KR20200127847A - Anisotropic media for full transmission of obliquely incident elastic waves - Google Patents

Abstract

An embodiment of the present invention is to provide an anisotropic medium for the complete transmission of obliquely incident elastic waves considering both longitudinal and transverse waves by using an anisotropic medium designed to completely transmit an elastic wave of the desired mode when the elastic wave is obliquely incident at the boundary of different media. The anisotropic medium for complete transmission of obliquely incident elastic waves according to an embodiment of the present invention comprises: an incident medium through which incident elastic waves that are obliquely incident at a predetermined tilt angle are transmitted, including longitudinal and transverse waves; a transmission medium through which transmission elastic waves including longitudinal and transverse waves are transmitted; and an anisotropic medium provided between the incident medium and the transmission medium to block transmission of a preset reflected elastic wave and completely transmit the transmitted elastic wave in a preset transmission mode by satisfying a preset complete transmission condition, wherein the complete transmission condition includes the phase matching condition of Equation (1) representing the wave number relationship of the eigenmode, which is represented by mutual coupling of longitudinal and transverse waves in the anisotropic medium and the polarization matching condition of Equation (2) representing the relationship between the polarization vector and the amplitude of the eigenmode.

Description

Anisotropic medium for complete transmission of oblique incident seismic waves{ANISOTROPIC MEDIA FOR FULL TRANSMISSION OF OBLIQUELY INCIDENT ELASTIC WAVES}

The present invention relates to an anisotropic medium for complete transmission of oblique incident acoustic waves.

In general, when a wave is incident on the boundary between different media, some waves are inevitably reflected and only some waves are transmitted. However, the complete transmission of the wave into the target system is a major concern in the industrial field. In this situation, techniques for maximizing the transmittance of waves have been continuously studied. Complete transmission of a wave means a phenomenon in which a wave incident from one medium is transmitted to another medium with 100% efficiency.

Classic full-transmission techniques include Fabry-Perot resonance and impedance matching techniques applied to single mode. When a single layer of medium is inserted at the boundary of the same medium, when the thickness of the layer becomes an integer multiple of half the wavelength of the incident wave, the wave completely penetrates the layer, which is called a Fabry-Perot resonance phenomenon. When a single layer of media is inserted at the boundary between different media, the layer thickness becomes an integer multiple of 1/4 of the incident wave wavelength, and when the layer's impedance is the geometric average of the impedances of the two media, the wave completely penetrates the layer. , This is called impedance matching.

Seismic waves have both longitudinal and transverse waves due to the interatomic bonds that make up the medium, so that reflection and transmission at the boundary of the medium are much more complicated. The biggest limitation of the conventional seismic complete transmission technology is that it is limited to vertical incidence. In general, when an elastic wave is obliquely incident on the boundary of different media, both longitudinal and transverse waves are reflected, and both longitudinal and transverse waves are transmitted. Existing technologies cannot completely transmit the desired mode of acoustic waves to the target system in this situation. However, the oblique incident seismic wave is widely used for non-destructive testing of specimen defects, and has great industrial application, and a technology capable of overcoming the low transmittance of oblique incident seismic waves, which is a technical limitation, is required.

An embodiment of the present invention is to provide an anisotropic medium for complete transmission of oblique incident seismic waves considering both longitudinal and transverse waves by using an anisotropic medium designed to completely transmit the seismic wave of a desired mode when the seismic wave is obliquely incident on the boundary of different media. For.

The anisotropic medium for completely transmitting oblique incident acoustic waves according to an embodiment of the present invention includes a longitudinal wave and a transverse wave, and an incident medium through which an incident acoustic wave obliquely incident with a predetermined inclination angle is transmitted, and a transmission acoustic wave including a longitudinal and transverse wave is transmitted. It includes a transmission medium, and an anisotropic medium that is provided between the incident medium and the transmission medium to block transmission of a preset reflected acoustic wave as it satisfies a preset complete transmission condition, and completely transmits the transmitted acoustic wave of a preset transmission mode, The complete transmission condition is the phase matching condition of Equation (1), which represents the wave number relationship of the eigenmode, which is represented by the mutual coupling of the longitudinal wave and the transverse wave, in the anisotropic medium, and the Equation (2) ) Polarization matching conditions are included.

