WO2018174339A1

WO2018174339A1 - Anisotropic medium for mode conversion of elastic wave, shear ultrasonic transducer using same, and sound insulating panel using same

Info

Publication number: WO2018174339A1
Application number: PCT/KR2017/006518
Authority: WO
Inventors: 김윤영; 양웅위; 권민우; 이형진
Original assignee: 서울대학교 산학협력단
Priority date: 2017-03-22
Filing date: 2017-06-21
Publication date: 2018-09-27
Also published as: KR101807553B1

Abstract

Provided is an anisotropic medium for mode conversion of an elastic wave. The anisotropic medium is disposed between external isotropic media and, as an anisotropic layer, causes a multimodal transmission phenomenon with respect to an incident elastic wave of a specific mode. The anisotropic medium has a non-zero mode-coupling stiffness constant, and the stiffness constant and excitation frequency-dependent thickness of the anisotropic layer satisfies the following equation (2), which is a same direction phase-matching condition, or the following equation (3), which is an opposite direction phase-matching condition. Thus, mode conversion Fabry-Perot resonance is generated. Equation (2): △φ≡kqld-kqsd=(2n+1)π, (kql: wave number of the anisotropic medium in a quasi-longitudinal mode, kqs: wave number of the anisotropic medium in a quasi-shear mode, d: thickness of the anisotropic medium, n: arbitrary integer) Equation (3): ∑φ≡kqld+kqsd=(2m+1)π, (m: arbitrary integer)

Description

Anisotropic Medium for Mode Conversion of Seismic Waves, Shear Ultrasonic Transducer Using the Same, and Sound Insulation Panel Using the Same

The present invention relates to an anisotropic medium for modulating a modulated wave, a shear ultrasonic transducer using the same, and a sound insulation panel using the same. More specifically, the present invention relates to an acoustic wave for converting a transverse wave into a longitudinal wave or a longitudinal wave into a transverse wave for industrial or medical purposes. The present invention relates to anisotropic medium for mode conversion of seismic waves that can be used in ultrasound, noise or vibration reduction, and seismic wave related technologies, a shear ultrasonic transducer using the same, and a sound insulating panel using the same.

In the wave-related fields such as electromagnetic waves, acoustic waves and elastic waves, interferometers of Fabry and Ferro using Fabry-Perot resonance, which consider only a single mode, have been widely applied.

When a wave passes through any monolayer or multilayer, muteple internal reflection and wave interference occur within the layer. That is, in the case of a single layer, a single mode incident wave can transmit 100% of the layer at the resonant frequency of Fabry and Ferro, where the thickness of the layer becomes an integer multiple of the half wavelength of the incident wave. There is a resonant frequency that can penetrate the% layer.

On the other hand, unlike electromagnetic and acoustic waves, in the case of elastic waves, both longitudinal waves (compressed waves) and transverse waves (shear waves) exist due to the solid atom coupling inside the medium, and the waves of the elastic waves are transmitted through any anisotropic layer or reflected by the anisotropic layer. At this time, due to the seismic mode coupling present in the anisotropic medium, it can be converted very easily from longitudinal to transverse waves or transverse to longitudinal waves.

However, even when such a mode change of the wave exists, the theory explaining the anisotropic medium transmission phenomenon regarding the multi-mode (longwave and transverse wave) and the technology capable of implementing it have not been developed until now.

Related prior arts are US Pat. No. 4,319,490 and US 2004-0210134.

Therefore, the technical problem of the present invention was conceived in this respect, the object of the present invention is to apply a mode conversion Fabry-Perot resonance (Transmodal Fabry-Perot resonance) to the high efficiency mode conversion from longitudinal to transverse wave or transverse wave to longitudinal wave The present invention relates to an anisotropic medium for mode conversion of elastic waves.

In addition, another object of the present invention relates to a shear ultrasonic transducer using an anisotropic medium for mode conversion of the acoustic wave.

In addition, another object of the present invention relates to a sound insulating panel using an anisotropic medium for mode conversion of acoustic waves.

In the anisotropic medium for modulating the seismic wave according to an embodiment for realizing the object of the present invention, it causes a multi-mode transmission phenomenon for a specific mode of seismic wave between the isotropic medium and incident as an anisotropic layer. Has a non-zero mode-coupling stiffness constant, and the thickness of the anisotropic layer

Equation (2) or

Formula (2)

(k _ql : wave number in quasi-longitudinal mode of anisotropic medium, k _qs : wave number in quasi-shear mode of anisotropic medium, d: thickness of anisotropic medium, n: arbitrary integer),

Formula (3)

(m: random integer)

The resonance of the mode conversion fabric, Ferro, is generated by satisfying Equation (3), which is an opposite phase matching condition.

