Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-07-28
2001-04-24
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S330000, C310S339000, C310S371000
Reexamination Certificate
active
06222304
ABSTRACT:
FIELD OF INVENTION
This invention relates to an improved transducer for inducing and/or sensing motion in an electro-active medium.
BACKGROUND OF INVENTION
Transducers using piezoelectric and ferroic electric materials are used to make accelerometers, displacement sensors and actuators and acoustic transducers including high frequency ultrasound transducers, microphones, hydrophones, loudspeakers and ultrasonic range finders. Ferroic electric herein and throughout this application includes ferroelectric, pyroelectric and electrostrictive. Former methods of performing these functions are electrostatic condenser microphones, dice and fill PZT transducers, bimorph and monomorph ferroelectric and piezoelectric transducers, flextensional transducers, cymbals and moonies. The monomorph and bimorph transducers are good sensors, but are very inefficient as speakers (projectors). This is because the two layers of the bimorph “fight” each other. When electrical energy is put in, 99.5% of the energy goes into internal strain and electric field energy, while only 0.5% is available to do external work. The typical energy efficiency of a bimorph or monomorph is therefore less than 0.5% (off resonance). Hence as an actuator these transducers are not very satisfactory.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved transducer for inducing and/or sensing motion in a fluid or solid medium.
It is a further object of this invention to provide such an improved transducer for inducing and/or sensing motion in a fluid or solid medium which is more efficient.
It is a further object of this invention to provide such an improved transducer for inducing and/or sensing motion in a fluid or solid medium which has greater bandwidth.
It is a further object of this invention to provide such an improved transducer for inducing and/or sensing motion in a fluid or solid medium which reduces the strain energy stored internally and allows more of the mechanical work to be done against an external load.
The invention results from the realization that a truly effective transducer with higher efficiency and broader bandwidth can be achieved using a micro-shell construction in which an electro-active medium is formed with an arch section which more efficiently responds to electrical and mechanical forces and electrodes are used to either apply an electric field and induce a strain to flex the arch section or sense an electric field induced by the strain in the arch section in response to application of an external force.
This invention features a micro-shell transducer including a substrate and an electron-active medium mounted on the substrate and including an arched section spaced from the substrate defining a chamber between the substrate and arched section. A pair of electrodes is mounted on the medium for applying an electric field across the medium for flexing the arched section.
The invention also features a micro-shell transducer including a substrate and an electro-active medium mounted on the substrate and including an arched section spaced from the substrate defining a chamber between the substrate and arched section. A pair of electrodes is mounted on the medium for sensing the electric field generated by a flexure of the medium.
In preferred embodiments the electro-active medium may include a piezoelectric material or a ferroic material. The ferroic material may include a ferroelectric material, a pyroelectric material or an electrostrictive material. The arched section may be a cylindrical section and the medium may further include a shoulder section on each side of the cylindrical section. The electrodes may be mounted one near each shoulder section. The electric field may extend across the arched section and induce strain in the arched section in the same direction to flex the arched section. The electrodes may be mounted on the top and bottom surfaces of the medium. The electric field may extend between the surface and induce strain across the arched section to flex the arched section. The medium may include a peripheral shoulder surrounding the arched section. The arched section may be generally spherical. The electrodes may be mounted one at generally the center of the arched section and one generally at its edge when the arched section is generally spherical. The electrical field may extend generally radially in the arched section and induce strain in the same direction to flex the arched section. The arched section may be convex upwardly or it may be concave downwardly and the substrate may include a recess for accommodating the arched section and chamber. The chamber may be sealed. There may be a plurality of arched sections.
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Dougherty Thomas M.
Iandiorio & Teska
The Charles Stark Draper Laboratory
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