KR20220059226A - Device for generating polarized elastic waves - Google Patents

Abstract

An objective of the present invention is to provide a device for generating polarized elastic waves, which realizes free conversion between circular polarization and linear polarization of elastic waves by using a polarization conversion filter made of an anisotropic medium to generate various polarized elastic waves including linear polarization, circular polarization, or elliptic polarization. According to an embodiment of the present invention, the device for generating polarized elastic waves comprises: a polarization conversion filter provided on a background material to convert an entering preset polarized elastic wave into a polarized elastic wave of at least one among linear polarization, circular polarization, and elliptic polarization to allow the polarized elastic wave to pass therethrough; and an anisotropic medium provided on the polarization conversion filter to satisfy a preset complete penetration condition to block the reflection of a preset reflecting elastic wave and allow a preset polarized elastic wave to completely pass therethrough. The complete penetration condition includes the condition in equation (1).

Description

Polarized elastic wave generator {DEVICE FOR GENERATING POLARIZED ELASTIC WAVES}

The present invention relates to a polarized acoustic wave generator.

In general, a technology related to circularly-polarized waves in the field of electromagnetic waves is well known and widely used. A circularly polarized wave is created when two linearly-polarized waves with the same speed and amplitude and perpendicular to each other travel with a phase difference of 90 degrees. Circularly polarized electromagnetic waves are generated by birefringent polarizers or metasurfaces, including nanostructures, etc., and the generated circularly polarized waves can be used for display, high-quality three-dimensional visualization, molecular asymmetry analysis, particle control, spin-dependent ( spin-dependent) optical devices, etc. However, unlike electromagnetic waves that do not require a medium and only have transverse waves, in seismic waves using a solid medium, P waves, which are longitudinal waves, SH waves (shear-horizontal waves), and SV waves (shear-vertical waves), which are transverse waves, exist simultaneously. Therefore, general theories and techniques for generating circularly polarized waves in the field of seismic waves have not been proposed or developed so far.

Even in the case of seismic waves, there are cases in which circular or elliptically polarized waves were observed in a very limited environment. As in electromagnetic waves, for example, birefringent polarizers that exist in nature are used. However, compared to electromagnetic waves, the wavelength of elastic waves is millions of times longer, so the size of the birefringent polarizer becomes very large. When a small-sized birefringent polarizer is used, a significant error occurs in the amplitude and phase of the transmitted wave, so a sophisticated circularly polarized wave cannot be generated, and an unwanted reflected wave is generated, resulting in low energy efficiency. That is, the prior art has a clear limitation in generating a circularly polarized wave in the acoustic wave field. Accordingly, various technologies based on circular polarization developed in the field of electromagnetic waves have not been developed in the field of acoustic waves. Accordingly, there is a demand for the development of an acoustic wave polarization conversion filter capable of overcoming this limitation.

An embodiment of the present invention uses a polarization conversion filter composed of an anisotropic medium to implement free conversion between linearly polarized and circularly polarized acoustic waves, thereby generating various polarized elastic waves including linear, circular, or elliptical polarized waves. An object of the present invention is to provide an elastic wave generator.

A polarization elastic wave generator according to an embodiment of the present invention comprises: a polarization conversion filter which converts a preset polarized elastic wave provided on a background material and incident thereon into at least one of linearly polarized, circularly polarized, or elliptical polarized elastic wave and transmits it; The polarization conversion filter includes an anisotropic medium that blocks reflection of a preset reflective acoustic wave and completely transmits a preset polarized acoustic wave as it satisfies a preset complete transmission condition, and the complete transmission condition is the expression of Equation (1) include conditions.

Equation (1)

(d : thickness of anisotropic medium, λ ₁ : wavelength of eigenmode 1, λ ₂ : wavelength of eigenmode 2, N ₁ : number of displacement field nodes of eigenmode 1, N ₂ : number of displacement field nodes of eigenmode 2, ρ ₀ : mass density of background medium, C ⁰ _S : shear modulus of background medium, ρ : mass density of anisotropic medium, C _T : shear modulus of anisotropic medium, C _HS-VS : shear mode coupling modulus of anisotropic medium)

The complete transmission condition may include the condition of Equation (2) in a state where the first resonant frequency of the anisotropic medium is set.

