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DESCRIPTION JPH01246998

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DESCRIPTION JPH01246998
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
airborne ultrasonic transducer used for an ultrasonic distance detector, a proximity object
detector, and the like. [Prior Art] When a transducer such as a piezoelectric ceramic is used as an
ultrasonic transducer for air, since the acoustic impedance of the transducer is much larger than
that of air, the transmission and reception efficiency of ultrasonic waves is extremely low. Then,
the ultrasonic transducer which closely_contact | adhered to the ultrasonic wave radiation |
emission surface of a vibrator | oscillator and which has an acoustic matching layer which has
the acoustic impedance of the middle between both is known, and the ultrasonic transducer
which raised transmission / reception performance of the ultrasonic wave is known. The
ultrasonic transducer has a structure in which the acoustic matching layer 2 is formed in close
contact with the ultrasonic wave emitting surface of the piezoelectric ceramic vibrator 1 as
shown in FIG. The velocity of sound C1 of the piezoelectric ceramic vibrator 1 is about 4000 m /
s. The density 11 is about 7400 # / m ? ?, and the acoustic impedance Z1 represented by the
product is about 7 О N of the power of about 3 О 10, S / rrI. Also, the velocity of sound C3 of
the air 3 from which the ultrasonic beam 10 is emitted is about 344 m / s. The density ? is
about 9 / rrl to about 1.2, and the acoustic impedance Z3 is about 413 N-8 / m ". Therefore, as
the acoustic impedance Z of the matching layer 2 as an intermediate value of both acoustic
impedances, the acoustic impedances of both Capsule 2. The optimum value is 1, 1 О 10 N 5, S /
m 8 given by the square root of the product of In order to bring the acoustic impedance Z close
to the optimum value, various investigations of the material of the matching layer 2 have been
conducted. For example, an epoxy resin is used as the resin composition, and a diameter of ten to
ten consisting of vinylidene chloride copolymer as micro hollow spheres. It is known that a
plastic balloon material of several hundred ?m is used. Figure 6 shows a plastic balloon for
epoxy resin (specific gravity 0.05. Addition of average particle size 40 ?m)! Sound velocity C2
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density ?? of the matching layer 2 obtained by changing (volume fraction), acoustic impedance
Z characteristic diagram, when the amount of plastic balloon added is 0.6 in volume fraction, the
acoustic impedance is about Even if it is 6.5 * 10 5 N, S / i, and the body proportion 0.7, it will be
about 4 * 10 5, an optimum value 1. This value is still larger than I X 10 5 N?S / rrl. FIG. 7 is a
characteristic diagram showing the relationship between the amount of addition of the plastic
balloon and the elastic modulus E of the matching layer, and the elastic modulus is 330 Af /-for
the epoxy resin alone, and the elastic modulus is 66 kf / at a mass fraction of 0.6. When the twovolume fraction is 0.7 at rrIA, it decreases to 54 # / ?, and the decrease in rigidity is significant.
If the specific gravity of the plastic balloon material is further reduced, it is not impossible to
bring the acoustic impedance Z close to the optimum value, but in this case, the elastic modulus E
is further reduced to indicate rubber elasticity, and dimensional accuracy The maintenance of T
also reduces the machinability to obtain T, and also K is susceptible to external damage.
