Date of Award
Ph.D. in Physics
Roger M. Waxler
Non-contact manipulation techniques or tweezers devices are invaluable for applications in physics, chemistry, biology, and engineering. Acoustic tweezers using either standing waves or focused beams have been investigated for more than a few decades with advantages of label-free operation, noninvasiveness, and biocompatibility when compared with the optical, magnetic, and electrical counterparts. Here, a new type of acoustic tweezers (i.e. acoustic tractors) is studied using acoustic Bessel and vortex beams that are able to pull objects against the beam's propagation over centimeter ranges. Stable acoustic tractors require transversely stable trapping in addition to axially negative pulling. Hence, the transverse forces acting on a spherical particle centered on the axis of axisymmetric and vortex Bessel beams were first investigated by using both the Gorkov potential and the partial wave expansion with the trapping behaviors more flexible than trapping by standing waves and focused beams used in conventional acoustic tweezers. Then, the physical parameters desired for simultaneous trapping and pulling of particles of different sizes were examined. The results reveal the possibility of achieving a simultaneous pulling and trapping of a small particle using Bessel beams. In addition, the Born approximation method was used to analyze the transverse trapping force for spherical particles and particles of different shapes and orientations. Compared with the full solution from the partial wave expansion, the Born approximation can simplify the computation and can also provide insight into the transverse radiation force. In addition, a mathematical framework based on phase shifts adapted from quantum scattering theory was used to analyze the axial radiation force. This phase shift approach can allow one to engineer object and beam parameters to design experimentally achievable axially pulling forces. Furthermore, the effects of realistic factors such as gravity, buoyancy, and acoustic streaming were also evaluated. The work here is useful for the further study of acoustic radiation force and will lead to an experimental demonstration of stable acoustic tractor beams. The study will also guide particle manipulations with engineered objects.
Fan, Xudong, "ACOUSTIC BESSEL AND VORTEX BEAMS: FORCES AND REFRACTION" (2021). Electronic Theses and Dissertations. 2155.