JP7122088B2 - wide angle retro sound reflector - Google Patents

Description

The present invention relates to an acoustic corner reflector that returns incident sound waves from a wide range of directions in the incident direction of the sound waves.

In order to improve the detection efficiency when observing an object by wave motion, a label is added to the object to enhance the reflection intensity.

As a marker for enhancing the reflection intensity, a corner reflector is known, which is composed of three plane reflectors that are perpendicular to each other and causes an incident wave to travel in the opposite direction to the incident direction of the wave (Non-Patent Document 1).

Such an action of reversing the progress of the incident wave and making it go backward to the incident direction of the wave is called retroreflection.

In the field of optics, a corner reflector is also known in which three planar reflectors are right-angled isosceles triangles (see Non-Patent Document 2).

"Encyclopedia of Ocean Acoustic Terms", edited by the Society of Ocean Acoustics p.69, May 1999 "Analysis of Light Corner Reflector", Production Research, pp.611-616, Dec. 1969

According to the known corner reflector, which is composed of three orthogonal plane reflectors, the range of incident angles that achieve retroreflection is limited, and no retroreflection operation is realized for incident waves from the edge direction. .

Therefore, in order to deal with this problem, multiple corner reflectors facing various directions are usually installed side by side to support a wide space. Requires a reflector.

Therefore, in the present invention, each reflector in a corner reflector, which is composed of three plane reflectors that are perpendicular to each other, is triangular, a triangular pyramidal space formed by the three reflectors is formed, and the triangular pyramidal space is filled with , is filled with a medium having a sound wave propagation speed lower than the sound wave propagation speed in the object space.

A known corner reflector is a triangular _pyramid structure _CR0 formed by three right-angled _isosceles triangular reflectors α, β, γ as shown in FIG. Wave motion is incident or retroreflected via

A wave S _A incident on such a known corner reflector is reflected by all three reflectors as shown in FIG. Retroreflection is achieved because the reflected wave S _C travels backward in the incident direction of the wave.

Therefore, the realization of retroreflection on the three-dimensional object space ₁ shown in FIG. Restricted within the scope of realization.

This retroreflection realization range is approximately +55 degrees and −35 degrees with respect to the direction of the straight line oG, which is the central axis of the triangular pyramid structure CR ₀ .

In the known configuration CR ₀ , the change in retroreflection intensity with respect to the angle of incidence from the straight line _oG direction is numerically calculated for the half space developed in front of the triangular aperture surface SP 0 , and the contour lines are shown in FIG. 4 .

From the results of FIG. 4, in the known configuration, retroreflection is realized only within a range of approximately 55 degrees (approximately 35 degrees depending on the direction) with respect to the front direction ( _oG direction) of the aperture surface SP0, and the triangular pyramid structure The points x, y, and z in FIG. 4, which are the _x , y, and z axis directions of CR0, are the limiting angles of retroreflection.

Therefore, in the present invention, the triangular pyramidal space formed by the three reflectors is filled with a low sound velocity medium having a sound wave propagation speed lower than that in the target space.

In this way, the present invention is configured to be filled with a low sound velocity medium, and by utilizing the refraction of sound waves at the interface between the target space and the filler due to the difference in sound speed between the two, retroreflection is achieved for a wide range of incident angles. Make it feasible.

The best mode of the present invention is to fill the triangular pyramid space formed by the three right-angled triangular reflectors with a low sound velocity medium having a sound wave propagation velocity lower than the sound wave propagation velocity in the target space. is realized.

In the present invention, as shown in CR in FIG. 5, a sound wave propagation velocity lower than the sound wave propagation velocity in the target space is generated in the triangular pyramid space formed by the three right-angled isosceles triangular reflectors α, β, and γ. It is a reflector constructed by filling a low _- temperature medium with a low sound velocity medium, and a sound wave is incident or retroreflected via a planar aperture surface SP, which is the surface of the filling medium.

