Polymer Coating of Glass Microballoons Levitated in a Focused Acoustic Field
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POLYMER COATING OF GLASS MICROBALLOONS LEVITATED IN A FOCUSED ACOUSTIC FIELD
AINSLIE T. YOUNG University of California, Los Alamos National Laboratory P. 0. Box 1663, Los Alamos, NM, 87545 MARK C. LEE, I-AN FENG, DANIEL D. ELLEMAN, and TAYLOR G. WANG California Institute of Technology, Jet Propulsion Laboratory 4800 Oak Grove Drive, Pasadena, California, 91103
ABSTRACT Inertial confinement fusion (ICF) glass microballoons (GMBs) levitated in a focusing radiator acoustic device can be coated with liquid materials by deploying the liquid into the levitation field with a stepped-horn atomizer. The GMB can be forced to the center of the coating liquid with a strong acoustically generated centering force. Water solutions of organic polymers, uv-curable liquid organic monomers, and paraffin waxes have been used to prepare solid coatings on the surface of GMBs using this technique.
INTRODUCTION Acoustic levitations of samples in gaseous media have been demonstrated by T. Wang, et al. [i] and others [2-41 in the audio and near-ultrasonic frequency These acousregions on materials with sizes of several millimeters or larger. A major tic energies can be readily generated with peizoelectric transducers. drawback in the use of piezoelectric transducers is their poor coupling coefficients with gaseous media. In order to levitate objects with any significant mass
in
ambient
environments,
large
surface
areas of transducers must
be used.
In addition, focusing of the levitation forces will help in concentrating these Hemispherical-focusing acoustic radiators provide both these features forces. in levitation systems designed to counter the forces of gravity in a terrestrial environment. [5] Recent work at the Jet Propulsion Laboratory has concentrated on the development of a focusing acoustic radiator device which can be employed in the fabrication of inertial confinement fusion (ICF) targets for laser fusion studies. This apparatus is designed to handle submillimeter samples such as 200- to 500pm-diam glass microballoons used as deuterium-tritium fuel containers in ICF studies. FOCUSING RADIATOR The levitation device consists of a section of a spherical shell with peizoelectric transducers, along with acoustic alignment equipment and data acquisition instrumentation, a sample deployment system , and ultraviolet and infrared sources for sample treatment. The focusing dish is constructed from a section of an aluminum spherical shell, 12-in diam and 0.6-in thick, occupying 3.63 sr of solid angle which has The aluminum shell is driven been machined to a smooth surface finish (Fig. 1).
68 by 130 pieces of about 1-in diam cylindrical piezoelectric transducer discs 0.4-in thick which have been lapped to conform to the outside surface of the aluminum shell. The designed fundamental frequency of this system is 10 kHz. The experimental free-field frequency response at the focal point gave the resonance at 107 kHz and two other resonances at 75 kHz and 163 kHz. The total clamped capacitance of the device was measure at 55,000
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