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JPS63240200

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DESCRIPTION JPS63240200
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric element capable of performing two or more ringing operations with different tones.
[Prior Art] A piezoelectric element is an electromechanical conversion means for converting
electricity into mechanical vibration, and can generate an ultrasonic wave and an audible sound
by being driven by an oscillation drive circuit. [Problems to be Solved by the Invention] The
conventional piezoelectric buzzer performs ringing operation with a single tone, and in order to
obtain a plurality of different tones, a plurality of piezoelectric buzzers must be installed. .
Therefore, the present invention enables a single piezoelectric element to sound with two or
more different tones. [Means for Solving the Problems] As shown in FIG. 1, in the piezoelectric
element of the present invention, the piezoelectric material layer 6 is disposed on the surface of
the first electrode (the diaphragm electrode 4), and this piezoelectric material layer A plurality of
feedback electrodes 10.12 (feedback electrodes 10.12.13 in the piezoelectric element 2 of FIG. 4)
are selectively provided on the surface 60 together with the second electrode (element electrode
8). [Operation] Since different feedback signals can be obtained from a plurality of feedback
electrodes 10.12 and ringing can be performed according to the feedback signals, sounds having
different timbres are selected according to the selected feedback electrodes 10.12. It is possible
to generate. [Embodiments] FIGS. 1 and 2 show an embodiment of a piezoelectric element
according to the present invention. As shown in FIG. 1 and FIG. 2, this piezoelectric element 2
has, for example, a circular, highly conductive diaphragm electrode 4 with good rigidity installed
as a first electrode, and concentrically formed on its surface A piezoelectric material layer 6 such
as a piezoelectric ceramic is provided, and a plurality of feedback electrodes 10.12 are provided
on the surface of the piezoelectric material layer 6 selectively as a second electrode together with
a device electrode 8 at a predetermined interval. As a result, a piezoelectric buzzer element is
formed. Therefore, in the case of this embodiment, the feedback electrode 10 is formed to extend
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in the form of a strip in the radial direction with the tip thereof at the center of the piezoelectric
material layer 6 and the element electrode 8 to surround the feedback electrode 10. It has a
horseshoe shape. Further, the feedback electrode 12 surrounds the periphery of the device
electrode 8 to form an annular shape, and the feedback electrode 10.12 is formed with the
device electrode 8 interposed therebetween. The element electrode 8 forms the main electrode
together with the diaphragm electrode 4. Therefore, except for special cases, the area of the
feedback electrode 10. A setting larger than 12 is appropriate. Then, lead wires L1, L2 and L: as
external lead terminals are connected to the diaphragm electrode 4, the element electrode 8 and
the feedback electrode 10.12 respectively by connection means such as soldering. , L4 is
connected.
With this configuration, the piezoelectric element 2 functions as an oscillating element to cause
ringing by automatic oscillation, or applies an excitation voltage of a specific frequency between
the diaphragm electrode 4 and the element electrode 8. As a result, ringing operation can be
generated by passive oscillation. In that case, the electromotive force generated in the feedback
electrode 10.12 can be applied as a feedback signal to the oscillation drive circuit side for each
feedback electrode 10.12, and sounds with different tones can be generated for each feedback
signal. In this case, the feedback electrode 10.12 can be used selectively. For example, it is also
possible to parallelize the other feedback electrode 12 with respect to one feedback electrode 10,
and in either case the vibration mode A different ringing action is obtained. In the embodiment,
although the diaphragm electrode 4 is set to be circular, it may be set to various shapes such as a
rectangle, a polygon and any size, and various piezoelectric material layers 6 and electrodes
8.10.12 are also various. By setting the shape and the size of the ring, it is possible to obtain the
ringing operation according to the shape. Next, FIG. 3 shows a specific configuration example of
a piezoelectric buzzer using the piezoelectric element 2 shown in FIG. 1 as a piezoelectric buzzer
element performing ringing operation. As shown in FIG. 3, the oscillation drive circuit 14 for
oscillating and driving the piezoelectric element 2 has a single transistor 16 as an active element,
and the element electrode 8 of the piezoelectric element 2 is disposed between the collector and
emitter of the transistor 16. And the diaphragm electrode 4 is connected. The drive voltage of the
collector of the transistor 16 and the element electrode 8 of the piezoelectric element 2 from the
terminal 18 through the resistor 20. , And the emitter of the transistor 16 and the diaphragm
electrode 4 of the piezoelectric element 2 are grounded. That is, the transistor 16 is connected in
parallel to the piezoelectric element 2, and charging / discharging of the piezoelectric element 2
is left to the switching of the transistor 16. Then, a bias is given to the base of the transistor 16
from the terminal 18 through the resistor 22, and the feedback signal vrb +% from the feedback
electrode 10 or the feedback electrode 12 selected by the switch 24 for selecting the feedback
electrode 10.12. The vrbz is given via the resistor 26. With this configuration, when the drive
voltage vec is applied from the power supply, a charging current flows between the element
electrode 8 of the piezoelectric element 2 and the diaphragm electrode 4 through the resistor 20
when the transistor 16 is nonconductive. The piezoelectric element 2 is charged, and the base
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current flows through the resistor 22 and the transistor 16 conducts.
