We have fabricated multiple layer ZnO acoustic transducers for highly efficient sound wave generation at millimeter-wave frequencies. The transducers consist of half-wave-thick layers of ZnO with alternating crystal structure. The two-way untuned conversion loss values were 27 dB near 29 GHz and 50 dB at 96 GHz measured at liquid nitrogen temperatures.
We have studied the saturation and stimulated decay of an 8 GHz focused acoustic beam in superfluid helium near 50 mK. Because the dispersion is a function of pressure, there are various regimes where different nonlinear processes dominate. At low pressures (upward dispersion) parametric self-enhancement of the noise causes rapid signal depletion. At intermediate pressures (linear dispersion) harmonic formation leads to saturation (a “shock wave”). At still higher pressures (downward dispersion) the power in the main focus far exceeds the shock onset threshold before depleting rapidly in what appears to be a four-phonon parametric enhancement of the spontaneous decay. We believe this to be the first experimental evidence of four-phonon parametric mixing in acoustics.
A scanning microscope stage has been developed for use at cryogenic temperatures. The stage uses a piezoelectric driving element and circular flexure hinges to achieve a slow scan travel of greater than lO!tm and a near-resonance travel of 100 11m ~hiIe ~m~ersed i~ liquid helium ~t 4.2 K. The scanner has been operated inside a pressure cell III a dllutlOn refngerator, where It dissipates less than 150,uW of heat at lOOmK.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.