The figure schematically illustrates a developmental automated hybrid acoustic/electrostatic apparatus for levitating both electrically charged and electrically neutral liquid drops with sizes up to about 1 mm. The apparatus is particularly suitable for experiments on the growth of protein crystals from solution and on the growth of cells and tissues, all under controlled conditions. In addition to the obvious advantage of levitation for preventing the chemical and thermal contamination that accompanies contact between drops and external objects, this apparatus provides controllable rotation about a horizontal axis (for example, to reduce sedimentation). Moreover, the direction of rotation can be varied to randomize the effective direction of gravitation. Thus, on Earth, the apparatus is expected to provide some of the advantages of low gravitation for suppressing the buoyancy-induced flows that interfere with the growth of high-quality protein crystals and for reducing the adverse effects that gravitation exerts on some cell and tissue cultures.
An electrically neutral drop can be levitated acoustically. An electrically charged drop can be levitated electrostatically and/or acoustically. An important advantage of using both kinds of levitation is that if the acoustic field is used to produce rotation, the intensity of this field can be minimized, thereby minimizing disturbances in the drop. It has been conjectured that aerodynamic drag from acoustic streaming in the surrounding air is the physical mechanism through which the acoustic field exerts torque on the drop. The direction and amount of torque can be controlled by horizontal displacement of the acoustic transducer from its nominal central position under the acoustic reflector.
The apparatus allows optical access for observation, diagnosis, and process control. For example, optical diagnoses could be performed by imaging, light-scattering, and spectroscopic techniques. Temperature and humidity can be controlled and purity can be maintained by placing the apparatus in a closed chamber. A focused beam of light from a laser or other radiant source can be used for directional heating of a levitated drop.
This Hybrid Acoustic/Electrostatic Levitation Apparatus provides relatively quiescent levitation under controlled conditions, plus optical access for observation, diagnosis, and process control.
This work was done by Eugene H. Trinh and Sang K. Chung of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com under the Physical Sciences category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to NPO-20165, volume and number of this NASA Tech Briefs issue, and the page number.