A wearable electromyography monitoring device based on tensile metamaterials and its fabrication method

Abstract

This invention discloses a wearable electromyography (EMG) monitoring device based on a tensile metamaterial and its fabrication method, relating to the field of EMG signal monitoring. The device includes a large tensile metamaterial mesh used to wrap the monitored area of ​​the human body as the main wearable component; flexible silver nanowire electrodes, which are connected to the tensile mesh through two layers: a PDMS film and a silver nanowire conductive layer; and a signal acquisition device including wires and an EMG signal acquisition card, wherein the signal acquisition card is connected to a Bluetooth module for data upload. Thanks to the designed tensile metamaterial, this invention ensures close contact with the human body surface during large deformations while avoiding excessive lateral contraction under large stretching, as is common in ordinary wearable devices. This guarantees good stability and accuracy of the detection signal. The detection method using a tensile mesh covering the flexible silver electrodes also ensures the breathability and comfort of the wearable device.

Description

Technical Field

[0001] This invention relates to the field of electromyography (EMG) signal monitoring, and in particular to an EMG monitoring wearable device based on a tensile metamaterial and its preparation method. Background Technology

[0002] In the current environment, wearable electronic monitoring devices are developing rapidly, and the performance requirements for these devices are constantly increasing. How to improve the effectiveness of their applications using existing optimization methods is an important consideration. The application of wearable electromyography (EMG) monitoring devices in the medical field has brought about a huge change in the concept of medicine, and they also have broad prospects in the field of sports monitoring, including collecting body signals during exercise to determine the state of exercise and providing timely feedback to improve the exercise experience. In practical applications, improving the stability and accuracy of monitoring human physiological signals is key. This requires the wearable device to fit closely to the human body and also to meet the comfort requirements of the wearable device matching the skin during monitoring.

[0003] Wearable devices are developing rapidly, but existing ordinary wearable devices will cause excessive lateral contraction and deformation when stretched on the human body. This can cause physical damage to some of the sensors and electrodes and reduce the accuracy of monitoring data. It can also cause the device to be too tight or shift when worn, resulting in discomfort or skin abrasions, affecting the user experience. It may also cause the wearable device to be unable to fit tightly to the skin or specific parts of the body due to deformation, affecting its normal operation. Furthermore, breathability when worn for a long time is also an important consideration.

[0004] Therefore, when developing wearable devices, it is necessary to solve the above problems and develop a wearable structure device that avoids excessive lateral compression to ensure good performance, high comfort, and good breathability for long-term wear. Summary of the Invention

[0005] This invention seeks to provide a wearable electromyography (EMG) signal monitoring device, which mainly provides a wearable stretchable mesh in surface contact to avoid excessive lateral contraction during stretching, and provides a self-made silver nanowire electrode to constitute the wearable EMG signal monitoring device, in order to solve the problems in the above-mentioned background art.

[0006] An electromyography (EMG) monitoring wearable device based on a tensile metamaterial includes an externally worn tensile metamaterial, silver nanowire electrodes, a data acquisition card, a power supply, and a Bluetooth module. The externally worn tensile metamaterial is connected to the data acquisition card via the silver nanowire electrodes. The data acquisition card is connected to the power supply. The Bluetooth module is wirelessly connected to the data acquisition card via Bluetooth signals.

[0007] A wearable electromyography monitoring device based on a dilatational metamaterial and its fabrication method include the following steps:

[0008] Step 1: Metamaterial Structure Design

[0009] By designing the parameters of the arc, a line diameter of 0.5 mm was selected. The cell structure was designed by combining arcs with longitudinal diameter t = 7 mm and transverse diameter t = 8 mm. The tensile properties of the tensile mesh can be adjusted by changing the parameter θ from 180° to 60°, where θ is the central angle of the arc. This forms the basic cell structure of the tensile metamaterial. A symmetrical anti-chiral tensile metamaterial unit was designed and proposed. Based on the mechanism of rotation of chiral structures during stretching, the structure is designed to be anti-symmetrical. During stretching, the upper and lower parts of the tensile unit rotate in opposite directions, resulting in the middle protruding outward and forming a significant large tensile effect.

