Piezoelectric sound generator

A piezoelectric sound generator which comprises a monolithic sintered body obtained by laminating a plurality of ceramic green sheets formed alternately with a plurality of electrodes and cofiring the same. Electrical connections between the electrodes in the sintered body are provided within through-holes formed at the vibrational node of the piezoelectric sound generator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a piezoelectric sound generator which is 
applied to, e.g., a piezoelectric buzzer or a piezoelectric loudspeaker, 
and more particularly, it relates to a piezoelectric sound generator 
including a monolithic sintered body which is obtained by laminating a 
plurality of ceramic green sheets and electrodes and cofiring the same. 
2. Description of the Prior Art 
FIG. 2 is a schematic sectional view showing a conventional piezoelectric 
buzzer as an example of a conventional piezoelectric sound generator. 
Referring to FIG. 2, a laminated type vibrator 2 is adhered to a metal 
plate 1. The vibrator 2 is formed by laminating three piezoelectric 
ceramic plates 2a, 2b and 2c so as to reduce its impedance and increase 
its sound pressure. 
In the piezoelectric buzzer as shown in FIG. 2, the piezoelectric ceramic 
plates 2a to 2c are previously fired separately and polarized in 
directions indicated by arrows in FIG. 2, to be integrally formed with 
electrodes 3a to 3d on the metal plate 1. The electrodes 3a and 3c are 
electrically interconnected with each other by an electric connecting part 
4a formed on the outer peripheral portion while the electrodes 3b and 3d 
are electrically interconnected with each other by an electric connecting 
part 4b also formed on the outer peripheral portion. In the piezoelectric 
buzzer as shown in FIG. 2, the vibrator 2 is formed by the three ceramic 
plates 2a to 2c, and is capable of generating high sound pressure because 
of its reduce impedance. 
Another prior device, disclosed in, Japanese Patent Application No. 
226577/1984 in the name of the assignee of the present application, is a 
piezoelectric buzzer which is in the background of the present invention, 
although this related art has not yet been published. FIG. 3 shows the 
piezoelectric buzzer as disclosed in the Japanese Patent Application No. 
226577/1984. Referring to FIG. 3, a monolithic ceramic vibrator 12 is 
adhered on a vibration plate 11 which comprises a metal or plastic plate. 
The ceramic vibrator 12 has three ceramic layers 12a to 12c, which are 
obtained by laminating three ceramic green sheets, alternating with layers 
of electrode paste adapted to form inner electrodes 13b and 13c, and 
cofiring the same. Electrodes 13a and 13d are formed simultaneously with 
the inner electrodes 13b and 13c or separately after the firing. The 
ceramic layers 12a to 12c are polarized in directions indicated by arrows 
in FIG. 3. The electrodes 13a and 13c are interconnected with each other 
by an electrode connecting part 14a formed on the outer periphery of the 
monolithic ceramic vibrator 12 while the electrodes 13b and 13d are 
interconnected with each other by an electrode connecting part 14b formed 
on the outer periphery of the monolithic ceramic vibrator 12. Thus, in the 
piezoelectric buzzer as shown in FIG. 3, the monolithic ceramic vibrator 
12 is integrally formed, whereby the respective ceramic layers 12a to 12c 
can be made very thin. Hence the impedance of the vibrator 12 is reduced 
in comparison with that of the piezoelectric buzzer as shown in FIG. 2, 
and remarkably higher sound pressure can be obtained. 
FIG. 4 is a side elevational view schematically showing vibration states of 
the conventional piezoelectric buzzer as shown in FIGS. 2 or 3. In the 
conventional piezoelectric buzzer, a ceramic vibrator 22 adhered to a 
vibration plate 21 vibrates upon application of a voltage so as to 
alternate between two bent states as shown in broken lines A and B in FIG. 
4, thereby generating sound waves. The modes X of such vibration are 
inside the outer periphery of the ceramic vibrator 22 as shown in FIG. 4, 
whereby the outer peripheral portions of the ceramic vibrator 22 are 
displaced a considerable distance by the vibration. 
On the other hand, the electric connecting parts 4a, 4b, 14a and 14b of the 
conventional laminated type piezoelectric buzzers are formed on the outer 
peripheral portions of the ceramic vibrators. Thus, the electric 
connecting parts 4a, 4b tend to 14a and 14b suppress the vibration of the 
ceramic vibrators, and as a result, it has not yet been possible to obtain 
the desired sound pressure at certain desired resonance frequencies. Such 
problems are not restricted to the piezoelectric buzzers as shown in FIGS. 
