Cantilever beam for piezoelectric energy harvesting system

Abstract

The invention relates to a cantilever beam for a piezoelectric energy harvesting system, wherein the cantilever beam (2, 20, 30) comprises two layers (21, 22, 31, 32) of polyvinylidene fluoride, and wherein a core layer (23, 33) of a gasket material is sandwiched between the two layers (21, 22, 31, 32) of polyvinylidene fluoride.

Description

Technical Field

[0001] This application relates to cantilever beams for energy harvesting systems, and more particularly to improved cantilever beams for piezoelectric energy harvesting systems. Background Technology

[0002] There are many untapped energy sources in the environment, such as heat, electromagnetic waves, and mechanical vibrations. Energy harvesting technologies have been developed to convert these environmental energies into electricity. Energy harvesting technologies include, for example, using energy sources that can be used as batteries for wireless sensors. There are also various other energy sources available for harvesting, such as solar energy, thermal energy, wind energy, and vibration. Furthermore, there are three main types of energy harvesting methods: electromagnetic, electrostatic, and piezoelectric.

[0003] One method of energy harvesting using piezoelectric materials is to convert mechanical energy from various sources, such as human movement, acoustic noise, or wind, into an electric current. When mechanical energy, such as sound waves, is applied to a piezoelectric polymer film, an electric charge is induced between the two surfaces. Using this property, piezoelectric materials can be applied as electromechanical energy converters.

[0004] US 7,649,305 B2 discloses a mechanism for capturing mechanical energy and converting it into electrical energy for continuously charging or providing emergency power to a mobile, battery-powered device. The mechanism includes a plurality of elongated piezoelectric elements mounted at one or more support points to one or more support structures. The plurality of piezoelectric elements are preferably constructed and arranged such that at least one element is present along at least each three-dimensional coordinate axis, having a primary deflection mode in the normal plane of the coordinate axis to allow energy harvesting from forces applied from any direction, regardless of the orientation of the energy harvesting mechanism relative to the source of the force.

[0005] Among piezoelectric materials, especially polymers exhibiting strong piezoelectric effects when subjected to mechanical stretching or external excitation, polyvinylidene fluoride (PVDF) films possess a remarkably high piezoelectric effect. Furthermore, they are inexpensive and easy to manufacture, chemically inert, lightweight, and safe. However, due to their typically very thin thickness, brittleness, and very short response time, PVDF films are generally not used as the basis for piezoelectric energy harvesting systems. Summary of the Invention

[0006] The objective of this invention is to provide an improved cantilever beam for a piezoelectric energy harvesting system.

[0007] According to one embodiment of the present invention, a cantilever beam for a piezoelectric energy harvesting system is provided, wherein the cantilever beam comprises two layers formed of polyvinylidene fluoride, wherein a core layer formed of a gasket material is sandwiched between the two layers formed of polyvinylidene fluoride.

[0008] Therefore, a cantilever beam for a piezoelectric energy harvesting system is provided, which is based on a polyvinylidene fluoride (PVDF) membrane. Thus, it fully utilizes the advantages of PVDF as a piezoelectric material; specifically, the PVDF membrane has a relatively high piezoelectric effect, and is inexpensive, easy to manufacture, chemically inert, lightweight, and safe. However, on the other hand, due to the construction of this cantilever beam, the problems that typically occur when the cantilever beam of a piezoelectric energy harvesting system is based on a PVDF membrane are negligible. For example, the brittleness of a PVDF-based cantilever beam can be reduced by placing a core layer of gasket material between two layers formed of PVDF. Therefore, an improved cantilever beam for a piezoelectric energy harvesting system is provided.

[0009] The two layers formed from polyvinylidene fluoride (PVDF) can have a predominantly β-type crystal structure. PVDF has four crystalline phases depending on its chain conformation: α, β, γ, and δ. Of these, α is the most thermodynamically stable and virtually polar. β and γ are polar phases, with the β phase being particularly important due to its spontaneous polarization and piezoelectric sensitivity. Therefore, when the two layers formed from PVDF have a predominantly β-type crystal structure, the cantilever beam can be further improved.