[0010] Step 2: Sample Production

[0011] A mesh model was created using 3D modeling software. After optimizing all parameters, the 3D model was sliced ​​using Creo software. The sample was then printed using FDM 3D printing technology. The printing consumable was polylactic acid (PLA) material with a diameter of 0.4 mm. To prevent damage to the printed mesh during printing or removal, the height of the cuboids connecting the two sides of the cell mesh was designed to be 1 mm, which is larger than the arc diameter of 0.5 mm, so that the mesh structure could be suspended for support during printing. The support material was polyvinyl alcohol (PVA) with a diameter of 0.4 mm, which is water-soluble. After the printed model was removed and placed in water for a period of time, it could form an individual metamaterial structure, thus not damaging or affecting the performance of the metamaterial mesh.

[0012] Step 3: Fabrication of polydimethylsiloxane (PDMS) substrate;

[0013] a) Mix the substrate and curing agent at a weight ratio of 10:1 in a beaker and stir thoroughly. The substrate is Dow Corning.

[0014] b) Let the mixed substrate stand for 1 hour. When there are no more air bubbles in the mixture in the beaker, the manufacturing of the PDMS substrate is complete.

[0015] c) Select two glass substrates with a side length of 2cm, wipe them clean, pour the prepared PDMS substrate onto the glass substrates, and use a spin coating equipment to uniformly spin coat, thereby forming a PDMS film with a thickness of approximately 2mm.

[0016] Step 4: Electrode Integration

[0017] a) Spin-coat the PDMS solution onto a glass slide with a side length of 2cm, place it in a 50℃ oven for 1 hour, and after taking it out, spray silver nanowires with a spray gun before the PDMS is completely cured. The PDMS that is not completely cured has high viscosity, which is more conducive to the adhesion of silver nanowires to its surface, so as to prevent the electrodes from peeling off excessively when performing electromyography signal monitoring.

[0018] b) After the spraying is completed, put the PDMS film back into the oven and wait for the electrode film to be completely cured before taking it out. Use commercial conductive copper tape to wrap around one edge of the electrode. After the commercial conductive cloth tape is connected to the surface of the copper tape, use insulating tape to cover the exposed conductive tape part to prevent signal interference. The commercial conductive cloth tape is coated with copper and nickel polyester fiber.

[0019] Step 5: Integration of Monitoring Devices

[0020] a) Connect the exposed portions of the conductive tape of the two manufactured silver nanowire electrodes to the acquisition card channel using snap-on wires. After cleaning the surface of the muscle area to be tested, simply fix the two electrodes side by side on the human body surface. Place the reference electrode in an area that does not participate in muscle movement. Cover the electrodes and test area with the designed tensile metamaterial. After covering, use nylon buckles to connect the two ends of the metamaterial mesh for wearing and fastening. After the wearing part is integrated, perform electromyography signal monitoring.

[0021] In relevant monitoring scenarios, the study applied electromyography (EMG) signals of human movements to detection, and analyzed the impact of metamaterials on the quality and stability of the monitored EMG signals.

[0022] The beneficial effects of this invention are:

[0023] By designing a tensile superstructure mesh material for wearable monitoring, the problem of excessive lateral contraction of ordinary wearable devices under large stretching, which leads to a decrease in monitoring signal quality and stability, is avoided.

