A double-sided asymmetric flexible strain sensor, a preparation method and application thereof

Abstract

The application discloses a double-sided asymmetric flexible strain sensor and a preparation method and application thereof, and belongs to the technical field of flexible electronic sensors.The double-sided asymmetric flexible strain sensor comprises three layers, wherein the upper layer is an upper conductive layer, the middle layer is a substrate, and the lower layer is a lower conductive layer; the upper conductive layer is a conductive silver paste layer with a wrinkle structure; the substrate is polydimethylsiloxane; and the lower conductive layer is a conductive silver paste layer with a smooth structure.The double-sided asymmetric flexible strain sensor realizes bending signal amplification, common-mode drift suppression and direction selective output through double-channel differential reading.Therefore, the double-sided asymmetric flexible strain sensor can play different roles in different application scenarios due to the special structure, and can be used as a differential signal angle sensor on one hand and can be used for direction discrimination through rectification effect on the other hand.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronic sensor technology, specifically relating to a double-sided asymmetric flexible strain sensor, its fabrication method, and its application. Background Technology

[0002] The research background of strain sensors is rooted in the core principle of converting mechanical deformation into electrical signals, and its development history clearly reflects the evolution from traditional rigid to modern flexible.

[0003] Early technologies were primarily based on the strain and piezoresistive effects of metals and semiconductors. In 1938, the United States developed a paper-based wire-wound resistance strain gauge, laying the foundation for sensors. Metal foil strain gauges, with nickel-chromium alloys at their core, became the cornerstone of industrial measurement due to their high stability, but their sensitivity was relatively low (K≈2-4). Subsequent semiconductor strain gauges utilized the piezoresistive effect of silicon, increasing sensitivity by tens of times (K≈50-100), meeting the needs for detecting minute deformations. These two types of traditional rigid sensors are still widely used in aerospace, structural health monitoring, and other fields.

[0004] The current trend is towards greater flexibility and lighter weight. Traditional rigid devices can no longer meet the emerging demand for conformal fitting with dynamic curved surfaces. However, the development of novel flexible strain sensors generally faces key technical bottlenecks such as insufficient cyclic stability, signal nonlinearity, dynamic hysteresis, and the difficulty in simultaneously achieving high sensitivity and wide measurement range. Therefore, current research focuses on overcoming these bottlenecks through new material design and innovative structures to meet the stringent requirements of high precision and long lifespan sensing in complex scenarios such as intelligent health monitoring and human-computer interaction. Summary of the Invention

[0005] To address or partially address the problems existing in related technologies, this invention proposes a bifacial asymmetric flexible strain sensor, its fabrication method, and its application.

[0006] This invention provides a double-sided asymmetric flexible strain sensor, comprising three layers: an upper conductive layer, a middle substrate, and a lower conductive layer; the upper conductive layer is a conductive silver paste layer with a wrinkled structure; the substrate is polydimethylsiloxane; and the lower conductive layer is a conductive silver paste layer with a smooth structure.

[0007] Preferably, the thickness of the upper conductive layer is 300 mm. -400 The substrate thickness is 1000. -1500 The thickness of the lower conductive layer is 300. -400 .

[0008] Preferably, the folded structure is a flexor muscle-like structure resembling a finger joint.

[0009] A method for fabricating a bifacial asymmetric flexible strain sensor includes the following steps: (1) After mixing polydimethylsiloxane and curing agent, stir evenly and remove air bubbles in the mixed solution by vacuuming to obtain a mixed solution; (2) Pour the mixed solution into the mold, then solidify it, peel off the film, and the resulting film has a wrinkled structure on one side and a smooth structure on the other side; (3) Plasma cleaning is performed on both surfaces of the thin film to obtain the substrate; (4) Apply a layer of conductive silver paste evenly to both sides of the substrate and then cure it to obtain a double-sided asymmetric flexible strain sensor.

[0010] Preferably, the mass ratio of polydimethylsiloxane to curing agent is 12:1, and the curing agent is 184 SiliconeElastomer Curing.

[0011] Preferably, in step (2), the curing temperature is 80°C and the curing time is 1 hour.

[0012] Preferably, in step (3), O2 plasma cleaning is used and the cleaning time is 10 min.

[0013] Preferably, in step (4), the curing temperature is 150°C and the time is 30 min.

[0014] The present invention also claims protection for the application of the bifacial asymmetric flexible strain sensor as a rectifier and a differential signal angle sensor.

