Cantilever beam and wind energy collector

Abstract

The invention discloses a cantilever beam and a wind energy collector, and relates to the field of wind power generation, the cantilever beam comprises a cantilever beam, and the projection shape of the cantilever beam in the thickness direction is trapezoidal; and the piezoelectric plate is attached to one side of the cantilever beam. The shape and the size of a traditional piezoelectric cantilever beam are optimized, the optimal size is determined, and therefore better electrical output performance is obtained. Meanwhile, a wind energy collector is provided on the basis of the improved cantilever beam, and the wind energy collector is faster in response in a low-wind-speed stage and more obvious in response in a high-wind-speed stage, and has lower starting wind speed, wider effective working wind speed range and higher output power.

Description

Technical Field

[0001] The invention relates to the technical field of wind energy power generation, in particular to a cantilever beam and a wind energy collector. Background Art

[0002] A piezoelectric cantilever beam is a device that uses the piezoelectric effect to convert mechanical energy into electrical energy and is commonly used in wind energy harvesters. Among them, the shape and size of the cantilever beam have an important influence on the performance of piezoelectric cantilever beam-type wind energy harvesters. However, the traditional cantilever beam shape design is usually based on a simple beam structure (such as a rectangle), but the size of the cantilever beam directly affects its vibration mode and energy collection efficiency. For different environmental conditions and application requirements, the current size optimization of the cantilever beam is not sufficient. A cantilever beam that is too large will increase the weight and cost of the system, while a cantilever beam that is too small will limit its performance under low wind speed conditions. Therefore, improving the shape design and size optimization of the cantilever beam to improve its ability to fully utilize wind energy under complex environmental conditions is one of the important directions of current technological development. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention is proposed.

[0004] Therefore, the first object of the present invention is to provide a cantilever beam that can solve the problem of poor performance caused by poor structural size design of traditional cantilever beams.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a cantilever beam, comprising a cantilever beam, the projection shape of which in the thickness direction is a trapezoid; and a piezoelectric sheet, which is attached to one side of the cantilever beam.

[0006] As a preferred solution of the cantilever beam of the present invention, the projection shape of the cantilever beam in the thickness direction is an isosceles trapezoid and the ratio of its upper base to its lower base is 0.5.

[0007] As a preferred solution of the cantilever beam of the present invention, the length between the upper base and the lower base of the trapezoidal projection in the thickness direction of the cantilever beam is 80 mm, and the length of the lower base is 40 mm.

[0008] As a preferred solution of the cantilever beam of the present invention, the thickness of the cantilever beam is 0.2 mm.

[0009] As a preferred solution of the cantilever beam of the present invention, the projection shape of the piezoelectric sheet in the thickness direction is a rectangle, and its width is the same as the upper base of the trapezoidal projection in the thickness direction of the cantilever beam.

[0010] As a preferred solution of the cantilever beam of the present invention, the thickness of the piezoelectric sheet is 0.2 mm.

[0011] As a preferred solution of the cantilever beam of the present invention, the cantilever beam is made of phosphor bronze, and the piezoelectric sheet is made of lead zirconate titanate.

[0012] Another object of the present invention is to provide a wind energy collector, which comprises a bluff body; the above-mentioned cantilever beam and piezoelectric sheet; one end of the cantilever beam is fixedly connected to one end of the bluff body.

[0013] As a preferred solution of the wind energy collector of the present invention, the shape of the bluff body is a cylinder.

[0014] As a preferred solution of the wind energy collector of the present invention, a base is further provided at one end of the cantilever beam away from the bluff body, and the cantilever beam is fixed on the base.

[0015] The beneficial effects of the present invention are as follows: the present invention optimizes the shape and size of the traditional piezoelectric cantilever beam, determines the optimal size, and thus obtains better electrical output performance. At the same time, based on the improved cantilever beam, a wind energy collector is proposed, which responds faster in the low wind speed stage and more obviously in the high wind speed stage, and has a lower starting wind speed, a wider effective working wind speed range, and a higher output power. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 Schematic diagram of the structure of the cantilever beam described in Example 1.

[0018] Figure 2 This is a simulated displacement cloud diagram of the rectangular cantilever beam described in Example 1.

[0019] Figure 3 This is a simulated potential cloud diagram of the rectangular cantilever beam described in Example 1.

[0020] Figure 4 This is a simulated stress cloud diagram of the rectangular cantilever beam described in Example 1.

[0021] Figure 5 This is a simulated strain cloud diagram of the rectangular cantilever beam described in Example 1.

[0022] Figure 6 This is a simulated displacement cloud diagram of the trapezoidal cantilever beam described in Example 1.

[0023] Figure 7 This is a simulated potential cloud diagram of the trapezoidal cantilever beam described in Example 1.

[0024] Figure 8 This is a simulated stress cloud diagram of the trapezoidal cantilever beam described in Example 1.

[0025] Fig. 9 This is a simulated strain cloud diagram of the trapezoidal cantilever beam described in Example 1.

[0026] Fig.10 This is a simulated displacement cloud diagram of the triangular cantilever beam described in Example 1.

