Temperature compensation humidity sensor using tapering optical fiber grating

Abstract

The present invention relates to a temperature-compensated humidity sensor using a tapered optical fiber grating, comprising: an optical circulator that transmits light emitted from a light source and input through an input terminal to an output terminal, and outputs light proceeding in reverse from the output terminal to a detection terminal; a sensing optical fiber connected to the output terminal of the optical circulator, having a first optical fiber grating formed in a tapered portion formed to reduce the outer diameter, and a second optical fiber grating formed spaced apart from the first optical fiber grating; a main moisture-reactive layer formed of a material that expands and contracts upon moisture and is coupled to surround the first optical fiber grating; a light detection unit that detects light output from the detection terminal of the optical circulator; and a calculation unit that calculates temperature information of an environment where the second optical fiber grating is installed from wavelength shift information of a second signal detected by the light detection unit after being reflected from the second optical fiber grating, and calculates humidity of an environment where the first optical fiber grating is installed corresponding to the temperature calculated through the second optical fiber grating from wavelength shift information of a first signal detected by the light detection unit after being reflected from the first optical fiber grating. A temperature-compensated humidity sensor using such a tapered optical fiber grating has the advantage that using the tapered optical fiber grating reduces the outer diameter of the optical fiber, allowing external strain to be easily transmitted and increasing sensitivity, while simultaneously reducing the thickness of the polyimide used as the humidity sensor to increase the response speed. In addition, by using a pair of optical fiber gratings, it provides a temperature-dependent compensation function, improves sensitivity, and offers the advantage of shortening the response time.

Description

Technology Field

[0001] The present invention relates to a temperature-compensated humidity sensor using a tapered optical fiber grating, and more specifically, to a temperature-compensated optical fiber humidity sensor that applies a tapered optical fiber grating to improve response sensitivity and response speed compared to using a general optical fiber grating, while simultaneously enabling humidity measurement while compensating for the influence of temperature. This project (result) is the result of the Local Government-University Cooperation-based Regional Innovation Project conducted in 2023 with funding from the Ministry of Education and support from the National Research Foundation of Korea. (Project Management No.: 2021RIS-002) Background Technology

[0002] Humidity sensors detect changes in humidity based on electrical signals, and recently, they are being installed in smart devices such as smartphones. In other words, as smart devices become more popularized, the types of built-in sensors are diversifying, and humidity sensors that recognize ambient humidity are a prime example. By using humidity sensors, one can visually check for comfortable living conditions.

[0003] Humidity sensors employed in smart devices and the like typically measure humidity by utilizing changes in the electrical properties of moisture-sensitive materials caused by moisture. These electrical properties include resistance, capacitance, and resonant frequency. Among these, resistive humidity sensors, whose electrical resistance changes with humidity, and capacitor-type humidity sensors, whose capacitance changes, are the most widely produced, leading to active research in this area.

[0004] Meanwhile, capacitor-type humidity sensors offer superior long-term reliability and linear sensor characteristics compared to resistive-type humidity sensors, making them widely applied in high-precision products and expanding their scope of application.

[0005] And the capacitor-type humidity sensor is manufactured in the form of a capacitor using a moisture-sensitive polymer, such as polyimide, whose dielectric constant changes when moisture is absorbed, as the dielectric.

[0006] A typical capacitor-type humidity sensor consists of a sensing capacitor and a reference capacitor. In this type of sensor, the capacitance value of the sensing capacitor fluctuates according to changes in humidity, while the value of the reference capacitance remains constant. To eliminate the offset of the sensing capacitor, the reference capacitor is formed to have the same size as the sensing capacitor and is placed adjacent to it. However, conventional humidity sensors have the disadvantage of requiring a relatively large amount of time and manpower for design and manufacturing due to their somewhat complex structure. Prior art literature

[0007] Registered Patent Publication No. 10-2237710: Capacitor-type humidity sensor The problem to be solved

