Brian Kappus

Cavitation luminescence in a water hammer: Upscaling sonoluminescence

Oscillatory acceleration and deceleration of a column of water leads to a pipe hammer as well as cavitation. With a small amount of xenon gas dissolved in the water, we can detect a stream of predominantly ultraviolet subnanosecond flashes of light which are attributed to collapsing bubbles. The observed emission can exceed 108 photons for a single collapse and has a peak power over 0.4 W.

Drop tube generates 10‐W flashes of sonoluminescence

Use of a low vapor pressure liquid such as phosphoric acid, with dissolved xenon in a vertically exited tube, generates ∼200‐ns flashes of sonoluminescence with a peak power of 10 W. We are in the process of characterizing the bubble motion by use of backlighting, stroboscopic, and streak photography. We will also broach the topic of disequilibrium between atom and electron temperatures. [Research funded by DARPA. We thank Carlos Camara and Shahzad Khalid for valuable discussions.] a)Deceased.

Spatiotemporal modulation for mid-air haptic feedback from an ultrasonic phased array

A tactile sensation can be experienced by focusing airborne ultrasound using a phased array. Nonlinear acoustic pressure alone is difficult to perceive so traditional methods use amplitude modulation in the range of 10–300 Hz to stimulate nerves on the hand most sensitive to those frequencies. We demonstrate that through rapid translation of focus points similar results can be obtained using spatiotemporal modulation. This allows for volumetric sensations to be created using maximum power possible from the array. This is made possible through a solving approach using a pseudo-inverse of the activation matrix followed by a power iteration eigenvalue solution. Advantages versus amplitude modulation and consequences for parametric audio will be discussed. A tactile sensation can be experienced by focusing airborne ultrasound using a phased array. Nonlinear acoustic pressure alone is difficult to perceive so traditional methods use amplitude modulation in the range of 10–300 Hz to stimulate nerves on the hand most sensitive to those frequencies. We demonstrate that through rapid translation of focus points similar results can be obtained using spatiotemporal modulation. This allows for volumetric sensations to be created using maximum power possible from the array. This is made possible through a solving approach using a pseudo-inverse of the activation matrix followed by a power iteration eigenvalue solution. Advantages versus amplitude modulation and consequences for parametric audio will be discussed.

Time resolved spectra of the transition to a sonoluminescing blackbody.

The passage of ultrasonic sound through a fluid leads to pulsations of an entrained bubble that are so nonlinear that acoustic energy density is concentrated by 12 orders of magnitude to generate picosecond flashes of ultraviolet light. The spectrum, for xenon bubbles, matches an 8000 K ideal Planck blackbody even though the micron radius of the bubble is small compared to the photon mean free path. To probe the formation of a blackbody we have weakened sonoluminescence by generating it with a water hammer. The implosions are now subsonic and the collapse densities are only 1021/cc. Nevertheless, time resolved spectroscopy of these 1‐s flashes indicates the formation of ideal blackbodies.