Equation (1)

: 고유모드 i의 파수(i=1,2,3,4), d: 이방성 매질의 두께, l, m, n: 정수)(

: Wave number of eigenmode i (i=1,2,3,4), d: thickness of anisotropic medium, l, m, n: integer)

Equation (2)

: 입사종파의 입사각,

: 입사횡파의 입사각,

: 투과종파의 굴절각,

: 투과횡파의 굴절각,

: 고유모드 i의 파수,

: 고유모드 i의 편광벡터,

: 고유모드 i의 변위진폭(i=1,2,3,4))(

: Incident angle of incident longitudinal wave,

: Incident angle of incident transverse wave,

: Refraction angle of transmission longitudinal wave,

: Refraction angle of transmitted transverse wave,

: Wave number of eigenmode i,

: Polarization vector of eigenmode i,

: Displacement amplitude of eigenmode i (i=1,2,3,4))

The incident medium and the transmission medium may include different media.

The anisotropic medium may be in contact with each other by surface contact between the incident medium and the transmission medium to the interface of the incident medium and the interface of the transmission medium.

The transmission mode may include a storage mode in which the modes of the incident acoustic wave and the transmitted acoustic wave are the same, and a conversion mode in which the modes of the incident acoustic wave and the transmitted acoustic wave are converted.

), 반지름(

), 회전각(

)과 단위 셀 꼭지점에 위치한 두 번째 슬릿의 길이(

), 반지름(

), 회전각(

), 단위 셀의 크기(a), 단위 셀의 개수(

)를 포함할 수 있다.The anisotropic medium may include an elastic metamaterial including a predetermined microstructure. In the elastic meta material, the microstructures of the unit cells may be periodically arranged in the vertical and horizontal directions. Here, the microstructure may have a slit shape including a rectangle and two semicircles. The microstructure includes a preset design variable, and the design variable is the length of the first slit located at the center of the unit cell (

), radius(

), rotation angle (

) And the length of the second slit at the vertex of the unit cell (

), radius(

), rotation angle (

), size of unit cell (a), number of unit cells (

) Can be included.

At the boundary between different incidence media and transmission media, the oblique incident seismic wave that considers both longitudinal and transverse waves is preserved through anisotropic media for complete transmission of the seismic waves inclined to different incident media and transmission media (longitudinal wave -> longitudinal wave, transverse wave- > Transverse wave) or conversion mode (longitudinal wave -> transverse wave, transverse wave -> longitudinal wave) has the effect of completely transmitting.

In addition, industrially, there is an effect such as improving the transmittance of elastic ultrasonic waves used for a wide range of non-destructive testing of defects in specimens.

1 is a diagram illustrating a situation in which an incident acoustic wave is obliquely incident from an incident medium to a transmission medium.
FIG. 2 is a diagram showing a situation in which the incident acoustic wave is completely transmitted to the transmission acoustic wave of a desired mode by inserting an engineered anisotropic medium at the boundary between the incident medium and the transmission medium.
3 is a diagram showing a microstructure of an engineered elastic meta material to implement the anisotropic medium proposed in the present invention.
4 is a diagram showing the operating principle of an anisotropic medium for completely transmitting oblique incident acoustic waves.
5A is a diagram showing a situation in which a microstructure is designed and manufactured in an incident medium to completely transmit an incident acoustic wave as a transmitted acoustic wave in a desired mode.
5B is a diagram showing a situation in which a microstructure is designed and manufactured in a transmission medium to completely transmit an incident acoustic wave as a transmission acoustic wave in a desired mode.
6A is a diagram showing an operating principle of a transducer according to a comparative example.
6B is a diagram showing an operating principle of a transducer to which the present invention is applied.
7A is a view showing an operating principle of a wedge-based pipe inspection according to a comparative example.
7B is a diagram showing the operating principle of a metawedge-based pipe inspection to which the present invention is applied.
8A is a diagram illustrating a situation in which ultrasonic waves generated by a medical ultrasonic device according to a comparative example are transmitted through human tissues.
8B is a diagram showing a situation in which an anisotropic medium proposed in the present invention is inserted into a medical ultrasound device according to a comparative example, and then an elastic wave is transmitted through a human tissue.
9 is a diagram showing an antireflective film or a completely absorbing film in which the reflected acoustic wave does not exist when the incident acoustic wave is incident by inserting an anisotropic medium at the boundary between two different media.