[0010] Furthermore, the cantilever beam can have a rectangular sheet shape, wherein the longitudinal side of the rectangular sheet is longer than the wide side of the rectangular sheet, and the cantilever beam is configured such that it can be connected to a device for storing or using energy via one of its longitudinal sides. By configuring the cantilever beam in this way, the long side of the cantilever beam can be electrically connected, or electrically and mechanically connected, to the device for storing or using energy, further improving robustness. Therefore, the brittleness of the polyvinylidene fluoride-based cantilever beam can be further reduced.

[0011] As gasket materials, aluminum, steel, copper, and laminated plastics such as polyethylene terephthalate (PET) are commonly used.

[0012] In the first embodiment, the core layer can be formed of steel. Using steel as the material for the core layer has the following advantages: the cantilever beam can vibrate at the maximum possible resonant frequency, and the vibration wave can be as long as possible.

[0013] Furthermore, the core layer formed of steel preferably has a thickness between 50 μm and 150 μm to achieve maximum power output.

[0014] According to another embodiment, the core layer is formed of polyethylene terephthalate (PET). Using polyethylene terephthalate as the material for the core layer has the advantage of enabling a considerable power output.

[0015] Furthermore, the core layer formed of polyethylene terephthalate preferably has a thickness between 400 μm and 560 μm to achieve maximum power output.

[0016] Furthermore, each of the two layers formed from polyvinylidene fluoride (PVDF) can have a thickness between 20 μm and 50 μm. Having PVDF layers with thicknesses between 20 μm and 50 μm offers the advantage of allowing applied dynamic stress to be converted in a very efficient manner. However, if these layers are too thin, there is a possibility of extractants migrating through them, as well as potential attacks from these components, which could penetrate the PVDF layer and attack other materials in the structure. Thicker layers would add unnecessary costs.

[0017] The two layers formed of polyvinylidene fluoride (PVDF) can be bonded to the core layer separately using epoxy resin. By fixing the PVDF layers to the core layer using epoxy resin, the flexibility of the composite is enhanced, while further reducing the risk of fracture. Furthermore, the use of epoxy resin results in superior mechanical properties and improved aging resistance, heat resistance, and corrosion resistance of the composite.

[0018] Furthermore, electrodes can be formed on top of and under each of the two layers made of polyvinylidene fluoride (PVDF). By sandwiching the PVDF layer between the two electrodes, a simple, flexible, and compact design capable of producing high capacity power density is provided.

[0019] The electrodes can be formed from aluminum, nickel, or copper. Thus, the electrodes can be simply formed by sputtering metal onto a polyvinylidene fluoride (PDVF) film, where the metallization of the PDVF film can include aluminum, nickel, or copper, providing electrodes that are more malleable and less susceptible to influence. However, the use of aluminum, nickel, or copper for the electrodes should be understood as merely examples; other materials can also be used to form the metallization on the PDVF layer, such as chromium, gold, silver, platinum, rhodium, or alloys of any of the aforementioned metals, etc.

[0020] According to another embodiment of the present invention, a piezoelectric energy harvesting system is provided, which includes the cantilever beam described above and a device for storing or using energy, wherein a first end of the cantilever beam is electrically connected to the device for storing or using energy.

[0021] Therefore, a piezoelectric energy harvesting system is provided, comprising a cantilever beam based on a polyvinylidene fluoride (PVDF) membrane. This system fully utilizes the advantages of PVDF as a piezoelectric material; specifically, the PVDF membrane possesses a relatively high piezoelectric effect, and is inexpensive, easy to manufacture, chemically inert, lightweight, and safe. However, due to the construction of this cantilever beam, the problems typically encountered when the cantilever beam of a piezoelectric energy harvesting system is based on a PVDF membrane are negligible. For example, the brittleness of a PVDF-based cantilever beam can be reduced by placing a core layer of gasket material between the two PVDF layers.

[0022] Furthermore, at least one end block may be attached to the second end of the cantilever beam, wherein the second end of the cantilever beam is opposite to the first end. By adding at least one end block to the second free end of the cantilever beam, the vibration amplitude level can be increased and the resonant energy level can be controlled.

[0023] The weight of at least one end block can be customized, thereby allowing the resonant frequency of the piezoelectric energy harvesting system to be tailored to the specific needs of the application.

[0024] Furthermore, according to one embodiment, a first terminal block is attached to the top surface of the second end of the cantilever beam, and a second terminal block is attached to the bottom surface of the second end of the cantilever beam. By placing such additional blocks on the surface of the cantilever beam opposite to the surface where the first terminal block is placed, the vibration time of the cantilever beam can be increased. Furthermore, the output voltage can be increased based on the ratio of the weight of the first terminal block to the weight of the second terminal block. Attached Figure Description

[0025] Embodiments of the present invention will now be described in conjunction with the accompanying drawings.

