A meta-device that realizes the reuse of low-frequency vibration suppression and triboelectric energy harvesting

Abstract

The present invention is a meta-device that realizes the multiplexing of low-frequency vibration suppression and triboelectric energy collection functions, including a base, a plane displacement device, an annular spacer, a supporting cylinder, a protective cover and a mass block, the inner side of the protective cover is connected to the central truncated cone part of the plane displacement device through the supporting cylinder, the supporting cylinder connects the plane displacement device and the protective cover, below the plane displacement device is an annular spacer with the same outer diameter as the plane displacement device, below the annular spacer is a base with the same diameter as the outer diameter of the annular spacer, and a friction nanogenerator is arranged between the base and the plane displacement device, and the friction nanogenerator includes an electronegative film and a flexible pad. The device of the present invention can realize both low-frequency vibration suppression and conversion of low-frequency vibration environmental energy into electrical energy, powering low-power electronic devices, and is compact and small in size. The small size also takes into account the protection of the device, thereby improving the reliability of the device.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent devices and intelligent equipment, and specifically relates to a super-structure device that realizes the multiplexing of low-frequency vibration suppression and friction electric energy collection functions. Background Art

[0002] Vibration is everywhere in the environment, especially in transportation and industrial production. Vibration seriously affects industrial production and people's daily life. In particular, low-frequency vibration has the characteristics of strong penetration, long propagation, and difficulty in attenuation due to its physical property of longer wavelength. It has always been the focus and difficulty in vibration control engineering. Long-term mechanical vibration will accelerate the fatigue of equipment structural parts, shorten service life, and reduce reliability. It is necessary to develop effective vibration suppression methods to achieve effective vibration suppression.

[0003] In order to effectively suppress the low-frequency vibration of the equipment, a reasonable structure needs to be designed. The local resonance metamaterial is a vibration suppression device with bandgap characteristics designed by using a special structure, which can effectively suppress the low-frequency vibration of the equipment within the bandgap frequency range of the device. ZL202011200568.X provides a double-layer pyramid-type lightweight vibration-damping metamaterial lattice structure. By adding a resonance unit made of the same material inside the structure, the lightweight lattice structure of the metamaterial has good broadband vibration-damping characteristics in the low-frequency range. However, the structural bandgap frequency proposed in this patent is still too high, and a bandgap below 100Hz cannot be achieved. ZL201922394944.2 provides a local resonance elastic metamaterial plate-type structure with ultra-low frequency vibration-damping characteristics, which can produce a structural bandgap of 35Hz-45Hz. However, the above device is not easy to integrate with common engineering components, such as wall panel structures. In addition, the above device only considers the function of vibration suppression, and fails to achieve the recycling of mechanical energy and the protection of the device.

[0004] In order to realize the intelligence and ubiquitous monitoring of equipment, sensors need to be deployed on the structure. In order to avoid frequent replacement of sensors' batteries due to large-scale deployment and reduce operation and maintenance costs, a feasible idea is to use environmental energy harvesting technology to convert environmental energy into electrical energy to power the sensors.

[0005] Vibration energy is a common energy source in environmental energy harvesting. By collecting these low-frequency vibration energies and converting them into electrical energy, and powering some low-power devices, such as wireless sensor network nodes, it can avoid the large maintenance costs caused by frequent battery replacement in large-scale wireless networks. So far, the mechanism of vibration energy harvesting is mainly based on electromagnetic induction, triboelectric effect and piezoelectric effect.

[0006] Electromagnetic vibration energy harvesting devices are mainly suitable for high-frequency, large-amplitude vibrations, and due to the presence of magnets and coils, it is difficult to achieve miniaturization and lightweight of the device.

[0007] Piezoelectric devices use the piezoelectric effect to achieve electromechanical energy conversion. Piezoelectric materials are usually PZT ceramic sheets, which are hard and contain lead, which is polluting to the environment.