[Problems to be Solved by the Invention] As described above, as the acoustic matching layer of
the ultrasonic transducer for air, emphasis has been placed on making the acoustic impedance 2
close to an optimum impedance. The basic principle of this type of matching layer is that the
thickness t of the matching layer is 1/4 of the wavelength ? of the ultrasonic wave in the
matching layer, as shown in FIG. . That is, it utilizes a phenomenon in which only ultrasonic
waves of a frequency corresponding to the wavelength ? are transmitted without being
attenuated (transmission factor 1), ie, so-called co-image transmission, when formed equal to a
quarter wavelength. When the thickness t of the matching layer or the wavelength ? of the
ultrasonic wave deviates from the above-mentioned co-imaging transmission condition, the ratio
Z of the acoustic impedance 2 of the matching layer to the acoustic impedance of the air or the
vibrator as shown in FIG. ! The ultrasonic wave transmission decreases significantly with the
increase of Z / Z or Z / Z3 (hereinafter referred to as impedance ratio). In the above-mentioned
ultrasonic transducer, the matching layer 2 has an optimum value of 1. The impedance ratio Z, /
Z, Z / Zs reaches about 270 even if it is lX 10 N, S / rrlVc, and if there is a slight deviation of
wavelength ? and thickness t, the transmission of ultrasonic waves becomes extremely difficult
Become. From this, it is considered more important to hold the thickness t of the matching layer
accurately and stably at 1?4 wavelength of the ultrasonic wave than holding the impedance ratio
at the optimum value. However, in the conventional matching layer, as the impedance 2
approaches the optimum value, the elastic modulus E is significantly reduced, and it is not only
difficult to obtain the thickness t accurately, but also it is susceptible to trauma. There is a
drawback that management is also difficult. An object of the present invention is to reduce the
decrease in elastic modulus due to the reduction in acoustic impedance, and to easily ensure the
accuracy of the thickness of the matching layer. [Means for Solving the Problems] In order to
solve the above problems, according to the present invention, an acoustic matching layer formed
by mixing micro hollow spheres in a resin composition is formed on an ultrasonic wave emitting
surface of an ultrasonic transducer. In the closely formed one, the micro hollow spheres are a
mixture of a plastic balloon material and a silica balloon material. [Operation] In the above
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means, as the hollow hollow spheres to be mixed in the resin composition, the plastic balloon
material and the silica balloon material are constituted so as to use the mixing material in a
predetermined ratio, and epoxy as the resin composition When the resin is mixed with a rigid
silica balloon material, the density A and the acoustic impedance Z of the matching layer tend to
decrease in proportion to the addition amount, while the elastic modulus E and the speed of
sound tend to increase inversely It is possible to reduce the decrease in elastic modulus of the
matching layer to which the mixed balloon material is added, so it is easy to accurately match the
thickness t of the matching layer to the 174 wavelengths of the in-matching layer ultrasonic
wave The acoustic impedance Z-can make effective use of co-image transmission, although it is
somewhat higher than the conventional one, and therefore an air ultrasonic transducer with high
ultrasonic transmission and reception performance. Can or Rukoto.
The present invention will be described based on examples. FIG. 1 is an explanatory view
showing an ultrasonic transducer according to an embodiment of the present invention, wherein
an acoustic matching layer 20 provided in close contact with an ultrasonic wave emitting surface
of an ultrasonic wave emitting surface 1 made of piezoelectric ceramic is used as a resin
composition. In the epoxy resin composition 12 of this invention, the plastic balloon material 13
(ratio llO, 05, average particle diameter 40 ?m) consisting of a vinyl chloride copolymer is used,
and the silica balloon material 14 (specific gravity 0.5. What compound | combined and
hardened | cured the average particle diameter of 50 micrometers at a predetermined ratio is
used. The matching layer 20 is formed by injecting the mixed liquid material into a mold, curing
it at room temperature and then machining to form a matching layer processed so that the
thickness t is equal to a quarter wavelength of ultrasonic waves. Then, the epoxy resin
composition used for the matching layer is closely fixed as an adhesive so as not to leave a
nitrogen gap on the surface of the vibrator 1. FIG. 2 is a characteristic diagram for explaining the
action of the silica balloon material, showing the sound velocity C1 density ? and the acoustic
impedance Z of the material obtained by compounding and curing only the silica balloon material