[0008] The present invention was devised to improve the above-mentioned problems, and aims to provide a temperature-compensated humidity sensor using a tapered optical fiber grating that can increase sensitivity and response speed by introducing a tapered optical fiber grating during humidity measurement, and simultaneously improve measurement precision by providing a temperature-dependent correction function using grating pairs. means of solving the problem

[0009] To achieve the above objective, a temperature-compensated humidity sensor using a tapered optical fiber grating according to the present invention comprises: a light source that emits light; an optical circulator that transmits light emitted from the light source and input through an input terminal to an output terminal, and outputs light proceeding in reverse from the output terminal to a detection terminal; a sensing optical fiber connected to the output terminal of the optical circulator, having a first optical fiber grating formed in a tapered portion formed to have a reduced outer diameter, and a second optical fiber grating formed spaced apart from the first optical fiber grating; a main moisture-reactive layer formed of a material that expands and contracts upon moisture and is coupled to surround the first optical fiber grating; and a light detection unit that detects light output from the detection terminal of the optical circulator. A calculation unit is provided for calculating temperature information of the environment in which the second optical fiber grating is installed from wavelength shift information of the second signal detected by the light detector unit after being reflected from the second optical fiber grating, and calculating humidity of the environment in which the first optical fiber grating is installed corresponding to the temperature calculated through the second optical fiber grating from wavelength shift information of the first signal detected by the light detector unit after being reflected from the first optical fiber grating.

[0010] In addition, the main moisture reaction layer is formed of polyimide material.

[0011] Preferably, it further comprises a waterproof layer formed of a waterproof material that surrounds and blocks the inflow of moisture and is coupled to the second optical fiber grid; and a sub-moisture reaction layer formed of a polyimide material on the outer surface of the waterproof layer.

[0012] In addition, the main moisture reaction layer is formed by bonding a film formed of polyimide material to surround the first optical fiber grid.

[0013] In addition, the above waterproof layer may be formed of a urethane material. Effects of the invention

[0014] According to the temperature-compensated humidity sensor using a tapered optical fiber grating of the present invention, using a tapered optical fiber grating reduces the outer diameter of the optical fiber, allowing external strain to be easily transmitted and increasing sensitivity. At the same time, it has the advantage of reducing the thickness of the polyimide used as a humidity sensor, thereby increasing the response speed. In addition, by using a pair of optical fiber gratings, it provides a correction function based on temperature, improves sensitivity, and offers the advantage of shortening the response time. Brief explanation of the drawing

[0015] FIG. 1 is a diagram showing a temperature-compensated humidity sensor using a tapered optical fiber grating according to the present invention, and FIG. 2 is an enlarged cross-sectional view of a tapered portion of FIG. 1 in which the first and second optical fiber grids are formed. FIG. 3 is a cross-sectional view showing the coating structure applied to the first optical fiber grating of FIG. 2 in more detail, and FIG. 4 is a cross-sectional view showing the coating structure applied to the second optical fiber grating of FIG. 2 in more detail, and Figure 5 is a graph showing the wavelength shift according to temperature of the first and second optical fiber gratings of Figure 1. Specific details for implementing the invention

[0016] Hereinafter, a temperature-compensated humidity sensor using a tapered optical fiber grating according to a preferred embodiment of the present invention will be described in more detail with reference to the attached drawings.

[0017] FIG. 1 is a drawing showing a temperature-compensated humidity sensor using a tapered optical fiber grating according to the present invention, and FIG. 2 is a longitudinal cross-sectional view showing an enlarged view of the tapered portion in which the first and second optical fiber gratings of FIG. 1 are formed.

[0018] Referring to FIG. 1 and FIG. 2 together, the temperature-compensated optical fiber humidity sensor (100) according to the present invention comprises a light source (110), an optical circulator (130), a sensing optical fiber (140), first and second optical fiber gratings (151) (152), a main moisture reaction layer (161), a light detection unit (170), and a calculation unit (180).

[0019] The light source (110) is controlled by the output unit (180) to emit light.

[0020] The light circulator (130) transmits light emitted from the light source (110) and input through the input terminal (130a) to the output terminal (130b), and outputs light proceeding in reverse from the output terminal (130b) to the detection terminal (130c).