[0027] Fig.11 This is a simulated potential cloud diagram of the triangular cantilever beam described in Example 1.

[0028] Fig.12 This is a simulated stress cloud diagram of the triangular cantilever beam described in Example 1.

[0029] Fig.13 This is a simulated strain cloud diagram of the triangular cantilever beam described in Example 1.

[0030] Fig.14 1 is the strain distribution diagram of each type of cantilever beam described in Example 1.

[0031] Fig.15 1 is a stress distribution diagram of each type of cantilever beam described in Example 1.

[0032] Fig.16 This is a curve diagram of the resonant frequency change of the trapezoidal cantilever beam described in Example 1 at different lengths and widths.

[0033] Fig.17 This is a curve diagram of the open circuit voltage variation of the trapezoidal cantilever beam described in Example 1 at different lengths and widths.

[0034] Fig.18 This is a curve diagram of output power variation of the trapezoidal cantilever beam in Example 1 at different lengths and widths.

[0035] Fig.19 This is a curve diagram of the resonant frequency change of the cantilever beam under different piezoelectric sheet lengths described in Example 1.

[0036] Fig. 20 This is a curve diagram of the open circuit voltage change of the cantilever beam under different piezoelectric sheet lengths described in Example 1.

[0037] Fig.21 This is a curve diagram of the output power change of the cantilever beam under different piezoelectric sheet lengths described in Example 1.

[0038] Fig. 22The graph is a curve of the resonant frequency change of the cantilever beam under different thicknesses of the cantilever beam and the piezoelectric sheet described in Example 1.

[0039] Fig.23 The open circuit voltage variation curve of the cantilever beam under different cantilever beam and piezoelectric sheet thicknesses described in Example 1 is shown.

[0040] Fig.24 The output power variation curve of the cantilever beam under different cantilever beam and piezoelectric sheet thicknesses described in Example 1 is shown.

[0041] Fig.25 This is a schematic diagram of the structure of the wind energy collector based on the trapezoidal cantilever beam described in Example 2.

[0042] Fig.26 This is a schematic diagram of the structure of the wind energy collector based on the rectangular cantilever beam described in Example 2.

[0043] Fig. 27 This is a graph showing the relationship between the output RMS voltage and the load resistance of the trapezoidal beam and rectangular beam wind energy collectors when the wind speed is 7 m / s as described in Example 2.

[0044] Fig.28 This is a graph showing the relationship between the output power and load resistance of the trapezoidal beam and rectangular beam wind energy collectors when the wind speed is 7 m / s in Example 2.

[0045] Fig.29 This is a graph showing the relationship between the output voltage of the rectangular beam wind energy collector and wind speed under different wind directions described in Example 2.

[0046] Fig.30 This is a graph showing the relationship between the output voltage of the ladder beam wind energy collector and wind speed under different wind directions described in Example 2.

[0047] Fig.31 This is a graph showing the relationship between the output power of the rectangular beam wind energy collector and wind speed under different wind directions in Example 2.

[0048] Fig.32 This is a graph showing the relationship between the output power of the trapezoidal beam wind energy collector and wind speed under different wind directions described in Example 2.

[0049] Fig.33 This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 0 degrees.

[0050] Fig.34 This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 15 degrees.

[0051] Fig.35This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 30 degrees.

[0052] Fig.36 This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 45 degrees.

[0053] Fig.37 This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 60 degrees.

[0054] Fig.38 This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 75 degrees.

[0055] Fig.39 This is a bar graph showing the variation of output power of the wind energy collector based on rectangular beams and trapezoidal beams described in Example 2 with wind speed at a wind direction angle of 90 degrees. DETAILED DESCRIPTION

[0056] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0057] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0058] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it an embodiment that is mutually exclusive with other embodiments, either individually or selectively.

[0059] Example 1

[0060] Reference Figure 1 to Figure 24 , which is the first embodiment of the present invention, provides a cantilever beam. The cantilever beam includes a cantilever beam 100 and a piezoelectric sheet 200.

[0061] Specifically, the cantilever beam 100 is a thin sheet with a certain thickness, and its shape is a trapezoid. Preferably, the cantilever beam 100 is in an isosceles trapezoid, and the ratio of the upper base to the lower base of the isosceles trapezoid is 0.5.

[0062] Preferably, the length of the fixed end of the cantilever beam 100 (i.e., the lower base of the isosceles trapezoid) is 40 mm. According to the above ratio, the length of the free end of the cantilever beam 100 (i.e., the upper base of the isosceles trapezoid) is 20 mm. The length of the cantilever beam 100 (i.e., the height of the isosceles trapezoid) is 80 mm and the thickness is 0.2 mm.

[0063] The piezoelectric sheet 200 is also a thin sheet with a certain thickness and a rectangular shape, and the piezoelectric sheet 200 is attached to a wide surface of the cantilever beam 100. The piezoelectric sheet 200 has a length of 40 mm, a width of 20 mm, and a thickness of 0.2 mm.

[0064] Preferably, the cantilever beam 100 is made of phosphor bronze, and the piezoelectric sheet 200 is made of lead zirconate titanate piezoelectric ceramic, specifically PZT-5A.

