Capacitive flexible dual-mode sensor based on composite sensitive material

Abstract

The application belongs to the technical field of capacitive flexible sensors, and particularly relates to a capacitive flexible bimodal sensor based on a composite sensitive material, which comprises a flexible sensing layer, a flexible insulating layer and an electrode layer; the flexible sensing layer is a composite structure of an HPMC / PEDOT:PSS / AgNPs composite material and a polyurethane sponge; the flexible insulating layer is a PDMS film; the electrode is composed of conductive cloth and has a wire leading-out and interlayer adhesion function; the capacitive flexible bimodal sensor is provided, and the core lies in that through the synergistic effect of an HPMC / PEDOT:PSS / AgNPs ternary composite system and a polyurethane sponge, bimodal sensing of pressure and proximity is realized.

Description

Technical Field

[0001] This invention belongs to the field of capacitive flexible sensor technology, specifically a capacitive flexible dual-mode sensor based on composite sensitive materials. Background Technology

[0002] Traditional single-mode pressure sensors can only provide a single type of pressure information, which cannot meet the complex and ever-changing needs of practical applications. For example, in the field of smart homes, traditional sensors have limited functionality and are difficult to achieve multi-dimensional interaction. Dual-mode sensors, on the other hand, can simultaneously sense the approach of an object and the pressure it is subjected to, enabling home devices to automatically adjust their status based on proximity and pressure levels, thus improving the intelligence and convenience of the home. In smart wearable devices, people have increasingly higher demands for the functionality and user experience of these devices. Proximity sensing can detect changes in distance from the human body, while pressure sensing can monitor the force applied during movement. The combination of the two can provide users with more accurate health data and exercise feedback.

[0003] Currently, although there have been some research results on proximity / pressure sensing dual-mode sensors, the research on dual-mode sensors is still in its early stages, and there are still many challenges in material selection, structural design, and signal processing. In-depth research on pressure dual-mode sensors is of great theoretical and practical significance for improving sensor performance and promoting technological progress in related fields. Therefore, this invention provides a capacitive flexible dual-mode sensor based on composite sensitive materials. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention selects a complementary HPMC / PEDOT:PSS / AgNPs composite material and employs a simple impregnation process to immerse the composite material in a polyurethane seam. The sensor constructed in this manner not only achieves sensing responses to both proximity and pressure signals but also effectively avoids the use of additional sensing device components. Furthermore, within the composite material, AgNPs, while a high dielectric constant material, are difficult to adhere to the surface of the dielectric layer. Introducing HPMC can both disperse AgNPs and assist in their adhesion to the dielectric layer surface. The introduction of PEDOT:PSS forms hydrogen bonds with HPMC, simultaneously enhancing the mechanical and electrical properties of the film. The synergistic effect of these components endows the sensor with excellent proximity and pressure detection capabilities. Such flexible electronic devices hold promise for providing multimodal sensing modes for precision monitoring and motion sensing applications.

[0005] The technical solution adopted by this invention to solve its technical problem is: a capacitive flexible dual-mode sensor based on composite sensitive materials, comprising:

[0006] Flexible sensing layer: The flexible sensing layer is a composite structure of HPMC / PEDOT:PSS / AgNPs composite material and polyurethane foam;

[0007] Flexible insulating layer: The flexible insulating layer is a PDMS film;

[0008] Electrode layer: The electrode is made of conductive cloth and has the functions of wire lead-out and interlayer adhesion.

[0009] Preferably, the raw materials for preparing the flexible sensing layer are in the following mass ratio: PEDOT:PSS:AgNPs:HPMC = 3:1:0.8:0.8, wherein HPMC is dissolved in deionized water to form a 5wt% aqueous matrix.

[0010] Preferably, PDMS and curing agent are mixed at a mass ratio of 10:1, poured into a 3D-printed 1×1.5×0.1cm cuboid template, cured at room temperature for 3 hours, and then peeled off to obtain a PDMS film with a thickness of 0.1cm.

