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

[Technical Field]

[0001] The present disclosure relates to a metamaterial that aims to achieve high wave energy transmittance through an acoustic barrier, and more particularly, to a metamaterial capable of maximizing wave energy transmittance by having a negative effective mass density and elastic moduli to resolve an impedance mismatch between a background medium and an acoustic barrier.[Background Art]

[0002] Metamaterials are artificially engineered materials that exhibit properties not found in nature, and are composed of a periodic arrangement of precisely designed unit cells. By changing the geometric shape of the unit cells, or adjusting the structural arrangement or the interconnections between the unit cells, it is possible to adjust the optical, electromagnetic, and acoustic properties of the metamaterial, so that the metamaterials are primarily used to control wave energy.

[0003] Early research on metamaterials primarily focused on controlling optical and electromagnetic waves. For example, metamaterials with a negative refractive index have been used to develop technologies such as "perfect lenses" that focus light directly without interference, and "unidirectional" propagation devices that propagate electromagnetic waves in a specific direction.

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

[0005] On the other hand, research on metamaterials aimed at "perfect transmission" via acoustic barriers is still in its infancy. An acoustic barrier is a medium with very high acoustic impedance compared to the background medium. As illustrated in FIG. 1, when waves such as acoustic waves or elastic waves are incident on an acoustic barrier, most of the wave energy is reflected, resulting in very low energy transmittance. An "acoustic invisibility cloak" is a metamaterial that surrounds a scatterer in a background medium. The acoustic invisibility cloak serves to transmit wave energy without any loss by making the scatterer unrecognizable as if there is no scatterer from the perspective of waves, but has a drawback in that it should completely surround the scatterer. Apart from metamaterials, examples of the technology for achieving high transmittance may include an acoustic impedance matching layer. However, since the acoustic impedance matching layer should be installed at both wave incidence and transmission regions, when the acoustic impedance matching layer cannot be installed within the transmission region, its usability is significantly reduced.

[0006] Increasing the transmittance of the wave energy through the acoustic barrier has various potential applications, such as identifying conditions beyond the acoustic barrier or transmitting energy beyond the acoustic barrier for medical treatment, and therefore research and development in this regard are required.

[0007] [Related Art Document] (Patent Document 1) Korean Patent No. 10-2354340 (Registered January 18, 2022)[Disclosure][Technical Problem]

[0008] The present disclosure was conceived to address the above problems, and an object of the present disclosure is to provide a metamaterial capable of maximizing wave energy transmittance by having a negative effective mass density and elastic moduli to eliminate an impedance mismatch between a background medium and an acoustic barrier.[Technical Solution]

[0009] In one general aspect, an acoustic barrier transmission metamaterial for wave energy, in which 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 have a structure in which a hard material at a central portion thereof is coated with a soft material.

[0010] The unit cells may be configured to have a structure in which a constant vertical cross-sectional shape extends in a longitudinal direction.

[0011] The unit cells may include multiple inclusions, and each of the inclusions may be radially distributed with respect to a center of a vertical cross-section of the base matrix.

[0012] The unit cells may have a symmetrical structure with respect to the center of the vertical cross-section of the base matrix.

[0013] The inclusion may be provided in four, and the four inclusions may respectively be spaced apart from the center of the vertical cross-section of the base matrix by an equal distance, and may be arranged one by one respectively in east, west, south, and north directions.

[0014] Design variables may include: a length (a) of one side of the vertical cross-section of the base matrix, a distance (s) from the center of the vertical cross-section of the base matrix to a center of a vertical cross-section of the inclusion, a diameter (r) or a length (d) of one side of a vertical cross-section of the hard material, and a thickness (t) of the soft material in the vertical cross-section.

[0015] An operating center frequency and a magnitude of effective properties of the metamaterial may be adjusted by adjusting a, s, r, d, and t.

[0016] The vertical cross-section of the base matrix may be formed in a polygon such that the unit cells are periodically arranged.

[0017] A vertical cross-section of the inclusion may be circular or polygonal.

[0018] A mass density of the soft material may be less than that of the hard material, and a mass density of the base matrix may be greater than that of the soft material and less than that of the hard material.

[0019] The base matrix may have a mass density in between 1,000 kg / m3 and 2,000 kg / m3 and a Young's modulus in between 1 GPa and 2 GPa, the soft material may have a mass density of 1,000 kg / m 3< or less and a Young's modulus of 0.1 GPa or less, and the hard material may have a mass density of 2,000 kg / m 3< or more and a Young's modulus of 30 GPa or more.

