Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1997-01-06
2004-04-13
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C417S474000
Reexamination Certificate
active
06720710
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to micro sized pumps which transport chemicals on micro sized devices for chemical analysis on such devices and to micro sized chemical analysis systems utilizing such pumps. Typically, the pumps are formed on silicon chips.
BACKGROUND OF THE INVENTION
Advances in micromachining techniques have enabled the mass production of miniature and microscopic electromechanical components that perform a variety of functions. These components fall generally into two categories: sensors and actuators. Sensors can be made to monitor measurands such as pressure, acceleration, chemical-vapor concentrations, light intensity and magnetic fields. Actuators include pumps and valves for fluid manipulation, heated chambers to induce chemical reactions, moveable mirrors for optical displays and relay switches for high-frequency communications.
In addition to direct miniaturization and mass production, a feature of micromachining is that it enables the implementation of new types of technologies. With miniaturization, physical laws of scaling inherently favor certain technologies and phenomena over others. In some cases, technologies that can be made by micromachining work well on the microscopic scale but have no analogy or usefulness in the macroscopic domain (e.g., the electrostatic micromotor).
The ultimate power of microfabrication lies in the ability to integrate multiple components into complex microelectromechanical systems (MEMS) that have high functionality and performance, yet are small, easy to use and to produce, and inexpensive. An example of a complex microelectromechanical system is the digital micromirror display marketed by Texas Instruments, based on an array of a plurality of individually-addressable micromirrors.
One of the attributes of these systems is that they can be made fully self-contained and can be operated remotely without direct user intervention for sample handling or other tasks. Operation can be controlled with a combination of electronic hardware and software. The necessary drive electronics can be included on or off chip. In this way the ease of operation of these potentially powerful microinstruments is much simpler than most conventional analytical instruments, and more comparable to individual sensors.
In the area of instrumentation, microfabrication, micromachining, holds much promise for making small low-cost, fast-operating, portable, easy-to-operate systems for chemical analysis, clinical diagnostics and other applications. These microinstruments will rely on the integration of fluid-handling components.
Interest in microinstruments has been spurred by the need for improved chemical and biological analysis techniques in applications such as environmental remediation, chemical-warfare-agent detection and clinical diagnostics. For example, the DOE estimates that the superfund cleanup will require tens of millions of soil samples to be analyzed each year. The cost and manpower devoted to sample collection and analysis is exorbitant, and could be greatly reduced by using inexpensive, in-situ analyzers. However, the technology to make such analyzers is not available presently: existing sensors are very limited in their capabilities, and so-called portable analytical instruments are expensive and complicated to use.
Micromachining techniques of the nature disclosed in the present document allow the provision of analytical-instrument performance in microinstruments that are comparable in size, cost and ease-of-use to individual sensors. These same techniques can also be used to make disposable medical instruments such as DNA-based diagnostic tests, and miniature scientific instruments based on a number of technologies such as gas and liquid chromatography, electrophoresis, and flow-injection analysis. Several of these analysis techniques can be combined into a single chip to create very sophisticated systems that separate and analyze tiny samples without human intervention.
Essential for these microinstruments are suitable pump technologies to transport samples and reagents on the microscale. Many types of micromachined pumps have been developed recently. Most of these are discrete pumps, meaning that they operate by creating a pressure differential that drives fluids through the system in which they are functioning. The most common are silicon-based diaphragm pumps, which rely on electrostatic or thermo-pneumatic actuation to deflect a membrane that displaces fluid through one of two integrated check valves. Higher pump rates and higher pumping pressures have been achieved by actuating micromachined diaphragms with off-chip piezoelectric elements. These types of pumps are useful but have limitations. They are complicated to fabricate, subject to clogging, and pressure is generally limited by valve leakage. Discrete pump technologies also do not work well for moving fluids through microtunnels, i.e., through enclosed tunnels with cross-sectional dimensions of less than about 500 microns. This is because the pressure required to maintain a given flow rate increases extremely rapidly as the cross-sectional area of the tunnel is reduced.
Recently there has been much development of electroosmotic and electrophoretic pumps for liquid-based microinstruments. Electroosmosis is the movement of a liquid, under an applied electric field, in a fine tube or membrane. Electrophoresis is the movement of charged particles under an electric field in a liquid or gel. Electroosmosis and electrophoresis are very useful pumping mechanisms for liquid-based microinstruments. However, they do not work with gases, and are sensitive to the properties of the liquid such as conductivity and pH. Electroosmosis is also sensitive to the surface properties of the tunnel.
U.S. Pat. No. 5,006,749 to R. M. White describes methods for making an ultrasonic micromotor to move solids and briefly mentions the possibility of moving liquid droplets or streams. The method of this patent does not, however, describe a useful pump structure for moving fluids along an enclosed flow path, distributed pumping or chemical analysis instruments.
There is also recent work on fluid transport by acoustic streaming on a microscale. Acoustic streaming is steady fluid flow or pressure induced by high-intensity sound. It was first described by Faraday in 1831 and addressed theoretically by Rayleigh in 1884. Acoustic streaming fluid velocities are generally proportional to the square of the (mechanical) displacement of the driving source, and to the square of the acoustic displacement and velocity fields in the fluid. Acoustic streaming has been observed in fluids contacting vibrating cylinders, spheres, and plates.
Recently, steady-state pumping and localized stirring have been demonstrated with a micromachined flexural-plate-wave delay line. Pumping velocities as high as 30 mm/sec in air and 0.3 mm/sec in water have been observed.
The present inventors have shown as disclosed herein that a related structure can produce air flow rates of over 18 mm/sec in an enclosed tunnel 50 micrometers high, 500 micrometers wide and 8 mm long.
Acoustic streaming has also been generated with surface acoustic wave (SAWs). Shiokawa et al. have shown that water droplets can be ejected from the surface of a lithium niobate SAW delay line. This work does not, however, discuss structures that can move fluids in enclosed tunnels or in microsystems, or by distributed pumping.
Neither the White nor the Shiokawa et al. works describes a useful pump structure for moving fluids along an enclosed flow path, distributed pumping, or use with chemical-analysis instruments. Additionally, the flexural-wave structure has inherent limitations that prevent their use in forming a flexural-plate-wave pump or delay line from an enclosed narrow channel, that is, a channel with width less than about a wavelength. This is because in these configurations flexural-plate waves are generated via bimorph actuation using transducers that are uniform across the plate width. A composite plate is formed by laminating an actu
Costello Benedict J.
Wenzel Stuart W.
Berkeley Microinstruments, Inc.
Dougherty Thomas M.
Fliesler Dubb Meyer & Lovejoy LLP
LandOfFree
Micropump does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Micropump, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micropump will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3217561