A flexible strain-humidity dual-mode sensor and its fabrication method

Abstract

This invention discloses a method for fabricating a flexible strain-humidity dual-mode sensor and the sensor itself. The fabrication method includes the following steps: S1, preparing a PVA / phosphate composite ion gel as a humidity-sensitive dielectric layer; S2, preparing a nanocellulose and graphene composite film as a flexible strain-sensing electrode; S3, integrating the ion gel and graphene electrode using interface bonding and silver paste electrode bonding processes; S4, assembling to form a sandwich-type parallel plate capacitor architecture dual-mode sensor. This invention achieves the integrated design of resistive strain sensing and capacitive humidity sensing, solving the industry problems of insufficient information dimensions in traditional single-mode sensors and signal aliasing and crosstalk in multi-mode sensors from a structural design perspective. It can simultaneously and independently acquire dual-dimensional physiological signals of respiratory airflow pressure and humidity, with high device integration and good signal decoupling effect, breaking through the core technical bottleneck of wearable respiratory monitoring.

Description

Technical Field

[0001] This invention belongs to the field of flexible sensor technology, specifically, it relates to a method for preparing a flexible strain-humidity dual-mode sensor and the sensor itself. Background Technology

[0002] Flexible wearable sensing technology has significant application value in respiratory health monitoring, chronic disease management, and daily health assessment. Among these, respiratory monitoring, as a non-invasive diagnostic method, is particularly crucial for early warning and rehabilitation tracking of diseases such as chronic obstructive pulmonary disease and bronchial asthma. Traditional respiratory monitoring devices mostly rely on single physical quantity sensing modules or use large medical equipment to acquire signals through chemical detection, single mechanical / humidity sensing, or other methods.

[0003] Traditional single-mode respiratory sensors can only capture limited information such as respiratory rhythm, making it difficult to simultaneously acquire multi-dimensional physiological parameters such as exhaled gas dynamics and humidity. Furthermore, multi-mode sensors generally suffer from signal aliasing and crosstalk issues, resulting in insufficient detection accuracy and failing to meet the needs of systematic assessment of local respiratory pathologies and overall health status. Therefore, developing highly integrated, crosstalk-resistant dual-mode sensing technology has become crucial to overcoming existing monitoring bottlenecks.

[0004] Currently, most wearable respiratory monitoring devices fail to achieve coordinated acquisition of multiple physical field parameters and are limited by material properties and structural design, resulting in shortcomings in system integration, long-term stability, and clinical applicability. The airflow pressure and humidity signals of exhaled gases naturally carry respiratory system and overall health information, but existing designs do not fully utilize the synergistic correlation characteristics of these two parameters, limiting the specificity and accuracy of disease diagnosis and hindering the transformation from a "passive diagnosis and treatment" to a "proactive prevention" health management model.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] To overcome the shortcomings of traditional single-mode sensors in simultaneously acquiring multi-dimensional respiratory physiological parameters, solve the problems of signal crosstalk and low detection accuracy in multi-mode sensing devices, and improve the mechanical flexibility, cyclic stability and clinical suitability of flexible respiratory sensors, this invention provides a method for preparing a flexible strain-humidity dual-mode sensor and the sensor itself.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for fabricating a flexible strain-humidity dual-mode sensor, comprising the following steps: S1. Prepare PVA / phosphate composite ionogel as a humidity-sensitive dielectric layer; S2. Prepare a composite film of nanocellulose and graphene as a flexible strain sensing electrode. S3. An interface bonding and silver paste electrode bonding process is used to integrate the ion gel and graphene electrode. S4. Assemble a dual-mode sensor to form a sandwich-type parallel plate capacitor architecture.

[0008] In a preferred embodiment, in step S1, the ratio of the composite ion gel is PVA powder: 85wt.% phosphoric acid solution: deionized water = 1g: 0.825mL: 9g.