[0020] A combination of the base matrix, the soft material, and the hard material may include at least one of epoxy-rubber-copper, PI-PDMS-copper, and PMMA-rubber-steel.

[0021] The metamaterial may have a negative effective property in an operating frequency band.

[0022] The metamaterial may have effective properties having magnitudes in an operating frequency band that are equal to those of the acoustic barrier.

[0023] The metamaterial may be in close contact with either a transducer that generates the wave energy or the acoustic barrier, or may be arranged in a space between the transducer and the acoustic barrier.[Advantageous Effects]

[0024] The metamaterial of the present disclosure has a negative effective mass density and elastic moduli to resolve an impedance mismatch between a background medium and an acoustic barrier, thereby maximizing wave energy transmittance.

[0025] Furthermore, according to the present disclosure, the metamaterial has a simple structure, making it easy and inexpensive to manufacture, the characteristics of the metamaterial, such as its operating center frequency and transmission bandwidth, can be easily adjusted through various combinations of constituent materials or modifications of geometric factors, and the metamaterial can implement sufficient transmittance even when accounting for some errors in the design variables.[BRIEF DESCRIPTION OF THE DRAWINGS]

[0026] FIG. 1 is a diagram illustrating general wave propagation. FIG. 2 is a diagram illustrating wave propagation according to an example of the present disclosure. FIG. 3 is a diagram illustrating a metamaterial according to an example of the present disclosure. FIG. 4 is a diagram for describing a principle of implementing resonance and negative material properties of the metamaterial. FIG. 5 is a diagram illustrating performance of the metamaterial according to an application example of the present disclosure. FIG. 6 is a diagram illustrating an effective mass density and Young's modulus of the metamaterial as a function of frequency. FIG. 7 is a diagram illustrating the performance of the metamaterial according to a combination of properties. FIG. 8 is a diagram illustrating the performance of the metamaterial according to a change in shape of an inclusion. FIG. 9 is a diagram illustrating the performance of the metamaterial according to errors in design variables. [Description of reference numerals]

[0027] 10: Metamaterial 100: Unit cell 110: Base matrix 120: Inclusion 121: Hard material 122: Soft material BA: Acoustic barrier TD: Transducer [Best Mode]

[0028] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings.

[0029] FIG. 2 is a diagram illustrating wave propagation according to an example of the present disclosure. As illustrated, a metamaterial 10 is provided between a wave generation apparatus (e.g., a transducer (TD)) and an acoustic barrier BA. When an incident wave 1 is incident on the acoustic barrier BA, a transmitted wave 2 is generated by passing through the acoustic barrier BA.

[0030] The metamaterial 10 resolves the impedance mismatch with the acoustic barrier, thereby increasing the transmittance of wave energy, thereby resulting in higher transmitted wave 2 energy. More specifically, the metamaterial has double-negative effective properties that are equal in magnitude but opposite in sign to those of the acoustic barrier. This effectively cancels out the presence of the barrier from a wave perspective, thereby increasing the transmittance of the wave energy through the acoustic barrier.

[0031] The metamaterial may be configured to be in close contact with the acoustic barrier as illustrated in FIG. 2A, designed as a front panel attached to the transducer as illustrated in FIG. 2B, or arranged in a space between the transducer and the acoustic barrier as illustrated in FIG. 2C.

[0032] Hereinafter, the structure and constituent materials of metamaterials satisfying these properties will be described in more detail.

[0033] First, the structure of the metamaterial will be described as follows.

[0034] FIG. 3 is a diagram illustrating a metamaterial according to an example of the present disclosure. The figure on the right is a perspective view of the entire metamaterial, the figure in the middle is an enlarged view of a unit cell of the metamaterial, and the figure on the left is a vertical cross-sectional view of the unit cell.

[0035] As illustrated, the metamaterial 10 has a structure in which unit cells 100 are repeatedly arranged, and the unit cells include a base matrix 110 and inclusions 120 buried within the base matrix. The metamaterial has a structure in which the unit cells are periodically arranged so that adjacent unit cells are in close contact with each other without gaps.

[0036] The inclusion 120 includes a hard material 121 and a soft material 122, and has a structure in which the hard material 121 is positioned in a central portion of the inclusion 120 and the soft material 122 is coated on an outer surface of the inclusion 120.

[0037] A single unit cell includes multiple inclusions, each of which may be radially distributed with respect to a center of the vertical cross-section of the base matrix. The unit cell having this structure may have a symmetrical structure with respect to the center of the vertical cross-section of the base matrix.

