Novel flexible soil pressure sensor and manufacturing method thereof

Abstract

The invention discloses a novel flexible soil pressure sensor and a manufacturing method thereof.The manufacturing method of the novel flexible soil pressure sensor mainly comprises the steps that a silane coupling agent is used for preprocessing a fiber bragg grating, and a silica gel liquid mixture is prepared; after the prepared silica gel liquid mixture is slowly poured into the middle shaft position of the soil pressure sensor mold and stopped, embedding the pretreated fiber bragg grating into a clamping groove reserved in the middle shaft of the soil pressure sensor mold, applying certain prestress to the fiber, and after the position of the fiber bragg grating is arranged, performing the pre-treatment on the fiber bragg grating to obtain a pre-treated fiber bragg grating; and continuously and slowly pouring the silica gel mixed solution to the top of the soil pressure sensor mold, curing and forming for 8 hours, and taking out the soil pressure sensor from the soil pressure sensor mold. The novel flexible soil pressure sensor prepared by the invention is a cake-shaped soil stress sensor with a cross-shaped fiber Bragg grating sensing unit, and has better repeatability and stability, higher sensitivity and better linear correlation.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, in particular to a novel flexible soil pressure sensor and a manufacturing method thereof. Background Art

[0002] The soil stress sensor mainly works on the principle of resistance strain. Its core part is the resistance strain gauge, which is an internal sensitive element made of special materials. It can sense the strain in the soil and produce a certain resistance change. When the soil is subjected to a certain force and deformed, the resistance strain gauge in the sensor will undergo a slight deformation, thereby affecting the size of the resistance value. By detecting the change in resistance value and using the bridge principle, the stress state in the soil can be accurately measured.

[0003] Fiber Bragg gratings can be used to measure soil stress, but the outer diameter of a bare fiber Bragg grating is about 100 μm, and its main component is SiO2. It is easy to break during use, and the pressure sensitivity of bare fiber is low. These characteristics require that in actual engineering, bare fiber needs to be encapsulated with materials to protect and enhance the sensitivity of the bare fiber. Encapsulation materials are crucial to the production of fiber Bragg grating sensors, as they play a role in protecting and enhancing the sensitivity of the optical fiber. Therefore, the production process of the encapsulation material needs to be as simple as possible to avoid damaging the optical fiber, and the encapsulation material needs to effectively transfer strain to the optical fiber to reduce losses.

[0004] At present, there are three main packaging methods for fiber Bragg grating sensors: two-end clamping, substrate, and embedded. The two-end clamping packaging method is to arrange the clamping components at both ends of the sensor, and the structural strain is transmitted to the fiber Bragg grating by the clamping components. The two-end clamping sensor can be pre-buried inside the structure to be measured, or it can be attached to the surface of the structure to be measured. The layout method is simple and convenient for disassembly and reuse. However, since the adhesive that sticks the clamping components and the sensor has a short working life and is easy to corrode, the durability of the two-end clamping sensor is poor. The substrate packaging method is to stick the fiber Bragg grating in the groove of the substrate, so that the fiber Bragg grating and the substrate form a test whole, and the structural strain is transmitted from the substrate to the fiber Bragg grating, which is simple and convenient. However, the interface compatibility of the substrate packaging is poor, and the loss during the strain transmission process is large, and the test accuracy is low. The embedded packaging method is to encapsulate the fiber Bragg grating inside the composite material, which reduces the strain transmission loss to a certain extent. However, there are high requirements for packaging equipment and conditions, and the choice of composite materials will also affect the sensitivity of the sensor. Summary of the invention

[0005] The object of the present invention is to provide a novel flexible earth pressure sensor and a manufacturing method thereof, so as to improve the sensitivity of the earth pressure sensor by improving the sensor packaging process.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A novel method for manufacturing a flexible soil pressure sensor, the steps of which include:

