Energy harvesting device

Abstract

An embodiment of the present invention provides an energy harvesting device including: an object; a propagation area disposed in a first area of the object; a coherence area disposed in a second area of the object and having a thickness varying along a width direction of the object; and an energy conversion unit disposed in the coherence area and converting elastic wave energy into electrical energy.

Description

energy harvesting devices

[0001] The present invention relates to an energy harvesting device.

[0002] A metalens is a structure or design that controls and manipulates the path of waves by adjusting the shape and material of a lens composed of periodic unit structures. The field of metalens, which has been actively studied in the fields of light and electromagnetic waves, has recently expanded to control elastic waves. Various wave phenomena have been realized by applying the refractive index distribution of Maxwell's fisheye lens, Lunberg lens, and Eaton lens.

[0003] Recently, among these elastic wave control methods, a design method for a Michaelian lens has been proposed, which transforms the refractive index distribution of a Maxwellian fisheye lens using conformal mapping theory. A Michaelian lens is designed to focus plane waves at a specific focal point. To design this refractive index distribution into a practical structure, the refractive index has been expressed by gradually changing the geometric variables of columns attached to a thin plate or holes drilled in a thin plate. However, these methods have the disadvantage of reducing the wave transmission efficiency due to high on-resistance, and the waves are scattered and their characteristics change.

[0004] In order to overcome the above-mentioned shortcomings, the present invention combines the refractive index distribution of a Michaelian lens with the Kirchhoff-Love plate theory, so that the effective refractive index is determined only by the thickness of the plate, thereby allowing all waves to be focused at the same focus regardless of frequency, and furthermore, by inducing a high strain field in a piezoelectric element through elastic wave energy focused at the same focus, development of an energy harvesting device capable of improving the performance of energy harvesting is required.

[0005] The present invention was created to solve the above problems, and its purpose is to provide a high-performance energy harvesting device capable of extracting electric energy in a wide frequency range by configuring it to be able to concentrate elastic wave energy at the same location (focus) even when the frequency changes.

[0006] In order to achieve the above purpose, an energy harvesting device according to one embodiment of the present invention may include an object, a radio wave region arranged in a first region of the object, a cohesive region arranged in a second region of the object and having a variable thickness along the width direction of the object, and an energy conversion unit arranged in the cohesive region and converting elastic wave energy into electrical energy.

[0007] In an embodiment of the present invention, the radio wave region may have a flat shape having a uniform thickness along the width direction.

[0008] In an embodiment of the present invention, the cohesive region may have a concave portion concave inward on the upper surface of the object.

[0009] In an embodiment of the present invention, the thickness may gradually decrease from one end of the concave portion to the other end based on the width direction and then gradually increase again.

[0010] In an embodiment of the present invention, the concave portion may have a shape that is symmetrical with respect to the center of the concave portion.

[0011] In an embodiment of the present invention, the concave portion may extend from one end of the cohesive region to the other end along the longitudinal direction of the object.

[0012] In an embodiment of the present invention, the elastic wave energy is aggregated at an aggregation location, and the aggregation location is arranged within the concave portion, but the location can be fixed regardless of the frequency of the elastic wave energy.

[0013] In an embodiment of the present invention, the aggregation position is determined using the effective refractive index of the object, and the effective refractive index is defined by the following formula: , in the above formula, n z eff is the effective refractive index, h(x) is the thickness of the coherent region, and h max can mean the maximum thickness of the cohesive region.

[0014] In an embodiment of the present invention, a refractive index gradient of the elastic wave energy can be formed in the cohesive region based on a change in the thickness along the width direction.

[0015] In an embodiment of the present invention, the refractive index gradient may correspond to the refractive index distribution of a Mikaelian lens.

[0016] In an embodiment of the present invention, the elastic wave energy is applied to a point on the propagation area, and the cohesive position can be spaced apart from the point by a predetermined distance along the longitudinal direction of the object.

[0017] In an embodiment of the present invention, the energy conversion unit includes a piezoelectric element, and the energy conversion unit is connected to the agglomeration location and can extract voltage using the agglomerated elastic wave energy.

[0018] The energy harvesting device according to embodiments of the present invention can improve energy harvesting performance by concentrating elastic wave energy at a specific location of the plate and inducing a high strain field in the piezoelectric element of the energy conversion unit.

