Thermolysis reaction actuating pump

Details Thermolysis reaction actuating pump Thermolysis reaction actuating pump

2001-12-31

2003-07-29

Freay, Charles G. (Department: 3746)

Pumps

By heating of pumped fluid

C417S053000, C417S118000, C417S065000, C222S146100

Reexamination Certificate

active

06599098

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a microelectromechanical system, and more particularly, to microelectromechanical system having a thermolysis reaction actuating pump.
BACKGROUND OF THE INVENTION
Microelectromechanical systems, often referred to as MEMs, typically are miniature embedded systems including one or many micro-machined components or structures. They often enable higher level functions, although in and of themselves their utility may be limited. For example, a micro-machine pressure sensor is typically useless by itself, but under the hood of a vehicle, such a pressure sensor can be used to control the fuel air mixture of the engine. MEMs often integrate smaller functions into one package for greater utility. For example, MEMs may be used in an acceleration sensor with an electronic circuit for self diagnostics. MEMs can also provide a cost benefit, directly through lower unit pricing, or indirectly by cutting service and maintenance costs.
Micro-mechanical structures, components and systems are miniature devices that enabled operation of complex systems. MEMs currently have a variety of applications including automotive, medical, consumer, industrial and aerospace. MEMs technology includes a variety of design and fabrication processes, many having their foundation in the semiconductor or integrated circuit industry.
Many microelectromechanical systems utilize sensing and actuation techniques. One of the objectives of sensing devices is to transduce a specific physical parameter into electrical energy. An intermediate conversion step may be required. For example, a pressure or acceleration is converted into mechanical stress, which is then converted into electricity. Temperature measurements use the dependency of various material properties on temperature is a common sensing technique. The characteristic is pronounced in the electrical resistance of metals wherein the temperature coefficient of resistance of most metals ranges between 10 and 100 ppm per ° C.
Two other common sensing techniques utilize piezoresistivity and piezoelectricity. Doped silicon exhibits piezoresistive behavior and can be utilized for many pressure and acceleration sensor designs. Measuring the change in resistance and amplifying the corresponding output signal is a technique well known to those skilled in the art. However, silicon piezoresistivity is dependent on temperature that must be compensated for with external electronics.
Capacitive sensing utilizes an external physical parameter that changes either the spacing or the relative dielectric constant between two plates of a capacitor. For example, an applied acceleration moves one of the plates closer to the other. For relative humidity sensors, the dielectric is an organic material whose permittivity is a function of the moisture content. Capacitive sensors provide the advantage of requiring very low-power and are relatively stable with temperature. Further, capacitive sensors can be utilized with electrostatic actuation to provide closed loop feedback.
Another sensing techniques utilizes electromagnetic signals to measure a physical parameter. Magnetoresistive sensors are utilized on the read heads of high-density computer disk drives to measure the change in conductivity of the material slab in response to the magnetic field of the storage bit. Another form of electromagnetic transducing uses Faraday's law to detect motion of a current carrying conductor through a magnetic field.
Once the particular parameter has been sensed and determined to be above a predetermined threshold, it is common for microelectromechanical systems to perform a specific task in response to the sensed parameter. Such a task is typically accomplished by any of a variety of common actuation methods. Typical actuation microelectromechanical systems include electrostatic, piezoelectric, thermal, magnetic, and phase recovery using shaped-memory alloys.
Electrostatic actuation relies on the attractive forces between two plates or elements carrying opposite charges. Two objects with an externally applied potential between them have opposite polarities. Therefore an applied voltage always results in an attractive electrostatic force. Electrostatic actuation can be naturally extended to closed-loop feedback. When sensing circuits detect that two plates of a capacitor are being separated under the effect of an external force (such as acceleration), an electrostatic feedback voltage is immediately applied by the controlled electronics to counteract the disturbance and maintain a fixed capacitance. The magnitude of the feedback voltage then becomes a measure of the disturbing force. This closed loop operation is used in many accelerometers and yaw rate sensors.
Piezoelectric actuation can provide significantly large forces particularly when thick piezoelectric films are utilized. Commercially available piezoceramic cylinders can provide up to a few newtons of force with applied potentials of a few hundred volts. However, thin film piezoelectric actuators can only provide a few millinewtons of force. Both piezoelectric and electrostatic methods offer the advantage of low power consumption because the electric current is very small. Thermal actuation typically requires more power than electrostatic or piezoelectric actuation but can provide actuation forces on the order of hundreds of millinewtons or higher.
There are at least three known approaches to utilizing thermal actuation. The first approach takes advantage of the difference in the coefficient of thermal expansion between two joined layers of the similar materials to cause bending with temperature. One layer expands more than the other as the temperature increases. This results in stress at the interface and consequent bending of the stacked layers. The amount of bending depends on the difference in the coefficient of thermal expansion of the layers in the absolute temperature.
A second approach known as thermopneumatic actuation heats a liquid inside of a sealed cavity. Pressure from expansion or evaporation exerts a force on the cavity walls. The method also depends on the absolute temperature of the actuator.
A third method utilizes the suspension of the beam of the same homogeneous material with one end anchored to a supporting frame of the same material. Heating the beam to the temperature above that of the frame causes a differential expansion of the beam's free end with respect to the frame. Holding the free end stationery gives rise to force proportional to the beam's length and the temperature differential. Such an actuator delivers a maximum force with zero displacement and no force when the displacement is maximal. Designs between these two extremes can provide both force and displacement. Typically a system of mechanical linkages can optimize the output of the actuator by trading off forces for displacement or vice versa. In this system the actuation is independent of fluctuations in ambient temperatures because it relies on the differences in the temperature between the beam and the supporting frame.
Electrical current in a conductive element that is located within a magnetic field produces an electromagnetic force in a direction perpendicular to the current and magnetic field. This force is proportional to the current, magnetic field, and the length of the element. These characteristics are utilized in magnetic actuation devices.
Shape-memory alloys provide the highest energy density available for actuation. The shape-memory alloys are a special class of alloys that return to a predetermined shape when heated above a critical transition temperature. The material remembers its original shape after being strained and deformed. When the alloy is below its transition temperature it has a low yield strength and is readily deformed into new permanent shapes. The deformation can be 20 times larger than the elastic deformation with no permanent strain. When heated above its transition temperature, the alloy completely recovers to its original shape through complex changes in i

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