Preparation method and application of multifunctional flexible sensor

Abstract

The invention relates to the technical field of sensor preparation, and discloses a preparation method and application of a multifunctional flexible sensor. According to the flexible sensor provided by the invention, through the innovative design of the flexible material, a sensing solution which is high in sensitivity, quick in response and easy to integrate is realized. The preparation method comprises the following steps: preparing the flexible pressure sensing layer, and preparing a PVDF-HFP / [EMIM] [TFSI] micro-dome dielectric layer and a TPU micro-dome film electrode by adopting a polyvinyl alcohol (PVA) anti-micro-dome template; preparing a flexible humidity sensing layer, namely preparing an Au interdigital electrode and a Cu (OH) 2 humidity sensitive layer by taking polyimide (PI) as a substrate; and finally assembling the two layers to form the multifunctional flexible sensor. The sensor has the advantages of high sensitivity, quick response and good stability and repeatability, can be applied to the fields of gesture recognition and intelligent control, intelligent health monitoring, environment monitoring and the like, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor preparation, and in particular to a preparation method and application of a multifunctional flexible sensor. Background Art

[0002] With the development of intelligent technology, the application of sensors in various fields has gradually expanded, especially in intelligent health monitoring, environmental monitoring, flexible electronic devices, etc., and the demand for sensors is increasing. To meet higher performance requirements, traditional sensors face new challenges in response speed, sensitivity, and adaptability. Especially in some complex environments, a single type of sensor often cannot meet the multi-dimensional monitoring needs simultaneously.

[0003] Humidity and pressure are two critical parameters that influence device performance and environmental conditions in many applications. For example, in smart wearable devices, robotics, and environmental monitoring systems, changes in humidity and pressure are often closely correlated with changes in the object's state. Most existing sensors can only detect humidity or pressure separately, lacking efficient solutions capable of simultaneous humidity and pressure detection. This results in unmet requirements for sensitivity, accuracy, response speed, and multifunctional integration, which in turn impacts the performance and intelligence of related applications.

[0004] In this context, the development of a flexible sensor that integrates multimodal detection functions of humidity and pressure strain has important commercial value in terms of high sensitivity, fast response, and easy integration. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for preparing and applying a multifunctional flexible sensor. The aim is to propose a humidity-pressure dual-mode sensor through innovative design of flexible materials. The sensor can simultaneously sense changes in humidity and pressure, and due to its microstructure and materials, it has high sensitivity and response speed, providing more accurate sensing solutions for applications such as intelligent control and environmental monitoring.

[0006] The multifunctional flexible sensor preparation method and application provided by the present invention include the following steps: S1. Preparation of flexible pressure sensing layer: S1.1. Preparation of polyvinyl alcohol (PVA) reverse micro-dome template; S1.2, preparing a polytetrafluoroethylene-hexafluoropropylene / 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide (PVDF-HFP / [EMIM][TFSI]) micro-dome dielectric layer on the reverse template; S1.3. Prepare a thermoplastic polyurethane (TPU) micro-dome thin film electrode on the dielectric layer to form a capacitive pressure strain sensor; S2. Preparation of flexible humidity sensing layer: S2.1, using polyimide PI as the sensor substrate; S2.2. Fabricate gold (Au) interdigital electrodes on a PI substrate. The corrosion resistance and oxidation resistance of Au make it highly stable in chemical solutions such as sodium hydroxide and ammonium persulfate, making it less likely to react with them. S2.3. Copper hydroxide (Cu(OH)2) is prepared as a humidity-sensitive layer on the interdigitated electrodes to form a resistive humidity sensor. The hydroxyl groups of the Cu(OH)2 material can stably adsorb water molecules, and its nanowire structure increases the specific surface area, providing more water molecule adsorption sites, thereby achieving high humidity sensitivity. S3. Assembly of multifunctional flexible sensor: The upper electrode of the TPU / Ag electrode layer in the flexible pressure sensing layer is placed below the PI substrate in the flexible humidity sensing layer, and the pressure sensitive layer is placed below the upper electrode and above the lower electrode.