[0019] Furthermore, the energy harvesting device is configured so that the effective refractive index is determined solely by the thickness of the plate, so that all elastic waves, regardless of frequency, are concentrated at the same focal point, enabling piezoelectric energy harvesting in both high- and low-frequency ranges. This overcomes the limitations of existing piezoelectric energy harvesting devices, which were limited to high-frequency ranges, and allows for simultaneous implementation in the low-frequency range for practical applications, enabling applications in a variety of signal processing devices, such as the Internet of Things, wireless communications, and structural safety monitoring.

[0020] FIG. 1 is a perspective view schematically illustrating an energy harvesting device according to one embodiment of the present invention.

[0021] Fig. 2 is a cross-sectional view showing the view taken from the A1-A1' direction of Fig. 1.

[0022] Fig. 3 is a cross-sectional view showing the view taken from the A2-A2' direction of Fig. 1.

[0023] FIG. 4 schematically illustrates an energy harvesting device and a supply unit connected thereto according to one embodiment of the present invention.

[0024] Figure 5a schematically illustrates the refractive index distribution of a Maxwell fisheye lens.

[0025] Figure 5c shows the dimensions before transformation (left) and after transformation (right) by the conformal mapping theory.

[0026] Figure 6 schematically illustrates the refractive index distribution of a Michaelian lens, which is converted from the refractive index distribution of the Maxwell fish-eye lens of Figure 5a by applying the conformal mapping theory.

[0027] Figure 7a is a graph showing the band structure according to the thickness of the cohesive region.

[0028] Figure 7b is a graph showing the effective refractive index according to the thickness of the cohesive region.

[0029] Figures 8a to 8c are graphs showing the results of elastic wave energy being concentrated at the location of aggregation according to different frequencies.

[0030] Figures 9a to 9c are graphs showing the results of elastic wave energy detection at the front end and the cohesion position of the cohesion region according to different frequencies.

[0031] Figures 10a to 10c are graphs showing the results of voltage extraction at each location of the cohesion region and at different locations of the cohesion region according to different frequencies.

[0032] Figures 11a to 11c are graphs showing the results of the cohesion position and the rate measurement at each different position of the cohesion region according to different frequencies.

[0033] Hereinafter, with reference to the attached drawings, preferred embodiments will be described in detail so that those skilled in the art can easily practice the present invention. However, in describing preferred embodiments of the present invention in detail, if it is determined that a specific description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the same reference numerals are used throughout the drawings for parts that have similar functions and actions. In addition, in this specification, terms such as “upper,” “upper part,” “top surface,” “lower,” “lower side,” “lower surface,” and “side” are based on the drawings, and in reality, they may vary depending on the direction in which the components are arranged.

[0034] Additionally, throughout the specification, when a part is said to be "connected" to another part, this includes not only cases where it is "directly connected," but also cases where it is "indirectly connected" with other components intervening. Furthermore, unless specifically stated otherwise, "including" a component does not exclude other components, but rather implies the inclusion of other components.

[0035] Fig. 1 is a perspective view schematically illustrating an energy harvesting device according to one embodiment of the present invention. Fig. 2 is a cross-sectional view illustrating a view taken along the line A1-A1' of Fig. 1. Fig. 3 is a cross-sectional view illustrating a view taken along the line A2-A2' of Fig. 1. And, Fig. 4 schematically illustrates an energy harvesting device and a supply unit connected thereto according to one embodiment of the present invention.

[0036] Referring to FIGS. 1 to 3, an energy harvesting device (10) may be a device for concentrating elastic wave energy applied to an object (100) in a specific area and then converting and extracting it into electrical energy. At this time, the energy harvesting device (10) may include an object (100), a propagation area (200), a cohesive area (300), and an energy conversion unit (400).

[0037] The object (100) may be formed in the form of a thin plate. In this case, the object (100) may be made of various metal materials. For example, the object (100) may be a thin plate made of aluminum.

[0038] The propagation region (200) may be a region to which elastic wave energy is applied by the transducer (23). The propagation region (200) may be formed in a first region of the object (100). For example, it may be a front region of the object (100) based on the direction in which the applied elastic wave energy is propagated or the longitudinal direction (Y) of the object (100).

[0039] The propagation region (200) may be connected to the second region of the object (100). At this time, the second region of the object (100) is a region where the cohesive region (300) is formed, and may be a rear region of the object (100) based on the direction (Y) in which elastic wave energy propagates. In this case, the rear end (202) of the propagation region (200) may be in contact with the front end (301) of the cohesive region (300), and the contacting portion will be referred to as a boundary surface. Accordingly, the object (100) may have a form in which the propagation region (200) and the cohesive region (300) are continuous along the longitudinal direction (Y).