In one embodiment, when the anisotropic medium satisfies the formulas (2) and (3), the elastic modulus of the anisotropic medium satisfies the following formula (4),

Formula (4)

(C ₁₁ : longitudinal (or compressive) modulus, C ₆₆ : transverse (or shear) modulus, C ₁₆ : modulus of modulus of modulus, p: mass density of anisotropic media, f _TFPR : modal change Fabry, Ferro resonant frequency )

It shows the symmetric transmittance and reflectance frequency response with respect to the incident acoustic wave based on the resonant frequency of mode conversion Fabry and Ferro,

Equation (5)

As shown in Equation (5), it may be possible to predict or select a resonance frequency at which the mode conversion occurs at the maximum between the longitudinal wave and the transverse wave.

In one embodiment, for the incident acoustic wave,

C ₁₁ = C ₆₆ (6)

(C ₁₁ : longitudinal modulus of anisotropic media, C ₆₆ : shear modulus of anisotropic media)

The wave polarization matching condition of Equation (6) can be satisfied.

In one embodiment, when the anisotropic medium satisfies Equation (6), the direction of particle vibration of quasi-long wave and quasi-transverse eigenmodes forms an angle of ± 45 ° from

Elastic modulus satisfies the following equation (7),

Formula (7)

Formula (8)

The perfect mode conversion resonant frequency in which the incident longitudinal wave (transverse wave) is completely converted into the transverse wave (long wave) and transmitted may satisfy the above Equation (8).

In one embodiment, the anisotropic medium,

First and second media having mirror symmetry with each other,

The first and second media,

Formula (9)

(

: Longitudinal modulus, shear modulus, modulus of modulus of elasticity of the first medium 210,

: Young's modulus, shear modulus and modulus-related modulus of elasticity of the second medium 220,

: Mass density of the first and second media)

The above formula (9) can be satisfied.

In one embodiment, each of the first and second media may be formed of an elastic metamaterial, including repeating first and second microstructures.

In one embodiment, the anisotropic medium may be implemented by repeating a slit or a curved or crushed slit microstructure having a single phase having a boundary line between different materials.

In one embodiment, the repeating microstructure of the anisotropic medium may be composed of slits, circular and polygonal holes, etc., having multiple phase boundaries where different materials contact each other, and may also include curved or crushed holes. do.

In one embodiment, the anisotropic medium may be implemented by repeating the microstructure including the resonator of the inclined form.

In one embodiment, the anisotropic medium has a size smaller than the wavelength of the incident wave, the microstructure including a supercell having a periodicity may be repeated.

In one embodiment, the anisotropic medium may be implemented by the unit cell shape of any one of a square, a rectangle, a parallelogram, a hexagon, and other polygons periodically including a microstructure.

In one embodiment, the anisotropic medium may be implemented by repeated microstructure composed of two or more different materials.

In one embodiment, the anisotropic medium may comprise a fluid or a solid.

In one embodiment, the external media may comprise an isotropic solid or an isotropic fluid.

In one embodiment, the anisotropic medium may be extended and applied not only when the acoustic wave is vertically incident but also when the elastic wave is obliquely incident.

In one embodiment, the seismic wave incident on the two-dimensional planar anisotropic medium can be extended to apply even when the seismic wave is incident on the three-dimensional space. In this case, the anisotropic medium may be used for various mode conversion between the longitudinal wave, the shear horizontal wave, and the vertical shear wave.

In one embodiment, when the anisotropic medium is implemented as a three-dimensional metamaterial in space, the shape of the microstructure inclined with respect to the wave incidence direction may be various rotating bodies, polyhedrons, or curved or crushed rotating bodies and polyhedrons, such as cylinders. The shape of the unit cell repeatedly filling the space including the corresponding microstructure may correspond to various polyhedrons such as a cube, a cube, a hexagonal column, and the like.

In the anisotropic medium for modulating the acoustic wave according to another embodiment for realizing the object of the present invention described above, the other side is located on one side of the external isotropic medium and the other side is applied to the elastic wave of the specific mode incident on the anisotropic layer which is a free end or a fixed end Has a non-zero mode-coupling stiffness constant, and the thickness of the anisotropic layer according to the

Equation (10) or

Formula (10)

Formula (11)

(m: random integer)

The resonance of the mode conversion Fabry and Ferro is generated by satisfying Equation (11), which is an opposite phase matching condition.

In one embodiment, when the anisotropic medium satisfies the formulas (10) and (11), the elastic modulus of the anisotropic medium satisfies the following formula (12),

Formula (12)

Formula (13)

As shown in Equation (13), it may be possible to predict or select a resonance frequency at which the mode conversion occurs to the maximum between the longitudinal wave and the transverse wave.

In one embodiment, the anisotropic medium may perform the acoustic wave mode conversion around the resonance frequency even when the phase matching conditions and the polarization matching conditions are satisfied within a certain range.

In one embodiment, the symbol C _ij (i, j = 1,2,3,4,5,6) of the longitudinal modulus, shear modulus and modulus of modulus of the anisotropic medium is the direction and the acoustic wave in which the anisotropic medium is located. Depending on the plane of incidence can be appropriately selected according to traditional preferences.

According to another aspect of the present invention, a shear ultrasonic transducer includes a metapatch mode converter including the anisotropic medium for mode conversion, and a specimen is placed on a bottom surface of the metapatch mode converter. A longitudinal wave is incident on the metapatch mode converter, and a defect signal reflected by the defect of the test piece is transmitted through the metapatch mode converter.