[0007] Preferably, when preparing the polytetrafluoroethylene-hexafluoropropylene / 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide (PVDF-HFP / [EMIM][TFSI]) micro-dome dielectric layer, an ionic liquid is used as the dielectric layer to form a double electric layer to improve the capacitance response.

[0008] Preferably, the flexible pressure sensing layer adopts an interlocking microstructure to reduce the initial contact area between the dielectric layer and the electrode layer, increase the area change after being subjected to force, and thus improve the sensitivity of the sensor.

[0009] Preferably, the microstructure is a micro-pointed dome structure.

[0010] The present invention proposes a multifunctional flexible sensor, which is prepared by the above-mentioned preparation method. The structure of the multifunctional flexible sensor is as follows from top to bottom: a humidity sensitive layer, an interdigitated electrode layer, a PI substrate and an isolation layer, a TPU / Ag electrode layer, a PVDF-HFP / [EMIM][TFSI] pressure sensitive layer, and a TPU / Ag electrode layer.

[0011] The present invention proposes an application of a multifunctional flexible sensor, which is integrated on a glove for application in gesture recognition and intelligent control, as well as in intelligent health monitoring and environmental monitoring scenarios.

[0012] Compared with related technologies, the multifunctional flexible sensor preparation method and application provided by the present invention have the following beneficial effects: The flexible sensor prepared by the multifunctional flexible sensor preparation method proposed in the present invention can simultaneously detect pressure, strain and humidity information, meet the needs of multi-dimensional monitoring in complex environments, has high sensitivity and rapid response capabilities, and can monitor environmental changes in real time; after multiple tests, the sensor has shown good stability and repeatability, ensuring long-term use; the sensor adopts a flexible design and is easy to integrate into various flexible electronic devices, and has broad application prospects; in addition, the preparation process of this method is simple, easy to control, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 3D schematic diagram of the overall device in Example 1 of the present invention; Figure 2 Flow chart of the preparation of the capacitive pressure strain sensor in Example 1 of the present invention; FIG3 (a) is a scanning electron microscope (SEM) image of the surface of the PVDF-HFP dielectric layer of the device in Example 1 of the present invention; FIG3 (b) is a SEM image of a 45° inclined surface of the PVDF-HFP dielectric layer of the device in Example 1 of the present invention; Figure 4 This is a SEM image of the electrode layer in Example 1 of the present invention; Figure 5 This is a flow chart of the preparation of the resistive humidity sensor in Example 2 of the present invention; Figure 6 This is a SEM image of the humidity sensitive layer in Example 2 of the present invention; Figure 7 (a) and (b) show the responses to different normal loading pressures in Example 1 of the present invention; Figure 8 : is a sensitivity comparison diagram of different sensor structures in this embodiment 1; Figure 9 Response of Example 1 of the present invention to different bending angles; Figure 10 This is a bending stability test of about 6,000 times for Example 1 of the present invention; Figure 11 This is a diagram of some gesture recognition signals in Example 3 of the present invention; Figure 12 Response curve diagram of the humidity sensor to different relative humidity in Example 2 of the present invention; Figure 13 This is a graph showing the recovery time of the humidity sensor in response to humidity changes in Example 2 of the present invention; Figure 14 The sensor prepared in Example 2 of the present invention detects oral and nasal breathing.

[0014] Figure numerals: 1. humidity sensitive layer; 2. interdigitated electrode layer; 3. PI substrate; 4. TPU / Ag electrode layer; 5. PVDF-HFP / [EMIM][TFSI] pressure sensitive layer. DETAILED DESCRIPTION

[0015] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] The purpose of the present invention is to provide a multifunctional flexible sensor capable of detecting pressure strain and humidity information and its application.

