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DESCRIPTION JP2014213278

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DESCRIPTION JP2014213278
Abstract: To select a case material capable of suppressing reverberation time. SOLUTION: A
plurality of case materials each made of an aluminum alloy manufactured under different
processing conditions are prepared. The particle size of the aluminum alloy contained in each of
the case materials is measured. An ultrasonic transducer is produced using a case material, and
each characteristic is measured. The particle size of the aluminum alloy and the characteristics of
the ultrasonic transducer are compared. Based on the comparison result, the case material used
to manufacture the case of the ultrasonic transducer is selected. [Selected figure] Figure 2
Ultrasonic transducer and method of selecting case material
[0001]
The present invention relates to an ultrasonic transducer and a method of selecting a case
material, and in particular, an ultrasonic transducer comprising a bottomed cylindrical case and a
piezoelectric element provided on the inner bottom surface of the case, and such an ultrasonic
transducer The present invention relates to a method of selecting a case material to be selected
as a material for manufacturing a case of
[0002]
Japanese Patent No. 4048886 (Patent Document 1) discloses an invention related to an
ultrasonic sensor.
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1
An ultrasonic sensor is an example of an ultrasonic transducer. A general ultrasonic transducer
includes a bottomed cylindrical case and a piezoelectric element provided on the inner bottom
surface of the case. When the piezoelectric element is driven, the piezoelectric element spreads
and vibrates. As a result, the bottom of the case vibrates bending, and the bottom of the case can
obtain a large displacement.
[0003]
Patent No. 4048886 gazette
[0004]
Ultrasonic sensors are one of the important characteristics of reverberation time.
When an ultrasonic sensor is used, for example, in a parking assist system of a car, when the
reverberation time is long, the electric signal reflected back from the obstacle is hidden in the
electric signal of the reverberation and exists nearby. It becomes difficult to detect an obstacle
properly. The shorter the reverberation time, the more the ultrasonic sensor can detect near
obstacles with high accuracy.
[0005]
The ultrasonic sensor generates ultrasonic waves by bending. As the metal material (case
material) of the case, it is preferable to select a material that is light and has a high coefficient of
restitution, in view of achieving high sound pressure and high sensitivity with ultrasonic waves.
Among such case materials, aluminum is often used in view of weathering reliability.
[0006]
In general, adopting a configuration that increases the amplitude of vibration to obtain high
sound pressure and high sensitivity, and adopting a configuration that quickly converges the
vibration to shorten reverberation time are generally used. It is in a contradictory relationship.
For example, in order to realize a shorter reverberation time, methods such as devising the shape
of the case, applying a damping material, or using a foamable resin are used. Often conflicting
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with high sound pressure and high sensitivity characteristics.
[0007]
In addition, the shape of the case is an important factor that determines the frequency,
directivity, etc., and thus there are many design restrictions. The method of strengthening the
damping makes it difficult to realize high sound pressure and high sensitivity. Foamable resins
are difficult to manage in foam and are likely to vary in characteristics.
[0008]
The present invention has been made in view of the circumstances as described above, and
manufactures an ultrasonic transducer that can realize suppressing reverberation time as
compared with the conventional case, and a case of such an ultrasonic transducer. It is an object
of the present invention to provide a method of selecting a case material to be selected as a case
material.
[0009]
The method of selecting a case material based on the present invention is selected as a material
of the case for manufacturing the case of an ultrasonic transducer including a cylindrical case
having a bottom and a piezoelectric element provided on the inner bottom surface of the case.
Method of selecting the case material to be made, which is a first step of preparing a plurality of
case materials made of aluminum alloy respectively manufactured under different processing
conditions, and particles of the aluminum alloy contained in each of the plurality of case
materials A second step of measuring the diameter, a third step of manufacturing a plurality of
ultrasonic transducers using a plurality of the case materials, and measuring characteristics of
each of the plurality of ultrasonic transducers, and a measurement in the second step The
particle size of the aluminum alloy contained in each of the plurality of case materials obtained
as a result and the plurality of ultrasonic transformers obtained as a measurement result in the
third step And a fourth step of comparing the respective characteristics of Yusa, based on the
comparison result of the fourth step, a fifth step of selecting a case member used for
manufacturing the case of the ultrasonic transducer, the.