[0011] A method for fabricating a capacitive flexible dual-mode sensor based on composite sensitive materials, applicable to a capacitive flexible dual-mode sensor based on composite sensitive materials, includes the following steps:

[0012] Step 1: Add 40 mg HPMC to 8 mL of deionized water and stir at 1000 rpm until completely dissolved to form a 5 wt% HPMC aqueous matrix; add AgNPs:PEDOT:PSS to the matrix at a mass ratio of 1:3 (i.e., 50 mg AgNPs, 150 mg PEDOT:PSS), and continue stirring at 1000 rpm for 1 h to obtain a uniformly dispersed composite solution;

[0013] Step 2: Immerse a polyurethane sponge with a size of 1×1.5cm into the composite solution, rotate it at 50rpm for 1 hour at room temperature, remove it and place it in a vacuum drying oven, dry it at 60℃ for 5 hours to obtain a flexible sensing layer loaded with composite sensitive material.

[0014] Step 3: Using a layer-by-layer self-assembly technique, stack the layers in the following order: "PDMS insulating layer - conductive cloth - PDMS insulating layer - conductive cloth - flexible sensing layer - conductive cloth - PDMS insulating layer". Leave a 0.2cm margin at the edge of the conductive cloth for wire soldering, and lead out the electrode signal through the wire.

[0015] Preferably, in the composite solution, PEDOT:PSS and HPMC enhance the mechanical properties of the film through hydrogen bonding, and AgNPs are uniformly dispersed in the HPMC matrix to improve the dielectric constant.

[0016] Preferably, it is capable of simultaneously sensing pressure signals from 0 to 66.6 kPa (sensitivity ≥ 0.5 kPa for 0-10 kPa). -1 (and 0-20cm proximity signal, response time ≤37.5ms.)

[0017] The beneficial effects of this invention are as follows:

[0018] 1. The present invention discloses a capacitive flexible dual-mode sensor based on composite sensitive materials. Silver nanoparticles, as a type of metal particle with a high dielectric constant, have the disadvantage of being easy to aggregate and difficult to adhere. The present invention introduces HPMC to assist in their dispersion and adhesion to the surface of the dielectric layer. After the HPMC adheres to the surface of the dielectric layer and dries, it forms a thin film. The mechanical properties of this thin film are poor. By using PEDOT:PSS to form hydrogen bonds with HPMC, the electromechanical properties of the thin film are improved.

[0019] 2. The present invention discloses a capacitive flexible dual-mode sensor based on composite sensitive materials. The present invention employs a simple layer-by-layer (LBL) self-assembly technique and a simple dip-coating and drying process; HPMC / PEDOT:PSS / AgNPs composite material is adhered to the surface of polyurethane foam; based on such material and structural foundation, the dual-mode sensor prepared by the present invention exhibits significant advantages such as high sensitivity and fast response time.

[0020] 3. The capacitive flexible dual-mode sensor based on composite sensitive materials described in this invention combines the sensor with a keypad password, utilizing the sensor's ability to identify proximity to simultaneously collect signals from four sensors; this assists in determining the entered password, greatly improving the accuracy of keypad password recognition. Attached Figure Description

[0021] The invention will now be further described with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 This is a schematic diagram of the dual-mode sensor manufacturing process;

[0024] Figure 3 It is a mechanical simulation of the porous structure of a sponge substrate;

[0025] Figure 4 These are SEM images of a flexible dielectric layer at different resolutions.

[0026] Figure 5 It is a diagram showing the interaction relationships between different materials;

[0027] Figure 6 yes Figure 3 Experimental verification diagram of the pressure sensitivity of the dual-mode sensor;

[0028] Figure 7 yes Figure 3 The response time curves of the dual-mode sensor sensing different pressure magnitudes;

[0029] Figure 8 yes Figure 3 The response curves of the dual-mode sensor for sensing different compression frequencies and different pressure intensities;

[0030] Figure 9 This is a simulation diagram of the electrostatic field of the sensing mechanism for non-contact signal sensing in this invention.

