Micro fiber type capacitive humidity sensor and preparation method thereof

Abstract

The invention provides a micro fiber type capacitive humidity sensor and a preparation method thereof. The micro fiber type capacitive humidity sensor structurally comprises a copper wire, and the diameter of the copper wire is smaller than 0.15 mm; the insulating layer integrally covers the copper wire to form an enamelled copper wire, the enamelled copper wire is twisted to form a twisted enamelled copper wire through a twisting process, and a capacitor electrode is formed; and the humidity sensitive medium integrally coats the outer side of the twisted enameled copper wire through an impregnation process. The size of the cross section of the micro fiber type capacitive humidity sensor is smaller than 0.045 mm < 2 >, and the micro fiber type capacitive humidity sensor has the advantages of being bendable and high in sensitivity, and the application scene of the humidity sensor can be widened.

Description

Technical Field

[0001] The present invention relates to the technical field of humidity sensors, and particularly to a microfiber capacitive humidity sensor and a preparation method thereof. Background Art

[0002] Humidity sensors have been widely used in fields such as agricultural production, industrial production, human living environment, and cultural relic protection. Existing humidity sensors mainly include capacitive, resistive, etc. Among them, capacitive humidity sensors have advantages such as good stability, fast response speed, low cost, easy maintenance, and easy miniaturization and integration, and have been widely used in commercial fields. The common structures of capacitive humidity sensors include flat type and interdigital type. The flat capacitive humidity sensor has certain limitations in application due to the relatively small contact area between its humidity-sensitive medium and the environment. In contrast, the interdigital capacitive humidity sensor has become the most widely used form of capacitive humidity sensors due to its larger contact area with the environment and the larger contact area between electrodes.

[0003] Although the interdigital capacitive humidity sensor has been widely used due to its advantages, its size is still relatively large, which limits further miniaturization and the expansion of related applications. For example, taking the interdigital capacitive humidity sensor mentioned by Ganbold E, Kim ES, Li Y, etc. [1] as an example, its structure mainly consists of a substrate, metal electrodes, and a humidity-sensitive layer. The width of the metal electrodes of this sensor is 0.1 mm, and the width between the electrodes is also 0.1 mm. Due to its multi-finger structure design, the final size of the sensor reaches 7.75 mm × 4.1 mm × 0.7 mm, and the cross-sectional area is approximately 2.87 mm 2 . The thickness of the sensor is mainly determined by the substrate, and the presence of the substrate also makes the interdigital capacitive humidity sensor usually not flexible, which further limits its potential in flexible application scenarios. Therefore, developing a humidity sensor that is both miniaturized and flexible is expected to significantly expand its application range.

[0004] Fiber-type capacitors achieve further reduction in the size of the capacitor and endow the capacitor with flexible characteristics by directly using conductive fibers to construct the capacitor structure, eliminating the use of traditional substrates. Recently, there have been relevant reports on the use of fiber-type capacitors in the field of humidity sensing.

[0005] Ma L, Wu R, Patil A, etc. [2]A new fiber-type capacitive humidity sensor using hygroscopic polyester fiber Kanglun as the humidity-sensitive dielectric layer is reported. The preparation method of the sensor is to wrap the Kanglun fiber between two copper wires. The excellent hygroscopicity of Kanglun fiber gives the sensor a high sensitivity of 82.4pF / %RH. However, the diameter of the copper wire used in this study is relatively large, and the spacing between the two copper wires is the diameter of the Kanglun fiber, which limits the possibility of further reducing the size of the sensor by reducing the spacing. In addition, the sensor exhibits large hysteresis, which has an adverse effect on the accurate calibration of humidity in practical applications.

[0006] Zhao H, Han K, Li Y et al. [3] A method for preparing a humidity sensor is reported in which two copper wires are twisted after introducing a humidity-sensitive dielectric material polyimide / poly(glycidyl methacrylate) on the surface of the copper wire. The humidity sensor has low hysteresis. However, the humidity-sensitive dielectric layer also serves as an insulating layer. The polyimide itself is not sensitive to moisture, which makes the sensitivity of the sensor only 0.029pF / %RH, limiting its use. In addition, the lateral size of the sensor is 0.6mm, which is still relatively macroscopic. Although the size of the copper wire can be reduced to achieve the purpose of reducing the size of the sensor, further reduction in the size of the sensor will further reduce the sensitivity and further limit its application.

