Acoustic barrier transmission metamaterial

Abstract

The present disclosure relates to a metamaterial for acoustic barrier transmission of wave energy. In one embodiment, the metamaterial has a structure in which unit cells are repeatedly arranged, the unit cells include a base matrix and inclusions buried in the base matrix, and the inclusions may have a structure in which a hard material at the central portion thereof is coated with a soft material.

Description

Acoustic barrier penetrating metamaterials

[0001] The present invention relates to a metamaterial for the purpose of high transmittance of wave energy to an acoustic barrier, and more specifically, to a metamaterial capable of maximizing the transmittance of wave energy by eliminating impedance mismatch between a background medium and an acoustic barrier by having an effective density and elastic modulus of negative values.

[0002] Metamaterials are artificially engineered materials with properties not found in nature. They consist of periodic arrangements of precisely designed, small unit structures. By altering the geometric shape of the unit structures, or by manipulating their arrangement or interconnections, the optical, electromagnetic, and acoustic properties of metamaterials can be manipulated. This is primarily used to control wave energy.

[0003] Early research on metamaterials focused primarily on controlling optics and electromagnetic waves. For example, metamaterials with negative refractive indices were used to develop technologies such as "perfect lenses," which focus light directly without interference, and "unidirectional" propagation devices, which propagate electromagnetic waves in only one direction.

[0004] Recently, research on metamaterials for controlling acoustic or elastic waves has been actively underway. In particular, research is focused on achieving "perfect absorption," "perfect blocking," and "perfect transmission" for extreme control of wave energy. Acoustic metasurfaces for "perfect absorption" and phononic crystals for "perfect blocking" are representative examples.

[0005] On the other hand, research on metamaterials aiming for "perfect transmission" through acoustic barriers is still in its infancy. The acoustic barrier in question is a medium with a very high acoustic impedance compared to the background medium. As shown in Figure 1, when waves such as sound or elastic waves are incident on the acoustic barrier, most of the wave energy is reflected, resulting in very low energy transmittance. A technology called an "acoustic invisibility cloak" is a metamaterial that encases scatterers within the background medium. This allows the wave to perceive the scatterer as absent, allowing the wave energy to be transmitted without loss. However, this technology requires the scatterer to be completely encased. Separate from metamaterials, an acoustic impedance matching layer exists as a technology for achieving high transmittance. However, since it must be installed on both the incident and transmitted regions, its utility is limited if it cannot be installed within the transmitted region.

[0006] Increasing the transmittance of wave energy through an acoustic barrier can be useful in various situations, such as understanding the situation beyond the acoustic barrier or transmitting energy across the acoustic barrier to enable medical treatment, so research and development in this area is required.

[0007] [Prior Art Document] (Patent Document 1) Korean Patent Gazette No. 10-2354340 (Registered on January 18, 2022)

[0008] The present invention has been devised to solve the above problems, and aims to provide a metamaterial capable of maximizing the transmittance of wave energy by eliminating the impedance mismatch between the background medium and the acoustic barrier by having an effective density and elastic modulus of negative values.

[0009] A metamaterial according to an example of the present invention is a metamaterial for acoustic barrier penetration of wave energy, wherein the metamaterial is formed by a structure in which unit cells are repeatedly arranged, and the unit cells include a base matrix and an inclusion embedded in the base matrix, and the inclusion may be formed by a structure in which a soft material is coated on a hard material at the center.

[0010] The above unit structure can be configured as a structure in which a certain vertical cross-sectional shape extends in the longitudinal direction.

[0011] The above-mentioned content is composed of a plurality of pieces, and the plurality of pieces of content can be distributed radially based on the center of the vertical cross-section of the mother body.

[0012] The above unit structure may have a symmetrical structure based on the center of the vertical cross-section of the above mother body.

[0013] The above-mentioned contents are composed of four, and the four contents can be arranged one by one in the east, west, south, and north directions, spaced apart from each other by the same distance based on the center of the vertical cross-section of the mother body.

