KR102274826B1 - Gradient-index phononic crystals and method for designing the same - Google Patents

Abstract

Various embodiments relate to refractive index-distributed acoustic quantum crystals, which have a specified size, are arranged in a matrix form having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a two-dimensional flat plate, and a unit having a hole in the center In the refractive index distribution acoustic quantum crystal including a cell, the size of the perforation of the unit cell may be set so that the refractive index distribution acoustic quantum crystal can act as a refractive index distribution lens with respect to a bending wave having a specified frequency. . Various other embodiments are possible.

Description

Refractive index distribution acoustic quantum crystal and its design method {GRADIENT-INDEX PHONONIC CRYSTALS AND METHOD FOR DESIGNING THE SAME}

Various embodiments to be described later relate to Gradient-Index Phononic Crystals (GRIN PCs) and a design method thereof, and more specifically, focusing and harvesting the wave energy of a flexural wave. It relates to a refractive index-distributed acoustic quantum crystal capable of improving performance and a design method thereof.

Metamaterials implement wave characteristics that do not exist in nature, such as negative refractive index, by using periodic artificial structures. As the study of metamaterials, which was active in the electromagnetic field in the past, has moved rapidly to the acoustic field, research on phononic crystals using the wave characteristics of seismic waves is becoming active. For example, acoustic quantum crystals can be used to microscopically focus sound in a region smaller than a wavelength, freely change the path of travel, or improve sound wave and ultrasound imaging quality. For this, artificial structure design technology that freely adjusts the elastic modulus, density, and refractive index through periodic arrangement of structures smaller than the wavelength is essential.

When an external force is applied to an elastic object, the position of the constituent particles constituting the object changes and a force is generated to return to the original state, and the vibration by this force spreads temporally and spatially. , seismic waves, etc.

Among these elastic waves, a bending wave is a wave generated by the bending motion of a solid medium having bending stiffness. When the wave energy of the bending wave is concentrated and harvested, greater energy can be harvested than when the sound energy is focused and harvested. Therefore, it is required to develop an acoustic quantum crystal capable of focusing the bending wave energy by controlling the behavior of the bending wave.

Various embodiments disclosed in this document may provide a refractive index-distributed acoustic quantum crystal for focusing the wave energy of a bending wave.

In addition, various embodiments may provide a method for designing a refractive index distributed acoustic quantum crystal in which the wave energy of the bending wave is focused and the point at which the wave energy of the bending wave is focused is formed outside the refractive index distributed acoustic quantum crystal.

In addition, various embodiments may provide an energy harvesting system capable of focusing the bending wave and harvesting the bending wave energy using a refractive index-distributed acoustic quantum crystal.

The technical problems to be achieved in this document are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. There will be.

Refractive index distribution acoustic quantum crystals according to various embodiments, for example, have a specified size, are arranged in a matrix form having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a two-dimensional flat plate, and a hole in the center In the refractive index distribution type acoustic quantum crystal including the formed unit cell, the size of the hole in the unit cell is set so that the refractive index distribution type acoustic quantum crystal can act as a refractive index distribution type lens for bending waves having a specified frequency can be

In various embodiments, the specified size of the unit cell may be set in comparison with the length of the wavelength of the bending wave having the specified frequency.

In various embodiments, the perforation may be circular.

In various embodiments, the size of the perforations of the unit cells arranged on the same layer is the same, and the size of the perforations of the unit cells is the minimum size of the perforations of the unit cells forming the uppermost layer and the lowermost layer, and the size of the perforations of the unit cells forming the middle layer. The size of the perforation is the largest, the size of the perforation is symmetric with respect to the middle layer, and the size of the perforation from the uppermost layer to the middle layer is the effective refractive index of the refractive index distribution acoustic quantum crystal for the bending wave having the specified frequency. The distribution along the Y-axis may be set to have the form of a hyperbolic secant (sech) function.

In various embodiments, the number of layers in which the unit cells are arranged is such that a focal point at which the wave energy of a bending wave traveling through the refractive index distributed acoustic quantum crystal is focused is formed outside the refractive index distributed acoustic quantum crystal. can be set.

