Acoustic Focusing for High Speed Particle Assembly in Viscous Fluids

PhD in Mechanical Engineering

Acoustic Focusing for Particle Assembly

Acoustic focusing uses sound interference to assemble material in space. The assembly forces depend on the acoustic contrast between the bulk fluid and the contained filler. As a result, this process can assemble across a broad range of sizes (mm to micron) and material types (cells, metals, carbon, oil).

The challenge of acoustic focusing for assembly, especially in manufacturing, is that common filler particles are small (sub-mm), and common bulk materials are viscous, e.g., thermoplastics. Both attributes of manufacturing processes lead to prohibitively long assembly times. Increased acoustic transducer power can mitigate the slow assembly times but quickly hits a ceiling as this same power drives a disruptive bulk flow that destroys the pattern.
The challenge of acoustic focusing for assembly, especially in manufacturing, is that common filler particles are small (sub-mm), and common bulk materials are viscous, e.g., thermoplastics. Both attributes of manufacturing processes lead to prohibitively long assembly times. Increased acoustic transducer power can mitigate the slow assembly times but is quickly limited by a disruptive bulk flow, driven by the same acoustic power, that destroys the pattern.
Below are a select list of elements from thesis work.
- Acoustic Focusing to Enhance Composite Properties
- LabVIEW Instrument Control
- Pulse Echo to Measure Sound Speed
- Sensitivity Analysis to Determine Relative Power Losses amongst assembly time variables

Acoustic Focusing to Enhance Composite Properties

In composite assembly, acoustic focusing enables one to assemble a homogenous material mix into a designed pattern. The designed process has enhanced properties compared to the homogenous mix as it uses the filler properties more effectively - stiffness, strength, and conductivity, to name a few. In this work, I use acoustic focusing to increase the conductivity of a composite.

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EXPERIMENTAL SETUP (labview, matlab, jig design)

ANALYSIS DETAILS - showcase uncertainty analysis (number of samples, use of experimental results to prediction models)

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Sample/DOF Target holder Design Evolution

Functional requirements:

Place samples on stage with precision, with minimal assembly
Modular - use for both holding samples and holding Depth of Field target

Flat plate (white) bolts into Thorlabs PR01 stage. Sample holder (black) sits on the plate. Pins and grooves at the interface ensure repeatable placement.

An early version of the sample holder had to be screwed into the stage.

Modular holder is a 3d printed assembly (FDM printer). It is comprised of two parts: a flat plate that screws into the stage (Thorlabs PR01) and a holder that sits on top of the flat plate. The interface is a flat surface (3 degrees of freedom). Pins on one surface sit in grooves on the other, aligning the two pieces. Magnets provide a positive force holding the pieces together.

Earlier versions of the sample holder were bolted directly onto the PR01 stage. Removal was cumbersome and led to alignment errors. In the updated design, switching samples or swapping in the Depth of Field target is as simple as lifting the holder off the plate and dropping another in its place.

Labview - Instrument Control

Image Analysis of ab - Image Processing, Image Orientation

Assembly progress captured as series of images, 20 fps. Across 4-5 trials per parameter, across the parameter space, my scripts needed to process thousands of images with minimal human interference. Key : self-aligning jigs for precision locating of samples, using markers in images during data capture. Scripts that use the markers to locate the region of interest in images.