract

To clarify the mechanism of thermoacoustic effects in a nanocrystalline porous silicon (nc-PS) device, ultrasonic emission characteristics have been investigated in relation to dynamic behavior. The nc-PS ultrasonic emitter is composed of a surface heater electrode, an nc-PS layer, and a single-crystalline silicon (c-Si) substrate. Due to a completely flat frequency response, this device emits an ideal impulse acoustic output with no reverberations for pulse driving. The relationship between acoustic output and transient surface temperature change can be well interpreted quantitatively by taking the heat capacity of the heater electrode into account. The experimental fact that the transient surface electrode temperature change is induced uniformly over the whole range of the emission area ensures the directivity of the acoustic pulse output.