Liquid waveguide packaging structure in optical fiber water leakage sensor
By introducing a low-refractive-index fluoroacrylate solid adhesive layer into the fiber optic water leakage sensor, the problems of sensitivity and light transmission efficiency in the detection of minute water leakage are solved, achieving efficient light signal acquisition and accurate detection.
Patent Information
- Application Number
- CN202510710292.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-29
- Publication Date
- 2025-10-21
AI Technical Summary
Existing fiber optic water leakage sensors have low sensitivity when detecting minute leaks, which cannot meet practical needs. Furthermore, the optical transmission efficiency decreases under dripping conditions, and the transmission efficiency of lossy waveguides is poor.
In fiber optic water leakage sensors, a low-refractive-index functional material, specifically a fluoroacrylate solid adhesive layer, is introduced and coated onto the surface of a solid material to regulate the refractive index, ensuring that light can be efficiently focused on the fiber optic sensing coupling area and reducing transmission loss.
The sensitivity of the fiber optic sensor for water leakage detection and the efficiency of optical transmission have been improved, enabling accurate detection of minute water leaks and ensuring stable acquisition and transmission of optical signals.
Smart Images
Figure CN120820282A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of sensor detection, and in particular relates to a liquid waveguide packaging structure in an optical fiber water leakage sensor. Background Art
[0002] Liquid leak detection technology is being widely adopted in locations with a risk of liquid leakage, such as underwater equipment, large-scale data processing centers, semiconductor manufacturing plants, smart homes, and libraries, as well as in petrochemical storage and transportation and water pipelines. Specific leak detection technologies are required for different locations, installation environments, and the variety of liquids being measured. While there is currently extensive research and application in leak detection, addressing the challenges of dripping and seepage measurement requires sensors with fast response times and high detection capabilities for trace amounts.
[0003] Li Yingjie of North University of China, in her research titled "Research on Key Technologies for Dark-Field Water Leakage Sensors Based on Fluidic Waveguides," demonstrated through rigorous experimental comparisons that, when aluminum alloy is used as the solid material and finely processed using CNC machine tools to precisely maintain a flow channel length of 1 mm, the optical waveguide system demonstrates satisfactory performance under current conditions. However, this technology has the following drawbacks: it cannot detect even trace leaks; its sensitivity is low, making it unsuitable for practical leak detection.
[0004] When there is no water dripping into the sensor, the refractive index of the solid material is higher than that of the air. At this time, the light cannot form a waveguide in the channel to form a reflection, and only part of the light enters the optical fiber, which avoids interference from other external light. When water leaks into the fluid channel, there is air above the liquid and the sensor structure. At this time, the air is the upper cladding, and the refractive index is lower than that of the core liquid. During the optical fiber transmission process, there is no lossy waveguide transmission in the upper part, which improves the light transmission efficiency and achieves ideal results. Figure 1 In practical applications, dripping water will cause the entire structure to be filled with water, resulting in the refractive index of the outer cladding being higher than that of the core liquid. This reduces the critical angle for total internal reflection, lowers the transmission efficiency of the lossy waveguide, and prevents some light from following the reflected propagation path during transmission in the liquid waveguide, increasing light transmission losses. Summary of the Invention
[0005] To address these issues, the present invention provides a liquid waveguide packaging structure for optical fiber water leak sensors. This structure incorporates a functional material capable of flexibly controlling the refractive index onto the surface of a solid material. This fundamentally eliminates the problem of excessive light refraction during transmission, ensuring that light is highly concentrated in the optical fiber sensing coupling region, creating favorable conditions for precise sensing.
[0006] The present invention adopts the following technical solutions: A liquid waveguide packaging structure in an optical fiber water leak sensor includes a liquid leak sensor diversion device, the liquid leak sensor diversion device including a rectangular housing made of an aluminum alloy material, a fluid channel and an optical fiber channel provided in the rectangular housing, the two ends of the fluid channel being a leakage collection hole and a water permeable hole, respectively, wherein the opening of the leakage collection hole is provided on the upper surface of the rectangular housing, and the opening of the water permeable hole is provided on one side in the width direction of the rectangular housing, the fluid channel extends vertically downward from the leakage collection hole and turns horizontally at the intersection of the optical fiber channels to communicate with the water permeable hole, that is, the fluid channel is divided into two sections: a vertical fluid channel and a horizontal fluid channel, and the vertical fluid channel and the horizontal fluid channel are perpendicular to each other. The two sections of the fluid channel and the optical fiber channel are spatially arranged perpendicular to each other, and the optical fiber channel is a straight channel on both sides in the width direction of the rectangular housing for installing the optical fiber; A light-transmitting channel is provided on one side of the horizontal fluid channel close to the water-permeable hole, and an LED light is provided at the bottom of the light-transmitting channel; the upper surface of the light-transmitting channel is not connected to the rectangular shell, and the inner side walls at the upper and lower ends of the horizontal fluid channel are respectively coated with a solid glue layer with a low refractive index that can meet the total reflection of the liquid waveguide.