[0026] Figure 1 A piezoelectric energy harvesting system according to an embodiment of the present invention is shown;

[0027] Figure 2 A cantilever beam for a piezoelectric energy harvesting system according to a first embodiment of the present invention is shown;

[0028] Figure 3 A cantilever beam for a piezoelectric energy harvesting system according to a second embodiment of the present invention is shown. Detailed Implementation

[0029] Figure 1 A piezoelectric energy harvesting system 1 according to an embodiment of the present invention is shown.

[0030] like Figure 1 As shown, the piezoelectric energy harvesting system 1 includes a cantilever beam 2 and an energy storage or utilization device 3, wherein the device 3 includes printed circuit boards and electronic components such as rectifier units, control units, and storage devices such as batteries and capacitors. Furthermore, the proximal end or first end 4 of the cantilever beam 2 is mechanically and electrically connected to the energy storage or utilization device 3. According to... Figure 1 In one embodiment, the cantilever beam 2 is anchored to and mechanically connected to the device 3 by screws 5. However, the mechanical connection of the cantilever beam to the device by screws should be understood as merely an example, and the cantilever beam may also be mechanically connected to the device by other suitable fasteners. Figure 1 Also shown is mounting 6, through which the piezoelectric energy harvesting system can be connected to the equipment or retained in the structure.

[0031] The piezoelectric energy harvesting system 1 includes a component that uses vibration or pressure to cause the piezoelectric layer to bend, compress, or be extracted, thereby generating an alternating voltage through the piezoelectric effect. Thus, kinetic energy is converted into electrical energy.

[0032] These piezoelectric energy harvesting systems are used in various ways because they can utilize the pressure or vibration caused by human exercise, the pressure or vibration caused by vehicles such as cars, the pressure or vibration caused by the natural environment, and so on.

[0033] Among possible piezoelectric materials, polyvinylidene fluoride (PVDF) films exhibit a remarkably high piezoelectric effect, while also being inexpensive, easy to produce, chemically inert, lightweight, and safe. However, due to their typically very thin thickness, PVDF films are generally not used as the basis for piezoelectric energy harvesting systems because of their brittleness and very short response time.

[0034] according to Figure 1 In one embodiment, the cantilever beam 2 comprises two layers formed of polyvinylidene fluoride, wherein a core layer formed of gasket material is sandwiched between the two layers formed of polyvinylidene fluoride.

[0035] Therefore, a cantilever beam 2 for a piezoelectric energy harvesting system 1 is provided, which is based on a polyvinylidene fluoride (PVDF) membrane. Thus, it fully utilizes the advantages of PVDF as a piezoelectric material; specifically, the PVDF membrane has a relatively high piezoelectric effect, and is inexpensive, easy to manufacture, chemically inert, lightweight, and safe. However, on the other hand, due to the construction of this cantilever beam, the problems that typically occur when the cantilever beam of a piezoelectric energy harvesting system is based on a PVDF membrane are negligible. For example, the brittleness of a PVDF-based cantilever beam can be reduced by placing a core layer formed of a gasket material between the two layers formed of PVDF. Therefore, an improved cantilever beam for a piezoelectric energy harvesting system is provided.

[0036] according to Figure 1 In one embodiment, the layers formed of polyvinylidene fluoride are arranged such that during bending, one of these layers (such as the top layer) generates a positive charge, while another layer (such as the bottom layer) placed on the opposite side of the core layer also generates a positive charge, wherein the two layers are connected in parallel.

[0037] In the piezoelectric energy harvesting system 1 shown, the vibration amplitude level can be increased by controlling the resonant energy level by attaching at least one end block to the distal or second free end 7 of the cantilever beam 2.

[0038] according to Figure 1In one embodiment, the first terminal block 8 is attached to the top surface 9 of the second end 8 of the cantilever beam 2, and the second terminal block 10 is attached to the bottom surface 11 of the second end 8 of the cantilever beam 2. The terminal blocks 8 and 10 can be formed, for example, using high-density metals such as tungsten or iron.

[0039] Furthermore, the first terminal block 8 and the second terminal block 10 are configured to be customized to the actual needs of the application. For example, in known applications, the first terminal block is selected to have a weight of 12g, and the second terminal block is selected to have a weight of 7g.