[0038] Furthermore, the unit cell may extend in a longitudinal direction (y-direction in the Fig. 3) and have a constant vertical cross-section shape (zx-cross-section in the Fig. 3) along the longitudinal direction. Accordingly, as illustrated, the base matrix and the inclusion may be configured in a columnar shape along the longitudinal direction.

[0039] The base matrix may be configured to have a vertical cross-section of a polygon, such as a square, rectangle, or regular hexagon, so that the unit cells are periodically arranged, i.e., adjacent unit cells are arranged to be in close contact with each other without gaps as described above. The inclusion may be of any shape that can be coated. For example, the vertical cross-section of the inclusion may be configured as a circle or polygon. In this case, since the metamaterial of the present disclosure may sufficiently perform a barrier transmission function even if the hard material is not completely coated by the soft material, the metamaterial has the advantage of a very high degree of freedom in terms of shape.

[0040] As a specific example of the metamaterial, as illustrated in FIG. 3A, one unit cell is configured with four inclusions, and the four inclusions may be spaced apart from the center of the vertical cross-section of the base matrix by an equal distance, and are arranged one by one in east, west, south, and north directions. The metamaterial may be formed by extending the vertical cross-section of the unit cells of FIG. 3A by a length w in a y-axis direction as illustrated in FIG. 3B, and repeatedly arranging the unit cells in x-axis and z-axis directions, so an overall final structure of the metamaterial having a cross-sectional area of h × w and a thickness d may be determined.

[0041] Next, the constituent material of the metamaterial will be described as follows.

[0042] The soft material has a lower mass density than the hard material, and the base matrix has a higher mass density than the soft material and a lower mass density than the hard material. In other words, the soft material has the lowest mass density, the base matrix has an intermediate mass density, and the hard material has the highest mass density.

[0043] As a specific example, the present disclosure may use epoxy as the base matrix, rubber as the soft material, and copper as the hard material. In this case, the mass density (ρ), Young's modulus (E), Poisson's ratio (v), 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, and η copper =0.002. This is organized in a table as follows. [Table 1]base matrix (epoxy)soft material (rubber)hard material (copper)Mass density (ρ)1,100 kg / m 3< 980 kg / m 3< 8,890 kg / m 3< Young's modulus (E)0.92 GPa3.41 MPa115 GPaPoisson's ratio (v)0.410.490.33Elastic loss factor (η)0.020.030.002

[0044] The base matrix, the soft material, and the hard material are not limited to the examples of combinations above. The base matrix should have a mass density in between 1,000 kg / m3 and 2,000 kg / m3, and a Young's modulus in between 1 GPa and 2 GPa. The soft material should have a mass density of 1,000 kg / m 3< or less and a Young's modulus of 0.1 GPa or less. The hard material should have a mass density of 2,000 kg / m 3< or more and a Young's modulus of 30 GPa or more. The results of the designed transmission performance of the metamaterial according to the combinations of various materials will be described later.

[0045] Hereinafter, the operating principles and performance of the metamaterial of the present disclosure will be described.

[0046] The effective properties of the metamaterial of the present disclosure, namely the effective mass density and elastic moduli, become negative in an operating frequency band. The physical reason may be described by monopole, dipole, and quadrupole resonances caused by a relative motion between the base matrix and the inclusions, specifically, between the base matrix and four inclusions. The operating frequency band may refer to a bandwidth (transmittance of 50% or more) relative to the operating center frequency.

[0047] FIG. 4 is a diagram for describing the principles of resonance and negative properties of the metamaterial. As illustrated in FIG. 4A, when the dipole resonance occurs in which four inclusions and the base matrix move laterally in opposite phases to each other, the negative effective mass density of the metamaterial is implemented. As illustrated in FIG. 4B, when the monopole resonance occurs in which four inclusions simultaneously move toward the center, a negative bulk modulus is implemented. As illustrated in FIG. 4C, when the quadrupole resonance occurs in which the upper and lower inclusions move toward the center and the left and right inclusions move outward, a negative shear modulus is implemented.

[0048] The effective properties of the metamaterial are derived through boundary effective medium theory. For the metamaterial to function as the wave energy barrier, it should have a negative mass 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 illustrated in FIG. 3A, according to the present disclosure, design geometric factors, namely, a length a of one side of the vertical cross-section of the base matrix, a distance s from the center of the vertical cross-section of the base matrix to the center of the vertical cross-section of the inclusion, a diameter r or a length d of one side of the vertical cross-section of the hard material (described later), and a thickness (t) of the coating of the vertical cross-section of the soft material may be included as design variables. By adjusting the geometric factors a, s, r or d, and t, the metamaterial may 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.

