Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-02-11
2001-07-17
Sircus, Brian (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06262517
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application contains subject matter related to U.S. Pat. No. 5,340,510, issued Aug. 23, 1994 to Leslie J. Bowen and incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to piezoelectric sensors, and particularly relates to piezocomposite acoustic sensors having a so-called 1-3 or 2-2 connectivity.
Typical 1-3 and 2-2 type piezocomposite acoustic devices are described in above-reference U.S. Pat. No. 5,340,510. In the 1-3 device, a one-dimensionally connected ceramic phase, i.e., an array of parallel rods, fibers, or other one-dimensionally extending fine ceramic elements is contained within a three-dimensionally connected polymer matrix. In the 2-2 device, a two-dimensionally connected ceramic phase, i.e., an array of parallel blades or plates is laminated with layers of a two-dimensionally connected polymer matrix. In either type of device, the ends of the elements are exposed at opposing planar surfaces of the ceramic/polymer composite. Typically, the electrodes are applied to these opposing planar surfaces. The ceramic phase is poled along the length (d
33
) direction of the ceramic elements, i.e., between the opposing, electroded, planar surfaces. To optimize the sensitivity of the devices, it is necessary to decouple the piezoelectric d
33
and d
31
coefficients, i.e., to minimize the effect of the acoustic vibration on the sides of the rods or blades.
In the field of piezocomposite sensors, it is well known that the sensitivity of the sensor is often highly dependent on the ambient pressure surrounding the sensor. This is particularly apparent at high pressures of up to 10,000 psi (about 70 MPa) or higher, e.g., in deep underwater hydrophone applications. Such high pressure applications have created a trade-off between sensitivity, on the one hand, and stability and robustness, on the other, of prior art devices. Increasing the pressure on the devices has resulted in a loss of sensitivity and, frequently, damage to the devices. Increasing the stability of the device, to decrease damage due to ambient pressure, has also decreased the sensitivity of the prior art devices. Additionally, minimization or optimization of the size and weight of the devices for certain applications must be balanced against the need for robustness in the devices.
Accordingly, it is an object of the present invention to provide a piezoelectric acoustic sensor which overcomes the disadvantages of the prior art.
It is another object of the invention to provide a piezoelectric acoustic sensor with high sensitivity and high robustness.
SUMMARY OF THE INVENTION
In accordance with these objects, the invention is a piezoelectric acoustic sensor including an array of parallel rod-like or blade-shaped ceramic elements encapsulated in a polymeric matrix to form a two-phase ceramic/polymer composite body exhibiting 1-3 or 2-2 connectivity. The ceramic elements are formed from a dense, poled, strongly piezoelectric or electrostrictive ceramic material. The composite body has upper and lower planar surfaces and at least four edge surfaces, upper and lower ends of the elements being exposed at the planar surfaces. Upper and lower electrodes at the upper and lower planar surfaces, respectively, have electrical contact with upper and lower ends of the elements, respectively, forming a composite body having upper and lower planar electroded surfaces. The electroded composite body includes a stiff portion, e.g., a cover plate, which may or may not provide one of the electrodes, extending across each of its upper and lower electroded surfaces, each of the stiff portions extends to the edge surfaces of the electroded composite body.
A stress-transferring arch, having a convex shape, is rigidly anchored to at least one edge of each stiff portion. A hinge portion of the arch, at the stiff portion edge, has a thickness of 0-10 mm. The arch is formed of a material having a stiffness of at least Shore D 80. The arch is shaped and disposed to direct ambient lateral stress toward the stiff portions, decoupling the ceramic elements from the ambient lateral stress and forming a stress resistant piezoelectric acoustic sensor. In a narrower embodiment, the strongly piezoelectric or electrostrictive ceramic material is a lead zirconate titanate or a derivative thereof.
REFERENCES:
patent: 4420826 (1983-12-01), Marshall, Jr. et al.
patent: 4845687 (1989-07-01), Bromfield
patent: 5030873 (1991-07-01), Owen
patent: 5030874 (1991-07-01), Saito et al.
patent: 5340510 (1994-08-01), Bowen
patent: 5363346 (1994-11-01), Maltby
patent: 5691960 (1997-11-01), Gentilman et al.
patent: 5796207 (1998-08-01), Safari et al.
patent: 6051910 (2000-04-01), Kaida et al.
Bowen Leslie J.
Schmidt Gerald E.
Materials Systems Inc.
Pearson & Pearson LLP
Sircus Brian
Zarroli Michael C.
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