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DESCRIPTION JPH04126498

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DESCRIPTION JPH04126498
[0001]
[Industrial field of application] The present invention relates to an ultrasonic sensor. The acoustic
impedance of a ceramic or magnetostrictive transducer has an order of magnitude greater
impedance than that of the medium, and it is necessary to match the acoustic impedance
between the transducer and the medium in order to increase the acoustic radiation efficiency. .
Conventionally, as a means for this purpose, a composite material obtained by kneading organic
or inorganic micro hollow spheres in a polymer (silicon, epoxy, etc.) resin is used to obtain an
acoustic impedance intermediate between the transducer and the medium, and Composite
members have been applied to the sound emitting surface of the transducer and used as
matching layers. However, it is difficult to knead the hollow spheres into a polymer resin
uniformly in density, and it is necessary to perform vacuum degassing to remove air bubbles
generated by the air introduced when kneading them, Since micro hollow spheres are powders
with extremely low specific gravity, special consideration is required to prevent scattering into
the air during the kneading process, and the linear expansion coefficient of the polymer
matching layer material and that of the transducer Because they are different, they have more
stable performance, such as a large characteristic fluctuation due to ambient temperature
changes, and also there are many difficult problems in manufacturing them by economical
means, and as a result, they are stable and yet An inexpensive ultrasonic sensor could not be
provided as a product. [Problems to be solved by the present invention] In the present invention,
temperature change is achieved by stabilizing the manufacturing process of the ultrasonic sensor
and increasing the economic effect, and by using a matching material close to the linear
expansion coefficient of the transducer. It is an object of the present invention to provide an
ultrasonic transducer having stable characteristics with respect to the above, and causes a large
cause of the performance of the ultrasonic sensor, dispersion due to mismatch of acoustic
impedance of air or liquid as medium, and use environment. The characteristic variation due to
13-04-2019
1
the temperature change is improved by the economical material and the manufacturing method
to stabilize the effective performance. It is well known that the cause of acoustic impedance
mismatch is that the difference between the acoustic impedance of the transducer and the
medium is quite different. To prevent this, a layer with an impedance matching function is placed
between them. It is also well known that doing is a good idea. However, as mentioned above, the
method for stably and economically producing these aligning members has not been established
yet. [Means for Solving the Problems] In the present invention, an inorganic fiber material widely
known as a heat insulating material is used as a matching member, and for example, a fibrous
material comprising calcium silicate needle crystals of Tobermolite, Xonotlite. Is produced by
reacting lime and silicic acid in an autoclave (the production conditions are 160-180 ° C. in the
former case and 180-220 ° C. in the latter case), and in general, the slurry is press-formed Are
used.
These fibrous materials are easy to form an air layer and have a very low bulk density of 0.1 to
0.4. And heat resistance temperature 1000 ° C, fire resistance, from the point where good
processability is widely used as heat insulation, heat insulation such as chemical industry,
construction interior as heat insulation material, heat insulation material. On the other hand, as
an ultrasonic transducer, the acoustic impedance of the acoustic matching member required is a
geometric mean value of the acoustic impedance of each of the transducer and the medium from
the generally known matching condition, and its thickness is 1/4 wavelength It is desirable that
when the medium is air, the acoustic impedance of air at normal temperature is about 400 kg /
m 2 S, and when the transducer is ceramic, the acoustic impedance is 30 × 10 6 kg / m 2 S.
