Document Type

Thesis

College

College of Engineering

Department

Mechanical Engineering

Degree

MSE in Mechanical Engineering

Date Completed

2015

First Committee Member

Lipkins, Bart

Second Committee Member

Rust, Michael

Third Committee Member

Dini, Said

Additional Committee Member(s)

Presz, Walter; Musiak, Ronald; Cheraghi, Hossein

Abstract

"This work reports on the comparison of the performance of a typical single element transducer made of a PZT-8 2-MHz ceramic crystal to that of a multi-element PZT-8 2-MHz crystal. From theory, an acoustic field with stronger gradients is expected to yield higher acoustic radiation forces. With higher acoustic radiation forces, higher separation efficiencies may be attained. Numerical and experimental analyses were conducted to compare performance of a multi- element crystal to a single element crystal. Two-dimensional numerical simulations were performed (COMSOL Multiphysics®) with a 1”- single element, 4-element, and 5-element kerfed crystal. The multi-element simulations used a 1” wide PZT crystal with 1/64” wide by 1/100” deep kerfs, or cuts. The two-dimensional crystals had a common ground electrode with four or five elements on the opposing side. Parametric studies were performed using a frequency range of 2.19 to 2.25 MHz with a total excitation voltage of 40 volts. The 1” single element electrode serves as a baseline simulation and the 4- element and 5-element simulations were run with varying phased element configurations, such as alternating in-phase and out-of-phase or in-phase of the edge of the crystal with out-of-phase on all internal elements. Acoustic pressure and velocity fields were used to calculate the acoustic radiation force, using Gorkov’s equation, on a 20-micron SAE-30 motor oil droplet. From these simulations, the results of interest are not only the magnitudes of the acoustic radiation force components in the lateral (x) and axial (y) directions, but the ratio of the lateral to axial radiation force component. For a standard 1” single element simulation, the ratio of the components is typically 1/10 for the frequencies with the strongest gradients. For the multi-element crystals, the magnitudes of the components increased an order over the standard 1” element and the ratio of the lateral to axial components increased by a factor of four for the best configuration, which indicates increased trapping capability."

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