[0040] The rear end (202) of the propagation region (200) may be inclined at a predetermined angle. More specifically, the rear end (202) of the propagation region (200) may be inclined so that the thickness (t) decreases steadily as it goes from the propagation region (200) to the cohesive region (300), as illustrated in FIG. 3. Due to the rear end (202) of the propagation region (200), an abrupt change in structure (e.g., thickness) may not occur at the boundary between the propagation region (200) and the cohesive region (300). Accordingly, when an elastic wave moves from the propagation region (200) to the cohesive region (300), the propagation of the elastic wave may be prevented from being disturbed by the structural change at the boundary. Meanwhile, the rear end (202) of the propagation region (200) may be formed to have a predetermined length (Yt). At this time, the length (Yt) of the rear end (202) described above may be an arbitrarily settable length.

[0041] The propagation region (200) may have a uniform thickness (t) along the width direction (X). In addition, the propagation region (200) may have a uniform thickness (t) in the longitudinal direction (Y), thereby allowing the entire first region of the object (100) to have a uniform thickness (t). Accordingly, the propagation region (200) may have a flat (plate) shape.

[0042] Elastic wave energy can be coagulated at a point (Pf) in a coagulation region (300) as it propagates along the propagation direction (Y) mentioned above after being applied to the propagation region (200).

[0043] The cohesive region (300) may have a shape in which the thickness (h) is at least partially variable. More specifically, the cohesive region (300) may have a thickness (h) that varies along the width direction (X) of the object (100).

[0044] The cohesive region (300) has a maximum thickness (h) at both side ends (303, 304) in the width direction (X). max ) may have. In this case, the thickness (h) of the cohesive region (300) may gradually decrease from one of the two side ends (303, 304) toward the center (C). Accordingly, the cohesive region (300) may have a minimum thickness (h) at its center (C). min ) may have. In addition, the thickness (h) of the cohesive region (300) may gradually increase in width from the center (C) mentioned above toward the other end (304) among the two side ends (303, 304). Accordingly, the cohesive region (300) may be provided with a concave portion (310) formed concavely inward on its upper surface.

[0045] As an example, the concave portion (310) may have a shape in which the radius of curvature (r) varies along the width direction (X). In this case, the maximum radius of curvature (x) at both side ends (303, 304) of the concave portion (310) max ) can be the maximum. This maximum radius of curvature (x max ) is the width of the concave portion (310) (2x max ) may be 1 / 2 of the radius of curvature (R) of the concave portion (310). The radius of curvature (R) of the concave portion (310) may decrease from the two side ends (303, 304) toward the center (C), and the radius of curvature (r) may be minimum at the center (C). Accordingly, when viewed from the side (e.g., in the direction parallel to the ZX plane), the cross-sectional shape of the concave portion (310) may be a shape that is curved downward.

[0046] The concave portion (310) may extend parallel to the propagation direction (or longitudinal direction) (Y) described above. More specifically, the concave portion (310) may extend from the front end (301) of the cohesive region (300) along the longitudinal direction (Y) of the object (100) to the rear end (302) of the cohesive region (300).

[0047] Meanwhile, in the drawing, the two side ends (303, 304) of the cohesive region (300) have a thickness (h max ) is a uniform flat shape, and only the shape in which the thickness (h) of the cohesive region (300) between the two side ends (303, 304) is variable is shown, but the present invention is not limited thereto.

[0048] The energy conversion unit (400) can convert elastic wave energy into electrical energy. For example, the energy conversion unit (400) may include an energy conversion element, such as a piezoelectric element. In this case, the energy conversion element may be an element that has the effect of generating voltage when deformed by stress.

[0049] The energy conversion unit (400) may be connected to the cohesion region (300). More specifically, the energy conversion unit (400) may be connected to a cohesion position (Pf) within the cohesion region (300). At this time, the cohesion position (Pf) is a point where elastic wave energy transmitted to the cohesion region (300) is cohesive, and details thereof will be described later.

[0050] Referring to FIG. 4, a power supply unit (20) may be connected to the energy harvesting device (10). For example, the supply unit (20) may include a function generator (21), a power amplifier (22), and a transducer (23). In this case, noise may be removed from an electrical signal of a specific frequency input from the function generator (21) while passing through the amplifier (22). Thereafter, the signal may be converted into an elastic wave by the transducer (23) and supplied to the energy harvesting device (10). At this time, the transducer (23) may be connected to a first region of the object (100), that is, a front end (201) of the propagation region (200). The elastic wave applied through the transducer (23) may be propagated via the object (100).