[0009] In a preferred embodiment, the composite ionogel preparation process is as follows: PVA powder is dissolved in deionized water, then phosphoric acid solution is added, stirred and dissolved at 90°C, filtered, and then vacuum dehydrated and crosslinked at room temperature for 24 hours to cure.

[0010] In a preferred embodiment, in step S2, the mass ratio of the composite film is 4.4 wt.% nanocellulose solution: 5 wt.% graphene slurry: deionized water = 1:1:3.

[0011] In a preferred embodiment, the composite film preparation process is as follows: after mixing the raw materials, stir them evenly at 65°C, perform oxygen plasma hydrophilic treatment on the PDMS substrate, and form a flexible conductive electrode by spraying with a spray gun.

[0012] In a preferred embodiment, in step S3, the silver paste electrode is connected in the following manner: silver paste electrodes are connected to both sides of the lower graphene composite film, and silver paste electrodes are connected to one side of the upper graphene composite film.

[0013] In a preferred embodiment, in step S4, the sensor assembly structure is a sandwich stack structure of substrate-graphene electrode-ion gel-graphene electrode-substrate, which is cured and integrated by standing at room temperature for 3 days after assembly.

[0014] Secondly, the present invention provides a flexible strain-humidity dual-mode sensor prepared by the above-described preparation method.

[0015] In a preferred embodiment, the sensor has an initial resistance of 8kΩ ± 1kΩ and an initial capacitance of 16pF ± 2pF.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention achieves the first integrated application of resistive strain sensing and capacitive humidity sensing through a complete process of PVA / phosphate composite ion gel preparation, nanocellulose-graphene composite thin film electrode preparation, interface integration and sandwich architecture assembly. It solves the industry problems of insufficient information dimension of traditional single-mode sensors and signal aliasing and crosstalk of multi-mode sensors from the structural design perspective. It can synchronously and independently collect dual-dimensional physiological signals of respiratory airflow pressure and humidity. The device has high integration and good signal decoupling effect, breaking through the core technical bottleneck of wearable respiratory monitoring. 2. This invention employs precisely defined raw material ratios, standardized preparation processes, and reliable electrode bonding technology. The composition ratio of ion gel and composite film is scientifically controllable. The oxygen plasma hydrophilic treatment, spray film formation, side-by-side silver paste bonding, and room temperature curing process not only ensure the bonding strength, conductivity stability, and performance uniformity of the sensitive layer and electrode layer, but also simplify the preparation steps, reduce the process difficulty, and significantly improve the mechanical flexibility and interface adhesion of the device, making it adaptable to repeated deformations in flexible wearable scenarios. 3. The sensor of this invention has stable initial electrical parameters, excellent detection performance and practical scene adaptability. The dual-mode signal is independently acquired without interference. It responds accurately and outputs stably within the target strain and humidity range. It also has good cycle durability and long-term working reliability. The device can be directly attached to the inner surface of a mask and can accurately capture respiratory characteristic signals. It provides a stable solution for daily monitoring and early warning of respiratory diseases and has extremely high practical value in the field of wearable health management. Attached Figure Description

[0017] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of an ion gel preparation process provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a graphene composite thin film electrode spraying process provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a silver paste electrode bonding process provided in an embodiment of the present invention; Figure 4 This is a flowchart of a dual-mode sensor assembly structure provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a dual-mode sensor structure provided in an embodiment of the present invention; Figure 6This is a physical image of a dual-mode sensor provided in an embodiment of the present invention; Figure 7 This is a graph showing the initial resistance and capacitance measurement data of a dual-mode sensor provided in an embodiment of the present invention; Figure 8 This is a test diagram of the tensile strain sensing performance of a dual-mode sensor provided in an embodiment of the present invention; Figure 9 This is a humidity sensing performance test diagram of a dual-mode sensor provided in an embodiment of the present invention; Figure 10 This is a tensile cycle stability test diagram of a dual-mode sensor provided in an embodiment of the present invention; Figure 11 This is a humidity retention stability test diagram of a dual-mode sensor provided in an embodiment of the present invention.

