Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-03-18
2001-01-16
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06175182
ABSTRACT:
BACKGROUND
Shear mode actuators made from ceramic piezoelectric materials such as lead zirconate titanate-based ceramics (PZT) are not widely used in industry or defense applications. This is because there is no simple and effective strain amplifying mechanism associated with these ceramic piezoelectric materials. The shear piezoelectric constant d
15
is larger than the linear constants d
31
and d
33
for materials such as PZT. A high electric (E) field applied to the ceramic piezoelectric material is required for strain generation. The E field for strain generation is on the order of 1 Kilovolt per centimeter for PZT material thickness. It is desirable to decrease the voltage required for the high E field, while increasing the shear angle of the ceramic material used. Currently, increasing length and decreasing thickness for a given volume of PZT material allows for reduction of the required voltage to drive the E field needed for strain generation. It also allows for the generation of a large shear generalized displacement for any given voltage. But, increasing length and decreasing thickness of the PZT actuator produces sizing problems and decreases actuator force otherwise available. These problems are compounded by the shear elastic stiffness C
44
which controls the blocking force being significantly lower than the linear constant C
11
.
It is an object of the present invention to provide a PZT actuator which generates large shear angles at low applied voltages, maintains a compact size and can be used in both linear and shear mode applications.
SUMMARY OF THE INVENTION
The present invention is pseudo-shear mode actuator and a method of making such an actuator. The actuator is made of at least two layers of ceramic material. The layers having a first end, a second end and a thickness that is less than length or width of the layer. There is a bond which bonds the first ends of the layers together and a spacer between the layers. The spacer runs from the bond to the second ends of the layers. The layers are poled in the same direction. The bond is conductive and one of the ends of the layers is connected to a positive electric current and the other end of the layers is connected to a negative electric current. When there is more than two layers, the bond placement and spacer placement alternate between the first and second ends as layers are added. The bonds which alternatively bond the first ends are connected to a positive electric charge and the bonds which alternatively bond the second ends are connected to a negative electric charge. The bond can be an epoxy bond. The spacer can be a polymer, grease or teflon. The layers are a ceramic piezoelectric material.
REFERENCES:
patent: 4978881 (1990-12-01), Wakita et al.
patent: 5175465 (1992-12-01), Um et al.
patent: 5245734 (1993-09-01), Issartel
patent: 5440194 (1995-08-01), Beurrier
Berlincourt, D. A., “Piezoelectric Properties of Poycrystalline Lead Titante Zirconate Compositions,” Proceedings of the IRE, IRE, pp. 220-229, (Feb. 1, 1960).
Clevit Corp., “Piezoelectric Technology Data for Designers, ” Clevite Corp. (Ohio), pp. 1-45, (Feb. 1, 1965).
Aokagi, M., “Trial Production of an Ultrasonic Motor Using Longitudinal and Torsional Vibrations of a Rod Vibrator Drive by Piezoelectric Plates Inserted in it Axial Direction,”Japan J. Appl. Phys., pp. 6106-6109, (Sep. 1, 1997).
Bauer, A., “Piezo Actuator Special Design, ” Fraunhofer Inst. (Jena, Germany), pp. 128-132, (Feb. 1, 1994).
Glazounov, A.E., “Piezoelectric Actuator Generating Torsional Displacement from Piezoelectric d15 Shear Response,”Applied Physics Letters, American Institute of Physics, vol. 72 (No. 20), pp. 2526-2528, (Feb. 1, 1998).
Chirvella Jose
Cross L. Eric
Wang Qing-Ming
Budd Mark O.
Monahan Thomas J.
Penn State Research Foundation
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