(Equation 2)

(d: thickness of anisotropic medium, λ ₁ : wavelength of eigenmode 1, λ ₂ : wavelength of eigenmode 2, N ₁ : number of displacement field nodes of eigenmode 1, N ₂ : number of displacement field nodes of eigenmode 2, ρ ₀ : mass density of background medium, C ⁰ _S : shear modulus of background medium, ρ : mass density of anisotropic medium, C _T : shear modulus of anisotropic medium, C _HS-VS : shear mode bonding elasticity of anisotropic medium Coefficient, f ₁ : first resonant frequency of anisotropic medium)

The anisotropic medium may include at least one of a material existing in nature, a chemically synthesized material, a composite material, or a three-dimensional elastic metamaterial including a sub-wavelength structure.

The three-dimensional elastic metamaterial may include unit cells having one or more microstructures inclined in a preset direction with respect to the vibration direction of the linearly polarized acoustic wave incident into the anisotropic medium.

The unit cell may have an asymmetric structure in top and bottom, left and right. A plurality of microstructures having different shapes may be included in the unit cell. The microstructure may be formed by a combination of different materials, including solids and fluids.

The three-dimensional elastic metamaterial may have a sub-wavelength structure in which unit cells including an empty space in the shape of a cylinder inclined in a preset direction are periodically arranged in vertical and horizontal directions.

The three-dimensional elastic metamaterial may have a sub-wavelength structure in which unit cells including two different inclined cuboid-shaped empty spaces are periodically arranged in vertical and horizontal directions.

By using the polarization conversion filter, 100% of a linearly polarized acoustic wave can be converted into a circularly polarized acoustic wave, and free conversion between linearly polarized and circularly polarized acoustic waves can be realized. It has the effect of generating seismic waves.

1 is a diagram illustrating an x-polarization wave, a y-polarization wave, a right circularly polarized wave, and a left circularly polarized wave according to an embodiment of the present invention.
2 is a diagram illustrating a situation in which a linearly polarized acoustic wave incident on a polarization conversion filter is converted into a circularly polarized acoustic wave and transmitted therethrough.
3A is a diagram illustrating a rectangular parallelepiped unit cell including an inclined cylinder-shaped empty space and a three-dimensional elastic metamaterial that is periodically arranged in vertical and horizontal directions.
3B is a diagram illustrating a rectangular unit cell including two different inclined rectangular parallelepiped-shaped empty spaces and a three-dimensional elastic metamaterial that is periodically arranged in the vertical and horizontal directions.
4 is a diagram illustrating a simulation result of polarization conversion of an acoustic wave according to an embodiment of the present invention.
5 is a diagram illustrating a circularly polarized acoustic wave generator and measurement device.
6A is a diagram illustrating equipment for evaluating mechanical properties of a specimen using a circularly polarized acoustic wave generator and a measuring device.
6B is a diagram illustrating the relationship between the shear modulus ratio of the specimen and the measured shear wave phase difference.
7 is a diagram illustrating equipment for evaluating defects of a specimen using a circularly polarized acoustic wave generator and a measuring device.

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

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

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

An apparatus for generating a polarization elastic wave according to an embodiment of the present invention includes a polarization conversion filter that converts an incident preset polarized elastic wave into at least one of a linear waveform, a circular waveform, and an elliptical polarization acoustic wave and transmits the converted acoustic wave. The polarization conversion filter may include an anisotropic medium that blocks reflection of a preset reflective acoustic wave and completely transmits a preset circularly polarized acoustic wave as it satisfies a preset complete transmission condition. By using a polarization conversion filter composed of an anisotropic medium, free conversion between linearly polarized and circularly polarized acoustic waves can be realized.