[0015] Preferably, the application is as follows: when the double-sided asymmetric flexible strain sensor is on a wrinkled surface, the double-sided asymmetric flexible strain sensor is used as a differential signal angle sensor when the sensor receives an upward bending force; when the sensor receives a downward bending force, the double-sided asymmetric flexible strain sensor is used as a rectifier.

[0016] When the folded surface of the double-sided asymmetric flexible strain sensor of this invention is in contact with the back of the hand and the finger joints, the planar structure facing the back of the hand is mainly subjected to tension during finger bending. The strain loading causes microcracks in the conductive layer to initiate and expand, resulting in the gradual destruction of the conductive path and an increase in resistance. Meanwhile, the flexor muscle-like microstructure facing the palm is mainly compressed during bending. The surface undulation structure gradually contacts and reconstructs the conductive path, generating an electrical response opposite to that of the back side. The double-sided asymmetric flexible strain sensor is used as a differential signal angle sensor.

[0017] The technical solution provided by this invention has the following beneficial effects: (1) The double-sided asymmetric flexible strain sensor of the present invention comprises a planar Ag response layer and a wrinkled Ag response layer respectively constructed on both sides of the same PDMS substrate, and achieves bending signal amplification, common-mode drift suppression and direction-selective output through dual-channel differential readout. Therefore, due to its special structure, the double-sided asymmetric flexible strain sensor can play different roles in different application scenarios. On the one hand, it can be used as a differential signal angle sensor, and on the other hand, it can be used for direction discrimination through rectification effect.

[0018] (2) The present invention does not cause significant irreversible damage to the conductive layer during the deformation process. The resistance changes are stable in multiple cyclic tests. Furthermore, the O2plasma treatment enhances the adhesion of the conductive silver paste to the substrate, thereby increasing the service life of the double-sided asymmetric flexible strain sensor.

[0019] (3) The present invention uses polydimethylsiloxane as a substrate and conductive silver paste as a conductive material, so that the entire sensor has excellent conductivity and flexibility.

[0020] (4) The present invention has a simple structure, is easy to prepare, and the sensor has good flexibility and a special structure, and has excellent applicability.

[0021] (5) The present invention integrates the double-sided asymmetric flexible strain sensor into the smart glove system and constructs a virtual reality interaction platform to verify its application feasibility in human-computer interaction scenarios. Attached Figure Description

[0022] Figure 1 The diagram shows the structure of the double-sided asymmetric flexible strain sensor of the present invention. (a) is a top view and (b) is a front view.

[0023] Figure 2 To illustrate the working principle of the smart glove of this invention, (a) is a schematic diagram of the equivalent circuit of the sensor, (b) is a schematic diagram of the response mode of the double-sided asymmetric topology under forward and reverse bending, and (c) is a diagram of the smart glove and the acquisition board device.

[0024] Figure 3 These are two linear sensitivities of the bifacial asymmetric flexible strain sensor of the present invention.

[0025] Figure 4 This describes the resistance drift behavior of the two channels on both sides of the double-sided asymmetric flexible strain sensor of the present invention.

[0026] Figure 5 This invention relates to the signal drift of the double-sided asymmetric flexible strain sensor under a small 5° bending angle.

[0027] Figure 6This invention provides the stability of the double-sided asymmetric flexible strain sensor under a small angle of 3° cycling.

[0028] Figure 7 This is the hysteresis behavior curve of the double-sided asymmetric flexible strain sensor of the present invention.

[0029] Figure 8 The present invention relates to the response changes of the two-sided asymmetric flexible strain sensor as the angular bending angle increases from 30°, 60°, 90° to 120°.

[0030] Figure 9 The image shows the response and recovery time curves of the double-sided asymmetric flexible strain sensor of the present invention when the angle changes by 20°.

[0031] Figure 10 This is a signal recognition diagram of the two channels of the double-sided asymmetric flexible strain sensor of the present invention under a small angle input.

[0032] Figure 11 This invention describes the differential output behavior of the double-sided asymmetric flexible strain sensor under two bending directions.

[0033] Figure 12 This is a schematic diagram of the signal acquisition and control process of an intelligent glove system.

[0034] Figure 13 This is used to virtually capture six consecutive action frames from a video.

[0035] Figure 14 This invention provides the multi-channel response of five channels for six different actions. Detailed Implementation

[0036] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate this invention.

[0037] Example 1 A method for fabricating a bifacial asymmetric flexible strain sensor includes the following steps: (1) Mix 2 g of polydimethylsiloxane with 0.2 g of curing agent and stir evenly. Then put it into a vacuum drying oven and vacuum for 30 min at 25 °C to remove air bubbles in the mixture solution to obtain a mixed solution.