[0051] Elastic waves can propagate along an object (100) in the longitudinal direction (Y) and be aggregated at an aggregate location (Pf) within an aggregate region (300). An energy conversion unit (400) is connected to this location (f) to convert the aggregated elastic wave energy into electrical energy (e.g., voltage). At this time, the elastic wave energy aggregated at the aggregate location (Pf) can be detected by a detector (11), such as a scanning LDV. In addition, the detection result of the detector (11) can be transmitted to the control unit (11a) and displayed and confirmed through a display device.

[0052] Meanwhile, the energy conversion unit (400) may include a resistance adjusting unit (12) and an oscilloscope (12a). In this case, the voltage extracted by the energy conversion unit (400) can be controlled by adjusting the resistance using the resistance adjusting unit (12). In addition, the resistance adjusting unit (12) can be used to calculate the optimal resistance in relation to the power according to the extracted voltage. In addition, the voltage state according to the change in the resistance value by the resistance adjusting unit (12) can be confirmed using the oscilloscope (12a).

[0053] Fig. 5a schematically illustrates the refractive index distribution of a Maxwellian fisheye lens, and Fig. 5b illustrates the dimensions before transformation (left) and after transformation (right) by the conformal mapping theory, respectively. Fig. 6 schematically illustrates the refractive index distribution of a Michaelian lens, which is obtained by transforming the refractive index distribution of the Maxwellian fisheye lens of Fig. 5a by applying the conformal mapping theory. Fig. 7a is a graph showing the band structure according to the thickness of the coherent region, and Fig. 7b is a graph showing the effective refractive index according to the thickness of the coherent region. Figs. 8a to 8c are graphs showing the results of elastic wave energy being concentrated at the coherent location according to different frequencies. Figs. 9a to 9c are graphs showing the results of elastic wave energy detection at the front end and the coherent location of the coherent region according to different frequencies, respectively. Figs. 10a to 10c are graphs showing the results of voltage extraction at the coherent location of the coherent region and at other locations of the coherent region according to different frequencies, respectively. And, FIGS. 11a to 11c are graphs showing the results of the measurement of the cohesion position in the cohesion region and the rate at each other position in the cohesion region according to different frequencies.

[0054] Referring to FIGS. 1 to 11, a method of converting and extracting elastic wave energy into electrical energy by using an energy harvesting device (10) according to an embodiment of the present invention may be as follows.

[0055] First, an elastic wave can be applied to a first region (i.e., a propagation region) (200) of an object (100) in the form of a thin plate by a supply unit (20). The elastic wave can be supplied to a point (P) of a front end (201) of the propagation region (200). The elastic wave can be propagated to a rear end (202) of the propagation region (200) along the longitudinal direction (Y) via the object (100). In this process, as the elastic wave moves away from the point (P) of the propagation region (200), it can reach the front end (301) of the cohesive region (300) in the form of a plane wave (PW), as illustrated in FIG. 5.

[0056] Next, elastic wave energy can be concentrated (aggregated) in a certain area of ​​the object (100). More specifically, the elastic wave energy is refractive index (n) determined by the thickness (h) of the aggregation area (300). z ) can be aggregated at the aggregation position (Pf) within the aggregation region (300). Here, the refractive index (n z ) is the effective refractive index, and the refractive index (n) in the condensed region (300) z ) may mean the relative refractive index for a position of 1. At this time, the refractive index (n) in the cohesive region (300) z ) is a flat part in the cohesive region (300) where the thickness (h) does not change, for example, it may be the two side ends (303, 304) of the cohesive region (300).

[0057] When an elastic wave propagates to a cohesive region (300), it may be refracted at the boundary between the propagation region (200) and the cohesive region (300), thereby changing the propagation direction. This can be achieved by forming a concave portion (310) to adjust the thickness (h) of the object (100), thereby implementing a refractive index distribution of a Mikaelian lens in the cohesive region (300). At this time, the refraction direction of the elastic wave is determined by the refractive index (n z ) is determined by the refractive index (n z ) can be controlled using the thickness (h) of the cohesive region (300). For example, the refractive index (n z ) is the minimum thickness (h) in the cohesive region (300). min ) is formed, which may be a straight line region extending parallel to the longitudinal direction (Y) passing through the center (C) of the cohesive region (300) (i.e., a region where the Y-axis value is 0 in the drawing).