2 and 3 employing the so-called laminated or unimorph type vibrators, but 
also exist in a piezoelectric buzzer employing a bimorph type and other 
related types of vibrator. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to overcome the 
aforementioned problem and provide a sound generator whose vibration is 
not suppressed by electric connecting parts, thereby to reliably obtain 
desired sound pressure. 
The present invention provides a piezoelectric sound generator employing a 
monolithic sintered body which is obtained by laminating a plurality of 
ceramic green sheets and a plurality of electrodes and cofiring the same, 
wherein at least one electric connecting part for connecting the 
electrodes with each other is formed in a through-hole provided in a 
position which does not restrict vibration. 
The position not restricting the vibration is generally located atanode or 
in the vicinity of a node. 
The piezoelectric sound generator according to the present invention is 
applicable to both unimorph and bimorph type vibrators. 
When the unimorph type vibrator is employed, the ceramic layers are 
polarized in alternating directions along the direction of thickness. In 
this case, alternate electrodes are electrically interconnected with each 
other by electric connecting parts. 
In the case of the bimorph type vibrator there are, provided first and 
second vibrating regions which vibrate in respective directions opposite 
to each other and are sequentially arranged along the direction of 
thickness. When an odd number of ceramic layers are provided, the central 
ceramic layer is not polarized, the first and second vibrating regions 
being arranged on both sides of the non-polarized ceramic layer, and the 
ceramic layers forming the first and second vibrating regions being 
polarized symmetrically about the non-polarized ceramic layer. Also in 
this case, alternate electrodes are electrically connected with each other 
by electric connecting parts. 
On the other hand, when an even number of ceramic layers are provided, the 
respective ceramic layers in the first and second vibrating regions are 
polarized in directions opposite to each other. In this case, the 
respective ceramic layers in the first and second vibrating regions, which 
layers are positioned adjacent to each other, are polarized in the same 
direction along the direction of thickness. Also in this case, alternate 
respective electrodes in each region are electrically interconnected with 
each other by electric connecting parts. 
According to the present invention, at least one electric connecting part 
is formed in a through-hole which is provided in a position not 
restricting vibration, whereby the through-hole portion is not 
substantially moved upon vibration and will not suppress the vibration, 
and hence sound waves can be reliably obtained having a desired sound 
pressure at a desired resonant frequency. 
In addition to the piezoelectric buzzer, the present invention is 
applicable to a piezoelectric loudspeaker such as a tweeter and other 
general piezoelectric sound generators.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will now be described, with 
reference to the accompanying drawings. 
FIG. 1 is a perspective view showing a piezoelectric buzzer 30 according to 
a first embodiment of the present invention. The piezoelectric buzzer 30 
comprises a vibration plate 31 comprising a metal or synthetic resin plate 
and a monolithic ceramic vibrator 32 adhered to the vibration plate 31. 
The monolithic ceramic vibrator 32 comprises a sintered body which is 
obtained by laminating a plurality of ceramic green sheets and a plurality 
of electrodes and cofiring the same, as hereinafter described in detail. 
An important feature of the piezoelectric buzzer 30 according to this 
embodiment resides in that an electric connecting part between the 
electrodes of the monolithic ceramic vibrator 32 is formed within a 
through-hole 34a which is provided in the vicinity of a vibration node 
(shown by a broken line X in FIG. 1) of the piezoelectric buzzer 30. Thus, 
it is understood that the through-hole 34a is not substantially moved 
during vibration of the piezoelectric buzzer 30 and will not suppress the 
vibration of the piezoelectric buzzer 30, whereby a desired sound pressure 
can be obtained. 
Following one further details of the structure of the embodiment shown in 
FIG. 1. 
FIG. 5 is a perspective view illustrating configurations of electrodes in 
the monolithic ceramic vibrator 32. As shown in FIG. 5, conductive paste 
layers 38, 39, 40 and 41 of platinum, palladium or silver-palladium are 
coated on ceramic green sheets 35, 36 and 37. Although the conductive 
paste layer 41 is formed on the back surface of the ceramic green sheet 
37, i.e., the surface opposite to the conductive paste layer 40, the same 
is shown as if it were separated from the sheet 37 in a direction away 
from the conductive paste layer 40, for easy understanding of this 
embodiment. 