A method of designing a refractive index-distributed acoustic quantum crystal according to various embodiments, for example, is arranged in a matrix form having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a two-dimensional flat plate, and a hole is formed in the center A method for designing a refractive index-distributed acoustic quantum crystal including a unit cell, the method comprising: calculating a wavelength of the bending wave having a specified frequency traveling in the flat plate having a constant thickness; determining the size of the unit cell from the wavelength; calculating a maximum effective refractive index and a minimum effective refractive index for the bending wave having the specified frequency that can be achieved with the unit cell having the determined size; determining a distribution shape of a target effective refractive index so that the acoustic quantum crystal can focus the wave energy of the bending wave; and optimizing the size of the perforation of the unit cell so that the acoustic quantum crystal satisfies the target distribution shape of the effective refractive index.

In various embodiments, the method may further include forming a hole having the optimized size in the center of the unit cell.

In various embodiments, in the process of calculating the maximum effective refractive index and the minimum effective refractive index for the bending wave, the uppermost layer and the lowermost layer of the refractive index distribution type acoustic quantum crystal have a minimum effective refractive index, and an intermediate layer of the refractive index distribution type acoustic quantum crystal may have a maximum effective refractive index.

In various embodiments, the process of determining the distribution shape of the target effective refractive index includes the distribution along the Y-axis of the effective refractive index for a bending wave having the specified frequency of the refractive index-distributed acoustic quantum crystal based on the intermediate layer. may be symmetric, and a distribution along the Y-axis of the effective refractive index from the uppermost layer to the middle layer may have the form of a hyperbolic secant (sech) function.

In various embodiments, the process of optimizing the size of the perforation of the unit cell may be repeated so that the squared value of the difference between the optimal effective refractive index according to the size of the perforation and the target effective refractive index is minimized.

In various embodiments, the perforation is circular, and the process of optimizing the size of the perforation of the unit cell may optimize the radius of the circle.

An energy harvesting system including a refractive index distributed acoustic quantum crystal according to various embodiments is, for example, a refractive index distributed acoustic quantum crystal according to claims 1 to 5 and a refractive index distribution according to claims 6 to 11 a refractive index distributed acoustic quantum crystal corresponding to any one of the refractive index distributed acoustic quantum crystals designed by the design method of the acoustic quantum crystal; and a piezoelectric element disposed at a point where the bending wave passing through the refractive index distribution acoustic quantum crystal is focused.

The refractive index-distributed acoustic quantum crystal according to various embodiments can increase the performance of harvesting the wave energy of the bending wave by focusing the bending wave, and the focal point of the wave energy of the bending wave is formed outside, so that the construction of the energy harvesting system is difficult. Easy.

In the refractive index distribution acoustic quantum crystal design method according to various embodiments, each unit cell is such that the refractive index distribution along the vertical direction of the refractive index distribution acoustic quantum crystal composed of a set of unit cells has a minimum error from the target effective refractive index. structure can be optimized.

The energy harvesting system using the refractive index distributed acoustic quantum crystal according to various embodiments has a simple structure and excellent harvesting performance because the energy focusing point is outside the refractive index distributed acoustic quantum crystal.

Effects obtainable in the present disclosure are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those of ordinary skill in the art to which the present disclosure belongs from the description below. will be.

1 is an example of a unit cell of a refractive index-distributed acoustic quantum crystal according to various embodiments of the present disclosure;
2 is a top view of a refractive index-distributed acoustic quantum crystal according to various embodiments of the present disclosure;
3 is a diagram illustrating a refractive index distribution along a Y-axis of a refractive index distribution acoustic quantum crystal according to various embodiments of the present disclosure;
4 is a flowchart illustrating a method of designing a refractive index distributed acoustic quantum crystal according to various embodiments of the present disclosure;
5A illustrates a relative magnitude of energy of a bending wave passing through a refractive index-distributed acoustic quantum crystal according to an exemplary embodiment.
5B illustrates the relative magnitude of energy of a bending wave passing through a refractive index-distributed acoustic quantum crystal according to an embodiment.
6 illustrates an energy harvesting system using a refractive index distributed acoustic quantum crystal according to various embodiments of the present disclosure.
7A illustrates a maximum output voltage of an energy harvesting system including a refractive index distributed acoustic quantum crystal according to various embodiments compared to an energy harvesting system not including a refractive index distributed acoustic quantum crystal.
7B is a diagram illustrating the maximum output power of the energy harvesting system including the refractive index distributed acoustic quantum crystal according to various embodiments compared to the energy harvesting system not including the refractive index distributed acoustic quantum crystal.