[0014] The design variables may include the length (a) of one side of the vertical cross-section of the parent body, the distance (s) from the center of the vertical cross-section of the parent body to the center of the vertical cross-section of the inclusion, the diameter (r) or the length (d) of one side of the vertical cross-section of the hard material, and the thickness (t) of the coating of the vertical cross-section of the soft material.

[0015] By adjusting the above a, s, r or d, and t, the operating center frequency and the size of the effective material properties of the metamaterial can be adjusted.

[0016] The vertical cross-section of the above-mentioned mother body may be configured as a polygon so that the unit structures are arranged periodically.

[0017] The vertical cross-section of the above-mentioned content may be circular or polygonal.

[0018] The density of the soft material may be less than the density of the hard material, and the density of the mother body may be greater than the density of the soft material and less than the density of the hard material.

[0019] The density of the above-mentioned mother body is 1,000 kg / m 3 More than 2,000 kg / m 3 Below, Young's modulus is 1 Gpa or more and 10 Gpa or less, and the density of the soft material is 1,000 kg / m 3 The Young's modulus is 0.1 Gpa or less, and the density of the above-mentioned material is 2,000 kg / m 3 The Young's modulus can be 30 Gpa or more.

[0020] The combination of the above-described parent material, soft material, and hard material may include at least one of epoxy-rubber-copper, PI-PDMS-copper, and PMMA-rubber-steel.

[0021] The above metamaterial may have negative effective properties in the operating frequency band.

[0022] The above metamaterial may have an effective material property size in the operating frequency band that is identical to the material property size of the acoustic barrier.

[0023] The metamaterial may be placed in close contact with the wave generating device that generates the wave energy, in close contact with the acoustic barrier, or in the space between the wave generating device and the acoustic barrier.

[0024] The metamaterial of the present invention has an effective density and elastic modulus of negative values, thereby eliminating the impedance mismatch between the background medium and the acoustic barrier, thereby maximizing the transmittance of wave energy.

[0025] In addition, the metamaterial of the present invention has a simple structure, so it is easy to manufacture and inexpensive, and the characteristics of the metamaterial, such as the operating center frequency or transmission bandwidth of the metamaterial, can be easily controlled through various modifications of the combination of constituent materials or geometric factors, and has the advantage of being able to implement sufficient transmittance even when taking into account some errors in design variables.

[0026] Figure 1 is a diagram showing the propagation of a general wave.

[0027] Figure 2 is a diagram showing the propagation of waves according to an example of the present invention.

[0028] FIG. 3 is a drawing showing a metamaterial according to an example of the present invention.

[0029] Figure 4 is a drawing for explaining the principle of implementing resonance and negative properties of metamaterials.

[0030] Figure 5 is a diagram showing the performance of a metamaterial according to an application example of the present invention.

[0031] Figure 6 is a diagram showing the effective density and Young's modulus of a metamaterial according to frequency.

[0032] Figure 7 is a diagram showing the performance of metamaterials according to combinations of physical properties.

[0033] Figure 8 is a diagram showing the performance of a metamaterial according to changes in the shape of the content.

[0034] Figure 9 is a diagram showing the performance of a metamaterial according to the error of the design variable.

[0035] Hereinafter, the present invention will be described with reference to the attached drawings.

[0036] FIG. 2 is a drawing showing the propagation of a wave according to an example of the present invention. As shown, a metamaterial (10) is provided between a wave generating device (TD) (e.g., a transducer) and an acoustic barrier (BA), and when an incident wave (1) is incident on the acoustic barrier (BA), a transmitted wave (2) is generated that passes through the acoustic barrier (BA).

[0037] The metamaterial (10) resolves the impedance mismatch with the acoustic barrier, thereby increasing the transmittance of wave energy. That is, the energy of the transmitted wave (2) can correspond to high energy. More specifically, the metamaterial has a dual negative effective property that is equal to and opposite in size to the physical property of the acoustic barrier, which means that it plays a role in canceling out the existence of the barrier from the wave perspective, thereby increasing the transmittance of wave energy to the acoustic barrier.

