Experiments have demonstrated the feasibility of generating fountains and fogs over a body of water (see Figure 1) by utilizing high-intensity ultrasound to induce acoustic streaming, cavitation, and atomization. The transducer used in the experiments had a 10-cm diameter and a 10-cm focal length, was immersed in water at a depth approximately equal to its focal length, and was excited at various amplitudes and at various frequencies from 100 kHz to 2 MHz. It was observed in the experiments that the fountain and fog effects depend on the amplitude and frequency of excitation.

Figure 1. Fountains and Fogs were induced over a water bath by ultrasound generated by a focusing transducer immersed in the bath.
Figure 2. A ULIFOG System would exploit effects like those of Figure 1 in synchronism with lighting and sound effects.
Through suitable control of the excitation waveforms applied to multiple immersed ultrasonic transducers, it should be possible to create, destroy, enlarge, diminish, or otherwise change fountains and fogs to produce diverse visual effects for artistic display. Optionally, a fountain-and-fog display generated in this manner could be synchronized with illumination and/or with music. Scattering of light from water columns, water drops, and fogs could be exploited to obtain striking visual effects.

An apparatus proposed for implementing this concept is called an ultrasonically induced plumbing-free switchable multi-fountains and fog (ULIFOG) system. In addition to ultrasonic transducers immersed in a water bath, a ULIFOG system (see Figure 2) would include (1) electronic circuits to excite the ultrasonic transducers with waveforms chosen to produce the desired fountain and fog effects, (2) one or more source(s) of light (e.g., lasers or colored lamps), (3) a source of music, and (4) a computer that would control the aforementioned subsystems and would coordinate the visible and audible aspects of the display.

The mechanical simplicity occasioned by elimination of the need for pipes, valves, and pumps is an advantage over prior fountain display systems. Another advantage over such systems is much faster response: For example, in an ULIFOG system, one could change a fountain into a fog in a millisecond by switching the frequency of excitation of the applicable transducer.

This work was done by Yoseph Bar-Cohen and Stacey Walker of Caltech for NASA’s Jet Propulsion Laboratory.