The terminology used herein is for reference only to specific embodiments and is not intended to limit the invention. Singular forms as used herein also include plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising" as used in the specification specifies a specific characteristic, region, integer, step, action, element and/or component, and other specific characteristic, region, integer, step, action, element, component and/or group It does not exclude the existence or addition of

Although not defined differently, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms defined in a commonly used dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal meaning unless defined.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

When an acoustic wave enters the boundary of different media at an angle, some waves (longitudinal and transverse waves) are inevitably reflected, and only some waves (longitudinal and transverse waves) are transmitted. A conceptual diagram for this situation is shown in FIG. 1.

1 shows a situation in which an incident acoustic wave 103 is incident at an angle from the incident medium 101 to the transmission medium 102. Here, the incident acoustic wave 103 can be assumed to be a longitudinal wave without losing generality. In addition, the same logic can be applied even when the incident elastic wave 103 is a transverse wave. In general, the reflected longitudinal wave 104, the reflected transverse wave 105, the transmissive longitudinal wave 106, and the transmissive transverse wave 107 are all present. The reflection angle and intensity of the reflected wave and the refractive angle and intensity of the transmitted wave are determined by the incident medium and the physical properties of the reflection medium, and the incident angle 108 of the incident acoustic wave.

The anisotropic medium for complete transmission of oblique incident seismic waves according to an embodiment of the present invention is engineered in consideration of both longitudinal and transverse waves, and inserts the anisotropic medium for complete transmissive oblique incident seismic waves into the boundaries of different media. When is obliquely incident, it is possible to realize complete transmission of the oblique incident acoustic wave in which unwanted reflected acoustic waves are removed and the acoustic waves of a desired mode are completely transmitted. A conceptual diagram for this is shown in FIG. 2.

FIG. 2 shows a situation in which an anisotropic medium 203 is inserted between the incident medium 201 and the transmission medium 202 so that the incident acoustic wave 204 completely passes through the transmitted acoustic wave 205. Unlike reflection and transmission of general acoustic waves, there are no unwanted reflected acoustic waves, and acoustic waves of a desired mode are completely transmitted. The incident elastic wave 204 may be a longitudinal wave or a transverse wave, and the transmitted elastic wave 205 may be a longitudinal wave or a transverse wave, so there are four types of complete transmission (longitudinal -> longitudinal, transverse -> transverse, longitudinal -> transverse, Transverse wave -> longitudinal wave) is possible, which can be implemented through different anisotropic media 203. At this time, a case in which the incident acoustic wave 204 and the transmitted acoustic wave 205 have the same mode is referred to as a storage mode (longitudinal wave -> longitudinal wave, transverse wave -> transverse wave), and the mode of the incident elastic wave 204 and the transmitted elastic wave 205 The other case is called full transmission in the conversion mode (longitudinal wave -> transverse wave, transverse wave -> longitudinal wave).

The anisotropic medium for complete transmission of oblique incident acoustic waves according to an embodiment of the present invention is provided with a design system (frequency, angle of incidence, mode of incident acoustic wave, mode of transmitted acoustic wave, physical properties of incident medium, physical properties of transmission medium, and anisotropic medium). A situation in which the thickness, etc. is determined) In order to completely transmit the incident acoustic wave 204 incident obliquely to the target system as the transmission acoustic wave 205 of a desired mode, a mathematical condition that the anisotropic medium 203 must satisfy is presented. For this, the anisotropic medium 203 must satisfy two conditions. One is a phase matching condition, and the other is a polarization matching condition.