Here, it is assumed that the switch 24 is closed to the contact a side and the feedback electrode
10 is selected. When the transistor 16 is considered, the charge of the piezoelectric element 2 is
discharged through the transistor 16, and in conjunction with this, the piezoelectric element 2
starts bending movement in the direction determined by the polarization direction. At this time, a
positive feedback signal Vfb1 is generated at the feedback electrode 10 of the piezoelectric
element 2, and the feedback signal v01 is fed back to the base of the transistor 16, so that the
transistor 16 continues to conduct. For this reason, after the bending movement of the
piezoelectric element 2 reaches the maximum point, it causes bending in the opposite direction
to return to a flat state. When the piezoelectric element 2 becomes flat, the base potential of the
transistor 16 becomes lower than the base-emitter saturation voltage, and the transistor 16 is
turned off. When the transistor 16 becomes nonconductive, a charging current flows between
the electrodes 8.4 of the piezoelectric element 2 and the piezoelectric element 2 performs
bending motion in the opposite direction to that during discharge, and a negative feedback signal
Vfbl is applied to the feedback electrode 10 As the feedback signal {circle over (1)} 1 pulls down
the base potential, the transistor 16 remains nonconductive. For this reason, while the
piezoelectric element 2 maintains the charged state, after the bending movement reaches the
maximum point, the piezoelectric element 2 is bent in the reverse direction to return to the flat
state again. When the piezoelectric element 2 becomes flat, the base potential of the transistor
16 becomes a potential exceeding the base-emitter saturation voltage required to cause the
transistor 16 to conduct, so the transistor 16 is turned on and the piezoelectric element 2 is
turned on. Discharge. By repeating such an operation, the ringing operation is caused according
to the bending motion period of the piezoelectric element 2, that is, the resonance frequency, and
an acoustic sound having a constant frequency is emitted. Such ringing operation is performed
based on the feedback signal v tbz from the feedback electrode 12 even when the switch 24 is
switched to the b-side contact. Therefore, since the oscillation frequency depends on the
feedback electrode 10.12 when the piezoelectric element 2 and the circuit constant are constant,
the feedback electrode 10.12 can be selected by selecting one of the feedback electrodes 10.12
with the switch 24. It is possible to obtain an acoustic output having a timbre determined by. The
piezoelectric element of the present invention is, for example, a feedback electrode 10.12.13 as
shown in FIG. 4 and FIG. 5, and the outside of the feedback electrode 12 of the embodiment
shown in FIG. 1 and FIG. And another feedback electrode 13 may be provided. In this way,
variations in selection and combination of the feedback electrodes 10.12.13 can be increased,
and a plurality of ringing can be generated.
[Experimental Results] The experimental results for the piezoelectric buzzer shown in FIG. 3 are
shown in FIG. As shown in (A) of FIG. 6 from the feedback electrode 12, when the power supply
voltage Vcc is set to 9.5 V, the drive current is set to 4.3 mA, and the oscillation operation is
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performed by selecting the feedback electrode 12. The frequency f: 5.26 kllz, the amplitude
voltage V-: 1.4 VP-P are obtained, and the output voltage is the frequency f: 5.26 kHz, as shown
in FIG. 6 (B). An amplitude voltage V, S: 5 VP-P was obtained. Similarly, when the power supply
voltage Vcc is set to 9.5 V, the drive current is set to 4.5 mA, and the feedback electrode 10 is
selected to perform the oscillation operation, the feedback electrode 10 (C in FIG. Frequency f:
5.46 kHz, amplitude voltage V: 3.9 VP-P are obtained, and the output voltage is frequency f: as
shown in FIG. 6 (D). 5.46 kHz, amplitude voltage V ,: 6.6 Vp-p was obtained. According to the
present invention, by providing a plurality of feedback electrodes, ringing operations having
different oscillation frequencies can be obtained by selection and combination thereof, and an
acoustic output having an arbitrary tone can be easily obtained. .
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a plan view showing an embodiment of the piezoelectric element of the present
invention, FIG. 2 is a sectional view taken along the line II--II of the piezoelectric element shown
in FIG. 1, and FIG. FIG. 4 is a plan view showing another embodiment of the piezoelectric element
of the present invention, and FIG. 5 is a view showing an equivalent circuit of the piezoelectric
element shown in FIG. FIG. 6 is a figure which shows the experimental result of the piezoelectric
buzzer shown in FIG.
2 ... piezoelectric element 4 ... diaphragm electric bridge (first electrode) 6 ... piezoelectric
material layer 8 ... element electric bridge (second electrode) 10.12.13 ... feedback electrode Fig.
2 Fig. 3 Time (μ5) (A) + 00 200 300 400 hours (μ 5) (B) Time cμ 5) (C) + 00 200 300 4 QQ
time (μ 5) (D) 6
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