Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-06-19
2001-07-17
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S330000, C310S332000
Reexamination Certificate
active
06262519
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of fluid flow control. More particularly, the invention concerns fluid flow in a microfluidic process, such as an ink jet printer and the like, that requires high reliability and accurate fluid flow control.
BACKGROUND OF THE INVENTION
Piezoelectric pumping mechanisms are used in a wide range of microfluidic applications ranging from the controlled metering and flow of intravenous solutions in biomedical environments to ink jet printing apparatus. Conventional piezoelectric pumps utilize piezoelectric transducers that comprise one or more uniformly polarized piezoelectric elements with attached surface electrodes. The three most common transducer configurations are multilayer ceramic, monomorph or bimorphs, and flextensional composite transducers. To activate a transducer, a voltage is applied across its electrodes thereby creating an electric field throughout the piezoelectric elements. This field induces a change in the geometry of the piezoelectric elements resulting in elongation, contraction, shear or combinations thereof. The induced geometric distortion of the elements can be used to implement motion or perform work. In particular, piezoelectric bimorph transducers, which produces a bending motion, are commonly used in micropumping devices. However, a drawback of the conventional piezoelectric bimorph transducers is that two bonded piezoelectric elements are needed to implement the bending. These bimorph transducers are difficult and costly to manufacture for micropumping applications (in this application, the word micro means that the dimensions of the apparatus range from 100 microns to 10 mm). Also, when multiple bonded elements are used, stress induced in the elements due to their constrained motion can damage or fracture an element due to abrupt changes in material properties and strain at material interfaces.
Therefore, a need persists for a piezoelectric pumping apparatus that utilizes a functionally gradient piezoelectric transducer that overcomes the aforementioned problems associated with conventional pumping apparatus.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method of controlling fluid flow in a microfluidic process which includes a piezoelectric pump that utilizes a functionally gradient transducer in which the pumping action is accomplished with a single functionally gradient piezoelectric element.
It is a feature of the method of the invention that a functionally gradient piezoelectric transducer in fluid communications with the microfluidic process expands to expel fluid from the microfluidic process and contracts to cause fluid to enter the microfluidic process.
To accomplish these and other objects of the invention, there is provided, in one aspect of the invention, a method of controlling fluid flow in a microfluidic process comprising the step of providing a piezoelectric pump in fluid communications with the microfluidic process. The piezoelectric pump comprises a pump body having a fluid containment chamber and inlet and outlet ports in fluid communication with the fluid containment chamber. The inlet and outlet ports have, respectively, a first valve and a second valve for controlling fluids passing therethrough and through the microfluidic process. A piezoelectric transducer is arranged in the pump body.
The piezoelectric transducer includes a functionally gradient piezoelectric element having first and second surfaces and is formed of piezoelectric material having a functionally gradient d-coefficient selected so that the functionally gradient piezoelectric element changes geometry in response to an applied voltage. When the voltage is applied, an electric field is produced in the functionally gradient piezoelectric element. More particularly, first and second electrodes respectively disposed over the first and second surfaces of the functionally gradient piezoelectric element are arranged so that voltage applied to the first and second electrodes induces the electric field in the functionally gradient piezoelectric element.
A source of power having first and second terminals connected to the first and second electrodes, respectively, of the piezoelectric transducer enables fluid flow through the fluid containment chamber which is in fluid communications with the microfluidic process. Thus, on the one hand, when the piezoelectric transducer is energized to pump fluid out of the fluid containment chamber and thus into the microfluidic process, the source of power provides a positive voltage to the first terminal and a negative voltage to the second terminal. On the other hand, when the piezoelectric transducer is energized to pump fluid into the fluid containment chamber, and thus out of the microfluidic process, the source of power provides a negative voltage to the first terminal and a positive voltage to the second terminal.
Accordingly, the method of piezoelectric pumping apparatus of the invention has numerous advantages over prior art developments, including: it enables the use of a single functionally gradient piezoelectric element to implement a desired geometric distortion thereby eliminating the need for multilayered or composite piezoelectric structures; it eliminates the need for multiple electrodes and associated drive electronics; and it minimizes or eliminates stress induced fracturing that occurs in multilayered or composite piezoelectric structures.
REFERENCES:
patent: 2928409 (1960-03-01), Johnson et al.
patent: 4356424 (1982-10-01), Marcus
patent: 4375042 (1983-02-01), Marcus
patent: 4939405 (1990-07-01), Okuyama et al.
patent: 5589725 (1996-12-01), Haertling
Chatterjee Dilip K.
Furlani Edward P.
Ghosh Syamal K.
Bailey, Sr. Clyde E.
Budd Mark O.
Eastman Kodak Company
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