, 편광벡터를

, 변위진폭을

라 설정한다. 위상매칭조건은 고유모드의 파수 사이의 관계를 나타낸다. 입사경계면과 투과경계면에서 고유모드의 위상 차이는 항상 П의 정수배가 되어야 한다. 이때, 모든 위상 차이가 П의 짝수배가 되면, 완전투과가 일어날 수 없기 때문에 하나 이상의 위상 차이는 П의 홀수배가 되어야 한다. 이방성 매질의 두께를 d라 하면 위상매칭조건은 수학식 1과 같이 주어진다.In the anisotropic medium 203, a longitudinal wave and a transverse wave are combined to each other, and there are a total of four eigenmodes. The wave number of each eigenmode

, The polarization vector

, Displacement amplitude

Set d. The phase matching condition represents the relationship between the wave numbers of the eigenmodes. The phase difference of the eigenmode at the incidence boundary and the transmission boundary should always be an integer multiple of P. At this time, if all of the phase differences are even multiples of P, then one or more phase differences must be odd multiples of P, because perfect transmission cannot occur. When the thickness of the anisotropic medium is d, the phase matching condition is given by Equation 1.

[Equation 1]

: 고유모드 i의 파수(i=1,2,3,4), d: 이방성 매질의 두께, l, m, n: 정수)(

: Wave number of eigenmode i (i=1,2,3,4), d: thickness of anisotropic medium, l, m, n: integer)

The polarization matching condition represents the relationship between the polarization vector and the amplitude of the eigenmode. The sum of the displacement vectors of the eigenmode at the incidence boundary plane must match the displacement vector of the incident acoustic wave 204. When this condition is satisfied, the reflected acoustic wave does not exist. In addition, the sum of the displacement vectors of the eigenmodes in the transmission boundary plane must be parallel to the displacement vector of the transmission acoustic wave 205 of the desired mode. When this condition is satisfied, only the transmitted acoustic wave 205 of a desired mode (longitudinal wave or transverse wave) is purely transmitted. In summary, if the anisotropic medium 203 satisfies the polarization matching condition, it is possible to completely transmit the acoustic wave of the desired mode without the reflected acoustic wave. Polarization matching conditions are given as in Equation 2.

[Equation 2]

: 입사종파의 입사각,

: 입사횡파의 입사각,

: 투과종파의 굴절각,

: 투과횡파의 굴절각,

: 고유모드 i의 파수,

: 고유모드 i의 편광벡터,

: 고유모드 i의 변위진폭(i=1,2,3,4)) (

: Incident angle of incident longitudinal wave,

: Incident angle of incident transverse wave,

: Refraction angle of transmission longitudinal wave,

: Refraction angle of transmitted transverse wave,

: Wave number of eigenmode i,

: Polarization vector of eigenmode i,

: Displacement amplitude of eigenmode i (i=1,2,3,4))

The characters included in Equations 1 and 2 are frequency, angle of incidence, mode of incident acoustic wave 204, mode of transmitted acoustic wave 205, physical properties of incident medium 201, physical properties of transmission medium 202, and anisotropic medium. Given the thickness of 203, it can be expressed as the physical properties of the anisotropic medium 203. And the physical properties of the anisotropic medium 203 are given by mass density (ρ) and six elastic modulus (C ₁₁ , C ₂₂ , C ₆₆ , C ₁₂ , C ₁₆ , C ₂₆ ), so a total of 7 design variables can be included. have. That is, since the number of design variables (7) is more than the number of equations (6) that must be satisfied, the anisotropic medium 203 can be properly designed for a desired design system to realize full transmission of oblique incident acoustic waves at all times. . The anisotropic medium for complete transmission of oblique incident seismic waves according to an embodiment of the present invention may include a material existing in nature, a chemically synthesized material, a composite material, and an elastic metamaterial including an engineered microstructure. Implementation of an anisotropic medium using an elastic meta material is presented in specific examples.

The anisotropic medium for complete transmission of oblique incident acoustic waves according to an exemplary embodiment of the present invention can realize complete transmission of oblique incident acoustic waves, which was not possible with conventional techniques. When an acoustic wave is transmitted obliquely at the boundary of different media using the conventional technique, a reflected acoustic wave is inevitably present, and thus the intensity of the transmitted acoustic wave is inevitably small. The intensity of the transmitted acoustic wave can be maximized by using an anisotropic medium for completely transmitting oblique incident acoustic waves. In theory, it is possible to transfer all (100%) energy of the incident acoustic wave to the transmitted acoustic wave of a desired mode.