[0024] The aforementioned wearable structure and monitoring method effectively avoid the problem of wearable devices losing their stable fit due to deformation, thereby improving the stability of signal acquisition. Furthermore, it ensures breathability during prolonged wear and monitoring. With the support of the stretching structure, it maintains a close fit to the skin when monitoring muscle movements without excessive distortion or tightness, thus improving wearing comfort. Attached Figure Description

[0025] Figure 1 This is an overall integrated diagram of the electromyography signal monitoring device of the present invention;

[0026] Figure 2 These are the basic circular arc units that make up the tensile metamaterial;

[0027] Figure 3 This is an enlarged view of the overall structure and cell elements of the stretched mesh;

[0028] Figure 4 This is a diagram showing the morphological changes of the expanded mesh of the present invention;

[0029] Figure 5 These are experimental and simulated Poisson's ratio plots of tensile metamaterials as a function of longitudinal strain;

[0030] Figure 6 This is an overall integrated diagram of the silver nanowire electrode;

[0031] Figure 7 This is a diagram showing the fabrication of the conductive portion of the silver nanowire electrode;

[0032] Figure 8 This is a graph showing the signal detected by an integrated wearable device when the arm clenches its fist.

[0033] Figure 9 This is a comparison chart showing the impact of having and not having a tensile metamaterial on the signal-to-noise ratio of the same action. Detailed Implementation

[0034] Please see Figures 1 to 9 As shown, an electromyography monitoring wearable device based on a tensile metamaterial includes an externally worn tensile metamaterial 1, a silver nanowire electrode 2, a data acquisition card 3, a power supply 4, and a Bluetooth module 5. The externally worn tensile metamaterial 1 is connected to the data acquisition card 3 through the silver nanowire electrode 2, the data acquisition card 3 is connected to the power supply 4, and the Bluetooth module 5 is wirelessly connected to the data acquisition card 3 through a Bluetooth signal.

[0035] The wearable electromyography (EMG) signal monitoring device provided by this invention includes a designed tensile metamaterial mesh, a cell structure composed of circular arcs, and a self-designed symmetrical anti-handed structure that exhibits a large negative Poisson's ratio effect. A basic mesh model was established using 3D modeling software, and finite element simulation was performed using Abaqus simulation software to optimize and verify the design, thereby proving whether the designed tensile structure possesses good negative Poisson's ratio behavior. After the 3D model was optimized for each parameter, it was sliced ​​using Creo software, and then the physical mesh was printed using FDM 3D printing technology. The printing consumable is PLA (polylactic acid) material with a diameter of 0.4 mm. PLA is a commonly used printing material in 3D printing; due to its good toughness and non-toxicity to the human body, it is suitable as part of wearable devices. Other materials can also be used in this design structure; the emphasis is on the structure itself, and the suitability of other materials is not considered.

[0036] To prevent damage to the printed mesh during printing or removal, the mesh model will be designed with the following in mind: Figure 3The height of the cuboids connected on both sides of the cell grid shown is designed to be 1mm, which is larger than the arc diameter of 0.5mm, so that the grid structure is suspended for support printing. The support material is PVA (polyvinyl alcohol) with a diameter of 0.4mm. This material is soluble in water. After the printed model is taken out, it is placed directly in water for a period of time to form a separate metamaterial structure. This will not damage or affect the performance of the metamaterial grid.

[0037] This wearable electromyography (EMG) signal monitoring device also includes self-manufactured silver nanowire electrodes, which facilitate connection and measurement with acquisition devices and leads when integrated into the wearable device. It also includes, for example,... Figure 6 Conductive cloth tape, conductive copper tape, and insulating tape are used for external protection to prevent external interference from affecting the stability and accuracy of electromyography signal measurement. The specific preparation steps are as follows:

[0038] Fabrication of PDMS (polydimethylsiloxane) substrates;

[0039] a) Mix the substrate (Dow Corning) and the curing agent in a weight ratio of 10:1 and stir thoroughly in a beaker;

[0040] b) Let the mixed substrate stand for 1 hour. When there are no more air bubbles in the mixture in the beaker, the manufacturing of the PDMS substrate is complete.

[0041] c) Select two glass substrates with a side length of 2cm, wipe them clean, pour the prepared PDMS substrate onto the glass substrates, and use a spin coating equipment to uniformly spin coat, thereby forming a PDMS film with a thickness of approximately 2mm.