[0040] Figure 2 A cantilever beam 20 for a piezoelectric energy harvesting system according to a first embodiment of the present invention is shown.

[0041] The cantilever beam 20 shown includes two layers 21 and 22 formed of polyvinylidene fluoride, wherein a core layer 23 formed of gasket material is sandwiched between the two layers 21 and 22 formed of polyvinylidene fluoride.

[0042] The two layers 21 and 22 formed of polyvinylidene fluoride have a predominantly β-type crystal structure. Each of the two layers 21 and 22 formed of polyvinylidene fluoride can be polarized, for example, to change its phase from α to β. This is achieved by placing the layer under a high electric field and heating it to a certain temperature, wherein the layer is held under the high electric field for a required amount of time.

[0043] Furthermore, the cantilever beam 20 shown has the shape of a rectangular plate, wherein the longitudinal side of the rectangular plate is longer than the wide side of the rectangular plate, and the cantilever beam 20 is configured such that the cantilever beam 20 is connected to a device for storing or using energy via one of its longitudinal sides.

[0044] Each layer formed of polyvinylidene fluoride can be prepared such that it has an approximate length between 60 mm and 80 mm and an approximate width between 10 mm and 20 mm. Specifically, according to Figure 2 In one embodiment, each polyvinylidene fluoride (PVDF) layer has a length l of 74 mm and a width w of 13 mm. However, the 74 mm length and 13 mm width of each PVDF layer should be understood as an example only; each PVDF layer may also have a length of 64 mm and a width of 12 mm, for example. Furthermore, the dimensions described are merely examples, and the cantilever beam may have different lengths and widths, for example, from 10 mm to 150 mm or even longer.

[0045] According to the first embodiment, the core layer 23 is formed of steel. Using steel as the material for the core layer has the following advantages: the cantilever beam can vibrate at the maximum possible resonant frequency, and the vibration wave can be as long as possible.

[0046] The core layer 23, made of steel, has a thickness between 50 μm and 150 μm to achieve maximum power output.

[0047] Furthermore, each of the two layers formed from polyvinylidene fluoride has a thickness between 20 μm and 50 μm to convert the applied dynamic stress in a very efficient manner.

[0048] like Figure 2 As shown, additional adhesive layers 24 and 25 are formed to fix layers 21 and 22 formed of polyvinylidene fluoride to the core layer 23, respectively. Epoxy resin is used to bond layers 21 and 22 formed of polyvinylidene fluoride to the core layer 23, respectively.

[0049] Also shown are layer electrodes 26a, 26b, 27a, and 27b, which are formed above and below each of the two layers 21 and 22 formed of polyvinylidene fluoride. These electrodes 26a, 26b, 27a, and 27b can be formed to a thickness of tens to hundreds of nanometers, and can be formed, for example, by sputtering deposition.

[0050] Furthermore, electrodes 26a, 26b, 27a, and 27b are formed of one of aluminum, nickel, or copper. However, the formation of electrodes from aluminum, nickel, or copper should be understood as merely an example; other materials may also be used for metallization on the electrodes, i.e., the polyvinylidene fluoride layer. Materials used for metallization may include chromium, gold, silver, platinum, rhodium, or alloys of any of the aforementioned metals, etc.

[0051] Figure 3 A cantilever beam 30 for a piezoelectric energy harvesting system according to a second embodiment of the present invention is shown.

[0052] like Figure 3 As shown, similar to the cantilever beam 20 according to the first embodiment, the cantilever beam 30 according to the second embodiment includes two layers 31 and 32 formed of polyvinylidene fluoride, wherein a core layer 33 formed of gasket material is sandwiched between the two layers 31 and 32 formed of polyvinylidene fluoride, wherein the two layers 31 and 32 are bonded to the core layer 33 by epoxy resin adhesive layers 34 and 35 respectively, wherein layer electrodes 36a, 36b, 37a, 37b are formed on the top and bottom of each of the two layers 31 and 32 formed of polyvinylidene fluoride.

[0053] Figure 3 The cantilever beam 30 according to the second embodiment shown is... Figure 2 The difference between the cantilever beams 20 shown according to the first embodiment is that the core layer 33 of the cantilever beam 30 according to the second embodiment is formed of polyethylene terephthalate (PET), thereby enabling a considerable power output.