[0017] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] See Figure 1 The flexible sensor structure proposed in the present invention is composed of a humidity sensitive layer 1, an interdigitated electrode layer 2, a PI substrate and an isolation layer 3, a TPU / Ag electrode layer 4, a PVDF-HFP / [EMIM][TFSI] pressure sensitive layer 5, and a TPU / Ag electrode layer 4 from top to bottom. The TPU / Ag electrode layer and the pressure sensitive layer are prepared using a secondary template method, and the template is a micro-pointed dome sapphire template.

[0019] In order to more clearly describe the technical route and advantages of the present invention, the present invention is described and explained in more detail below with reference to the accompanying drawings.

[0020] Example 1 This embodiment introduces the preparation process of the flexible pressure sensing layer. Figure 2 As shown, it includes: reverse template preparation, electrode layer preparation, and dielectric layer preparation. Based on the above scheme, multiple specific implementation schemes of flexible pressure sensors are given.

[0021] Specific implementation plan 1 includes the following process: Reverse template preparation Step (1) 3 g of polyvinyl alcohol (PVA) was dissolved in 17 g of deionized water, and heated and stirred on a magnetic stirrer at 95° C. for 10 h to prepare a PVA transparent solution with a mass fraction of 15%.

[0022] Step (2) The PVA solution was evenly coated on the micro-dome sapphire template, heated and dried at 65 ° C for 1 h, and the reverse template was obtained after separation; In the preparation of the dielectric layer, PVDF-HFP polymer is mainly used as the main matrix, and [EMIM][TFSI] ionic liquid is uniformly mixed in the matrix. The upper surface has a micro-pointed dome structure to enhance the capacitance change rate. As shown in Figure 3 (a, b), the surface of the dielectric layer film has a regular arrangement of protrusions with a diameter of about 2㎛ and a height of about 2㎛. Specifically: Step (3) PVDF-HFP particles were dissolved in DMF solution, and [EMIM][TFSI] ionic liquid was added, and heated and stirred at 60 ° C on a magnetic stirrer for 4 h to obtain a PVDF-HFP / [EMIM][TFSI] / DMF mixed solution; Step (4) uniformly coating the PVDF-HFP / [EMIM][TFSI] / DMF mixed solution on the reverse template, heating and drying at 60° C. for 2 h, evaporating the DMF solution, and separating to obtain a micro-dome ionic capacitor layer.

[0023] In the preparation of the electrode layer, Figure 4 As shown in the figure, the micro-dome TPU film is covered by a layer of Ag, proving that the electrode layer is successfully prepared. Step (5) dissolving the TPU particles in a DMF / THF mixed solution to obtain a TPU solution with a mass fraction of 10 wt%; Step (6) uniformly coating the TPU solution on the sapphire counter template, heating and drying at 60° C. for 2 h, and peeling off to obtain a micro-dome TPU film; Step (7) silver is plated on the surface of the micro-dome TPU film by magnetron sputtering to obtain a micro-dome electrode.

[0024] The difference between the specific implementation scheme 2 and the specific implementation scheme 1 is that the dielectric layer prepared in step (4) adopts a planar template; The difference between the specific implementation scheme 3 and the specific implementation scheme 1 is that a flat template is used when preparing the electrode layer in step (6); Specific implementation scheme 4 is different from specific implementation scheme 1 in that the dielectric layer and electrode layer prepared in step (4) and step (6) adopt a planar template.

[0025] Example 2 This embodiment introduces the preparation process of the flexible humidity sensing layer. Figure 5 As shown, it includes: preparation of interdigital electrode layer, preparation of Cu(OH)2 precursor, and preparation of Cu(OH)2 sensing layer. Based on the above scheme, several specific implementation schemes of flexible pressure sensor are given.