According to another aspect of the present invention, a sound insulation panel includes a metapanel mode converter including the anisotropic medium for mode conversion, and solid media coupled to both sides of the metapanel mode converter. Fluid media are respectively coupled to the outside of the solid media, the longitudinal wave generated from an external sound source through the one fluid medium is incident and then converted into a transverse wave to block the transmission of the sound source to the fluid medium on the other side.

According to embodiments of the present invention, mode conversion of an ultra-high efficiency acoustic wave may be performed through an anisotropic medium satisfying a condition in which resonance of mode conversion Fabry and Ferro occurs.

In particular, the anisotropic medium can be implemented through a variety of structures and various materials, it is possible to perform a variety of forms of acoustic wave mode conversion, it is possible to manufacture a structure of various combinations according to the technical needs.

FIG. 1A is a schematic diagram showing a state in which a seismic wave is transmitted without mode conversion in the prior art, and FIG. 1B is a graph showing a state in which resonance of Fabry and Ferro occurs due to a single mode in FIG. 1A.

Figure 2a is a schematic diagram showing the state of the acoustic wave passing through the mode conversion anisotropic medium according to an embodiment of the present invention, Figure 2b is a resonance phenomenon of the mode conversion Fabry, Ferro by the mode conversion anisotropic medium of Figure 2a It is a graph showing the state that occurs.

3A is a graph showing the transmittance and reflectance when the phase wave satisfies the phase matching conditions when the wave enters the anisotropic medium, and FIG. 3B shows the transmittance when the wave does not satisfy the phase matching condition when the wave enters the anisotropic medium. And reflectivity graph (f: frequency, d: thickness of the anisotropic medium).

4A to 4C are graphs for explaining the influence on the mode conversion rate of the wave polarization matching condition in the anisotropic medium 100.

FIG. 5A is a schematic diagram showing a state of an acoustic wave passing through an anisotropic medium in the case where perfect resonance of mode conversion Fabry and Ferro occurs. FIG. 5B illustrates resonance of perfect mode conversion Fabry and Ferro by the anisotropic medium of FIG. 5A. It is a graph showing an example of frequency response that occurs.

Figure 6a is a schematic diagram showing the state of the acoustic wave transmitted through the anisotropic medium of the double layer according to another embodiment of the present invention, Figure 6b is a graph showing the transmission and reflection frequency response of the elastic wave by the anisotropic medium of the double layer of Figure 6a to be.

FIG. 7A is a schematic diagram showing a state of an acoustic wave passing through a single layer including only the first medium of the anisotropic medium of the double layer of FIG. 6A, and FIG. 7B illustrates transmission and half frequency response of the acoustic wave by the first medium of FIG. 7A. It is a graph shown.

8 is a schematic diagram showing a state of an acoustic wave passing through an anisotropic medium when one interface is a free end or a fixed end according to another embodiment of the present invention.

FIG. 9A is a graph illustrating a reflectance frequency response when a free end boundary condition is applied to an opposite boundary surface to which an acoustic wave of the anisotropic medium is incident in the anisotropic medium of FIG. 8, and FIG. 9B is a fixed end boundary condition applied to the boundary plane. It is a graph showing the reflectance frequency response in the case.

10 is a schematic diagram showing a state in which an anisotropic medium is applied to a shear mode ultrasonic transducer according to another embodiment of the present invention to generate shear ultrasonic waves.

FIG. 11 is a schematic diagram illustrating a state of measuring shear ultrasonic defect signals using the shear mode ultrasonic transducer of FIG. 10.

12 is a schematic diagram showing a state in which an anisotropic medium is applied to a sound insulating panel according to another embodiment of the present invention.

13 is a cross-sectional view showing the microstructure of the anisotropic medium of the double layer.

14A to 14F are cross-sectional views illustrating microstructures of anisotropic media according to other embodiments of the present invention.

15A to 15C are cross-sectional views illustrating examples of anisotropic media according to other embodiments of the present invention.

As the inventive concept allows for various changes and numerous modifications, the embodiments will be described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms.

The terms are used only for the purpose of distinguishing one component from another. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this application, the terms "comprise" or "consist of" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention.

Referring to FIG. 1A, in the prior art, when an acoustic wave 11 is incident in parallel with a principal axis of an isotropic layer or anisotropic layer, mode coupling between longitudinal and transverse waves in the layer is performed. Therefore, the transmission wave 12 and the reflection wave 13 are generated without mode conversion.

Hereinafter, the case in which the

outer mediums

14 and 15 surrounding the layered material 10 are isotropic materials and the same solid materials for convenience of explanation will be described by way of example.

However, in the embodiments of the present invention described below, as well as the prior art, the external media adjacent to the left and right sides of the anisotropic layer are not limited to each other, and the external media may include not only a solid material but also a fluid material. .

In the drawings to be described later, description and illustration of an external isotropic medium are omitted for convenience of description.

