A method for manufacturing an electromagnetic self-powered strain sensor

Abstract

The application discloses a kind of electromagnetic self-powered strain sensor manufacturing methods, it is related to sensor technical field, the method is based on electromagnetic induction principle Design energy collection device includes sleeve with coil winding on outer wall and fixed magnet and levitation magnet arranged in sleeve, determine the structural parameter of reaching power supply demand in combination with energy conversion analysis of energy collection device, then according to the design structure and structural parameter, energy collection device is obtained, and energy collection device is excited by external vibration in the movement process of the monitored moving object to generate alternating current energy and supply power to sensing monitoring device through rectification energy storage circuit, so that sensing monitoring device can continuously and stably sense the strain at the position to be detected of the monitored moving object without other power supply.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and in particular to a method for manufacturing an electromagnetic self-powered strain sensor. Background Technology

[0002] Human motion recognition technology is a very important research topic. After monitoring and collecting human posture data, human motion data can be identified. This human motion data can provide a data foundation for subsequent analysis and control, and has wide applications in fields such as medical rehabilitation, human-computer interaction and sports science.

[0003] Traditional human posture data monitoring relies primarily on specialized wearable devices, which are complex in structure and can restrict and affect human movement, resulting in limited application scenarios and impacting data acquisition accuracy. With the development of sensor technology, various flexible strain sensors have been developed. These strain sensors have higher integration levels, and their flexibility allows them to adhere well to the human body for posture data acquisition, resulting in higher sensitivity and better application performance compared to wearable devices. However, because strain sensors require electrical power, external power supplies can still restrict human movement due to cable limitations, while using an independent power supply limits the sensor's operating time. Summary of the Invention

[0004] This application addresses the aforementioned problems and technical needs by proposing a method for manufacturing an electromagnetic self-powered strain sensor. The technical solution of this application is as follows:

[0005] A method for manufacturing an electromagnetic self-powered strain sensor, the method comprising:

[0006] The design structure of the energy harvesting device is determined. The energy harvesting device includes a sleeve with a coil wound on the outer wall and a fixed magnet and a levitation magnet arranged inside the sleeve. The ends of the levitation magnet and the fixed magnet with the same polarity are arranged opposite each other. The fixed magnet is fixed inside the sleeve, and the levitation magnet is movably arranged in the sleeve and can move along the axial direction of the sleeve under the action of external vibration excitation. The magnetic flux of the coil changes with the movement of the levitation magnet.

[0007] Under the constraint that the output voltage of the energy harvesting device reaches the minimum voltage required for the diode to conduct in the rectifier energy storage circuit, the structural parameters of the energy harvesting device are determined. The structural parameters of the energy harvesting device include the structural parameters of the sleeve, the structural parameters of the coil, the structural parameters of the fixed magnet, and the structural parameters of the levitation magnet.

[0008] An energy harvesting device is fabricated according to its design structure and structural parameters, and a sensing and monitoring device is fabricated according to its design structure and structural parameters. The coil of the energy harvesting device is connected to the power supply terminal of the sensing and monitoring device through a rectifier energy storage circuit to fabricate an electromagnetic self-powered strain sensor. The sensing and monitoring device is used to sense the strain at the detection position of the moving object to be monitored, and the energy harvesting device is used to be arranged on the moving object to be monitored and generate AC power when it is excited by external vibration during the movement of the moving object.

[0009] Its further technical solution includes fabricating an energy harvesting device and a sensing and monitoring device, comprising:

[0010] The sleeve is fabricated using fused deposition modeling (FDM) technology according to its structural parameters. The coil is fabricated on the outer wall of the sleeve using direct writing filament technology according to its structural parameters. A fixed magnet with corresponding structural parameters is fixed inside the sleeve, and a suspended magnet with corresponding structural parameters is placed inside the sleeve to create an energy harvesting device.

[0011] A resistive strain sensing unit is fabricated by printing a conductive carbon paste onto an insulating substrate using direct writing printing technology. Electrodes are then printed onto the sensing layer using conductive silver paste and connected to conductive wires. A resistance strain sensing unit is fabricated by connecting a resistance meter to the conductive wires of the resistive strain sensing unit. The resistive strain sensing unit is then placed at the detection position of the moving object to be monitored.

[0012] A further technical solution involves the coil's structural parameters, including the specifications of the metal wire wound to form the coil and the number of turns. The coil is fabricated by printing on the outer wall of the sleeve, comprising:

[0013] After attaching a double-sided adhesive polyimide film to the outer wall of the sleeve, the sleeve with the attached polyimide film is fixed on the rotating shaft of the printer. A syringe is fixed on the horizontal axis of the printer. The rotating shaft of the printer is controlled to drive the sleeve to rotate, and the syringe is controlled to move along the horizontal axis. During the rotation of the sleeve and the movement of the syringe, a metal wire with corresponding specifications is guided out from the syringe. Under the action of the polyimide film, the metal wire adheres to the outer wall of the sleeve to form a spiral coil with a corresponding number of turns.

