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George Lewis Jr.
The action shot of the "ultrasonic fountain" shows the interaction of High Intensity Focused Ultrasound (HIFU) waves with water. The ultrasound transducer is typical of medical physical therapy ultrasound devices; operating at 1.5 MHz and with a diameter of 2.54 cm. The difference in this picture is that the transducer is powered 20x greater than typical, and the energy from the transducer is focused to a 1mm^3 volume creating a HIFU spot near the surface of the water. Since ultrasound is a mechanical wave, the HIFU spot sees large pressure changes as the sound travels via compression and rarefaction in the propagation fluid, which results in cavitation and micro-bubble formation in the water. The transfer of ultrasound energy/momentum into the fluid causes the water to stream and/or move in the direction of the ultrasound field. Combining the cavitation and acoustic streaming, the water molecules are shot into the air (some of which are vaproized by the HIFU) creating a beautiful acoustic fountain.
This work was supported by the National Science Foundation and the National Institutes of Health
Lewis et al. Development of a portable high intensity focused ultrasound system. Rev. Sci. Inst. 2008; Lewis et al. Design and characterization of a high-power ultrasound driver with ultra-low output impedance. Rev. Sci. Inst. (In Press) 2009
Reporters can freely use this image. Credit: Cornell University.