In addition, when the resonance phenomenon of Fabry and Ferro occurs in a single mode in the layer without the mode coupling, as shown in FIG. 1B, the transmittance of the single mode is 100%. At this time, in the case of the single layer 10, the resonance conditions of Fabry and Ferro, in which the thickness of the layer becomes an integer multiple of the half wavelength of the incident wave, are expressed by the following equation (1).

Formula (1)

(k: number of waves for single mode inside layer 10, d: layer thickness, n: positive integer)

Referring to FIG. 2A, the anisotropic medium 100 for mode conversion according to the present embodiment has a transmission phenomenon as an anisotropic layer, and has a non-zero mode-coupling stiffness constant.

Accordingly, as shown, when the acoustic wave 101 is incident on the anisotropic medium 100, in addition to the transmission wave 102 and the reflected wave 103, the transverse wave 104 at the time of incidence of different modes that are converted, that is, longitudinal wave 104. ) And the shear wave reflected wave 105 are generated together.

On the other hand, even in such a case, there is a condition under which so-called 'transmodal Fabry-Perot resonance' occurs in which the mode conversion transmittance is maximum, which is a conventional single unit represented by Equation (1). It can be said that it differs in various forms from the mode resonance condition.

First, in mode conversion through a weakly mode-coupled anisotropic layer where the modulus of stiffness of the anisotropic medium 100 is relatively small compared to other stiffness coefficients, the transmittance is indicated, as shown in FIG. 2B. (When a sect enters the layer).

That is, referring to FIG. 2B, a part of the longitudinal wave, which is the incident wave 101, is converted into a transverse wave to generate the transmitted wave 104. The maximum transmittance occurs when the wave modes of the anisotropic medium 100 have a specific phase difference. Done. That is, in the case of the one-dimensional vertical incidence in FIG. 2A, the maximum transmission conversion rate from the longitudinal wave to the transverse wave or from the transverse wave to the longitudinal wave occurs near the resonance frequency satisfying the phase matching condition of Equation (2) below.

As a result, it is possible to generate a 'transmodal Fabry-Perot resonance' through the anisotropic medium 100 satisfying the following Equation (2).

Formula (2)

(k _ql : wave number in quasi-longitudinal mode of anisotropic medium (100), k _qs : wave number in quasi-shear mode of anisotropic medium (100), d: anisotropic medium (100) Thickness, n: any integer)

On the other hand, when the condition of the 'mode-modulated Fabry-Perot resonance' having the weak mode coupling is called a co-directional phase-matching condition, anisotropic medium ( Inside of 100), there is also a contra-directional phase-matching condition, which is defined by the following equation (3) in the case of one-dimensional vertical incidence as shown in FIG. 2A.

Formula (3)

(m: random integer)

That is, in FIG. 3A, the incident seismic wave is subjected to both the 'mode-modulated Fabry-Perot resonance' conditions (the same and opposite phase matching conditions) of Equations (2) and (3). When the anisotropic medium 100 is satisfied, the transmittance and reflectance are shown when the anisotropic medium 100 is transmitted. FIG. 3B illustrates the anisotropic medium 100 when the conditions of Formulas (2) and (3) are not satisfied. The transmittance and reflectance in the case of transmitting light are shown.

As shown, when the modulus of elasticity of the anisotropic medium 100 satisfies the two phase matching conditions, the following equation (4) is satisfied.

Formula (4)

In this case, the acoustic wave incident on the anisotropic medium 100 exhibits a symmetric transmittance and a reflectance frequency response with respect to the resonant frequency. In this case, the resonance in which the mode conversion occurs to the maximum with only the two phase matching conditions is achieved. The frequency can be accurately predicted as in the following equation (5).

Equation (5)

On the other hand, with respect to the anisotropic medium 100 having an elastic modulus that does not satisfy all of the phase matching conditions, the transmittance and reflectance frequency responses are asymmetrical with respect to the resonance frequency. It can only approximate the resonance frequency at which the mode conversion occurs at the maximum.

Inside the anisotropic medium 100 according to the present embodiment, in addition to the phase matching conditions represented by Equations (2) and (3) under the above-described 'mode-modulated Fabry-Perot resonance' condition There is a polarization-matching condition, and when the elastic wave 101 is incident vertically on the anisotropic medium 100 is defined by the following equation (6).

C ₁₁ = C ₆₆ (6)

That is, in the anisotropic medium 100 in which the wave polarization matching condition of Equation (6) is satisfied, the particle vibration directions of quasi-long wave and quasi-transverse intrinsic modes have an angle of ± 45 ° from the horizontal.

4A to 4C, in the case of one-dimensional vertical incidence into the anisotropic medium 100, the transmittance frequency response in the anisotropic medium 100 satisfying the wave polarization matching condition of Equation (6) is shown in FIG. As shown in 4b, through this, the anisotropic medium 100 enables high conversion rate and high purity mode conversion of the acoustic wave near the mode conversion resonance point.

The wave polarization matching condition is a condition that can be applied independently of the above two phase matching conditions. The general anisotropy material of FIGS. 4A to 4C also does not satisfy the phase matching condition. Therefore, the frequency response of longitudinal transmittance and transverse transmittance is not symmetrical around the mode conversion resonance point.

