Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-06-01
2001-10-02
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S331000
Reexamination Certificate
active
06297578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive element. In particular, the present invention relates to a piezoelectric/electrostrictive element of the uni-morph type to be used, for example, for actuators, filters, displays, transformers, microphones, sounding bodies (such as speakers), various vibrators, resonators, oscillators, discriminators, gyroscopes, and sensors. The element referred to herein includes elements which convert electric energy into mechanical energy, i.e., into mechanical displacement, force, or vibration, as well as elements which perform conversion reversely from the latter to the former.
2. Description of the Related Art
Recently, it has been demanded, in the fields of optics, precision manufacturing, etc., to use a displacement element for adjusting the optical path length or the position on the order of submicron, and a detecting element for detecting minute displacement after converting it into an electric variation.
In order to respond to such a demand, there have been developed piezoelectric/electrostrictive elements to be used for actuators, which utilize occurrence of displacement based on the inverse piezoelectric effect caused when an electric field is applied to a piezoelectric material such as a ferroelectric substance, or for sensors which utilize a phenomenon (piezoelectric effect) reverse to the foregoing.
For example, the unimorph type piezoelectric/electrostrictive element structure has been widely used in speakers.
The present applicant has also previously used piezoelectric/electrostrictive film-type elements made of ceramics, in various applications, as described, for example, in Japanese Laid-Open Patent Publication Nos. 3-128681 and 5-49270.
As shown in
FIG. 30
, the previously proposed piezoelectric/electrostrictive film-type elements have the following structure. Namely, the element comprises a ceramic substrate
104
having at least one window (hollow space)
100
and including a thin-walled vibrating section
102
provided integrally to cover and close the window
100
so that at least one thin-walled wall section (i.e., vibrating section
102
) is formed. The element further includes, on an outer surface of the vibrating section
102
of the ceramic substrate
104
, a piezoelectric/electrostrictive operating section
112
comprising a combination of a lower electrode
106
, a piezoelectric/electrostrictive layer
108
, and an upper electrode
110
, in which the piezoelectric/electrostrictive operating section
112
is integrally stacked and formed in accordance with a film-forming method. The portion of the ceramic substrate
104
other than the hollow space
100
functions as a fixed section
114
for supporting the vibrating section
102
.
The previously proposed piezoelectric/electrostrictive element serves as a compact and inexpensive electromechanical conversion element with high reliability. The known piezoelectric/electrostrictive element provides a large displacement at a low driving voltage. Moreover the response speed is quick, and the generated force is large. It is acknowledged that such a piezoelectric/electrostrictive element is useful as a constituent component of actuators, filters, displays, and sensors.
However, this piezoelectric/electrostrictive element has a so-called sandwich structure in which the piezoelectric/electrostrictive operating section
112
has an upper electrode
110
and the lower electrode
106
formed on the piezoelectric/electrostrictive layer
108
. This piezoelectric/electrostrictive element, comprises a piezoelectric/electrostrictive operating section
112
having the sandwich structure, a vibrating section
102
, and; and fixed section
114
, that results in a bending displacement characteristic as shown in FIG.
31
B. Namely, the bending displacement characteristic is symmetrical in positive and negative directions of the electric field in relation to a reference electric field point (point of the electric field=0) as a center.
It is assumed that the direction of the bending displacement is positive when the main piezoelectric/electrostrictive element is displaced in a convex manner in a first direction (direction for the upper electrode
110
formed on the piezoelectric/electrostrictive layer
108
to face the free space), while the direction of the bending displacement is negative when the main piezoelectric/electrostrictive element is displaced in a concave manner.
The displacement characteristic is obtained by observing the displacement of the main piezoelectric/electrostrictive element as follows. Namely, the piezoelectric/electrostrictive layer
108
is subjected to a polarization treatment by applying a predetermined voltage between the upper electrode
110
and the lower electrode
106
. After that, the voltage applied between the upper electrode
110
and the lower electrode
106
is continuously changed so that the electric field applied to the piezoelectric/electrostrictive element changes, for example, to be electric fields of +3E→−3E→+3E.
At first, an electric field for polarization (for example, +5E) is applied in the positive direction to the piezoelectric/electrostrictive element to perform the polarization treatment for the piezoelectric/electrostrictive layer
108
. After that, the voltage application between the upper electrode
110
and the lower electrode
106
is stopped to give a no-voltage-loaded state. Simultaneously with the start of measurement, a sine wave having a frequency of 1 Hz and peak values of ±3E (see
FIG. 31A
) is applied to the piezoelectric/electrostrictive element. During this process, the displacement amount is continuously measured at respective points (Point A to Point D) by using a laser displacement meter.
FIG. 31B
shows a characteristic curve obtained by plotting results of the measurement on a graph of electric field-bending displacement. As indicated by arrows in
FIG. 31B
, the displacement amount of the bending displacement continuously changes in accordance with continuous increase and decrease in electric field.
Specifically, it is assumed that the measurement is started from an electric field +3E. At first, as shown in
FIG. 32A
, the electric field is applied to the piezoelectric/electrostrictive element in the same direction as that of the polarization direction. Accordingly, the piezoelectric/electrostrictive layer
108
is elongated in a direction across the upper electrode
110
and the lower electrode
106
, and it is contracted in a direction parallel to the upper electrode
110
and the lower electrode
106
. As a result, the entire piezoelectric/electrostrictive element is displaced in the negative direction in an amount of about 0.9 &Dgr;y.
After that, when the electric field is changed from +3E to −0.5E, the displacement amount is gradually decreased. When the electric field is in the negative direction, as shown in
FIG. 32B
, the electric field is applied in the direction opposite to the polarization direction. Therefore, elongation occurs in the piezoelectric/electrostrictive layer
108
in the direction parallel to the upper electrode
110
and the lower electrode
106
, and the displacement is changed to the positive direction.
Next, when the electric field is changed in a direction of −0.5E→−3E, the polarization direction is gradually inverted. Namely, the polarization direction is gradually aligned with the direction of the electric field. As for Point B→Point C→Point C in
FIG. 31B
, it is assumed that the polarization is inverted approximately completely at Point c, because no hysteresis is observed between Point c and Point C.
As shown in
FIG. 33A
, the alignment of the polarization direction with the direction of the electric field allows the piezoelectric/electrostrictive layer
108
to change from the state of horizontal elongation to a state of contraction. At a stage at which the electric field is −3E, the displacement amount is approx
Nanataki Tsutomu
Takahashi Masao
Takeuchi Yukihisa
Budd Mark O.
Burr & Brown
NGK Insulators Ltd.
LandOfFree
Piezoelectric/electrostrictive element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Piezoelectric/electrostrictive element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Piezoelectric/electrostrictive element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575775