[0031] Figure 10 yes Figure 9 Response curves for proximity of the dual-mode sensor;

[0032] Figure 11 yes Figure 9 Response curves of the dual-mode sensor at different proximity distances;

[0033] Figure 12 yes Figure 9 The response curves of the dual-mode sensor sensing different proximity frequencies. Detailed Implementation

[0034] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0035] This invention provides a multifunctional flexible sensor. Figure 1 This is a structural diagram of the sponge and nanocomposite material after assembly provided in the embodiments of the present invention.

[0036] For details, please refer to Figure 1 Using a simple layer-by-layer (LBL) self-assembly technique, materials are assembled... Figure 1 The components are assembled in sequence, and the conductive cloth wrapped with the flexible insulating layer is led out using wires to serve as the test wires of the sensor.

[0037] This invention provides a multifunctional sensor. Figure 2 The preparation method of this invention includes the following steps:

[0038] Step 1: Add 150 mg of PEDOT:PSS and 50 mg of AgNPs to 8 ml of deionized water. While stirring, add 40 mg of HPMC particles and continue stirring for 1 h to form a uniformly dispersed composite solution. Add 1×1.5 cm of polyurethane sponge and stir for 1 h. After drying, a flexible dielectric layer is obtained.

[0039] Step 2: Use 3D printing to make a 1×1.5×0.1 cm template. Mix PDMS and curing agent evenly in a 10:1 ratio and add them to the printed template. Let it stand for 3 hours to allow it to fully cure and then peel it off to obtain a flexible insulating layer.

[0040] Step 3: Cut the conductive cloth to a size of 1×1.5 cm, and use the adhesiveness of the conductive cloth to attach the wires between the two layers of PDMS as the electrode layer of the capacitive sensor.

[0041] Figure 3 Qualitative analysis of the mechanical structure of the porous sponge substrate was performed using COMSOL software. Figure 3 As can be seen, when the dodecahedral structure of the sponge faces external pressure, the connecting skeleton from the top to the middle bears the main stress. As the pressure increases further, the upper part still bears the main pressure, but the middle to the bottom also begins to bear pressure. The overall structure is evenly stressed and suitable for use as a dielectric layer in sensors.

[0042] Figure 4 Here are SEM images of the dielectric layer before and after impregnation; from Figure 4 As can be seen from 'a', the sponge skeleton before impregnation exhibits... Figure 3 The dodecahedral structure shown contains numerous voids, which helps to impregnate the sponge with as much composite material as possible; from Figure 4 As can be seen from b, the surface of the impregnated sponge undergoes significant changes due to the HPMC film, which also facilitates the adhesion of the composite material within the sponge; from Figure 4 As can be seen from c, silver nanoparticles, as metals, adhere to the HPMC film in a granular form. PEDOT:PSS is uniformly dispersed in the HPMC film, presenting a smooth and flat surface. These three materials are effectively attached to the surface of the sponge skeleton. Figure 4 In the figure, d represents the elemental spectrum of the sponge skeleton surface. It can be seen from the figure that the surface of the sponge skeleton is covered with a large amount of uniform S element, which is unique to PEDOT:PSS and can verify the uniform dispersion of PEDOT:PSS. At the same time, the surface of the sponge skeleton is also rich in a large amount of uniform Ag element.

[0043] Figure 5The interaction between the composite materials was presented. First, AgNPs, as metal nanoparticles, have the characteristic of easily agglomerating, which makes it difficult for silver nanoparticles to be uniformly attached to the surface of the dielectric layer. To solve this problem, HPMC was added. HPMC, as a macromolecular polysaccharide, can effectively disperse AgNPs and prevent their aggregation. However, the HPMC film formed after drying has weak mechanical properties. By introducing PEDOT:PSS to form hydrogen bonds with HPMC, the mechanical properties of the HPMC film can be effectively improved.

