Date of Award
Ph.D. in Physics
Physics and Astronomy
In this study, the physics and applications of the ultrasonic radiation force at the interface between two immiscible fluids were investigated. These studies were performed using low-profile discrete-stepped lenses to the modify the phase of the incident radiation generating multiple field morphologies. In its first application to acoustics, a fraxicon lens was developed to approximate the field generated by an axicon. This type of lens creates a minimally diffractive Bessel beam and long depth of focus that is useful in ultrasonic imaging, therapy, and non-destructive evaluation techniques. Fields modified by fraxicon, Fresnel, and axicon lenses were characterized experimentally by scanning hydrophone measurements and by numerical simulations. The results shogood agreement with each lens type. A theoretical framework for the focusing efficiency of fraxicon and Fresnel phase plate lens was also developed which compared well to the numerical simulations. Ultrasound focused by these lenses was then used to deform the boundary between two sets of fluids. First a water to carbon~tetrachloride boundary was explored. A central finding was that the near field features of the fraxicon provided the stability to extract a droplet from a fluid interface, a novel effect, allowing it to be transported over relatively large distances. Similar phenomena of acoustic trapping and transport typically requires arrays of multiple transducers or standing waves. Here a single sided transducer with a passive lens was used. This phenomenon has applications in chemical engineering, microfluidics, and advanced testing techniques. The trapping force was calculated from theory using simulations of the field and the results compared well to observations. Next the boundary between canola oil and water was investigated. Due to the impedance mismatch at the boundary significant heating occurred when it was insonified causing a decrease in the surface tension over time. When the surface tension is low enough, jetting of the oil into the water occurs. The findings in this work could lead to a broad range of applications involving fluid transport and manipulation.
Lirette, Robert Lee, "Acoustic Radiation Force on a Fluid to Fluid Boundary by Phase Plate Focused Ultrasound" (2019). Electronic Theses and Dissertations. 1627.