[0008] In 2012, Professor Wang Zhonglin's team at Georgia Institute of Technology in the United States first produced a new type of energy conversion device from mechanical energy to electrical energy based on the principles of friction electrification and electrostatic induction, the friction nanogenerator. Compared with traditional transducers, friction nanogenerators have the advantages of low production cost and good low-frequency performance. For example, ZL201710010956.3 provides a friction nanogenerator including an elastic structure for collecting environmental vibration energy, but the friction nanogenerator is a multi-layer folding structure with multiple friction layers, the structure is bloated, and fatigue damage is prone to occur at the corners of the U-shaped concave structure under resonant frequency vibration conditions. Zhu Guang et al. also proposed a new type of spring-supported separation structure friction nanogenerator, using the mechanical vibration source in the article to apply an external load to the device, driving the two friction layers of the proposed friction nanogenerator to contact and separate, and realizing the conversion of vibration energy to electrical energy. However, in this scheme, the entire device is exposed to the outside world, which greatly reduces the reliability of the device, and the parallel connection of the springs increases the stiffness coefficient (Zhu G, Lin ZH, Jing Q, Bai P, Pan C, Yang Y, Zhou Y, Wang ZL. Toward large-scale energy harvesting by a nanoparticle-enhanced triboelectric nanogenerator. Nano Lett. 2013 Feb 13; 13(2): 847-53. doi: 10.1021 / nl4001053. Epub 2013 Jan 31. PMID: 23360548). Summary of the invention

[0009] Based on the above technical defects, the present invention provides a meta-device that realizes the multiplexing of low-frequency vibration suppression and friction electric energy harvesting functions. The device can not only realize low-frequency vibration suppression but also convert low-frequency vibration environmental energy into electrical energy. The device is compact and small in size. The converted electrical energy can be used to provide electrical energy to sensors and low-power wireless communication devices, and realize the monitoring of environmental vibrations. At the same time, the protection of the device is also taken into consideration to improve the reliability of the device.

[0010] In order to achieve the above object, the present invention is achieved through the following technical solutions:

[0011] The present invention is a meta-structure device that realizes the multiplexing of low-frequency vibration suppression and triboelectric energy collection functions, including a base, the meta-structure device includes a plane displacement device, an annular spacer, a support cylinder, a protective cover and a mass block, the plane displacement device, the support cylinder, the protective cover and the mass block together form a structure with a local resonance mechanism, the inner side of the protective cover is connected to the central truncated cone part of the plane displacement device through the support cylinder, the support cylinder connects the plane displacement device and the protective cover, the protective cover is used to protect the internal structure to improve the reliability of the device, and the plane displacement device is below a plane displacement device with an outer diameter of about the same as the plane displacement device. The device has an annular partition with the same diameter as the annular partition, which is a cylindrical structure with a diameter of 20 mm, an inner diameter of 17 mm, and a height of 3 mm. The cylindrical structure forms a cylindrical cavity between the planar displacement device and the base. A flexible pad is placed in the cylindrical cavity. The flexible pad is cylindrical. The diameter of the flexible pad is consistent with the inner diameter of the annular partition. The height of the flexible pad is slightly lower than the height of the annular partition. Below the annular partition is a base with a diameter the same as the outer diameter of the annular partition. A friction nanogenerator is arranged between the base and the planar displacement device, and the friction nanogenerator includes an electronegative film and a flexible pad.

[0012] The further improvement of the present invention is that: the middle of the plane displacement device is a truncated cone, the outer periphery of the plane displacement device is a circular ring, the truncated cone and the circular ring are connected by a bending beam, the number of the bending beams is three, the thickness of the three bending beams is the same and they are in the same plane, a supporting cylinder is bonded to one side of the truncated cone close to the protective cover, and an electronegative film is bonded to the other side of the truncated cone, when the structure vibrates, the bending beam is deformed, and the central truncated cone will produce reciprocal displacement. In this way, the electronegative film bonded to one side of the truncated cone can be in contact with and separated from the flexible pad.

[0013] A further improvement of the present invention is that the supporting cylinder is used to connect the planar displacement device and the protective cover. The diameter of the supporting cylinder is slightly smaller than the diameter of the central cone of the planar displacement device, and the height is much smaller than its own diameter. It is flat, which can make the central cone of the planar displacement device vibrate more smoothly, thereby making the contact and separation of the friction nanogenerator more complete, thereby improving the output performance of the structure.

