Prof. Robert A. Heard Profile

Prof. Robert A. Heard

at Carnegie Mellon Univ

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Proceedings Article | 29 March 2019 Presentation + Paper

Ultrasonic microparticle alignment and direct ink writing using glass capillaries

Erin Dauson, Kelvin Gregory, Robert Heard, Irving Oppenheim, Stephanie Wong, Cheyney (Chiheng) Zhou

Proceedings Volume 10968, 109680N (2019) https://doi.org/10.1117/12.2515277

KEYWORDS: Transducers, 3D printing, Microfluidics, Ultrasonics, Capillaries, Particles

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We envision implementing direct ink writing for 3-D printing while aligning microfibers in the resin using standing wave ultrasonics; the aligned fibers would control desired mechanical properties such as strength and ductility, and 3-D printing would match the mechanical properties to the particular part geometry. At this time we work with highviscosity fluids as a physical simulant of representative resins, and spherical polystyrene microparticles or glass microrods instead of microfibers. In this paper we show experimental results using square glass capillaries (with interior dimensions ranging from 0.4 to 1.0 mm) as our microfluidic systems, which are inherently well-suited by their geometry to act as print nozzles, sandwiched between two piezoceramic plates that generate the ultrasonic standing waves. We report experimental data for particle alignment as we change from our initial test fluid, water, to high-viscosity fluids. Similarly, we report experimental data of the fluid behavior pertinent to direct ink writing; we enforce controlled volumetric flow rates (which correspond to print speeds) for high-viscosity fluids under pressurized flow through glass capillaries of varying cross-sectional areas and varying lengths, observing and measuring the approximate ink line width and height. Our use of commercially available square glass capillaries (sandwiched between piezoceramic transducers that are driven at frequencies away from transducer resonance) is novel and distinguishes our approach from that of other research groups; the underlying physics of our devices differs from that of Lund-type acoustic resonators.

Proceedings Article | 22 March 2018 Presentation + Paper

Ultrasonic alignment of microparticles in nozzle-like geometries

Molly Whittaker, Erin Dauson, Jaime Parra-Raad, Robert Heard, Irving Oppenheim

Proceedings Volume 10596, 105960X (2018) https://doi.org/10.1117/12.2296868

KEYWORDS: Acoustics, Microfluidics, Particles, Resonators, Transducers, Ultrasonics, 3D printing, Prisms, Silicon, Polymethylmethacrylate, Piezoelectric driven mechanisms

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Additive manufacturing (3-D printing) is presently limited by the mechanical properties of the materials, such as polymer resins, that are otherwise efficient and economical for part-forming. Reinforcing the resin with microscale fibers and/or particles would be an effective mechanism to achieve desired mechanical properties such as strength and ductility. Our work combines standing wave ultrasonics and microfluidics to align microparticles in devices that can act as print nozzles, based in part on our prior work with cell sorting. In this paper three different approaches are presented illustrating different engineering tradeoffs, and demonstrating laboratory results of particle alignment. First acoustic resonators are discussed, in which the ultrasonic standing waves result mostly from the mechanical properties of the microfluidic structure, excited by a piezoceramic transducer. Next non-resonant microfluidic structures are discussed, in which ultrasonic standing waves are produced directly by symmetrical transducer deployment. Finally, devices that combine nozzle-like structures, which themselves are suitable acoustic resonators, subjected to symmetrical ultrasonic excitation are presented. We will show that all three configurations will align microparticles, and discuss the tradeoffs among them for subsequent configuration of a print nozzle.

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