[0065] In order to better verify that the dimensions of the above-mentioned cantilever beam are their optimal dimensions, the optimization process of each dimension is described below.

[0066] Firstly, as an important energy capture and conversion element of the wind energy collector, the shape and size of the cantilever beam have a significant impact on the output performance of the collector, so the cantilever beam is subjected to static simulation to select the optimal shape of the cantilever beam 100.

[0067] The material of the piezoelectric sheet 200 selected for the simulation analysis is PZT-5A, and the cantilever beam 100 is phosphor bronze. The basic parameters of the materials are shown in Table 1:

[0068] Table 1 Basic parameters of piezoelectric cantilever beam materials

[0069]

[0070] The adhesive between the piezoelectric sheet 200 and the cantilever beam 100 is relatively thin and isotropic, so the effect on the vibration of the cantilever beam 100 is relatively weak and can be ignored in the simulation setting. The shapes of the cantilever beams 100 used in this simulation comparison are rectangular, trapezoidal, and triangular. The dimensions of the piezoelectric sheet 200 used on the cantilever beam 100 are all 40×20×0.2mm. 3 The bottom width of the cantilever beam 100 is 40 mm, the height is 80 mm, the thickness is 0.1 mm, and the upper bottom width of the trapezoid is 20 mm.

[0071] A fixed constraint is applied to the clamped end of the cantilever beam, and a side load of 0.005N is applied to the free end along the thickness direction of the cantilever beam 100 (a point load is applied at the top corner of the triangular beam). The damping type of the linear elastic material and the piezoelectric material of the simulation model both adopts an isotropic loss factor, and the size is 0.001. The piezoelectric sheet 200 is polarized along the thickness direction, and the polarized piezoelectric sheet 200 is an isotropic material perpendicular to the polarization direction. The upper surface of the piezoelectric sheet 200 is the negative electrode, which is set to ground and has an electric potential of 0; the lower surface is the positive electrode, which is set to the terminal and connected to the two ends of the load resistor of the circuit module. The cantilever beam is meshed using a free tetrahedral mesh, and the minimum unit size is 1.44mm. A steady-state study is performed on the piezoelectric cantilever beam. A 3D plot group is added below the result object, the surface object is selected, the contour object is inserted, and a discrete cloud map is plotted.

[0072] Specifically, the statics simulation analysis of the rectangular cantilever beam is carried out. The displacement cloud map, potential cloud map, stress cloud map and strain cloud map of the rectangular cantilever beam are obtained by comsol simulation as follows: Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown in the figure, it can be seen that the displacement of the rectangular cantilever beam decreases from the free end to the fixed end, and the maximum displacement is 0.37mm; the electric potential at the root of the cantilever beam 100 and the upper end boundary of the piezoelectric sheet 200 is the highest, and the maximum potential is 0.50V; the stress of the rectangular cantilever beam decreases from the fixed end to the free end, and the stress distribution is not particularly uniform, mainly concentrated at the root of the cantilever beam 100 near the clamping end, because when the cantilever beam 100 is subjected to bending and vibration along the thickness direction of the cantilever beam 100, the bending stress here is the largest, and the maximum stress is 5.75GPa; the free end of the rectangular cantilever beam has the smallest strain, and the strain near the root of the cantilever beam 100 is the largest, which is 5.1×10 -5 .

[0073] Static simulation analysis of the trapezoidal cantilever beam. The displacement cloud map, potential cloud map, stress cloud map, and strain cloud map obtained by the simulation of the trapezoidal cantilever beam are shown as follows: Figure 6 , 7 , 8, and 9. As shown in the figure, the displacement of the trapezoidal cantilever beam decreases from the free end to the fixed end, and the maximum displacement is 0.49 mm. When the excitation force and the cross-sectional area of ​​the clamping end are the same, the displacement of the free end of the trapezoidal cantilever beam is larger than that of the rectangular cantilever beam, indicating that the rigidity of the trapezoidal cantilever beam is smaller and the vibration amplitude of the free end is larger; the maximum voltage generated by the trapezoidal cantilever beam is 0.49 V; the stress concentration effect at the clamping end of the trapezoidal cantilever beam is the most obvious, and the maximum stress generated is 6.1 GPa, and the maximum strain is 5.40×10 -5 , compared with the rectangular cantilever beam, the stress and strain distribution is more uniform, and the stress and strain are also larger.

[0074] Static simulation analysis of the triangular cantilever beam. The displacement cloud map, potential cloud map, stress cloud map, and strain cloud map obtained by the simulation of the triangular piezoelectric cantilever beam are shown as follows: Fig.10 , Fig.11 , Fig.12 , Fig.13 As shown in the figure, the displacement at the top corner of the triangular beam is the largest, reaching 0.85mm, which is 2.3 times the maximum displacement of the rectangular beam and 1.7 times the maximum displacement of the trapezoidal beam. This shows that the triangular beam has the smallest stiffness and is most likely to bend; the maximum potential generated by the triangular beam is 0.61V. The triangular beam has the smallest area but the highest electrical output, which means that the power density of the triangular cantilever beam is very high; the stress and strain distribution of the triangular beam is the most uniform, and the stress and strain at the upper end of the cantilever beam 100 is on average greater than the stress and strain at the lower end. The maximum stress is 8.07GPa, and the maximum strain is 64×10 -6 , which is significantly greater than the stress-strain of rectangular beams and trapezoidal beams.