[0026] Step (1) using polyimide (PI) as a substrate, covering it with a mask, and depositing Au interdigital electrodes on the PI substrate using magnetron sputtering technology; Step (2) remove the mask and again use magnetron sputtering to deposit Cu on the Au interdigital electrodes as; Step (3) 270 mg of NaOH and 61.5 mg of (NH4)2S2O8 solution were added to 15 ml of deionized water; Step (4) immersing the copper-plated interdigitated electrode in the mixed solution prepared in step (3) above for about 10 minutes; Step (5) After washing with deionized water, the Cu(OH)2 humidity sensor is obtained. The SEM image of its sensing layer is as follows: Figure 6 As shown, the structure is in the shape of a nanowire.

[0027] In step (6), the flexible pressure-capacitive sensor prepared by implementing solution 1 in Example 1 is placed below the sensor prepared in steps (1-4) in Example 2, and packaged into a multifunctional flexible sensor.

[0028] Example 3 Based on Examples 1 and 2, this example provides a process for fabricating a multifunctional flexible sensor. Au interdigital electrodes are fabricated on a PI substrate; a Cu(OH)2 humidity-sensitive layer is fabricated above the Au interdigital electrodes; a TPU / Ag top electrode is placed below the PI layer; and a pressure-sensitive layer is placed below the top electrode and above the bottom electrode.

[0029] Performance characterization: Figure 1 This is a three-dimensional schematic diagram of the dual-mode sensor. The device's capacitance response to different pressures and its current change to different relative humidity were tested. A voltage of 1 V was applied to the upper and lower electrodes of the flexible capacitive pressure sensor prepared in Example 1 to form a loop, and the capacitance in the loop was measured.

[0030] First, to measure the multimode sensor's performance in detecting normal pressure, Figures 7(a) and 7(b) show time on the horizontal axis and relative capacitance change on the vertical axis. Figures 7(a) and 7(b) show the stable capacitance response under different pressures, with three responses for each pressure, and the corresponding pressure above the peak. It can be seen that: 1. Under the same pressure, the device has a stable response capacitance, with a high repetition rate of the waveform, and small capacitance fluctuations when the same pressure is applied; 2. Under different pressures, the capacitance increases with increasing pressure, indicating that the capacitance increases with increasing pressure and the capacitance change is stable. Figure 8The sensitivity curves of each specific solution of Example 1 to pressure are shown, where specific solution 1 is named "Sensor1", specific solution 2 is named "Sensor2", specific solution 3 is named "Sensor3", and specific solution 4 is named "Sensor4". It can be seen that specific solution 1 with an interlocking micro-dome structure has the largest response and the highest sensitivity. Figure 8 It can be seen that the sensor disclosed in this embodiment has an extremely small detection limit (5 Pa), a wide detection range and high sensitivity.

[0031] Secondly, Example 1 also has the ability to accurately detect bending strain. Figure 9 This is the response diagram of Example 1 to three cycles of different bending angles of 15°, 25°, 35° and 45°, which proves that the sensor prepared in Example 1 has accurate resolution of the bending angle and excellent repeatability. Figure 10 This is a 90° bending cycle test of Example 1. It can be seen from the figure that the device response size remains basically consistent after about 6000 bending tests, and the device proves the long-term stability of the device.

[0032] In order to realize the application of sensor-based gesture recognition and intelligent control, sensors are integrated into gloves. Each sensor accurately captures hand movement information, and then uses the built-in high-speed signal conversion and processing unit to quickly convert analog signals into digital signals. It is then transmitted to the terminal in real time through efficient wireless transmission methods such as low-power Bluetooth. Figure 11 The glove demonstrates some gesture recognition signals. With simple, natural gestures like palm pressure, index finger tapping, or thumb and index finger pinching, the glove's pressure sensor, with its high sensitivity, quickly detects pressure changes and instantly transmits the signal to the smart home control system via the wireless transmission module. The control system, relying on a rich pre-stored instruction set, accurately identifies the gesture's corresponding operation, seamlessly enabling functions like turning on lights, adjusting the air conditioning temperature, and switching TV channels, allowing for seamless, intelligent home control.

