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DESCRIPTION JPH06269090

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DESCRIPTION JPH06269090
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric ultrasonic transducer using a piezoelectric ceramic element, and more particularly
to a piezoelectric ultrasonic transducer used for obstacle detection or distance measurement.
[0002]
In the following description, acoustic impedance refers to the ratio of sound pressure to volume
velocity.
[0003]
2. Description of the Related Art Piezoelectric ultrasonic transducers are also called ultrasonic
sensors or ultrasonic microphones, and are conventionally used in many fields.
FIG. 6 is a cross-sectional view schematically showing the simplest configuration of this type of
transducer. The case main body 32 is formed of a conductive thin plate whose peripheral edge is
bent and formed, the lid 33 is bonded and fixed to the opening side of the case main body 32,
and the case 34 having a sealed structure is formed by the case main body 32 and the lid 33. Is
configured. The piezoelectric ceramic element 31 formed in a substantially disc shape is adhered
to the inner central flat portion of the case main body 32, and the piezoelectric ceramic element
31 and the case main body 32 respectively have lead terminals 35a and 35b via lead wires 36a
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and 36b. The piezoelectric ultrasonic transducer 30 is constituted by the case 34, the
piezoelectric ceramic element 31 and the like. When an AC voltage is applied to the piezoelectric
ceramic element 31 through the lead terminals 35a and 35b, the piezoelectric ceramic element
31 stretches and contracts, causing the case body 32 to generate a sound wave, and this sound
wave It radiates in the direction of arrow A in the figure.
[0004]
FIG. 7 is a cross-sectional view schematically showing another piezoelectric ultrasonic transducer
40 conventionally used, and in the figure, 42 shows a case main body. The case body 42 is
formed in a substantially cylindrical shape using a material having a large acoustic impedance
and having a ceiling portion 42a, and a lid 43 is bonded and fixed to the opening 42b side of the
case body 42. A cover 44 and a case 44 of a sealed structure are formed. Furthermore, a disc
member 47 formed of a material having a small acoustic impedance is adhered to the ceiling
portion 42 a of the case main body 42. A piezoelectric ceramic element 41 formed in a
substantially disc shape is adhered to a central flat portion in the case main body 42, and the
electrodes 41a and 41b formed on both sides of the piezoelectric ceramic element 41 are
respectively connected via lead wires 46a and 46b. The piezoelectric ultrasonic transducer 40 is
connected to the lead terminals 45a and 45b, and the case 44, the piezoelectric ceramic element
41, and the like. When an AC voltage is applied to the piezoelectric ceramic element 41 through
the lead terminals 45a and 45b, the piezoelectric ceramic element 41 stretches and contracts,
causing the case body 42 to flex and vibrate. It propagates to the air through the member 47,
and a sound wave is emitted in the direction of arrow B in the figure (Japanese Utility Model
Laid-Open No. 62-177198).
[0005]
FIG. 8 is a cross-sectional view schematically showing a conventional piezoelectric ultrasonic
transducer 50 with a horn, wherein 55 is a case formed into a substantially hollow cylindrical
body shape using a conductive thin plate. Is shown. A piezoelectric ceramic element 51 formed in
a substantially disc shape is bonded to a substantially central portion of the case 55, and the
piezoelectric ceramic element 51 is held by the case 55 using a support 54. A conical horn 53
having a linear shape in cross section is disposed on the top surface of the piezoelectric ceramic
element 51, and an opening 57a and a plurality of sound emission holes 57b are formed on the
top surface of the case 55 above the conical horn 53. A parabolic horn 58 having a curved
surface shape that protrudes downward from the side surface of the case 55 to the upper side is
formed. Further, lead terminals 56a and 56b are fixed to the lower portion of the case 55, and
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the lead terminals 56a and 56b are connected to the piezoelectric ceramic element 51 via lead
wires, and these types 55, piezoelectric ceramic element 51, parabolic horn 58 etc. An ultrasonic
transducer 50 is configured. When an AC voltage is applied to the piezoelectric ceramic element
51 through the lead terminals 56a and 56b, the piezoelectric ceramic element 51 stretches and
vibrates, and this vibration propagates to the air through the conical horn 53 and is further
opened. A sound wave is emitted from the parabolic horn 58 in the direction of the arrow C in
the figure after passing through the portion 57a and the sound emission hole 57b (Japanese
Patent Application Laid-Open No. 58-85699).