[0010]
Preferably, in the second step, the particle size of the aluminum alloy is measured by image
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analysis.
Preferably, the comparison in the fourth step is performed by evaluating the particle diameter of
the aluminum alloy contained in each of the plurality of case materials obtained as the
measurement result in the second step by cumulative distribution.
[0011]
An ultrasonic transducer according to the present invention includes a bottomed cylindrical case
made of an aluminum alloy, and a piezoelectric element provided on the inner bottom surface of
the case, the case being included in a predetermined area of the case When the maximum value
of the particle diameter of each particle is drawn as a cumulative distribution from the small
diameter side, the particle diameter D50 at 50% of the accumulated particles becomes 150 μm
or less, and the arbitrary particle of the aluminum alloy particle group The condition that the
particle diameter D90 which is 90% of the accumulation becomes 260 μm or less is satisfied.
[0012]
An ultrasonic transducer according to another aspect of the present invention comprises a case
material selected by the above method for selecting a case material according to the present
invention.
[0013]
According to the present invention, it is possible to realize an ultrasonic transducer which can
reduce the reverberation time as compared to the prior art, and to select a case material to be
selected as a case material for manufacturing such an ultrasonic transducer case. You can get the
way.
[0014]
It is a sectional view showing an ultrasonic sensor in an embodiment.
It is a figure which shows the material of 6 types of case materials prepared as a candidate in the
case material selection, processing conditions, and a particle size regarding the selection method
of the case material in embodiment.
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It is a figure which each shows observation visual field RR (predetermined area | region)
corresponding to case material 1. FIG.
It is a figure which each shows the observation visual field RR (predetermined area | region)
corresponding to the case material 2. FIG.
It is a figure which each shows observation visual field RR (predetermined area | region)
corresponding to case material 3. FIG. It is a figure which shows the observation visual field RR
(predetermined area | region) corresponding to the case material 4, respectively. It is a figure
which shows the characteristic of six ultrasonic transducers produced using each of case
materials 1-6.
[0015]
Hereinafter, an embodiment based on the present invention will be described with reference to
the drawings. When the number, amount, and the like are mentioned in the description of the
embodiment, the scope of the present invention is not necessarily limited to the number, the
amount, and the like unless otherwise specified. In the description of the embodiments, the same
parts and corresponding parts may be denoted by the same reference numerals, and repeated
descriptions may not be repeated.
[0016]
Embodiment With reference to FIG. 1, an ultrasonic transducer 100 in the embodiment will be
described. FIG. 1 is a cross-sectional view showing an ultrasonic transducer 100. The ultrasonic
transducer 100 includes a case 10, a piezoelectric element 20, a sound absorbing material 30, a
substrate 40, external connection terminals 51 and 52, internal wires 53 and 54, and a filler 60.
[0017]
The case 10 includes a disk-shaped bottom plate and a cylindrical side wall provided along the
periphery of the bottom plate. The case 10 has a bottomed cylindrical shape in which the lower
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end 11 side is closed and the upper end 12 side is opened. The inner surface of the bottom plate
is an inner bottom surface 13. The case 10 is made of a highly elastic and lightweight aluminum
alloy. The case 10 is manufactured by cutting a case material made of such an aluminum alloy.
[0018]
The piezoelectric element 20 is made of, for example, a lead zirconate titanate ceramic. The
piezoelectric element 20 is disposed on the inner bottom surface 13 of the case 10 and is fixed to
the inner bottom surface 13 using an adhesive or the like. The piezoelectric element 20 has a flat
plate shape, and a drive electrode pair is provided on both flat plate surfaces. The sound
absorbing material 30 is made of felt or the like, one main surface is in contact with the
piezoelectric element 20, and the other main surface is in contact with the filler 60. The present
invention is not limited to this configuration, and the sound absorbing material 30 may be
provided so as to face the piezoelectric element 20 without being in contact with the
piezoelectric element 20.
