JPH05292587A - Sound insulating method of ultrasonic sensor and sound insulating material based upon the same - Google Patents

Abstract

PURPOSE:To obtain the sound insulating method of the ultrasonic sensor which provides sufficient sound insulation performance even under high pressure with simple constitution. CONSTITUTION:This method provides sound insulation for the reverse surface of the ultrasonic sensor, and a multi-layered structure body consisting of different kind of media 13, 14, and 15 which deform small against pressure and differ in acoustic impedance is arranged on the reverse surface of an ultrasonic vibrator 12 and insulates an ultrasonic wave traveling to the reverse surface. The array intervals alpha2, alpha3, and alpha4 of the different kind of media 13, 14, and 15 of the multi-layered structure body are so determined that a transmitted wave from the outermost layer has less than a desired value by utilizing the transmission theory of a sound wave in the multi-layered media; and the interval alpha1 between the multi-layered structure body and ultrasonic vibrator is so set that impedance characteristics of the ultrasonic wave do not vary owing to resonance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sound insulation for the back and side surfaces of an ultrasonic transducer of an ultrasonic sensor.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional ultrasonic sensor 1 uses one surface as a wave transmitting / receiving surface and the other back surface is covered with a sound insulating material 2 such as sponge or cork so as not to transmit / receive the wave. It was being appreciated.

However, the sound insulating material 2 of this type has a lower sound insulating effect as the frequency of the incoming sound wave decreases, and when used under a high pressure, the sound insulating material 2 is compressed and the sound insulating effect is lost. In addition, there is a problem that this compression leads to destruction of the ultrasonic sensor itself.

In order to electrically insulate sound, two ultrasonic sensors are made to face each other at a predetermined interval, a detection signal from an ultrasonic sensor located in front is delayed and the ultrasonic sensor from the other ultrasonic sensor is delayed. There is a method of canceling by adding the detection signal and the signal from the front by making them in phase with each other and adding the signals from the back by making them in opposite phase.
This method requires at least two ultrasonic sensors and an electric circuit including a delay circuit and an adder circuit, and has a problem that the configuration becomes complicated.

Therefore, the applicant first formed a groove of a predetermined depth having an arbitrary locus in the flat plate-shaped first medium facing the back surface of the ultrasonic sensor, and made the ultrasonic propagation velocity different from that of the first medium. The second medium that is provided is located in the groove, the ultrasonic waves radiated from the back surface of the ultrasonic transducer are equally divided, and these two kinds of mediums having different ultrasonic propagation velocities are respectively passed, thereby passing the ultrasonic waves. We proposed a method to cancel the phases of the subsequent ultrasonic waves by making them opposite to each other. However, this method has a problem in that it is difficult to process the sound insulating material and the cost is high, because a complicated shape of the sound insulating material having a groove is essential.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. The object of the present invention is to have a simple structure and be sufficient even under high pressure. An object of the present invention is to provide a sound insulation method of an ultrasonic sensor that can obtain a sound insulation effect and a sound insulation material based on the sound insulation method.

[0007]

In order to solve the above-mentioned problems, the sound insulation method of the present invention is a method of sound insulation on the back surface of an ultrasonic sensor, wherein the back surface of the ultrasonic transducer is deformed by pressure. In this configuration, a multi-layered structure of different kinds of mediums having a small number of different acoustic impedances is arranged, and the multi-layered structure shields ultrasonic waves directed to the back surface. The array spacing of the different types of media in the multilayer structure is determined so that the transmitted wave from the outermost layer is equal to or less than a desired value by using the transmission theory of sound waves in the multilayer medium, The spacing between the acoustic wave transducers is set so that the impedance characteristics of ultrasonic waves do not change due to resonance.

[0008]

[Function] As the sound insulation material, a multi-layered structure of different media having different acoustic impedances and less deformed by pressure is used. Further, the arrangement interval of the multi-layered structure is determined by using the sound wave transmission theory so that the transmitted wave from the outermost layer is desired. When the multilayer structure is arranged on the back surface side of the ultrasonic transducer so that the impedance characteristics of the ultrasonic wave do not change due to resonance, the ultrasonic waves directed to the back surface are blocked. Further, even under a high pressure, the sound insulation effect does not change because it is a multi-layer structure that is less likely to be deformed by pressure.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an ultrasonic sensor according to the sound insulation method of the present invention. FIG. 2 is an explanatory diagram of a transmission theory of sound waves in a multi-layer medium, and FIG. 3 is a diagram showing actual measurement results of sound insulation characteristics of the ultrasonic sensor of FIG.