A linearly polarized wave refers to a wave in which the vibration direction of an electric field or medium displacement is constant, and a circularly polarized wave refers to a wave in which the vibration direction rotates while the magnitude of the electric field or medium displacement is constant. Among linearly polarized waves, a wave whose vibration direction is parallel to the x-axis is called x-polarized waves, and a wave whose vibration direction is parallel to the y-axis is called a y-polarized wave. A circularly polarized wave is generated when an x-polarized wave and a y-polarized wave with the same velocity and amplitude travel with a phase difference of 90 degrees. At this time, when the phase of the y-polarization wave is 90 degrees ahead of the phase of the x-polarization wave, a left circular polarization (LCP) wave is generated, and the phase of the x-polarization wave is 90 degrees ahead of the phase of the y-polarization wave In this case, right circular polarization (RCP) is generated. A conceptual diagram for a linearly polarized wave and a circularly polarized wave can be represented as shown in FIG. 1 . 1 is a diagram illustrating an x-polarization wave 101, a y-polarization wave 102, a right circularly polarized wave 103, and a left circularly polarized wave 104 according to an embodiment of the present invention. Elliptically-polarized waves are generated when the phase difference between an x-polarized wave and a y-polarized wave having the same velocity is not 90 degrees, and the shape can be determined by the phase difference between the two waves. In the field of seismic waves, x-polarized waves are called SH waves (shear-horizontal waves), y-polarized waves are called SV waves (shear-vertical waves), and z-polarized waves are called P waves (primary waves) or longitudinal waves. , left-handed circularly-polarized acoustic waves are called left-handed circularly-polarized shear waves (LCS waves), and right-handed circularly-polarized acoustic waves are called right-handed circularly-polarized shear waves (RCS waves).

An embodiment of the present invention may implement an acoustic wave polarization conversion that 100% converts a vertically incident linearly polarized acoustic wave into a circularly polarized acoustic wave using a polarization conversion filter composed of an anisotropic medium. In this case, the incident acoustic wave may be a P wave, an SH wave, or an SV wave, and the transmitted acoustic wave may be an LCS wave or an RCS wave, which may be implemented through different filters. For example, the same isotropic material may be adjacent to the left and right of the polarization conversion filter according to the embodiment of the present invention, and the SV wave may be vertically incident on the polarization conversion filter to generate the LCS wave.

2 is a diagram illustrating a situation in which a linearly polarized acoustic wave incident on a polarization conversion filter according to an embodiment of the present invention is converted into a circularly polarized acoustic wave and transmitted therethrough. Referring to FIG. 2 , when the polarization conversion filter 202 is inserted into the background medium 201 , the linearly polarized acoustic wave 203 vertically incident on the polarization conversion filter 202 is 100% of the circularly polarized acoustic wave 204 . It can be seen that the situation is transformed and transmitted. If the polarization conversion filter 202 is used, the pure circularly polarized acoustic wave 204 can be completely transmitted without the reflected acoustic wave.

In the embodiment of the present invention, in order to 100% convert the linearly polarized acoustic wave 203 into the circularly polarized acoustic wave 204 , a mathematical condition that an anisotropic medium constituting the polarization conversion filter 202 must satisfy may be presented. For example, one of the two eigenmodes in an anisotropic medium must satisfy the half-wave resonance condition and the other must satisfy the quarter-wave resonance condition. . In addition, an impedance matching condition between the background medium 201 and the anisotropic medium must be satisfied. The conditions related thereto are expressed as Equation (1).

[Equation 1]

(d : thickness of anisotropic medium, λ ₁ : wavelength of eigenmode 1, λ ₂ : wavelength of eigenmode 2, N ₁ : number of displacement field nodes of eigenmode 1, N ₂ : number of displacement field nodes of eigenmode 2, ρ ₀ : mass density of background medium, C ⁰ _S : shear modulus of background medium, ρ : mass density of anisotropic medium, C _T : shear modulus of anisotropic medium, C _HS-VS : shear mode coupling modulus of anisotropic medium)

If the first resonant frequency of the anisotropic medium is selected by the user, the physical property values of the anisotropic medium satisfying Equation 1 above can be calculated by Equation 2 below.

[Equation 2]

(d: thickness of anisotropic medium, λ ₁ : wavelength of eigenmode 1, λ ₂ : wavelength of eigenmode 2, N ₁ : number of displacement field nodes of eigenmode 1, N ₂ : number of displacement field nodes of eigenmode 2, ρ ₀ : mass density of background medium, C ⁰ _S : shear modulus of background medium, ρ : mass density of anisotropic medium, C _T : shear modulus of anisotropic medium, C _HS-VS : shear mode bonding elasticity of anisotropic medium Coefficient, f ₁ : first resonant frequency of anisotropic medium)

As an anisotropic medium having physical property values given in Equation 2, it is one of three-dimensional elastic metamaterials including materials existing in nature, chemically synthesized materials, composite materials, and subwavelength structures. Substances containing more than one species may be utilized. A method of implementing an anisotropic medium constituting a polarization conversion filter capable of generating a circularly polarized wave by utilizing a three-dimensional elastic metamaterial will be described in a specific embodiment.