[0049] Meanwhile, although not illustrated separately, in addition to the case where four inclusions are provided as illustrated in FIG. 4, in the case where the unit cell includes multiple inclusions as described above, and the multiple inclusions are radially distributed with respect to the center of the vertical cross-section of the base matrix while having a symmetrical structure with respect to the center, the negative acoustic properties of the metamaterial may of course be implemented by the same principle.

[0050] FIG. 5 is a diagram illustrating performance of the metamaterial according to an application example of the present disclosure. This application example assumed a 6 mm thick skull phantom, acting as an acoustic barrier, within a background medium (water) blocking the transmission of 1 MHz ultrasound. The properties of the skull phantom, which acts as the acoustic barrier, are ρ skull =1,900 kg / m 3< and E skull =16 GPa.

[0051] A comparison was made between a case where there is the skull phantom without the metamaterial and a case where the metamaterial was attached to the skull phantom, as illustrated in FIG. 5A. The metamaterial according to the present example is configured to have a thickness of 6 mm by arranging four unit cells in the wave propagation direction. Each unit cell includes four inclusions, and the geometric factors of each unit cell are designed to satisfy a = 150 µm, r = 18 µm, t = 18 µm, and s = 36 µm.

[0052] As illustrated in FIG. 5B, when there is only the skull phantom (w / o) without the metamaterial, it may be confirmed that the transmittance of the wave energy is very low, at around 20%. In contrast, when the metamaterial is attached to the skull phantom (w / o), the transmittance at the center frequency of 1 MHz increases by more than fourfold, reaching 84%, and the bandwidth relative to the center frequency is approximately 0.031.

[0053] The reason the transmittance increases near the center frequency of 1 MHz when the metamaterial is installed is because the effective properties of the metamaterial are derived from values that are approximately equal in magnitude and opposite in sign to those of the skull phantom in the frequency band.

[0054] FIG. 6 is a diagram illustrating the effective mass density and Young's modulus of the metamaterial as a fuction of frequency. As illustrated, by calculating the ratios between the effective properties of the metamaterial and the properties of the skull phantom as the function of frequency, both the mass density ratio and the Young's modulus ratio approach -1 in the vicinity of 1 MHz. This means that at 1 MHz, the metamaterial acoustically cancels out the barrier, achieving high transmittance. In this way, the metamaterial of the present disclosure may be designed so that its effective properties, i.e., the effective mass density and elastic moduli, have negative values in the operating frequency band.

[0055] The present disclosure will be described in more detail below through each embodiment.

[0056] First, in a first embodiment, it is confirmed that it is possible to design the metamaterial to maximize the transmittance of the wave energy even when the combination of the base matrix, soft material, and hard material constituting the metamaterial changes, or the target center frequency changes.

[0057] In this example, the design results and the wave energy transmission performance of the metamaterial were verified for cases in which the center frequency is 2 MHz and the base matrix, the soft material, and the hard material are polyimide (PI), polydimethylsiloxane (PDMS), and copper (PI-PDMS-copper), and PMMA, rubber, and steel (PMMA-rubber-steel), respectively.

[0058] In this example, water and a 6 mm-thick skull phantom were used as the background medium and acoustic barrier, respectively, as illustrated in FIG. 5A. As described above, the metamaterial was designed by performing optimization so that the ratio of the effective properties of the metamaterial to the properties of the skull phantom in the vicinity of the center frequency of 2 MHz is -1. The metamaterial according to the present example is configured to have a thickness of 6 mm by arranging four unit cells in the wave propagation direction as illustrated in FIG. 5A, and each unit cell includes four inclusions. In the case of the PI-PDMS-copper combination, the geometric factors of each unit cell were designed to satisfy a=150 µm, r=11 µm, t=5 µm, and s=44 µm, and in the case of the PMMA-rubber-steel combination, the geometric factors of each unit cell were designed to satisfy a=150 µm, r=13 µm, t=7 µm, and s=38 µm.

[0059] FIG. 7 is a diagram illustrating the performance of the metamaterial according to the combination of properties. As illustrated, when applying the metamaterials of the combinations of the PI-PDMS-copper and the PMMA-rubber-steel, the energy transmission of the wave energy exhibits the maximum transmittances of 91% and 79% in the center frequency of 2 MHz, respectively, and that the bandwidth relative to the center frequency is derived as 0.047 and 0.045, respectively.