[0075] Comparative analysis of the static simulation results of rectangular, trapezoidal, and triangular piezoelectric cantilever beams shows that under the same stress conditions and clamping end width, the triangular beam has the largest deformation, the best effect in improving the uneven stress distribution, and the best output performance.

[0076] On the other hand, the axial strain and stress distribution of rectangular beams, trapezoidal beams, and triangular beams are studied. After steady-state research is performed using Comsol, a 3D cross section is added below the data set object, and a 1D plot group is added below the result object. The data set selects the 3D cross section, the y-axis data expression selects solid.mises and strain solid.ep1, and the x-axis data selects arc length. The distribution diagrams of stress and strain in the axial direction are drawn, such as Fig.14 and Fig.15 As shown in the figure, it can be seen that the farther the distance from the clamping end, the smaller the stress and strain of the cantilever beam 100, and at the same distance from the clamping end, the stress and strain of the triangular beam are the largest, followed by the trapezoidal beam, and the smallest for the rectangular beam; the stress-strain curve of the rectangular beam with the distance from the clamping end is the steepest, that is, the stress and strain decrease the fastest under the unit arc length; the stress-strain curve of the trapezoidal beam is flatter than that of the rectangular beam, that is, the stress and strain are more evenly distributed on the axis; when the distance from the clamping end is 0-30mm, the strain curve of the triangular beam decreases with the increase of the arc length, and when the distance from the clamping end is greater than 30mm, the strain curve of the triangular beam increases with the increase of the arc length and then tends to be stable; when the distance from the clamping end is 40-80mm, the stress curve of the triangular beam is approximately a horizontal straight line, that is, the stress does not decrease with the increase of the arc length, which is consistent with the stress distribution cloud diagram of the triangular beam, which shows that the stress and strain distribution at the far end of the triangular beam is particularly uniform.

[0077] However, since the tip of the triangular cantilever beam is not conducive to installing the bluff body 300, it is not considered for the time being, and thus the structure of the trapezoidal cantilever beam 100 is selected for optimization.

[0078] From the above simulation results, it can be seen that the free end displacement of the trapezoidal beam is larger than that of the rectangular beam, and the stress and strain distribution is more uniform. Therefore, the trapezoidal beam is used instead of the rectangular beam to obtain better output performance.

[0079] First of all, it should be noted that in order to make the geometric volume of the energy harvester as small as possible while ensuring the basic output performance, it is proposed that the volume of the cantilever beam does not exceed 80×40×0.4mm 3 The main optimized structural parameters include the fixed end width, free end width, cantilever beam 100 length, cantilever beam 100 thickness, piezoelectric sheet 200 thickness, piezoelectric sheet 200 length, and piezoelectric sheet 200 width. COMSOL finite element simulation software was used to explore the influence of the geometric dimensions of each component on the mechanical properties and output performance of the collector, and to determine the optimal structural dimensions.

[0080] Add piezoelectric effect in multi-physics field coupling, select solid mechanics, electrostatics, and circuits, calculate the characteristic frequency of the piezoelectric vibrator first, and then conduct frequency domain research. Fill in the characteristic frequency in the frequency text box, expand the research extension bar, check the auxiliary scan checkbox, add the parameter name R_load (load resistance), the parameter value list 10^range(2,0.2,10), add a one-dimensional drawing group below the result object after frequency domain calculation, select abs(cir.R1_v) (output voltage) and 0.5*realdot(cir.R1_i,cir.R1_v) (output power) for the y-axis data, and select R_load (load resistance) for the x-axis data to obtain the relationship curve between the output voltage and power of the piezoelectric vibrator and the load resistance.

[0081] First, optimize the upper and lower base ratio of the trapezoidal cantilever beam 100. The fixed end width of the trapezoidal cantilever beam 100 is selected as 40 mm, the length is 80 mm, the ratio of the free end width to the fixed end width is r, the value range of r is 0.1 to 1, and the free end width range is 4 to 40 mm. The cantilever beam 100 is phosphor bronze, and the thickness of the cantilever beam 100 and the thickness of the piezoelectric sheet 200 are both 0.2 mm, and the piezoelectric sheet 200 completely covers the entire cantilever beam 100. The larger r is, the larger the free end width is, and the shape of the piezoelectric cantilever beam changes from trapezoidal to rectangular.