[0014] The further improvement of the present invention is that the electronegative film is an electret material, one side of the electret material realizes the electrode function of the electronegative film by bonding a double-sided conductive tape and the other side of the electronegative film is surface treated, and the surface charge density of the electronegative film is increased by a high-voltage electric field polarization treatment method, thereby improving the output performance of the structure, and the production cost is low and easy to implement.

[0015] A further improvement of the present invention is that the flexible pad is made of Ecoflex TMA series of silicone-doped multi-walled carbon nanotubes are made. Doping with multi-walled carbon nanotubes is beneficial to improving the dielectric constant and capacitance of the flexible pad. The effects of different doped multi-walled carbon nanotubes on the electrical output of the friction nanogenerator are analyzed experimentally to determine the optimal doping concentration of multi-walled carbon nanotubes.

[0016] A further improvement of the present invention is that the mass block is cylindrical and is bonded to the middle portion of the outer side of the protective cover.

[0017] The beneficial effects of the present invention are:

[0018] 1. The present invention utilizes a local resonance metamaterial structure to achieve low-frequency vibration suppression, and the resonant frequency of the present invention can be adjusted by changing the additional mass and adjusting the structural parameters of the planar displacement device to achieve suppression of vibrations of different frequencies.

[0019] 2. The present invention places the meta-structure devices periodically to form a periodic structure, which can generate a low-frequency structural band gap near the frequency designed by the present invention, indicating that there is a strong interaction between the substrate structure and the present invention. Experiments show that within the structural band gap range of the present invention, the vibration of the substrate structure can be greatly suppressed, and the band gap range can be adjusted by modifying the parameters of the planar displacement device and the mass size of the mass block.

[0020] 3. For the treatment of the two pole materials of the triboelectric nanogenerator, the negative friction layer is selected from the electronegative electret film, and it is subjected to high-voltage electrostatic field polarization treatment to increase its surface charge density. The positive friction layer is selected as a flexible pad, which is made of Ecoflex TM The flexible pad is made of a series of silicone doped multi-walled carbon nanotubes. The flexible pad is beneficial to improving the mechanical damping of the device and preventing the plane displacement device and the base from colliding and making noise. Doping with multi-walled carbon nanotubes is beneficial to improving the dielectric constant and capacitance of the flexible pad, thereby improving the energy output performance of the friction nanogenerator.

[0021] 4. The protective cover, supporting cylinder, plane displacement device, partition and base in the present invention are all insulated and can be made by 3D printing technology, which has simple process, low cost and is conducive to mass production;

[0022] 5. After actual testing, the low-frequency and broadband vibration suppression effect of this superstructure device is obvious. While reducing the vibration of the substrate, the energy collected by the friction nanogenerator continues to power multiple LED lights and calculators. It can quickly charge the capacitor, and when further connected to the power management circuit and the load, it can power low-power electronic devices such as Bluetooth devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the present invention.

[0024] Figure 2 It is a structural disassembly diagram of the present invention.

[0025] Figure 3 It is a schematic diagram of the plane displacement device in the present invention.

[0026] Figure 4 It is a schematic diagram of the friction nanogenerator in the present invention.

[0027] Figure 5 It is a schematic diagram of the power generation principle of the present invention.

[0028] Figure 6 It is a schematic diagram of a single super-structure device performance test system of the present invention.

[0029] Figure 7 This is the first order natural frequency measurement of the present invention.

[0030] Figure 8 The effect of the content of multi-walled carbon nanotubes in the flexible pad of the present invention on the output of the device.

[0031] Fig. 9 It is the open circuit voltage output by a single device under resonant frequency excitation of the present invention.

[0032] Fig.10 It is the short-circuit current output by a single device under resonant frequency excitation of the present invention.

[0033] Fig.11 Schematic diagram of a sample aluminum plate for vibration suppression comparison experiment of the present invention.

[0034] Fig.12 It is the displacement result of the response end in the vibration suppression experiment of the present invention.

[0035] Fig.13 This is the charging curve of a 1000 μF capacitor after four devices of the present invention are connected in parallel.