[0058] Once the thickness (h) of the cohesive region (300) is determined, the refractive index (n z ) can be fixed regardless of the frequency of the applied elastic wave, which will be described below. Meanwhile, since the rear end (202) of the propagation region (200) is formed to be inclined from the propagation region (200) toward the cohesion region (300), the propagation region (200) and the cohesion region (300) can be connected in a continuous form. As a result, as described above, when passing through the boundary between the propagation region (200) and the cohesion region (300), it is possible to prevent propagation of the elastic wave from being interrupted due to the shape difference between the two regions (200, 300).

[0059] By implementing the refractive index distribution of the Michaelian lens as described above, elastic waves can be propagated to and coagulated at a coagulation location (Pf) within the coagulation region (300). In this case, the coagulation location (Pf) may be a location corresponding to the focus of the Michaelian lens.

[0060] More specifically, the cohesion position (Pf) may be a position spaced apart from the aforementioned point (P) by a focal distance (Yf) along the longitudinal direction (Y). The focal distance (Yf) may be greater than the propagation length (Y1) and shorter than the entire length of the object (100). Here, the propagation length (Y1) may mean the distance from the aforementioned point (P) of the propagation area (200) to the front end (301) of the cohesion area (300). At this time, the propagation length (Y1) may be equal to the length (Y2) of the cohesion area (300).

[0061] In addition, the cohesion position (Pf) may be spaced apart from the front end (301) of the cohesion region (300) by a preset distance (f). At this time, the preset distance (f) may mean a distance obtained by subtracting the propagation length (Y1) from the focal length (Yf) described above. With this distance, as the focal length (Yf) is determined, the cohesion position (Pf) may be located within the concave portion (310).

[0062] Meanwhile, the implementation of the refractive index distribution of the Michaelian lens described above can be achieved by transforming the refractive index distribution of a Maxwellian fisheye lens, as shown in Fig. 5a, by applying the theory of conformal mapping with an exponential function relationship. At this time, the exponential function relationship described above can be defined by the following equation.

[0063] ... formula

[0064] In this conversion process, if the conformal mapping theory is applied to the “refractive index distribution of the Maxwellian fish-eye lens” of a perfect geometric shape (concentric spherical shape with radius R) in a virtual space as shown in the left drawing of Fig. 5b, it can be converted into a distorted shape in an actual dimension as shown in the right drawing of Fig. 5b. Accordingly, the “refractive index distribution of the Markaelian lens” as shown in Fig. 6 can be implemented. The thickness (h) of the coherent region (300) for implementing such a refractive index distribution can be determined based on the radius (R) of the Maxwellian fish-eye lens before conversion. At this time, the relationship between the radius (R) of the Maxwellian fish-eye lens and the thickness (h) of the coherent region (300) is defined by the following equation (4), which will be described later.

[0065] In the Markaelian lens transformed in this way, as shown in Fig. 6, an elastic wave can be transformed into a plane wave (PW) form as it is incident on a point (P1) and propagates. Thereafter, the elastic wave is refracted as it passes through the A1 region due to the refractive index gradient of the Markaelian lens and is condensed at another point (P2). Comparing this with an object (100) in which the refractive index gradient of the Markaelian lens is implemented, the A1 region of the Markaelian lens of Fig. 6 can correspond to the coherent region (300) of the object (100). In addition, in the Markaelian lens, the point (P2) where the elastic wave is condensed corresponds to the coherent position (Pf) within the coherent region (300), and the length (R') of the A1 region can correspond to a preset distance (f) of the coherent region (300).

[0066] The refractive index conversion described above can be defined as in equation (1) below.

[0067] ... Formula (1)

[0068] Here, in the above formula (1), n0 is the maximum refractive index in the dimension after transformation, n z means the change in refractive index along the width direction (X) of the cohesive region (300) in the converted real dimension. And, βx is the conformal mapping constant, and R is the radius of the Maxwell fish-eye lens. In this case, the conformal mapping constant (β x ) and the radius (R) of the Maxwell fish-eye lens corresponds to an arbitrarily settable constant, and n0 is the above-mentioned β x and can be determined by setting R.

[0069] In addition, according to the Kirchhoff-Love plate theory applied to thin plates, the wave number of the first bending wave mode of elastic waves propagating through a thin plate-shaped object (100) can be defined by the following equation (2).