By utilizing the present invention, the intensity of transmitted acoustic waves other than the desired mode is set to zero, so that the pure mode transmitted acoustic waves can be transmitted. There is no conventional technique in which incident acoustic waves are transmitted obliquely as pure longitudinal waves. The reason is that the transverse waves are necessarily transmitted together. A conventional technique for transmitting an incident acoustic wave as a pure transverse wave exists in a method using Snell's critical angle. However, this method has a disadvantage in that energy efficiency is low (less than 30% at the boundary between plastic and metal) due to the presence of reflected acoustic waves. In addition, there is also a limitation that it is applicable only to incident acoustic waves having an incident angle greater than or equal to the critical angle. As described above, the oblique incident acoustic wave complete transmission phenomenon, which was not possible with the prior art, can be implemented by using the present invention.

In the present invention, the principle of the technique of implementing the oblique incident acoustic wave complete transmission is a method using an eigenmode in an anisotropic medium, not based on resonance, and thus has the advantage that the transmittance does not react sensitively to changes in frequency and angle of incidence. In the case of the prior art, when the Fabry-Perot resonance is used, the transmittance is rapidly lowered according to the change of the frequency and the incident angle, and when the impedance matching is used, the transmittance is rapidly lowered according to the change of the incident angle.

The anisotropic medium for complete transmission of oblique incident seismic waves according to an embodiment of the present invention may be a material existing in nature, a chemically synthesized material, a composite material, etc., but it may be difficult to find or synthesize an appropriate material having desired physical properties. have. Therefore, a method of implementing an anisotropic medium using an elastic metamaterial including microstructures that can freely design the extreme physical properties of a material will be described.

The elastic metamaterial to be applied to the embodiment of the present invention has a structure in which microstructures in a unit cell are periodically arranged in vertical and horizontal directions. Various patterns can be used for the microstructure inside the unit cell. The anisotropic medium for completely transmitting oblique incident acoustic waves according to an embodiment of the present invention may include a microstructure based on a slit structure.

), 반지름(

), 회전각(

)과 단위 셀 꼭지점에 위치한 두 번째 슬릿의 길이(

), 반지름(

), 회전각(

), 단위 셀의 크기(a), 단위 셀의 개수(

) 등이 있다. 미소구조가 갖는 총 8개의 설계 변수를 적절히 조절하면 수학식 1과 수학식 2를 만족하는 물성을 갖는 경사입사 완전투과용 이방성 매질을 설계할 수 있다. 도 3에 나타난 슬릿 형태의 미소구조의 경우 단위 셀이 상하좌우로 비대칭적인 구조를 갖기 때문에 매질의 극한 이방성을 구현하는데 더 효과적이다.3 shows an elastic meta material having a slit-shaped microstructure composed of a rectangle and two semicircles. The design variable of the slit-shaped microstructure is the length of the first slit located at the center of the unit cell (

), radius(

), rotation angle (

) And the length of the second slit at the vertex of the unit cell (

), radius(

), rotation angle (

), size of unit cell (a), number of unit cells (

), etc. If the total eight design variables of the microstructure are properly adjusted, it is possible to design an anisotropic medium for completely transmissive oblique incidence having physical properties that satisfy Equations 1 and 2. In the case of the slit-shaped microstructure shown in FIG. 3, since the unit cell has an asymmetric structure in the vertical and horizontal directions, it is more effective in realizing the extreme anisotropy of the medium.