[0036] Among them: 1-mass block; 2-protective cover; 3-base; 4-planar displacement device; 5-support cylinder; 6-flexible pad; 7-interlayer; 8-electronegative film; 9-first electrode; 10-second electrode; 11-bending beam. DETAILED DESCRIPTION

[0037] The following will disclose the embodiments of the present invention with drawings. For the purpose of clear description, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present invention. That is, in some embodiments of the present invention, these practical details are not necessary. In addition, for the purpose of simplifying the drawings, some conventional structures and components will be depicted in a simple schematic manner in the drawings.

[0038] The present invention discloses a meta-device that realizes the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions, including a structure with a local resonance mechanism, wherein the structure with a local resonance mechanism is composed of a plane displacement device, a supporting cylinder, a protective cover and a mass block, wherein the protective cover 2 is an annular structure closed at one end, and is used to protect the internal structure of the device and improve the reliability of the device, wherein the mass block 1 is cylindrical, and the cylindrical mass block 1 is bonded to the middle part of the outer side of the protective cover 2, and the supporting cylinder 5 is flat, and the diameter of the supporting cylinder 5 is slightly smaller than the diameter of the central truncated cone of the plane displacement device 4, so that the central truncated cone of the plane displacement device 4 is more stable, and the inner side of the protective cover 2 is connected to the central truncated cone part of the plane displacement device 4 through the supporting cylinder 5, and the supporting cylinder 5 connects the plane displacement device 4 and the protective cover 2, and the plane Below the displacement device 4 is an annular spacer 7 with the same outer diameter as the plane displacement device 4, below the annular spacer 7 is the base 3 with the same diameter as the outer diameter of the annular spacer 7, a friction nanogenerator is arranged between the base 3 and the plane displacement device 4, the friction nanogenerator includes an electronegative film 8 and a flexible pad 6, the middle of the plane displacement device 4 is a truncated cone, the outer periphery of the plane displacement device 4 is a circular ring, the truncated cone and the circular ring are connected by a bending beam 11, the number of the bending beams 11 is three, and the three bending beams 11 have the same thickness and are in the same plane, the support cylinder 5 is bonded to the side of the truncated cone close to the protective cover, and the electronegative film 8 is bonded to the other side of the truncated cone, when the structure vibrates, the bending beam is deformed, and the central truncated cone will produce reciprocating displacement. In this way, the electronegative film bonded to one side of the truncated cone can be contacted and separated from the flexible pad. The annular spacer 7 is a columnar structure, and the columnar structure forms a cylindrical cavity between the planar displacement device 4 and the base 3, and the flexible pad 6 is placed in the cylindrical cavity.

[0039] The present invention is described below with reference to specific examples.

[0040] like Figure 1 and Figure 2As shown, the present invention is a meta-device including a mass block 1, a protective cover 2, a base 3, a plane displacement device 4, a support cylinder 5, a flexible pad 6 and a partition 7. The cylindrical mass block 1 is bonded to the middle part of the outer side of the protective cover 2. The mass block 1 is a magnet, and its weight can be easily adjusted by combining magnets of different sizes. The radius of the magnet is 10mm, and the height of the magnet is 4.6mm. The protective cover 2 is a ring-shaped structure with one end closed. It is a structure in which a small cylinder with the same central axis is dug out from a cylinder with a diameter of 23mm and a height of 5mm. The diameter of the small cylinder is 21mm and the height is 4mm. The inner side of the protective cover 2 is connected to the central truncated cone part of the plane displacement device 4 through a flat support cylinder 5. The support cylinder 5 has a radius of 10mm and a thickness of 3mm. The plane displacement device 4 has a radius of 20mm and a thickness of 0.8mm. Below the plane displacement device 4 is an annular partition 7 with a diameter of 20 mm, an inner diameter of 17 mm and a height of 3 mm, and below the partition 7 is a cylindrical base 3 with a diameter of 20 mm and a height of 2 mm. Since the partition 7 has a certain height, a cylindrical cavity is formed between the plane displacement device 4 and the base 3. This cylindrical cavity is used to place the flexible pad 6, which is cylindrical, with a diameter of 17 mm and a height of 2 mm. The device is manufactured according to the above specific dimensions and fixed on the vibrating structure, which is equivalent to a subsystem attached to the substrate. When the natural frequency of the subsystem is the same as the external excitation frequency, the subsystem undergoes local resonance, which is equivalent to the vibration mechanical energy of the substrate being "absorbed" by the subsystem, which can significantly reduce the vibration of the substrate.