[0019]
The substrate 40 is disposed in the case 10 and sealed by the filler 60. The filler 60 is filled in
the space on the upper end 12 side of the sound absorbing material 30 inside the cylinder of the
case 10. The lower end portions in FIG. 1 of the external connection terminals 51 and 52 are
electrically connected to the substrate 40, and the upper end portions in FIG. 1 are drawn out
from the inside of the cylinder of the case 10. The internal wiring 53 electrically connects the
external connection terminal 51 to the piezoelectric element 20. The internal wiring 54
electrically connects the external connection terminal 52 to the piezoelectric element 20.
[0020]
The piezoelectric element 20 spreads in the radial direction and vibrates when a drive voltage is
applied. When the ultrasonic transducer 100 is used as a transmitter, a drive signal is applied to
the piezoelectric element 20 through the external connection terminals 51 and 52. The
piezoelectric element 20 spreads and vibrates, and bending vibration is excited on the bottom of
the case 10, whereby the ultrasonic transducer 100 transmits ultrasonic waves. On the other
hand, when the ultrasonic transducer 100 is used as a wave receiver, the bottom surface of the
case 10 receives ultrasonic waves and vibrates, causing the piezoelectric element 20 to spread
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and vibrate to the external connection terminals 51 and 52. A receive signal is generated. The
relationship between the drive signal and the heavy wave signal also allows the ultrasonic
transducer 100 to function as an ultrasonic sensor.
[0021]
(Selection Method) In order to manufacture the case 10 of the ultrasonic transducer 100, an
optimal case material is selected as the material of the case 10. Hereinafter, an example of a
method of selecting a case material will be described. FIG. 2 is a diagram showing materials,
processing conditions, and particle sizes of six types of case materials (case materials 1 to 6)
prepared as candidates for selecting an optimal case material.
[0022]
As shown in FIG. 2, the materials of the case members 1 to 6 are all aluminum alloy A5052 (the
numerical value after A indicates the type according to JIS). The heat treatment time to be added
to each aluminum alloy when producing case materials 1 to 6 is 4 hours, 8 hours, 16 hours, 32
hours, 16 hours, and 16 hours, respectively. From each of the case materials 1 to 6, six types of
cases 10 having the same shape and the same size are manufactured by cutting. These six cases
10 are each made of an aluminum alloy manufactured under different processing conditions, and
have different particle sizes.
[0023]
Next, the particle size of the aluminum alloy contained in each of the six cases 10 is measured.
The said measurement is performed as follows, for example. First, etching processing is applied
to the surfaces of the six cases 10 to make them easy to observe, and then the surfaces of the
cases 10 are observed using a scanning electron microscope (SEM). At this time, in the surface of
the case 10, an arbitrary predetermined area is set as an observation field of view RR (see FIGS. 3
to 6), and two diagonal lines L1 and L2 are drawn in the observation field of view RR.
[0024]
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3 to 6 respectively show, as an example, the observation visual field RR of the case 10
corresponding to the case materials 1 to 4 in FIG. The particle groups M1 to M4 of the case 10
corresponding to the case materials 1 to 4 are respectively illustrated in FIGS. With respect to the
particle group M1 of the case 10 corresponding to the case material 1, 100 particles are
arbitrarily selected from the particles intersecting (minimizing) the diagonal lines L1 and L2.
[0025]
More specifically, in the particle group M1 (FIG. 3) of the case 10 corresponding to the case
material 1, 100 particles are arbitrarily selected from the particle groups intersecting the
diagonal lines L1 and L2. Also in the particle group M2 (FIG. 4) of the case 10 corresponding to
the case material 2, 100 particles are arbitrarily selected from the particle groups intersecting
the diagonal lines L1 and L2. This is similarly performed for case 10 corresponding to case
materials 3 to 6.
[0026]
For each of the 100 particles, the maximum value of the particle size of each particle is measured
in the minimum measurement unit (for example, 5 μm). When a scanning electron microscope is
used, a two-dimensional image (photograph) is obtained. Focusing on one particle depicted in
this two-dimensional image, any point on the outline forming the outer edge of the particle and
any other point on the outline forming the outer edge of the particle Of the straight lines
connecting the points, the longest is taken as the maximum value of the particle size. This is done
similarly for each of the 100 particles. The maximum value of the grain size of the aluminum
alloy can be easily measured by such image analysis using a scanning electron microscope.