[0038] The metamaterial may be configured to adhere to the acoustic barrier as in (a) of Fig. 2, designed as a front material attached to the wave generating device as in (b) of Fig. 2, or placed in the space between the wave generating device and the acoustic barrier as in (c) of Fig. 2.

[0039] Below, we will examine in more detail the structure and constituent materials of metamaterials that satisfy these properties.

[0040] First, let's look at the structure of metamaterials.

[0041] FIG. 3 is a drawing showing a metamaterial according to an example of the present invention, (c) of FIG. 3 is a perspective view of the entire metamaterial, (b) of FIG. 3 is an enlarged view of a unit structure of the metamaterial, and (a) of FIG. 3 is a vertical cross-sectional view of the unit structure.

[0042] As illustrated, the metamaterial (10) is composed of a structure in which unit cells (100) are repeatedly arranged, and the unit cells include a base matrix (110) and inclusions (120) embedded within the base matrix. The metamaterial has a plurality of unit cells arranged periodically, and thus, adjacent unit cells can be tightly arranged without any gaps.

[0043] The content (120) includes a hard material (121) and a soft material (122), and has a structure in which the hard material is positioned at the center and the soft material is coated on the outer surface.

[0044] In one unit structure, the inclusions are composed of multiple pieces, and each of the multiple inclusions can be distributed radially based on the center of the vertical cross-section of the parent body, and the unit structure of this structure can have a symmetrical structure based on the center of the vertical cross-section of the parent body.

[0045] In addition, the unit structure may extend in the longitudinal direction (y direction in the drawing) and have a constant vertical cross-section shape (zx cross-section in the drawing) along the longitudinal direction. Accordingly, as illustrated, the mother body and the inclusions may be configured in a columnar shape along the longitudinal direction.

[0046] The matrix may be configured with a vertical cross-section as a polygon, such as a square, rectangle, or regular hexagon, so that the unit structures are periodically arranged, that is, so that adjacent unit structures are tightly arranged without any gaps as described above, and the inclusions may have any shape that allows coating; for example, the vertical cross-section of the inclusions may be configured as a circle or polygon. In this case, the metamaterial of the present invention has the advantage of having a very high degree of freedom in shape because it can sufficiently perform the barrier penetration function even if the hard material is not completely coated with the soft material.

[0047] As a specific example of a metamaterial, as shown in (a) of Fig. 3, one unit structure is composed of four inclusions, and the four inclusions can be arranged one by one in the east, west, south, and north directions, spaced apart by the same distance from the center of the vertical cross-section of the parent body.

[0048] The metamaterial can be formed by extending the vertical cross-section of the unit structure of Fig. 3 (a) in the y-axis direction by a length w as in Fig. 3 (b), and repeatedly arranging it in the x-axis and z-axis directions, so that the overall final structure of the metamaterial with a cross-sectional area of ​​hxw and a thickness of d can be determined.

[0049] Next, let's look at the constituent materials of metamaterials.

[0050] The soft material has a lower density than the hard material, and the matrix has a higher density than the soft material and a lower density than the hard material. In other words, the soft material has the lowest density, the matrix has an intermediate density, and the hard material has the highest density.

[0051] As a specific example, the present invention can use epoxy as a base material, rubber as a soft material, and copper as a hard material. In this case, the density (ρ), Young's modulus (E), Poisson's ratio (ν), and elastic loss factor (η) of epoxy, rubber, and copper, respectively, are ρ epoxy =1,100 kg / m 3 , ρ rubber =980 kg / m 3 , ρ copper =8,890 kg / m 3 , E epoxy =0.92 GPa, E rubber =3.41 MPa, E copper =115 GPa, ν epoxy =0.41, ν rubber =0.49, ν copper =0.33, η epoxy =0.02, η rubber =0.03, η copper =0.002. If we organize this into a table, it is as follows.