[0014] A further technical solution is that the structural parameters of the sleeve include the radial parameters and the length of the sleeve; the structural parameters of the two magnets are identical; and the structural parameters of each magnet include the magnet's dimensions, weight, and magnetic induction intensity. The structural parameters of the energy harvesting device are determined as follows:

[0015] Determine the diameter of the sleeve, the structural parameters of the coil, the dimensional parameters of the magnet, and the weight of the magnet;

[0016] The design structure of the energy harvesting device is based on the diameter of the sleeve, the structural parameters of the coil, and the dimensional parameters of the two magnets, and a finite element model is established.

[0017] Under different magnetic induction intensities of the magnet, the finite element model was used to perform finite element analysis on the motion process of the suspended magnet from the fixed magnet to the direction away from the fixed magnet, and the voltage-distance curve of the energy harvesting device under the current magnetic induction intensity was obtained. The voltage-distance curve indicates the change curve of the output voltage of the energy harvesting device with the distance between the two magnets.

[0018] Based on the voltage-distance curves of the energy harvesting device under different magnetic induction intensities, the magnetic induction intensity required to make the output voltage of the energy harvesting device reach the minimum voltage required for the diode in the rectifier energy storage circuit to conduct is determined.

[0019] The length of the sleeve is determined based on the established magnetic induction intensity.

[0020] A further technical solution involves using a finite element model to perform finite element analysis on the motion of the levitated magnet from the fixed magnet in a direction away from the fixed magnet, including:

[0021] Based on the system equilibrium equation of the levitated magnet during its motion and combined with Faraday's law of electromagnetic induction, finite element analysis is performed to determine the change in magnetic flux and the corresponding output voltage generated during the motion of the levitated magnet from the fixed magnet toward the direction away from the fixed magnet, and the voltage-distance curve is obtained.

[0022] The system equilibrium equation for the levitation magnet during its motion is:

[0023]

[0024] Where, m f F is the mass of the levitation magnet, g is the acceleration due to gravity; x1(t) represents the displacement of the energy harvesting device along the axial direction of the sleeve caused by external vibration excitation at time t, and x2(t) represents the displacement of the levitation magnet along the axial direction of the sleeve relative to its initial static equilibrium position at time t; M (x2(t)) is the repulsive force between the levitated magnet and the stationary magnet at time t, and F M (x2(t)) is related to x2(t); c e (x2(t)) is the electromagnetic damping at time t and is related to x2(t); f is the sum of air viscosity force and inner wall contact friction, and the sign factor sgn(x2(t)) is used to adjust the direction of f to be opposite to the direction of x2(t).

[0025] A further technical solution is that the method for manufacturing an electromagnetic self-powered strain sensor also includes:

[0026] A fixed magnet is held in place by a bottom clamp, while a suspended magnet is held in place by a top clamp via a pressure sensor. The top clamp is controlled to move the suspended magnet relative to the fixed magnet. The repulsive force between the suspended and fixed magnets is read from the pressure sensor at different distances between them. The repulsive force F between the suspended and fixed magnets at any time t is then obtained by fitting the data. M (x2(t)) is:

[0027]

[0028] Where a, b, and c are all correction coefficients obtained from the fitting, H1 is the magnetic flux density of the levitated magnet, H2 is the magnetic flux density of the stationary magnet, and R... M (t) is the distance between the suspended magnet and the fixed magnet at time t, and μ0 is the vacuum permeability.

[0029] A further technical solution involves determining the magnetic flux density required to make the output voltage of the energy harvesting device reach the minimum voltage required for the diodes in the rectifier energy storage circuit to conduct, including:

[0030] The relationship between the device displacement x1(t) and the magnet displacement x2(t) is determined based on the system equilibrium equation, and the magnet displacement range is determined by combining the unique range of the device generated by the external vibration excitation of the moving object to be monitored.

[0031] For any given magnetic induction intensity, when the output voltage of the energy harvesting device within the magnet displacement range of the voltage-distance curve under the magnetic induction intensity reaches the minimum voltage required for the diode to conduct in the rectifier energy storage circuit, the magnetic induction intensity is determined such that the output voltage of the energy harvesting device reaches the minimum voltage required for the diode to conduct in the rectifier energy storage circuit.

[0032] A further technical solution involves determining the length of the sleeve based on the determined magnetic induction intensity, including:

[0033] Based on the characteristic that the repulsive force between the levitated magnet and the fixed magnet in a static state is equal to the weight of the levitated magnet, the distance d between the levitated magnet and the fixed magnet is calculated when the energy harvesting device is in a static state, and the length of the sleeve is determined to be 2d.

[0034] A further technical solution is that the coil is wound and fixed to the outer wall of the sleeve using a segmented structure.

[0035] A further technical solution involves coating the surface of the levitation magnet with a lubricant.

[0036] The beneficial technical effects of this application are:

[0037] This application discloses a method for fabricating an electromagnetic self-powered strain sensor. The method involves designing a cylindrical energy harvesting device based on the principle of electromagnetic induction, determining the structural parameters required to meet power supply needs through energy conversion analysis of the energy harvesting device, and then fabricating the energy harvesting device according to the design and parameters. This energy harvesting device is then connected to the fabricated sensing and monitoring device via a rectifier energy storage circuit to produce the electromagnetic self-powered strain sensor. All components of the fabricated electromagnetic self-powered strain sensor are arranged on the moving object to be monitored. During the movement of the moving object, the energy harvesting device generates AC power through external vibration excitation and supplies power to the sensing and monitoring device via the rectifier energy storage circuit. This allows the sensing and monitoring device to continuously and stably sense the strain at the detection location of the moving object without requiring an external power source. The fabricated electromagnetic self-powered strain sensor exhibits particularly good performance in human motion recognition technology. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the circuit structure of an electromagnetic self-powered strain sensor according to an embodiment of this application.