[0042] Electrode integration

[0043] a) Place the prepared PDMS film in a 50℃ oven for 1 hour, then... Figure 7 As shown, after the PDMS film was taken out, silver nanowires were sprayed onto it using a spray gun before it was fully cured. The PDMS that was not fully cured had high viscosity, which made it easier for the silver nanowires to adhere to its surface, thus preventing excessive peeling during electromyography signal monitoring.

[0044] b) After the PDMS film is sprayed, put it back into the oven and wait for the electrode film to dry completely before taking it out. Use conductive copper tape to wrap around one edge of the electrode. After the conductive cloth tape is connected to the surface of the copper tape, use insulating tape to cover the exposed conductive tape part to prevent signal interference.

[0045] Specific steps for integrating a wearable electromyography (EMG) signal monitoring device:

[0046] a) The manufactured electrode film is fastened to one end of the conductive cloth tape using a snap-on wire, and the other end of the wire is connected to the electromyography signal acquisition card.

[0047] b) The conductive layer of the silver nanowire electrode is attached to the skin of the monitored human body, and the non-conductive layer is attached to the tensile metamaterial mesh. At the same time, nylon buckles are used to connect the two ends of the metamaterial mesh for wearing and fastening, so that the metamaterial mesh is attached to the skin, forming the wearable part. The reference electrode is placed in the human body area that does not participate in muscle movement.

[0048] c) The device connects to the host computer via Bluetooth for data processing. The acquisition unit is then secured to another part of the body with tape for easy portability, thus completing the design and manufacture of a wearable electromyography (EMG) signal monitoring device.

[0049] Example 1:

[0050] External wearable tensile metamaterial structure and physical design.

[0051] For externally wearable tensile metamaterials, the basic design inspiration comes from the combination of circular arcs, through the design and selection of appropriate parameters, such as... Figure 2 The design incorporates arcs with a diameter of 0.5 mm. The cell structure combines arcs with longitudinal diameters t = 7 mm and transverse diameters t = 8 mm. The tensile properties of the tensile mesh can be adjusted by changing the central angle θ of the arcs from 180° to 60°, thus forming the basic cell structure of the tensile metamaterial. While chiral structures are generally used for the two-dimensional morphological design of tensile metamaterials, their tensile effect is limited. Therefore, this invention innovatively proposes a symmetrical anti-chiral structure for the tensile metamaterial unit, such as... Figure 3 The cell structure and overall grid diagram shown are designed with antisymmetry based on the mechanism of rotation of chiral structures during stretching. The expansion unit rotates in opposite directions when stretched, resulting in the middle protruding outward and forming a significant expansion effect.

[0052] The unit structure is arranged in a honeycomb pattern to form an overall structural mesh. This mesh model is created using 3D software and then printed by an Ultimaker 3D printer using the FDM (Fused Deposition Modeling) method. The printing material is PLA (polylactic acid) with a diameter of 0.4 mm.

[0053] Example 2:

[0054] Simulation and physical testing of the tensile properties of diastolic metamaterials.

[0055] Mechanical tensile tests were conducted on the printed prototype of the designed tensile metamaterial on a universal testing machine at a stretching speed of 5 mm / min. Poisson's ratio was calculated by analyzing the transverse and longitudinal deformations. Simultaneously, uniaxial tensile tests were performed on the model using the finite element software Abaqus to obtain the morphology before and after the deformation. Figure 4As shown, both simulations and experiments simultaneously verify the changes in the horizontal and vertical directions. The Poisson's ratio in both simulations and experiments is given by the formula:

[0056]

[0057] Where ε⊥ represents the transverse strain and ε″ represents the longitudinal strain, the Poisson's ratio results are as follows: Figure 5 As shown, this basically proves that the designed structure has good tensile behavior and a wide range of adjustment. Since the metamaterial is a mesh structure, its air permeability is also good.