[0007] Therefore, the technical problem that needs to be solved urgently is: how to make the humidity sensor have high sensitivity while further reducing the size of the sensor and expanding the application field of the humidity sensor.

[0008] References

[0009] 1.Ganbold E, Kim ES, Li Y, et al. Highly Sensitive Interdigitated Capacitive Humidity Sensors Based on Sponge-Like Nanoporous PVDF / LiClComposite for Real-Time Monitoring[J]. ACS AppliedMaterials&Interfaces, 2023,15(3):4559–4568.

[0010] 2. Ma L, Wu R, Patil A, et al. Full-Textile Wireless Flexible Humidity Sensor for Human Physiological Monitoring[J]. Advanced Functional Materials, 2019, 29(43).

[0011] 3. Zhao H, Han K, Li Y. Strip-type flexible capacitive humidity sensor based on composite of polyimide and poly(glycidyl methacrylate): Fabrication, humidity sensitive performance and potential for detecting water content in liquids[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2023, 675: 132092. Summary of the Invention

[0012] The present invention is made to solve the above problems, and aims to provide a microfiber capacitive humidity sensor and a preparation method thereof.

[0013] The present invention provides a microfiber capacitive humidity sensor, which has the following characteristics: including a copper wire; an insulating layer, the insulating layer entirely covers the copper wire to form an enameled copper wire, and the enameled copper wire is obtained in the form of a twisting process to get a twisted enameled copper wire, which constitutes the capacitor electrode; and a humidity-sensitive medium, the humidity-sensitive medium is entirely coated on the outside of the twisted enameled copper wire through an impregnation process.

[0014] In the microfiber capacitive humidity sensor provided by the present invention, it may also have the following characteristics: wherein, the diameter of the copper wire is 0.001 mm to 0.15 mm.

[0015] In the microfiber capacitive humidity sensor provided by the present invention, it may also have the following characteristics: wherein, the material of the insulating layer is a polymer material, and the insulating layer is one of polyimide, polyester, polyurethane, polyvinyl chloride and polypropylene.

[0016] In the microfiber capacitive humidity sensor provided by the present invention, it may also have the following characteristics: wherein, the twisting number of the twisting process is greater than 30 twists / m.

[0017] In the microfiber capacitive humidity sensor provided by the present invention, it may also have the following characteristics: wherein, the humidity-sensitive medium is a composite material, one phase of the humidity-sensitive medium is a polymer phase, and one phase is a non-polymer phase.

[0018] In the microfiber capacitive humidity sensor provided by the present invention, it may also have the following characteristics: wherein, the polymer phase is cellulose, and the cellulose is one of polyvinyl alcohol, polyacrylic acid, and polyacrylamide.

[0019] In the microfiber capacitive humidity sensor provided by the present invention, it may also have the following characteristics: wherein, the non-polymer phase is one of graphene oxide, barium titanate, titanium dioxide, and zinc oxide.

[0020] The present invention also provides a preparation method for a microfiber capacitive humidity sensor, which specifically includes the following steps: Step S1, using an insulating polymer to coat a copper wire to form an insulated enameled copper wire; Step S2, obtaining a twisted enameled copper wire by twisting the enameled copper wire and assembling it into a capacitor electrode; Step S3, modifying the twisted enameled copper wire using a plasma method to obtain a modified twisted enameled copper wire; Step S4, dissolving two humidity-sensitive materials in an aqueous solution and compounding them to obtain an aqueous solution of the humidity-sensitive medium; Step S5, immersing the modified twisted enameled copper wire in the aqueous solution of the humidity-sensitive medium, taking it out and drying it after immersion; Step S6, if the aqueous solution of the humidity-sensitive medium cannot coat the twisted enameled copper wire after immersion, perform multiple immersions.