Hereinafter, various embodiments of the present document will be described with reference to the accompanying drawings.

The various embodiments of this document and terms used therein are not intended to limit the technical features described in this document to specific embodiments, and should be understood to include various modifications, equivalents, or substitutions of the embodiments. In connection with the description of the drawings, like reference numerals may be used for similar or related components. The singular form of the noun corresponding to the item may include one or more of the item, unless the relevant context clearly dictates otherwise. As used herein, "A or B", "at least one of A and B", "at least one of A or B," "A, B or C," "at least one of A, B and C," and "A , B, or C" each may include any one of the items listed together in the corresponding one of the phrases, or all possible combinations thereof. Terms such as “first”, “second”, or “first” or “second” may simply be used to distinguish the component from other components in question, and may refer to components in other aspects (e.g., importance or order) is not limited.

1 is an example of a unit cell of a refractive index distributed acoustic quantum crystal according to various embodiments, FIG. 2 is a top view of a refractive index distributed acoustic quantum crystal according to various embodiments, and FIG. 3 is a refractive index according to various embodiments A diagram showing the refractive index distribution along the Y-axis of a distributed acoustic quantum crystal.

1 to 3 , in the refractive index-distributed acoustic quantum crystal 100 according to various embodiments, the unit cell 111 having the perforation 113 formed in the center is a two-dimensional flat plate in the Y-axis direction and X It is arranged in the form of a matrix having a column arrangement in the axial direction to focus the wave energy of the bending wave. For example, the two-dimensional flat plate may be an aluminum flat plate having a thickness (t) of 2 mm. However, the present invention is not limited thereto, and the two-dimensional flat plate may be used as a refractive index distributed acoustic quantum crystal if it is a solid flat plate capable of generating a bending wave and propagating it.

In various embodiments, the refractive index distributed acoustic quantum crystal 100 includes a unit cell 111 , wherein the unit cell 111 has a specified size a and a hole 113 is formed in the center. can be In this case, the unit cell 111 may have a square top to bottom surface, and the perforation 113 may have a circular shape (radius r). The shape of the perforation may have a shape other than a circular shape. The refractive index for the bending wave may be changed according to the shape and size of the perforation formed at the center of the unit cell.

In various embodiments, the size (a) of the unit cell, that is, the horizontal and vertical lengths (a) of the unit cell, is a refractive index-distributed acoustic quantum crystal (100) in which the wave energy of a bending wave having a specified frequency is formed in a two-dimensional plate. ) may be set against the wavelength of the bending wave having the specified frequency so that it can be focused by. For example, when the designated frequency of a bending wave traveling in a refractive index-distributed acoustic quantum crystal formed on a 2 mm thick aluminum plate is 50 kHz, the wavelength of the lowest mode of the bending wave is approximately 19.2 mm, and the unit cell is the bending In order to satisfy the isotropic refractive index characteristic for the wave, the size of the unit cell may be determined at about 1/4 of the wavelength of the bending wave. In an embodiment, the size (a) of the unit cell may be determined to be 5 mm.

In various embodiments, the refractive index-distributing acoustic quantum crystal may act as a gradient-index lens (GRIN lens) with respect to a bending wave having a specified frequency. In order for the refractive index distribution acoustic quantum crystal to act as a gradient-index lens (GRIN lens) for a bending wave having a specified frequency, the unit cell corresponding to the same effective refractive index in the same layer of the refractive index distribution acoustic quantum crystal This arrangement, the distribution of the effective refractive index for the bending wave having a specified frequency along the Y-axis of the refractive index distribution acoustic quantum crystal may be determined to have the form of a hyperbolic secant (sech) function. In this case, the size of the perforation of the unit cell constituting the refractive index-distributed acoustic quantum crystal may be adjusted. That is, unit cells having the same size of perforations are arranged in the same layer of the refractive index-distributed acoustic quantum crystal, and the size of perforations of the unit cells corresponding to each layer is the Y-axis of the effective refractive index for a bending wave having a specified frequency. The distribution according to can be set to have the form of a hyperbolic secant (sech) function.