[0033] Cu(OH)2 humidity sensors rely on the adsorption of water molecules to change resistance, thereby sensing humidity. At low humidity, water molecules primarily interact with hydroxyl groups on the Cu(OH)2 surface, forming a stable chemical adsorption layer. At high humidity, chemical adsorption sites become saturated, and physical adsorption becomes more pronounced, allowing more water molecules to adhere to the surface through weak interactions (such as van der Waals forces).

[0034] In order to measure the performance of the humidity sensor prepared in Example 2, a voltage of 1 V was applied across the interdigital electrodes and the output current of the device was measured. Figure 12The current changes of the humidity sensor under different relative humidity (RH) are shown. The horizontal axis is time, and the vertical axis is the current when a 1V voltage is applied across the electrodes. The sensor has a clear gradient response and high sensitivity to different relative humidity. Figure 13 The humidity sensor demonstrated fast response and recovery times of 1.5s and 2.5s at 29% RH and 75% RH, respectively. The flexible humidity sensor fabricated in this invention exhibits high relative humidity resolution and fast response time, demonstrating its ability to deliver exceptional performance in numerous key areas. Figure 14 The sensor is placed at the mouth and nose to detect oral and nasal breathing based on the different humidity intensities exhaled from the mouth and nose, and at the same time detect the frequency of humidity changes to accurately monitor the respiratory rate.

[0035] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a multifunctional flexible sensor, characterized in that: The following steps are involved: S1. Preparation of flexible pressure sensing layer: S1.1, preparing a polyvinyl alcohol (PVA) reverse micro-dome template; S1.2, preparing a polytetrafluoroethylene-hexafluoropropylene / 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide (PVDF-HFP / [EMIM][TFSI]) micro-dome dielectric layer on the reverse template; S1.3, preparing a thermoplastic polyurethane elastomer (TPU) micro-dome thin film electrode on the dielectric layer to form a capacitive pressure strain sensor; S2. Preparation of flexible humidity sensing layer: S2.1, using polyimide PI as the sensor substrate; S2.2, preparing metallic gold (Au) interdigital electrodes on a PI substrate; S2.

3. Preparing copper hydroxide (Cu(OH)2) as a humidity sensitive layer on the interdigitated electrodes to form a resistive humidity sensor; S3. Assembly of multifunctional flexible sensor: The upper electrode of the TPU / Ag electrode layer in the flexible pressure sensing layer is placed below the PI substrate in the flexible humidity sensing layer, and the pressure sensitive layer is placed below the upper electrode and above the lower electrode.

2. The method for preparing a multifunctional flexible sensor according to claim 1, wherein: In the preparation of polytetrafluoroethylene-hexafluoropropylene / 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide (PVDF-HFP / [EMIM][TFSI]) micro-dome dielectric layers, ionic liquids were used as dielectric layers to form a double electric layer to enhance the capacitive response.

3. The method for preparing a multifunctional flexible sensor according to claim 1, wherein: The flexible pressure sensing layer adopts an interlocking microstructure to reduce the initial contact area between the dielectric layer and the electrode layer, increase the area change after being subjected to force, and thus improve the sensitivity of the sensor.

4. The method for preparing a multifunctional flexible sensor according to claim 3, wherein: The microstructure is a micro-pointed dome structure.

5. A multifunctional flexible sensor, characterized in that: The multifunctional flexible sensor is prepared by the preparation method of the multifunctional flexible sensor described in any one of claims 1 to 4 above, and the structure of the multifunctional flexible sensor is, from top to bottom: a humidity sensitive layer, an interdigitated electrode layer, a PI substrate and an insulating layer, a TPU / Ag electrode layer, a PVDF-HFP / [EMIM][TFSI] pressure sensitive layer, and a TPU / Ag electrode layer.

6. Application of a multifunctional flexible sensor, characterized in that: The multifunctional flexible sensor is integrated on the glove for application in gesture recognition and intelligent control, as well as in intelligent health monitoring and environmental monitoring scenarios.

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