[0008] Pretreatment of the fiber Bragg grating: wipe the fiber Bragg grating with dust-free paper dipped in anhydrous ethanol, and protect the non-test section of the fiber Bragg grating with a fiber protection sleeve, then immerse the fiber Bragg grating in a silane coupling agent. After the measuring section is completely soaked by the silane coupling agent, take out the optical fiber and let it stand at room temperature until the coupling agent is hydrolyzed and dried;

[0009] When using the optical fiber protection sleeve to protect the non-test section of the optical fiber Bragg grating, use 502 glue to fix it to prevent the optical fiber from being torn during demolding and subsequent testing;

[0010] Preparation of silica gel solution: first pour silica gel solution into a clean beaker with peeled skin, slowly drip curing agent with a dropper, stir evenly clockwise with a glass rod while adding curing agent, stir until there is no floccules and bubbles in the mixed liquid, and fully mix the two solutions to obtain a silica gel liquid mixture;

[0011] Sensor packaging: slowly pour the prepared silica gel liquid mixture into the middle axis position of the soil pressure sensor mold and stop, then embed the pre-treated fiber Bragg grating into the slot reserved on the middle axis of the soil pressure sensor mold, apply prestress to the optical fiber, arrange the position of the fiber Bragg grating, and continue to slowly pour the silica gel mixed solution to the top of the soil pressure sensor mold;

[0012] The sensor is demoulded and cured at room temperature for 8 hours before taking out the cured earth pressure sensor from the earth pressure sensor mold.

[0013] Among them, the processed fiber Bragg grating is embedded in the slot reserved on the central axis of the soil pressure sensor mold, and a certain prestress is applied to the optical fiber to straighten it and reduce the test error.

[0014] Preferably, the mass ratio of the silica gel solution to the curing agent is 100:3.

[0015] Preferably, the soil pressure sensor mold is cylindrical and includes an upper box device and a lower box device;

[0016] The side walls of the upper box device and the lower box device are respectively provided with four card retaining grooves for fixing optical fibers;

[0017] A circular glue injection port is provided on the top of the upper box device for injecting a silica gel liquid mixture.

[0018] Preferably, the four card retaining slots provided on the upper box device are arranged in an array with the center position of the side wall of the upper box device as the center of the circle; the four card retaining slots provided on the lower box device are arranged in an array with the center position of the side wall of the lower box device as the center of the circle.

[0019] Preferably, the longest operation time of the sensor package does not exceed 10 minutes to avoid exothermic curing of the silicone liquid mixture in the cup.

[0020] In another embodiment, a novel flexible soil pressure sensor is manufactured by a novel flexible soil pressure sensor manufacturing method according to any one of claims 1 to 5, characterized in that it comprises: a fiber Bragg grating and a flexible conductive substrate; the fiber Bragg grating is arranged in the middle of the flexible conductive substrate, and the fiber Bragg gratings are arranged in two groups and are cross-arranged with each other.

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0022] The sensor made of optical fiber soaked in silane coupling agent according to the performance of silane coupling agent can improve the bonding force between optical fiber and packaging material silica gel, so that the load can be more accurately transmitted to the buried sensing optical fiber, and the sensitivity of the sensor to load perception is improved. The new flexible soil pressure sensor obtained by silica gel solution encapsulation is a round cake-shaped soil stress sensor with a cross-shaped fiber Bragg grating sensing unit, which has better repeatability and stability, higher sensitivity, and better linear correlation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 This is a flowchart of the steps of a method for making a novel flexible soil pressure sensor of the present invention;

[0025] Figure 2 It is a structural schematic diagram of the lower box device of the pressure sensor mold of the present invention;

[0026] Figure 3 It is a structural schematic diagram of the upper box device of the pressure sensor mold of the present invention;

[0027] Figure 4 is a schematic diagram of a novel flexible earth pressure sensor of an embodiment;

[0028] Figure 5 is a time course curve diagram of average wavelength change of the sensor group 6 in Example;