[0006]
In recent years, there has been an increasing demand for accurate detection of longer distance
objects using sensors for detecting obstacles, measuring distances, etc. There is a need for a
piezoelectric ultrasonic transducer having a large sound pressure, a high S / N ratio, and a sealed
structure and environmental resistance.
[0007]
In the piezoelectric ultrasonic transducer 30 shown in FIG. 6, the case 34 has a sealed structure
and has environmental resistance.
However, since the density of air as a medium is smaller than that of the piezoelectric ceramic
element 31, it is difficult to apply an acoustic load to the air, and the vibration energy of the case
34 can not be sufficiently transmitted to the air. There was a problem that it was not possible to
make In addition, there is a problem that when the input energy is increased to increase the
sound pressure, the piezoelectric ceramic element 31 may generate heat or be damaged.
[0008]
Further, in the piezoelectric ultrasonic transducer 40 shown in FIG. 7, the case 44 has a sealed
structure and is environmentally resistant. Furthermore, although the disk member 47 with low
acoustic impedance is adhered on the case 44 and some improvement in acoustic matching to air
is achieved, there is still a problem that the sound pressure level of ultrasonic waves is
insufficient. The
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[0009]
Further, in the piezoelectric ultrasonic transducer 50 shown in FIG. 8, the conical horn 53 and
the parabolic horn 58 are disposed, or the opening 57a and the sound emission hole 57b are
formed, so that the acoustic matching with air can be improved. Somewhat is planned. However,
the sound pressure level of the ultrasonic wave is still insufficient, and the opening 57a and the
sound emission hole 57b do not provide a sealed structure, and the environmental resistance is
impaired.
[0010]
The present invention has been made in view of such problems, and it is possible to increase the
sound pressure of an ultrasonic wave to be transmitted, to increase the S / N ratio, and to
accurately detect long-distance ones. It is an object of the present invention to provide a
piezoelectric ultrasonic transducer capable of maintaining the environmental resistance in a
sealed structure.
[0011]
SUMMARY OF THE INVENTION In order to achieve the above object, a piezoelectric ultrasonic
transducer according to the present invention comprises a vibration case having a sealing
property to which a ring-shaped piezoelectric ceramic element is bonded, and the vibration case.
And a horn disposed at the front, wherein the horn has a shape substantially equal to the outer
contour of the piezoelectric ceramic element, and a vibration space located in front of the
piezoelectric ceramic element is formed, the inner side of the piezoelectric ceramic element It is
characterized in that the horn has an opening having a shape substantially equal to the contour,
and an opening located in front of the vibration space and a convex sound wave reflection
surface located in front of the opening.
[0012]
The piezoelectric ceramic element as a vibration source has an extremely large density with
respect to air as a sound propagation medium.
Therefore, when the piezoelectric ceramic element emits a sound wave, the acoustic load
received from air is extremely small, and hence the energy used as the sound wave is small.
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[0013]
In order to solve this problem, the inventors of the present invention conducted a vibration
measurement test using the apparatus shown in FIG.
In the figure, reference numeral 12 denotes a diaphragm formed in a disk shape, and it can be
considered that the diaphragm 12 is constituted by an internal diaphragm 12a and an external
diaphragm 12b as shown in FIG. 5 (b). . A ring-shaped piezoelectric ceramic element 11 is
adhered to the lower surface of the external diaphragm 12b to form a bimorph structure 24, and
the outer peripheral portion of the bimorph structure 24 is restrained and held by a clamp 25 or
the like. When power is supplied to the device 20 configured as above and the piezoelectric
ceramic element 11 is vibrated, the vibration is small in the external diaphragm 12b and large in
the internal diaphragm 12a as shown by the dotted line in the figure. It was obtained. Thus, in
the apparatus in which the ring-shaped piezoelectric ceramic element 11 is adhered to the
diaphragm 12, the acoustic load is easily applied because the internal diaphragm 12a portion is
light, and a large amplitude can be obtained. Makes it easy to On the other hand, since the
amplitude of the piezoelectric ceramic element 22 provided on the outer peripheral portion is
small, the heat generation and damage of the piezoelectric ceramic element 22 are reduced, the
reliability can be improved and the energy conversion efficiency is improved.