[0041] In addition, the natural frequency of the device can be expressed as:

[0042]

[0043] Where ω represents the natural frequency of the device; k represents the equivalent stiffness of the device; and m represents the equivalent mass of the device.

[0044] Therefore, in the present invention, the equivalent stiffness of the device can be effectively changed by modifying parameters such as the thickness of the planar displacement device, and the equivalent mass of the system can be effectively changed by changing parameters such as the size of the mass block, thereby realizing the tuning of the dynamic characteristics of the device. The purpose of tuning is to adapt to the external excitation frequency to achieve the best vibration suppression effect.

[0045] A friction nanogenerator is arranged between the plane displacement device 4 and the base 3. The friction nanogenerator is as follows: Figure 4 , including an electronegative film 8 and a flexible pad 6 and electrodes connected thereto.

[0046] In this embodiment, FEP film is used as the electronegative film, and its surface charge density is increased by high-voltage electrostatic field polarization treatment. The flexible pad 6 is made of Ecoflex TMA series of liquid silicone doped with multi-walled carbon nanotubes is poured into a mold after magnetic stirring, left to stand to expel bubbles, and then heated until dry and demolded. The advantage of the flexible pad in this embodiment is that it can serve as a positive friction layer of the friction nanogenerator, prevent the plane displacement device from hitting the base and making noise, and increase the damping ratio of the device. In addition, Figure 4 In the embodiment, the double-sided conductive aluminum tape is used as the first electrode 9 and the second electrode 10 to transfer the induced charge generated by the electrification layer to the external circuit.

[0047] The basic working principle of contact-separation friction nanogenerator is as follows Figure 5 As shown, when the FEP layer 8 contacts the bottom flexible pad 6, due to the different electrification characteristics, the surface of the FEP layer 8 captures electrons and becomes negatively charged, while the flexible pad 6 becomes positively charged due to losing electrons, and induced charges will be generated on their respective electrodes, thereby forming a potential difference. When connected to an external circuit, the electrons will move, forming a conduction current.

[0048] like Figure 6 The figure shows the performance test system of this embodiment. A signal generator is used to generate a sinusoidal signal, which is used as an excitation signal to drive the vibrator through a power amplifier. The excitation force is measured by a force sensor, and the force is controlled at 5N. The device is placed on a vibration platform, and the vibration characteristics of the center point of the invention are measured by a high-speed laser displacement sensor. Lead wires are drawn out from the friction nanogenerator, and a digital multimeter NI-PXI-4071 is used to collect current signals; a digital multimeter NI-PXI-4070 is used to collect voltage signals.

[0049] like Figures 7 to 10 The test results are shown in Figure 1. First, the vibration characteristics of the present invention are explored. The center displacement of the present invention is measured by a high-speed laser displacement sensor. The spectrum analysis is performed in a wide frequency band. The results are shown in Figure 1. Figure 7 As shown, it is found that its first resonant frequency is 40Hz. So the excitation frequency is adjusted to 40Hz, and the excitation force is controlled at 5N. Under this condition, use Figure 6 The test system shown in the figure tests the output performance of the device. The effect of the content of multi-walled carbon nanotubes in the flexible pad on the output of the device is analyzed experimentally. The results are shown in Figure 8 As shown in Figure 2, the output is optimal when the content of multi-walled carbon nanotubes in the flexible mat is 10%. Fig. 9 , Fig.10 As shown, the device outputs a maximum peak-to-peak voltage of 502.3V and a peak-to-peak current of 17.3μA.