The ceramic green sheet 35 is provided with a through-hole 34a which is 
connected with the conductive paste layer 38 and has a conductive part in 
its inner wall, which through-hole 34a is formed in the vicinity of the 
vibration node of the vibrator 32. The ceramic green sheet 36 is provided 
with a through-hole 34b in a position aligned with the through-hole 34a 
upon lamination. The through-hole 34b is also provided with a conductive 
part in its inner wall, and the conductive paste layer 39 is removed from 
the sheet 36 around the periphery of the through-hole 34b so that the 
through hole 34b is not connected with the conductive paste layer 39. The 
through-holes 34a and 34b are thus adapted to connect the conductive paste 
layers 38 and 40 with each other. 
The ceramic green sheet 36 is provided, in a position separated from the 
through-hole 34b and in the vicinity of the vibration node of the 
vibration member, with a through-hole 42a which is connected with the 
conductive paste layer 39. Further, the ceramic green sheet 37 is provided 
with a through-hole 42b in a position aligned with the through-hole 42a 
upon lamination. The conductive paste layer 40 is removed around the 
periphery of the through-hole 42b so that the through-hole 42b is not 
connected with the conductive paste layer 40. Thus, the conductive paste 
layers 39 and 41 are connected with each other by the through-holes 42a 
and 42b after lamination. 
The aforementioned respective ceramic green sheets 35 to 37 are laminated 
and cofired, thereby to obtain a sintered body 43 as shown in FIG. 6. In 
the sintered body 43, the electrodes are electrically interconnected with 
each other by the through-holes 34a, 34b, 42a and 42b as hereinabove 
described. This arrangement is shown in greater detail in FIG. 7. In 
cofiring the sintered body 43, the conductive paste layers are baked to 
serve as electrodes, which electrodes are hereafter described with the 
same reference numerals as the corresponding conductive paste layers. The 
electrodes 38 and 41 may be simultaneously formed with the electrodes 39 
and 40, or may be separately formed after firing by baking, sputtering, 
vapor deposition or the like. 
FIG. 7 is a partially fragmented sectional view showing the electrical 
interconnections provided by the through-holes 42a and 42b. The 
through-holes 42a and 42b are aligned with each other upon lamination. 
Therefore, the electrode 39, which is electrically connected with the 
through-hole 42a, is electrically connected through the through-holes 42a 
and 42b with the electrode 41 which is electrically connected with the 
through-hole 42b. 
FIG. 8 shows an arrangement of electrical connections for polarizing the 
sintered body obtained in the aforementioned manner. Referring to FIG. 8, 
numerals 34 and 42 respectively denote electric connecting parts which are 
formed by the through-holes 34a and 34b, and 42a and 42b, in broken lines. 
Assuming that, in the state shown in FIG. 8, a plus potential is supplied 
through the electrode 38 and a minus potential is supplied through the 
electrode 41, the respective ceramic layers 35, 36 and 37 will be 
polarized in the directions shown by arrows in FIG. 8. 
The sintered body 43 polarized in the aforementioned manner is adhered to 
the vibration plate 31, thereby to obtain the piezoelectric buzzer 30 
shown in FIG. 1. In order to drive the piezoelectric buzzer, a plus 
potential is supplied through the electrode 38 and a minus potential is 
supplied through the electrode 41 in the same electrical connection 
arrangement as shown in FIG. 8, whereby the respective ceramic layers 35, 
36 and 37 expand as shown by circled bidirectional arrows in FIG. 8, while 
the ceramic layers 35 to 37 contract when the said potentials are 
inverted. Thus, the piezoelectric buzzer 30 expands and contracts 
similarly to a conventional unimorph type ceramic vibrator by alternately 
switched potentials such as in an AC signal, thereby to vibrate and 
generate sound waves. 
In the embodiment shown in FIG. 1, further, the electric connecting parts 
formed by the through-holes 34a, 34b, 42a and 42b are provided in the 
vicinity of the vibration node. In other words, the electric connecting 
parts 34 and 42 are formed in positions that are scarcely displaced by 
vibration of the piezoelectric buzzer 30, and hence the electric 
connecting parts will not restrict the vibration. Thus, desired sound 
pressure can be obtained. 