[0039] Figure 2 This is a schematic diagram of a partially exploded structure of a resistive strain sensing unit according to one embodiment.

[0040] Figure 3 This is a schematic diagram of the structure of an energy harvesting device according to one embodiment.

[0041] Figure 4 yes Figure 3 A schematic diagram of the kinematic force analysis of an energy harvesting device.

[0042] Figure 5 This is a schematic diagram illustrating an application scenario of an electromagnetic self-powered strain sensor used for human motion recognition, according to one embodiment of this application. Detailed Implementation

[0043] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0044] This application discloses a method for fabricating an electromagnetic self-powered strain sensor. The electromagnetic self-powered strain sensor mainly comprises three parts: an energy harvesting device, a rectifier energy storage circuit, and a sensing and monitoring device. In application, the energy harvesting device is placed on the moving object to be monitored and generates alternating current during the object's movement due to external vibration excitation. The rectifier energy storage circuit is also placed on the moving object to rectify and convert the alternating current output from the energy harvesting device into direct current, which is then stored to power the sensing and monitoring device. Please refer to [reference needed]. Figure 1The circuit structure shown includes a bridge rectifier composed of four diodes, a capacitor C, a Zener diode D, and a resistor R1. In practice, an inductively coupled amplification structure is also connected between the energy harvesting device and the rectifier energy storage circuit. The sensing and monitoring device is used to detect strain data at the detection location of the moving object to be monitored. Theoretically, the moving object to be monitored can be any moving object requiring strain monitoring; in human motion recognition technology, it refers to the human body.

[0045] Rectifier-storage circuits are commonly used circuit structures. Therefore, the focus of this method for fabricating an electromagnetic self-powered strain sensor is on the fabrication of the energy harvesting device and the sensing and monitoring device, which are described below:

[0046] 1. Fabrication of sensor monitoring device

[0047] First, the design structure and structural parameters of the sensing and monitoring device must be determined. The sensing and monitoring device in this embodiment comprises two parts, such as... Figure 1 The resistance meter 1 and the resistive strain sensing unit 2 are used in the sample. The resistance meter 1 is a small portable resistance meter that is readily available and is very small in size.

[0048] The resistive strain sensor unit 2 is placed at the detection position of the moving object to be monitored. As the object moves at the detection position, the resistance of the resistive strain sensor unit 2 changes under the strain at the detection position. The ohmmeter 1 can collect the resistance change of the resistive strain sensor unit 2, thereby realizing strain data monitoring. The specific dimensions of the resistive strain sensor unit 2 can be designed according to the actual needs such as the shape and area of ​​the detection position.

[0049] Then, the sensing and monitoring device is fabricated according to its design structure and structural parameters. This application uses direct writing printing technology to fabricate the resistive strain sensing unit 2, giving it accurate monitoring capabilities for high strain and good wearability. Please refer to... Figure 2 The schematic diagram shown is of a partially exploded structure of the resistive strain sensing unit 2. The method for fabricating the resistive strain sensing unit 2 includes:

[0050] First, an insulating substrate 21 is selected. Then, a direct-write printing technique is used to print a sensing layer onto the insulating substrate using conductive carbon paste. Carbon paste lines are then printed on the substrate surface to form the sensing layer 22. Conductive carbon paste has strong plasticity and good stretchability, making it very suitable as a sensing element. It should be noted that, although... Figure 2The schematic diagram shows that the sensing layer 22 has a linear structure, but in practical applications, it is generally printed in the most widely used serpentine structure. Finally, using direct writing printing technology, conductive silver paste is used to print electrodes 23 on the sensing layer 22 and connect them to conductive lines 24. After encapsulation, a resistive strain sensing unit 2 is fabricated. Then, the conductive lines of the fabricated resistive strain sensing unit 2 are connected to the ohmmeter 1 to fabricate a sensing and monitoring device. The conductive lines of the resistive strain sensing unit 2 are also used to connect to the rectifier energy storage circuit.

[0051] Specifically, when printing sensor layer 22, conductive carbon paste is first prepared: the carbon paste material (CH-8 / MOD2, JELCON) is stirred at 2000 rpm for 2 minutes using a planetary mixer, then loaded into the printing syringe, and centrifuged at 3000 rpm for 3 minutes to remove air bubbles, thus preparing the required conductive carbon paste. After preparing the conductive carbon paste, it is loaded into the opaque printing syringe of the direct writing printing device. After adjustments, for conductive carbon paste with a viscosity of 30000 cP, the printing syringe needle inner diameter is 1 mm, the line spacing is 1.5 mm, the printing speed is 5 mm / s, the printing time is approximately 20 seconds, and the extrusion pressure is 0.25 MPa, which yields good print quality. After printing the conductive carbon paste, it is dried in an oven at 120℃ for 120 minutes to complete the curing and form a carbon paste capacitor.