[0058] Example 3:

[0059] Silver nanowire electrodes fabricated on a PDMS substrate.

[0060] like Figure 6 As shown, this wearable electromyography (EMG) signal monitoring device also includes self-manufactured silver nanowire electrodes. To facilitate connection with the acquisition device and wires during integration into the wearable device, conductive cloth tape, conductive copper tape, and insulating tape are also included for external protection to prevent external interference from affecting the stability and accuracy of EMG signal measurements. The specific preparation steps are as follows:

[0061] 1) Fabrication of PDMS substrate;

[0062] a) Mix the substrate (Dow Corning) and the curing agent in a weight ratio of 10:1 and stir thoroughly in a beaker;

[0063] b) Let the mixed substrate stand for 1 hour. When there are no more air bubbles in the mixture in the beaker, the manufacturing of the PDMS substrate is complete.

[0064] c) Select two glass substrates with a side length of 2cm, clean them, pour the prepared PDMS substrate onto the glass substrates, and use a spin coating device to uniformly spin coat the substrates to form a PDMS film with a thickness of approximately 2mm.

[0065] 2) Electrode integration

[0066] a) Place the prepared PDMS film in a 50℃ oven for 1 hour, then remove it as follows: Figure 7 As shown, silver nanowires were sprayed using a spray gun when the PDMS film was not fully cured. The incompletely cured PDMS has high viscosity, which makes it easier for the silver nanowires to adhere to its surface, thus preventing excessive peeling during electromyography signal monitoring.

[0067] b) After spraying, place it back in the oven and wait for the electrode film to dry completely before removing it. Figure 6As shown, conductive copper tape is wrapped around the edge of one end of the electrode. After the conductive cloth tape is attached to the surface of the copper tape, insulating tape is used to cover the exposed conductive tape portion to prevent signal interference.

[0068] Example 4

[0069] After integration, the wearable electromyography (EMG) monitoring device monitors the position of the brachioradialis muscle in the arm during fist clenching.

[0070] The designed and manufactured externally stretched wearable mesh and silver nanowire electrodes are used in conjunction with the data acquisition device for such purposes. Figure 1 Wearable monitoring is used, where the lead wire in the acquisition card 3 is a three-lead wire. Two leads are connected to silver nanowire electrodes 2 placed in the brachioradialis muscle, and one lead uses a commercial electrode placed in a position not involved in muscle movement as a reference electrode. After integration, the arm's fist-clenching and unclenching movements are monitored, with fist-clenching and unclenching movements performed at approximately the same intervals. The data collected and processed by MATLAB are as follows: Figure 8 As shown, this demonstrates that the device can effectively recognize fist-clenching movements and that the signal is stable and effective.

[0071] Example 5

[0072] A wearable electromyography (EMG) signal monitoring device compares the quality of the monitoring signal when a hand picks up the same book, with and without the support of a metamaterial mesh.

[0073] To analyze the effects of the tensile metamaterial, the silver nanowire electrodes were first fixed in place using only transparent tape, and then the action signal of a hand picking up a book was monitored. Subsequently, the integrated device was covered with a metamaterial mesh around the arm, and the action signal of the hand picking up the same book was also monitored. The signal-to-noise ratio (SNR) of the acquired signals was calculated using the following formula:

[0074] SNR = 20log10(V) S / V n )

[0075] Where V S Vn is the maximum output voltage, and Vn is the noise voltage. A higher signal-to-noise ratio indicates a better signal quality. The calculated data results are as follows: Figure 9 As shown, the results indicate that the addition of tensile metamaterials can improve the signal-to-noise ratio of the monitoring signal, making the monitoring signal more stable and effective.

