Humidity monitoring sensor based on Joule thermal characteristics and preparation method

Abstract

The invention discloses a Joule thermal characteristic-based humidity monitoring sensor and a preparation method thereof, and relates to the technical field of wireless humidity monitoring. The main body structure is a device structure combining the controllable heating layer of the laser-induced graphene and the graphene oxide humidity-sensitive layer of the porous structure, the processes such as a laser direct writing technology, a template method and dispensing are mainly adopted, a complex preparation process is not needed, the preparation cost is reduced, the structure is simple, and the cost is low; electrical signal transmission is not needed, wireless humidity monitoring is achieved based on the Joule heat principle and by means of a Joule heat effect humidity monitoring method through the influence of humidity on temperature, namely, temperature change is detected by means of a thermal infrared imager, and electrical signal transmission is not needed.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless humidity monitoring, and specifically to a humidity monitoring sensor based on Joule heat characteristics and a preparation method thereof. Background Art

[0002] As a core device in the field of environmental monitoring, humidity sensors have important applications in meteorological monitoring, industrial production, agricultural greenhouses, and smart homes. Existing humidity sensing technologies based on electrical signals mainly include capacitive and resistive types. Capacitive sensors utilize the characteristic that the dielectric constant of humidity-sensitive materials (such as alumina, porous polymers) changes with humidity to measure the ambient relative humidity. Resistive humidity sensors monitor humidity based on the characteristic that the resistance value of certain materials (such as polymer films, metal oxides) changes with humidity. In recent years, the sensing mechanism based on the self-heating effect has become a research hotspot. It actively regulates the temperature through the Joule heat effect of materials, and can achieve in-situ temperature drift compensation. For example, materials such as graphene are used to construct self-heating sensors due to their high electrothermal conversion efficiency. However, in the prior art, the Joule heat effect is only used as an auxiliary temperature control means and has not been used for the technical development of environmental humidity monitoring.

[0003] Traditional humidity monitoring methods all have their own limitations. The measurement accuracy of capacitive humidity sensors is easily affected by factors such as temperature and electromagnetic interference; the response speed of resistive humidity sensors is relatively slow. In addition, these humidity monitoring methods need to rely on wired or wireless modules for signal transmission and are easily interfered by electromagnetic signals. There is an urgent need for a new humidity monitoring method to meet the application requirements of different scenarios.

[0004] Therefore, a new solution needs to be proposed for the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a humidity monitoring sensor based on Joule heat characteristics and a preparation method thereof to solve the problem that electrical-based humidity monitoring relies on wired or wireless modules for signal transmission.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a humidity monitoring sensor based on Joule heat characteristics, at least including the following steps:

[0007] S1: Use a small laser engraver to prepare a square laser-induced graphene layer on the surface of a polyimide film (PI) as a heating layer based on Joule heat;

[0008] S2: Cover a layer of fine salt on the surface of the heating layer, and evenly cover the uncured polydimethylsiloxane (PDMS) on the fine salt layer by drop coating. Use vacuum treatment to make it evenly penetrate the entire fine salt layer, and cure the polydimethylsiloxane in an 80°C oven. Cut off the excess polydimethylsiloxane on the surface of the heating layer;

[0009] S3: Put the sensor base combination prepared from the polyimide film, heating layer, and polydimethylsiloxane into hot water, so that the fine salt in the fine salt layer dissolves, thereby forming a porous layer with a microporous structure above the heating layer;

[0010] S4: Attach the graphene oxide liquid dispersion to the porous layer by repeated drop coating multiple times as a water vapor molecule adsorption layer, and prepare a humidity monitoring sensor based on the Joule heat characteristic.

[0011] Further, the thickness of the polyimide film is 125 μm, the size of the square laser-induced graphene layer is 1 cm * 2 cm, the power of the small laser engraver is set to 8% - 11% of the maximum power, and the engraving speed is set to 80 mm / s.

[0012] Further, the thickness of the fine salt layer is 2 mm - 4 mm.

[0013] Further, the concentration of the graphene oxide liquid is 5 mg / ml.

[0014] A humidity monitoring sensor based on the Joule heat characteristic is processed by a preparation method of a humidity monitoring sensor based on the Joule heat characteristic.