[0029] Figure 6It is the fitting curve diagram of the average wavelength change and load of the six groups of sensors under three cycles of loading and unloading;

[0030] In the figure: 1. Upper box device; 2. Lower box device; 3. Card slot; 4. Glue filling port. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Embodiment 1 A method for manufacturing a novel flexible earth pressure sensor, the steps comprising:

[0033] S1. Pretreatment of Fiber Bragg Grating: Wipe the Fiber Bragg Grating with dust-free paper dipped in anhydrous ethanol, and protect the non-test section of the Fiber Bragg Grating with a fiber protection sleeve, then immerse the Fiber Bragg Grating in a silane coupling agent. After the measuring section is completely soaked with the silane coupling agent, take out the optical fiber and let it stand at room temperature until the coupling agent is hydrolyzed and dried. When the non-test section of the Fiber Bragg Grating is protected with a fiber protection sleeve, use 502 glue to fix it to prevent the fiber from being torn during demolding and subsequent tests.

[0034] At the same time, before using the soil pressure sensor mold, clean the mold surface and inside with dust-free paper dipped in anhydrous alcohol, and then evenly apply vaseline inside the mold, perforations, and petal gaps to facilitate demolding.

[0035] Among them, the fiber Bragg grating parameters are shown in Table 1:

[0036] Table 1 Fiber Bragg grating parameters

[0037]

[0038] S2. Preparation of silica gel solution: prepare a silica gel liquid mixture according to the mass ratio of silica gel solution to curing agent of 100:3. First, pour 40g silica gel solution into a clean beaker with peeled skin, slowly drip 1.2g curing agent with a dropper, and stir evenly clockwise with a glass rod while adding the curing agent. Stir until there is no floccules or bubbles in the mixed solution, and fully mix the two solutions to obtain a silica gel liquid mixture.

[0039] S3. Sensor packaging: slowly pour the prepared silicone liquid mixture into the soil pressure sensor mold at the center axis position (5mm) and stop. Then, embed the pre-treated fiber Bragg grating into the reserved slot on the center axis of the soil pressure sensor mold and apply a certain prestress to the optical fiber. After arranging the position of the fiber Bragg grating, continue to slowly pour the silicone mixed solution to the top of the soil pressure sensor mold. The maximum operation time of the sensor packaging shall not exceed 10 minutes.

[0040] The pressure sensor mold is cylindrical and includes an upper box device 1 (such as Figure 3 ) and lower box device 2 (such as Figure 2 ); the side walls of the upper box device 1 and the lower box device 2 are respectively provided with four card retaining grooves 3 for fixing optical fibers; the top of the upper box device 1 is provided with a circular glue injection port 4 for injecting glue liquid mixture. The four card retaining grooves 3 provided on the upper box device 1 are arranged in an array with the center position of the side wall of the upper box device 1 as the center of the circle; the four card retaining grooves 3 provided on the lower box device 2 are arranged in an array with the center position 2 of the side wall of the lower box device as the center of the circle.

[0041] S4. Demould the sensor. After curing at room temperature for 8 hours, take out the cured earth pressure sensor from the earth pressure sensor mould.

[0042] Example 2 A new type of flexible soil pressure sensor (such as Figure 4 ), comprising: a fiber Bragg grating and a flexible conductive substrate; the fiber Bragg grating is arranged in the middle of the flexible conductive substrate, and the fiber Bragg grating is arranged in two groups and is cross-arranged with each other.

[0043] Example 3

[0044] The method of Example 1 is directly used to obtain three sets of new flexible earth pressure sensors, which are numbered B-1, B-2 and B-3 respectively.