[0070] … Formula (2)

[0071] Here, k is the wave vector, which means the wave number, and ρ al Silver density, Val is Poisson's ratio, E al is Young's modulus, ω is the operating frequency. And, h is the thickness of the thin plate, which in the case of the present invention means the thickness of the cohesive region (300). Accordingly, in equation (2), the density (ρ al ) corresponds to the physical properties of the object (100), so the “relationship between the wavenumber (k) and the frequency (ω)” can be determined by the thickness (h) of the cohesive region (300).

[0072] Looking at Fig. 7a, the band structure (BS) can change depending on the change in the thickness (h) of the condensed region (300). For example, when the thickness (h) increases, the band structure (BS) can have a form in which the slope increases more steeply. At this time, the slope of the band structure (BS) is the phase velocity (v) of the wave. p ), so the refractive index (n) z ) and the thickness (h) of the cohesive region (300) can be expressed by the following equation (3).

[0073] … Formula (3)

[0074] Here, n z eff is the effective refractive index in the transformed real dimension, h max is the maximum thickness of the aforementioned cohesive region (300), and h(x) means the thickness according to the width of the cohesive region (300). Based on equation (3), the refractive index (n z ) is defined as the thickness (h) of the cohesive region (300), so by controlling only the thickness (h) of the cohesive region (300), the refractive index (n z ) can be determined. Using this formula (3), the refractive index (n) according to the change in thickness (h) along the width direction (X) in the concave portion () of the shape described above z ) can be calculated. The elastic wave refracted according to this refractive index gradient is concentrated at one point within the cohesive region (300), and this point may correspond to the cohesive position (Pf) described above.

[0075] In addition, the thickness (h) of the cohesive region (300) can be determined using the following equation (4), which is obtained by combining the equations (1) and (3) above. At this time, the variables included in equation (4) have the same meaning as described above.

[0076] … Formula (4)

[0077] Referring to Fig. 7b, when the thickness (h) of the cohesive region (300) is greater than a certain size, the refractive index (n) remains constant despite the change in the thickness (h). z ) can be confirmed to be insignificant. In comparison, when the thickness (h) of the cohesive region (300) is below a certain size, the refractive index (n) according to the change in the thickness (h) z ) changes are clearly evident. Therefore, the condensed region (300) is formed with a relatively thin thickness (h), which is due to the refractive index (n z ) can be advantageous in controlling the maximum thickness (h) of the cohesive region (300). max) can be an arbitrarily settable value. Meanwhile, the minimum thickness (h min ) is too thin, problems such as bending may occur in the cohesion area (300), so it is important to determine an appropriate thickness considering structural stability. For example, the maximum thickness (h) of the cohesion area (300) max ) is 3mm, the minimum thickness (h) min ) may be, but is not limited to, 1.249 mm.

[0078] In addition, by adjusting the thickness (h) of the cohesive region (300), the position (i.e., cohesive position) (Pf) where elastic wave energy is cohesive within the cohesive region (300) can be set. The cohesive position (Pf) may correspond to a position spaced apart from the point (P) where the elastic wave of the propagation region (200) is applied by the focal length (Yf) of the Michaelian lens. Accordingly, the cohesive position (Pf) is determined by the refractive index (n z ) and can be determined inversely proportional to the radius of curvature (R) of the concave portion (310) formed in the cohesive region (300). In this case, the “pre-set distance (f)” for determining the cohesive position (Pf) can be expressed as in the following equation (5).

[0079] … Formula (5)

[0080] Here, β is a conformal mapping constant, and R may denote the radius of a Maxwell fish-eye lens. These may be arbitrarily set to values ​​necessary for determining a desired aggregation position (Pf) during the design process of the energy harvesting device (10). For example, by setting the conformal mapping constant (β) to 1 and the radius (R) of the Maxwell fish-eye lens to 105 mm, the preset distance (f) can be designed to be approximately 164.9 mm.

[0081] As discussed above, based on Equations (4) and (5), the preset distance (f) can be determined only by the thickness (h) of the concave portion (310), regardless of the frequency. That is, the “coagulation position (Pf)”, which is the position where elastic wave energy is coagulated within the coagulation region (300), can be determined only by using the thickness (h) of the concave portion (310). Accordingly, the coagulation region (300) and the object (100) including it can function as a wave concentrating structure, such as a stigmatic lens, having the same focus for the first-order bending wave, regardless of the frequency. Consequently, the elastic wave energy can be coagulated at the same coagulation position (Pf) even when the operating frequency is changed.