By using the polarization conversion filter according to the embodiment of the present invention, free conversion between linearly polarized acoustic waves and circularly and elliptical polarized acoustic waves is possible. The linearly polarized acoustic waves handled in the embodiment of the present invention include P waves, SH waves, and SV waves. The circularly polarized acoustic waves include left-handed circularly-polarized shear waves (LCS waves) and right-handed circularly-polarized shear waves (RCS waves). ) is there. When the present invention is utilized, polarization conversion between linearly polarized light and circularly polarized light (P wave, SH wave or SV wave <->LCS wave, RCS wave), polarization conversion between circularly polarized light (LCS wave <->RCS wave), linear Polarization conversion between polarizations (P wave <-> SH wave <-> SV wave) is possible, and this can be implemented through different filters. At this time, since the prior art has a limitation in generating a sophisticated circularly polarized acoustic wave, a specific embodiment focuses on a filter that converts a linearly polarized acoustic wave (SH wave or SV wave) into a circularly polarized acoustic wave (LCS wave or RCS wave) Explain.

As the anisotropic medium for forming the polarization conversion filter according to the embodiment of the present invention, materials existing in nature, chemically synthesized materials, composite materials, etc. may be used, but there may be difficulties in finding or synthesizing an appropriate material having desired properties. can Therefore, it is possible to implement an anisotropic medium by using a three-dimensional elastic metamaterial including a sub-wavelength structure that can freely design the extreme properties of the material. The three-dimensional elastic metamaterial to be applied to the embodiment of the present invention has a structure in which the sub-wavelength structure in the unit cell is periodically arranged in the vertical, left-right directions, and various patterns are present in the sub-wavelength structure inside the unit cell. can be used

In order to be implemented as a three-dimensional elastic metamaterial, the anisotropic medium may include one or more microstructures inclined with respect to the vibration direction of an acoustic wave incident into the anisotropic medium as a unit cell. For example, as the unit cell of the three-dimensional elastic metamaterial, a rectangular unit cell including an inclined cylinder or a rectangular parallelepiped-shaped empty space may be utilized, which may be formed as shown in FIGS. 3A and 3B , respectively.

3A is a diagram illustrating a rectangular unit cell 301 including an inclined cylinder-shaped empty space 302 and a three-dimensional elastic metamaterial 303 that is periodically arranged in the vertical and horizontal directions. 3B shows a rectangular unit cell 304 including two different inclined rectangular parallelepiped-shaped empty spaces (305 and 306, respectively) and a three-dimensional elastic metamaterial 307 arranged periodically in the vertical and horizontal directions. . Since the unit cells shown by way of example in FIGS. 3A and 3B have an asymmetric structure up, down, left and right, anisotropy of the medium can be implemented. For example, as shown in FIG. 3A , a unit cell of a three-dimensional elastic metamaterial may have design variables such as L _x , L _y , L _z , L _h when it has a cylindrical empty space. In addition, as shown in FIG. 3B , when the rectangular parallelepiped-shaped empty space is provided, design variables such as L _x , L _y , L _z , l ₁ , t ₁ , l ₂ , and t ₂ may be provided. By adjusting these design parameters, it is possible to realize an anisotropic medium capable of freely converting between linear and circular polarization of acoustic waves. These three-dimensional elastic metamaterials may be manufactured using a traditional processing method such as drilling, or may be manufactured using an additive manufacturing method such as 3D printing. The microstructure inside the unit cell may be composed of different materials, including solids and fluids, in a complex way. Two or more microstructures having different shapes may exist inside the unit cell. The structure of the unit cell is not limited to a rectangular parallelepiped and may be configured as a polygon or a polyhedron on a plane or space.