4 shows the principle of an anisotropic medium for oblique incident complete transmission according to an embodiment of the present invention. 4, if the physical properties of the anisotropic medium 403 inserted between the incident medium 401 and the transmission medium 402 are designed to satisfy Equations 1 and 2, the incident acoustic wave 404 is in a desired mode. It may be completely transmitted through the transmission acoustic wave 405. At this time, a unique wave transformation 406 occurs inside the anisotropic medium 403. The wave transformation 406 inside the anisotropic medium 403 is the displacement of the inside of the anisotropic medium 403 caused by the interference of the four eigenmodes (407, 408, 409, 410, respectively) that exist inside the anisotropic medium 403. This is the chapter. 407 is the displacement field of eigenmode 1, and 408 is the displacement field of eigenmode 2. And 409 is the displacement field of eigenmode 3, and 410 is the displacement field of eigenmode 4. For example, aluminum (ρ=2700kg/m ³ , E=70 GPa, ν=0.33) was used as the incident medium, PEEK (ρ=1320kg/m ³ , E=4.2292 GPa, ν=0.3992) was used as the transmission medium 402. Assuming that, when a longitudinal wave of 90 kHz is incident with an angle of incidence of 60 degrees, the physical properties of the anisotropic medium 403 are ρ=1669.2kg/m ³ , C ₁₁ =24.191 GPa, C ₂₂ =43.202 GPa, C ₆₆ =12.364 GPa, If C ₁₂ =5.019 GPa, C ₁₆ =-3.276 GPa, C ₂₆ =-7.732 GPa, and the thickness is 0.05m, the longitudinal wave is 100% transmitted, and the physical properties of the anisotropic medium 403 are ρ=2610kg/m ³ , C ₁₁ =72.699 GPa, C ₂₂ =95.991 GPa, C ₆₆ =9.9562 GPa, C ₁₂ =-7.84 GPa, C ₁₆ =10.333 GPa, C ₂₆ =3.2985 GPa, and if the thickness is 0.05 m, the transverse wave is 100% transmitted. When the anisotropic medium 403 does not exist, the transmittance of the longitudinal wave is only 39.4% and the transmittance of the transverse wave is only 20.2%. % Amplification. In addition to the exemplified physical properties, by using the anisotropic medium 403 having appropriate physical properties that satisfy Equations 1 and 2, it is possible to implement full transmission of oblique incident seismic waves.

The microstructure of the elastic metamaterial may be made of an incident medium as a substrate or a transmission medium as a substrate. This is shown in Figs. 5A and 5B, respectively. Which medium to use as a substrate can be judged by comprehensively considering the manufacturing possibility, cost, and time.

5A shows a situation in which a microstructure 502 is fabricated in the incident medium 501 so that the incident acoustic wave 503 is completely transmitted to the transmitted acoustic wave 504. The microstructure 502 may be implemented as an anisotropic medium made of the incident medium 501 as a substrate. 5B shows a situation in which a microstructure 506 is fabricated in the transmission medium 505 and the incident acoustic wave 507 is completely transmitted to the transmission acoustic wave 508. The microstructure 506 may be implemented as an anisotropic medium made of the transmission medium 505 as a substrate.

In one embodiment of the present invention, the anisotropic medium for completely transmitting oblique incident acoustic waves may be used to increase the performance of a transducer system for excitation and measurement of acoustic waves. A conventional acoustic wave transducer system is shown in FIG. 6A, and an acoustic wave transducer system to which the present invention is applied is shown in FIG. 6B. The efficiency of the system can be improved by removing the reflected acoustic waves that inevitably occur in the existing system and the transmitted acoustic waves of unwanted modes by using an anisotropic medium for complete transmission of oblique incident acoustic waves. If the performance of the seismic transducer system is improved, it is expected that more precise industrial and medical ultrasonic non-destructive testing will be possible.

Figure 6a shows the principle of operation of a conventional transducer. A case where a longitudinal wave is to be transmitted obliquely to the transmission medium 603 using the transducer 601 and the wedge 602 will be described. When the incident acoustic wave 604 enters the boundary between the wedge 602 and the transmission medium 603, in addition to the longitudinal wave 605 of the transmitted acoustic wave transmitted, the transverse wave 606 of the transmitted acoustic wave and the longitudinal wave 607 of the reflected reflected acoustic wave , All the transverse waves 608 of the reflected acoustic wave are present. A case in which a transverse wave is transmitted at an angle to the transmission medium 611 using the transducer 609 and the wedge 610 will be described. When the incident acoustic wave 612 is incident at an angle greater than Snell's critical angle, the transverse wave 613 of the pure transmitted acoustic wave is transmitted, but the longitudinal wave 614 of the reflected reflected acoustic wave and the transverse wave 615 of the reflected reflected acoustic wave exist. . In conclusion, conventional transducers have poor efficiency due to inevitably generated reflected acoustic waves.