[0018] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0020] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] Reference Figures 1 to 5 This invention provides a method for fabricating a flexible strain-humidity dual-mode sensor, the specific steps of which are as follows: Preparation of S1, PVA / phosphate composite ion gel ( Figure 1 ) The ingredients were prepared according to the mass-to-volume ratio of PVA powder: phosphoric acid solution: deionized water = 1g: 0.825mL: 9g, with the phosphoric acid solution concentration being 85wt.%. Weigh 8g of PVA powder and add 72g of deionized water. Heat to 90℃ and stir magnetically for 2-3 hours until completely dissolved to obtain a PVA solution. Cool the PVA solution to 50°C, add 6.6 mL of 85 wt.% phosphoric acid solution, and stir continuously for 2 hours; The solution was filtered through cotton cloth, and the filtrate was placed in a vacuum drying oven at room temperature for dehydration and cross-linking for 24 hours to obtain a composite ion gel.

[0023] S2, Preparation of composite thin film electrodes of nanocellulose and graphene ( Figure 2 ) The nanocellulose solution, graphene slurry, and deionized water were mixed in a mass ratio of 1:1:3, with a nanocellulose solution concentration of 4.4 wt.% and a graphene slurry concentration of 5 wt.%. Weigh 10g of nanocellulose solution and 10g of graphene slurry, mix them, slowly add 30g of deionized water, and stir evenly at 65℃ to obtain a composite dispersion. Oxygen plasma hydrophilic treatment is applied to the PDMS substrate to improve film adhesion; The composite dispersion was uniformly sprayed onto the PDMS substrate 10 times using an airbrush to form a fully covered flexible conductive composite thin film electrode.

[0024] S3, Silver paste electrode overlap ( Figure 3 ) Conductive silver paste is coated on both sides of the lower PDMS-graphene electrode and on one side of the upper PDMS-graphene electrode. The silver electrode wires are overlapped with the silver paste area and cured by heating at a low temperature of 60~80℃ to form electrode leads with low contact resistance.

[0025] This overlapping method is simple in process, has low contact resistance, and can adapt to the deformation of flexible devices, laying the foundation for subsequent connection to external circuits and the realization of reliable signal transmission.

[0026] S4, Device Assembly ( Figure 4 ) The composite ion gel was uniformly spread on the surface of the lower PDMS-graphene electrode. Align the PDMS-graphene electrode covering the top layer to form a sandwich stacked structure; The sensor was left to stand at room temperature for 3 days to allow the ionogel to fully solidify and bond tightly to the electrode interface, thus completing the sensor fabrication.

[0027] This process enables the highly integrated construction of a strain-humidity dual-mode sensing unit in a single flexible system, and lays the device foundation for wearable respiratory monitoring applications.

[0028] Figure 5 This is the device structure of the present invention. Figure 6 This is a physical image of the device of the present invention. Figure 7 These are the initial resistance and capacitance values ​​tested in this invention. As shown in the figure, its structure employs a sandwich-style layered design: the upper and lower layers are PDMS flexible substrates, with graphene composite films prepared on the surface of each substrate as electrodes via spraying; the middle layer is a composite ionogel dielectric layer formed by cross-linking polyvinyl alcohol (PVA) with phosphoric acid; the graphene composite film electrodes are electrically led out by coating and curing silver paste. In its initial state (no strain, standard humidity environment), the device has a specific reference resistance value of 8kΩ±1kΩ and a reference capacitance value of 16pF±2pF, corresponding to the initial resistance of the graphene composite film electrode and the initial capacitance of the ionogel dielectric layer, respectively. This provides a decoupled monitoring reference for resistance changes caused by strain and capacitance changes caused by humidity, achieving highly integrated, low-crosstalk dual-mode sensing functionality.