[0007] Furthermore, the low-refractive-index solid adhesive layer is fluorine-based acrylate.
[0008] Furthermore, the solid-state refractive index of the low-refractive-index solid glue layer is 1.36, and the water absorption rate at room temperature is 2%.
[0009] Furthermore, the thickness of the low-refractive-index solid adhesive layer is 0.5-0.8 mm.
[0010] like Figure 2 As shown in the schematic diagram of Fresnel formula, θ r =θ i ;n1sinθ i =n²sinθ t ; According to the principle of optical fiber transmission, when n1>n2, that is, the light-dense medium is incident on the light-sparse medium, it can be known from the incidence law that θ i Less than θ t When θ t =90°, the corresponding incident angle is called the critical angle of total reflection, and is expressed as θ c Represents: sinθ c =n2 / n1.
[0011] like Figure 3 As shown, n1<n2≤n3; α 12 =arcsin(n2 / n1);α 13 =arcsin(n3 / n1); α<α 13 ≤α 12 .
[0012] By changing the refractive index of the external solid material or the core liquid, the propagation behavior of light in a waveguide can be influenced. According to Fresnel's equations and waveguide transmission theory, the reflection and refraction properties of light at the interface between two media depend on the difference in refractive index. When the refractive index of the external solid material or the core liquid changes, the transmission loss, mode distribution, and penetration depth of the evanescent field in the waveguide will also change accordingly. These changes can be quantified by monitoring the output optical power, spectral characteristics, or phase information, thereby enabling the monitoring of liquid properties.
[0013] The beneficial effects of the present invention are as follows: This invention introduces a functional material capable of flexibly regulating the refractive index onto the surface of a solid material. This fundamentally eliminates the problem of excessive refraction during light transmission, ensuring that light is highly concentrated in the optical fiber sensing coupling area, creating favorable conditions for precise sensing. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 This is the water leakage effect diagram under ideal conditions; Figure 2 This is the principle diagram of Fresnel formula; Figure 3 This is the principle diagram of lossy waveguide transmission; Figure 4 This is a structural diagram of the flow guide device of the liquid leakage sensor; Figure 5 Schematic diagram of coating a low-refractive-index solid adhesive layer on the guide device of a liquid leakage sensor; Figure 6 This is a schematic diagram of the leakage principle of the fluid structure after coating with a low-refractive-index solid adhesive layer; Figure 7 This is a graph showing the time and optical power before and after coating the low-refractive-index solid glue layer; Figure 8 This is the change diagram of optical power and discrimination before and after water drop without coating low refractive index solid glue layer; Figure 9 This is a graph showing the changes in optical power and discrimination before and after applying a low-refractive-index solid glue layer and dripping water; Figure 10 This is a microscope image of a horizontal fluid channel without coating of a low-refractive-index solid glue layer; Figure 11 A microscope image of a horizontal fluid channel coated with a low-refractive-index solid gel layer; Figure 12 This is an observation diagram of the change in coating time and response time of the low refractive index solid glue layer; Figure 13 is the response curve when the saline concentration is 5%; Figure 14 is the response curve when the saline concentration is 10%; Figure 15 is the response curve when the saline concentration is 15%; Figure 16 is the response curve when the saline concentration is 20%; Figure 17 is the response curve when the saline concentration is 25%; Figure 18 The corresponding refractive index and leakage discrimination curves for different saline concentrations; Among them: 1- rectangular shell; 2- fluid channel; 3- optical fiber channel; 4- leakage collection hole; 5- water permeable hole; 6- light-transmitting channel; 7- LED light; 8- low refractive index solid glue layer; 9- leakage. DETAILED DESCRIPTION
[0015] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail, but are not limited thereto. Unless otherwise specified, the raw materials used in the examples are all common commercial products; unless otherwise specified, the methods used are all commonly used methods in the art.