[0044] Figure 6 This is a sensitivity curve shown in a specific embodiment of the present invention when subjected to pressures ranging from 0 to 66.6 kPa; where sensitivity is represented by S, S=(ΔC / C0) / ΔP, ΔC=C0-C P Here, C0 represents the initial capacitance value of the sensor, C P The capacitance value under pressure is represented by ΔP, which represents the relative pressure change. The sensitivity of this device is mainly divided into two stages: the first stage is from 0 kPa to 10 kPa, with a sensitivity of approximately 0.5115 kPa. -1 The second stage, ranging from 10 kPa to 66.6 kPa, has a sensitivity of approximately 0.1188 kPa. -1 In the first stage, as pressure is applied, the dielectric layer of the sensor is compressed, resulting in a decrease in the spacing between the capacitor electrodes. Simultaneously, because the air inside the sponge is expelled during compression, the sponge interior is occupied by AgNPs with high dielectric constants, leading to an increase in the dielectric constant of the dielectric layer. The combined effect of these two effects results in higher sensitivity for the sensor in the first stage. In the second stage, since the air is largely eliminated, the bending of the internal framework of the dielectric layer transforms into compression, while the dielectric constant remains unchanged, resulting in lower sensitivity for the sensor in the second stage. The results indicate that the fabricated sensor exhibits good sensitivity within a small pressure range.

[0045] Figure 7 The specific experimental procedure for testing the response time of the sensor to capacitance changes under different pressures is as follows: First, the sampling interval of the measuring tool was switched to fast mode. Then, the response of the sensor to capacitance signals under different pressure conditions of 3.3 kPa, 6.6 kPa, and 20 kPa was tested. Analysis of the experimental data shows that the sensor exhibits a fast response characteristic of 25 ms-37.5 ms and a fast recovery characteristic of 25 ms-62.5 ms to different pressures.

[0046] Figure 8The cyclic response characteristics of the sensor's capacitance change rate under different pressure conditions and corresponding to different pressure frequencies were explained. The specific experimental procedure is detailed below: First, the sensor was applied sequentially with initial pressures of 3.3 kPa, 6.6 kPa, and 20 kPa. Then, the capacitance signals generated when a constant pressure was applied to the sensor at different frequencies of 50 mm / min, 100 mm / min, and 200 mm / min were detected. Analysis of the experimental data showed that the capacitance change of the sensor accelerated with increasing frequency. This indicates that the sensor's capacitance response is largely unaffected by compression frequency interference and exhibits good pressure resolution.

[0047] Figure 9 This is the mechanism by which a dual-mode sensor identifies proximity. When no object is nearby, the electrostatic field around the sensor is uniform, pointing downwards. When an object approaches the top of the sensor, the approaching object forms a new capacitor with the upper electrode of the sensor. This capacitor is composed of the object as the upper electrode, air as the dielectric layer, and the upper electrode of the sensor as the lower electrode. The formation of the new capacitor weakens the capacitance of the sensor, causing an edge field effect. This effect becomes more pronounced when the object gets closer. This effect manifests as a decrease in the capacitance value of the sensor.

[0048] Figure 10 This paper presents the response curves of a dual-mode sensor to iron sheets at different distances from 0 to 20 cm. The specific experimental procedure is as follows: a 1×1 cm iron sheet is fixed to the compression arm of a universal testing machine. The distance between the compression arm and the sensor is reduced to the initial position shown in the figure. Then, the compression arm is moved further away from the sensor to perform the corresponding detection. The results show that the prepared sensor has good recognition ability for the gradual movement of the robotic arm with the fixed square patch away, which is consistent with... Figure 9 The simulation results are consistent.

