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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1-a is an explanatory view showing the
displacement of the piezoelectric element. Fig. I-b is an explanatory view showing a state of
displacement when a metal plate and a piezoelectric element are attached. FIG. 2 is a crosssectional view showing an example of a piezoelectric buzzer in which a piezoelectric element is
directly attached to a back cover. FIG. 3 is a cross-sectional view showing an embodiment of the
present invention. FIG. 4 is a cross-sectional view for explaining the operation of FIG. 3; 1 и и и
Piezoelectric element, 1a и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и
и и и иииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии
Part, 7d и и и и и и и и и и и и и и и и и и и и и и и и и и и back cover, 9 и и и и и и и.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric
element of a piezoelectric buzzer, the main object of which is to provide a piezoelectric buzzer
with a large volume. Piezoelectric buzzers have a simple structure of attaching a piezoelectric
element to a flat plate such as a metal plate or a plastic plate (1), and emit a sound wave by a
kind of bimetal structure utilizing the difference in displacement between the flat plate and the
piezoelectric element It is. The operation principle will be described with reference to FIG. 1, and
FIG. 1- 0 shows the displacement of the piezoelectric element 1. When the electrode 1a on the
upper surface of the piezoelectric element is connected to a positive potential and the electrode
1h on the lower surface is connected to a negative potential, an electric field is applied to the
piezoelectric element from the upper side to the lower side of the drawing. At this time, it is
assumed that the piezoelectric element has a property of extending in the direction of arrow A
indicated by a solid line. This is called positive polarization. Therefore, in the case described
above, when the piezoelectric element has the property of contracting in the direction of the
arrow B indicated by the broken line, this is negative polarization. FIG. 1-h shows the state of the
displacement when an electric field is applied to the metal plate 2 whose periphery is fixed and
the piezoelectric element 7 uniformly plus polarized is attached. In the case of fixing the outer
periphery, the state of bending of the metal plate 2 is reversed at the central portion C and the
peripheral portion. The central portion C has a convex curvature at the top and a convex
curvature at the peripheral portion, and a portion 3 having no curvature moving from convex to
convex is called a node. Therefore, when piezoelectric elements polarized in the same direction
are attached to a gold (2) vane to make a piezoelectric buzzer, it is most efficient to attach the
piezoelectric elements to the inside than this node, and as a result, the volume is large. By the
way, today, an electronic watch having a long battery life is desired in the market, and since the
reduction of the power consumption of the circuit is at the limit, a lithium battery having a large
power capacity is being used as a countermeasure. However, the shape of the lithium battery is a
thin disk and has a diameter of about two. Therefore, when a piezoelectric buzzer of a type in
which the back cover is a diaphragm and the piezoelectric element is directly attached thereto is
used, lithium is connected to the circuit 5 by the coil spring 4 etc. to the electrode 1? on the
upper surface of the piezoelectric element 1 as shown in FIG. It is necessary to attach the
piezoelectric element 1 larger than the outer shape of the battery 6. At this time, the back cover
8 becomes a diaphragm fixed on the outer periphery, and when the piezoelectric element is
attached outside the node as described above in FIG. 1-b, the expansion and contraction direction
of the piezoelectric element and the curvature of the back cover are reversed. Vibration is
suppressed and the volume is reduced. The present invention eliminates this drawback and
provides a piezoelectric buzzer with no volume reduction for a piezoelectric buzzer to which a
piezoelectric element having an area from the node to the outside of the diaphragm is attached
(a). Hereinafter, the present invention will be described by way of examples.
FIG. 3 shows an embodiment of the present invention. 8 is a circular back cover, 7 is a circular
piezoelectric element of the present invention, and is fixed to the back cover 8 with an adhesive
or the like. Reference numeral 9 is a node of the back cover 8. The piezoelectric element 7 has
positive polarity at its inner 7C portion and negative polarity at its outer edge 7d with the node 9
as a boundary. When an electric field is applied to this piezoelectric element, the back cover 8 is
deformed as shown in FIG. 4, and the deformation curvature of the back cover 8 matches the
expansion and contraction direction of the piezoelectric element 7. Therefore, there is no volume
reduction as described above, and the size of the piezoelectric element electrode can be
increased, which is convenient for mounting and has a large advantage. As described above, in
the present embodiment, the polarization direction of the piezoelectric element is changed with
the node of the diaphragm as a boundary. However, it is not necessary to be particularly limited
to the node. Conversely, it suffices to change the polarization according to the desired vibration
form, change the polarization direction by half circle, or generate the second-order third-order
high-order vibration easily by giving the polarization direction six times in the same circle.
Needless to say, it is also possible to ???
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description, jps56105888
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