[0021] Functions and effects of the invention

[0022] According to the microfiber capacitive humidity sensor and its preparation method involved in the present invention, the following beneficial effects are achieved: the cross-sectional size of the humidity sensor of the present invention is less than 0.045 mm 2 , and it can adapt to a wider range of application scenarios; the fiber-type design of the present invention that does not require a planar substrate endows the sensor with good bendability and can be woven; the composite humidity-sensitive medium material used in the present invention endows the sensor with the advantages of high sensitivity and low hysteresis. Description of the drawings

[0023] Figure 1 is the preparation method of the microfiber capacitive humidity sensor in Embodiments 1-3 of the present invention;

[0024] Figure 2 is the cross-sectional structure diagram of the microfiber capacitive humidity sensor of the present invention in Embodiments 1-3;

[0025] Figure 3 is the humidity response performance of the microfiber capacitive humidity sensor in Embodiment 1 of the present invention;

[0026] Figure 4 is the humidity response performance of the microfiber capacitive humidity sensor according to Embodiment 2 of the present invention; and

[0027] Figure 5 is the humidity response performance of the microfiber capacitive humidity sensor according to Embodiment 3 of the present invention. Detailed Embodiments

[0028] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication with each other; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0029] In order to make the technical means, creative features, achieved purposes, and functions of the present invention easy to understand, the following embodiments will specifically describe the microfiber capacitive humidity sensor of the present invention and its preparation method in conjunction with the accompanying drawings.

[0030] Figure 1 is the preparation method of the microfiber capacitive humidity sensor in Embodiments 1-3 of the present invention. Figure 2 is the cross-sectional structure diagram of the microfiber capacitive humidity sensor of the present invention in Embodiments 1-3.

[0031] As Figure 1-2 shown, the microfiber capacitive humidity sensor 100 in this embodiment includes a copper wire, an insulating layer, and a humidity-sensitive medium.

[0032] The diameter of the copper wire 30 is 0.05 mm.

[0033] The material of the insulating layer 20 of the insulating layer 20 is polyester, and the whole covers the copper wire 30 to form an enameled copper wire 30. The enameled copper wire 30 is obtained in the form of a twisting process to obtain a twisted enameled copper wire 30, which constitutes the capacitor electrode. The twisting number of the twisting process is 1200 twists / m.

[0034] The humidity-sensitive medium 10 is integrally coated on the outside of the twisted enameled copper wire 30 through an impregnation process.

[0035] The humidity-sensitive medium 10 is a composite material, one phase of which is a polymer phase and one phase is a non-polymer phase.

[0036] Among them, the polymer phase is cellulose and the non-polymer phase is graphene oxide.

[0037] In this embodiment, the preparation method of the microfiber capacitive humidity sensor 100 specifically includes the following steps:

[0038] Step S1: Use an insulating polymer polyester to coat the copper wire 30 to form an insulated enameled copper wire 30.

[0039] Step S2: Twist the enameled copper wire 30 by a twisting method with a twisting number of 1200 twists / m to obtain a twisted enameled copper wire 30, and assemble it into a capacitor electrode.

[0040] Step S3: Modify the twisted enameled copper wire 30 using a plasma method to obtain a modified twisted enameled copper wire 30.

[0041] Step S4: Dissolve two humidity-sensitive materials, cellulose and graphene oxide, in an aqueous solution and compound them to obtain a humidity-sensitive medium aqueous solution.

[0042] Step S5: Immerse the modified twisted enameled copper wire 30 in the humidity-sensitive medium aqueous solution, and take it out and dry it after immersion.

[0043] Step S6: Repeat the immersion 4 times.

[0044] Embodiment Two

[0045] Compared with Embodiment One, in this embodiment, the diameter of the copper wire 30 is 0.1 mm.

[0046] For the sake of easy expression, in this embodiment, the same symbols are given to the same structures as in Embodiment One, and the same descriptions are omitted.

[0047] Embodiment Three

[0048] Compared with Embodiment One, in this embodiment, the diameter of the copper wire 30 is 0.1 mm, and the polymer phase in the humidity-sensitive medium 10 is polyvinyl alcohol.