Therefore, the matching layer preferably has an acoustic impedance value of 1.1 × 10 5 kg / m
2 S. The acoustic impedance of the said material is about 0.7-2.8 * 10 <5> kg / m <2> S, and the
conditions as an acoustic matching member are satisfy | filled. [Operation] The acoustic matching
layer made of this material radiates the energy generated from the transducer into the medium
very efficiently, and the radiation level shows a value equal to or higher than that of the plastic
matching layer according to the conventional method. Also, the thermal expansion coefficient (of
this matching material) is close to about 1 × 10 −6 / ° C. and the thermal expansion
coefficient of the transducer 6 to 10 × 10 −6 / ° C., and the heat of the bonding surface of the
transducer and the matching material The mechanical stress due to the factor is significantly
reduced as compared with the polymer matching material, and it is possible to obtain a stable
characteristic against temperature change in the use environment. [Example 1] An ultrasonic
sensor comprising an inorganic fiber, for example, a calcium silicate plate attached to the sound
wave emitting surface of a piezoelectric element, and an outer peripheral portion thereof fixed by
metal or plastic ring having acoustic impedance larger than its acoustic impedance. Shows very
stable performance. [Example 2] A polymer based resin (silicon, epoxy, etc.) is impregnated into
the transducer surface of the matching material of the previous embodiment, and the matching
member provided with a gradient of acoustic impedance in the sound wave radiation direction
has more stable characteristics. You can get Of course, it is also possible to use the resin to be
13-04-2019
2
impregnated for bonding the transducer and the matching material. [Effects of the Invention] The
present invention is intended to supply the market at the most economical price as well as
performance by using generally known stable materials as matching members. It is also effective
to apply resin coating on the surface, side or whole of the ceramic matching layer to improve the
moisture resistance and waterproofness, and to stabilize the characteristics of the ultrasonic
sensor.
Furthermore, it is also within the scope of the present invention to have an acoustic impedance
gradient inside by positively utilizing the porosity and water absorption of the matching member
and impregnating the silicon or epoxy resin on the transducer affixing side of the matching
material. It belongs to. Also, if a layer made of silicon or epoxy resin is added to the transducer
side as the second matching layer, and the above matching layer is superposed on the transducer
side, the impedance matching between layers is extremely smooth, and a plurality of
conventional matchings are performed. It is possible to reduce the reflection of sound waves on
the matching layer superposition surface, which has been considered as a drawback in the case
of providing a layer. An ultrasonic sensor having such a configuration has extremely stable
characteristics.
[0002]
Brief description of the drawings
[0003]
1 and 2 are cross-sectional views showing the structure of an airborne ultrasonic sensor
according to an embodiment of the present invention, and FIG. 3 is a structural cross-sectional
view of a conventional ultrasonic sensor.
[Industrial field of application] The present invention relates to an ultrasonic sensor. The acoustic
impedance of a ceramic or magnetostrictive transducer has an order of magnitude greater
impedance than that of the medium, and it is necessary to match the acoustic impedance
between the transducer and the medium in order to increase the acoustic radiation efficiency. .
Conventionally, as a means for this purpose, a composite material obtained by kneading organic
or inorganic micro hollow spheres in a polymer (silicon, epoxy, etc.) resin is used to obtain an
acoustic impedance intermediate between the transducer and the medium, and Composite
members have been applied to the sound emitting surface of the transducer and used as
matching layers. However, it is difficult to knead the hollow spheres into a polymer resin
13-04-2019
3
uniformly in density, and it is necessary to perform vacuum degassing to remove air bubbles
generated by the air introduced when kneading them, Since micro hollow spheres are powders
with extremely low specific gravity, special consideration is required to prevent scattering into
the air during the kneading process, and the linear expansion coefficient of the polymer
matching layer material and that of the transducer Because they are different, they have more
stable performance, such as a large characteristic fluctuation due to ambient temperature
changes, and also there are many difficult problems in manufacturing them by economical
means, and as a result, they are stable and yet An inexpensive ultrasonic sensor could not be
provided as a product. [Problems to be solved by the present invention] In the present invention,
temperature change is achieved by stabilizing the manufacturing process of the ultrasonic sensor
and increasing the economic effect, and by using a matching material close to the linear
expansion coefficient of the transducer. It is an object of the present invention to provide an
ultrasonic transducer having stable characteristics with respect to the above, and causes a large
cause of the performance of the ultrasonic sensor, dispersion due to mismatch of acoustic
impedance of air or liquid as medium, and use environment. The characteristic variation due to
the temperature change is improved by the economical material and the manufacturing method
to stabilize the effective performance. It is well known that the cause of acoustic impedance
mismatch is that the difference between the acoustic impedance of the transducer and the
medium is quite different. To prevent this, a layer with an impedance matching function is placed
between them. It is also well known that doing is a good idea. However, as mentioned above, the
method for stably and economically producing these aligning members has not been established
yet. [Means for Solving the Problems] In the present invention, an inorganic fiber material widely
known as a heat insulating material is used as a matching member, and for example, a fibrous
material comprising calcium silicate needle crystals of Tobermolite, Xonotlite. Is produced by
reacting lime and silicic acid in an autoclave (the production conditions are 160-180 ° C. in the
former case and 180-220 ° C. in the latter case), and in general, the slurry is press-formed Are
used.
