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DESCRIPTION JP2011077919

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DESCRIPTION JP2011077919
An ultrasonic transducer for use in air that can be downsized and reduced in manufacturing cost
as compared with the prior art and can expand the degree of freedom of frequency adjustment
without using an adhesive or the like for bonding a piezoelectric element to a diaphragm portion.
And provide a method of manufacturing the same. An ultrasonic transducer (1) comprises a
cured resin (4), a piezoelectric element (3), and an element base (2). The element base 2 has a
hole axis along the main surface normal direction of the piezoelectric element 3. The cured resin
4 and the piezoelectric element 3 constitute a diaphragm portion that vibrates in the main
surface normal direction. The piezoelectric element 3 closes the inside of the cylinder of the
element base 2 at a position separated from the end of the element base 2 in the normal
direction of the main surface, and is driven in a spreading vibration mode in the main surface.
The cured resin 3 is injected and cured in a cylinder in the main surface normal direction than
the piezoelectric element 3 in the element base 2. [Selected figure] Figure 2
Ultrasonic transducer
[0001]
The present invention relates to an ultrasonic transducer that transmits or receives ultrasonic
waves by driving a piezoelectric body.
[0002]
As an ultrasonic transducer for air application, a piezoelectric element is bonded to the bottom of
a bottomed cylindrical case to form a diaphragm, and the piezoelectric element is spread and
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driven in a vibration mode to vibrate the bottom of the case to oscillate ultrasonic waves. The
following are known (see, for example, Patent Document 1).
Such an ultrasonic transducer is manufactured by attaching a piezoelectric element to the bottom
of a case with an adhesive. In this case, when the amount of adhesive and the bonding position
vary, there is a problem that the transmission / reception accuracy of ultrasonic waves also
varies. In order to suppress the variation of the adhesive, it is necessary to set the pressing
conditions precisely using a dedicated pressing jig and then carry out the bonding process. At
this time, if foreign matter is caught in the adhesive, the piezoelectric element may be broken, so
it is necessary to manage foreign matter, flatness and the like of the component.
[0003]
In addition, as an ultrasonic transducer for air use, the piezoelectric element, a cylindrical base
provided with a recess for housing the piezoelectric element, and the outer surface of the
piezoelectric element and the outer surface of the base are covered from the outside of the base.
There is known an ultrasonic sensor provided with an exterior material made of resin. The
ultrasonic transducer bends the exterior material by bending the piezoelectric element and drives
it in a vibration mode to oscillate an ultrasonic wave. (For example, refer patent document 2). FIG.
1A is a cross-sectional view for explaining an exterior material forming step in a conventional
ultrasonic transducer, and FIG. 1B is a plan cross-sectional view. In the exterior material forming
step, the ultrasonic transducer 101 in a state in which the piezoelectric element 103-the base
104-the weight 102-the sound absorbing material 105 are combined is put into the mold 111.
Then, a resin is injected and cured in a gap in the mold 111 to form the exterior material 106,
and the outside of the piezoelectric element 103 and the base 104 is molded with the exterior
material 106. Thereafter, the ultrasonic transducer 101 is manufactured by extracting it from the
mold 111.
[0004]
Japanese Utility Model Application Publication No. 09-284896 Publication WO2007 / 102460
[0005]
In the ultrasonic transducer having a configuration in which the piezoelectric element 103 is
covered with the exterior material 106, since the piezoelectric element 103 and the exterior
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material 106 can be joined with the resin serving as the exterior material 106 without using an
adhesive, The problem of variation can be avoided.
However, since the exterior material 106 is molded using the mold 111, a new problem occurs.
For example, in order to make the exterior material 106, a mold 111 is separately required, and
the process becomes complicated. Also, the exterior material 106 is formed by filling the resin
with the mold 111, but if the gap between the base 104 and the mold 111 is too narrow, the
resin becomes difficult to flow, so the exterior material 106 is formed. There is a limit in making
the thickness of the thin and a reduction in size as an ultrasonic transducer.
[0006]
Further, in the ultrasonic transducer, it is effective to bend the piezoelectric element 103 and the
package 106 at a desired resonance frequency, but in order to adjust the frequency, the package
106 is cut after the resin is cured. Sometimes. When frequency adjustment is performed by
cutting the exterior material 106, adjustment can be performed only in the direction in which the
frequency decreases, and adjustment can not be performed to increase the frequency. Also, it
takes much time for cutting time and removal of cutting chips.
[0007]
In view of the above problems, the present application does not use an adhesive or the like for
bonding the piezoelectric element to the diaphragm portion, and can be smaller in size and lower
in manufacturing cost than conventional, and can expand the degree of freedom of frequency
adjustment. The purpose is to provide an ultrasonic transducer for use.