[0052] Parent material (epoxy) Soft material (rubber) Hard material (copper) Density (ρ) 1,100 kg / m 3 980 kg / m 3 8,890 kg / m 3Young's modulus (E) 0.92 GPa 3.41 MPa 115 GPa Poisson's ratio (ν) 0.41 0.49 0.33 Elastic loss factor (η) 0.02 0.03 0.002

[0053] The matrix, soft material, and hard material are not limited to the examples of the above combinations, and the density of the matrix is ​​1,000 kg / m 3 More than 2,000 kg / m 3 Below, Young's modulus is 1 GPa or more and 10 GPa or less, and the density of the soft material is 1,000 kg / m 3 The Young's modulus is 0.1 GPa or less, and the density of the material is 2,000 kg / m 3 The use of materials with a Young's modulus of 30 GPa or higher is recommended. The results of design penetration performance of metamaterials using various material combinations will be described later.

[0054] Below, the operating principle and performance of the metamaterial of the present invention will be examined.

[0055] The effective properties of the metamaterial of the present invention, i.e., the effective density and elastic modulus, become negative in the operating frequency band, and the physical reason for this can be explained by the monopole, dipole, and quadrupole resonance caused by the relative motion between the parent and the inclusions, specifically, between the parent and the four inclusions. The operating frequency band may mean the bandwidth (transmittance of 50% or more) relative to the operating center frequency.

[0056] FIG. 4 is a drawing for explaining the principle of implementing resonance and negative properties of a metamaterial. In the case where dipole resonance occurs, in which four inclusions and the parent body move laterally in opposite phases as in FIG. 4 (a), the negative effective density of the metamaterial is implemented. In the case where monopole resonance occurs, in which four inclusions move toward the center simultaneously as in FIG. 4 (b), a negative bulk elastic modulus is implemented. In the case where quadrupole resonance occurs, in which the upper and lower inclusions move toward the center and the left and right inclusions move outward as in FIG. 4 (c), a negative shear elastic modulus is implemented.

[0057] The effective properties of metamaterials are derived through boundary effective medium theory. In order for the metamaterial to perform the role of a wave energy barrier transmission, it must have a negative density and a negative Young's modulus that are equal in magnitude and opposite in sign to the properties of the acoustic barrier. To this end, as shown in Fig. 3 (a), the present invention includes geometric factors, namely, the length of one side of the vertical cross-section of the matrix (a), the distance from the center of the vertical cross-section of the matrix to the center of the vertical cross-section of the inclusion (s), the diameter (r) or one side length (d) of the vertical cross-section of the hard material (described later), and the thickness (t) of the coating of the vertical cross-section of the soft material, as design variables, and by adjusting the geometric factors a, s, r or d, and t, the metamaterial can be designed by performing optimization based on the Nelder-Mead method so that the property ratio between the acoustic barrier and the metamaterial becomes -1.

[0058] Meanwhile, although not shown separately, in addition to the case where the inclusions are composed of four as in Fig. 4, in the case where the inclusions are composed of multiple inclusions as described above and the multiple inclusions are distributed radially based on the center of the vertical cross-section of the parent body and have a symmetrical structure based on the center, it goes without saying that the negative properties of the metamaterial can be implemented by the same principle.

[0059] Figure 5 is a diagram showing the performance of a metamaterial according to an application example of the present invention. In this application example, it is assumed that a skull phantom with a thickness of 6 mm, which acts as an acoustic barrier in water as a background medium, blocks the transmission of 1 MHz ultrasound. The material properties of the skull phantom, which acts as an acoustic barrier, are ρ skull =1,900 kg / m 3 , E skull =16 Gpa.

[0060] A case where only a skull phantom exists without a metamaterial and a case where a metamaterial is attached to the skull phantom as in Fig. 5 (a) were compared. The metamaterial in this example consists of four unit structures arranged in the direction of wave propagation, each unit structure having a thickness of 6 mm, and each unit structure containing four inclusions. The geometrical parameters of each unit structure are designed to satisfy a=150 μm, r=18 μm, t=18 μm, and s=36 μm.