[0021] The sensing optical fiber (140) is connected to the output terminal (130b) of the optical circulator (130), and a first optical fiber grating (151) and a second optical fiber grating (152) are formed spaced apart from the first optical fiber grating (151) in the tapered portion (140b) (T) formed to have a smaller outer diameter.

[0022] That is, the sensing optical fiber (140) has a normal optical fiber portion (140a)(S) formed by a first core (141a) having a normal outer diameter and a first clad (142a) surrounding the first core (141a), and a tapered portion (140b)(T) having an outer diameter smaller than that of the normal optical fiber portion (140a)(S) through a process of stretching while applying heat to the normal optical fiber portion (140a)(S). Additionally, the tapered portion (T) is composed of a second core (141b) having an outer diameter equal to or smaller than that of the first core (141a) and a second clad (142b) having an outer diameter smaller than that of the first clad (142a).

[0023] In addition, the grating spacing of the first optical fiber grating (151) and the grating spacing of the second optical fiber grating (152) are formed differently from each other. That is, the first optical fiber grating (151) has a grating formed with a first spacing, and the second optical fiber grating (152) has a grating formed with a second spacing different from the first spacing.

[0024] The main moisture reaction layer (161) is formed of a material that expands and contracts upon moisture and is bonded to surround the first optical fiber grid (151), and the detailed structure is explained with reference to FIG. 3.

[0025] The main moisture reaction layer (161) is bonded in the form of a film to the outer surface of the second clad (142b) that surrounds the second core (141b) of the tapered portion (140b) where the first optical fiber grid (151) is formed.

[0026] The main moisture reaction layer (161) is formed by bonding a film formed of polyimide material to surround the first optical fiber grid (151) with an adhesive (162).

[0027] Of course, the main moisture-reactive layer (161) may be made of a material other than polyimide that expands upon moisture.

[0028] Meanwhile, the main moisture reaction layer (161) can undergo expansion due to temperature other than moisture, and to compensate for this expansion characteristic due to temperature, the second optical fiber grid (152) is constructed to reflect the temperature effect equally by surrounding and bonding the material applied to the main moisture reaction layer (161) while maintaining a waterproof state. To this end, a waterproof layer (165) and a sub moisture reaction layer (166) are sequentially laminated on the outer surface of the second optical fiber grid (152), and this is explained with reference to FIG. 4.

[0029] The waterproof layer (165) is formed of a waterproof material that surrounds the second clad (142b) which encloses the second core (141b) of the tapered portion (140b) where the second optical fiber grid (152) is formed, and blocks the inflow of moisture into the tapered portion (140b) where the second optical fiber grid (152) is formed.

[0030] The waterproof layer (165) may be formed from a urethane material, a polyurea material, or a polyurethane material. Preferably, to increase manufacturing efficiency, the waterproof layer (165) is formed by spraying a waterproof spray that supports the formation of a coating by adhesion by a spray method onto the tapered portion (140b) where the second optical fiber grid (152) is formed.

[0031] The sub-moisture reaction layer (166) is formed of a polyimide material, which is the same material as the main moisture reaction layer (161), to surround the outer surface of the waterproof layer (165).

[0032] That is, the sub-moisture reaction layer (166) is formed by bonding a film formed of polyimide material to surround the second optical fiber grid (152) with an adhesive (162).

[0033] When the first and second optical fiber gratings (151) are formed in the tapered portion (140b)(T) formed to have a smaller outer diameter, the length expanded by external strain is further increased, thereby increasing the Bragg wavelength shift and improving measurement sensitivity. Additionally, the main and sub moisture reaction layers (161)(166) that react to moisture due to the small outer diameter can be made of thin polyimide film, which provides the advantage of shortening the reaction time.

[0034] The light detection unit (170) detects light output from the detection unit (130c) of the light circulator (130) and provides it to the output unit (180).

