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JPH0465999

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DESCRIPTION JPH0465999
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of isolating the back of an ultrasonic sensor. 2. Description of the Related Art As shown
in FIG. 3, an ultrasonic sensor uses one side of a vibrator 1 as a wave receiving surface, and the
other side is a sound insulating material 2 such as sponge or cork so that it does not detect
incoming waves. It is covered with 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 is generated. The effect is only lost (there is a problem that this compression also leads
to the destruction of the container of the ultrasonic sensor itself). The present invention has been
made to solve the above-mentioned problems, and an object of the present invention is to
provide a sound insulation method which can obtain sufficient sound insulation characteristics
even under high pressure. [Means for Solving the Problems] In order to solve the above
problems, in the present invention, two ultrasonic sensors A and B are opposed to each other at a
predetermined interval, and a detection signal from one ultrasonic sensor A is detected. By
delaying and adding it to the detection signal from the other ultrasonic sensor B, the rain
detection signals for the ultrasonic waves from the rear of the ultrasonic sensor B are canceled
out in reverse phase, and the ultrasonic sensors from the front of the ultrasonic sensor A Only
ultrasonic waves are detected. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG.
1 shows an embodiment of a specific configuration for implementing the sound insulation
method of the present invention. With the two ultrasonic sensors A and B facing each other at a
distance d, the detection signal from the ultrasonic sensor A is delayed by the delay circuit C, and
the delayed signal and the signal from the delay sensor B are Addition is performed by the
addition circuit. Now, assuming that an ultrasonic wave of X = pa−ej2fffot (pa is a constant) is
incident from the side (front) of the ultrasonic sensor A, the outputs Va and Vb of the ultrasonic
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1
sensors A and B are Va = Pa E′πfot Vb = Pb−ej2πfo (t−d / v) (where v is the speed of sound).
A signal obtained by delaying the sensor output Va by the delay circuit C is Vc = Pa−ej2πfo
(t−τ). Here, when Pa = Pb and τ = d / v, the output of the addition circuit becomes VdF−2
Pa−ej 27 rr 0 (t−r), and the signal from the front of the ultrasonic sensor A is obtained. Next,
when the same ultrasonic wave X ′ is incident from the side (rear) of the ultrasonic sensor B,
the ultrasonic sensor B has an output Va ′ of Va′−Pa, e ′ ′ ′ πfot. The output of 'is Vb' =
Pb, ej2πfo (t + d / v).
Therefore, the output of the delay circuit E is Vc ′ = Pa, ej2πro (t−τ), and also assuming that
Pa = Pb, τ = d / v, the output of the adder is Vd′−Pa, e × 2πfot (E 2 2πfor +, −j2πfoτ) 2P8. ej 2π ′ ′ t, cos 27 r for. Here, when setting to become, it becomes and it becomes Vd "-〇
. Follow? When sound waves are incident on the ultrasonic sensor from the front and back, only
the sound waves from the front are output and the sound waves from the back are canceled. r = d
/ v, λ. Is the wavelength of fo (.lambda.O-V / fo). Then Vd '= Q and f. Think of a frequency other
than Vd,-2P0. ej2πrt (t−τ) Vda ′ = 2 P a−e
cos 2 yr rt v, and the ultrasonic wave from
the front is detected, while the output signal of the ultrasonic wave from the rear is cos 2 y rft r
− cos 2 y r f − '4 f. Thus, sound is isolated when an ultrasonic wave of a satisfying frequency
f satisfying 2n + 1 □ π · 2m + 1 (m = o, 1.2 ···) is received from the rear side. Also, assuming that
the level ratio R of the detection signals from the front and the rear is set to, the addition outputs
VdF ′ and V dB ′ of the ultrasonic waves from the front and the rear become: If the case of the
case 2 is examined here, it becomes as shown in FIG. As understood from this figure, the
ultrasonic waves from the rear are completely isolated. As can be understood from the above
description, the distance between the two ultrasonic sensors A and B and the delay time τ may
be changed according to the wavelength of the sound wave to be isolated, but both ultrasonic
sensors A and B have almost the same level. Since it is necessary to make the signal incident,
when one ultrasonic sensor hides the other and the signal levels of both sensors are greatly
different (for example, when it is larger than the wavelength of the sensor), both ultrasonic
sensors are shifted from each other Just do it. As described above, the present invention uses two
ultrasonic sensors, and delays the signal detected by one ultrasonic sensor and adds it to the
detection signal from the other ultrasonic sensor. Since the detection signals of the sound waves
from one side are mutually offset, the sound insulation material used in the conventional
ultrasonic sensor becomes unnecessary, and hence it can be used under high pressure.
[0002]
Brief description of the drawings
[0003]
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2
FIG. 1 is a block diagram showing an embodiment of an ultrasonic sound insulation apparatus to
which the sound insulation method of the present invention is applied, FIG. 2 is a waveform
diagram showing the output of the apparatus of FIG. It is a sectional view of an ultrasonic sensor.
A, B: ultrasonic sensor, C: delay circuit, D: addition circuit. Patent Assignee Furuno Electric Co.,
Ltd.
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