In the configuration according to the present invention, which is filled with a low sound velocity _medium shown _in 2 of FIG. The direction of sound wave propagation is deflected by refraction at the aperture plane due to the sound velocity difference of .

In FIG. 6, if C ₀ >C ₁ , the relationship between the incident angle (θ _in ) and the output angle (θ _out ) is sin θ _in /sin θ _out =C ₀ /C ₁ from the wave refraction condition. , θ _in >55 degrees.

Therefore, as can be seen from the _{numerical calculation} results shown in FIG. , the incident angle range for achieving retroreflection is greatly expanded by filling the low-temperature medium 2 .

Thus, according to the present invention, the angle of the _{retroreflective} area is widened to approximately 90 degrees with respect to the front direction of the _aperture surface SP, and incident sound waves from almost all directions in front of the aperture surface SP can be retroreflected.

Another configuration according to the invention is that the filling sound velocity medium 2 is a solid material having a sound wave velocity lower than that in the object space 1 .

Assuming that the target space 1 is underwater (sound velocity: 1500 m/s), silicon rubber (sound velocity: 900 m/s) is a solid material having a low sound wave propagation velocity.

Thus, by making the low-frequency medium 2 a solid material, the mechanical strength of the retrosonic wave reflector is improved.

Another configuration according to the invention is that the filling low-temperature medium 2 is a liquid material having a sound wave propagation speed lower than that in the object space 1 .

Assuming that the target space 1 is underwater, examples of liquid materials having a low sound wave propagation velocity include silicone oil (sound velocity: 760 m/s) and carbon tetrachloride (sound velocity: 930 m/s).

In this way, in the configuration in which the low sound velocity medium 2 to be filled is a liquid material, a thin film having a high acoustic transmittance is arranged on the opening surface, and the low sound velocity medium 2 is held separately from the target space 1 .

In this way, by using a liquid material for the low-temperature medium 2, the refraction angle at the aperture surface can be further increased due to the low-temperature characteristics, and the angle of the retrosonic wave reflector can be further widened.

Another configuration according to the invention consists in constructing the planar reflectors α, β, γ of a material with a significantly higher acoustic impedance than the filling sound velocity medium 2 .

If the low-frequency medium 2 is made of resin or liquid material, iron (acoustic impedance: 45×10 ⁶ kg/m ² /s) or aluminum (acoustic impedance: 17×10 ⁶ kg/m 2 /s) can be used as the high acoustic impedance material constituting the plane reflector. /m ² /s) are effectively selected.

Another configuration according to the invention consists in constructing the planar reflector from a material that has a significantly lower acoustic impedance than the filling sound velocity medium 2 .

If the low-frequency medium 2 is made of a resin or a liquid material, a gas-phase flat surface such as air or an air-containing composite material such as a closed-cell sponge is effectively selected as the low acoustic impedance material constituting the planar reflector. .

Another configuration according to the present invention is obtained by using the retrosonic wave reflector CR according to the present invention shown in FIG. A four-element retro-sound reflector 3 is formed.

With such a configuration, as shown in FIG. 9, a wider retroreflective area exceeding 180 degrees is realized.

On the other hand, in the case of configuration 4, which is not filled with a low-frequency medium and has the known configuration CR ₀ as an element, the azimuth characteristics shown in FIG. 10 are obtained. direction), the intensity of retroreflection decreases, making it impossible to cover a wide area.

Another configuration according to the present invention is to construct a retrosonic wave reflector with four elements shown in FIG. 8 by combining three flat plate reflectors A, B, and C shown in FIG.

According to such a construction method, it is possible to easily construct a composite retrosonic wave reflector with four elements using a small number of members.

Another configuration according to the present invention is, as shown in FIG. 12, an eight-element retrosonic wave reflector 5 by arranging four-element retrosonic wave reflectors on both front and back surfaces.

Such a configuration provides a retro-sound reflector that adapts to all three-dimensional surrounding spaces.

Another configuration according to the present invention is to construct a composite retrosonic wave reflector with eight elements shown in FIG. 12 by combining four flat plate reflectors A', B', C', and D' shown in FIG.