[0049] Figure 11 To investigate the accuracy of capacitance changes in a robotic arm at different proximity levels when it approaches and moves away at the same frequency, the specific experimental procedure is detailed below: First, the sensor and the robotic arm are placed in their initial state. The robotic arm is then controlled to move upwards by 1 cm, 2 cm, and 3 cm sequentially from the initial position at a speed of 50 mm / min, and then return. Each movement distance is repeated four times. The results show that the sensor has a stable response when recognizing different proximity levels at the same frequency.

[0050] Figure 12To investigate the accuracy of capacitance changes in a robotic arm when it approaches and moves away at different frequencies at the same proximity, the specific experimental procedure is detailed below: First, the sensor and robotic arm are placed in their initial state. The robotic arm is then controlled to move upward by 1 cm at three different speeds of 50 mm / min, 100 mm / min, and 200 mm / min in a predetermined sequence, and then return. Each movement distance is repeated four times. The results show that the sensor has a stable response when recognizing different frequencies at the same proximity.

[0051] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A capacitive flexible dual-mode sensor based on composite sensitive materials, characterized in that, include: Flexible sensing layer: The flexible sensing layer is a composite structure of HPMC / PEDOT:PSS / AgNPs composite material and polyurethane foam; The composite material is prepared from a composite solution consisting of HPMC, PEDOT:PSS and AgNPs. In the composite solution, PEDOT:PSS and HPMC enhance the mechanical properties of the film through hydrogen bonding, and AgNPs are uniformly dispersed in the HPMC matrix to improve the dielectric constant. Flexible insulating layer: The flexible insulating layer is a PDMS film; Electrode layer: The electrode is made of conductive cloth and has the functions of wire lead-out and interlayer adhesion.

2. The capacitive flexible dual-mode sensor based on composite sensitive materials according to claim 1, characterized in that: The raw materials for preparing the flexible sensing layer are PEDOT:PSS:AgNPs = 3:1 by mass, wherein HPMC is dissolved in deionized water to form a 5wt% aqueous matrix.

3. The capacitive flexible dual-mode sensor based on composite sensitive materials according to claim 1, characterized in that: PDMS and curing agent were mixed at a mass ratio of 10:1 and poured into a 3D-printed 1×1.5×0.1cm cuboid template. After curing at room temperature for 3 hours, the mixture was peeled off to obtain a PDMS film with a thickness of 0.1cm.

4. A method for fabricating a capacitive flexible dual-mode sensor based on a composite sensitive material, the method being applicable to the capacitive flexible dual-mode sensor based on a composite sensitive material as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Add 40 mg HPMC to 8 mL of deionized water and stir at 1000 rpm until completely dissolved to form a 5 wt% HPMC aqueous matrix; add AgNPs:PEDOT:PSS in a mass ratio of 1:3, i.e., 50 mg AgNPs and 150 mg PEDOT:PSS, and continue stirring at 1000 rpm for 1 hour to obtain a uniformly dispersed composite solution. Step 2: Immerse a polyurethane sponge with a size of 1×1.5cm into the composite solution, rotate it at 50rpm for 1 hour at room temperature, remove it and place it in a vacuum drying oven, dry it at 60℃ for 5 hours to obtain a flexible sensing layer loaded with composite sensitive material. Step 3: Using a layer-by-layer self-assembly technique, the PDMS film in claim 3 is cut into 1×1.5cm conductive cloth. Then, the flexible sensing layer obtained in step 2 is stacked in the following order: "PDMS film - conductive cloth - PDMS film - conductive cloth - flexible sensing layer - conductive cloth - PDMS film - conductive cloth - PDMS film". A 0.2cm margin is left at the edge of the conductive cloth for wire bonding, and electrode signals are led out through the wires.

5. The method for fabricating a capacitive flexible dual-mode sensor based on composite sensitive materials according to claim 4, characterized in that: Capable of simultaneously sensing pressure signals from 0 to 66.6 kPa, with a sensitivity of ≥0.5 kPa from 0 to 10 kPa. -1 ; 0-20cm proximity distance signal and response time ≤37.5ms.

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