In various embodiments, the size of the refractive index distributed acoustic quantum crystal may be determined by the size of the unit cell and the number of unit cells. In this case, each layer of the refractive index distributed acoustic quantum crystal may include 13 unit cells, and each layer of 13 unit cells may be stacked in 11 to 17 layers in the Y-axis direction. In addition, the number of layers of the refractive index distributed acoustic quantum crystal according to various embodiments is set so that the focal point at which the wave energy of the bending wave traveling through the refractive index distributed acoustic quantum crystal is focused is formed outside the refractive index distributed acoustic quantum crystal can be The energy focus point of the bending wave by the refractive index distribution acoustic quantum crystal composed of 14 layers exists outside the crystal, especially on the emission side, and when it is smaller than 14 layers (eg, 11 layers), the focal point moves backward, 14 In the case of more layers (eg, layer 17), the focal point may be moved closer to the crystal.

In an embodiment, the refractive index-distributed acoustic quantum crystal 100 may have a structure in which each layer in which 13 unit cells are gathered is stacked in 17 layers, as in the example shown in FIG. 2 . In this case, the first layer 110a as the uppermost layer and the seventeenth layer 110b as the lowest layer have the minimum effective refractive index achievable in the unit cell, and the ninth layer 190 as the middle layer has the maximum effective refractive index achievable in the unit cell. can have The refractive index distribution from the first layer to the seventeenth layer may be set to have the form of a hyperbolic secant (sech) function. In the refractive index distributed acoustic quantum crystal according to an embodiment, a focal point at which a bending wave traveling from an incident side is focused and a wave energy of the bending wave is focused may be formed outside the crystal, that is, on an exit side. The refractive index distribution acoustic quantum crystal composed of 17 layers can focus the most energy on the emitting side of the bending wave.

4 is a flowchart illustrating a method of designing a refractive index distributed acoustic quantum crystal according to various embodiments of the present disclosure;

Referring to Figure 4, the refractive index distribution acoustic quantum crystal design method 200 according to various embodiments is arranged in a matrix form having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a two-dimensional flat plate, A method of designing a refractive index-distributed acoustic quantum crystal capable of condensing the wave energy of a bending wave by including a unit cell with a hole formed in the center, the process of calculating the wavelength of the bending wave (210), determining the size of the unit cell process 220, calculating the maximum effective refractive index and the minimum effective refractive index achievable by the unit cell 230, determining the distribution shape of the target effective refractive index 240, the perforation to be formed in the unit cell It may include a process of optimizing the size ( 250 ) and a process of forming a hole in the center of the unit cell ( 260 ).

In various embodiments, in step 210, the wavelength of a bending wave having a specified frequency that travels in a two-dimensional plate having a constant thickness may be calculated. For example, the wavelength of a bending wave of 50 kHz frequency traveling through an aluminum plate having a thickness of 2 mm can be calculated to be approximately 19.2 mm in the minimum mode.

In various embodiments, in step 220 , the size of the unit cell of the refractive index distributed acoustic quantum crystal may be determined from the wavelength of the bending wave derived from the calculation in step 210 . In order for the unit cell to satisfy the isotropic refractive index characteristic with respect to the bending wave, the size of the unit cell may be determined at about 1/4 of the wavelength of the bending wave. For example, the unit cell may have a horizontal and vertical size of 5 mm.

In various embodiments, step 230 may calculate a maximum effective refractive index and a minimum effective refractive index for a bending wave having a specified frequency that can be achieved with a unit cell having a size determined in step 220 . For example, assuming that a circular hole is formed in a unit cell with a size of 5 mm, the radius of the circular hole can be considered within a range of at least 0 to a maximum of 2 mm, and at 50 kHz in a unit cell formed with a minimum radius and a maximum radius, respectively. The maximum phase velocity and minimum phase velocity of the bending wave can be calculated as 959.66 m/s and 825.87 m/s, respectively. In this case, the minimum effective refractive index corresponding to the maximum phase velocity is 1, and the maximum effective refractive index corresponding to the minimum phase velocity is 1.162. The refractive index distributed acoustic quantum crystal according to an embodiment may have a structure in which each layer in which 13 unit cells are gathered is stacked as 17 layers, as shown in the example shown in FIG. 2 , and the uppermost first layer and the lowermost layer The seventeenth layer of phosphorus may have a minimum effective refractive index of 1 achievable in a unit cell, and the ninth layer as an intermediate layer may have a maximum effective refractive index achievable in a unit cell of 1.162.