[0082] Table 2 shows the effect of the upper and lower bottom ratio on the resonant frequency and electrical output. As the trapezoidal cantilever beam approaches the rectangular cantilever beam, the resonant frequency of the device decreases, and the open circuit voltage and output power decrease, especially when r≥0.7, that is, the free end width ≥28mm, the output performance of the piezoelectric vibrator decreases linearly. It can be seen that the smaller the free end width of the cantilever beam 100, that is, the closer it is to a triangle, the better the output performance of the piezoelectric vibrator, but the smaller the free end width, the more difficult it is to install the blunt body 300 at the top of the cantilever beam 100, and the more likely the cantilever beam 100 is to undergo torsional motion. Considering that the electrical output of the piezoelectric vibrator is not much different when r is in the range of 0.3 to 0.6, taking the upper and lower bottom ratio r=0.5 can not only ensure that the cantilever beam can vibrate at a lower frequency, but also obtain better output performance. In addition, selecting r=0.5 as the middle value can ensure the performance stability within the range, while avoiding the instability or sensitivity that may be caused by extreme values. At the same time, when r=0.5, the ratio of the upper bottom to the lower bottom length is 1:2, and the structure is relatively symmetrical. This symmetry can bring manufacturing convenience and structural stability, and help improve the reliability and consistency of the piezoelectric vibrator.

[0083] Table 2 Effect of upper and lower base ratio on resonant frequency and electrical output

[0084]

[0085] Secondly, optimize the length and width of the trapezoidal cantilever beam 100. Specifically, the length of the cantilever beam 100 varies in the range of 60 to 100 mm with a step size of 10 mm, and the width of the fixed end varies in the range of 30 to 50 mm with a step size of 5 mm. The upper and lower base ratio is 0.5, the cantilever beam 100 is phosphor bronze, the piezoelectric sheet 200 completely covers the cantilever beam 100, and the thickness of the cantilever beam 100 and the piezoelectric sheet 200 are both 0.2 mm. A force of 0.0005 is applied to the free end of the cantilever beam 100. The COMSOL simulation is used to solve the resonant frequency, open circuit voltage and output power of trapezoidal cantilever beams of different lengths and widths, as shown in Tables 3, 4 and 5, respectively. The tabular data is organized and plotted into three-dimensional surface graphs using Origin software, as shown in Tables 3, 4 and 5, respectively. Fig.16 , Fig.17 , Fig.18 As shown, the effect of the length and width of the cantilever beam 100 on the resonant frequency, open circuit voltage and output power is intuitively demonstrated.

[0086] Table 3 Effect of cantilever beam length and width on resonant frequency

[0087]

[0088] Table 4 Effect of cantilever beam length and width on open circuit voltage

[0089]

[0090] Table 5 Effect of cantilever beam length and width on output power

[0091]

[0092] It can be seen from the above table that when the width of the cantilever beam 100 is constant, the resonant frequency decreases linearly with the increase of the length; when the length of the cantilever beam 100 is constant, the width increases and the resonant frequency remains basically unchanged. When the width of the cantilever beam 100 is constant, the open circuit voltage increases with the increase of the length. This is because the larger the length, the larger the force arm, the greater the bending moment of the cantilever beam 100 under the same shear force, the greater the stress and strain generated by the cantilever beam 100, and therefore the greater the open circuit voltage; but when the length of the cantilever beam 100 exceeds 90mm, the open circuit voltage decreases sharply, which may be due to the cantilever beam 100 exceeding the limit and being damaged. When the length of the cantilever beam 100 is constant, the larger the width, the smaller the open circuit voltage. This is because as the width increases, the stiffness of the cantilever beam 100 also increases, the amplitude of the bending vibration of the cantilever beam 100 decreases, and the charge generated decreases, so the open circuit voltage decreases. Similar to the relationship between the open circuit voltage and the output power, the output power is positively correlated with the length of the cantilever beam 100 within a certain range, and negatively correlated with the width of the cantilever beam 100. When the length of the cantilever beam 100 is 80 mm and the width is 35 mm, the maximum output power reaches 74.03 μW. Under the principle of maximizing the output power and taking into account the resonant frequency of the device, the maximum value is obtained within the specified size range. Therefore, the length of the cantilever beam 100 is selected to be 80 mm, and the width of the fixed end of the cantilever beam 100 is 40 mm. It should be noted that the selection of a slightly wider cantilever beam 100 (40 mm) will increase the stability and durability of the structure. In actual manufacturing and use, the wider cantilever beam 100 can better withstand external stress and environmental influences, reducing the possibility of damage. In addition, manufacturing tolerances and safety margins need to be considered in actual design. Selecting a width of 40 mm can provide more design room to ensure that even if there are some errors in actual production, the equipment can still achieve the performance required by the design.

[0093] Next, the length of the piezoelectric sheet 200 is optimized. From the above, the length of the trapezoidal cantilever beam 100 is determined to be 80 mm, the width of the fixed end is 40 mm, and the width of the free end is 20 mm. In order to further study the effect of the length of the piezoelectric sheet 200 on the resonant frequency and electrical output of the device, the width of the piezoelectric sheet 200 is set to 20 mm, and the length of the piezoelectric sheet 200 is varied in the range of 10 to 80 mm with a step length of 10 mm. The device resonant frequency, open circuit voltage and output power obtained by simulation under different lengths of piezoelectric sheets 200 are shown in Table 6.

