Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-08-02
2001-08-07
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S800000
Reexamination Certificate
active
06271621
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a pressure sensor using a piezoelectric composite. Two types of sensors are disclosed herein.
BACKGROUND OF THE INVENTION
Piezoelectric pressure sensors have many applications such as underwater hydrophones, strain sensors and vibration sensors. Many types of piezoelectric sensors have been proposed regarding different piezoelectric materials, methods of construction and various other features.
For example, piezoelectric cables are disclosed in U.S. Pat. Nos. 4,278,000, 4,568,851 and 4,849,946. As the typical inner conductor, there are disclosed a single metal wire, a small twisted steel wire of about 0.3 mm in diameter and a conductive polymer layer. Since flexibility is very significant in the piezoelectric cable, piezoelectric polymers and piezoelectric composites are used as the piezoelectric material. As the typical piezoelectric polymer, polymers such as polyvinylidene fluoride(PVDF), polyvinyl difluoride/tri-fluoride ethylene copolymer (VDF/TrFE) and the like are disclosed. As the typical piezoelectric composite, composites such as silicone rubber, chloroprene rubber, urethane rubber and the like containing piezoelectric ceramic powders such as lead titanate (PbTiO3), solid solution of lead titanate-lead zyrconate (PbTiO3—PbZrO3) and the like are disclosed. As the outer conductor, there are disclosed a vacuum deposited metal film, a coated film of a conductive paste, a metal foil, a conductive rubber or polymer layer and others. As the protective jacket, polyethylene or polyvinyl chloride are known to be used.
The piezoelectric composites described above are often required to be cured to increase the physical strength and thermal stability. For example, a composite comprising chloroprene rubber and lead titanate is cured at 170° C. under a pressure of 150 kg/cm
2
after they are mixed, as reported in “Huntai to Kogyo” Vol. 22, No. 1, p. 53-54 , 1990. Other composites are also cured, as reported in 1984 Ultrasonic Symposium, p. 504 and “Ferroelectronics”, Vol. 77, p. 39 , 1988. Since curing requires a particular apparatus and process, the composite is preferably produced without curing.
The conventional piezoelectric polymers and composites described above are thermally stable at a temperature less than 70-100° C. However, when the coaxial cables are applied in temperature applications above 100° C., for example in a electrical heating blanket, a temperature near a heating wire increases to about 120° C. at maximum. In this case, high thermal stability is required at 120° C.
Vacuum deposited or coated films are one of the most suitable outer conductors because of their low mechanical impedance. However, when producing these films, an expensive apparatus and complicated processes are required. For example, when a vacuum deposited metal film is produced, there are required a vacuum depositing apparatus equipped with an evacuating system, an evaporating system and other necessary apparatuses. Moreover, many processes are required such as valve operations and deposition operations to deposit the metal film around the circumferential surface of the piezoelectric layer under suitable conditions such as cleaning the surface of the piezoelectric layer, deposition rate control, deposition temperature control, film thickness control and others. When a coated film is used, there are also required an expensive coating apparatus and several complicated processes. When a thin metal foil is used as the outer conductor, an expensive apparatus and complicated processes are not required. However, the metal foil is problematic because it is often difficult to firmly wind the metal foil around the circumferential surface of the piezoelectric layer because of the weak physical strength of the metal foil. For example, a thinner aluminum foil less than 15 &mgr;m in thickness is easily broken by hand. The conductive rubber or polymer layers are advantageous because these layers can be produced by the same extruding process as the piezoelectric and protective layers. However, when the rubber or polymer layers are used as the outer conductor, an expensive extruding apparatus and complicated processes are required.
On the other hand, many planar pressure sensors have also been developed. As the piezoelectric material, piezoelectric ceramics such as lead titanate (PbTiO3), solid solution of lead titanate-lead zyrconate (PbTiO3—PbZrO3) and the like are also used together with piezoelectric polymers and piezoelectric composites described above, as shown in “Piezoelectric Ceramic” (Bernard Jaffe, William R. Cook Jr. and Hans Jaffe, Academic Press, 1971, p. 262). Metal films such as gold, palladium and platinum have been fired or evaporated on the piezoelectric ceramics as the conductor. However, the piezoelectric ceramics cannot be applied to a curved surface because of their brittle property.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a piezoelectric composite with high thermal stability, which can be produced without curing.
Another object of the present invention is to provide a conductor, which can be used both as a outer conductor in a piezoelectric cable and as a conductor in a planar pressure sensor.
Still another object of the present invention is to provide a cable, which can detect not only pressure but also temperature.
The present invention discloses two kinds of pressure sensors using a piezoelectric composite comprising amorphous chlorinated polyethylene, crystalline chlorinated polyethylene and piezoelectric ceramic powder. The first type is a piezoelectric cable comprising an inner conductor of a metal helix. The volume within the metal helix is filled with insulating fine polymer fibers. A piezoelectric composite layer circumferentially surrounds the inner conductor; an outer conductor of a metal film is attached on a polymer membrane. The metal film contacting the composite layer is separate from the inner conductor and a protective jacket of an insulating and elastic material surrounding the outer conductor. The second type is a planar sensor comprising a piezoelectric composite in a planar form sandwiched with conductors of two metal films attached on polymer membranes. Each metal film contacting the composite is separated from each other.
When temperature is also required to be detected along with pressure by the piezoelectric cable, the present invention provides a cable which can detect both pressure and temperature, where a temperature is detected from a temperature dependence of resistance of the metal helix of the inner conductor.
REFERENCES:
patent: 4128489 (1978-12-01), Seo
patent: 4191193 (1980-03-01), Seo
patent: 4278000 (1981-07-01), Saito et al.
patent: 4369391 (1983-01-01), Micheron
patent: 4443730 (1984-04-01), Kitamura et al.
patent: 4568851 (1986-02-01), Soni et al.
patent: 4849946 (1989-07-01), Beauducel
patent: 62-92381 (1987-04-01), None
“Piezoelectric Flexible Composites Consist of Piezoelectric Ceramic Powder and Synthetic Rubber”; hisao Banno et al.; Huntai to Kogyo, vol. 22 (No. 1) p 53-54 Dec. 1990 .
“Assessment of Degree of Poling in 0-3 Piezoelectric Composites by X-ray Methods”; Karl F. Schoch et al.; Ferroelectrics, vol. 77; pp. 39-46, Dec. 1988.
“Flexible Composite Piezoelectric Sensors”; R. E. Newnham et al.; Ultrasonic Symposium pp 501-506 Dec. 1984 .
Fujii Yuko
Ito Masahiko
Nagai Takeshi
Ogino Hiroyuki
Dougherty Thomas M.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P
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