[0050] Four samples of this embodiment are placed periodically on an aluminum plate to form a periodic structure plate of a superstructure device, which can generate a structural band gap. The length × width × height of the aluminum plate is 300mm × 70mm × 2mm. According to calculations, the structural band gap range is 40-50Hz, that is, within this frequency range, elastic waves will not be able to propagate. Fig.11 As shown, two sample aluminum plates were prepared to compare the vibration suppression performance. The first sample aluminum plate was placed with four meta-devices of this embodiment, and the second sample aluminum plate was placed with four equal-mass units of the same mass but without a local resonance mechanism. The test structure was suspended by an elastic rope to form a free boundary condition. The exciter generated an exciting force on one side, and the response point was selected on the other side near the boundary of the structure. A laser displacement sensor was used to monitor the vibration displacement of the response point. The results are shown in Figure 2. Fig.12 As shown in the figure, the experimental results show that within the structural band gap range, the vibration amplitude of the aluminum plate is greatly reduced, up to 87%. Connecting four devices of the present invention in parallel on the aluminum plate can simultaneously and continuously light up 640 LED lights and power a calculator. In order to more intuitively show its output performance, the device charges a 1000μF capacitor, and the charging curve is shown in Fig.13 , when further connected to the power management circuit and the load, it can power low-power electronic devices such as Bluetooth devices.

[0051] The present invention will provide a compact and small-scale meta-device that can both suppress low-frequency vibrations and convert low-frequency vibration environmental energy into electrical energy. The device can generate a low-frequency structural band gap near the frequency we designed, and can also monitor environmental vibrations while also taking into account the protection of the device to improve the reliability of the device.

[0052] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A meta-device that realizes the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions, comprising a base (3), characterized in that: The metastructure device further comprises a planar displacement device (4), a supporting cylinder (5), a protective cover (2) and a mass block (1); the planar displacement device (4), the supporting cylinder (5), the protective cover (2) and the mass block (1) together constitute a structure having a local resonance mechanism; the inner side of the protective cover (2) is connected to the central truncated cone portion of the planar displacement device (4) via the supporting cylinder (5); the supporting cylinder (5) connects the planar displacement device (4) and the protective cover (2); below the planar displacement device (4) is an annular spacer (7) having an outer diameter identical to that of the planar displacement device (4); below the annular spacer (7) is the base (3) having a diameter identical to that of the outer diameter of the annular spacer (7); the planar displacement device The center of the plane displacement device (4) is a truncated cone, the outer circumference of the plane displacement device (4) is a circular ring, the truncated cone and the circular ring are connected by a curved beam (11), the support cylinder (5) is bonded to the side of the truncated cone close to the protective cover, and the other side of the truncated cone is provided with a bonding electronegative film (8), the protective cover (2) is a ring-shaped structure with one end closed, and is used to protect the internal structure of the device and improve the reliability of the device, the support cylinder (5) is flat, and the diameter of the support cylinder (5) is slightly smaller than the diameter of the central truncated cone of the plane displacement device (4), so that the central truncated cone of the plane displacement device (4) is more stable, and the mass block (1) is cylindrical, and the cylindrical mass block (1) is bonded to the middle part of the outer side of the protective cover (2).

2. The meta-device for realizing the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions according to claim 1, characterized in that: A friction nanogenerator is arranged between the base (3) and the planar displacement device (4), and the friction nanogenerator comprises an electronegative film (8) and a flexible pad (6).

3. The meta-device for realizing the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions according to claim 1, characterized in that: The electronegative film (8) is an electret material, and one side of the electret material realizes the electrode function of the electronegative film by bonding a double-sided conductive tape, and the other side of the electronegative film is surface treated.

4. The meta-device for realizing the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions according to claim 2, characterized in that: The annular spacer (7) is a columnar structure with a diameter of 20 mm, an inner diameter of 17 mm, and a height of 3 mm. The columnar structure forms a columnar cavity between the planar displacement device (4) and the base (3), and the flexible pad (6) is placed in the columnar cavity.

5. The meta-device for realizing the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions according to claim 4, characterized in that: The flexible pad (6) is cylindrical, the diameter of the flexible pad (6) is consistent with the inner diameter of the annular spacer (7), and the height of the flexible pad (6) is slightly lower than the height of the annular spacer (7).

6. The meta-device for realizing the multiplexing of low-frequency vibration suppression and triboelectric energy harvesting functions according to claim 1, characterized in that: The number of the curved beams (11) is three, and the three curved beams (11) have the same thickness and are located in the same plane.

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