[0015] Further, a humidity monitoring sensor based on the Joule heat characteristic includes a polyimide film layer, a heating layer, and a porous humidity-sensitive layer. A heating layer is prepared on the upper surface of the polyimide film layer, and a porous humidity-sensitive layer is prepared on the surface of the heating layer away from the polyimide film layer;

[0016] The heating layer is heated by connecting a DC voltage to both ends of the laser-induced graphene heater, and the heating temperature can be effectively regulated by the voltage;

[0017] The porous humidity-sensitive layer forms a porous structure by the cooperation of the fine salt layer and polydimethylsiloxane; after the graphene oxide on the surface of the porous structure adsorbs water vapor molecules, it will affect the surface temperature distribution. Use an infrared thermal imager to obtain temperature data, so as to realize the monitoring of environmental humidity according to the change of temperature.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The main structure of the present invention is a device structure combining a controllable heating layer of laser-induced graphene and a porous graphene oxide humidity-sensitive layer. It mainly uses processes such as laser direct writing technology, template method, and drop coating. It does not require complex preparation processes, reduces the preparation cost, and has a simple structure and low cost.

[0020] 2. The present invention does not require electrical signal transmission. Based on the principle of Joule heat, a humidity monitoring method using the Joule heat effect realizes wireless humidity monitoring by the influence of humidity on temperature, that is, uses an infrared thermal imager to detect temperature changes without using electrical signal transmission.

[0021] 3. The humidity monitoring sensor based on the Joule heat characteristics proposed by the present invention has better performance in adapting to harsh environments and higher reliability. Since the heating method is adopted, it can effectively regulate its own temperature according to the environmental conditions, and solve the safety problems caused by factors such as dust and water vapor condensation in the environment on electronic devices leading to short circuits or leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 It is a schematic structural diagram of the whole of the present invention;

[0024] Figure 2 It is a schematic diagram of the working principle of the present invention;

[0025] Figure 3 It is a schematic diagram of the temperature change curve of the present invention with humidity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention.

[0027] The Joule heat effect refers to the phenomenon of heat energy generated due to resistance when an electric current passes through a conductor. By using the adsorption of water vapor molecules by certain materials (such as nanomaterials or composite materials) to affect the generation and distribution of Joule heat, the present invention proposes a new humidity monitoring method to realize wireless humidity monitoring by measuring the temperature change of the material after power-on.

[0028] Specific embodiments are proposed as follows:

[0029] Example 1:

[0030] A preparation method of a humidity monitoring sensor based on the Joule heat characteristic, at least including the following steps:

[0031] S1: Use a small laser engraver to prepare a square laser-induced graphene layer on the surface of a polyimide film (PI) as a heating layer based on Joule heat;

[0032] S2: Cover a layer of fine salt on the surface of the heating layer, and uniformly cover the fine salt layer with uncured polydimethylsiloxane (PDMS) by drop coating. Use vacuum treatment to make it uniformly penetrate the entire fine salt layer, and cure the polydimethylsiloxane in an 80 °C oven, and cut off the excess polydimethylsiloxane on the surface of the heating layer;

[0033] S3: Put the sensor base combination jointly prepared by the polyimide film, the heating layer and the polydimethylsiloxane into hot water, so that the fine salt in the fine salt layer dissolves, thereby forming a porous layer with a microporous structure above the heating layer;

[0034] S4: Attach the graphene oxide liquid dispersion to the porous layer by repeated drop coating for multiple times as a water vapor molecule adsorption layer, and prepare a humidity monitoring sensor based on the Joule heat characteristic.

[0035] The thickness of the polyimide film is 125 μm, the size of the square laser-induced graphene layer is 1 cm * 2 cm, the power of the small laser engraver is set to 8% - 11% of the maximum power, and the engraving speed is set to 80 mm / s.

[0036] The thickness of the fine salt layer is 2 mm - 4 mm.

[0037] The concentration of the graphene oxide liquid is 5 mg / ml.

[0038] Example two:

[0039] This example proposes a humidity monitoring sensor based on the Joule heat characteristic based on the above Example one, and is processed by a preparation method of a humidity monitoring sensor based on the Joule heat characteristic.

[0040] Refer to Figure 1 , a humidity monitoring sensor based on the Joule heat characteristic, including a polyimide film layer, a heating layer and a porous humidity-sensitive layer. A heating layer is prepared on the upper surface of the polyimide film layer, and a porous humidity-sensitive layer is prepared on the surface of the heating layer away from the polyimide film layer;

[0041] The heating layer is heated by connecting a DC voltage to both ends of the laser-induced graphene heater, and the heating temperature can be effectively regulated through the voltage;

[0042] Refer to Figure 2, the porous humidity-sensitive layer forms a porous structure by cooperating with the fine salt layer and polydimethylsiloxane; after the graphene oxide on the surface of the porous structure adsorbs water vapor molecules, it will affect the surface temperature distribution. The infrared thermal imager is used to obtain temperature data, so as to realize the monitoring of environmental humidity according to the change of temperature.