Claims

1. A method for fabricating an electromyography monitoring wearable device based on a tensile metamaterial, characterized in that: The wearable electromyography (EMG) monitoring device based on the tensile metamaterial includes an external wearable tensile metamaterial (1), a silver nanowire electrode (2), a data acquisition card (3), a power supply (4), and a Bluetooth module (5). The external wearable tensile metamaterial (1) is connected to the data acquisition card (3) through the silver nanowire electrode (2), and the data acquisition card (3) is connected to the power supply (4). The Bluetooth module (5) is wirelessly connected to the data acquisition card (3) through Bluetooth signal. The wearable EMG monitoring device based on the tensile metamaterial is used for the detection of EMG signals of human movement in relevant monitoring scenarios. The method includes the following steps: Step 1: Metamaterial Structure Design By designing the parameters of the arc, a line diameter of 0.5 mm was selected. The cell structure was designed by combining arcs with longitudinal diameter t=7 mm and transverse diameter t=8 mm. The tensile properties of the tensile mesh were adjusted by changing the parameter θ from 180° to 60°, where θ is the central angle of the arc. This formed the basic cell structure of the tensile metamaterial. A symmetrical anti-chiral tensile metamaterial unit was designed. Based on the mechanism of rotation of chiral structures during stretching, the symmetrical anti-chiral tensile metamaterial unit was designed with antisymmetry. During stretching, the upper and lower parts of the tensile metamaterial unit rotate in opposite directions, resulting in the middle protruding outward and forming a significant large tensile effect. Step 2: Sample Production A mesh model was created using 3D modeling software. After optimizing all parameters, the 3D model was sliced ​​using Creo software. The sample was then printed using FDM 3D printing technology. The printing material was polylactic acid (PLA) with a diameter of 0.4 mm. To prevent damage to the printed mesh during printing or removal, the height of the cuboids connecting the two sides of the cell mesh was designed to be 1 mm, which is larger than the arc diameter of 0.5 mm, so that the mesh structure could be suspended for support during printing. The support material was polyvinyl alcohol (PVA) with a diameter of 0.4 mm. The support material is water-soluble. After the printed model was removed, it was placed in water for a period of time to form a separate metamaterial structure. Step 3: Fabrication of polydimethylsiloxane (PDMS) substrate a) Mix the substrate and curing agent at a weight ratio of 10:1 and stir thoroughly in a beaker; b) Let the mixed substrate stand for 1 hour. When there are no more air bubbles in the mixture in the beaker, the manufacturing of the PDMS substrate is complete. c) Select two glass substrates with a side length of 2cm, wipe them clean, pour the prepared PDMS substrate onto the glass substrates, and use a spin coating equipment to uniformly spin coat the substrates to form a PDMS film with a thickness of 2mm. Step 4: Electrode Integration a) Spin-coat the PDMS solution onto a glass slide with a side length of 2cm, place it in a 50℃ oven for 1 hour, and after taking it out, spray silver nanowires with a spray gun before the PDMS is completely cured. The PDMS that is not completely cured has high viscosity, which is more conducive to the adhesion of silver nanowires to its surface, so as to prevent the electrodes from peeling off excessively when performing electromyography signal monitoring. b) After the spraying is completed, put the PDMS film back into the oven and wait for the electrode film to be completely cured before taking it out. Use commercial conductive copper tape to wrap around one edge of the electrode. After the commercial conductive cloth tape is connected to the surface of the copper tape, use insulating tape to cover the exposed conductive tape part to prevent signal interference. The commercial conductive cloth tape is coated with copper and nickel polyester fiber. Step 5: Integration of Monitoring Devices The exposed portions of the conductive tape of the two manufactured silver nanowire electrodes were connected to the acquisition card channel using snap-on wires. After cleaning the surface of the muscle area to be tested, the two electrodes were simply fixed side by side on the human body surface. The reference electrode was placed in an area that did not participate in muscle movement. The designed tensile metamaterial was covered on the electrodes and the test area. After covering, the two ends of the metamaterial mesh were connected with nylon buckles for wearing and fastening. After the wearable part was integrated, electromyography signal monitoring was performed.

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