[0027]
The maximum value of the particle diameter of each of the 100 particles obtained by the above
measurement is sequentially drawn as a cumulative distribution from the smaller diameter side
(the smaller one). This is performed for each of the cases 10 corresponding to the case materials
1 to 6. In FIG. 2, for each of the cases 10 corresponding to the case materials 1 to 6, the value of
the particle diameter D10 which is 10% cumulative, the value of the particle diameter D50 which
is 50% cumulative, and the particle diameter which is 90% cumulative It shows the value of D90.
As to the case material 5 and the case material 6, although the basic material is common to
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A5052, the detailed composition values (not shown) are different, so the value of particle
diameter D10 and the value of particle diameter D90 And are different from each other.
[0028]
Referring to FIG. 7, next, six ultrasonic transducers are manufactured using each of case
materials 1 to 6. After the ultrasonic transducer made of the case material 1 is manufactured, the
characteristics of the ultrasonic transducer, such as reverberation time, sound pressure,
sensitivity, resonant frequency, and directivity (full width at half maximum), are measured. The
same is applied to case materials 2 to 6 as well. These measurement results are shown in FIG.
[0029]
As shown in FIG. 7, six ultrasonic transducers manufactured using each of case materials 1 to 6
have substantially the same characteristics in sound pressure, sensitivity, resonance frequency
and directivity (full width at half maximum) ing. On the other hand, the reverberation time of the
case materials 4 and 6 is longer than that of the case materials 1 to 3 and 5. Comparing FIG. 2
(the particle size of the aluminum alloy contained in each of the case materials 1 to 6 obtained as
the measurement result) with FIG. 7 (the characteristics of each of the six ultrasonic transducers
obtained as the measurement result), The following comparison results are obtained.
[0030]
When the case materials 1 to 4 are compared, it is understood that, for the case material 4, the
value of the particle diameter D50 which is 50% of the accumulation exceeds 150 μm and is the
largest among the case materials 1 to 6. That is, it can be read that the grain size of the
aluminum alloy changes with the heat treatment time at the time of case manufacture. Further,
when Case Material 3 and Case Materials 5 and 6 are compared, in Case Material 6, the value of
the particle diameter D90 which becomes 90% of the accumulation exceeds 260 μm, and is the
largest among Case Materials 1 to 6 Recognize. Furthermore, as for the case material 6, it can be
read that the variation in particle diameter is also larger than that of the other case materials.
The case materials 1 to 3 satisfy the conditions that the particle diameter D50 of 50% in
cumulative amount is 150 μm or less and the particle diameter D90 of 90% in cumulative
amount is 260 μm or less.
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[0031]
Therefore, from the comparison results of FIG. 2 and FIG. 7, it is understood that the
reverberation time can be set to 1.2 ms or less by using the case materials 1 to 3 and 5. In other
words, select a case material that satisfies the condition that the 50% cumulative particle
diameter D50 is 150 μm or less and the 90% cumulative particle diameter D90 is 260 μm or
less, and the case 10 made of such a case material is selected. By using it, it turns out that the
reverberation time of the ultrasonic transducer 100 can be made 1.2 ms or less.
[0032]
The case materials 1 to 6 all have different particle sizes but have substantially the same
characteristics in sound pressure, sensitivity, resonance frequency and directivity (full width at
half maximum). The difference in particle size is considered to have little effect on these
properties. On the other hand, in order to shorten the reverberation time, the vibration of the
aluminum case must be reduced in a short time. In order to reduce the vibration quickly, it is
necessary to quickly consume the energy of the vibration, and for this purpose, it is possible to
quickly converge the vibration by consuming kinetic energy by the vibration in some way.
[0033]
It is thought that such a result is obtained by decreasing the grain size of aluminum, the grain
boundary (the contact area between the grain and the grain) increases, and the frictional heat
generated at the grain boundary increases. Be That is, by making the grain size smaller and
making grain boundaries larger, kinetic energy can be efficiently converted into thermal energy
in a short time, so that the vibration converges quickly and the reverberation time can be
shortened. It is considered possible. It is preferable not only to reduce the particle size but also to
reduce the variation in particle size.