[0061] As shown in (b) of Fig. 5, when only the skull phantom exists without the metamaterial (w / o), the wave energy transmittance is very low at around 20%. In contrast, when the metamaterial is attached to the skull phantom (w / ), the transmittance at the center frequency of 1 MHz increases by more than four times to 84%, and the bandwidth with respect to the center frequency is around 0.031.

[0062] The reason why the transmittance increases near the center frequency of 1 MHz when installing the metamaterial is because the effective properties of the metamaterial in that frequency band are derived as values ​​that are almost equal in magnitude and opposite in sign compared to the properties of the skull phantom.

[0063] FIG. 6 is a diagram showing the effective density and Young's modulus of a metamaterial according to frequency. As shown, when calculating the ratio between the effective properties of the metamaterial and the properties of the skull phantom according to frequency, it can be confirmed that both the density ratio and the Young's modulus ratio are close to -1 around 1 MHz. This means that the metamaterial acoustically cancels out the barrier at 1 MHz, thereby realizing high transmittance. In this way, the metamaterial of the present invention can be designed so that the effective properties, that is, the effective density and elastic modulus, have negative values ​​in the operating frequency band.

[0064] Below, the present invention will be examined in more detail through each embodiment.

[0065] First, in the first embodiment, it is confirmed that it is possible to design a metamaterial to maximize the transmittance of wave energy even when the combination of the parent material, soft material, and hard material constituting the metamaterial is changed or the target center frequency is changed.

[0066] In this example, the design results and wave energy transmission performance of the metamaterial were confirmed for the case where the center frequency is 2 MHz and the parent, soft material, and hard material are PI (Polyimide), PDMS (Polydimethylsiloxane), and copper, respectively (PI-PDMS-copper), and the case where PMMA, rubber, and steel are (PMMA-rubber-steel).

[0067] In this example, the background medium and the acoustic barrier were water and a 6 mm thick skull phantom, respectively, as shown in Fig. 5 (a). As described above, the metamaterial was designed by optimizing the ratio of the effective properties of the metamaterial to the properties of the skull phantom near the center frequency of 2 MHz to be -1. The metamaterial of this example is composed of 6 mm thick unit structures arranged in the direction of wave propagation, as shown in Fig. 5 (a), and each unit structure contains 4 inclusions. In the case of the PI-PDMS-copper combination, the geometric parameters of each unit structure were designed to satisfy a = 150 μm, r = 11 μm, t = 5 μm, s = 44 μm, and in the case of the PMMA-rubber-steel combination, the geometric parameters of each unit structure were designed to satisfy a = 150 μm, r = 13 μm, t = 7 μm, s = 38 μm.

[0068] Figure 7 is a diagram showing the performance of metamaterials according to the combination of properties. As shown, when metamaterials of PI-PDMS-copper combination and PMMA-rubber-steel combination are applied, it can be confirmed that the maximum transmittance of wave energy at a center frequency of 2 MHz is 91% and 79%, respectively, and the bandwidth relative to the center frequency is 0.047 and 0.045, respectively.

[0069] Next, in the second embodiment, it is confirmed that the design of a metamaterial is possible regardless of the shape of the inclusion. More specifically, since the physical principle by which the metamaterial of the present invention performs the role of acoustic barrier penetration is independent of the shape of the inclusion, the inclusion can be manufactured into a polygonal line or a three-dimensional bead type depending on the manufacturing conditions.

[0070] In this example, the design results and barrier penetration performance for a square cross-sectional shape of the inclusion were verified. Figure 8 is a diagram illustrating the performance of the metamaterial according to changes in the shape of the inclusion.