[0060] Next, in a second embodiment, it was confirmed that the metamaterial design is possible regardless of the shape of the inclusion. More specifically, since the physical principle by which the metamaterial of the present disclosure performs the role of the acoustic barrier transmission is independent of the shape of the inclusion, the inclusions may be manufactured as polygonal lines or three-dimensional bead types depending on the manufacturing conditions.

[0061] In this example, the design results and the barrier transmission performance for the case in which the inclusion has a square cross-sectional shape were confirmed. FIG. 8 is a diagram illustrating the performance of the metamaterial according to a change in shape of an inclusion.

[0062] In this example, the center frequency is 2 MHz, the base matrix, the soft material, and the hard material are PI, PDMS, and copper, respectively (PI-PDMS-copper), and the background medium and the barrier use water and a 6-mm-thick skull phantom, respectively, as illustrated in FIG. 5A. The metamaterial according to the present example is configured to have a thickness of 6 mm by arranging four unit cells in the wave propagation direction, as illustrated in FIG. 5A, and each unit cell includes four inclusions. In this case, the metamaterial was designed to satisfy the geometric factors of each unit cell, as illustrated in FIG. 8A, namely, the length of one side of the square PI base 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 from the center to the inclusion s = 39 µm.

[0063] Furthermore, the square-structured metamaterial of this example was compared with the circular-structured metamaterial made of the PI-PDMS-copper described in the first embodiment.

[0064] As illustrated in FIG. 8B, the wave energy transmission performance of the square-structured metamaterial yields a transmittance of 88%, which is slightly reduced compared to that of the circular-structured metamaterial, and that the bandwidth relative to the center frequency of the square-structured metamaterial is derived as 0.049, which is slightly increased compared to that of the circular-structured metamaterial.

[0065] Next, in a third embodiment, the sensitivity of the transmission performance of the metamaterial to errors is confirmed. Since the size of the inclusion within the unit cell of the metamaterial is very small on the scale of several tens of µm, it is necessary to investigate the sensitivity of the transmission performance to errors that may occur during fabrication in order for the metamaterial to operate in the ultrasonic band from several hundred kilohertz to several megahertz.

[0066] In this example, the metamaterial was designed using the metamaterial illustrated in FIG. 3, and the base matrix, the soft material, and the hard material of the unit cell were each designed as the combination of epoxy, rubber, and copper (epoxy-rubber-copper). The transmission performance was investigated when each design variable, that is, a, r, t, and s was given an error (tolerance) within 5%. Specifically, three types of errors such as large errors (4 to 5%), medium errors (1 to 4%), and small errors (0 to 1%) were applied to the design variables a, r, t, and s, so a total of 81 combinations of metamaterials were investigated for their transmission performance.

[0067] FIG. 9 is a diagram illustrating the performance of the metamaterial according to errors in design variables. As illustrated, the investigation results confirmed that the center frequency shifted within 5%, and the maximum transmittance was maintained at a level of approximately 80 to 85%. As a comparative example, when there is no error, the maximum transmittance corresponds to 84% as illustrated in FIG. 5B. The shift in the center frequency depends on the error applied to the design variable a that determines the size of the base matrix, and it may be confirmed that fabrication errors in the design variables other than the unit cell size have only a negligible effect on the performance of the metamaterial.

[0068] As described above, the metamaterial of the present disclosure has the negative effective mass density and elastic moduli in the operating frequency band to resolve the impedance mismatch between the background medium and the acoustic barrier, thereby maximizing the wave energy transmittance.

[0069] Furthermore, according to the present disclosure, the metamaterial has a simple structure, making it easy and inexpensive to manufacture, the characteristics of the metamaterial, such as its operating center frequency and transmission bandwidth, can be easily adjusted through various combinations of constituent materials or modifications of geometric factors, and the metamaterial can implement sufficient transmittance even when accounting for some errors in the design variables.

[0070] Furthermore, the metamaterial of the present disclosure may be utilized in various fields.

[0071] For example, the metamaterial of the present disclosure may be utilized in the medical field. In the case of the medical field, the metamaterial is as follows. It is known that ultrasound energy cannot pass through the skull due to acoustic impedance mismatch between the human skull and the surrounding medium, and thus brain imaging or treatment of brain disorders using ultrasound is considered impossible. By utilizing the acoustic barrier transmission metamaterial of the present disclosure to deliver the ultrasound energy to brain regions 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 requiring routine or repeated screening.

