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JPH04120899

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DESCRIPTION JPH04120899
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
sound insulation on the back and side of an ultrasonic transducer of an ultrasonic sensor. 2.
Description of the Related Art As shown in FIG. 5, an ultrasonic sensor 1 uses one side as a
transmission / reception wavefront, and the other back surface is covered with a sound
insulation material 2 such as sponge or cork so as not to transmit or receive waves. . However,
the sound insulation effect of this type of sound insulation material 2 decreases as the frequency
of the incoming sound wave decreases, and when used under high pressure, the sound insulation
material 2 is compressed and the sound insulation Not only the effect is lost, but also the
problem is that the compression leads to the destruction of the ultrasonic sensor itself. To
electrically isolate the sound, the two ultrasonic sensors are opposed with a predetermined gap,
and the detection signal from the ultrasonic sensor located in front is delayed and the detection
signal from the other ultrasonic sensor is detected. There is a method of adding the signals from
the front to the same phase and adding them by adding the signals from the front, and canceling
by adding the signals from the rear to the opposite phase and adding them, but in this method, at
least two ultrasonic sensors and delay The circuit and the electric circuit of the adder circuit are
required, and there is a problem that the configuration becomes complicated. The present
invention has been made to solve the above-described problems, and provides a sound insulation
method that has sufficient sound insulation characteristics even under high pressure while
having a simple configuration, and a sound insulation suitable for implementing the sound
insulation method. The purpose is to provide materials. According to the method of isolating
sound on the back surface of an ultrasonic sensor according to the present invention, ultrasonic
waves emitted from the back surface of an ultrasonic transducer are equally divided so as to have
an ultrasonic wave propagation velocity. It is characterized in that the phases of the ultrasonic
waves after passing are made opposite to each other to cancel each other by passing through two
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1
different types of media respectively. The sound insulation material based on the sound
insulation method of the present invention forms a groove having a predetermined depth as an
arbitrary locus in a flat plate-shaped first medium opposed to the back surface of the ultrasonic
sensor, and an ultrasonic wave different from the first medium A second medium having a
propagation velocity is located in the groove. As shown in FIG. 1, for example, a ring-shaped first
medium of substantially the same outer diameter and having a thickness d is in contact with the
back surface of the disk-shaped ultrasonic sensor 1; In the middle space portion of the medium A,
a second medium B of the same thickness is fitted. When the ultrasonic wave propagation
velocity in the first medium A and the second medium B is vl, and, respectively, the ultrasonic
wave emitted from the back surface of the ultrasonic sensor 1 or the first medium A and the
second medium Assuming that each sound wave (sound pressure) when it is emitted to the third
medium C (for example, in water) after passing through B is P1 and P, P = K eJω (t + d / v +) P,
− ejω (t + d / v,) Here, if the cross-sectional areas of the media A and B are equal, it is possible
to pass 2 = to-.
Therefore, the sound wave P synthesized for the third medium C is P = P, + P2Kejωt (ejωd / vI +
ejωd / v2) KejωL (cosurr, + jsinr + coslτ, + jsinωτ2) Ke − ′ ′ t + CO 8 ω r 2) + j (sin ω τ,
+ sin ω τ 2) J ω t 2 Ke CO 8 ω (τ 1 − τ 2) / 2 [C 08 (7 J (T, −τ 2) / 2 + sin ω (τ, 10 τ 2)
/ 2] Therefore, cos ω (τ 1 − τ,) The sound pressure of the sound wave emitted to the third
medium C is O if the vl and V2 (that is, the appropriate medium and d are set) such that / 2 = 0.
Thereby, if the cross-sectional area of the first medium A and the cross-sectional area of the
second medium B are equalized, the ultrasonic waves emitted from the back surface of the
ultrasonic sensor 1 are the first medium A and the second medium. It is completely
soundproofed by B, so that these media A, B act as sound insulation. EXAMPLE FIG. 2 shows a
sound insulation material X suitable for carrying out the sound insulation method of the present
invention, wherein a disc-shaped first medium A of thickness (h to d) has a depth d Concentric
grooves Q are formed. The seawater filled in the groove Q is the second medium B, and the third
medium C is also seawater. As described above, the reason why the bottom portion Z of the
thickness h is provided in the first medium A is to hold the first medium A divided into a plurality
of rings in a ring shape by the formation of the groove Q. The bottom Z also functions as a
conventional mechanical sound insulation material for the ultrasonic sensor 1. Further, since the
sound waves P and & P2 which have passed through the sound insulation material X are
uniformly mixed, a plurality of concentric grooves Q are formed in the first medium A as shown
in FIG. 3 (A). Incidentally, as the shape of the groove Q, as shown in FIG. 3 (B) and FIG. 3 (C), it
may be a lattice shape or a parallel groove, or it may face the ultrasonic sensor 1. The area of the
groove Q is made approximately equal to the medium of 1. Further, as shown in FIG. 2, the
ultrasonic wave sensor 1 and the sound insulation material X are separated by a cap G so that
the vibration of the ultrasonic sensor 1 is not directly transmitted to the sound insulation
material X. The first medium 'JtA uses aluminum (its ultrasonic wave propagation velocity vl =
6260 m / s) and the second medium uses seawater (its ultrasonic wave propagation velocity v2 =
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500 m / s) and the outer diameter of the groove The ultrasonic wave frequency was measured
under the condition of 3Q KHz, with 13.5 mm, inner diameter 45 mm, depth d) 6.4 mm, and the
cap G of the ultrasonic sensor 1 and the sound insulation material 8 mm. Is shown in the graph
of FIG.
According to this graph, it has been found that a sound insulation effect of approximately 25 to
30 dB can be obtained. The ultrasonic sensor l can have an arbitrary shape, and if the depth d of
the groove Q is made random to obtain a random phase difference, the sound wave passing
through the sound insulating material X is not directed. In addition, the sound insulation effect
can be obtained for other ultrasonic waves having different frequencies. As described above, the
present invention takes advantage of the fact that the ultrasonic waves of two types of media
have different propagation speeds and cancels the sound waves after passing through the two
types of media in antiphase. Can be used under high pressure. Moreover, since the electric circuit
is unnecessary, it can be configured at low cost.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a view used to explain the principle of the sound insulation method of the present
invention, and FIG. 2 is a view showing a cross section of the sound insulation material suitable
for carrying out the sound insulation method of the present invention. A) to FIG. 3 (C) are plan
views showing the shape of the groove formed in the first medium, FIG. 4 is a view showing the
measurement results of the sound insulation characteristics of the sound insulation material
shown in FIG. FIG. 5 is a cross-sectional view of a conventional ultrasonic sensor.
1 · · Ultrasonic sensor, A first medium, B · · · second medium, C · · third medium, Q · · · G · · · gap.
Patent Assignee Furuno Electric Co., Ltd. Attorney Attorney Atsushi Satoshi
03-05-2019
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