[0016] For the liquid leak sensor's flow guide device, a more suitable aluminum alloy material is a solid material. A functional material capable of flexibly regulating the refractive index is introduced onto the surface of the solid material. This fundamentally eliminates the problem of excessive refraction of light during transmission, ensuring that light can be concentrated in the fiber optic sensing coupling area with extremely high concentration, creating favorable conditions for precise sensing. Furthermore, the performance of the optical waveguide is not only affected by the solid material, but is also closely related to the refractive index of the leaking water. Different liquid media have different refractive indices, which directly affect the transmission characteristics of light in the waveguide. Therefore, to further study the effect of the liquid's refractive index on the performance of the optical waveguide, we also analyzed the effects of different liquid media and their refractive index changes on the light transmission characteristics.
[0017] Example 1 A single-component, highly transparent, low-refractive UV-curing adhesive XG-D1360 was selected, which is composed of fluorine-based acrylate and purchased from Xigu Technology-Tuo Shadowless Adhesive.
[0018] This curing adhesive is often used for fine coating protection at optical fiber fusion splices. It has an excellent ability to prepare special film coatings, excellent moisture resistance and flexibility, and can effectively reduce optical loss at the coupling point.
[0019] Before coating solid structures, a strict surface cleaning process is implemented to ensure the coating surface is spotless and free of any residual impurities. In a light-proof environment, a fine soft-bristled brush is used to apply the coating to exposed areas within the structure at a thickness of 0.5-0.8mm. Due to the fluidity of the colloid, the coating must be applied in sections and multiple times. This coating process reduces the generation of bubbles, avoids scattering and absorption losses during transmission, and ensures the stability of the lightwave system.
[0020] Figure 5 Schematic diagram of coating a low-refractive-index solid adhesive layer on the guide device of a liquid leakage sensor; Figure 6 Schematic diagram of the leakage principle of the fluid structure after coating with a low-refractive-index solid glue layer.
[0021] When the type or solute concentration of the leaking liquid changes, the refractive index of the leaking liquid also changes, affecting the transmission characteristics of light in the optical fiber. When light passes through the area of the optical fiber in contact with the liquid, its refraction and reflection properties will change accordingly, resulting in changes in light transmission loss, which is ultimately reflected in the output signal of the optical power meter.
[0022] Example 2 To verify whether the low-refractive index solid glue coated on the surface of the solid material can effectively reduce the refraction and absorption loss of the optical waveguide during transmission. Use a pipette to add 0.5ml of clean water to the leakage collection hole of the solid material, and collect key indicators such as optical power loss and light intensity attenuation amplitude. Comparing the experimental data of the solid structure without solid glue coating, evaluate the effect of the solid material coated with low-refractive index solid glue on the transmission performance of the optical waveguide when clean water is used as the detection liquid. After the water dripping test, the structure needs to be air-dried to ensure the consistency of the initial experimental value and environment, and multiple experiments are performed to ensure the accuracy of the performance.
[0023] According to the definition, the liquid leakage discrimination E r =10log(P w / P a ), where P a 、P w The optical transmission power before and after dripping water is respectively used to judge the optimization effect of low-refractive index solid glue on optical transmission performance under the current experimental conditions.
[0024] The experimental results show that Figure 7The recorded light intensity curve over time was analyzed and it was found that within half a minute of continuous observation, the light power collected by the coated group after dripping water increased significantly compared with the control group that was not coated with low-refractive index solid glue. By collecting the light power before and after dripping water, after coating with low-refractive index solid glue, the light power was 850nw-957nw, which increased by about 700nw compared to 150nw-200nw of the control group, and the discrimination was improved by at least 5dB, which means that the energy loss of light during transmission has been effectively controlled, and more light can be stably transmitted along the optical waveguide. Combined with Figure 7 、 8 After repeated experiments, the data obtained show that when clean water is dripped into the solid material coated with low-refractive index solid glue, the light intensity fluctuation amplitude becomes larger, and it can quickly respond to the water leakage signal, but the leakage discrimination basically remains in a relatively stable range, ensuring that the light signal can be collected with a relatively constant intensity, providing a solid guarantee for subsequent accurate detection based on the changes in the light signal.
[0025] Example 3 Given the risk of peeling when wetted by liquids, which can severely impact performance and stability, the adhesive-coated material is first subjected to multiple water flushing cycles to simulate the conditions it might encounter in a humid or liquid-sensitive environment. Following the flushing cycle, the material's key performance indicators are tested again to ensure that the material maintains its original performance levels despite these conditions.