6B shows an operating principle of a new transducer using an anisotropic medium for completely transmitting oblique incident acoustic waves according to an embodiment of the present invention. A case in which a longitudinal wave is to be transmitted at an angle will be described with reference to the drawing on the left. The system consists of a conventional transducer 616, a wedge 617, and an anisotropic medium 619 inserted between the wedge 617 and the transmission medium 618. The anisotropic medium 619 completely transmits the incident acoustic wave 620 as a longitudinal wave 621 of a pure transmitted acoustic wave. A case in which a transverse wave is to be transmitted at an angle will be described with reference to the drawing on the right. The system likewise consists of a conventional transducer 622, a wedge 623, and an anisotropic medium 625 inserted between the wedge 623 and the transmission medium 624. The anisotropic medium 625 completely transmits the incident acoustic wave 626 as a transverse wave 627 of a pure transmitted acoustic wave. Since there is no reflected acoustic wave, it is more efficient than conventional transducers.

The anisotropic medium for complete transmission of oblique incident seismic waves may be used for wedge-based piping inspection or for improving the performance of wedge-based flow meters. A case of using a general wedge is shown in FIG. 7A, and a case of using a metawedge using complete transmission of oblique incident acoustic waves is shown in FIG. 7B. The use of an anisotropic medium for complete transmission of oblique incident acoustic waves has the advantage of having higher performance than the conventional technology because it is possible to transmit the desired mode of elastic waves through the pipe with 100% efficiency.

7A shows the principle of operation of a conventional wedge-based pipe inspection. The system is composed of a transmission transducer 701, a transmission wedge 702, a pipe 703, a reception wedge 704, and a reception transducer 705. When the incident acoustic wave 706 of Snell's critical angle or more enters the boundary between the transmission wedge 702 and the pipe 703, some acoustic waves are reflected (longitudinal wave 707 of reflected elastic wave and transverse wave 708 of reflected elastic wave), pure The transverse wave 709 of the transmitted acoustic wave is transmitted through the pipe 703. And when the transverse wave is incident on the boundary between the pipe 703 and the receiving wedge 704, some transverse waves are reflected, and some elastic waves (the longitudinal wave 711 of the transmission elastic wave and the transverse wave 712 of the transmission elastic wave) are transmitted to the receiving wedge 704 ). The efficiency of the system is low due to the presence of the undesired mode acoustic wave and the transverse wave 710 of the reflected acoustic wave.

7B shows the principle of operation of a new metawedge-based pipe inspection to which the present invention is applied. The system includes a transmission transducer 713, a transmission wedge 714, a transmission anisotropic medium 715, a pipe 716, a reception anisotropic medium 717, a reception wedge 718, and a reception transducer ( 719). The transmission anisotropic medium 715 completely transmits the incident acoustic wave 720 to the pipe 716 as a transverse wave 721 of the transmitted acoustic wave. The receiving anisotropic medium 717 completely transmits the wave to the receiving wedge 718 as a longitudinal wave 722 of a transmitted acoustic wave again. Since there is no reflected acoustic wave, it has the advantage of being more efficient than the existing system.

In one embodiment of the present invention, the anisotropic medium for completely transmitting oblique incident acoustic waves may be utilized in medical ultrasound technology. This is shown in Figs. 8A and 8B. In the past, as shown in FIG. 8A, when an ultrasonic wave was transmitted from a transducer to a human tissue, analysis was difficult because the transmittance was low and several modes were mixed. However, the use of an anisotropic medium for complete transmission of oblique incident acoustic waves can greatly improve medical ultrasonic signals as shown in FIG. 8B.

FIG. 8A shows a situation of a transmitted acoustic wave 803 through which ultrasonic waves generated in a conventional medical ultrasonic device 801 are transmitted through a human tissue 802. At this time, there is a disadvantage in that the transmittance is low and several modes are mixed due to the presence of the reflected acoustic wave. FIG. 8B shows a situation of a transmitted acoustic wave 807 that transmits the acoustic wave through the human tissue 806 after inserting the anisotropic medium 805 for completely transmitting oblique incident acoustic wave into the conventional medical ultrasonic device 804. At this time, there is an advantage in that 100% of the acoustic wave of the desired mode is transmitted, which is advantageous for ultrasonic signal analysis.