[0082] In this regard, looking at Fig. 8, Figs. 8a, 8b, and 8c are examples showing the results of concentrating elastic wave energy when elastic waves having different frequencies are supplied, respectively. More specifically, Fig. 8a shows the simulation results (left figure) and the actual experimental results (right figure) showing that, in the case of an elastic wave of 40 kHz, elastic wave energy is concentrated at the cohesion location (Pf).

[0083] Figure 8b shows simulation results (left figure) and actual experimental results (right figure) showing that elastic wave energy is concentrated at the cohesion location (Pf) for elastic waves of 50 kHz. Furthermore, Figure 8c shows simulation results (left figure) and actual experimental results (right figure) showing that elastic wave energy is concentrated at the cohesion location (Pf) for elastic waves of 60 kHz.

[0084] Referring to Fig. 9, Figs. 9a, 9b, and 9c are different examples showing the results of concentrating elastic wave energy when elastic waves having different frequencies are supplied. More specifically, Fig. 9a shows the simulation result (a22) and the actual experimental result (a21) showing that an elastic wave of 40 kHz was propagated to the front end (301) of the cohesive region (300) in the form of a plane wave, and the simulation result (a12) and the actual experimental result (a11) showing that the elastic wave energy passed through the front end (301) and was concentrated at the cohesive position (Pf).

[0085] Fig. 9b shows the simulation result (b22) and the actual experimental result (b21) showing that a 50 kHz elastic wave propagated to the front end (301) of the cohesive region (300) in the form of a plane wave, and the simulation result (b12) and the actual experimental result (b11) showing that the elastic wave energy passed through the front end (301) and was concentrated at the cohesive location (Pf). And, Fig. 9c shows the simulation result (c22) and the actual experimental result (c21) showing that a 60 kHz elastic wave propagated to the front end (301) of the cohesive region (300) in the form of a plane wave, and the simulation result (b12) and the actual experimental result (b11) showing that the elastic wave energy passed through the front end (301) and was concentrated at the cohesive location (Pf).

[0086] In this way, as confirmed in FIGS. 8 and 9, when the thickness (h) of the cohesive region (300) is configured to be the same, it can be confirmed that the wave energy of elastic waves propagated to the cohesive region (300) in the form of plane waves is concentrated at a position (i.e., cohesive position) (Pf) corresponding to the same focal distance, regardless of whether the frequency is different.

[0087] Next, the energy conversion unit (400) can convert elastic wave energy into electrical energy. At this time, the energy conversion unit (400) can be connected to the “aggregation location (Pf)” determined based on the thickness (h) of the aggregation region (300) as described above. Accordingly, the energy conversion unit (400) converts elastic wave energy concentrated at the aggregation location (Pf) into electrical energy, thereby extracting a higher voltage compared to when connected to another location within the aggregation region (300), and consequently, improving energy harvesting performance.

[0088] In this regard, referring to Fig. 10, Figs. 10a, 10b, and 10c are examples showing the results of conversion into electrical energy according to the change in resistance when elastic waves having different frequencies are supplied, respectively. More specifically, Fig. 10a shows the voltage extraction result (a11) at the cohesion position (Pf) and the voltage extraction result (a21) at another position [e.g., the front end (301)] where wave energy is not concentrated, in the case of an elastic wave of 40 kHz.

[0089] Fig. 10b shows, in the case of a 50 kHz elastic wave, the voltage extraction result (b11) at the cohesion position (Pf) and the voltage extraction result (b21) at another position where wave energy is not concentrated [e.g., the shear portion (301)]. And, Fig. 10c shows, in the case of a 60 kHz elastic wave, the voltage extraction result (c11) at the cohesion position (Pf) and the voltage extraction result (c21) at another position where wave energy is not concentrated [e.g., the shear portion (301)].

[0090] Also, referring to FIG. 11, FIGS. 11a, 11b, and 11c are examples showing the results of conversion into electrical energy according to the change in resistance when elastic waves having different frequencies are supplied. More specifically, FIG. 11a shows the results of power measurement (a11) according to the voltage extracted from the cohesion position (Pf) in the case of an elastic wave of 40 kHz, and the results of power measurement (a21) according to the voltage extracted from another position [e.g., the front end (301)] where wave energy is not concentrated.