[0049] In the preparation method of the microfiber capacitive humidity sensor 100, Step S4 is replaced with:

[0050] Dissolve two humidity-sensitive materials, polyvinyl alcohol and graphene oxide, in an aqueous solution and compound them to obtain a humidity-sensitive medium aqueous solution.

[0051] For the sake of easy expression, in this embodiment, the same symbols are given to the same structures as in Embodiment One, and the same descriptions are omitted.

[0052] Figure 3 It is the humidity response performance of the microfiber capacitive humidity sensor in Embodiment 1 of the present invention. Figure 4 It is the humidity response performance of the microfiber capacitive humidity sensor in Embodiment 2 of the present invention.Figure 5 It is the humidity response performance of the microfiber capacitive humidity sensor in Embodiment 3 of the present invention. Table 1 is a summary of the performance of the microfiber capacitive humidity sensors in each embodiment.

[0053] Table 1

[0054]

[0055] As Figure 3-5 shown in and Table 1, the sensitivities of the microfiber capacitive humidity sensors 100 in Embodiments 1-3 are 0.20 pF / %RH, 0.53 pF / %RH, and 0.45 pF / %RH respectively, which are all much greater than the sensitivities of the humidity sensors in the prior art, and the size of the microfiber capacitive humidity sensor 100 is smaller.

[0056] The cross-sectional size of the microfiber capacitive humidity sensor 100 in Embodiment 1 is less than 0.005 mm 2 , and at the same time, the microfiber capacitive humidity sensors 100 in Embodiments 1-3 all have excellent flexibility and weavability.

[0057] Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A microfiber capacitive humidity sensor, characterized in that, Including: Copper wire; An insulating layer, the insulating layer entirely covers the copper wire to form an enameled copper wire, and the enameled copper wire is twisted to obtain a twisted enameled copper wire through a twisting process, which constitutes the capacitor electrode; And A humidity-sensitive medium, the humidity-sensitive medium is integrally coated on the outer side of the twisted enameled copper wire through an impregnation process.

2. The microfiber capacitive humidity sensor according to claim 1, wherein: Among them, The diameter of the copper wire is 0.001 mm to 0.15 mm.

3. The microfiber capacitive humidity sensor according to claim 1, wherein: Among them, The material of the insulating layer is a polymer material, and the insulating layer is one of polyimide, polyester, polyurethane, polyvinyl chloride and polypropylene.

4. The microfiber capacitive humidity sensor according to claim 1, wherein: Among them, The twisting number of the twisting process is greater than 30 twists / m.

5. The microfiber capacitive humidity sensor according to claim 1, wherein: Among them, The humidity-sensitive medium is a composite material, and one phase of the humidity-sensitive medium is a polymer phase and one phase is a non-polymer phase.

6. The microfiber capacitive humidity sensor according to claim 5, wherein: Among them, The polymer phase is cellulose, and the cellulose is one of polyvinyl alcohol, polyacrylic acid and polyacrylamide.

7. The microfiber capacitive humidity sensor according to claim 5, wherein: Among them, The non-polymer phase is one of graphene oxide, barium titanate, titanium dioxide and zinc oxide.

8. A preparation method of the microfiber capacitive humidity sensor as described in claim 1, characterized in that, Specifically, it includes the following steps: Step S1, using an insulating polymer to coat the copper wire to form an insulated enameled copper wire; Step S2, twisting the enameled copper wire to obtain a twisted enameled copper wire and assembling it into a capacitor electrode; Step S3, using a plasma method to modify the twisted enameled copper wire to obtain a modified twisted enameled copper wire; Step S4, dissolving two humidity-sensitive materials in an aqueous solution and compounding them to obtain a humidity-sensitive medium aqueous solution; Step S5, putting the modified twisted enameled copper wire into the humidity-sensitive medium aqueous solution for impregnation, and taking it out and drying it after impregnation; Step S6, if after impregnation, the humidity-sensitive medium aqueous solution cannot cover the twisted enameled copper wire, then perform multiple impregnations.

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