On the other hand, the structure of an actual 3D elastic metamaterial capable of converting a linearly polarized acoustic wave into a circularly polarized acoustic wave is presented. Here, the background material is aluminum (ρ ₀ =2,700 kg/m ³ , E ₀ =90 GPa, V ₀ =0.33), the incident wave is a 110 kHz SV wave, and the substrate of the three-dimensional elastic metamaterial is iron (ρ Assume that ₁ = 7,850 kg/m ³ , E ₁ =200 GPa, V ₁ =0.30). 3b with design variables L _x = 3.0 mm, L _y = 2.9 mm, L _z = 2.9 mm, l ₁ = 2.3 mm, t ₁ = 0.8 mm, l ₂ = 0.9 mm, t ₂ = 0.5 mm. If the unit cells are repeatedly arranged 4 times in the wave propagation direction (z direction), the incident SV wave is 100% converted into an LCS wave. To verify this situation, a three-dimensional seismic simulation was performed using commercial software (COMSOL Multiphysics), and the results are shown in FIG. 4 . At this time, if the effective physical properties of the designed three-dimensional elastic metamaterial (ρ _CCVM = 4,793 kg/m ³ , C _T ^CCVM = 25.29 GPa, C _HS-VS ^CCVM = -9.901 GPa) are substituted into Equations 1 and 2, the It can be confirmed that the expression is satisfied (in this case, N ₁ = 1, N ₂ = 3). In addition to the three-dimensional elastic metamaterial structure or effective physical properties presented as an example, if an anisotropic medium having an appropriate structure or effective properties satisfying Equations 1 and 2 is used, polarization conversion of elastic waves can be implemented.

4 is a diagram illustrating a simulation result of polarization conversion of an acoustic wave according to an embodiment of the present invention. Referring to FIG. 4 , when the three-dimensional elastic metamaterial 402 satisfying Equations 1 and 2 is inserted into the background medium 401 , the incident linearly polarized elastic wave 403 is circularly polarized without a reflected elastic wave. 100% of the converted acoustic wave 404 may be transmitted.

The polarization conversion filter according to an embodiment of the present invention may be used as a circularly polarized acoustic wave generator and measurer. The polarization conversion filter may be implemented as a transducer for generating and measuring circular polarization by being inserted between a specimen and an existing ultrasonic generator such as a longitudinal wave or transverse wave transducer. Circularly polarized acoustic wave generator and measuring device can be widely used in the development of circularly polarized acoustic wave-based equipment in the elastic wave area. A conceptual diagram for this is shown in FIG. 5 .

5 is a diagram illustrating a circularly polarized acoustic wave generator and measurer 501 . Referring to FIG. 5 , the circularly polarized acoustic wave generator and measurer includes a conventional longitudinal or transverse wave transducer 502 and a polarization conversion filter 503 , and includes a function of transmitting a circularly polarized acoustic wave 505 to a specimen 504 and All functions of measuring the circularly polarized acoustic wave 506 coming from the specimen may be implemented.

The circularly polarized acoustic wave generator and measurement device according to an embodiment of the present invention may be used as a mechanical property evaluation device. In particular, it can be used to evaluate the shear mode anisotropy of the specimen. The shear anisotropy evaluation equipment according to an embodiment of the present invention includes a circularly polarized acoustic wave generator and a measuring device, and after highly efficiently incident circularly polarized acoustic waves from one side of the specimen, the phase difference between the SH wave and the SV wave (Ф _SH - Ф By measuring _SV ), the ratio (C ₆₆ /C ₅₅ ) between the shear modulus of the specimen is measured. A conceptual diagram for this is shown in FIG. 6A, and the relationship between the ratio between the shear modulus of the specimen and the measured phase difference between the SH wave and the SV wave is shown in FIG. 6B.

FIG. 6A is a diagram illustrating equipment for evaluating mechanical properties of a specimen 603 using a circularly polarized acoustic wave generator 601 and a measuring device 602 . Referring to FIG. 6A , a circularly polarized acoustic wave 604 may be transmitted to a specimen through a circularly polarized acoustic wave generator from one side, and the acoustic wave 605 passing through the specimen may be measured from the other side by a circularly polarized acoustic wave measuring device.

6B is a diagram illustrating the relationship between the shear modulus ratio of the specimen and the measured shear wave phase difference. The circularly polarized acoustic wave generator and measuring device according to an embodiment of the present invention may be used as a residual stress measuring device of a specimen. Residual stress measurement of specimens is importantly used for precision machining and structural integrity evaluation. However, in the case of a strain gauge used in the prior art, since the stress is calculated by measuring the deformation of the object, there is a limit in obtaining information about the initial stress condition or residual stress. The residual stress measuring device according to an embodiment of the present invention includes a circularly polarized acoustic wave generator and a measuring device, and after highly efficiently incident circularly polarized acoustic wave from one side of the specimen, measures the shape of the circularly polarized acoustic wave transmitted from the other side of the specimen. Estimate the residual stress. Since the velocities of the SH wave and SV wave are affected by the initial stress condition, the shape of the transmitted circularly polarized acoustic wave changes due to the phase difference between the SH wave and the SV wave, and by measuring this, the residual stress can be reasonably estimated.