[0038] (2) Pour 1 g of the mixed solution into the prepared photosensitive resin mold, and then cure it at 80 °C for 1 h. Carefully peel the film with the special structure from the mold. One side of the film has a finger joint biomimetic structure pattern, and the other side has a smooth surface.

[0039] (3) Place the film in a plasma cleaner and use O2 plasma to clean both surfaces of the film for 10 minutes to enhance its roughness. The purpose is to better adhere the conductive silver paste and obtain the substrate.

[0040] (4) Apply a layer of conductive silver paste evenly to both sides of the substrate, and then cure it on a hot stage at 150 °C for 30 min to obtain a double-sided asymmetric flexible strain sensor.

[0041] The fabricated bi-faceted asymmetric flexible strain sensor structure is as follows: Figure 1 As shown in the top view, its surface has wrinkles that mimic the structure of a flexor muscle. The device consists of three layers: silver paste-PDMS-silver paste. In this embodiment, the thickness of the upper conductive layer silver paste is 300 mm. The thickness of the substrate is 1200. The thickness of the lower conductive layer silver paste is 300 mm. .

[0042] Comparative Example 1 A method for fabricating a biplane symmetrical flexible strain sensor includes the following steps: (1) Mix 2 g of polydimethylsiloxane with 0.2 g of curing agent and stir evenly. Then put it into a vacuum drying oven and vacuum for 30 min at 25 °C to remove air bubbles in the mixture solution to obtain a mixed solution.

[0043] (2) Pour 1 g of the mixed solution into an unstructured mold and then cure it at 80 °C for 1 h. Carefully peel the film from the mold to obtain a film with smooth sides.

[0044] (3) The film is placed in a plasma cleaner and cleaned with O2 plasma for 10 minutes to enhance its roughness. The purpose is to better adhere the conductive silver paste and obtain the substrate.

[0045] (4) Coat both sides of the substrate with a layer of conductive silver paste, and then cure it on a hot stage at 150 °C for 30 min to obtain flexible strain sensing.

[0046] The fabricated flexible strain sensor consists of three layers: silver paste-PDMS-silver paste, with both silver paste layers exhibiting a smooth surface. In this comparative example, the thickness of both conductive silver paste layers is 300 mm. The thickness of the substrate is 1200. . If the PDMS substrate undergoes creep and stress relaxation during prolonged stress, such time-related disturbances may act on both channels simultaneously in a similar manner. The two-sided symmetrical structure in Comparative Example 1 cannot cancel the background signal generated by the two-sided smooth structure, resulting in a larger drift error. Furthermore, the two-sided smooth structure does not generate a differential signal during bending, and without a special structure, it cannot achieve a rectification effect.

[0047] Example 1 Applications of double-sided asymmetric flexible strain sensors as rectifiers: A small light bulb and wires were fixed on the structural surface of a double-sided asymmetric flexible strain sensor and then fixed to a robotic arm. After powering on, the brightness of the light bulb was observed when the robotic finger was bent at 30°, 60°, 90°, and 120°. During the observation, it was found that the brightness of the light bulb did not change with the angle. Therefore, it can be concluded that when the wrinkled structure surface is facing upward and the finger joint is bent downward, the overall resistance of the thin film does not change. Thus, the differential signal angle sensing with the finger joint imitation flexor muscle structure has the potential to act as a rectifier.

[0048] Depend on Figure 11 As can be seen, with the structure facing down, the double-sided asymmetric flexible strain sensor is in close contact with the finger joints on the back of the hand. When the mechanical finger bends upward (positive bending: bending towards the back of the hand), the differential signal always remains at a low level and does not change significantly with the angle. This input-output relationship is similar in form to the rectification effect.

[0049] Example 2 Applications of double-sided asymmetric flexible strain sensors: A double-sided asymmetric flexible strain sensor was fixed on the knuckles on the back of a robotic hand, with the pleated structure side close to the fingers on the back of the hand. After connecting the testing equipment, the robotic fingers were bent in the opposite direction from 0 to 120°. The changes in resistance on both sides were observed. It can be observed that different signal changes occur during the bending process, and the signal difference between the two sides of the sensor increases with the degree of bending. Therefore, this thin film with a special structure has the potential to be used as a differential signal angle sensor.