[0052] When printing electrode 23, conductive silver paste (EN-06B8, ENSON) is loaded into the opaque printing syringe of the direct writing printing device. After connecting the printing syringe to the air pressure control valve, it is clamped on the CNC three-axis motion platform and printed using the 3D printing direct writing method.

[0053] 2. Construct an energy harvesting device

[0054] The purpose of an energy harvesting device is to capture the mechanical vibration energy of a moving object during its motion and convert it into usable alternating current. Considering structural simplicity, manufacturability, and miniaturization, this application presents a cylindrical energy harvesting device based on the principle of electromagnetic induction. This device, designed based on electromagnetic principles, utilizes a changing magnetic field to generate current in a conductor, thereby achieving energy harvesting and conversion. The most fundamental principle of this energy harvesting device is Faraday's law of electromagnetic induction, which states that in a changing magnetic field, an induced electromotive force is generated in a closed conductor loop, thus producing a current. According to this principle, the energy harvesting device generates electrical energy by changing the strength or direction of the magnetic field.

[0055] A cross-sectional schematic diagram of the energy harvesting device defined in this application is shown below. Figure 3As shown, the energy harvesting device design includes a sleeve 3 and a fixed magnet 4 and a levitation magnet 5 arranged within the sleeve 3. The fixed magnet 4 is fixed inside the sleeve 3, and the levitation magnet 5 is movably arranged inside the sleeve 3. The ends of the levitation magnet 5 and the fixed magnet 4 with the same polarity are arranged opposite each other. To simplify the design, the fixed magnet 4 and the levitation magnet 5 have the same specifications. In another embodiment, to minimize the friction between the levitation magnet 5 and the inner wall of the sleeve, the surface of the levitation magnet 5 is coated with a lubricant. A coil 6 is wound around the outer wall of the sleeve 3.

[0056] Under external vibration excitation, the levitation magnet 5 moves axially along the sleeve 3, and the magnetic flux of the coil 6 changes with the movement of the levitation magnet 5, thereby generating current. This cylindrical structure design not only improves the space utilization efficiency of the energy harvesting device, but also more effectively captures magnetic field changes in various directions, which is very important for improving energy conversion efficiency.

[0057] In another embodiment, the coil 6 is wound and fixed to the outer wall of the sleeve 3 in a segmented structure. This segmented coil 6 is used for energy conversion to minimize eddy current losses and improve the magnetic field distribution inside the energy harvesting device. In practical use, to reduce the number of connection points and miniaturize the structure, the coil 6 is fixed to the outer wall of the sleeve 3 in two segments, such as... Figure 3 As shown, the AC voltage output from coil 6 is more stable and the voltage ripple is reduced.

[0058] In determining the energy harvesting device to be used Figure 3 Following the design structure shown, further determination of the energy harvesting device's structural parameters is needed. The power generation effect varies depending on the structural parameters used. To ensure the energy harvesting device can continuously and stably achieve self-powering, its structural parameters must be determined under the constraint that the output voltage of the energy harvesting device reaches the minimum voltage required for the diode in the rectifier energy storage circuit to conduct. This ensures that the output voltage of the energy harvesting device is sufficient to turn on the rectifier energy storage circuit. A typical minimum voltage required for the diode to conduct in a rectifier energy storage circuit is 1.4V.

[0059] The structural parameters of the energy harvesting device include those of the sleeve, coil, stationary magnet, and levitation magnet. The sleeve's structural parameters include its radial diameter and length. The coil's structural parameters include the specifications of the metal wire wound to form the coil and the number of turns. The two magnets have identical structural parameters; each magnet's structural parameters include its dimensions, weight, and magnetic flux density.

[0060] The applicant's research revealed that the magnetic flux density of the magnet has a primary impact on the output voltage of the energy harvesting device, while other structural parameters have a relatively minor effect. Therefore, when determining the structural parameters of the energy harvesting device, the focus should be on determining the magnetic flux density of the magnet, while other parameters can be set according to actual needs to reduce design complexity. The method for determining the structural parameters includes the following steps:

[0061] 1. Determine the diameter of the sleeve, the structural parameters of the coil, the size parameters of the magnet, and the weight of the magnet. These structural parameters can be customized according to actual needs.

[0062] The dimensions and weight of the magnet can be customized. After determining the dimensions of the magnet, the diameter of the sleeve should be set to be as consistent as possible with the diameter of the magnet to increase the magnetic flux of the outer coil of the sleeve in the horizontal cross-section. Considering processing errors and assembly issues, the inner diameter of the sleeve can be slightly larger than that of the magnet.

[0063] The diameter of the metal wire used in the coil should be as large as possible to reduce the internal resistance of the coil. The more turns the coil has, the higher the output voltage will be, but at the same time the internal resistance of the coil will also increase. Therefore, a suitable number of turns can be selected according to actual needs, rather than using the number of turns as the main adjustment parameter of the output voltage.