[0091] Fig. 11b shows, in the case of an elastic wave of 50 kHz, the power measurement result (b11) according to the voltage extracted from the cohesion position (Pf) and the power measurement result (b21) according to the voltage extracted from another position [e.g., the shear portion (301)] where wave energy is not concentrated. And, Fig. 11c shows, in the case of an elastic wave of 60 kHz, the power measurement result (c11) according to the voltage extracted from the cohesion position (Pf) and the power measurement result (c21) according to the voltage extracted from another position [e.g., the shear portion (301)] where wave energy is not concentrated.

[0092] Looking at the voltage extraction and power measurement results of FIGS. 10 and 11 above, it can be confirmed that in the case of the cohesive location (Pf) where elastic wave energy is cohesive, a higher voltage is extracted compared to when the elastic wave energy is extracted at other locations where it is not cohesive.

[0093] In addition, since the power is proportional to the square of the voltage, a higher power can be measured at the aggregation position (Pf), similar to the voltage extraction result. For example, it can be confirmed that the power measured at the aggregation position (Pf) is about 2.6 to 3.8 times higher than that at other positions. Meanwhile, in the field of energy harvesting, whether the power is 1 mW or more is a standard for determining whether the device has high performance. According to this standard, the power measured at the optimal resistance for each frequency is 1 mW or more, and it can be confirmed that the energy harvesting device (10) according to the present invention has high electric energy conversion performance.

[0094] As described above, the energy harvesting device (10) according to embodiments of the present invention can improve energy harvesting performance by concentrating elastic wave energy at a specific location (Pf) within the cohesive region (300) and inducing a high strain field in the piezoelectric element of the energy conversion unit (400).

[0095] In addition, the energy harvesting device (10) is configured so that the effective refractive index is determined only by the thickness (h) of the cohesive region (300), so that all elastic waves are concentrated at the same focus (Pf) regardless of frequency, thereby enabling piezoelectric energy harvesting to be implemented not only in the high-frequency region but also in the low-frequency region. Accordingly, the shortcomings of existing piezoelectric energy harvesting devices that were limited to the high-frequency region are overcome, and since they are simultaneously implemented in the low-frequency region so that they can be applied in real life, they can be applied to various signal processing devices such as the Internet of Things, wireless communication, and structural safety monitoring.

[0096] Although the embodiments of the present invention have been described 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 spirit or essential characteristics thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

[0097] The present invention can be applied to an industrially usable energy harvesting device.

Claims

1. Object; A radio wave region arranged in the first region of the above object; A cohesive region arranged in a second region of the object and having a thickness that varies along the width direction of the object; and An energy harvesting device, comprising: an energy conversion unit disposed in the above-mentioned cohesive region and converting elastic wave energy into electrical energy.

2. In paragraph 1, An energy harvesting device in which the above-mentioned radio wave region is a flat shape having a uniform thickness along the width direction.

3. In paragraph 2, An energy harvesting device in which the above-mentioned cohesive region has a concave portion that is concave inwardly on the upper surface of the object.

4. In paragraph 3, An energy harvesting device in which the thickness gradually decreases from one end of the concave portion to the other end based on the width direction and then gradually increases again.

5. In paragraph 4, An energy harvesting device, wherein the concave portion has a shape that is symmetrical with respect to the center of the concave portion.

6. In paragraph 5, An energy harvesting device in which the above concave portion extends from one end of the cohesive region to the other end along the longitudinal direction of the object.

7. In paragraph 3, The above elastic wave energy is concentrated at the cohesive location, An energy harvesting device wherein the above-mentioned cohesive position is arranged within the above-mentioned concave portion, but the position is fixed regardless of the frequency of the elastic wave energy.

8. In paragraph 7, The above agglomeration location is determined using the effective refractive index of the object, The above effective refractive index is defined by the following formula: In the above formula, n z eff is the effective refractive index, h(x) is the thickness of the coherent region, and h max An energy harvesting device, which means the maximum thickness of the cohesive region.

9. In paragraph 8, An energy harvesting device, wherein a refractive index gradient of elastic wave energy is formed in the above-mentioned cohesive region based on a change in the thickness along the width direction.

10. In paragraph 9, An energy harvesting device in which the above refractive index gradient corresponds to the refractive index distribution of a Mikaelian lens.

11. In Article 10, The above elastic wave energy is applied to a point on the above propagation area, An energy harvesting device, wherein the above-mentioned cohesive position is spaced apart from the above-mentioned point by a predetermined distance along the longitudinal direction of the object.

12. In paragraph 11, The above energy conversion unit includes a piezoelectric element, An energy harvesting device in which the energy conversion unit is connected to the cohesion position and extracts voltage using the cohesive elastic wave energy.

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