[0034]
The aluminum alloy itself is a material having a large thermal conductivity, and the converted
heat rapidly diffuses and disappears. Therefore, it is considered that converting the kinetic
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energy generated at the bottom of the case 10 into thermal energy in a short time has a great
effect on shortening the reverberation time. In this embodiment, paying attention to the particle
size of aluminum alloy which is one element for converting kinetic energy into thermal energy in
a short time, the reverberation time and the particle size are compared, and the particle size is
smaller. Select case material.
[0035]
Therefore, the ultrasonic transducer 100 provided with the case 10 made of the case material
selected by the selection method focusing on the particle size and the reverberation time can
realize that the reverberation time can be reliably suppressed as compared with the related art.
[0036]
In the method of selecting the case material of the present embodiment, the particle diameter of
the aluminum alloy contained in each of the case materials 1 to 6 is evaluated by the cumulative
distribution (10%, 50%, 90%). The particle diameter of the aluminum alloy contained in each of
the case materials 1 to 6 may be evaluated by the method of the above, and one having a smaller
reverberation time may be selected.
The number of case materials 1 to 6 is not limited to six, and a plurality of other case materials
may be prepared and selected.
[0037]
In the present embodiment, the grain size of the aluminum alloy is measured by image analysis
using a scanning electron microscope. However, the grain size of the aluminum alloy is not
limited to the image analysis method, and may be measured by an intercept method or the like.
Good. The intercept method is a method in which several arbitrary straight lines are drawn in an
image, and the number of particles crossing the straight lines (intercept number) is measured to
determine the average particle size of the particles.
[0038]
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The measurement of the particle size is not limited to the above-mentioned method, and, for
example, geometric diameter such as sieve diameter, Martin diameter, directional diameter,
equivalent diameter such as volume equivalent diameter, circle equivalent diameter, sphere
equivalent diameter It may measure by what is substituted to the diameter of the sphere
equivalent to physical quantity. The evaluation method of the particle size is not limited to the
above-described method, and may be calculated according to various average particle diameter
definition expressions such as number average, length average, and area average. As the average
particle size, “arithmetic mean value of particle diameter” defined in JIS Z 8901: 2006 “Test
powder and test particle” may be adopted, or arithmetic mean, median value and representative
value It may be evaluated by a statistical method such as diameter.
[0039]
In the present embodiment, an A5000 series aluminum alloy containing A5052 is used as a case
material to be selected. The A5000 series aluminum alloy is stronger than the A1000 series
aluminum having a purity of 99% or more, and hardly deforms even if it receives an external
factor. The present invention is not limited to the A5000 series aluminum alloy, and the present
embodiment can be applied in the same manner as described above even when another type of
aluminum alloy is used as a case material selection target.
[0040]
In the above-mentioned ultrasonic transducer 100, although the piezoelectric element 20
consists of lead zirconate titanate ceramics, it is not restricted to this. For example, the
piezoelectric element 20 may be made of a piezoelectric material of lead-free piezoelectric
ceramics such as potassium sodium niobate and alkaline niobate ceramic. In the abovementioned ultrasonic transducer 100, although external connection terminals 51 and 52 have
pin terminal shape, it does not restrict to this. For example, each pin terminal may be a lead wire.
[0041]
As mentioned above, although embodiment based on this invention was described, embodiment
disclosed this time is an illustration and restrictive at no points. The technical scope of the
present invention is indicated by the claims, and is intended to include all modifications within
the meaning and scope equivalent to the claims.
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[0042]
The ultrasonic transducer according to the present invention may be used, for example, as a back
sonar of a car, a corner sonar of a car, and a parking spot sensor for detecting the presence of a
space between an obstacle such as a side wall in parallel parking and the car. it can.
[0043]
DESCRIPTION OF SYMBOLS 10 case, 11 lower end, 12 upper end, 13 inner bottom, 20
piezoelectric elements, 30 sound absorbing materials, 40 board | substrates, 51, 52 external
connection terminal, 53, 54 internal wiring, 60 filler, 100 ultrasonic transducer, L1, L2 diagonal ,
M1 to M4 particle group, RR observation field of view.
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