Referring to FIG. 5A, when the elastic modulus of the anisotropic medium 100 according to the present embodiment satisfies the phase matching conditions and polarization matching conditions of Equations (2), (3), and (6) , The elastic modulus satisfies the following equation (7).

Further, in the layer composed of the anisotropic medium, the resonance of the perfect mode conversion Fabry and Ferro occurs at the resonance frequency satisfying the following Equation (8).

Formula (7)

Formula (8)

Thus, when the longitudinal wave is incident as the incident wave 101, only the transverse wave is transmitted 102, and depending on the Poisson's ratio of the isotropic medium outside the layer, but the outer medium is isotropic metal medium, approximately 90% or more Mode conversion transmittance will occur. In this case, the wave mode of the incident wave 101 can be both a longitudinal wave and a transverse wave.

On the other hand, the reflected wave is reflected in the longitudinal wave without the mode conversion (103), when the external medium is an isotropic metal medium, it has a mode ratio conversion reflectance of less than about 10%.

That is, when the perfect mode conversion resonance occurs, perfect mode isolation occurs in which the

longitudinal waves

101 and 103 and the transverse wave 102 are isolated to the left and right of the anisotropic medium 100, respectively.

Meanwhile, referring to FIG. 5B, the transmittance and reflectance frequency responses of the anisotropic medium 100 in which the perfect mode conversion Fabry and Ferro resonance are generated are shown. It can be seen that the resonance of the ferro (100% mode ratio conversion transmittance) also occurs completely.

Through the anisotropic medium 200 of the double layer according to the present embodiment, it is possible to minimize the reflection of incident waves that are difficult to implement with the anisotropic medium 100 of the single layer described above and to maximize or minimize the acoustic wave mode conversion transmittance. .

That is, as shown in FIG. 6A, the anisotropic medium 200 includes a first medium 210 and a second medium 220, and constitutes the first and

second media

210 and 220. The microstructures of the elastic metamaterials have mirror symmetry with each other. Thus, the reflection of the incident wave can be minimized and the acoustic wave mode conversion transmittance can be maximized. In this case, the elastic wave mode conversion transmittance may be, for example, 99% or more.

In this case, when the single-wave acoustic wave 211 is one-dimensional vertical incidence into the anisotropic medium 200, the mirror symmetry condition of the microstructure is as shown in Equation (9).

Formula (9)

(

: Mass density of the first and second media)

As shown in FIGS. 7A and 7B, when the elastic wave 211 enters through the first medium 210, a mode in which approximately 40% of the transmitted

waves

102 and 104 are converted (horizontal wave at longitudinal wave incident, Or a longitudinal wave at the time of incidence of a transverse wave), and similarly, when reflected, the reflected

waves

103 and 105 are converted and reflected in a similar ratio.

That is, by using the anisotropic medium 200 of the double layer superimposed on the single layer in which the mode conversion occurs as described above, it is possible to minimize the reflectance than the single layer and to achieve almost complete mode conversion transmission performance.

8 is a schematic diagram showing a state of an acoustic wave passing through an anisotropic medium when one interface is a free end or a fixed end according to another embodiment of the present invention. FIG. 9A is a graph illustrating a reflectance frequency response when a free end boundary condition is applied to an opposite boundary surface to which an acoustic wave of the anisotropic medium is incident in the anisotropic medium of FIG. 8, and FIG. 9B is a fixed end boundary condition applied to the boundary plane. It is a graph showing the reflectance frequency response in the case.

Referring to FIG. 8, in the present embodiment, when one interface 106 of the anisotropic medium 100 is in a free end or fixed end condition, the anisotropic medium is reflective. type) It can be used for converting seismic mode.

The free end condition may be approximately applied when the external medium 15 through which the acoustic wave penetrates is a gas-like material in FIG. 1A, and the fixed end condition indicates that the external medium 15 has a very high mass density and rigidity. It can be approximated as a solid material.

If the thickness of the anisotropic medium according to the elastic modulus and the excitation frequency of the anisotropic medium is a reflection type co-directional phase matching condition of the following equation (10),

Formula (10)

Formula (11)

If the above equation (11), which is the reflective opposite phase matching condition, is satisfied, resonance of the reflective mode conversion Fabry and Ferro occurs, which causes the incident to the physical properties (Poisson's ratio in the case of isotropic material) of the appropriate external medium 107. The maximum length can be converted into a horizontal wave (long wave) reflecting a longitudinal wave (seam wave).

At this time, the elastic moduli of the reflective anisotropic medium are given by the following equation (12).

Formula (12)

In addition, since the resonant frequency of the reflection mode conversion Fabry and Ferro in which the mode conversion reflectance is maximized is given by the following equation (13), the resonance frequency of the appropriate external medium 107 can be adjusted in the same manner as in the case of the transmission mode conversion. Predictions and choices are possible.

Formula (13)

That is, when the anisotropic medium for the reflective mode conversion satisfies the wave polarization matching condition equation (6) together with the two reflective phase matching conditions exactly or approximately, the physical properties of the appropriate external medium 107 are perfectly satisfied. Resonance of the perfect reflection mode conversion Fabry and Ferro, which converts one incident mode into another mode and reflects it, can occur.