[0043] For further illustration, the following examples are given:

[0044] By controlling the voltage, the initial temperature is maintained at T0 under the humidity RH0, the environmental humidity is changed, the corresponding real-time temperature T1 on the surface is obtained, and according to the humidity-temperature curve (refer to Figure 3 ), the corresponding environmental humidity value is obtained.

[0045] In summary:

[0046] The present invention proposes a wireless humidity monitoring method based on the Joule heat effect, which solves the problem that the humidity monitoring method based on electricity depends on wired or wireless modules for signal transmission.

[0047] 1. The humidity monitoring method based on electricity depends on wired or wireless modules for signal transmission, resulting in / vulnerable to electromagnetic interference problems. The present invention monitors humidity based on the change of thermal signals by adopting the Joule heat effect, without the need for electrical signal transmission.

[0048] 2. The Joule heat monitoring method can design a self-compensation mechanism to reduce the influence of temperature on measurement, improve the stability in complex environments, and control the temperature drift within the range of ±0.2% RH, while the traditional method drifts ±0.5% RH per degree Celsius.

[0049] 3. The traditional electrical sensors have the problem of difficult desorption in the high-humidity (>80% RH) range. The local temperature rise generated by the Joule heat in the present invention is beneficial to accelerating water desorption and expanding the upper limit of the measurement range (>90% RH).

[0050] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for preparing a humidity monitoring sensor based on the Joule heat characteristic, characterized by at least including the following steps: S1: Use a small laser engraver to prepare a square laser-induced graphene layer on the surface of a polyimide film as a heating layer based on Joule heat; S2: Cover a layer of fine salt on the surface of the heating layer, and uniformly cover the fine salt layer with uncured polydimethylsiloxane by drop coating. Use vacuum treatment to make it uniformly penetrate the entire fine salt layer, and cure the polydimethylsiloxane in an 80°C oven. Cut off the excess polydimethylsiloxane on the surface of the heating layer; S3: Put the sensor base combination jointly prepared from the polyimide film, the heating layer, and the polydimethylsiloxane into hot water, so that the fine salt in the fine salt layer dissolves, thereby forming a porous layer with a microporous structure above the heating layer; S4: Attach the graphene oxide liquid dispersion to the porous layer by the method of repeated drop coating for multiple times as a water vapor molecule adsorption layer, and prepare a humidity monitoring sensor based on the Joule heat characteristic.

2. The preparation method of a humidity monitoring sensor based on the Joule heat characteristic according to claim 1, wherein: The thickness of the polyimide film is 125 μm, the size of the square laser-induced graphene layer is 1 cm * 2 cm, the power of the small laser engraver is set to 8% - 11% of the maximum power, and the engraving speed is set to 80 mm / s.

3. The preparation method of a humidity monitoring sensor based on the Joule heat characteristic according to claim 1, characterized in that: The thickness of the fine salt layer is 2 mm - 4 mm.

4. The preparation method of a humidity monitoring sensor based on the Joule heat characteristic according to claim 1, characterized in that: The concentration of the graphene oxide liquid is 5 mg / ml.

5. A humidity monitoring sensor based on the Joule heating characteristic, characterized in that: It is processed and obtained by the method for preparing a humidity monitoring sensor based on the Joule heat characteristic described in claims 1 - 4.

6. The humidity monitoring sensor based on the Joule heat characteristic according to claim 5, characterized in that: It includes a polyimide film layer, a heating layer, and a porous humidity-sensitive layer. The heating layer is prepared on the upper surface of the polyimide film layer, and the porous humidity-sensitive layer is prepared on the surface of the heating layer away from the polyimide film layer; The heating layer is heated by connecting a DC voltage to both ends of the laser-induced graphene heater, and the heating temperature can be effectively regulated by the voltage; The porous humidity-sensitive layer is formed by the cooperation of the fine salt layer and polydimethylsiloxane to generate a porous structure; after the graphene oxide on the surface of the porous structure adsorbs water vapor molecules, it will affect the surface temperature distribution. Use an infrared thermal imager to obtain temperature data, and thus monitor the environmental humidity according to the change of temperature.

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