[0050] like Figure 2 As shown in (a), based on this two-sided confrontational electromechanical coupling mechanism, the sensor no longer relies on the single-channel resistance change of the traditional single-sided structure to characterize bending. Instead, it synchronously acquires signals from both sides and performs differential output, superimposing the resistance increase response on one side with the resistance decrease response on the other side to convert it into a higher amplitude effective output, thereby amplifying the bending signal at the sensor front end. Figure 2As shown in (b), the palmar-side wrinkled topology and the dorsal-side planar topology have intrinsic differences in force mode and conductivity path evolution mechanism, and the device exhibits significantly different signal forms during bending in the target direction and in the reverse direction. Figure 2 As shown in (c), the hardware composition of the smart glove integrated with double-sided asymmetric flexible sensors is illustrated. Five double-sided asymmetric sensing units are integrated at the five finger positions of the glove, and then connected to a data acquisition circuit board to collect the bending signals of each finger. The figure also shows a partial enlarged view of the sensor unit and its associated data acquisition circuit board.

[0051] from Figure 3 It can be seen that the double-sided asymmetric flexible strain sensor can be divided into two relatively clear linear operating regions within the test range. In the low-angle region (0°-35°), the differential signal is more sensitive to angle changes, exhibiting a large response slope of 0.025. In the higher-angle range (35°-100°), the output still maintains a monotonically increasing trend, but the slope decreases to 0.005. This indicates that the double-sided asymmetric flexible strain sensor has higher resolution under small-angle bending conditions, while maintaining a stable and readable output over a larger bending range.

[0052] from Figure 3 It can be seen that there is a linear relationship between the bending angle and the sensitivity; when the bending angle is 0°-35°, y1=0.025x1+0.528, where y1 is the sensitivity and x1 is the bending angle; when the bending angle is 35°-100°, y2=0.005x2+0.220, where y2 is the sensitivity and x2 is the bending angle.

[0053] pass Figure 4 The resistance drift behavior of the two channels of the double-sided asymmetric flexible strain sensor under a 60° static bending condition for 2 hours can be observed. It can be seen that during the long holding period, both the folded and planar structural surfaces exhibit a slow upward trend. The linear fitting results in the figure also show that the fitting slopes of both the structural surface and the planar channel are positive, indicating that the drift directions are consistent.

[0054] pass Figure 5 As can be seen, under a small-angle bending condition of 5°, both the wrinkled and planar channels of the double-sided asymmetric flexible strain sensor can output clear and distinguishable resistance response signals. The resistance of the planar channel changes from 2.092 Ω to 2.072 Ω, corresponding to a drift error of approximately 0.95%; the resistance of the wrinkled channel changes from 3.160 Ω to 3.303 Ω, corresponding to a drift error of approximately 4.52%. During short-duration low-angle bending, both channels maintain a relatively stable output platform, indicating that the device has good readability under small-amplitude bending input.

[0055] pass Figure 6 It can be seen that the bifacial asymmetric flexible strain sensor exhibits good cyclic stability under a 3° bending condition. After approximately 140 consecutive cyclic loading cycles, the response amplitudes of the channels on both the folded and planar structural surfaces did not show significant attenuation, and the output waveform remained stable, indicating that the bifacial asymmetric flexible strain sensor still possesses good repeatability and cyclic consistency under repeated bending conditions.

[0056] pass Figure 7 It can be seen that as the bending angle increases from 0° to 100° and then returns, both channels exhibit a certain degree of loading / unloading path deviation, but the overall hysteresis level is low. The hysteresis errors of the folded structure surface channel and the planar structure surface channel are approximately 7.0% and 6.6%, respectively, indicating that the double-sided asymmetric flexible strain sensor has relatively controllable hysteresis behavior over a wide angle range.

[0057] pass Figure 8 As can be seen, as the bending angle increases from 30°, 60°, and 90° to 120°, both channels exhibit clear stepwise response changes, and different angles correspond to different steady-state output platforms. This indicates that the double-sided asymmetric flexible strain sensor can not only distinguish discrete bending states, but also has good angle resolution over a wide angle range.

[0058] pass Figure 9 It can be seen that under a 20° bending condition, the double-sided asymmetric flexible strain sensor exhibits a fast response and recovery process, with a response time of approximately 0.2 s and a recovery time of approximately 0.1 s. This result indicates that the device can quickly follow external bending inputs and recover to its initial state after unloading, meeting the basic real-time requirements for finger movement monitoring.

[0059] pass Figure 10 It can be seen that under small angle inputs of 1°, 2°, 3°, and 4°, both channels can provide identifiable resistance perturbation signals, and the responses corresponding to different angles are somewhat distinguishable. This indicates that the device is not only suitable for detecting larger finger bends, but also has the ability to perceive minute movements, which is of great significance for fine gesture recognition and subtle motion capture.

