Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-03-30
2001-05-29
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S324000, C310S369000, C310S800000
Reexamination Certificate
active
06239535
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of transducers. More particularly, the present invention relates to an omni-directional ultrasonic transducer apparatus.
DESCRIPTION OF RELATED ART
In the environment of transducers, it is known that an ultrasonic transducer may be formed with either a linear or curved film incorporated therein. Each of the types of film is described in the following.
Referring first to
FIG. 4
, a linear polymer piezoelectric film
50
is shown. When an AC voltage is applied to electrodes
52
on surfaces of the film
50
, the film length in the molecular chain direction shrinks or expands. In other words, the PVDF (polymer piezoelectric material) is stretched during the process, and molecular chains are aligned in parallel. This is due to excitation in the linear direction.
Alternatively, a cylindrical piezoelectric film
54
is shown in
FIG. 5
whereby the stretched axis is wrapped around a cylinder (not shown). Here, when an AC voltage is applied to electrodes
56
on surfaces of the cylindrical film
54
, the length vibration is converted to radial vibration. This is the principle of PVDF tweeter as disclosed in “Electroacoustic Transducers with Piezoelectric High Polymer Films”, J. Audio Eng. Soc. Vol. 23, No.1, pp. 21-26, (1975) by M. Tamura et al. The high polymer element in the piezoelectric film is a poly-vinylidene fluoride) (PVDF) in film form.
The cylindrical PVDF vibrator has a certain mass and stiffness for radial expansion or shrinkage, and this mass and stiffness enable a resonance whose frequency is
f
0
=(½ pR)ÖY/r where R is the radius in meters, Y is Young's modulus (N/m
2
), and r is density (Kg/m
3
). (1)
This equation is shown in a paper by A. S. Fiorillo entitled “Design and Characterization of a PVDF Ultrasonic Range Sensor”, IEEE Trans. Ultrasonics, Ferroelectrics and Frequency Control”, Vol. 39, No. 6, pp. 688-692 (1992), which is for semi-circularly curved film with both ends clamped, but it has the same resonance frequency as a cylinder.
In IEEE paper, the cylindrical PVDF film is mounted on a smooth-surfaced spool. The radius of the spool determines the resonance frequency through equation (1). The PVDF film can be directly wrapped around a cylindrical surface of the spool with almost no gap between the surface of the film and the surface of the spool. Even though the appearance is of no gap, the film is actually supported on the spool by many tiny points of surface roughness. It has been determined that most of the supported area has gaps of from 2-20 microns between the contacts of the many tiny points of surface roughness. Since actual vibration amplitudes are about 1 micron peak to peak for a 150 Vpp drive, there are enough spaces to vibrate and actually permit the device to work.
However, in the known application of a film to a spool as described, two problems have been discovered by the inventors of the instant application. First, it has been discovered that with the “gap-free” wrapping attempted in the known art, there is a problem of uncontrollable resonance frequency. Secondly, in the “gap-free” wrapping, there is a reduced vibration of the PVDF film.
In other words, since the air found in the 2~20 micron region (the “back air space”) has a stiffness and spring effect, this also increases the effective stiffness of the PVDF film and in turn increases the resonance frequency of the film. Also, many points of contact are present between the cylinder and the PVDF film such that energy is lost due to friction, and the vibration of the PVDF film is thereby reduced. Since a thickness of the back air space is not controlled in the known art, nor recognized that it could or should be controlled, the resonance frequency and reduction in vibration also can not be controlled. Instead, it has been discovered by the inventors that if back air thickness exceeds a certain value, the spring effect of back air becomes less and even becomes negligible, thereby solving both problems of uncontrollable resonance frequency and reduction in vibration.
Accordingly, a need in the art exists for an ultrasonic transducer apparatus in which a thickness of a space between a PVDF film and a spool supporting the film is controlled. Controlling of the thickness of the space between the PVDF film and the spool has been discovered by the inventors to reduce a spring effect of air trapped therebetween and ultimately controls resonance frequency and improves vibration in a manner not heretofore known in the art.
OBJECTS AND SUMMARY OF AN EMBODIMENT OF THE INVENTION
It is an object of an embodiment of the invention to provide an ultrasonic transducer apparatus having a controlled resonance frequency.
It is another object of an embodiment of the invention to provide an ultrasonic transducer apparatus having an air thickness of a predetermined value between a spool and a film surrounding the spool.
It is yet another object of an embodiment of the invention to provide an ultrasonic transducer apparatus in which the air thickness of a predetermined value between the spool and the film surrounding the spool is selected to substantially negate a spring effect of the air therebetween.
It is a still further object of an embodiment of the invention to provide a cost effective ultrasonic transducer apparatus for eliminating the problems found in the known art of ultrasonic transducer.
These and other objects of the present invention are achieved by providing a transducer apparatus including a spool member having a body portion and first and second elevated regions formed on the body portion. A piezoelectric polymer film such as a PVDF film surrounds the spool member and is spaced apart from the body portion of the spool member by an elevation of the elevated region, thereby forming a predetermined gap between the electrode film and the body portion of the spool member. The predetermined gap is at least 0.1 mm to enable a predetermined resonance frequency in the piezoelectric film. Opposite lateral ends of the piezoelectric film are secured together such that secured ends of the piezoelectric film have substantially the same resonance frequency as a remainder of the electrode film.
Advantages of an embodiment of the invention as described more fully hereinbelow include a cost effective assembly for providing an ultrasonic transducer assembly having improved resonance. This is accomplished by reducing a spring effect between a film surrounding a spool in an ultrasonic transducer assembly by forming a predetermined back air space between the film and the spool.
Additionally, the ultrasonic transducer of the instant disclosure reduces the complexity and cost previously associated with the use of ultrasonic transducers. The stored coils are easily accessible and manageable in a manner not previously known in the art.
REFERENCES:
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patent: 3832580 (1974-08-01), Yamamuro et al.
patent: 3862477 (1975-01-01), Ayers et al.
patent: 4064375 (1977-12-01), Russell et al.
patent: 4486869 (1984-12-01), Carter
patent: 4558249 (1985-12-01), Lerch et al.
patent: 4825116 (1989-04-01), Itoh et al.
patent: 5357486 (1994-10-01), Pearce
patent: 5361240 (1994-11-01), Pearce
Park Kyung-Tae
Swan Jeffrey D.
Toda Minoru
Zaks Susan Huang
Budd Mark O.
Duane Morris & Heckscher
Measurement Specialties Inc.
Plevy Arthur L.
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