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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a conventional
piezoelectric sounding body, FIG. 3 is a plan view showing a piezoelectric diaphragm used for the
piezoelectric sounding body, and FIG. FIG. 6 is a cross-sectional view showing an embodiment of
the piezoelectric sounding body of the present invention, and FIGS. 7 to 9 are diaphragms of the
piezoelectric sounding body according to the present invention. The top view which shows an
Example, FIG. 10 is a sound pressure-frequency characteristic view of the piezoelectric sounding
body by this invention. 8 ··· Case · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
elastic thin plate, 13 · · · · · · · · · · · · · · · · piezoelectric vibration plate
DETAILED DESCRIPTION OF THE INVENTION In the present invention, a piezoelectric ceramic
plate and an elastic thin plate such as a metal plate are bonded to each other, or a piezoelectric
diaphragm which induces flexural vibration of one having piezoelectric ceramic plates laminated
to each other. According to a piezoelectric sounding body that generates a direct sound from the
piezoelectric diaphragm, the expansion of the frequency band and the flattening of the sound
pressure-frequency characteristic are performed to generate a melody or a voice. As a
conventional piezoelectric speaker, as shown in FIG. 1 to FIG. 4, the elastic thin plate 2 made of
circular metal is circular at the -L portion of the case 1 as shown in FIG. 1 to FIG. Alternatively,
the peripheral portion of the piezoelectric diaphragm 4 or the node portion of the piezoelectric
diaphragm 4 formed by bonding the square-shaped piezoelectric ceramic plate 3 is supported by
the projecting portion 5H of the case 1, and the lead wire 6 for applying the signal voltage is
provided. Vibration by applying a signal voltage 4 is vibrated and sound from sound emission
hole 7 of the front or case 1 of the piezoelectric diaphragm 4 has been a structure in which
radiation. The piezoelectric sounding body has a feature of low power consumption, thinness and
light weight, and has been used as a buzzer in many electronic devices in recent years. However,
since this piezoelectric speaker has a very sharp resonance characteristic with the piezoelectric
diaphragm 4, the sound pressure-frequency characteristic becomes very high near the resonance
frequency as shown in FIG. The change was unremarkably large, and it was not possible to
reproduce natural sound with emphasis on sound power of a specific frequency as the factory
Lithea force that generates melody and voice. The resonance frequency of the piezoelectric
diaphragm 4 in the 853 piezoelectric speaker is determined by the material, thickness, diameter
and support structure of the piezoelectric diaphragm 4 of the piezoelectric diaphragm 4, and the
fundamental first resonance and second or higher harmonics Resonance occurs. When the
piezoelectric diaphragm 4 is circular as in the prior art, the first and second or higher order
resonance frequencies appear one by one according to the diameter of the piezoelectric
diaphragm 4 and the resonance Q is very high. Because the sound pressure in the vicinity of the
resonance frequency and the sound pressure at the other frequencies are largely different, the
characteristics become as shown in FIG. In FIG. 5, fl is a first order, f2 is a second order, and f5 is
a third order resonance frequency. In particular, when circular vibration is supported at the
periphery, the ratio h / f + of the first and second resonance frequencies is about 3.9, and the
ratio + 3 / f2 of the second and third resonance frequencies is about 2. As the distance between
the respective resonance frequencies is wide, there is a disadvantage that the sound pressure is
greatly reduced particularly in the middle of them. The present invention eliminates the abovementioned conventional drawbacks. That is, the present invention provides a piezoelectric
sounding body in which the piezoelectric diaphragm has an elliptical shape 864 and has many
resonance frequencies.
Hereinafter, an embodiment of the present invention will be described with reference to FIG. 6 to
FIG. First of all, in FIG. 6, 8 is a case of open upper surface made of synthetic resin or the like,
and a sound emission hole 9 is provided on the bottom surface of the substrate 8 and a step 10
is provided on the inner periphery of the earth portion. It is provided. A peripheral portion of a
piezoelectric diaphragm 13 made of an elastic thin plate 12 made of metal or the like to which
the piezoelectric ceramic plate 11 is attached is bonded to the case 80 step portion 10 by
adhesion or the like. A lead wire 14 is connected to the piezoelectric ceramic plate 119 elastic
thin plate 11, and this lead wire 14 is used for applying a signal application voltage and is drawn
out of the case 8. As shown in FIG. 7, the piezoelectric diaphragm 13 has an elliptical shape for
both the piezoelectric ceramic plate 111 and the elastic thin plate 12, and as shown in FIG. 8, the
piezoelectric ceramic plate 11 is circular and the elastic thin plate 12 has an elliptical shape.
Furthermore, as shown in FIG. 9, short straight portions may be made continuous to form an oval
shape having a large nine-square shape. Further, as another piezoelectric vibration plate 13, two
elliptical piezoelectric ceramic plates may be bonded. The elliptical piezoelectric vibrating plate
13 can be considered as a composite of a circular vibrating plate whose diameter continuously
changes from the length a of its major axis to the length b-4 of its minor axis. The next resonant
frequency is also determined by the major axis a. 決 ま る, determined by the minor axis from a.
It can exist continuously up to + Ib. Similarly, the high-order primary resonance frequency can be
continuously present from fna determined by the major axis a to fnb determined by the minor
axis, and it is possible to generate a senden diaphragm 13 having a very large number of
resonant frequencies. can do. In particular, it has an elliptical shape so that f, b determined by the
short axis of the highest frequency in the first resonance frequency is slightly lower than f 2 L
determined by the long axis a of the lowest frequency in the second resonance frequency The
major axis length a and the minor axis length b of the piezoelectric diaphragm 13 are set so that
the primary resonance and the secondary resonance of the elliptical diaphragm 13 generate
almost continuous frequencies, and so on. The second and third resonances, and higher order
resonances above -9 also generate frequencies 868 continuously. Therefore, the sound pressure
cage generated between the resonance frequencies is also reduced, and the frequency response
change of the sound pressure can be reduced as a whole. Since the resonant frequency is
inversely proportional to the square of the diameter of the piezoelectric diaphragm, assuming
that the proportional constant is K, +, a = / a2. f, b = / b '! And 2 / -f as described above. Since 39: F2a = s, sx / a ', so that: FIb = to / b' 43. sK / a '=, ((2aK1 ヨ ウ Kt Le K Ha b ˜ 472.0 1) It is
most preferable to set the minor axis length b of the ellipse a little larger than 1 / 2.0 of the
major axis length a It is effective.
Piezoelectric sounding body peripherally supported on case 8 as shown in FIG. 6 according to the
elliptical piezoelectric diaphragm of the present invention of FIG. 7 in which the length b of the
short axis is set to 1 / 1.6 of the length a of the long axis The sound pressure-frequency
characteristics of are shown in FIG. As shown in this characteristic, the piezoelectric sounding
body using the earth electrode diaphragm according to the present invention has a conventional
level change due to the sound pressure frequency (smaller compared to the conventional one,
and the range is expanded, resulting in natural voice and melody If the piezoelectric sounding
body is used as a speaker terminal 897, the present invention is very effective and highly useful.