An anisotropic medium for complete transmission of oblique incident acoustic waves may be inserted between two different media to transmit all incident wave energy, thereby implementing a non-reflective film or a completely absorbing film without reflection. This is shown in Figure 9.

9 is a reflected acoustic wave (longitudinal wave 905 or transverse wave 906) when an anisotropic medium 903 is inserted between two different media (incident medium 901 and transmission medium 902) and incident acoustic wave 904 is incident. )) does not exist. Here, the anisotropic medium 903 may include an anti-reflective film or a completely absorbing film. All of the energy of the incident acoustic wave 904 is transferred to the transmitted acoustic wave 907.

Signal analysis of an obliquely incident seismic wave can be used in fields such as non-destructive testing for diagnosing machine abnormalities, wedge-based piping inspection and wedge-based flowmeters, medical ultrasonic treatment technology, medical ultrasonic imaging technology, and ultrasonic exciters. The anisotropic medium for complete transmission of oblique incident acoustic waves according to an exemplary embodiment of the present invention can be applied to such fields to improve the strength and quality of an acoustic wave signal.

Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this is also It is natural to fall within the scope of the present invention.

201; Incident medium 202; Transmission medium
203; Anisotropic medium 204; Incident acoustic wave
205; Transmission acoustic wave

Claims (8)

An incident medium through which incident acoustic waves that are obliquely incident at a predetermined inclination angle are transmitted, including longitudinal and transverse waves,
A transmission medium through which transmission acoustic waves including longitudinal and transverse waves are transmitted, and
It includes an anisotropic medium that is provided between the incident medium and the transmission medium to block transmission of a preset reflected acoustic wave as it satisfies a preset complete transmission condition, and completely transmits a transmission acoustic wave in a preset transmission mode,
The conditions for complete transmission are
The phase matching condition of Equation (1) representing the wave number relationship of the eigenmode expressed by mutual coupling of longitudinal and transverse waves in the anisotropic medium, and
Anisotropic medium for complete transmission of oblique incident acoustic waves comprising the polarization matching condition of Equation (2) representing the relationship between the polarization vector and amplitude of the eigenmode.
Equation (1)

(

: Wave number of eigenmode i (i=1,2,3,4), d: thickness of anisotropic medium, l, m, n: integer)
Equation (2)

(

: Incident angle of incident longitudinal wave,

: Incident angle of incident transverse wave,

: Refraction angle of transmission longitudinal wave,

: Refraction angle of transmitted transverse wave,

: Wave number of eigenmode i,

: Polarization vector of eigenmode i,

: Displacement amplitude of eigenmode i (i=1,2,3,4)) In claim 1,
The incident medium and the transmission medium are anisotropic medium for complete transmission of oblique incident acoustic waves including different media. In paragraph 2,
The anisotropic medium is an anisotropic medium for complete transmission of oblique incident acoustic waves in contact with each other in surface contact between an interface of the incident medium and an interface of the transmission medium between the incident medium and the transmission medium. In claim 1,
The transmission mode is
A storage mode in which the incident acoustic wave and the transmitted acoustic wave have the same mode, and
An anisotropic medium for complete transmission of oblique incident acoustic waves, comprising a conversion mode in which modes of the incident acoustic waves and the transmitted acoustic waves are converted. In claim 1,
The anisotropic medium is an anisotropic medium for complete transmission of oblique incident acoustic waves including an elastic metamaterial including a predetermined microstructure. In clause 5,
The elastic meta material is an anisotropic medium for complete transmission of oblique incident acoustic waves in which the microstructures of unit cells are periodically arranged in vertical and horizontal directions. In paragraph 6,
The microstructure is an anisotropic medium for complete transmission of oblique incident acoustic waves having a slit shape including a rectangle and two semicircles. In clause 7,
The microstructure includes preset design variables,
The design variable is the length of the first slit located at the center of the unit cell (

), radius(

), rotation angle (

) And the length of the second slit at the vertex of the unit cell (

), radius(

), rotation angle (

), size of unit cell (a), number of unit cells (

) Containing anisotropic medium for complete transmission of oblique incident seismic waves.

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