[0064] 2. Based on the design structure of the energy harvesting device, a finite element model is established according to the diameter of the sleeve, the structural parameters of the coil, and the size parameters of the two magnets. This step can be achieved using existing modeling software. When modeling, the length of the sleeve can be taken as large as possible.

[0065] 3. Under different magnetic induction intensities of the magnets, the motion of the suspended magnet from the fixed magnet in the direction away from the fixed magnet was analyzed using a finite element model, and the voltage-distance curve of the energy harvesting device under the current magnetic induction intensity was obtained. The obtained voltage-distance curve indicates the change of the output voltage of the energy harvesting device with the distance between the two magnets.

[0066] When performing finite element analysis, the system equilibrium equations of the levitated magnet during its motion are combined with Faraday's law of electromagnetic induction to determine the change in magnetic flux and the corresponding output voltage generated during the motion of the levitated magnet from the fixed magnet toward the direction away from the fixed magnet, thereby obtaining the voltage-distance curve.

[0067] This energy harvesting device can be described as a damped vibration model, where the levitation magnet 5 moves axially under external vibration excitation. Please refer to... Figure 4The force analysis diagram is as follows: When the energy harvesting device is subjected to external vibration excitation, it will generate a device displacement x1 along the axial direction of the sleeve. Let x1(t) be the device displacement at time t. The device displacement will cause the levitation magnet 5 to also generate a displacement in the same direction along the axial direction of the sleeve. However, the motion of the levitation magnet 5 is subject to the combined action of multiple forces, therefore, the displacement of the levitation magnet 5 along the axial direction of the sleeve is not equal to the device displacement x1. Let x2 be the magnet displacement along the axial direction of the sleeve relative to the initial static equilibrium position of the levitation magnet, and let x2(t) be the magnet displacement at time t. In this application, x1(t) and x2(t) are defined as positive along the direction away from the fixed magnet 4 and negative along the direction towards the fixed magnet 4. The entire system is in equilibrium. Based on the forces acting on the levitation magnet under external vibration excitation and Newton's second law, the system equilibrium equation of the energy harvesting device can be constructed as follows:

[0068]

[0069] Where, m f is the mass of the suspending magnet, g is the acceleration due to gravity. f is the sum of the air viscosity force and the contact friction of the inner wall, and the sign factor sgn(x2(t) is used to adjust the direction of f to be opposite to the direction of x2(t).

[0070] F M (D(t)) is the repulsive force between the levitating magnet 5 and the fixed magnet 4 at time t, F M (D(t)) is related to the distance D(t) between the levitation magnet 5 and the fixed magnet 4 at time t. The distance D(t) between the levitation magnet 5 and the fixed magnet 4 at time t is d + x2(t), where d refers to the axial distance between the levitation magnet 5 and the fixed magnet 4 when the levitation magnet 5 is in its initial static equilibrium position without being subjected to external vibration excitation. This is a known quantity after the structural design of the energy harvesting device is completed.

[0071] The study of the force between two magnets still lacks a specific and accurate computational model to quantitatively describe it. The Coulomb model is used as an approximate magnetic force analysis model in mainstream theory, but it cannot accurately calculate the magnetic force over small distances. The energy harvesting device in this application is relatively small, with an actual height of only about 160 mm. Therefore, the distance between the two magnets is small, and the Coulomb model cannot be directly used to calculate the repulsive force between them. To accurately characterize the relationship between the repulsive force between the levitated magnet 5 and the fixed magnet 4 and the distance between the two magnets, the fabrication method of this electromagnetic self-powered strain sensor also includes:

[0072] An experimental scenario was constructed using a first magnet and a second magnet with known magnetic induction intensity: the first magnet was held by a bottom clamp, and the second magnet was held and fixed by a top clamp via a pressure sensor. Initially, the second magnet and the first magnet were positioned opposite each other at a known distance. Then, the top clamp was controlled to move the second magnet toward the first magnet, and the repulsive force between the two magnets at different distances between them was read from the pressure sensor. The repulsive force F between the two magnets at any time t was obtained by fitting the following function. M (R M (t) and the distance R between the two magnets M The relationship between (t):

[0073]

[0074] Where a, b, and c are all correction coefficients obtained from the fitting, H1 is the magnetic flux density of the first magnet, H2 is the magnetic flux density of the second magnet, and R... M (t) is the distance between the first magnet and the second magnet at time t, and μ0 is the vacuum permeability.

[0075] c e (x2(t)) is the electromagnetic damping at time t and is related to x2(t). When the levitation magnet 5 is excited by external vibration and moves, it will cause a change in the magnetic flux in coil 6. Kinetic energy is converted into electrical energy through the magnetic field. At this time, the output voltage U obtained by Faraday's law of electromagnetic induction is:

[0076]

[0077] in It is the magnetic flux within the coil, which varies with the displacement of the magnet. e This is the electromagnetic coupling coefficient, through which the electromagnetic damping c can be obtained. e The expression for (x2(t)). For the axial magnetic induction B inside a single coil. x The flux inside a single coil is obtained by dividing it by the area, and the flux inside N coils is added together to obtain the total flux.