[0026] To investigate the durability and adhesion stability of the adhesive under normal temperature and conditions, we tested the adhesive-coated structure for 5, 15, 30, 60, and 120 days, verifying whether the adhesive had fallen off and the overall stability of the structure. During each test, we recorded the adhesive's state, the optical power after dripping with water, and other related properties in detail for quantitative testing. By collecting and analyzing data at these different time points, we systematically evaluated the performance trends of the adhesive over the long term, providing strong data support and theoretical basis for its practical application.
[0027] After carefully observing the adhesion of the solid glue on the solid structure with the help of a microscope, the results showed that the solid glue coating did not show any adverse phenomena such as peeling or flaking. Figure 10 、 Figure 11 In addition, no peeling occurred after multiple flushing tests. Figure 11The data shown here is obtained after repeated experiments after different exposure times. This data demonstrates that long-term exposure to the adhesive does not affect the experimental results. The optical power reaches its peak at approximately 20 seconds, and the peak values corresponding to the different exposure times are similar. Based on these experimental phenomena and data, it is fully confirmed that the adhesive can maintain its stability and reliability when exposed to ambient temperature.
[0028] Example 4 The study accurately measured the changes in light transmission parameters, including optical power loss and intensity attenuation, in a solid-material optical waveguide coated with a low-refractive-index solid gel, when using salt water of varying concentrations as the test liquid. A series of sodium chloride saline solutions with varying concentrations were prepared. Since they were not heated during the experiment, the maximum concentration gradient was set at 5%, 10%, 15%, 20%, and 25%. The refractive index of the salt water was accurately measured using an Abbe refractometer.
[0029] Starting from the lowest concentration of saline solution, use a pipette to slowly and accurately add 0.5ml of saline to the leakage collection hole, continuously monitor the changes in light transmission parameters over time, record the light power data, and form a light transmission parameter change curve corresponding to different saline concentrations. For each concentration of saline experimental data, calculate key indicators such as the light intensity attenuation amplitude, compare the differences in these indicators under different saline concentrations, and draw the relationship between light intensity attenuation amplitude and saline concentration. Figures 13 to 17 , intuitively showing the trend of optical waveguide effect changing with salt water concentration. Figures 13 to 17 It can be seen that as the salt water concentration increases, the peak value of the optical power gradually rises.
[0030] Relationship between contrast light intensity attenuation amplitude and salt water concentration Figure 18 We can find that after dripping water, the received optical power will continue to rise with the increase of salt water concentration, and the discrimination value will rise linearly. As the refractive index of the liquid increases, the refractive index of the core liquid exceeds the refractive index of the cladding low-refractive-index glue, and the liquid is totally reflected inside the structure, which enhances the light intensity received by the optical fiber.
[0031] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.
Claims
1. A liquid waveguide packaging structure in an optical fiber water leak sensor, comprising a liquid leak sensor guide device, the liquid leak sensor guide device comprising a rectangular housing made of aluminum alloy, a fluid channel and an optical fiber channel provided within the rectangular housing, the ends of the fluid channel being respectively a leakage collection hole and a water permeable hole, wherein: The opening of the leakage collection hole is set on the upper surface of the rectangular shell, and the opening of the water permeable hole is set on one side of the rectangular shell in the width direction. The fluid channel extends vertically downward from the leakage collection hole and turns horizontally at the intersection of the optical fiber channel to connect with the water permeable hole. That is, the fluid channel is divided into two sections: a vertical fluid channel and a horizontal fluid channel. The vertical fluid channel and the horizontal fluid channel are perpendicular to each other. The two sections of the fluid channel and the optical fiber channel are arranged perpendicular to each other in space. The optical fiber channel is a straight channel on both sides of the width direction of the rectangular shell for installing optical fibers. The invention is characterized in that: a light-transmitting channel is provided on the side of the horizontal fluid channel close to the water-permeable hole, and an LED light is provided at the bottom of the light-transmitting channel; the upper surface of the light-transmitting channel is not connected to the rectangular shell, and the inner side walls at the upper and lower ends of the horizontal fluid channel are respectively coated with a solid glue layer with a low refractive index that can meet the total reflection of the liquid waveguide.
2. The liquid waveguide packaging structure in an optical fiber water leak sensor according to claim 1, characterized in that: The low-refractive-index solid adhesive layer is fluorine-based acrylate.
3. The liquid waveguide packaging structure in an optical fiber water leakage sensor according to claim 1, characterized in that: The solid refractive index of the low-refractive-index solid glue layer is 1.36, and the water absorption rate at room temperature is 2%.
4. The liquid waveguide packaging structure in an optical fiber water leakage sensor according to claim 1, characterized in that: The thickness of the low-refractive-index solid glue layer is 0.5-0.8 mm.