[0029] Figure 8 The figure shows the time-resistance change rate curve of the tensile strain test of the device in this invention. Tensile strain testing was performed on the device to evaluate its tensile performance. The figure illustrates the resistance change at four different degrees of stretching within the range of 4% to 10%. Here, "degree of stretching" is defined as the ratio of the deformed length of the strain sensor to its original length (with the deformation direction consistent with the original length direction). The vertical axis represents the rate of change of resistance after stretching relative to the initial resistance. The results show that the sensor fabricated based on this design exhibits stable response characteristics within the strain range of 4% to 10%.

[0030] Figure 9 The figure shows the humidity-capacitance change rate curve of the device in this invention, obtained through humidity response testing to evaluate its humidity monitoring performance. The figure illustrates the capacitance change of the device within a relative humidity range of 30% to 80%. The vertical axis represents the rate of change of capacitance value at different humidity levels relative to the initial capacitance at 30% RH. Experimental results show that the sensor fabricated based on this design exhibits stable response within a relative humidity range of 30% to 80%, demonstrating good monitoring consistency.

[0031] Figure 10 The time-resistance change rate curve of the tensile strain test is the result of the long-term stability test in this invention. After 600 cycles of 15% tensile strain, the electrical performance of the device remains relatively stable, showing good cycle durability.

[0032] Figure 11This figure shows the humidity response performance of the device in this invention under long-term stability testing, specifically the capacitance change curves over time in different humidity environments. The figure presents the capacitance-time response curves of the device for five consecutive days under relative humidity conditions of 30%, 50%, and 80%. The test results show that after five days of continuous monitoring, the capacitance response of the device remained basically stable, verifying its good long-term operational reliability.

[0033] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for fabricating a flexible strain-humidity dual-mode sensor, characterized in that, Includes the following steps: S1. Prepare PVA / phosphate composite ionogel as a humidity-sensitive dielectric layer; S2. Prepare a composite film of nanocellulose and graphene as a flexible strain sensing electrode. S3. An interface bonding and silver paste electrode bonding process is used to integrate the ion gel and graphene electrode. S4. Assemble a dual-mode sensor to form a sandwich-type parallel plate capacitor architecture.

2. The preparation method according to claim 1, characterized in that: In step S1, the ratio of the composite ion gel is PVA powder: 85wt.% phosphoric acid solution: deionized water = 1g: 0.825mL: 9g.

3. The preparation method according to claim 2, characterized in that, The composite ionogel preparation process is as follows: PVA powder is dissolved in deionized water, then phosphoric acid solution is added, stirred and dissolved at 90°C, filtered, and then vacuum dehydrated and crosslinked at room temperature for 24 hours to cure.

4. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of the composite film is 4.4 wt.% nanocellulose solution: 5 wt.% graphene slurry: deionized water = 1:1:

3.

5. The preparation method according to claim 4, characterized in that, The composite film preparation process is as follows: after mixing the raw materials, stir at 65°C until uniform, perform oxygen plasma hydrophilic treatment on the PDMS substrate, and form a flexible conductive electrode by spraying with a spray gun.

6. The preparation method according to claim 1, characterized in that, In step S3, the silver paste electrode is connected in the following manner: silver paste electrodes are connected to both sides of the lower graphene composite film, and silver paste electrodes are connected to one side of the upper graphene composite film.

7. The preparation method according to claim 1, characterized in that: In step S4, the sensor assembly structure is a sandwich stack structure of substrate-graphene electrode-ion gel-graphene electrode-substrate, which is cured and integrated by standing at room temperature for 3 days after assembly.

8. A flexible strain-humidity dual-mode sensor prepared by the preparation method according to any one of claims 1-7.

9. The sensor as described in claim 8, characterized in that: The sensor has an initial resistance of 8kΩ±1kΩ and an initial capacitance of 16pF±2pF.

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