[0014]
According to the piezoelectric ultrasonic transducer according to the present invention, the
vibration case having a sealing property to which the ring-shaped piezoelectric ceramic element
is bonded, and the horn disposed in front of the vibration case are provided. It has a shape
substantially equal to the outer contour of the piezoelectric ceramic element, and a vibration
space located in front of the piezoelectric ceramic element is formed, has a shape substantially
equal to the inner contour of the piezoelectric ceramic element, and is forward of the vibration
space Since the opening located and the convex sound wave reflection surface located in front of
the opening are formed in the horn, acoustic load is applied to the diaphragm of the vibration
case inside the ring-shaped piezoelectric ceramic element. While being easy to take, the
amplitude becomes large, and it becomes easy to achieve acoustic matching with air. Further,
since the opening of the horn is formed in front of the vibration case inside the piezoelectric
ceramic element, and the sound wave reflection surface gradually spreads, acoustic matching
with air can be more easily achieved, so that Sound pressure can be further increased. As a result,
the S / N ratio is increased, and it is possible to accurately detect a far distance. In addition, since
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the outer peripheral portion of the piezoelectric ceramic element is restrained by the inner
peripheral surface of the horn, the vibration mode in which the vibration of the piezoelectric
ceramic element is suppressed is achieved, heat generation and breakage are prevented, and
acoustic efficiency can be enhanced. . Furthermore, since the vibration case is formed in a sealed
structure, environmental resistance is maintained, and the reliability of the piezoelectric
ultrasonic transducer can be improved.
[0015]
Examples and Comparative Examples Hereinafter, examples of the piezoelectric ultrasonic
transducer according to the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing a piezoelectric ultrasonic transducer
having a resonance frequency of about 30 kHz according to the embodiment, and 11 in the
figure shows a piezoelectric ceramic element. The piezoelectric ceramic element 11 is formed of
a material SPEM-6F and is formed in a ring shape having an outer diameter of approximately 14
mm, an inner diameter of approximately 8 mm, and a thickness of approximately 1.0 mm. The
diaphragm 12 is formed of a stainless steel into a substantially disc shape having a diameter of
30 mm and a thickness of 0.5 mm, and the piezoelectric ceramic element 11 is adhered to the
lower surface of the diaphragm 12 using an epoxy adhesive. ing. Further, a case main body 13
formed in a substantially cylindrical shape is adhered and fixed to the outer peripheral portion of
the diaphragm 12, and a substantially disc-shaped lid 14 is adhered and fixed to a lower portion
of the case main body 13. A vibration case 15 having a sealed structure is constituted by the case
body 13 and the lid 14. Lead terminals 16a and 16b are fixed to the lid 14, the lead terminal 16a
is connected to the piezoelectric ceramic element 11 through the lead wire 17a, and the lead
terminal 16b is connected to the diaphragm 12 through the lead wire 17b. . On the other hand, a
horn 18 is disposed on the vibration case 15. The horn 18 is made of aluminum and is formed in
a substantially cylindrical shape having an outer diameter of about 30 mm and a height of about
21 mm. A vibrating space 19 of approximately 14 mm and a height H of approximately 1.0 mm
is formed, and the vibrating space 19 is disposed above the outer diameter portion of the
piezoelectric ceramic element 11 with a tolerance of ± 0 mm. Further, an opening 19a having a
diameter of about 8 mm is formed at the upper center of the vibration space 19, and the opening
19a is disposed above the inner diameter (or diaphragm 12a) of the piezoelectric ceramic
element 11 with a tolerance of ± 0 mm. . Further, a sound wave reflection surface 19b is formed
above the opening 19a, and the sound wave reflection surface 19b is formed above the opening
19a in a curved shape having a convex shape in sectional view. The horn 18 and the vibration
case 15 are bonded and fixed to the lower end face 18a of the horn using an epoxy-based
adhesive, and the piezoelectric ultrasonic transducer 10 is configured.
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[0016]
Below, the result of having measured transmission sound pressure on the conditions of 30 cm x
10 Vrsm input using the piezoelectric ultrasonic transducer 10 comprised in this way is
demonstrated. As a comparative example, the conventional piezoelectric ultrasonic transducer 30
shown in FIG. 6 was used.