[0078]

[0079] When a load is connected to the circuit, a current is generated in the circuit, and the coil in the circuit can be equivalent to an inductor L. Therefore, the electromechanical coupling equation of the entire circuit is:

[0080] L·dI / dt+(r+R)·I=ke·dx2 / dt

[0081] Where I is the time-varying current in the circuit, r is the coil resistance, and R is the resistance of the load connected to the energy harvesting device. In this model, considering that the frequency of the external vibration excitation of the moving object to be monitored is often low in the application scenario of this application, the inductance L can be ignored in low-frequency excitation scenarios. After introducing the load into the system, we need to find the electromagnetic damping c in the equation. e The expression for (x2(t)). Since electrical energy is obtained by converting mechanical energy through electromagnetic damping, according to the law of conservation of energy, the formula is as follows:

[0082] F e ·dx1 / dt=c e (x2)·(dx2 / dt) 2 =U 2 / (R+r)

[0083] Where F e It is the force generated by electromagnetic damping, which can be derived from the equation above:

[0084]

[0085] In the actual finite element analysis, the magnetic flux equation and electromagnetic field simulation in COMSOL software are used. First, a finite element model is established in COMSOL. Given the two-dimensional symmetrical configuration of the energy harvesting device, the space on which the model is based is defined within a rectangular region bounded by a magnetically insulating boundary condition, which simulates the effect of metallic shielding. In this finite element model, both the magnet and the multi-turn coil are represented by a matrix geometry to simplify the mesh construction and thus reduce the complexity of the solution. Since the purpose of the finite element simulation in this application is to determine the output voltage induced in the coil, which is obtained by integrating the field over a region, the simulation calculation of the output voltage exhibits extremely high robustness to singularities in the field. Therefore, although the sharp corners of the rectangle introduce local singularities in the magnetic field, their impact on the simulation process of this application is negligible. To define the displacement of the magnet and the surrounding air domain, the dynamic mesh function is used in COMSOL. Since the coil and the surrounding air domain do not deform, a dynamic mesh can be used to describe the displacement of the magnet and the air domain above and below it. When performing domain motion analysis, if the motion phenomenon is significant, the sliding mesh technique is required.

[0086] In the finite element analysis, the magnetic induction intensities of two magnets are configured, and the levitated magnet is controlled to move sinusoidally at a set frequency from its initial position (i.e., in contact with the fixed magnet). The analysis and solution of the finite element model are performed in two steps. First, a steady-state analysis of the magnetic field is performed to calculate the magnetic field generated by the levitated magnet at its initial position (i.e., in contact with the fixed magnet). This analysis step provides accurate initial conditions. Then, a transient analysis of the magnetic field and dynamic mesh is performed to obtain the voltage-distance curve under the current magnetic induction intensity. The magnetic induction intensities of the magnets are changed, and the above process is repeated for finite element analysis to obtain voltage-distance curves under different magnetic induction intensities.

[0087] 4. Based on the voltage-distance curves of the energy harvesting device under different magnetic induction intensities, determine the minimum magnetic induction intensity required for the output voltage of the energy harvesting device to reach the minimum voltage required for the diodes in the rectifier energy storage circuit to conduct. This includes:

[0088] Based on the aforementioned system equilibrium equations, the relationship between the device displacement x1(t) and the magnet displacement x2(t) can be determined. Since the external vibration excitation of the moving object under monitoring has an amplitude range, and this amplitude range can be determined through prior statistical analysis, the range of device displacement generated by the external vibration excitation of the moving object under monitoring is known. Based on the range of device displacement x1(t) indicated by the device displacement range, and combined with the relationship between device displacement x1(t) and magnet displacement x2(t), the range of magnet displacement x2(t) can be determined, thereby determining the range of displacement of the suspending magnet under external vibration excitation.

[0089] Then, for any magnetic induction intensity, when the output voltage of the energy harvesting device under that magnetic induction intensity reaches the minimum voltage required for the diode to conduct in the rectifier energy storage circuit within the determined magnet displacement range, it means that the output voltage meets the requirements during the movement of the levitated magnet. Therefore, it can be determined that the current magnetic induction intensity can make the output voltage of the energy harvesting device reach the minimum voltage required for the diode to conduct in the rectifier energy storage circuit. The current magnetic induction intensity can be selected as the magnetic induction intensity of the two magnets in the energy harvesting device.

[0090] 5. Determine the length of the sleeve based on the determined magnetic induction intensity.

[0091] When stationary, the levitation magnet 5 is subjected to a downward gravitational force m. f The levitation magnet 5 remains stationary at its initial static equilibrium position due to the upward repulsive force between itself and the fixed magnet 4, and the mass m of the levitation magnet 5. fIt is known that the repulsive force on the levitation magnet 5 can be calculated according to the repulsive force calculation formula determined above. The magnetic induction intensity of the magnet in the above repulsive force calculation formula has been determined through the above steps. Based on the characteristic that the repulsive force between the levitation magnet 5 and the fixed magnet 4 in the static state is equal to the weight of the levitation magnet, the distance d between the levitation magnet and the fixed magnet can be calculated when the energy harvesting device is in the static state. Thus, the length of the sleeve is determined to be 2d, which ensures that the coil can effectively sense the change in magnetic flux during the up-and-down vibration of the magnet, thereby generating an induced current.