[0072] For example, the metamaterial of the present disclosure may be utilized in the defense field. It is very important to avoid sonar systems that detect the location of submarines or warships during maritime exploration and military operations. By applying the barrier-transmitting metamaterial to the surfaces of submarines, warships, torpedoes, etc., it may be utilized as an acoustic detection evasion technology that minimizes the reflection of ultrasound generated by active sonar.

[0073] For example, the metamaterial of the present disclosure may be utilized in the security field. In order to enable rapid rescue operations in disaster sites or crime scenes involving hostage situations that are concealed by thick concrete walls or metallic structures, such as building collapses, ship sinking, or fire scenes, it is important to accurately identify locations of rescue targets. The development of the barrier-transmitting acoustic radar technology based on the metamaterial of the present disclosure will enable rapid identification and response to situations where the interior is visually obstructed.

[0074] Although exemplary embodiments of the present disclosure have been described with reference to the accompanying drawings, those skilled in the art will appreciate that various modifications and alterations may be made without departing from the spirit or essential feature of the present disclosure. Therefore, it should be understood that the above-mentioned embodiments are exemplary in all aspects but are not limited thereto.

Claims

1. An acoustic barrier transmission metamaterial for wave energy, wherein 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 have a structure in which a hard material at a central portion thereof is coated with a soft material.

2. The acoustic barrier transmission metamaterial of claim 1, wherein the unit cells are configured to have a structure in which a constant vertical cross-sectional shape extends in a longitudinal direction.

3. The acoustic barrier transmission metamaterial of claim 2, wherein the unit cell includes multiple inclusions, and each of the inclusions is radially distributed with respect to a center of a vertical cross-section of the base matrix.

4. The acoustic barrier transmission metamaterial of claim 3, wherein the unit cells have a symmetrical structure with respect to the center of the vertical cross-section of the base matrix.

5. The acoustic barrier transmission metamaterial of claim 3, wherein the inclusion is provided in four, and the four inclusions are respectively spaced apart from the center of the vertical cross-section of the base matrix by an equal distance, and are arranged one by one respectively in east, west, south, and north directions.

6. The acoustic barrier transmission metamaterial of claim 3, wherein design variables include: a length (a) of one side of the vertical cross-section of the base matrix, a distance (s) from the center of the vertical cross-section of the base matrix to a center of a vertical cross-section of the inclusion, a diameter (r) or a length (d) of one side of a vertical cross-section of the hard material, and a thickness (t) of coating of a vertical cross-section of the soft material.

7. The acoustic barrier transmission metamaterial of claim 6, wherein an operating center frequency and a magnitude of effective properties of the metamaterial are adjusted by adjusting a, s, r, d, and t.

8. The acoustic barrier transmission metamaterial of claim 3, wherein the vertical cross-section of the base matrix is formed in a polygon such that the unit cells are periodically arranged.

9. The acoustic barrier transmission metamaterial of claim 3, wherein a vertical cross-section of the inclusion is circular or polygonal.

10. The acoustic barrier transmission metamaterial of claim 1, wherein a mass density of the soft material is less than that of the hard material, and a mass density of the base matrix is greater than that of the soft material and less than that of the hard material.

11. The acoustic barrier transmission metamaterial of claim 1, wherein the base matrix has a mass density in between 1,000 kg / m3 and 2,000 kg / m3 and a Young's modulus in between 1 GPa and 2 GPa, the soft material has a mass density of 1,000 kg / m3 or less and a Young's modulus of 0.1 GPa or less, and the hard material has a mass density of 2,000 kg / m3 or more and a Young's modulus of 30 GPa or more.

12. The acoustic barrier transmission metamaterial of claim 1, wherein a combination of the base matrix, the soft material, and the hard material includes at least one of epoxy-rubber-copper, PI-PDMS-copper, and PMMA-rubber-steel.

13. The acoustic barrier transmission metamaterial of claim 1, wherein the metamaterial has a negative effective property in an operating frequency band.

14. The acoustic barrier transmission metamaterial of claim 1, wherein the metamaterial has effective properties having magnitudes in an operating frequency band that are equal to those of the acoustic barrier.

15. The acoustic barrier transmission metamaterial of claim 1, wherein the metamaterial is in close contact with either a transducer that generates the wave energy or the acoustic barrier, or is arranged in a space between the transducer and the acoustic barrier.

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