FIG. 9 shows an arrangement of electrical connections for a second 
embodiment of the present invention. The second embodiment also relates to 
a unimorph type vibrator, in which an even number of ceramic layers are 
formed, as opposed to an odd number in the first embodiment. In the second 
embodiment, four ceramic layers 51 to 54 are laminated between respective 
pairs of electrodes 55 to 59, and adjacent ones of the respective ceramic 
layers 51 to 54 are polarized in opposite directions. The electrodes 55 to 
59 are electrically connected with each other in an alternate manner by 
electric connecting parts 60 and 61, which are formed within respective 
through-holes. Thus, after the ceramic layers 51 to 54 are polarized in 
the directions shown by arrows in FIG. 9, a plus potential is supplied 
through the electrode 55 and minus potentials are supplied through the 
electrodes 56 and 58, which are connected with each other by the 
through-hole 60, whereby the respective ceramic layers 51 to 54 expand as 
shown by circled bidirectional arrows in FIG. 9 and contract upon 
inversion of the potentials, whereby the piezoelectric buzzer 30 can 
generate sound waves similarly to the embodiment as shown in FIG. 1. 
The structure of the embodiment shown in FIG. 9 will now be described with 
reference to FIGS. 10 and 11. First, as shown in FIG. 10, ceramic green 
sheets 51 to 54 (the ceramic green sheets are indicated by reference 
numerals identical to those of the corresponding ceramic layers in FIG. 9) 
for forming the ceramic layers 51 to 54 are prepared and provided with 
conductive paste layers 55 to 59 as shown in FIG. 10. Although the 
conductive paste layer 59 is formed on the back surface of the ceramic 
green sheet 54, i.e., on the surface opposite to the conductive paste 
layer 58, the same is shown as if it were separate from the green sheet 
54, for easy understanding of this embodiment. 
Referring to FIG. 10, the ceramic green sheet 51 is provided with 
through-holes 60a and 61a at locations in the vicinity of the vibration 
node of the vibration member obtained. The conductive paste layer 55 is 
partially removed from a portion around the periphery of the through-hole 
60a so that the through-hole 60a is not connected with the conductive 
paste layer 55. On the other hand, the through-hole 61a is connected with 
the conductive paste layer 55. In a similar manner, through-holes 60b and 
60c and through-holes 61b, 61c and 61d are formed in the ceramic green 
sheets 52, 53 and 54. The through-hole 60a is formed so as to be aligned 
with the through-holes 60b and 60c while the through-hole 61a is formed to 
be aligned with the through-holes 61b, 61c and 61d upon lamination of the 
ceramic green sheets 51 to 54. Around the periphery of the through-hole 
60a, a conductive part having an appropriate surface area may be formed on 
the ceramic green sheet 51 for connecting the piezoelectric buzzer 30 with 
an external device such as an AC signal source. 
The ceramic green sheets 51 to 54 as shown in FIG. 10 are laminated and 
cofired thereby to obtain a sintered body 62 as shown in FIG. 11. The 
conductive paste layers 55 to 59 are baked at the same time the sintered 
body 62 is obtained to serve as electrodes, which are hereafter described 
with the same reference numerals as the corresponding conductive paste 
layers. The electrodes 55 and 59 and the electric connecting part 60 may 
be formed simultaneously with or separately from the electrodes 56 to 58 
by baking, sputtering, vapor deposition or the like. The sintered body 62 
is provided with the electric connecting part 60 formed by the 
through-holes 60a, 60b and 60c and the electric connecting part 61 formed 
by the through-holes 61a, 61b, 61c and 61d, to obtain the electrical 
connection arrangement shown in FIG. 9. Thus, after polarization in the 
directions shown by arrows in the state of electric connection as shown in 
FIG. 9, a plus potential is supplied through the electrode 55 and a minus 
potential is supplied through the through-hole 60a, which is electrically 
connected with the electrodes 56 and 58, whereby adjacent ones of the 
respective ceramic layers 51 to 54 are polarized in opposite directions. 
Then, in a similar manner to the embodiment as shown in FIG. 1, the 
sintered body 60 is adhered to a vibration plate to be applied with 
driving voltage through the electrode 55 and the through-hole 60a, thereby 
to form a piezoelectric buzzer. For example, when a plus potential is 
applied through the electrode 55 and a minus potential is applied through 
the through-hole 60a, the respective ceramic layers 51 to 54 expand as 
shown by circled bidirectional arrows in FIG. 9, while the same contract 
upon inversion of the potentials. Thus, the potentials are alternately 
applied to obtain sound waves. 
In addition to the aforementioned unimorph type vibrators, the present 
invention is also applicable to a bimorph type vibrator, and description 
will now be made of embodiments which relate to such bimorph type 
vibrators. A bimorph type vibrator includes first and second vibrating 
regions expanding and contracting in directions reverse to each other, 
which vibrating regions are provided in the direction of thickness. 