[0054] The core layer 33, formed of polyethylene terephthalate, has a thickness between 400 μm and 560 μm to achieve maximum power output.

[0055] Explanation of reference numerals in the attached figures

[0056] 1. Piezoelectric energy harvesting system

[0057] 2 Cantilever Beam

[0058] 3 Equipment

[0059] 4 First end

[0060] 5 screws

[0061] 6 Installation components

[0062] 7 Second End

[0063] 8 First terminal block

[0064] 9 Top side

[0065] 10 Second terminal block

[0066] 11 Bottom side

[0067] 20 cantilever beams

[0068] 21st floor

[0069] 22nd floor

[0070] 23 Core Layer

[0071] 24 Adhesion Layer

[0072] 25 Adhesion layer

[0073] 26a electrode

[0074] 26b electrode

[0075] 27a electrode

[0076] 27b electrode

[0077] 30 Cantilever Beam

[0078] 31st floor

[0079] 32 floors

[0080] 33 Core Layer

[0081] 34 Adhesion Layer

[0082] 35 Adhesion layer

[0083] 36a electrode

[0084] 36b electrode

[0085] 37a electrode

[0086] 37b electrode

[0087] l length

[0088] w width

Claims

1. A cantilever beam for a piezoelectric energy harvesting system, wherein the cantilever beam (2, 20, 30) comprises two layers (21, 22, 31, 32) formed of polyvinylidene fluoride, and a core layer (23, 33) formed of gasket material sandwiched between the two layers (21, 22, 31, 32) formed of polyvinylidene fluoride. The two layers (21, 22, 31, 32) formed of polyvinylidene fluoride have a predominantly β-type crystal structure. in, The two layers formed of polyvinylidene fluoride each have a length between 60 mm and 80 mm and a width between 10 mm and 20 mm.

2. The cantilever beam according to claim 1, wherein the cantilever beam (20, 30) has the shape of a rectangular plate, wherein the longitudinal side of the rectangular plate is longer than the wide side of the rectangular plate, and wherein the cantilever beam (20, 30) is configured such that the cantilever beam (20, 30) can be connected to a device for storing or using energy via one of its longitudinal sides.

3. The cantilever beam according to claim 1 or 2, wherein the core layer (23) is formed of steel.

4. The cantilever beam according to claim 3, wherein the core layer (23) has a thickness between 50 μm and 150 μm.

5. The cantilever beam according to claim 1 or 2, wherein the core layer (33) is formed of polyethylene terephthalate.

6. The cantilever beam according to claim 5, wherein the core layer (33) has a thickness between 400 μm and 560 μm.

7. The cantilever beam according to any one of claims 1-6, wherein each of the two layers (21, 22, 31, 32) formed of polyvinylidene fluoride has a thickness between 20 μm and 50 μm.

8. The cantilever beam according to any one of claims 1-7, wherein the two layers (21, 22, 31, 32) formed of polyvinylidene fluoride are respectively bonded to the core layer (23, 33) by epoxy resin.

9. The cantilever beam according to any one of claims 1-8, wherein the electrodes (26a, 26b, 27a, 27b, 36a, 36b, 37a, 37b) are formed on the top and bottom of each of the two layers (21, 22, 31, 32) formed of polyvinylidene fluoride.

10. The cantilever beam according to claim 9, wherein the electrodes (26a, 26b, 27a, 27b, 36a, 36b, 37a, 37b) are formed of aluminum, nickel or copper.

11. A piezoelectric energy harvesting system, wherein the system (1) comprises a cantilever beam (2) according to any one of claims 1-10 and a device (3) for storing or using energy, and wherein a first end (4) of the cantilever beam (2) is electrically connected to the device (3) for storing or using energy.

12. The piezoelectric energy harvesting system according to claim 11, wherein at least one end block (8, 10) is attached to the second end (7) of the cantilever beam (2), wherein the second end (7) of the cantilever beam (2) is opposite to the first end (4).

13. The piezoelectric energy harvesting system of claim 12, wherein the weight of the at least one terminal block (8, 10) is customized.

14. The piezoelectric energy harvesting system according to claim 12 or 13, wherein the first terminal block (8) is attached to the top side (9) of the second end (7) of the cantilever beam (2), and wherein the second terminal block (10) is attached to the bottom side (11) of the second end (7) of the cantilever beam (2).

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