First, an embodiment of an ultrasonic sensor according to the sound insulation method of the present invention will be described with reference to FIG. The ultrasonic sensor 10 includes an aluminum case 15 and the aluminum case 15.
Silicon oil 13 filled therein and the silicon oil 1
Ultrasonic transducer 12 and aluminum plate 14 immersed in 3
And a urethane rubber cover 11 which seals the aluminum case 15 and serves as an ultrasonic wave transmitting / receiving surface. The arrow on the right side of the figure is the direction of ultrasonic sound insulation.

In the ultrasonic sensor 10 having such a structure, the first layer medium is the silicon oil 13 and the second layer is the second layer with silicon oil and aluminum which are materials that are not easily deformed by pressure on the back surface of the ultrasonic sensor. The medium is an aluminum plate 14, the third layer medium is silicon oil 13, and the fourth layer medium is an aluminum case 15.
It constitutes a sound insulating material of a multilayer structure of a multilayer medium as a layer medium.

Next, how to use the transmission theory of sound waves in a multilayer medium in a multilayer structure will be described with reference to FIG. A _i is the amplitude of the transmitted wave, B _i is the amplitude of the reflected wave, and x _i
Indicates the x-coordinate value in the traveling direction of the ultrasonic wave, and the vertical solid line indicates the boundary of each medium. It is assumed that the ultrasonic waves emitted from the back surface of the ultrasonic transducer travel from the left side to the right side of the drawing. Amplitude A _i · A _{i + 1} of transmitted wave and amplitude B _{i of} reflected wave in adjacent media
Since the relationship of B _{i + 1} can be obtained by the transmission theory of sound waves in a multilayer medium, the transmitted wave from the outermost layer is desired by calculating the ratio of the amplitudes A _i and B _i of each layer. The thickness of each layer can be determined so as to be not more than the value of. The process is shown below.

The displacement δ _{n in} each medium is expressed by δ _n = A _n exp [j (wt-k _n x _n )] + B _n exp [j (wt + k _n x _n )]-Equation 1 (A _n , B _n Is a complex number, k _n is a wavelength constant, and n is an integer). Since the displacement δ _i and the strain E _i are continuous at the boundary of each medium, δ _i = δ _{i + 1} -Equation 2 E _i (dδ _i / dx) = E _{i + 1} (dδ _{i + 1} / dx) -Equation 3 (1 ≦ i ≦ n−1). By substituting the equation 1 into the equations 2 and 3, and rearranging, aa _i + bB _i = cA _{i + 1} + dB _{i + 1} ─Equation 4 kA _i + fB _i = gA _{i + 1} + hB _{i + 1} ─Equation 5 Here, a = exp (-jk _i x _i ), b = exp (jk _i
x _i ), c = exp (-jk _{i + 1} x _{i + 1} ), d = exp (jk
_{i + 1} x _{i + 1} ), e = −jk _i E _i a, f = jk _i E _i b, g = −jk _{i + 1} E _{i + 1} c, h = jk _{i + 1} E _{i + 1}
d, From Equation 4 and Equation 5, A _i = [(cf-bg) / (af-be)] A _{i + 1} + [(df-bh) / (af-be)] B _{i + 1} B _i = [ (Cf-ag) / (be-af)] A _{i + 1} + [(df-ah) / (be-af)] B _{i + 1} is obtained. Therefore, _assuming that the thickness of the first layer medium is x ₁ = 0, the amplitude of the transmitted wave of the outermost layer is A _n = 1.0 + j0.0, and the amplitude of the reflected wave of the outermost layer is B _n = 0.0 + j0.0. , Calculate the ratio of the amplitudes A _i , B _i of each layer. Then, the thickness of each layer is determined so that the transmitted wave from the outermost layer becomes a desired value or less.