14 in the epoxy resin composition 12 There is. In the figure, ? and Z show a tendency to
decrease as the volume fraction of the silica balloon material 14 increases, but the sound velocity
C tends to increase conversely. FIG. 3 is an elastic modulus characteristic diagram. The elastic
modulus E of the material containing only the silica balloon material 14 and the silica balloon
material as the mixed balloon material are about 30% constant in volume fraction (horizontal axis
Matching layer 200 elastic modulus E (in the range of 30% or more in the horizontal axis) formed
by changing the volume fraction of the plastic balloon material 13 to be added in a range of 0 to
60%). ) Is also shown. By blending 30% by volume fraction of the silica balloon material 14, the
elastic modulus E of the matching layer in which the mixed balloon material is blended is overall
compared to that of the conventional matching layer (see FIG. 7) Elevated, for example, the
elastic modulus at a silica balloon material of 30%, a plastic balloon material of 50%, and the
volume ratio of the mixed balloon material as a whole is 80%, and the elastic modulus is 137%. A
value comparable to the modulus of elasticity of the matching layer is obtained, as a result of
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which precision machining of the material molded by molding can be performed, and the
thickness of the matching layer can be accurately finished to a quarter wavelength. FIG. 4 is an
acoustic characteristic diagram of the matching layer in the example, in which the sound velocity
of the matching layer 20 is 30% when the volume percentage of the silica balloon material 30%,
the plastic balloon material 50%, and the mixed balloon material as a whole is 80%. C: 2000 m /
s, Ц M degree ?: 500 Ai '/ rfl ?, acoustic impedance Z: 1 О 10 6 N, S / d, elastic modulus E: 137
# / 7, acoustic impedance: optimum value 1.Although it is almost 1 digit higher than 1 О 10 N
and S / J, it has high machinability and easy securing of dimensional accuracy, so that resonance
transmission is effectively used to achieve high ultrasonic transmission / reception performance.
The matching layer can be obtained easily.
The volume fraction of the silica balloon material 14 is not limited to 30%, and the volume
fraction of the entire mixed balloon material occupied by about 80% of which the casting process
is easy and the volume fraction of the ? silica balloon material 14 By selecting the ratio f in the
range of about 10 to 40%, it is possible to optionally form matching layers having different
elastic moduli and acoustic impedances. [Effects of the Invention] In the present invention, as
described above, a mixture of a plastic balloon material and a silica balloon material is used as
the micro hollow spheres to be blended into one resin composition. As a result, the elastic
modulus of the matching layer is significantly reduced accompanying the lowering of the
acoustic impedance only by the plastic balloon material, which makes it difficult to ensure the
dimensional accuracy of the matching layer which is essential for resonant transmission. Since
the problem of not being noticed is eliminated, the reduction of the elastic modulus is suppressed
by the compounding of the silica balloon material, and the trauma becomes difficult, and the
precision machining processability is improved. It becomes easy to hold the wavelength
precisely, and it is possible to provide an airborne ultrasonic transducer with high ultrasonic
transmission / reception performance by effectively utilizing resonance transmission that
transmits the ultrasonic wave of this wavelength without loss.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is an explanatory view showing an apparatus according to an embodiment of the present
invention, FIG. 2 is a characteristic diagram for explaining the function of the silica balloon
material, and FIG. 3 is an elastic modulus characteristic diagram of the matching layer according
to the embodiment. The figure is a characteristic diagram showing the acoustic characteristics of
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the example matching layer, FIG. 5 is a schematic sectional view showing the conventional
device, FIG. 6 is a characteristic diagram showing the acoustic characteristics of the conventional
matching layer, and FIG. The elastic modulus characteristic diagram of the matching layer, and
FIG. 8 is a principle characteristic diagram showing the ultrasonic wave transmission of the
matching layer.
DESCRIPTION OF SYMBOLS 1 ... ultrasonic wave perturbator, 2, 20 ... acoustic matching layer
(matching layer), 12 ... resin composition, 13 ... plastic balloon material, 14 ... silica balloon
material, t. иии Thickness of matching layer (1?4 wavelength), C и и и Speed of sound, ? ? ? и и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и elastic modulus, ? ? и и и wavelength Party 1 Fig. 1 Silica
bar 1 yarn thread volume (volume fraction) Fig. 2 Science ? 1) Mi and
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