[0008]
The ultrasonic transducer of the present invention comprises a diaphragm portion and a
cylindrical support portion.
The diaphragm portion vibrates along the main surface normal direction. The cylindrical support
portion has a hole axis along the main surface normal direction of the diaphragm portion. The
diaphragm portion includes a piezoelectric element and a hardening resin, and the piezoelectric
element closes the inside of the cylindrical support at a position away from the end of the
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cylindrical support in the normal direction of the main surface, and in the spreading vibration
mode It is driven. The cured resin is injected and cured in a cylinder in the main surface normal
direction with respect to the piezoelectric element in the cylindrical support portion. In this
configuration, the curing resin together with the piezoelectric element constitutes the diaphragm
portion, and the piezoelectric element spreads and vibrates, whereby the entire diaphragm
portion bends and vibrates. The cured resin is formed by using the cylindrical support portion as
a resin molding die, and a die is unnecessary. Therefore, the manufacturing cost can be reduced,
and a smaller ultrasonic transducer can be obtained. Further, by controlling the amount of resin
injected at the time of resin molding, it is possible to realize adjustment for reducing the
frequency of the ultrasonic wave and adjustment for increasing the frequency, and it is possible
to increase the degree of freedom of frequency adjustment.
[0009]
The tubular support portion of the present invention preferably includes a resin support member
and a space forming member. The cured resin is injected and cured in the resin support member.
The space forming member forms a vibration space of the diaphragm portion. In this
configuration, since the resin support member and the space forming member are separately
provided, their respective molding is easy, and the manufacturing cost can be reduced.
[0010]
Preferably, the space forming member of the present invention is made of a material having a
specific gravity greater than that of the cured resin and the resin supporting member. In this
configuration, since the peripheral edge of the resin supporting member is held by the space
forming member having a specific gravity greater than that of the resin supporting member,
unnecessary vibration is less likely to be transmitted to the space forming member, and
reverberation can be suppressed.
[0011]
The cylindrical support portion of the present invention is preferably provided with a thin
portion in the vicinity of the connection position with the piezoelectric element. When the
cylindrical support portion firmly fixes the piezoelectric element, the amplitude of the vibrating
portion may be reduced. However, by providing the thin portion, the amplitude of the diaphragm
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portion can be increased.
[0012]
According to this invention, in the ultrasonic transducer in which the entire vibration plate
portion vibrates in a bending manner, the cured resin can be molded using the cylindrical
support portion as a resin mold without using an adhesive or a mold. Therefore, since an
adhesive or the like is not used for bonding the piezoelectric element to the diaphragm portion, it
is possible to suppress the variation in transmission / reception accuracy caused by the
application variation of the adhesive. In addition, since no mold is used, the manufacturing
process is facilitated, and the creation of a small ultrasonic transducer is also facilitated.
[0013]
Furthermore, the frequency of the ultrasonic wave can be controlled by the amount of resin filled
in the cylindrical support portion, and not only adjustment to lower the frequency but also
adjustment to increase the frequency can be performed, and the degree of freedom of frequency
adjustment can be increased. It becomes possible.
[0014]
It is a figure explaining the manufacturing process of the ultrasonic transducer of a prior art
example.
It is a figure explaining the example of composition of the ultrasonic transducer concerning a 1st
embodiment of the present invention. FIG. 7 is a view illustrating the manufacturing process of
the ultrasonic transducer of FIG. 2; It is a figure explaining the example of frequency adjustment
of an ultrasonic wave. It is a figure explaining the example of composition of the ultrasonic
transducer concerning other embodiments of the present invention.
[0015]
Hereinafter, an ultrasonic transducer according to an embodiment of the present invention will
be described.
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[0016]
FIG. 2A is a schematic cross-sectional view of the ultrasonic transducer 1 according to the
present embodiment, and FIG. 2B is a schematic plan view of the ultrasonic transducer 1.
The ultrasonic transducer 1 is used as a back sonar, corner sonar, parking spot, etc. of a car, and
as a transmitter that transmits ultrasonic waves to a target, or a receiver that detects a reflected
wave from a target, ranging Used for devices etc.