[0071] In this example, the center frequency is 2 MHz, and the matrix, soft material, and hard material are composed of PI, PDMS, and copper in that order (PI-PDMS-copper), and the background medium and the barrier are water and a 6 mm thick skull phantom, respectively, as shown in Fig. 5 (a). The metamaterial of this example is composed of four unit structures arranged in the direction of wave propagation, as shown in Fig. 5 (a), with a thickness of 6 mm, and each unit structure includes four inclusions. At this time, it was designed to satisfy the geometric factors of each unit structure, as shown in Fig. 8 (a), namely, the length of one side of the square PI matrix a = 150 μm, the length of one side of the square copper hard material d = 21 μm, the thickness of the PDMS soft material t = 4 μm, and the distance s = 39 μm from the center to the inclusion.

[0072] And, the square structure metamaterial of this example was compared with the circular structure metamaterial made of PI-PDMS-copper material examined in the first embodiment.

[0073] As shown in (b) of Fig. 8, the wave energy transmission performance of the metamaterial with a square structure is derived as a transmittance of 88%, which is slightly reduced compared to the wave energy transmission performance of the metamaterial with a circular structure, and it can be confirmed that the bandwidth of the metamaterial with a square structure is derived as 0.049, which is slightly increased compared to the bandwidth of the metamaterial with a circular structure.

[0074] Next, in the third embodiment, we examine the sensitivity of the metamaterial's transmission performance to errors. Because the inclusions within the metamaterial's unit structure are extremely small, on the order of tens of μm, it is necessary to investigate the sensitivity of the metamaterial's transmission performance to errors that may occur during the fabrication stage to ensure its operation in the ultrasonic frequency range from hundreds of kilohertz to several megahertz.

[0075] In this example, the metamaterial was designed as the metamaterial of Fig. 3, and the unit structure's matrix, soft material, and hard material were designed as a combination of epoxy, rubber, and copper materials in that order (epoxy-rubber-copper), and the transmission performance was investigated when an error of less than 5% was assigned to each design variable, that is, a, r, t, and s. Specifically, the transmission performance of a total of 81 combinations of metamaterials was investigated by assigning three types of errors to the design variables a, r, t, and s: large error (4-5%), medium error (1-4%), and small error (0-1%).

[0076] Fig. 9 is a diagram showing the performance of the metamaterial according to the error of the design variable. As shown, the results of the investigation show that the center frequency shifts within 5%, and the maximum transmittance is maintained at the level of 80-85%. As a comparative example, the maximum transmittance in the case of no error is 84%, as seen in Fig. 5 (b). The shift of the center frequency is dependent on the error given to the design variable a, which determines the size of the matrix, and it can be confirmed that the manufacturing error of the design variables, excluding the size of the unit structure, has a minimal effect on the performance of the metamaterial.

[0077] As described above, the metamaterial of the present invention has a negative effective density and elastic modulus in the operating frequency band, thereby eliminating the impedance mismatch between the background medium and the acoustic barrier, thereby maximizing the transmittance of wave energy.

[0078] The metamaterial of the present invention has a simple structure, so it is easy to manufacture and inexpensive, and the characteristics of the metamaterial, for example, the operating center frequency or transmission bandwidth of the metamaterial, can be easily controlled through various modifications of the combination of constituent materials or geometric factors, and has the advantage of being able to implement sufficient transmittance even when taking into account some errors in design variables.

[0079] In addition, the metamaterial of the present invention can be utilized in various fields.

[0080] For example, the metamaterial of the present invention can be utilized in the medical field. In the medical field, it is known that ultrasound-based brain imaging or brain disease treatment is impossible because ultrasound energy cannot pass through the skull due to the acoustic impedance mismatch between the skull and the surrounding medium. If the acoustic barrier-penetrating metamaterial of the present invention is utilized to transmit ultrasound energy to the brain region beyond the skull, it is possible to provide fast and safe brain imaging diagnosis and brain disease treatment services for emergency stroke patients for whom securing the golden time is crucial or patients who require routine or repeated screening.

[0081] For example, the metamaterial of the present invention can be utilized in the defense sector. Avoiding sonar systems that detect the location of submarines, warships, and other vessels is crucial for ocean exploration and military operations. By applying barrier-penetrating metamaterials to the surfaces of submarines, warships, torpedoes, and other vessels, the reflection of ultrasonic waves generated by active sonar can be minimized, enabling acoustic detection and avoidance technology.