In the case of the anisotropic medium for the reflective mode conversion, the difference between the anisotropic medium and the transmissive mode conversion is almost perfect mode conversion according to the physical properties of the external medium 107 even though the wave polarization matching condition (6) is approximately satisfied. Can be implemented.

9A and 9B illustrate reflectance frequency characteristics of the anisotropic medium when the longitudinal wave mode enters the reflective anisotropic medium from the external medium 107. As shown in FIG. 9A, FIG. The reflectance frequency response when the free end boundary condition is applied to the opposite boundary surface 106 to which the acoustic wave 101 of 100 is incident, and FIG. 9B shows the fixed frequency boundary condition when the fixed end boundary condition is applied to the boundary surface 106. Reflectance frequency response.

10 is a schematic diagram showing a state in which an anisotropic medium is applied to a shear mode ultrasonic transducer according to another embodiment of the present invention to generate shear ultrasonic waves. FIG. 11 is a schematic diagram illustrating a state of measuring shear ultrasonic defect signals using the shear mode ultrasonic transducer of FIG. 10.

In general, the anisotropic medium 100 for elastic wave mode conversion described above may be specifically applied to develop a shear mode (or shear wave mode) shear mode ultrasound transducer. Shear-mode ultrasound differs from longitudinal wave ultrasound in particle motion direction, phase speed, and attenuation factor, so that defects 1004 are difficult to detect in conventional longitudinal mode. It can be used critically for detection with high sensitivity and energy efficiency. Conventional piezoelectric element-based ultrasonic transducers are excellent in generating and measuring longitudinal waves, but it is known that selective excitation of shear waves is quite difficult. Therefore, while conventionally used to convert the longitudinal wave generated by the conventional ultrasonic transducer to the shear wave using the ultrasonic wedge (wedge / transducer interface and wedge / specimen (in the case of industrial non-destructive inspection field, the specimen is a metal material) At the interface, it is also known that the return loss of ultrasonic energy due to differences in the properties of transducers, wedges and specimens is quite severe.

The anisotropic medium 100 described through the foregoing embodiments may be applied to a meta-patch mode converter 1001 that is attached to the front surface of the conventional ultrasonic transducer 1002 and is very easy to be compatible.

That is, as shown in Figure 10, the anisotropic medium 100 is provided as a metapatch mode converter 1001 is applied to the shear mode ultrasonic transducer 1000, to generate a high efficiency shear wave 102 using the same Can be.

That is, the incident longitudinal wave 101 reflects a very small amount of reflected waves 103 and passes through the metapatch mode converter 1001 to generate a highly efficient shear wave 102, thereby making it difficult to detect a conventional longitudinal wave. The structural defect 1004 of 1003 can be measured more easily.

In addition, as shown in FIG. 11, when the anisotropic medium 100 is provided as the metapatch mode converter 1001, the shear wave 101 reflected by the structural defect 1004 of the specimen 1003 is converted and measured. By making this possible longitudinal wave 102, the longitudinal wave 102 converted to such a high signal strength can be measured more easily.

As described above, the anisotropic medium 100 may be applied to the shear mode ultrasonic transducer 1000 for the sensor measuring the longitudinal wave 102 converted into a high signal strength.

The anisotropic medium for acoustic wave mode conversion described above through the embodiments may be specifically applied as a TFPR-based sound insulating panel based on mode conversion resonance. When wave energy propagates from a solid medium to a fluid medium, in the case of vertical incidence, shear waves (transverse waves) are not propagated into the fluid medium without shear modulus and are trapped inside the solid medium.

12 is the sound insulation panel 2000 in which the anisotropic medium 100 is used as the metapanel mode converter 2001, and the sound wave blocking function of the sound insulation panel 2000 based on the mode conversion fabric, the resonance of the ferro (TFPR). It is shown.

That is, referring to FIG. 12, a part of the sound wave 111 incident from the external fluid medium 2004 into the sound insulation panel 2000 becomes the longitudinal wave mode seismic wave within the solid medium 2002 and the meta-panel mode converter Meta. It passes through a panel mode converter 2001 and, with a small amount of reflected wave 103, is converted back into a shear wave 102 with high efficiency.

At this time, the converted shear wave 102 does not penetrate into the next fluid medium 2005 without shear stiffness and is mostly reflected at the boundary thereof, so that the shear wave 102 is trapped inside the solid sound insulation panel as the shear wave 110. Transmission of the 113 can be effectively blocked.

In this case, the relative layer thicknesses of the

solid mediums

2002 and 2003 with respect to the metapanel mode converter 2001 constituting the mode conversion resonance sound insulation panel 2000 may be appropriately changed.

FIG. 13 illustrates an example of the microstructure of the anisotropic medium 200 of the bilayer described with reference to FIG. 6A. Referring to FIG. 13, the anisotropic medium 200 of the bilayer may include a first medium 210 and a second layer. A medium 220 may be included, and each medium may satisfy, partially satisfy, or approximately satisfies all of the above-described 'mode conversion fabric, resonance conditions of ferro'.