[0017]
The ultrasonic transducer 1 includes an element base 2, a piezoelectric element 3, a cured resin
4, a weight 5, a mounting base 6, a sound absorbing material 7, driving terminals 8A and 8B, and
mounting terminals 9A and 9B. The element base 2 as a resin supporting portion has a shape in
which an opening is partially provided at the bottom of a bottomed cylindrical shape. The
piezoelectric element 3 has a disk shape whose polarization direction is in the normal direction
of the main surface, and is provided at a position closing the bottom opening in the cylinder of
the element base 2. The cured resin 4 is filled in the cylinder of the element base 2. The
piezoelectric element 3 and the cured resin 4 function as a diaphragm portion, and bend and
vibrate in the normal direction of the main surface by driving the piezoelectric element 3 in the
spreading vibration mode. The weight 5 as a space forming member has a cylindrical shape with
a bottom and supports the element base 2 by securing a vibration space of the diaphragm
portion on the side opposite to the main surface normal direction of the piezoelectric element 3.
The weight 5 is made of a material such as a metal having a specific gravity greater than that of
the element base 2 and the cured resin 4, and unnecessary vibration can not easily be
transmitted to the space forming member, thereby suppressing reverberation. The mounting
base 6 has a cylindrical shape made of an easy-to-process material, and supports the weight 5.
The element base 2, the weight 5, and the mounting base 6 as a whole have a bottomed
cylindrical shape, and constitute the cylindrical support portion of the present invention. The
sound absorbing material 7 is disposed in the vibration space to suppress reverberation in the
vibration space. The drive terminal 8A is soldered to an external electrode (not shown) provided
on the top surface of the piezoelectric element 3. The drive terminal 8 B is soldered to an
external electrode (not shown) provided on the lower surface of the piezoelectric element 3. The
mounting terminal 9A protrudes from the side surface of the mounting base 6 so as to be flush
with the bottom surface of the mounting base 6, and is connected to the drive terminal 8A. The
mounting terminal 9B protrudes from the side surface of the mounting base 6 so as to be flush
with the bottom surface of the mounting base 6, and is connected to the drive terminal 8B.
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[0018]
When the ultrasonic transducer 1 is used as a transmitter, the mounting terminals 9A and 9B are
connected to the drive electrodes of the set substrate to apply a drive signal. As a result, an
electric field is applied in the polarization direction (principal axis direction) of the piezoelectric
element 3 and a spread vibration in which the piezoelectric element 3 is expanded and
contracted in the radial direction is generated. Then, the diaphragm portion constituted by the
piezoelectric element 3 and the cured resin 4 is subjected to bending vibration, and ultrasonic
waves are transmitted. When the piezoelectric element 3 receives ultrasonic waves and vibrates
when it is used as a wave receiver, a wave receiving signal is generated between the drive
terminals 8A and 8B.
[0019]
In this configuration, the piezoelectric element 3 and the drive terminals 8A and 8B have a dripproof structure covered by the element base 2 and the cured resin 4 and have high
environmental resistance to water droplets, moisture, and the like. Further, the dimension in the
direction perpendicular to the main surface normal direction of the piezoelectric element is
mainly determined by the wall thickness of the weight 5, and this dimension can be changed
according to the product.
[0020]
Next, the manufacturing process of the ultrasonic transducer 1 will be described.
[0021]
FIG. 3 is a view for explaining the state of the ultrasonic transducer 1 in the manufacturing
process.
FIG. 3A is a state diagram in the mounting terminal installation process. In this process, the
mounting base 6 is prepared, and the mounting terminals 9A and 9B are mounted in the
mounting base 6 by insert molding. Following this process, a weight installation process is
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performed.
[0022]
FIG. 3 (B) is a state diagram in the weight installation process. In this process, a weight 5
provided with a hole for inserting a bar-shaped wire is prepared, and the weight 5 is mounted on
the mounting base 6 from the main surface normal direction while inserting the bar-shaped wire
into the hole of the weight 5. Following this process, a sound absorbing material installation
process is carried out.
[0023]
FIG. 3C is a state diagram in the sound absorbing material installation step. In this step, the
sound absorbing material 7 is prepared, and bonded to a position in the vibration space of the
weight 5 with an adhesive or the like. Following this step, an element-based mounting step is
carried out.
[0024]
FIG. 3D is a state diagram of the element base mounting step. In this process, the element base 2
is prepared, and the element base 2 is mounted on the weight 5 in the main surface normal
direction. As shown in FIG. 2B, the inner shape of the element base 2 is a substantially cylindrical
shape provided with an inner groove at two places, and is mounted on the weight 5 while
inserting a rod-like wire in the inner groove. Following this step, a piezoelectric element
mounting step is performed.
[0025]
FIG. 3E is a state diagram in the piezoelectric element mounting step. In this step, first, the drive
terminals 8A and 8B are soldered to both surfaces of the piezoelectric element 3 to form a
structure having a plan view on the right side in the figure. Then, this structure is mounted on
the element base 2 so that the rod-like wire enters into the holes provided in the drive terminals
8A and 8B. Then, the drive terminals 8A and 8B are soldered to the bar-like wires, respectively.