[0060] pass Figure 11 It can be seen that the differential output behavior of the double-sided asymmetric flexible strain sensor is observed in both bending directions. During the reverse bending process (normal finger bending), the differential signal gradually increases with the bending angle, exhibiting a continuous and discernible response output. However, during forward bending, the differential signal remains at a low level, showing little change with the angle. This input-output relationship is formally similar to the rectification effect.

[0061] Example 3 The purpose of this example is to demonstrate the practicality of a bifacial asymmetric flexible strain sensor as a differential signal angle sensor: A double-sided asymmetric flexible strain sensor was integrated into a smart glove system, and a virtual reality interaction platform was constructed to verify its application feasibility in human-computer interaction scenarios. The wearer outputs finger flexion information in real time through the glove, which is then mapped to hand movements on the virtual interface, thereby enabling the grasping and releasing of virtual objects. The double-sided asymmetric flexible strain sensor is fixed to the finger joints on the back side of the robotic hand, with the pleated structure surface close to the finger side of the back of the hand.

[0062] pass Figure 12 A schematic diagram of the signal acquisition and control process for the smart glove is provided. The resistance signals output from the five finger channels are read by the acquisition circuit, converted into corresponding control commands, and transmitted to the virtual interactive interface. By comprehensively judging the output status of each channel, the virtual hand movements are mapped.

[0063] pass Figure 13 Six consecutive action frames from the virtual grasping video are presented, corresponding to selecting an object, touching the object, grasping the object, holding in the air, releasing the object, and the object landing. These processes demonstrate that the smart glove can complete a relatively complete grasping task chain.

[0064] pass Figure 14 The output differences of the five finger channels during the six action phases were further summarized. It can be seen that different actions correspond to different multi-channel response combinations. During the contact, grasping, and holding phases, the output levels of the multiple finger channels are significantly different from the initial selection or release states. After release, the channel signals gradually return to a lower bending level.

[0065] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A bifacial asymmetric flexible strain sensor, characterized in that, It comprises three layers: an upper conductive layer, a middle substrate, and a lower conductive layer; the upper conductive layer is a conductive silver paste layer with a wrinkled structure; the substrate is polydimethylsiloxane; and the lower conductive layer is a conductive silver paste layer with a smooth structure.

2. The bifacial asymmetric flexible strain sensor as described in claim 1, characterized in that, The thickness of the upper conductive layer is 300 mm. -400 The substrate thickness is 1000. -1500 The thickness of the lower conductive layer is 300. -400 .

3. The bifacial asymmetric flexible strain sensor as described in claim 1, characterized in that, The folded structure is a flexor muscle-like structure resembling a finger joint.

4. The method for fabricating the bifacial asymmetric flexible strain sensor as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) After mixing polydimethylsiloxane and curing agent, stir evenly and remove air bubbles in the mixed solution by vacuuming to obtain a mixed solution; (2) Pour the mixed solution into the mold, then solidify it, peel off the film, and the resulting film has a wrinkled structure on one side and a smooth structure on the other side; (3) Plasma cleaning is performed on both surfaces of the thin film to obtain the substrate; (4) Apply a layer of conductive silver paste evenly to both sides of the substrate and then cure it to obtain a double-sided asymmetric flexible strain sensor.

5. The method for fabricating the bifacial asymmetric flexible strain sensor as described in claim 4, characterized in that, The mass ratio of polydimethylsiloxane to curing agent is 12:

1.

6. The method for fabricating the bifacial asymmetric flexible strain sensor as described in claim 4, characterized in that, In step (2), the curing temperature is 60-80℃ and the curing time is 1 hour.

7. The method for fabricating the bifacial asymmetric flexible strain sensor as described in claim 4, characterized in that, In step (3), O2 plasma cleaning is used for 10 minutes.

8. The method for fabricating the bifacial asymmetric flexible strain sensor as described in claim 4, characterized in that, In step (4), the curing temperature is 120-150℃ and the time is 30min.

9. The application of the biplane asymmetric flexible strain sensor according to any one of claims 1-3 as a rectifier and differential signal angle sensor.

10. The application as described in claim 9, characterized in that, Specifically, when the upper conductive layer of the double-sided asymmetric flexible strain sensor faces upward, and the sensor receives an upward bending force, the double-sided asymmetric flexible strain sensor is used as a differential signal angle sensor; when the sensor receives a downward bending force, the double-sided asymmetric flexible strain sensor is used as a rectifier.

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