[0092] After determining the design structure and structural parameters of the energy harvesting device, the energy harvesting device can be manufactured according to the design structure and structural parameters, including:

[0093] First, sleeve 3 is fabricated using fused deposition modeling (FDM) technology with thermoplastic material according to the sleeve's structural parameters. Then, coil 6 is fabricated on the outer wall of the sleeve using direct writing filament printing technology according to the coil's structural parameters. Finally, a fixed magnet 4 is fixed inside the sleeve, and a levitation magnet 5 is placed inside the sleeve to create the energy harvesting device.

[0094] To expedite the fabrication of coil 6, this embodiment employs five-axis conformal surface printing technology. The printing method includes: attaching a double-sided adhesive polyimide film (PI film) to the outer wall of sleeve 3; then fixing sleeve 3 with the attached polyimide film onto the rotating shaft of the printer; and fixing a syringe on the horizontal axis of the printer. The printer's rotating shaft is then controlled to rotate the sleeve according to the coil's structural parameters, and the syringe is controlled to move along the horizontal axis. During the rotation of the sleeve and the movement of the syringe, a metal wire is guided out from the syringe. Under the action of the polyimide film, the metal wire adheres to the outer wall of the sleeve, forming a spiral coil.

[0095] Finally, the coil of the energy harvesting device is connected to the conductive wire of the sensing and monitoring device through a rectifier energy storage circuit, thus obtaining the electromagnetic self-powered strain sensor of this application. One application of this electromagnetic self-powered strain sensor in human motion recognition technology is as follows: Figure 5 As shown, the resistive strain sensing unit 2 is attached to the lower leg of the human body to sense strain. The energy harvesting device 100 and the monitoring board 200, which integrates a rectifier energy storage circuit and a resistance meter, are all fixed to the leg. Therefore, during human movement, continuous energy conversion and strain monitoring can be achieved, maintaining stable operation without the need for an external power supply. In addition to... Figure 5 In addition to detecting leg movements, the sensor is highly integrated in size, so it can also be used to monitor human hand movements and even finger movements, which has high application value.

[0096] The above descriptions are merely preferred embodiments of this application, and this application is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of this application should be considered to be included within the protection scope of this application.

Claims

1. A method for manufacturing an electromagnetic self-powered strain sensor, characterized in that, The electromagnetic self-powered strain sensor manufacturing method comprises the following steps: determining the design structure of the energy collection device, the energy collection device comprising a sleeve with a coil wound on the outer wall, and a fixed magnet and a floating magnet arranged in the sleeve, the same polarity ends of the fixed magnet and the floating magnet being oppositely arranged, the fixed magnet being fixed in the sleeve, and the floating magnet being movably arranged in the sleeve and capable of moving along the axial direction of the sleeve under the external vibration excitation, the magnetic flux of the coil changing with the movement of the floating magnet; determining the structural parameters of the energy collection device under the constraint condition that the output voltage of the energy collection device reaches the minimum voltage required for the conduction of the diode in the rectification energy storage circuit, the structural parameters of the energy collection device comprising the structural parameters of the sleeve, the structural parameters of the coil, the structural parameters of the fixed magnet, and the structural parameters of the floating magnet; manufacturing the energy collection device according to the design structure and the structural parameters of the energy collection device, and manufacturing the sensing monitoring device according to the design structure and the structural parameters of the sensing monitoring device, connecting the power supply end of the sensing monitoring device through the rectification energy storage circuit, and manufacturing the electromagnetic self-powered strain sensor, the sensing monitoring device being used for sensing the strain at the to-be-detected position of the to-be-monitored moving object, and the energy collection device being used for being arranged on the to-be-monitored moving object and generating alternating current energy under the external vibration excitation during the movement of the to-be-monitored moving object.

2. The electromagnetic self-powered strain sensor fabrication method of claim 1, wherein, The manufacturing of the energy collection device and the sensing monitoring device comprises: printing the sleeve according to the structural parameters of the sleeve using the fused deposition modeling printing technology, printing the coil on the outer wall of the sleeve according to the structural parameters of the coil using the direct writing printing wire technology, fixing the fixed magnet with the corresponding structural parameters in the sleeve, and placing the floating magnet with the corresponding structural parameters in the sleeve to manufacture the energy collection device; printing the sensing layer on the insulating base layer using the conductive carbon paste by the direct writing printing technology, printing the electrode on the sensing layer using the conductive silver paste by the direct writing printing technology, and connecting the conductive wire to manufacture the resistance strain sensing unit, and connecting the resistance meter to the conductive wire of the resistance strain sensing unit to manufacture the sensing monitoring device, the resistance strain sensing unit being used for being arranged at the to-be-detected position of the to-be-monitored moving object.

3. The method of claim 2, wherein the method further comprises: The structural parameters of the coil comprise the specification parameters of the metal wire wound to form the coil and the number of turns of the coil, and the printing of the coil on the outer wall of the sleeve comprises: The polyimide film with double-sided adhesion is attached to the outer wall of the sleeve, and the sleeve with the attached polyimide film is sleeved on the rotating shaft of the printer to be fixed, and a syringe is fixed on the horizontal shaft of the printer; the rotating shaft of the printer is controlled to drive the sleeve to rotate, and the syringe is controlled to move along the horizontal shaft, and a metal wire with corresponding specification parameters is guided out of the syringe during the rotation of the sleeve and the movement of the syringe, and the metal wire is attached to the outer wall of the sleeve to form a spiral coil with corresponding number of turns under the action of the polyimide film.