Further, the distance x ₁ between the multilayer structure and the ultrasonic transducer is λ / 2 = (sound velocity in medium / operating frequency) / 2 so that the impedance characteristic of ultrasonic waves does not change due to resonance. And

Next, a specific example of the ultrasonic sensor 10 to which the above-mentioned transmission theory is applied will be described. In FIG. 1, the thickness of each medium is determined so that the transmission wave from the outermost layer is equal to or less than a desired value by utilizing the transmission theory of the sound wave in the multilayer medium described above, and the frequency of the ultrasonic wave is 62 kHz. , Α ₂ = 25 mm, α ₃ = 8 mm, α ₄ = 15 mm. In addition, the distance α between the ultrasonic transducer 12 and the aluminum plate 14
_{The value 1} is set to α ₁ = 6 mm from λ / 2 = (sound velocity in medium / use frequency) / 2 so that impedance characteristics of ultrasonic waves do not change due to resonance.

FIG. 3 shows the specific ultrasonic sensor 10 described above.
It is a figure which shows the actual measurement result of the sound insulation characteristic of. 0 ° indicates the ultrasonic wave emission direction, and 180 ° indicates the ultrasonic sound insulation direction. This graph shows that a sound insulation effect of 35.3 dB can be obtained.

As described above, the transmission waves from the four layers are set to desired values by using silicon oil or aluminum, which is less likely to be deformed by pressure, as the medium, and by utilizing the transmission theory of sound waves in the multilayer structure by the multilayer medium. As described below, a sound insulating material having a layered structure in which the thickness of each medium is determined is arranged on the back surface side of the ultrasonic transducer 12 so that the impedance characteristic of the ultrasonic wave does not change due to resonance. When an ultrasonic wave emitted from the back surface of the ultrasonic transducer 12 is passed, a sound insulation effect is produced. Further, even under a high pressure, since it is a sound insulating material composed of four layers using silicon oil or aluminum as a medium, which is less likely to be deformed by pressure, a sufficient sound insulating effect can be obtained. In addition, since it has a layered structure, even if a metal such as aluminum is used as a medium, it may be plate-shaped, so that it does not require time and labor and is inexpensive.

Further, since the outermost four layers are made of aluminum, it can be used as a sound insulating material and a case, and because of the oil immersion, the ultrasonic vibrator 12 has a pressure balance structure between the outside and the inside, and pressure resistance design is easy. ..

Although silicon oil is used as the oil in the above embodiment, other oils such as castor oil or rubber type such as urethane rubber may be used. The aluminum plate may be any other metal. Further, the sound insulation layer is not limited to four layers and may be any number of layers.

[0020]

The sound insulation method and the sound insulation material of the present invention have a basic structure of a multi-layered structure of different media having a small deformation due to pressure and a different acoustic impedance, and by appropriately arranging the multi-layered structures. Since the sound insulation effect is produced, a sufficient sound insulation effect can be obtained even under a high pressure, and even if a metal is used as a medium, it can be plate-shaped, and therefore it does not require labor for processing and is inexpensive.

[Brief description of drawings]

FIG. 1 is a sectional view of an ultrasonic sensor according to a sound insulation method of the present invention.

FIG. 2 is an explanatory diagram of a transmission theory of sound waves in a multilayer medium.

FIG. 3 is a diagram showing measurement results of sound insulation characteristics of the ultrasonic sensor of FIG.

FIG. 4 is a sectional view of a conventional ultrasonic sensor.

[Explanation of symbols]

 10 Ultrasonic Sensor 11 Urethane Rubber 12 Ultrasonic Transducer 13 Silicon Oil (Multilayer Structure) 14 Aluminum Plate (Multilayer Structure) 15 Aluminum Case (Multilayer Structure)

Claims (2)

[Claims] 1. A method of insulating sound from the back surface of an ultrasonic sensor, wherein a multi-layered structure of different media having different acoustic impedances and less deformed by pressure is arranged on the back surface of the ultrasonic transducer. A sound insulation method for ultrasonic sensors that shields ultrasonic waves from the body toward the back. 2. A sound insulation material based on the sound insulation method for an ultrasonic sensor according to claim 1, wherein the array spacing of different kinds of media having different acoustic impedances and having less deformation due to pressure of the multilayer structure is equal to that of sound waves in the multilayer medium. Using the transmission theory, the transmission wave from the outermost layer is set to be less than the desired value, and the distance between the multilayer structure and the ultrasonic transducer is set so that the impedance characteristics of ultrasonic waves do not change due to resonance. Sound insulation material for ultrasonic sensors.