[0094] Table 6 Effect of piezoelectric sheet 200 length on resonant frequency and electrical output

[0095]

[0096] In addition, from Fig.19 It can be seen that the device resonant frequency increases linearly first and then decreases linearly as the length of the piezoelectric sheet 200 increases. When the length of the piezoelectric sheet 200 is 50 mm, the device resonant frequency is the highest. Fig. 20 It can be seen that when the length of the piezoelectric sheet 200 increases from 20 mm to 30 mm, the open circuit voltage increases exponentially. When the length of the piezoelectric sheet 200 continues to increase, the open circuit voltage drops sharply. This is because the piezoelectric sheet 200 is attached to the cantilever beam 100, and the longer the piezoelectric sheet 200 is, the greater the equivalent stiffness of the device. Fig.21 It can be seen that the change trend of the device output power is basically consistent with the open circuit voltage. When the length of the piezoelectric sheet 200 is 30mm, the device harvests a peak power of 752.52μW. Since the piezoelectric sheet 200 with a size of 20×30 is not easy to buy on the market, and the output performance of the piezoelectric sheet 200 with a length of 40mm is not much different from that of the piezoelectric sheet 200 with a length of 30mm, the piezoelectric sheet 200 is selected to be 40mm in length and 20mm in width.

[0097] Next, the thickness of the cantilever beam 100 and the piezoelectric sheet 200 are optimized. In order to explore the influence of the thickness of the cantilever beam 100 and the thickness of the piezoelectric sheet 200 on the vibration characteristics and output characteristics of the device, the thickness of the cantilever beam 100 is changed in the range of 0.1mm to 0.5mm with a step length of 0.1mm, and the thickness of the piezoelectric sheet 200 is changed in the range of 0.2mm to 0.7mm with a step length of 0.1mm. The length and width of the cantilever beam 100 are 80×40(20)mm. 2 , piezoelectric sheet 200 length and width are 40×20mm 2 The effects of different cantilever beam 100 thicknesses and piezoelectric sheet 200 thicknesses on the device resonant frequency, open circuit voltage and output power are shown in Table 7, Table 8 and Table 9, respectively.

[0098] Table 7 Effect of cantilever beam 100 thickness and piezoelectric sheet 200 thickness on resonant frequency

[0099]

[0100] Table 8 Effect of cantilever beam 100 thickness and piezoelectric sheet 200 thickness on open circuit voltage

[0101]

[0102] Table 9 Effect of cantilever beam 100 thickness and piezoelectric sheet 200 thickness on output power

[0103]

[0104] from Fig. 22It can be seen that no matter the thickness of the cantilever beam 100 or the thickness of the piezoelectric sheet 200 increases, the resonance frequency of the device increases with the increase of the total thickness of the cantilever beam, because the thicker the cantilever beam, the greater the stiffness of the device. Fig.23 It can be seen that when the width of the piezoelectric sheet 200 is constant, the device open circuit voltage is highest when the thickness of the cantilever beam 100 is 0.2 mm; when the thickness of the cantilever beam 100 is constant, the device open circuit voltage is highest when the thickness of the piezoelectric sheet 200 is 0.2 mm or 0.3 mm. Fig.24 It can be seen that when the thickness of the piezoelectric sheet 200 remains unchanged, the output power of the device increases first and then decreases as the thickness of the cantilever beam 100 increases. This is because the thicker the metal substrate is, the less likely it is to bend and deform, the smaller the stress strain of the cantilever beam is, and the less charge is generated; when the thickness of the cantilever beam 100 remains unchanged, the output power of the device increases first and then decreases or keeps decreasing as the thickness of the piezoelectric sheet 200 increases. This is because the thickness of the piezoelectric sheet 200 not only affects the piezoelectric effect but also the bending stiffness of the device; when the thickness of the cantilever beam 100 is 0.2mm, the output power of the device exceeds 500μW, which is much greater than the output of the cantilever beam 100 with other thicknesses. When the thickness of the piezoelectric sheet 200 is 0.2mm, the output power of the device reaches a peak value of 610.61μW. Therefore, the thickness of the cantilever beam 100 and the thickness of the piezoelectric sheet 200 are both selected to be 0.2mm, at which time the device output performance is optimal.

[0105] In summary, after the above optimization, the best size of the cantilever beam is that the cantilever beam 100 has a length of 80 mm, a fixed end width of 40 mm, a free end width of 20 mm, and a thickness of 0.2 mm. The piezoelectric sheet 200 has a length of 40 mm, a width of 20 mm, and a thickness of 0.2 mm.

[0106] Example 2

[0107] Reference Figure 24 to Figure 39 , which is the second embodiment of the present invention, and is based on the previous embodiment. This embodiment provides a wind energy collector, which includes a bluff body 300 and a base 400 in addition to the cantilever beam 100 and the piezoelectric sheet 200 described in the first embodiment.

[0108] Specifically, the bluff body 300 is a hollow cylinder, the bottom of which is fixedly connected to the free end of the cantilever beam 100 .

[0109] The base 400 is two “L”-shaped metal clamps used to fix the fixed ends of the cantilever beam 100 .

