Measuring and testing – Vibration – Acoustic levitation
Reexamination Certificate
2003-01-08
2004-07-27
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Acoustic levitation
24, 24
Reexamination Certificate
active
06766691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of droplet or particle cluster formation and in particular to a method of shaping and inducing a density change in a particle cluster by means of a combination of acoustic and optical energy.
2. Description of the Prior Art
The word “particle” in this document shall denote a volume element that contains a single body of material that is in either a liquid or a solid phase. A particle has a mass density and a shape, which is defined by the surface boundary of the material. Two examples of particles are (1) a liquid droplet or (2) a metal crystal. The word “particle cluster” in this document denotes a plurality of particles that are close enough one to another as to influence each other's motion either directly (through collisions) or indirectly (due to interactions with external forces). A particle cluster has an average number density and a shape, which defines the spatial distribution of particles. Two examples of particle clusters are (1) a group of several liquid droplets and (2) a group of several metal crystals.
Acoustic levitation of an object within a chamber has heretofore been accomplished by the use of one or a few acoustic standing wave patterns, wherein the acoustic wavelength was between about one-quarter and twice the length of the chamber. The chamber had to have highly sound reflective walls to provide a Q (a measure of sound reflectance) of at least about fifty. The object remained at a region of low acoustic pressure, because as it drifted in a particular direction, radiation pressure of the standing wave pattern pushed the object back. While harmonics of a fundamental or lowest frequency could be used, these higher harmonics restricted the size of the object. For these acoustic levitators, the object size had to be small compared to the acoustic wavelength, such as no more than about 20% of the wavelength. U.S. Pat. No. 4,573,356 describes the general state of the art of the use of acoustic standing wave patterns to levitate objects and is incorporated by reference.
The prior art use of acoustic standing wave patterns, involved the use of one or only a few transducers which all emitted sound of relatively long wavelengths within a high Q chamber. A large sample requires a very long wavelength and long chamber. It is difficult to produce high intensity sound of long wavelengths and corresponding low frequencies. The force that could be applied to a levitated object was limited by the small number of transducers that could be easily used. Movement and shaping of the object required complicated control or required alteration of the chamber dimensions.
Acoustically levitating an object with acoustic energy from a large number of transducers to avoid the need for a chamber of high Q for simplified control of the position, shape of large objects with respect to the sound wavelength is known in the art. Guigne et al. U.S. Pat. No. 5,500,493 describes such an acoustic levitation apparatus. Acoustic energy is used to position an object, which simplifies the application of forces in defined directions to the object and which allows the application of large forces to the object. The system includes transducers that direct separate acoustic beams at the object with the system constructed so the beams do not create standing wave patterns. A plurality of beams whose phases at the object are not closely controlled, are directed at different surface areas of the object so the beams do not substantially overlap at the object and create possible canceling effects. A very large force is applied to the bottom of an object lying in a gravity environment, by directing a plurality of beams at the same area at the bottom of the object, and with the beams being controlled so they are substantially in phase at the object area. This plurality of beams can also replace one or all of the transducers to provide much stronger forces to position and manipulate the object. The wavelength of the acoustic energy in each beam is preferably much less than one-tenth the diameter of the object in order to obtain efficient momentum transfer of energy to the object. Guigne, however, fails to recognize that such a system can be used for controlling the shape or average number density of particle clusters.
Kaduchak et al U.S. Pat. No. 6,467,350 is also directed to acoustic levitation of particles. However, Kaduchak did not recognize the utility of acoustically shaping the particle cluster for the purpose of rapid prototyping. The standing-wave field produced by an acoustic levitation device is strongly dependent upon the spatial alignment of the system components and often requires moderate to high electrical input power levels to drive the acoustic generators and achieve the desired levitation. This is especially true for levitating solid and liquid samples in air. To achieve the foregoing Kaduchak employed a method for concentrating particles suspended in a fluid including the steps of matching the distance between reflector and radiating element or between two radiating elements, i.e. tuning the resonant levitation cavity, to the acoustic resonance of the interior volume thereof when filled with the fluid; applying periodic electrical excitation to the acoustic radiating element (i.e. a piezoelectric transducer) such that resonant acoustic waves are generated in the interior volume of the levitation cavity, and subjecting the fluid having particles suspended therein to the steady-state force pattern formed by the resonant acoustic waves such that the particles move to the region of the steady-state force pattern and are concentrated.
Kaduchak also disclosed an apparatus for concentrating particles suspended or entrained in a fluid comprising a cylindrical piezoelectric transducer having a hollow interior portion and wherein the breathing-mode acoustic resonance of the cylindrical piezoelectric transducer is matched to the acoustic resonance of the interior portion thereof when the interior portion or levitation cavity is filled with the fluid. A function generator applies periodic electrical excitation to the surface of the cylindrical piezoelectric transducer such that resonant acoustic waves in are generated in the hollow interior portion of the cylindrical piezoelectric transducer. A means is provided for introducing the fluid having particles suspended or entrained therein into the region of the equilibrium force pattern formed by the resonant acoustic waves such that the particles move to the region of the equilibrium force pattern and are concentrated.
Photopolymers are well known in the art and have been used for the construction of various devices. For example extensive use of photopolymers has been made in printing. In flexographic printing as one example, also known as relief printing, ink is transferred from a pool of ink to a substrate by way of a printing plate. The surface of the plate is shaped so that the image to be printed appears in relief, in the same way that rubber stamps are cut so as to have the printed image appear in relief on the surface of the rubber. Typically, the plate is mounted on a cylinder, and the cylinder rotates at high speed such that the raised surface of the printing plate contacts a pool of ink, is slightly wetted by the ink, then exits the ink pool and contacts a substrate web, thereby transferring ink from the raised surface of the plate to the substrate to form a printed substrate.
Photopolymerizable resin compositions generally comprise an elastomeric binder, herein sometimes referred to as a prepolymer or an oligomer, at least one monomer and a photoinitiator. To prepare the plates, there is generally formed a photopolymerizable layer interposed between a support and one or more cover sheets that may include slip and release films to protect the photosensitive surface. Prior to processing the plate, the cover sheets may be removed, and the photosensitive surface is exposed to actinic radiation in an imagewise fashion. Upon imagewise exposure to actinic radi
Culick Fred E. C.
Venturelli Philip A.
California Institute of Technology
Dawes Daniel L.
Miller Rose M.
Myers Dawes Andras & Sherman LLP
Williams Hezron
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