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.

Effects of Thermal Effusivity in Nanocrystalline Porous Silicon on Long-Term Operation of Thermally Induced Ultrasonic Emission

“…As previously reported, 12) this device operates well for pulse driving. To accelerate the aging effect, the nc-PS device was kept in a high-temperature and wet-air ambience (85 C and 85%) for 0 -100 h. The ðCÞ 1=2 values of the nc-PS layer were determined in various stages of operation by the thermoreflectance method based on a photothermal modulation technique, 13) as shown in Fig.…”

Thermal properties of nanoporous silicon materials

“…When the short electrical impulse is supplied into the surface heater, the temperature is raised and recovers instantly and uniformly, because thermal outfl ows from the terminal edges are impeded by the PSi (Watabe et al ., 2006). Figure 3.8 shows a measured spatial distribution of the peak temperature at the heater electrode under a pulse input.…”

Ultrasonic Emission from Nanocrystalline Porous Silicon

“…The graph shows that PSUE device generates a short duration impulse for an impulse current. Impulse characteristics are also reported in [18]. Measured acoustic pressure amplitudes at a distance of 30 cm from the device surface are plotted in Fig.…”