[0110] In order to verify the improvement effect of the trapezoidal cantilever beam 100 optimization scheme described in Example 1 on the output performance of the wind energy collector, this embodiment proposes a trapezoidal piezoelectric cantilever beam and a rectangular piezoelectric cantilever beam according to the determined optimal size. The two cantilever beams differ only in the width of the clamping end. A comparative experimental study is conducted on the wind energy collector based on the trapezoidal cantilever beam and the wind energy collector based on the rectangular cantilever beam. The two collectors are respectively as follows: Fig.25 and Fig.26 shown.

[0111] The wind energy collector consists of a cantilever beam and a cylindrical bluff body 300 fixed at the free end of the cantilever beam 100. The piezoelectric sheet 200 is pasted near the fixed end of the cantilever beam 100, because the stress and strain at the fixed end of the cantilever beam 100 is the largest according to the above simulation results. The x direction is perpendicular to the thickness direction of the cantilever beam 100, the y direction is parallel to the thickness direction of the cantilever beam 100, 0° represents the downwind direction, and 90° represents the crosswind direction. The wind direction angle θ is the angle between the x direction and the wind direction. The cylindrical bluff body 300 has a diameter of 40 mm and a length of 100 mm. It is printed from low-density black nylon. When the wind speed exceeds the starting wind speed, the bluff body 300 begins to vibrate. The higher the wind speed, the more severe the vibration phenomenon. When wind flows through the bluff body 300, vortices that periodically shed alternately are generated on the leeward side of the bluff body 300, thereby generating periodic pressure perpendicular to the wind direction acting on the bluff body 300. The bluff body 300 supported by the cantilever beam periodically oscillates in a direction perpendicular to the wind direction, driving the elastic cantilever beam 100 to bend and deform periodically, and the piezoelectric sheet 200 tightly bonded to the cantilever beam 100 generates bending strain, thereby completing the conversion of mechanical energy into electrical energy through the d31 working mode.

[0112] In order to make the piezoelectric wind energy harvester work in the best state, the ZX11M AC / DC resistance box is connected in series with the piezoelectric wind energy harvester to conduct impedance matching experiments. Since the piezoelectric sheet 200 made of piezoelectric ceramic material has a small dielectric constant, the equivalent capacitance of the piezoelectric harvester is low and the impedance is high, usually at the MΩ level, so the load resistance value should be adjusted from large to small. When the wind direction is 0° and the wind speed is 7m / s, the load resistance value is gradually adjusted from 5MΩ to 0.001MΩ, and the output RMS voltage values ​​of the trapezoidal beam and rectangular beam piezoelectric wind energy harvesters are recorded respectively, as shown in Fig. 27 As shown in the figure, the output RMS voltage of the trapezoidal beam and rectangular beam piezoelectric wind energy harvesters increases with the increase of load resistance. The larger the load resistance, the closer the output RMS voltage is to the open circuit voltage. In addition, under the same load resistance, the output RMS voltage of the trapezoidal beam piezoelectric wind energy harvester is significantly greater than that of the rectangular beam. According to the formula P = Vrms 2 / R (where Vrms is the root mean square voltage) to calculate the output power of the trapezoidal beam and rectangular beam piezoelectric wind energy harvesters, respectively, as Fig.28As shown in the figure, the output power increases first and then decreases with the increase of load resistance, and reaches the maximum value at 0.1MΩ. The optimal resistance is the resistance load value corresponding to the maximum output power of the energy harvester, that is, the optimal resistance of the trapezoidal beam and the rectangular beam is 0.1MΩ.

[0113] On the other hand, under different wind directions (0°, 15°, 30°, 45°, 60°, 75°, 90°), the output voltage of the rectangular beam and trapezoidal beam piezoelectric wind energy harvesters varies with wind speed as shown in the following table: Fig.29 and Fig.30 As shown. The wind speed adjustment range is 2m / s~8m / s, with a sampling interval of 0.5m / s. The output voltage of the rectangular beam and trapezoidal beam piezoelectric wind energy harvesters increases significantly with the increase of wind speed, and there are significant differences in the voltage output performance of the two. In the medium and high wind speed stage (4~8m / s), the rectangular beam piezoelectric wind energy harvester has the largest output voltage when the wind direction is 0°, and reaches a peak voltage of 1.34V at a wind speed of 8m / s. When the wind direction angle increases to 15°, the peak voltage decreases to 1.18V, and the output voltage decreases with the increase of the wind direction angle. When the wind direction is 90°, the output voltage is the smallest, which is 0.78V; in the low wind speed stage (2~4m / s), the rectangular beam piezoelectric wind energy harvester has the largest output voltage when the wind direction angle is 30°, and the output voltage is the smallest when the wind direction angle is 90°.