[0035] The output unit (180) controls the operation of the light source (110), calculates the humidity of the environment in which the first optical fiber grating (151) is installed from the signal detected by the light detection unit (180), and outputs the calculated humidity information through the output unit (190). The output unit (190) may be equipped with a communication unit that transmits the output information to a display device or management terminal controlled by the output unit (180) to display the output information.

[0036] The calculation unit (180) calculates temperature information of the environment in which the second optical fiber grating (152) is installed from wavelength shift information of the second signal detected by the light detector (170) after being reflected from the second optical fiber grating (152). Additionally, the calculation unit (180) calculates humidity of the environment in which the first optical fiber grating (151) is installed, corresponding to the temperature calculated through the second optical fiber grating (152), from wavelength shift information of the first signal detected by the light detector (170) after being reflected from the first optical fiber grating (151). That is, the calculation unit (180) calculates humidity of the environment in which the first optical fiber grating (151) is installed from a correction value in which the wavelength shift component caused by the temperature calculated through the second optical fiber grating (152) is excluded from the wavelength shift information of the first signal detected by the light detector (170) after being reflected from the first optical fiber grating (151).

[0037] That is, as can be confirmed through FIG. 5, when the ambient temperature of the second optical fiber grating (FBG2) changes from the first temperature (T1) to the second temperature (T2), the reflected wavelength shifts, and it can be seen that in the same humidity environment, when the ambient temperature of the first optical fiber grating (FBG1) changes from the first temperature (T1) to the second temperature (T2), the reflected wavelength shifts. Therefore, a calculation unit (180) is constructed to determine the wavelength shift caused by the temperature of the first optical fiber grating (151) from the temperature information obtained through the second optical fiber grating (152), and to calculate the humidity by reflecting only the wavelength shift caused by the humidity of the first optical fiber grating (151).

[0038] The output unit (180) can be constructed to calculate humidity corresponding to the temperature using a lookup table (not shown) in which humidity corresponding to the wavelength shift of the first optical fiber grating (151) according to the temperature is obtained and recorded by experiment.

[0039] According to the temperature-compensated humidity sensor using the tapered optical fiber grating described above, it supports humidity measurement using the tapered optical fiber grating while also providing a temperature-dependent compensation function, as well as offering the advantages of improved sensitivity and reduced response time. Explanation of the symbols

[0040] 110: Light source 130: Optical circulator 140: Sensing optical fiber 140b: Tapering section 151, 152: First and second optical fiber gratings 161: Main moisture reaction layer 165: Waterproofing layer 166: Sub-moisture reaction layer 170: Photodetector 180: Output section

Claims

Claim 1 A light source that emits light; an optical circulator that transmits light emitted from the light source and input through an input terminal to an output terminal, and outputs light proceeding in reverse from the output terminal to a detection terminal; a sensing optical fiber connected to the output terminal of the optical circulator, having a first optical fiber grating formed in a tapering portion formed to reduce the outer diameter, and a second optical fiber grating formed spaced apart from the first optical fiber grating; a main moisture-reactive layer formed of a material that expands and contracts upon moisture and is coupled to surround the first optical fiber grating; a light detection unit that detects light output from the detection terminal of the optical circulator; and a method for calculating temperature information of an environment where the second optical fiber grating is installed from wavelength shift information of a second signal reflected from the second optical fiber grating and detected by the light detection unit, and calculating humidity of the environment where the first optical fiber grating is installed corresponding to the temperature calculated through the second optical fiber grating from wavelength shift information of a first signal reflected from the first optical fiber grating and detected by the light detection unit. A temperature compensation humidity sensor using a tapered optical fiber grating, comprising: a producing unit; a waterproof layer formed of a waterproof material that blocks the inflow of moisture and is bonded to surround the second optical fiber grating; and a sub-moisture reaction layer formed of a polyimide material on the outer surface of the waterproof layer; wherein the main moisture reaction layer is formed of a polyimide material, the main moisture reaction layer is formed by bonding a film formed of a polyimide material to surround the first optical fiber grating, and the waterproof layer is formed of a urethane material. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete

Images