The circularly polarized acoustic wave generator and measurer according to an embodiment of the present invention may be used as a defect evaluation device for a specimen. In the case of guided ultrasound non-destructive testing equipment used in the prior art, only the presence or absence of a defect can be determined, and there is a limit in obtaining information about the size or shape of the defect. The defect evaluation apparatus according to an embodiment of the present invention includes a circularly polarized acoustic wave generator and a measuring device, and estimates information on whether a defect exists, a defect size, a shape of a defect, etc. in a specimen by measuring the shape of a transmitted or reflected circularly polarized acoustic wave. A conceptual diagram for this is shown in FIG. 7 .

7 is a diagram illustrating equipment for evaluating the defect 704 of the specimen 703 by using the circularly polarized acoustic wave generator 701 and the measuring device 702 . Referring to FIG. 7 , when the circularly polarized acoustic wave 705 is incident on the specimen 703 , the circularly polarized acoustic wave 706 reflected and transmitted circularly polarized acoustic wave 706 is reflected according to the presence of defects, the size of the defects, and the shape of the defects in the specimen 703 . The defect 704 of the specimen 703 may be evaluated by using the change in the shape of the elastic wave 707 .

Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and it is possible to carry out various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this is also It goes without saying that they fall within the scope of the present invention.

201; background medium 202 ; Polarization Conversion Filter
203; linearly polarized acoustic wave 204 ; circularly polarized acoustic wave

Claims (9)

A polarization conversion filter that converts a preset polarized acoustic wave provided on the background material and incident into at least one of linearly polarized, circularly polarized, or elliptical polarized acoustic wave and transmits it; and
An anisotropic medium that is provided in the polarization conversion filter and completely transmits the preset polarized acoustic wave while blocking the reflection of the preset reflective acoustic wave as it satisfies the preset complete transmission condition
includes,
The complete transmission condition includes the condition of Equation (1).
Equation (1)

(d : thickness of anisotropic medium, λ ₁ : wavelength of eigenmode 1, λ ₂ : wavelength of eigenmode 2, N ₁ : number of displacement field nodes of eigenmode 1, N ₂ : number of displacement field nodes of eigenmode 2, ρ ₀ : mass density of background medium, C ⁰ _S : shear modulus of background medium, ρ : mass density of anisotropic medium, C _T : shear modulus of anisotropic medium, C _HS-VS : shear mode coupling modulus of anisotropic medium) In claim 1,
The complete permeation condition is
A polarized acoustic wave generator including the condition of Equation (2) in a state where the first resonant frequency of the anisotropic medium is set.
(Equation 2)

(d: thickness of anisotropic medium, λ ₁ : wavelength of eigenmode 1, λ ₂ : wavelength of eigenmode 2, N ₁ : number of displacement field nodes of eigenmode 1, N ₂ : number of displacement field nodes of eigenmode 2, ρ ₀ : mass density of background medium, C ⁰ _S : shear modulus of background medium, ρ : mass density of anisotropic medium, C _T : shear modulus of anisotropic medium, C _HS-VS : shear mode bonding elasticity of anisotropic medium Coefficient, f ₁ : first resonant frequency of anisotropic medium) In claim 1,
The anisotropic medium is a polarized acoustic wave generator including at least one of a material existing in nature, a chemically synthesized material, a composite material, or a three-dimensional elastic metamaterial including a sub-wavelength structure. In claim 3,
and the three-dimensional elastic metamaterial includes unit cells having one or more microstructures inclined in a predetermined direction with respect to the vibration direction of the linearly polarized acoustic wave incident into the anisotropic medium. In claim 4,
The unit cell is a polarized acoustic wave generator having an asymmetric structure vertically and horizontally. In claim 4,
A polarized acoustic wave generator including a plurality of microstructures having different shapes inside the unit cell. In claim 4,
The microstructure is a polarized acoustic wave generator in which different materials including a solid and a fluid are compositely formed. In claim 4,
The three-dimensional elastic metamaterial is a polarized elastic wave generator having a sub-wavelength structure in which unit cells including an empty space in the shape of a cylinder inclined in a preset direction are periodically arranged in vertical and horizontal directions. In claim 4,
The three-dimensional elastic metamaterial is a polarized elastic wave generator having a sub-wavelength structure in which unit cells including two different inclined cuboid-shaped empty spaces are periodically arranged in vertical and horizontal directions.

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