[0114] from Fig.30 It can be seen that within the wind speed range of 2 to 8 m / s, the output voltage of the trapezoidal beam piezoelectric wind energy harvester is the highest overall at a wind direction of 15°, and reaches a peak voltage of 2.49V at a wind speed of 8 m / s, which is about twice the maximum output of the rectangular beam harvester, followed by a wind direction of 30°, with a peak voltage of 2.23V. The output voltage of the trapezoidal beam piezoelectric wind energy harvester decreases in the order of wind directions of 15°, 30°, 0°, 45°, 60°, 90°, and 75°. The output voltages are very close when the wind directions are 60° and 90°, and the peak voltage is the smallest when the wind direction is 75°, which is only 1.51V. Under the same wind direction and wind speed, the output voltage of the trapezoidal beam is higher than that of the rectangular beam, that is, the trapezoidal beam exhibits better working performance than the rectangular beam.

[0115] Under different wind directions, the output power of rectangular beam and trapezoidal beam piezoelectric wind energy harvesters varies with wind speed. Fig.31 and Fig.32 As shown. The rectangular beam piezoelectric wind energy harvester reaches a peak power of 17.96μW at a wind speed of 8m / s and a wind direction of 0°. When the wind direction angle increases to 15°, the output power decreases to 13.92μW. This is because the vibration direction deviates from the crosswind direction, the component of the crosswind force along the vibration direction becomes smaller, the vibration amplitude of the cantilever beam becomes smaller, and the electrical output naturally decreases. When the wind direction is 90°, the rectangular beam harvester has the lowest output power, which is only 6.13μW.

[0116] When the wind speed is 8m / s, the output power of the wind energy harvester based on the rectangular beam does not exceed 20μW in each wind direction, but the minimum output power of the wind energy harvester based on the trapezoidal beam reaches 22.80μW (θ=75°). When θ=15°, the trapezoidal beam piezoelectric wind energy harvester reaches a peak power of 62.00μW, which is about 3.5 times the maximum output of the rectangular beam harvester, and is 249.42% higher than the rectangular beam. Compared with the rectangular beam piezoelectric wind energy harvester, the trapezoidal beam piezoelectric wind energy harvester responds faster in the low wind speed stage and more obviously in the high wind speed stage, with a lower starting wind speed, a wider effective working wind speed range and a higher output power.

[0117] In order to further verify the improvement effect of trapezoidal cantilever beam on the output performance of wind energy collector compared with rectangular cantilever beam, since the output power difference between the two is not obvious in the wind speed range of 2-5m / s, the relationship between the output power of piezoelectric wind energy collector based on rectangular beam and trapezoidal beam and wind speed under different wind directions is studied only in the wind speed range of 5-8m / s. Figure 3-18 As shown in the figure, the red column represents the output power of the piezoelectric wind energy harvester based on the rectangular beam, and the blue column represents the rectangular beam. It can be clearly seen from the figure that the electrical output of the trapezoidal piezoelectric cantilever beam is always better than that of the rectangular piezoelectric cantilever beam, and the gap between the two increases with the increase of wind speed. When the wind direction angle θ = 15°, the output performance difference between the trapezoidal beam and the rectangular beam is the most obvious. When the wind direction angle θ = 75°, the output difference between the two is the smallest. This is because the output power of the trapezoidal beam collector is the highest when θ = 15° and the lowest when θ = 75°, while the output power of the rectangular beam collector changes less with wind direction. Therefore, using a trapezoidal cantilever beam instead of a traditional rectangular cantilever beam as a vibration power generation element can obtain better electrical output performance.

[0118] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A cantilever beam, characterized in that: include, The cantilever beam (100) has a trapezoidal projection shape in the thickness direction; A piezoelectric sheet (200) is attached to one side of the cantilever beam (100).

2. The cantilever beam according to claim 1, characterized in that: The projection shape of the cantilever beam (100) in the thickness direction is an isosceles trapezoid, and the ratio of its upper base to its lower base is 0.

5.

3. The cantilever beam according to claim 1, characterized in that: The length between the upper base and the lower base of the trapezoidal projection of the cantilever beam (100) in the thickness direction is 80 mm, and the length of the lower base is 40 mm.

4. The cantilever beam according to claim 1, characterized in that: The cantilever beam (100) has a thickness of 0.2 mm.

5. The cantilever beam according to claim 1, characterized in that: The projection shape of the piezoelectric sheet (200) in the thickness direction is a rectangle, and its width is the same as the upper base of the trapezoidal projection in the thickness direction of the cantilever beam (100).

6. The cantilever beam according to claim 1, characterized in that: The thickness of the piezoelectric sheet (200) is 0.2 mm.

7. The cantilever beam according to claim 1, characterized in that: The material of the cantilever beam (100) is phosphor bronze, and the material of the piezoelectric sheet (200) is lead zirconate titanate.

8. A wind energy collector, characterized in that: include, Blunt body (300); The cantilever beam (100) and the piezoelectric sheet (200) as claimed in any one of claims 1 to 7; One end of the cantilever beam (100) is fixedly connected to one end of the bluff body (300).

9. The wind energy collector according to claim 8, characterized in that: The bluff body (300) is in the shape of a cylinder.

10. The wind energy collector according to claim 9, characterized in that: A base (400) is also provided at one end of the cantilever beam (100) away from the bluff body (300), and the cantilever beam (100) is fixed on the base (400).

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