Accordingly, the incident acoustic wave 211 may be transmitted 212 without mode conversion or transmitted 214 by performing mode conversion, reflection 213 without mode conversion, or reflection 215 by performing mode conversion.

In this case, each of the first medium 210 and the second medium 220 of the anisotropic medium 200 of the bilayer each have a first microstructure 230 and a second mirror symmetry with each other as shown in FIG. 13. It may have a microstructure 240.

That is, the so-called elastic meta material may be realized through the anisotropic medium 200 having the structure in which the first and

second microstructures

230 and 240 are repeated.

In the above, the case where the elastic wave is perpendicularly incident on the two-dimensional planar anisotropic medium has been described.

However, it is possible to extend and apply to the case where the elastic wave is obliquely incident on the two-dimensional planar anisotropic medium and also when the elastic wave is incident on the three-dimensional space.

In particular, when a seismic wave is incident on a three-dimensional space, a shear wave includes a shear horizontal wave and a shear vertical wave that vibrate in a horizontal direction and a vertical direction, and in this case, the anisotropic medium is modulated in any mode. Depending on whether the coefficient has a coefficient, the mode conversion resonance between the horizontal and vertical waves as well as the mode conversion resonance between the vertical and horizontal waves can be generated.

The microstructures shown in FIGS. 14A to 14C are examples of the microstructures of the anisotropic medium capable of implementing the acoustic wave mode conversion resonance. Various anisotropic media satisfying the resonance conditions of Fabry and Ferro can be realized.

For example, as shown in FIG. 14A, a slit 310 or a curved slit-like microstructure having a single phase in which different materials contact each other may be repeated to implement the anisotropic medium 300. Can be.

As shown in FIG. 14B, the anisotropic medium 301 may be implemented in a form in which a slit 311 having one single phase and another slit 312 perpendicular thereto are repeated. In particular, through the slit structure of FIG. 14B, it is possible to generate almost perfect mode conversion Fabry and Ferro resonances.

As shown in FIG. 14C, the microstructure including the inclined resonator 410 may be repeated to implement the anisotropic medium 400.

In addition, the anisotropic medium may be realized through the supercell 500 in which the

microstructures

510, 520, 530, and 540 of various shapes are combined with each other. In this case, the size of the supercell is the wavelength of the incident wave. It must be smaller and have periodicity. As shown in FIGS. 14D and 14F, the unit cell or the super cell may have a rectangular shape 610 and a hexagonal shape 710, so that the

anisotropic medium

600 and 700 may be implemented at regular intervals. do.

The microstructure of the anisotropic medium may include all unit cell shapes capable of periodic arrangement such as parallelograms, hexagons, and other polygons, in addition to square or rectangular shapes, and not only a single phase but also two or more different shapes. It may also consist of a multi-phase comprising material.

In addition, the microstructured material may be a fluid as well as a solid.

Referring to FIG. 15A, the two anisotropic media 200 may be configured to have two

different media

210 and 220 continuous to each other. Referring to FIG. 15B, the anisotropic media 800 may have two different media. The

media

810, 820 may comprise mirror symmetric microstructures as described above and may be configured to be continuous with each other.

In addition, referring to FIG. 15C, the three anisotropic media 900 may be configured such that three

different media

910, 920, and 930 are continuous with each other.

Although not shown, the media of FIGS. 15A to 15C may be repeatedly configured with each other as a multilayer to form an anisotropic media.

As described above, the anisotropic medium has more various physical properties through various microstructured metamaterials and multiple layers, and thus, it is possible to perform frequency wideband high efficiency mode conversion or selective narrowband high efficiency mode conversion for a specific frequency. Can be.

According to the embodiments of the present invention, the mode conversion of the seismic wave may be performed through an anisotropic medium satisfying the condition in which the resonance of the mode conversion Fabry and Ferro occurs.

In particular, the anisotropic medium can be implemented through a variety of structures and various materials, it is possible to perform the acoustic wave mode conversion of various characteristics, for this purpose it can be produced a structure of various combinations according to the technical needs.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

Claims

It is located between the external isotropic media and causes the multimode transmission phenomenon for the specific mode of acoustic wave incident as anisotropic layer, has non-zero mode-coupling stiffness constant, and the frequency with the elastic coefficients. According to the thickness of the anisotropic layer,

Equation (2) or

Formula (2)

(k ql : wave number in quasi-longitudinal mode of anisotropic medium, k qs : wave number in quasi-shear mode of anisotropic medium, d: thickness of anisotropic medium, n: arbitrary integer),

Formula (3)

(m: random integer)

An anisotropic medium for mode conversion which generates resonance of mode conversion Fabry and Ferro by satisfying Equation (3), which is an opposite phase matching condition.
The method of claim 1,

When the anisotropic medium satisfies the formulas (2) and (3), the elastic modulus of the anisotropic medium satisfies the following formula (4),

Formula (4)