FIG. 12 is a perspective view illustrating configurations of ceramic green 
sheets and electrodes which are employed in a third embodiment of the 
present invention. In the third embodiment, an odd number of ceramic green 
sheets 71, 72 and 73 are prepared and provided with conductive paste 
layers 74, 75, 76 and 77. The ceramic green sheet 71 is formed with 
through-holes 78a and 79a in positions close to a vibration node. The 
conductive paste layer 74 is removed in portions around the peripheries of 
the through-holes 78a and 79a so that the through-holes 78a and 79a are 
not electrically connected with the conductive paste layer 74. On the side 
of the green sheet 71 that has the conductive paste layer, conductive 
parts 80 and 81 are formed around the peripheries of, the through-holes 
78a and 79a, respectively, and are conductively connected therewith. The 
conductive parts 80 and 81 are provided to have appropriate surface areas, 
to be electrically connected with an external device. 
The ceramic green sheet 72 is also formed with two through-holes 78b and 
82b in positions close to the vibration node. The through-hole 78b is 
formed in a position aligned with the upwardly positioned through-hole 78a 
upon lamination. On the other hand, the through-hole 82b is formed in a 
position to be in contact with neither the upwardly positioned 
through-hole 79a nor 78a upon lamination. The electrode 75 is removed in a 
portion around the periphery of the through-hole 78b so that the 
through-hole 78b is not electrically connected with the electrode 75. 
The ceramic green sheet 73 is formed with a through-hole 82c similarly to 
the through-hole 78b, which through-hole 82c is formed in a position 
aligned with the upwardly positioned through-hole 82b. The through-hole 
82c is provided on its back surface side, i.e., on the the same side of 
the green sheet 73 as the electrode 77, with a conductive part 83, which 
can be connected with the through-holes 82b and 82c upon lamination. The 
conductive paste layer 77 is removed in a portion around the conductive 
part 83 so that the conductive part 83 is not connected with the 
conductive paste layer 77. 
The respective ceramic green sheets 71 to 73 as shown in FIG. 12 are 
laminated and cofired thereby to obtain a sintered body 84 as shown in a 
perspective view in FIG. 13. At the same time the sintered body 84 is 
obtained, the conductive paste layers 74 to 77 are baked to form 
electrodes, which electrodes will be hereafter described with the same 
reference numerals as the corresponding conductive paste layers. The 
electrodes 74 and 77 and the conductive parts 80, 81 and 83 may be 
simultaneously formed with the electrodes 75 and 76, or separately formed 
by baking, sputtering, vapor deposition or the like. 
In order to electrically connect the conductive parts 80 and 81 formed on 
the upper surface of the sintered body 84 for polarization, conductive 
paste, for example, is coated and baked to form a conductive part 85 for 
connection (see FIG. 15). Thus obtained is the electrical connection 
arrangement shown in FIG. 14. Namely, the electrodes 75 and 76 are 
electrically interconnected, via the through-holes 79 and 78, 
respectively, by the conductive part 85. Therefore, when a plus potential 
is supplied through the conductive part 85 for connection while minus 
potentials are supplied through the electrodes 74 and 77, the ceramic 
layers 71 and 73 are polarized as shown by arrows in FIG. 14 while the 
ceramic layer 72 is not polarized. 
Then, as shown in a perspective view in FIG. 16, the conductive part 85 is 
partially removed and thereby divided into conductive parts 85a and 85b, 
connection, thereby so as to cut off the electric connection of the 
through-holes 79 and 78. Further, the divided conductive part 85a, which 
is connected to the through-hole 78, is electrically connected with the 
electrode 74 by a conductive part 86. Then, the lowermost electrode 77, 
which is not shown in FIG. 16, is electrically connected with the 
conductive part 83 by, e.g., coating conductive paste and baking the same. 
Thus obtained is the electric connection arrangement shown in FIG. 17, in 
which the ceramic layer 71 serves as a first vibration region and the 
ceramic layer 73 serves as a second vibration region. Then, a plus 
potential is supplied through the divided conductive portion 85b while a 
minus potential is supplied through the electrode 74. This causes one of 
the ceramic layers, for example the first vibration region, to expand, 
while the other ceramic layer, for example the second vibration region, 
contracts, as indicated by bidirectional arrows in FIG. 17, which causes 
the entire bimorph to bend. Thus, the sintered body vibrates by alternate 
application of the potentials, to be employed as a piezoelectric buzzer. 
