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Research Papers

Effect of Placing a Probe in an Acoustic Drop Levitator

[+] Author and Article Information
Jared N. Baucom

Mem. ASME
U.S. Naval Research Laboratory,
Multifunctional Materials Branch,
4555 Overlook Avenue, SW,
Washington, DC 20375

Marriner H. Merrill

Mem. ASME
U.S. Naval Research Laboratory,
Multifunctional Materials Branch,
4555 Overlook Avenue, SW,
Washington, DC 20375
e-mail: marriner.merrill@nrl.navy.mil

Christopher R. Field, Kevin J. Johnson

U.S. Naval Research Laboratory,
Naval Technical Center for Safety
and Survivability,
4555 Overlook Avenue, SW,
Washington, DC 20375

G. Asher Newsome

Nova Research, Inc.,
1900 Elkin Street, Suite 230,
Alexandria, VA 22308
e-mail: graham.newsome.ctr@nrl.navy.mil

1Present address: Technetics Group, Columbia, SC 29209.

2Corresponding author.

3Present address: Field R&D Services, Arlington, VA 22201.

Contributed by the Noise Control and Acoustics Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received March 11, 2015; final manuscript received September 21, 2015; published online October 27, 2015. Assoc. Editor: Nicole Kessissoglou. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Vib. Acoust 138(1), 011011 (Oct 27, 2015) (7 pages) Paper No: VIB-15-1088; doi: 10.1115/1.4031672 History: Received March 11, 2015; Revised September 21, 2015

In this paper, we use computational modeling to explore the effects of placing a probe within the active volume of an acoustic levitator. A two-step computational approach is used to visualize the levitation nodes using thousands of simulated particles driven by the acoustophoretic force and gravity. Our analysis shows that the size and position of a probe can strongly alter the shape, location, and intensity of existing levitation nodes. This has a direct impact on the ability to use acoustic levitation for drop suspension in the presence of disruptive probes.

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Figures

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Fig. 1

The distribution of standing axial pressure waves in an acoustic drop levitator depicted as a transverse wave. Nodes along the dashed axis coincide with regions of zero acoustophoretic force, where particles or droplets can be expected to levitate. This schematic assumes a dense particle levitating in a gas phase (the assumed case for a system where a sample is acoustically trapped and then probed).

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Fig. 2

A basic ADL with an idealized probe inlet (inset). The corresponding model geometry and dimensions are also shown.

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Fig. 3

The acoustic pressure field in the modeled ADL without a probe inlet. White dashed circles show predicted levitation nodes along the axis, and black dashed circles show predicted ring-node levitation.

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Fig. 4

Visualization particle locations after 400 ms. Particles are shown in a 1 mm-thick slice of the YZ-plane. The acoustic pressure field is shown in the background for comparison.

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Fig. 5

Experimental validation showing a photograph of the ADL with two levitated beads of foam (right and inset) and the predicted location of the visualization particles after 400 ms. The geometry and driving frequency were the same in each case. Off-axis levitation was also observed experimentally, though the nodes were less stable.

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Fig. 6

The effect of probe size and position on the acoustic pressure field is shown for two inlet diameters (5.0 mm on the left and 2.5 mm on the right) and positions (1, 10, and 20 mm from the centerline). The pressure field is shown in the yz-plane.

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Fig. 7

Two orthogonal views of the pressure distribution for a 2.5 mm probe located 1 mm from the centerline. The two distributions are distinctly different and indicative of the asymmetry caused by the presence of an obstruction in the ADL.

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Fig. 8

Visualization particle location without (a) and with (b) a probe. (a) and (b) show all particles and indicate the slice taken to focus on the lowest node (z = 5 5 mm). In (c), the XY location of the visualization particles for the lowest node are shown without the probe (gray ring node and black center node) and with the probe (dark gray lobes left, middle, and right).

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Fig. 9

Acoustic pressure as a function of height above transducer surface along the centerline of the acoustic volume for two probe diameters (5.0 mm and 2.5 mm) and three offset distances (20, 10, and 1 mm). Probe diameter only had a significant effect for the 1 mm case, as indicated.

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