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Following this step, a resin filling and curing step is carried out.
[0026]
FIG. 3F is a state diagram in the resin filling and curing step. In this step, the liquid resin is
dropped into a dish-like space consisting of the element base 2 and the piezoelectric element 3,
and the liquid resin is filled up to the edge of the element base 2. Next, the liquid resin is heatcured using a heating device to produce a cured resin 4.
[0027]
In the resin filling and curing process, potting equipment can be used, and the manufacturing
cost can be reduced compared to using a mold and a filling equipment. Further, by controlling
the amount of resin to be injected, it is possible to realize adjustment to lower the frequency of
the ultrasonic wave and adjustment to increase the frequency.
[0028]
Next, an example of frequency adjustment of ultrasonic waves will be described. FIG. 4 (A) is a
partial perspective view of the ultrasonic transducer 11, FIG. 4 (B) is a cross-sectional view, and
FIG. 4 (C) is a graph showing an analysis result. Here, analysis is performed by the ultrasonic
transducer 11 having a configuration different from that of the above embodiment. In addition,
the same code | symbol is attached | subjected to the structure equivalent to the ultrasonic
transducer 1 shown in FIG. 2, and description is abbreviate | omitted.
[0029]
In this analysis, the frequency of ultrasonic waves was detected when the thickness (resin
thickness T) in the main surface normal direction of the diaphragm portion made of the cured
resin 4 and the piezoelectric element 3 was changed. When the resin thickness T was 0.20 mm,
0.25 mm, 0.30 mm, 0.35 mm, and 0.40 mm, the frequencies of the ultrasonic waves changed to
approximately 27 kHz, 30 kHz, 33 kHz, 37 kHz, and 41 kHz, respectively. From this, by
controlling the resin thickness T, it can be said that the frequency of the number of ultrasonic
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waves can be set arbitrarily. Therefore, it is possible to perform adjustment to increase the
frequency by increasing the resin thickness T by increasing the resin amount to be filled in the
resin filling and curing process, and reduce the frequency by reducing the resin amount T and
decreasing the resin thickness T. It will be possible to make adjustments. For example, frequency
adjustment can be performed by filling in a smaller amount than the resin amount assumed in
the resin filling and curing step, performing frequency measurement, and additionally filling in
the insufficient resin.
[0030]
Next, another embodiment of the present invention will be described.
[0031]
FIG. 5A is a cross-sectional view of the ultrasonic transducer 21.
The ultrasonic transducer 21 has a configuration in which the mounting base 6 in the ultrasonic
transducer 1 of the above-described embodiment is omitted and integrated with the weight 25.
[0032]
In this configuration, since the mounting terminals 9A and 9B are attached to the weight 25
made of a material such as metal having a large specific gravity, the weight 25 needs additional
processing, but the number of parts can be reduced.
[0033]
5B is a cross-sectional view of the ultrasonic transducer 31. FIG.
The ultrasonic transducer 31 has a configuration in which the weight 25 in the ultrasonic
transducer 21 of the above-described embodiment is omitted and integrated with the element
base 32.
[0034]
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In this configuration, by configuring the element base 32 with a material such as metal having a
large specific gravity, it is possible to realize the function of reflecting the ultrasonic wave by the
weight. However, in that case, in addition to the additional processing for attaching the mounting
terminals 9A and 9B to the element base 32, it is necessary to perform additional processing for
configuring the vibration space of the diaphragm portion. The score can be reduced.
[0035]
FIG. 5C is a cross-sectional view of the ultrasonic transducer 41. The ultrasonic transducer 41
includes an element base 42 in which a thin portion 40 is formed in proximity to a connection
position with the piezoelectric element 3 instead of the element base 32 in the ultrasonic
transducer 31 of the above-described embodiment. The thin portion 40 is provided around the
outer periphery of the element base 42.
[0036]
In this configuration, even if the piezoelectric element 3 is firmly fixed by the metal element base
42, the thin portion 40 weakens the restraint to increase the amplitude of the bending vibration
of the piezoelectric element 3 and the cured resin 4 it can.
[0037]
FIG. 5D is a plan view for explaining a configuration example of the distance measuring device
51. FIG.
The distance measuring device 51 uses ultrasonic transducers 52, 53 having substantially the
same shape as the ultrasonic transducer 1 described above as a transmitter and a receiver, and
the ultrasonic transducers 52, 53 have a common weight. 55 (and a common mounting base) and
integrated.
[0038]
1, 11, 21 Ultrasonic transducer 2. Element base 3 Piezoelectric element 4 Cured resin 5 Weight 6
Mounting base 7 Sound absorption material 8A, 8B Drive terminal 9A, 9B Mounting terminal
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