In various embodiments, step 240 may determine a distribution form of a target effective refractive index so that the refractive index-distributed acoustic quantum crystal can focus the wave energy of the bending wave traveling through the two-dimensional plate. In order for the refractive index distribution acoustic quantum crystal to act as a gradient-index lens (GRIN lens) for a bending wave having a specified frequency, the unit cell corresponding to the same effective refractive index in the same layer of the refractive index distribution acoustic quantum crystal This arrangement, the distribution of the effective refractive index for the bending wave having a specified frequency along the Y-axis of the refractive index distribution acoustic quantum crystal may be determined to have the form of a hyperbolic secant (sech) function. The function can be expressed by Equations 1 and 2.

Equation 1

Equation 2

는 굴절률분포형 음향양자결정의 Y축 크기의 반이고,

는 최상층에서 중간층까지의 굴절률분포형 음향양자결정의 Y축에 따른 유효 굴절률의 분포 함수이고, 중간층에서 최하층까지의 굴절률분포형 음향양자결정의 Y축에 따른 유효 굴절률의 분포는 최상층에서 중간층까지의 굴절률분포형 음향양자결정의 Y축에 따른 유효 굴절률의 분포와 대칭되는 함수로 얻을 수 있다. 다양한 실시 예에 따른 굴절률분포형 음향양자결정의 Y축에 따른 유효 굴절률의 분포는 도 3에 도시된 바와 같다. here,

is half the size of the Y-axis of the refractive index-distributed acoustic quantum crystal,

is the distribution function of the effective refractive index along the Y axis of the refractive index distributed acoustic quantum crystal from the uppermost layer to the middle layer, and the distribution of the effective refractive index along the Y axis of the refractive index distributed acoustic quantum crystal from the middle layer to the lowest layer is from the uppermost layer to the middle layer. It can be obtained as a function symmetrical with the distribution of the effective refractive index along the Y-axis of the refractive index-distributed acoustic quantum crystal. The distribution of the effective refractive index along the Y-axis of the refractive index-distributed acoustic quantum crystal according to various embodiments is shown in FIG. 3 .

In various embodiments, unit cells having the same size of perforations are arranged in the same layer of the refractive index-distributed acoustic quantum crystal, and the size of perforations of the unit cells corresponding to the uppermost layer to the middle layer is bending with a specified frequency from the uppermost layer to the middle layer The distribution along the Y-axis of the effective refractive index for the wave may be gradually increased as shown in Equation 1, and the size of the perforation of the unit cell corresponding to the lowest layer in the middle layer may be gradually decreased so as to be symmetrical to Equation 1 above.

In an embodiment, each layer of the refractive index distributed acoustic quantum crystal may include 13 unit cells, and each layer of the 13 unit cells may be stacked as 17 layers in the Y-axis direction. In the first layer, which is the top layer, the radius of the circular perforations of the unit cells constituting the first layer is determined so as to have the minimum effective refractive index, and the ninth layer as the middle layer has the circular perforations of the unit cells constituting the ninth layer so that the maximum effective refractive index is obtained is determined, the effective refractive index from the first layer to the ninth layer gradually increases according to Equation 1, and the radius of the perforation may also increase. The radius of the circular perforation of the unit cell constituting the 17th layer is determined so that the lowest layer, which is the 17th layer, has the same minimum effective refractive index as the first layer, and the effective refractive index from the ninth layer to the 17th layer is from the first layer to the ninth layer It can be gradually reduced to be symmetrical with the effective refractive index up to the layer.

For example, in step 230, assuming that a circular hole is formed in a unit cell with a size of 5 mm, the radius of the circular hole formed at the center of the unit cell of each layer is a certain constant value within the range of at least 0 to at most 2 mm. can be selected, in order to design a precise refractive index-distributed acoustic quantum crystal for focusing the bending wave, a process of optimizing the size of the perforation of the unit cell of each layer is required.

In various embodiments, in step 250 , the size of the perforation of the unit cell may be optimized for each layer so that the refractive index distributed acoustic quantum crystal satisfies the distribution shape of the target effective refractive index determined in step 240 . In step 250, the size of the perforations of the unit cells constituting each layer may be determined such that the square value of the difference between the target effective refractive index of each layer and the optimal effective refractive index of each layer corresponding to Equation 3 below is the minimum. .

