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JPS5779898

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DESCRIPTION JPS5779898
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view and a side view of a conventional
piezoelectric buzzer, and FIG. 2 is a top view and a side view showing an embodiment of the
piezoelectric buzzer according to the present invention. Fig. 3 is a characteristic diagram showing
the relationship between the ratio of the diameter of the substrate to the diameter of the hole, the
sound pressure, and the resonance frequency in the piezoelectric buzzer of the present invention.
DETAILED DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a
piezoelectric buzzer capable of obtaining a high sound pressure at a relatively low frequency. The
basic structure of a conventional piezoelectric buzzer is shown in FIG. Reference numeral 1
denotes a piezoelectric ceramic plate, which is usually provided with electrodes (not shown)
made of baked silver or the like or provided on upper and lower surfaces and bonded to a
substrate 2. A metal plate is usually used as the substrate 2. The electrode of the bonding portion
to the piezoelectric ceramic plate 10 substrate 2 is generally conducted to the substrate 2, and
two faces of the piezoelectric ceramic plate 1; When the piezoelectric ceramic plate 1 is applied,
the piezoelectric ceramic plate 1 expands and contracts in the radial direction, and a bending
motion is generated between the piezoelectric ceramic plate 1 and the substrate 2 to generate a
sound by vibration according to the applied frequency. The support of the piezoelectric buzzer is
generally performed at the periphery or at the nodes. In addition, a piezoelectric buzzer by a selfoscillation type oscillation circuit in which a part of the electrode on the side not conducted to
the substrate 2 is separated into three poles and the three poles are used as a feedback signal is
similarly configured. The oscillation frequency is superior in the case of two poles in that it is
determined by the resonance point including the support structure. Therefore, in the
piezoelectric buzzer, the largest sound pressure is obtained at the resonance point where the
input innobiance is small. However, since the resonance point of the piezoelectric bushing is
generally at a frequency of several kilohertz or more, it is necessary to reduce the thickness of
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the piezoelectric ceramic plate 1 and the substrate 2 or to increase the radial direction in order
to reduce this. However, the former has its limit determined by its processability and strength,
and the latter has application requirements for use as a piezoelectric buzzer. It has to be small
and thin, and the conventional piezoelectric buzzer "" has the disadvantage that it is difficult to
design only high frequencies. SUMMARY OF THE INVENTION The present invention provides a
piezoelectric buzzer which can lower the resonance point than the conventional buzzer and can
obtain a large sound pressure at a relatively low frequency, except for the above-mentioned
drawbacks. The basic structure of the piezoelectric buzzer according to the present invention is
shown in FIG. Show in the mouth. In FIG. 2, the substrate 3 has a hole 4 of diameter d
concentrically with its diameter. The piezoelectric buzzer has a basic structure in which the
substrate 3 having the holes 4 and the piezoelectric ceramic plate 6 are bonded to each other. In
the piezoelectric buzzer according to the present invention having such a structure, as shown in
FIG. 3, when the ratio of the diameter d of the hole 4 of the substrate 3 to the diameter of the
substrate 3 is 0.5 or less Instead, the resonant frequency f decreases in inverse proportion to the
hole diameter ratio. Therefore, if the hole diameter ratio is set to a certain size, it is possible to
set the frequency low without lowering the sound pressure.
In practice, when the hole diameter ratio exceeds 0.7, the adhesion with the piezoelectric ceramic
plate 5 becomes a problem, and the sound pressure is extremely reduced. 4-Thus, the
piezoelectric buzzer according to the present invention can obtain a large sound pressure even at
a relatively low frequency with a very simple external structure, and is particularly effective in
constructing a small-sized piezoelectric buzzer, and has an industrial value. Is very expensive.
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