Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-07-14
2002-04-02
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S462000, C310S309000, C216S017000, C216S066000, C216S101000
Reexamination Certificate
active
06363712
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to microtechnology and the fabrication process for developing micromechanical and microelectrical systems such as micro-actuated elements, microengines, or micromachines. More particularly, the present invention is directed to a means of fabricating a gas-driven microturbine that is capable of providing autonomous propulsion in which the rapidly moving gases are directed through a micromachined turbine to power mechanical, electrical, or electromechanical devices by direct mechanical linkage of turbo-electric generator components in a domain ranging from tenths of micrometers to thousands of micrometers. By optimally selecting monopropellants or bipropellants to be the fuel set, a more efficient gas-driven microturbine can be realized from the increased mass flow rate of the gas stream due to the higher combustion reaction energies of these fuel sets. Additionally, compressed gas can be utilized to provide a high-flow gas stream for the gas-driven microturbine. The present invention is adaptable to many defense and non-defense applications, including the provision of mechanical power for miniature devices such as fans, geared mechanisms, mechanical linkages, actuators, biomedical procedures, manufacturing, industrial, aviation, computers, safety systems, and electrical generators.
BACKGROUND OF THE INVENTION
In the last decade, great interest has developed in the emerging field of microtechnology. Microminiature machines (micromachines) represent an emerging technology with significant national and international interest. Generally, these micromachines comprise the larger class of components usually referred to as microelectromechanical systems (MEMS) that are fabricated using now-standard semiconductor manufacturing techniques. The systems are integrated microdevices combining electrical and mechanical components fabricated using integrated-circuit-compatible batch-processing techniques and range in size from micrometers to millimeters. The inherent motivation for developing MEMS is the ability to perform specialized applications through smaller, faster, lighter, and more accurate micromechanical devices. These systems can control, sense, and actuate on the microscale and function individually or in arrays to generate effects on the macroscale.
The area of micromechanics deals with actuators and sensors which are on the order of micrometers. This ability results in applications which take advantage of potentially high packing densities for simple microdevices which, when combined in a system, can perform complex and precise mechanical and electrical functions. Another important aspect is found in micropositioning applications since these microdevices can be moved by small distances which can be measured or monitored accurately. Micromechanical devices are significant because they can have small moments of inertia, but they are currently limited in their abilities to generate adequate output forces and torques for specialized applications. However, the result of extensive research in micromechanics and advances in polysilicon surface-micromachining have led to the development of microscopic motors of considerably low-mass, incorporating mechanisms on silicon wafers for -a number of technological applications such as micro-sensors to detect or measure changes in pressure, acceleration, temperature, vapor, or sound. Micromechanical technology can be incorporated into automobiles to diagnose and sense engine-performance or into applications involving the deployment of air bags or into sensors that can detect air pressure in tires.
One of the earliest devices fabricated from the surface-micromachining process was a device called the resonant gate resistor. This device was disclosed in an article written by Nathanson, et al., entitled, “The Resonant Gate Resistor,” IEEE, Trans. Electron Devices, Vol. ED-14, pp. 117-133, March 1967. The device consisted of a transistor with a free-standing metal cantilever beam serving as the transistor gate. Subsequent work in this area led to the development of a polysilicon surface-micromachining technique described in an article by Howe, et al., entitled, “Polycrystalline Silicon Micromechanical Beams,” J. Electrochem. Soc.: Solid-State Science and Technology, Vol. 103, No. 6, pp. 1420-1423, June 1983.
Working with methods of producing microelectric circuitry but optimized for producing micromechanical devices, the polysilicon surface-micromachining process generally involves etching a pattern in films supported by a silicon substrate by exposing the polysilicon through a photoresist mask. By selectively etching sacrificial layers from a multilayer sandwich of patterned polysilicon films and interleaved sacrificial oxide films and through material deposition and selective removal of these various film layers, highly specialized and unique components can be structurally fabricated. The basic process involves fabricating a single layer of mechanical polysilicon to form simple micromechanical devices. However, with just one layer of polysilicon, the mechanical structures have restricted movement through elastic members attached to the substrate and provide limited mechanical movement. Therefore, the need to fabricate more sophisticated and specialized structures necessitates the deposition of multiple layers of polysilicon to form complex mechanical structures such as sliders and self-restraining pin joints. With two layers of polysilicon deposition, it is possible to fabricate rotating entities, but the ability to harness the rotary motion produced from a gear or turbine is limited; that is, there needs to be a means to fully couple the energy produced from mechanical devices formed from a two-layer polysilicon deposition. To address this problem, a third layer of poly silicon deposition would allow a gear or turbine formed from a two-layer polysilicon deposition to be interconnected by a mechanical linkage for direct actuation of ancillary components. A discussion of the polysilicon surface-micromachining batch-fabrication process is discussed in greater detail in the articles given by J. J. Sniegowski, et al., “Microfabricated Actuators and Their Application to Optics,” Proc. SPIE Miniaturized Systems with Micro-Optics and Micromachines, 2383, San Jose, Calif. 1995, pp. 46-64; and E. J. Garcia, et al., “Surface Micromachines Microengine,” Sensors and Actuators A, 48 (1995), pp. 203-214.
The small sizes of the micromotors and recent advances in polysiliconsurface-micromachining combine to exhibit unique and novel electromechanical characteristics that are vastly different from conventional motors. Electrostatic forces in the microdomain are found to scale more favorably than the magnetic alternatives for devices designed to micro-dimensions and the use of micro-size field-generating structures enables more intense electrostatic fields to be created. Conventional motors are typically magnetically driven but he windings and magnetizable material to make such motors make it nearly impossible to duplicate or produce on the silicon chips in the microdomain due to the inherent size limitations.
U.S. Pat. No. 5,262,695 (Kuwano et al.) discloses two possible drive systems (wired and wireless) for a micromachine. A wired system has the energy source located outside the micromachine unit. This setup allows for the ability to produce smaller machines with the drive energy supplied through a feed cable. However, the cable imposes movement and control limitations on the operation of the machine. In the case of the wireless system, machine movement is less restricted since the energy source is generally mounted on the machine but this setup increases the size and weight of the entire micromachine and impairs the contemplated function(s) of the micromachine. Kuwano proposes an electrostatic motor for use as a mechanical power generating mechanism to be mounted on a micromachine that includes a rotatable semiconductor substrate and a drive electrode disposed in proximity to the substrate. Kuwano&apo
Aeschliman Daniel P.
McWhorter Paul J.
Miller William M.
Rodgers Murray S.
Sniegowski Jeffrey J.
Caress Virginia B.
Durkis James C.
Freay Charles G.
Gartenberg Ehud
Kehl Dickson G.
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