(C 11 : longitudinal (or compressive) modulus, C 66 : transverse (or shear) modulus, C 16 : modulus of modulus of modulus, p: mass density of anisotropic media, f TFPR : modal change Fabry, Ferro resonant frequency )

It shows the symmetric transmittance and reflectance frequency response with respect to the incident acoustic wave based on the resonant frequency of mode conversion Fabry and Ferro,

Equation (5)

Anisotropic medium for mode conversion, characterized in that the prediction or selection of the resonant frequency that the mode conversion occurs to the maximum between the longitudinal wave and the transverse wave as shown in the equation (5).
The method of claim 1, wherein the incident acoustic wave,

C 11 = C 66 (6)

(C 11 : longitudinal modulus of anisotropic media, C 66 : shear modulus of anisotropic media)

An anisotropic medium for mode conversion characterized by satisfying the wave polarization matching condition of the formula (6).
The method of claim 3,

When the anisotropic medium satisfies Equation (6), the particle vibration directions of quasi-long wave and quasi-transverse eigen modes form an angle of ± 45 ° from horizontal,

Elastic modulus satisfies the following equation (7),

Formula (7)

Formula (8)

An anisotropic medium for mode conversion, wherein a perfect mode conversion resonant frequency in which incident longitudinal waves (transition waves) are completely converted into transverse waves (long waves) and transmitted satisfies Equation (8).
The method of claim 1, wherein the anisotropic medium,

First and second media having mirror symmetry with each other,

The first and second media,

Formula (9)

(
: Longitudinal modulus, shear modulus, modulus of modulus of elasticity of the first medium 210,
: Young's modulus, shear modulus and modulus-related modulus of elasticity of the second medium 220,
: Mass density of the first and second media)

Anisotropic medium for mode conversion, characterized by satisfying the above formula (9).
The method of claim 5,

Each of the first and second media includes repeating first and second microstructures, wherein the anisotropic medium for mode conversion is implemented with an elastic metamaterial.
The method of claim 1,

An anisotropic medium for mode conversion, characterized in that the microstructure of the slit (slit) or curved or crushed slit form having a single phase with a boundary between different materials is repeatedly implemented.
The method of claim 1,

Anisotropic medium for mode conversion, characterized in that the microstructure including the inclined resonator is repeatedly implemented.
The method of claim 1,

An anisotropic medium for mode conversion, characterized in that the microstructure including a supercell having a size smaller than the wavelength of the incident wave and having a periodicity is repeatedly implemented.
The method of claim 1,

Anisotropic medium for mode conversion, characterized in that the unit cell shape of any one of a square, a rectangle, a parallelogram, a hexagon, and other polygons are implemented in a periodic arrangement including a microstructure.
The method of claim 1,

Anisotropic medium for mode conversion, characterized in that the microstructure composed of two or more different materials is repeated.
The method of claim 1,

Anisotropic medium for mode conversion comprising a fluid or a solid.
The method of claim 1,

The external medium is anisotropic medium for mode conversion, characterized in that it comprises an isotropic solid or isotropic fluid.
An anisotropic layer, located at one side of the outer isotropic medium and the other side is a free or fixed end, which causes multiple modes of reflection on the incident modulus, and non-mode-coupling stiffness constants. The thickness of the anisotropic layer according to the elastic modulus and the excitation frequency

Equation (10) or

Formula (10)

(k ql : wave number in quasi-longitudinal mode of anisotropic medium, k qs : wave number in quasi-shear mode of anisotropic medium, d: thickness of anisotropic medium, n: arbitrary integer),

Formula (11)

(m: random integer)

An anisotropic medium for mode conversion which generates resonance of mode conversion Fabry and Ferro by satisfying Equation (11), which is an opposite phase matching condition.
The method of claim 14,

When the anisotropic medium satisfies the formulas (10) and (11), the elastic modulus of the anisotropic medium satisfies the following formula (12),

Formula (12)

(C 11 : longitudinal (or compressive) modulus, C 66 : transverse (or shear) modulus, C 16 : modulus of modulus of modulus, p: mass density of anisotropic media, f TFPR : modal change Fabry, Ferro resonant frequency )

It shows the symmetric transmittance and reflectance frequency response with respect to the incident acoustic wave based on the resonant frequency of mode conversion Fabry and Ferro,

Formula (13)

The anisotropic medium for mode conversion, characterized in that the prediction or selection of the resonant frequency that the mode conversion occurs to the maximum between the longitudinal wave and the transverse wave as shown in the equation (13).
The method according to claim 1 or 14,

It includes a meta-patch mode converter including the anisotropic medium for mode conversion,

A specimen is placed on the bottom of the metapatch mode converter, a longitudinal wave is incident on the metapatch mode converter, and a defect signal reflected by the defect of the specimen is transmitted through the metapatch mode converter. Shear ultrasonic transducer.
The method according to claim 1 or 14,

A metapanel mode converter including the mode converting anisotropic medium; And

Solid media coupled to both sides of the metapanel mode converter,

And a fluid medium coupled to the outside of the solid media, respectively, to inject a longitudinal wave generated from an external sound source through one fluid medium to block transmission of the sound source to the fluid medium of the other side.