Equation 3

는 각 층의 목표 유효굴절률(

)과 각 층의 최적 유효굴절률(

) 사이의 차의 제곱으로 정의되고, 과정 250을 통해 최소가 될 수 있다. Here, the function

is the target effective refractive index (

) and the optimal effective refractive index of each layer (

) is defined as the square of the difference between ) and can be minimized through process 250.

가 10^-6 오차 범위에 수렴하도록 최적화 과정이 반복됨으로써, 굴절률분포형 음향양자결정이 지정된 주파수를 갖는 굽힘파에 대해 굴절률분포형 렌즈(Gradient-Index lens, GRIN lens)로 작용하기 위한 각 층의 최적화된 타공의 크기가 결정될 수 있다. 예를 들어, 최적화된 원형의 타공의 반지름의 크기가 각 층마다 결정될 수 있고, 제작 공차를 반영하기 위하여 타공의 반지름의 크기는 최적화된 원형의 타공의 반지름의 크기를 소수 둘째 자리에서 반올림되어 결정될 수 있다. In step 250, the function of Equation 3

The ^{optimization process is repeated to converge to the 10 -6} error range, so that the refractive index-distributed acoustic quantum crystal is formed in each layer to act as a gradient-index lens (GRIN lens) for a bending wave having a specified frequency. The size of the optimized perforation can be determined. For example, the size of the radius of the optimized circular perforation can be determined for each layer, and in order to reflect the manufacturing tolerance, the size of the radius of the optimized circular perforation is rounded to two decimal places. can

Figure 5a shows the simulation result of the relative magnitude of the bending wave energy passing through the refractive index distribution acoustic quantum crystal having the size of the radius of the optimized hole, and Figure 5b shows the size of the radius of the optimized circular hole by the second decimal. It shows the simulation result of the relative magnitude of the energy of the bending wave passing through the refractive index-distributed acoustic quantum crystal with the radius determined by rounding to the spot.

Referring to FIGS. 5A and 5B , the focusing ability of the bending wave energy of the refractive index-distributed acoustic quantum crystal having the optimized size of the radius of the perforation (or having the optimized unit cell) and the size of the radius of the optimized circular perforation It can be confirmed that there is no significant difference in the focusing ability of the bending wave energy of the refractive index-distributed acoustic quantum crystal having a radius determined by rounding to two decimal places (or having a rounded unit cell).

In various embodiments, in step 250, a hole having a size determined through the optimization process in step 240 may be formed in the center of the unit cell. For example, unit cells are arranged in a matrix form having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a 2 mm thick aluminum plate, and at the center of the unit cell, a refractive index-distributed acoustic quantum crystal is applied to a 50 kHz bending wave. It is possible to laser cut a circular hole to have a target effective refractive index distribution.

6 illustrates an energy harvesting system using a refractive index distributed acoustic quantum crystal according to various embodiments of the present disclosure.

Referring to FIG. 6 , the energy harvesting system 1000 using a refractive index distributed acoustic quantum crystal according to various embodiments is a refractive index distributed acoustic quantum crystal 100 and a piezoelectric element capable of focusing the wave energy of a bending wave ( 300) may be included. The refractive index distribution acoustic quantum crystal has a specified size, is arranged in a matrix form having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a two-dimensional flat plate, and unit cells 111 with a hole 113 formed in the center. ), and unit cells having the same size of perforations are arranged on the same layer, and the size of perforations of the unit cells corresponding to each layer is a refractive index distribution lens for a bending wave having a specified frequency for acoustic quantum crystals. It can be set to work. For example, the two-dimensional flat plate may be an aluminum flat plate, the unit cells constituting the refractive index-distributed acoustic quantum crystal may have the same horizontal and vertical sizes, and a circular hole may be formed in the center. In order for the refractive index distribution acoustic quantum crystal to act as a gradient-index lens (GRIN lens) for a bending wave having a specified frequency, the unit cell corresponding to the same effective refractive index in the same layer of the refractive index distribution acoustic quantum crystal This arrangement, the distribution of the effective refractive index for the bending wave having a specified frequency along the Y-axis of the refractive index distribution acoustic quantum crystal may be determined to have the form of a hyperbolic secant (sech) function.