[0082] For example, the metamaterial of the present invention can be utilized in security fields. Accurately identifying the locations of victims is crucial for rapid rescue in disaster sites obscured by thick concrete walls or metal structures, such as building collapses, shipwrecks, fires, or crime scenes involving hostage situations. Developing barrier-penetrating acoustic radar technology based on the metamaterial of the present invention will enable rapid identification and response to situations where the interior is visually obstructed.

[0083] While the embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

[0084] [Explanation of symbols]

[0085] 10: Metamaterials

[0086] 100: Unit structure

[0087] 110: Mother

[0088] 120: Contains

[0089] 121: Hard material

[0090] 122: Soft materials

[0091] BA: Acoustic barrier

[0092] TD: Wave Generator

Claims

1. As a metamaterial for acoustic barrier penetration of wave energy, The above metamaterial is composed of a structure in which unit cells are repeatedly arranged. The above unit structure includes a base matrix and inclusions embedded within the base matrix, The above-mentioned content is formed by a structure in which a soft material is coated on a hard material in the center. Metamaterials.

2. In paragraph 1, The above unit structure is composed of a structure in which a certain vertical cross-sectional shape extends in the longitudinal direction. Metamaterials.

3. In paragraph 2, The above-mentioned contents are composed of multiple components, The above multiple contents are each distributed radially based on the center of the vertical cross-section of the mother body. Metamaterials.

4. In paragraph 3, The above unit structure has a symmetrical structure based on the center of the vertical cross-section of the above mother body. Metamaterials.

5. In paragraph 3, The above contents are composed of four parts, The above four contents are placed one at a time in the east, west, south, and north directions, spaced apart from each other by the same distance based on the center of the vertical cross-section of the above mother body. Metamaterials.

6. In paragraph 3, The length of one side of the vertical cross section of the above body (a), The distance (s) from the center of the vertical cross-section of the above-mentioned mother body to the center of the vertical cross-section of the above-mentioned content, The diameter (r) of the vertical cross-section of the above-mentioned material or the length (d) of one side, and Including the thickness (t) of the coating of the vertical cross-section of the above soft material as a design variable, Metamaterials.

7. In paragraph 6, By controlling the above a, s, r or d, and t, the operating center frequency and the size of the effective material properties of the metamaterial can be controlled. Metamaterials.

8. In paragraph 3, The vertical cross-section of the above-mentioned mother body is composed of polygons, and the above-mentioned unit structures are configured to be arranged periodically. Metamaterials.

9. In paragraph 3, The vertical cross section of the above-mentioned content is circular or polygonal, Metamaterials.

10. In paragraph 1, The density of the above soft material is less than the density of the above hard material, The density of the above-mentioned mother material is greater than the density of the above-mentioned soft material and less than the density of the above-mentioned hard material. Metamaterials.

11. In paragraph 1, The density of the above mother body is 1,000 kg / m 3 More than 2,000 kg / m 3 and the Young's modulus is 1 Gpa or more and 10 Gpa or less, The density of the above soft material is 1,000 kg / m 3 and the Young's modulus is 0.1 Gpa or less, The density of the above-mentioned material is 2,000 kg / m 3 The ideal is a Young's modulus of 30 Gpa or higher. Metamaterials.

12. In paragraph 1, The combination of the above-mentioned parent, soft material, and hard material comprises at least one of epoxy-rubber-copper, PI-PDMS-copper, and PMMA-rubber-steel. metamaterial 13. In paragraph 1, The above metamaterial has a negative effective material property in the operating frequency band. Metamaterials.

14. In paragraph 1, The above metamaterial has an effective material property size in the operating frequency band equal to the material property of the acoustic barrier. Metamaterials.

15. In paragraph 1, The above metamaterial is or in close contact with a wave generating device that generates the above wave energy, or adheres to the above acoustic barrier, placed in the space between the above wave generating device and the acoustic barrier, Metamaterials.

Images