These fibrous materials are easy to form an air layer and have a very low bulk density of 0.1 to
0.4. And heat resistance temperature 1000 ° C, fire resistance, from the point where good
processability is widely used as heat insulation, heat insulation such as chemical industry,
construction interior as heat insulation material, heat insulation material. On the other hand, as
an ultrasonic transducer, the acoustic impedance of the acoustic matching member required is a
geometric mean value of the acoustic impedance of each of the transducer and the medium from
the generally known matching condition, and its thickness is 1/4 wavelength It is desirable that
when the medium is air, the acoustic impedance of air at normal temperature is about 400 kg /
m 2 S, and when the transducer is ceramic, the acoustic impedance is 30 × 10 6 kg / m 2 S.
Therefore, the matching layer preferably has an acoustic impedance value of 1.1 × 10 5 kg / m
2 S. The acoustic impedance of the said material is about 0.7-2.8 * 10 <5> kg / m <2> S, and the
conditions as an acoustic matching member are satisfy | filled. [Operation] The acoustic matching
13-04-2019
4
layer made of this material radiates the energy generated from the transducer into the medium
very efficiently, and the radiation level shows a value equal to or higher than that of the plastic
matching layer according to the conventional method. Also, the thermal expansion coefficient (of
this matching material) is close to about 1 × 10 −6 / ° C. and the thermal expansion
coefficient of the transducer 6 to 10 × 10 −6 / ° C., and the heat of the bonding surface of the
transducer and the matching material The mechanical stress due to the factor is significantly
reduced as compared with the polymer matching material, and it is possible to obtain a stable
characteristic against temperature change in the use environment. [Example 1] An ultrasonic
sensor comprising an inorganic fiber, for example, a calcium silicate plate attached to the sound
wave emitting surface of a piezoelectric element, and an outer peripheral portion thereof fixed by
a metal or plastic ring having an acoustic impedance larger than its acoustic impedance. Shows
very stable performance. [Example 2] A polymer based resin (silicon, epoxy, etc.) is impregnated
into the transducer surface of the matching material of the previous embodiment, and the
matching member provided with a gradient of acoustic impedance in the sound wave radiation
direction has more stable characteristics. You can get Of course, it is also possible to use the
resin to be impregnated for bonding the transducer and the matching material. [Effects of the
Invention] The present invention is intended to supply the market at the most economical price
as well as performance by using generally known stable materials as matching members. It is
also effective to apply resin coating on the surface, side or whole of the ceramic matching layer
to improve the moisture resistance and waterproofness, and to stabilize the characteristics of the
ultrasonic sensor.
Furthermore, it is also within the scope of the present invention to have an acoustic impedance
gradient inside by positively utilizing the porosity and water absorption of the matching member
and impregnating the silicon or epoxy resin on the transducer affixing side of the matching
material. It belongs to. Also, if a layer made of silicon or epoxy resin is added to the transducer
side as the second matching layer, and the above matching layer is superposed on the transducer
side, the impedance matching between layers is extremely smooth, and a plurality of
conventional matchings are performed. It is possible to reduce the reflection of sound waves on
the matching layer superposition surface, which has been considered as a drawback in the case
of providing a layer. An ultrasonic sensor having such a configuration has extremely stable
characteristics.
13-04-2019
5
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