According to such a configuration, it is possible to easily configure a composite retrosonic wave reflector with eight elements with a small number of members.

By using the retrosonic wave reflector according to the present invention, a wide angle of retroreflection is realized, and the position or shape of an object can be clearly grasped from a long distance in observation by ultrasonic waves in underwater civil engineering work or the like.

FIG. 4 is an explanatory diagram showing the configuration of a retrosonic wave reflector in a known technique; FIG. 4 is an explanatory diagram showing the principle of retroreflection of a retrosonic wave reflector in a known technique; FIG. 4 is an explanatory diagram showing a retroreflection realization range of a retrosonic wave reflector in a known technique; It is the numerical calculation result which showed the retroreflection realization range of the retroreflector in a known technique. FIG. 2 is an explanatory diagram showing the configuration of a wide-angle retrosonic wave reflector according to the present invention; FIG. 4 is an explanatory diagram showing a retroreflection realizable range of a wide-angle retrosonic wave reflector according to the present invention; It is the numerical calculation result which showed the retroreflection realizable range of the wide-angle retroreflection sound wave reflector in this invention. FIG. 4 is an explanatory diagram showing the configuration of a wide-angle retrosonic wave reflector with four elements according to the present invention; FIG. 4 is an explanatory diagram showing a retroreflection realizable range of a wide-angle retrosonic wave reflector with four elements according to the present invention; FIG. 4 is an explanatory diagram showing a retroreflection realizable range of a retrosonic wave reflector based on four elements of uniform sound velocity; FIG. 4 is an explanatory diagram showing a technique for creating a wide-angle retrosonic wave reflector using four elements in the present invention; FIG. 4 is an explanatory diagram showing the configuration of a wide-angle retrosonic wave reflector with eight elements in the present invention; FIG. 4 is an explanatory diagram showing a technique for creating a wide-angle retrosonic wave reflector using eight elements according to the present invention;

1 Object space 2 Low sound velocity medium 3 Wide-angle retro-sound reflector with 4 elements 4 Retro-sound reflector with 4 elements (no sound velocity filler)
Wide angle retro sound wave reflector with 5 8 elements

Claims (11)

In an acoustic reflector formed by an orthogonal three-plane reflector that retroreflects incident sound waves from the target space, the target space is underwater, and the internal space with the orthogonal three-plane reflector as an interface is more than the speed of sound in the target space. A retrosonic wave reflector characterized by being filled with an acoustic propagation medium having a low sound velocity and having a planar opening surface of the acoustic propagation medium . 2. A retrosonic wave reflector according to claim 1, characterized in that the three orthogonal planes are right-angled triangles. 2. A retrosonic wave reflector according to claim 1, characterized in that the three orthogonal planes are right-angled isosceles triangles. 2. A retrosonic wave reflector characterized in that the sound propagation medium having a low sound velocity according to claim 1 is made of a solid material. 2. A retrosonic wave reflector characterized by using a liquid material as the sound propagation medium having a low sound velocity according to claim 1. 2. A retrosonic wave reflector, wherein the planar reflector according to claim 1 is made of a material having an acoustic impedance higher than that of the acoustic propagation medium. 2. A retrosonic wave reflector, wherein the planar reflector according to claim 1 is made of a material having an acoustic impedance lower than that of an acoustic propagation medium. 7. A retrosonic wave reflector comprising four elements, comprising the retrosonic wave reflector according to any one of claims 1 to 6 as elements, wherein the four elements are combined by sharing one intersecting axis of three orthogonal planes in the elements. 9. A retrosonic wave reflector of four elements, characterized in that the retrosonic wave reflector according to claim 8 is composed of a combination of three plate reflectors. An eight-element retrosonic wave reflector, characterized in that the retrosonic wave reflectors according to claim 8 are joined together. 11. An eight-element retrosonic wave reflector characterized by comprising a combination of four flat plate reflectors.

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