[0017]
FIG. 2 is a curve diagram showing the measurement results of transmission sound pressure, and
curve (a) shows the case of the example and curve (b) shows the case of the comparative
example. As is clear from this figure, the transmission sound pressure is about 120 dB in the case
of the example, and can be about 8 dB higher than 112 dB (compared with our case) in the
comparative example, and the effective sound pressure level is It could be increased about twice
or more.
[0018]
The piezoelectric ultrasonic transducer 10 according to the present embodiment can easily apply
an acoustic load to the vibration case 15 inside the ring-shaped piezoelectric ceramic element 11,
and can increase the amplitude, and Acoustic matching can be easily achieved. Further, since the
opening 19a of the horn 18 is formed in front of the vibration case 15 inside the piezoelectric
ceramic element 11, and the sound wave reflection surface 19b is gradually expanded, acoustic
matching with air can be made easier. The sound pressure in the air can be further increased. As
a result, the S / N ratio can be increased, and it is possible to accurately detect something at a
long distance. Further, since the outer peripheral portion of the piezoelectric ceramic element 11
is restrained by the horn inner peripheral surface 18a and the vibration mode is set to suppress
the vibration of the piezoelectric ceramic element 11, heat generation and breakage can be
prevented, and the acoustic efficiency is enhanced. Can. Furthermore, since the vibration case 15
is formed in a sealed structure, environmental resistance can be maintained, and the reliability of
the piezoelectric ultrasonic transducer 10 can be improved.
[0019]
In the embodiment, the resonance frequency is 30 kHz and the thickness H (FIG. 1) of the
vibration space 19 is about 1 mm. However, as shown in FIG. 3, the thickness of the vibration
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space 19 is another embodiment. When t is 2 mm and 0.5 mm, almost the same effect can be
obtained as in the embodiment.
[0020]
In the embodiment, the tolerance of the vibration space 19 and the opening 19a is set to ± 0
mm, but as shown in FIG. 4, the tolerance of the vibration space 19 and the opening 19a is within
± 10% of the respective dimensions. The same effect as in the case of the embodiment can be
obtained.
[0021]
In the embodiment, stainless steel is used as the material of the diaphragm 12. However, as
another embodiment, when an aluminum alloy such as duralmin, titanium, titanium alloy or the
like having a specific gravity smaller than that is used, it is more than that of the embodiment. As
the acoustic impedance decreases, higher sound pressure can be obtained.
[0022]
In the embodiment, a hard material corresponding to continuous input is used as the
piezoelectric ceramic element 11, but as another embodiment, a voltage sensitivity is set using a
soft material if it is used in a pulse or not continuously input. In addition, bimorph type devices
can be used to obtain higher performance transmission / reception characteristics.
[0023]
As described above in detail, in the piezoelectric ultrasonic transducer according to the present
invention, there is provided a vibration case having a sealing property to which a ring-shaped
piezoelectric ceramic element is bonded, and a vibration case in front of the vibration case. And a
horn having a substantially equal shape to the outer contour of the piezoelectric ceramic
element, wherein a vibration space is formed in front of the piezoelectric ceramic element, and
the inner contour of the piezoelectric ceramic element is formed. The ring-shaped piezoelectric
ceramic element has substantially the same shape, and an opening located in front of the
vibration space and a convex sound wave reflection surface located in front of the opening are
formed on the horn. The acoustic load can be easily applied to the diaphragm of the vibration
case at the inside of the case, and the amplitude can be increased, and acoustic matching with air
can be easily achieved. Can.
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Further, since the opening of the horn is formed in front of the vibration case inside the
piezoelectric ceramic element, and the sound wave reflection surface is gradually expanded,
acoustic matching with air can be achieved more easily. Sound pressure in the air can be further
increased.
As a result, the S / N ratio can be increased, and it is possible to accurately detect something at a
long distance.
Further, since the outer peripheral portion of the piezoelectric ceramic element is restrained by
the inner peripheral surface of the horn, a vibration mode is obtained in which the vibration of
the piezoelectric ceramic element is suppressed, heat generation and breakage can be prevented,
and acoustic efficiency is enhanced. Can.
Furthermore, since the vibration case is formed in a sealed structure, environmental resistance
can be maintained, and the reliability of the piezoelectric ultrasonic transducer can be improved.
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