4. The method of claim 1, wherein the method further comprises: The structural parameters of the sleeve include a radial parameter of the sleeve and a length of the sleeve, and the structural parameters of the two magnets are the same, and the structural parameters of each magnet include a size parameter of the magnet, a weight and a magnetic induction intensity of the magnet; The method for determining the structural parameters of the energy collection device comprises: determining the diameter of the sleeve, the structural parameters of the coil, the size parameter of the magnet and the weight of the magnet; a finite element model is established according to the diameter of the sleeve, the structural parameters of the coil and the size parameters of the two magnets based on the design structure of the energy collection device; under different magnetic induction intensities of the magnet, the finite element model is used to perform finite element analysis on the movement process of the floating magnet from the fixed magnet to the direction away from the fixed magnet, and a voltage-distance curve of the energy collection device under the current magnetic induction intensity is obtained, the voltage-distance curve indicating the change curve of the output voltage of the energy collection device with the distance between the two magnets; according to the voltage-distance curves of the energy collection device under different magnetic induction intensities, the magnetic induction intensity that makes the output voltage of the energy collection device reach the minimum voltage required for the conduction of the diode in the rectification energy storage circuit is determined; the length of the sleeve is determined according to the determined magnetic induction intensity.

5. The method of claim 4, wherein the method further comprises: The method for performing finite element analysis on the movement process of the floating magnet from the fixed magnet to the direction away from the fixed magnet by using the finite element model comprises: based on the system balance equation of the floating magnet in the movement process and Faraday's law of electromagnetic induction, the magnetic flux change generated in the movement process of the floating magnet from the fixed magnet to the direction away from the fixed magnet and the corresponding output voltage are determined to obtain the voltage-distance curve; the system balance equation of the floating magnet in the movement process is: Where, m f F is the mass of the levitation magnet, g is the acceleration due to gravity; x1(t) represents the displacement of the energy harvesting device along the axial direction of the sleeve caused by external vibration excitation at time t; x2(t) represents the displacement of the levitation magnet along the axial direction of the sleeve relative to its initial static equilibrium position at time t; M (D(t)) is the repulsive force between the levitated magnet and the fixed magnet at time t, and F M (x2(t)) is related to the distance D(t) = d + x2(t) between the levitation magnet and the fixed magnet at time t, where d is the axial distance between the levitation magnet and the fixed magnet when the levitation magnet is in its initial static equilibrium position without external vibration excitation; c e (x2(t)) is the electromagnetic damping at time t and is related to x2(t); f is the sum of air viscosity force and inner wall contact friction, and the sign factor sgn(x2(t)) is used to adjust the direction of f to be opposite to the direction of x2(t).

6. The method of claim 5, wherein the method further comprises: The method for manufacturing the electromagnetic self-powered strain sensor further comprises: The first magnet is clamped by a bottom clamp, the second magnet is clamped fixed by a top clamp through a pressure sensor, the top clamp drives the second magnet to move towards the first magnet, and the repulsion force of the pressure sensor at different distances between the second magnet and the first magnet is read, and the repulsion force F between the two magnets at any t time is fitted M (R M (t)) and the distance R M (t) between the two magnets is: wherein a, b, c are correction coefficients obtained by fitting, H1 is the magnetic induction intensity of the first magnet, H2 is the magnetic induction intensity of the second magnet, R M (t) is the distance between the first magnet and the second magnet at time t, and μ0 is the vacuum permeability.

7. The method of claim 5, wherein the method further comprises: determining the magnetic induction intensity that makes the output voltage of the energy collection device reach the minimum voltage required for the conduction of the diode in the rectification energy storage circuit comprises: determining the relationship between the device displacement x1(t) and the magnet displacement x2(t) according to the system balance equation, and determining the magnet displacement range in combination with the device displacement range generated by the external vibration excitation of the to-be-monitored moving object; for any magnetic induction intensity, when the output voltages of the voltage-distance curve of the energy collection device under the magnetic induction intensity all reach the minimum voltage required for the conduction of the diode in the rectification energy storage circuit within the magnet displacement range, the magnetic induction intensity is determined to make the output voltage of the energy collection device reach the minimum voltage required for the conduction of the diode in the rectification energy storage circuit.

8. The method of claim 6, wherein the method further comprises: The length of the sleeve is determined according to the determined magnetic induction intensity, which comprises: Based on the feature that the repulsive force between the floating magnet and the fixed magnet in the static state is equal to the gravity of the floating magnet, the distance d between the floating magnet and the fixed magnet when the energy collection device is in the static state is calculated, and the length of the sleeve is determined as 2d.

9. The method of claim 1, wherein the method further comprises: The coil is wound in a segmented structure and fixed to the outer wall of the sleeve.

10. The method of claim 1, wherein the method further comprises: The surface of the floating magnet is coated with a lubricant.

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