Also in this embodiment, the electric connecting parts 78, 79 and 82, which 
are formed by the through-holes, are provided in the vicinity of the 
vibration node as hereinabove described, whereby the vibration of the 
piezoelectric buzzer is not restricted. 
FIG. 18 is a perspective view showing configurations of ceramic green 
sheets and electrodes employed in a piezoelectric buzzer according to a 
fourth embodiment of the present invention. In the fourth embodiment, an 
even number of layers of ceramic green sheets 91, 92, 93 and 94 are 
prepared and provided with conductive paste layers 95 to 99. 
The respective ceramic green sheets 91 to 94 have through holes in the 
vicinity of a vibration node for forming electric connecting parts. More 
specifically, the ceramic green sheet 91 has through-holes 101a, 102a and 
103a formed in the vicinity of the vibration node, while the conductive 
paste layer 95 is partially removed so that the through-holes 101a and 
102a are not connected with the conductive paste layer 95. On the other 
hand, the through-hole 103a can be connected with the conductive paste 
layer 95. 
The through-holes 101a and 102a have connected to the peripheries thereof, 
conductive parts 104 and 105, respectively. 
In a similar manner, the ceramic green sheets 92 and 93 have through-holes 
102b and 102c formed in positions aligned with the through-hole 102a upon 
lamination, while the respective ceramic green sheets 92 to 94 have 
through-holes 103b, 103c and 103d formed in positions aligned with the 
through-hole 103a. Within these through-holes 103b, 103c and 103d, 
however, only the through-hole 103c is connected with the electrode 97 
positioned on the upper surface of the ceramic green sheet 93 which is 
provided with the through-hole 103c. 
The respective ceramic green sheets 91 to 94 as shown in FIG. 18 are 
laminated and cofired, thereby to obtain a sintered body 106 as shown in 
FIG. 19. The conductive paste layers 95 to 99 are baked at the same time 
the sintered body 106 is obtained to serve as electrodes, which are 
hereafter described with the same reference numerals as the conductive 
paste layers. The electrodes 95 and 99 and the conductive parts 104 and 
105 may be simultaneously formed with the electrodes 96 to 98, or may be 
separately formed by baking, sputtering, vapor deposition or the like 
after firing. 
FIG. 20 shows the electrical connections for polarizing the sintered body 
106. As shown in from FIG. 20, the conductive part 104 and the electrode 
96 are electrically connected with each other by an electric connecting 
part 101 which is formed in the through-hole 101a, while the conductive 
part 105 is electrically connected with the electrode 98 by an electric 
connecting part 102 which is formed in the through-holes 102a to 102c. 
Similarly, the electrode 95 is electrically connected with the electrodes 
97 and 99 by an electric connecting part 103 which is formed in the 
through-holes 103a to 103d. In this arrangement, when voltages V.sub.1, 
V.sub.2 and V.sub.3 having the relation V.sub.2 -V.sub.1 =V.sub.3 -V.sub.2 
are respectively applied through the conductive part 104, the electrode 95 
and the conductive part 105, the respective ceramic layers 91 to 94 are 
polarized in directions indicated by arrows in FIG. 20. 
Then, as shown in a perspective view in FIG. 21, a conductive part 107 is 
formed to electrically connect the conductive part 104 with the conductive 
part 105. FIG. 22 shows the electrical connections completed in the 
aforementioned manner. In order to drive the sintered body 106, a plus 
potential may be applied through the electrode 95 and a minus potential 
may be applied through the conductive part 107 for connection as shown in 
FIG. 22, whereby the ceramic layers 91 and 92 serving as a first vibrating 
region expand in the direction of thickness while the ceramic layers 93 
and 94 serving as a second vibrating region contract in the direction of 
thickness as indicated by circled bidirectional arrows in FIG. 22, and 
hence the sintered body 106 is downwardly bent as a whole. The plus and 
minus potentials may be alternately applied to the electrode 95 and the 
conductive part 107 so as to obtain sound pressure similarly to the 
piezoelectric buzzers according to the embodiments hereinabove described. 
Also in this embodiment, the electric connecting parts 101, 102 and 103 
for connecting the respective electrodes are provided in the vicinity of 
the vibration node as hereinabove described, whereby the vibration of the 
sintered body 106 is not restricted and sound waves can be obtained at 
desired sound pressure and at a desired frequency. 
Although embodiments of the present invention have been described and 
illustrated in detail, it is clearly understood that the same is by way of 
illustration and example only and is not to be taken by way of limitation, 
the spirit and scope of the present invention being limited only by the 
terms of the appended claims.