In various embodiments, the piezoelectric element 400 may convert mechanical wave energy into electrical energy and may be disposed at a focal point where the wave energy of the bending wave is focused through the refractive index-distributed acoustic quantum crystal 100 . . Since the focal point at which the wave energy of the bending wave traveling through the refractive index distribution type acoustic quantum crystal is focused is formed outside the refractive index distribution type acoustic quantum crystal, the piezoelectric element 400 is located outside the refractive index distribution type acoustic quantum crystal 100 . , in particular, may be disposed on the emitting side 300 of the bending wave. For example, the energy focusing point of the refractive index distributed acoustic quantum crystal shown in FIG. 2 may be formed at a point about 48.7 mm away from the refractive index distributed acoustic quantum crystal 100 .

The energy harvesting system using the refractive index distributed acoustic quantum crystal according to various embodiments may further include an energy harvesting circuit (not shown). The energy harvesting circuit may be electrically connected to the piezoelectric element. In addition, the energy harvesting circuit may be connected to a measuring device to measure the energy focusing and harvesting ability of the refractive index distributed acoustic quantum crystal.

7A shows the maximum output voltage of the energy harvesting system including the refractive index distributed acoustic quantum crystal according to various embodiments compared to the energy harvesting system that does not include the refractive index distributed acoustic quantum crystal, and FIG. 7B shows various implementations. The maximum output power of the energy harvesting system including the refractive index distributed acoustic quantum crystal according to the example is shown in comparison with the energy harvesting system not including the refractive index distributed acoustic quantum crystal.

7A and 7B , the maximum output voltage of the energy harvesting system including the refractive index distributed acoustic quantum crystal according to various embodiments is 3.57 V, and the same two-dimensional material does not include the refractive index distributed acoustic quantum crystal. The maximum output voltage of the energy harvesting system using the specimen is 1.84 V. It can be confirmed that the maximum output voltage of the energy harvesting system including the refractive index distributed acoustic quantum crystal according to various embodiments is about twice as large as that of the energy harvesting system not including the refractive index distributed acoustic quantum crystal.

The maximum output power of the energy harvesting system including the refractive index distribution acoustic quantum crystal according to various embodiments is 1.25 mW when the 4.8 kΩ resistor is connected, and the maximum output power of the energy harvesting system not including the refractive index distribution acoustic quantum crystal is 0.33 mW. It can be confirmed that the maximum output power of the energy harvesting system including the refractive index distributed acoustic quantum crystal according to various embodiments is about 4 times greater than that of the energy harvesting system not including the refractive index distributed acoustic quantum crystal.

Claims (12)

In a refractive index-distributed acoustic quantum crystal comprising a unit cell having a specified size, arranged in a matrix having a layer arrangement in the Y-axis direction and a column arrangement in the X-axis direction on a two-dimensional plate,
The size of the perforation of the unit cell is set so that the refractive index distribution type acoustic quantum crystal can act as a refractive index distribution type lens with respect to a bending wave having a specified frequency,
The number of layers in which the unit cells are arranged is set such that a focal point at which wave energy of a bending wave traveling through the refractive index distribution acoustic quantum crystal is focused is formed outside the refractive index distribution acoustic quantum crystal. type acoustic quantum crystal.
The method according to claim 1,
The specified size of the unit cell is set in comparison with the length of the wavelength of the bending wave having the specified frequency, refractive index distribution acoustic quantum crystal.
The method according to claim 1,
The perforation is a circular, refractive index distribution acoustic quantum crystal.
The method according to claim 1,
The size of the perforations of the unit cells arranged on the same layer are the same,
The size of the perforation of the unit cell is, the size of the perforation of the unit cell forming the uppermost layer and the lowermost layer is the minimum, and the size of the perforation of the unit cell forming the middle layer is the maximum, and the size of the perforation is symmetrical with respect to the middle layer,
The size of the perforations from the uppermost layer to the middle layer is that the distribution along the Y-axis of the effective refractive index of the refractive index-distributed acoustic quantum crystal with respect to the bending wave having the specified frequency is a hyperbolic secant (sech) function. A refractive index-distributed acoustic quantum crystal that is set to have a shape.
delete delete delete delete delete delete delete In the energy harvesting system comprising a refractive index distribution acoustic quantum crystal,
A refractive index distributed acoustic quantum crystal corresponding to any one of the refractive index distributed acoustic quantum crystals according to claim 1 ; and
An energy harvesting system including a refractive index distribution acoustic quantum crystal comprising a; a piezoelectric element disposed at a point where the bending wave passing through the refractive index distribution acoustic quantum crystal is focused.

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