[0045] In the steps of the method for manufacturing a novel flexible soil pressure sensor in Example 1, there is no need to soak the fiber Bragg grating in a silane coupling agent during the pretreatment process of the fiber Bragg grating, and another three groups of flexible soil pressure sensors are directly prepared and numbered A-1, A-2 and A-3. The sensor parameters are shown in Table 2:

[0046] Table 2 Sensor parameters

[0047]

[0048] The above six groups of sensors were subjected to sensor positive stress tests using a sensor positive stress test platform. The time course curves of the average wavelength changes of the six groups of sensors output during three cyclic loading tests are shown in the figure below. Figure 5 As shown by Figure 5It can be seen that when the sensor is loaded and unloaded, its central wavelength will fluctuate to a certain extent. The fluctuations are different under different cyclic loads, but the direction and trend of the overall curve are similar. It can be seen that under the three cyclic load tests, the repeatability of the central wavelength data of each sensor is good.

[0049] The hysteresis of the above six groups of sensors under three cyclic loads is calculated, as shown in Table 3:

[0050] Table 3 Sensor hysteresis

[0051]

[0052]

[0053] As shown in Table 3, the hysteresis of the sensors made of optical fibers soaked in silane coupling agent is less than 5%, which is much smaller than that of the sensors made of optical fibers not soaked in silane coupling agent. This shows that the repeatability and stability of the sensors are better and they have good monitoring performance.

[0054] The repeatability errors of the above six groups of sensors under three cyclic loads are calculated, as shown in Table 4:

[0055] Table 4 Sensor repeatability error

[0056]

[0057] As shown in Table 4, the repeatability error of the sensors made of optical fibers soaked in silane coupling agent is less than 10%, which is much smaller than that of the sensors made of optical fibers not soaked in silane coupling agent. This shows that the sensors treated with silane coupling agent have higher repeatability and can be used repeatedly.

[0058] The fitting curves of the average wavelength change and load of each sensor under three cycles of loading and unloading of the above six groups of sensors are calculated as follows: Figure 6 The sensitivity, linearity and fitting expressions of the six groups of sensors under three cycles of loading and unloading are statistically analyzed, as shown in Table 5:

[0059] Table 5 Sensor sensitivity, linearity and fitting expression

[0060]

[0061] From Table 5 and Figure 6The listed correlation coefficients show that no matter in the loading stage or the unloading stage, the wavelength change of each sensor has a good linear relationship with the load, and the linearity is above 99%, and the wavelength change is positively correlated with the applied load. The sensitivity of the sensors made of optical fibers soaked in silane coupling agents is higher than that of the sensors made of optical fibers not treated with silane coupling agents, indicating that silane coupling agents can improve the bonding force between optical fibers and packaging materials such as silicone, so that the load can be more accurately transmitted to the buried sensing optical fibers, thereby improving the sensitivity of the sensors to load perception.

[0062] From the correlation coefficients listed in the table above, it can be seen that no matter in the loading stage or the unloading stage, the wavelength change of each sensor has a good linear relationship with the load, and the linearity is above 99%, and the wavelength change is positively correlated with the applied load. The sensitivity of the sensors made of optical fibers soaked in silane coupling agents is higher than that of the sensors made of optical fibers not treated with silane coupling agents, indicating that silane coupling agents can improve the bonding force between optical fibers and packaging materials such as silicone, so that the load can be more accurately transmitted to the buried sensing optical fibers, thereby improving the sensitivity of the sensors to load perception.

[0063] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0064] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A novel method for manufacturing a flexible earth pressure sensor, characterized in that: The preparation method comprises the following steps: Pretreatment of the fiber Bragg grating: wipe the fiber Bragg grating with dust-free paper dipped in anhydrous ethanol, and protect the non-test section of the fiber Bragg grating with a fiber protection sleeve, then immerse the fiber Bragg grating in a silane coupling agent. After the measuring section is completely soaked by the silane coupling agent, take out the optical fiber and let it stand at room temperature until the coupling agent is hydrolyzed and dried; Preparation of silica gel solution: first pour silica gel solution into a clean beaker with peeled skin, slowly drip curing agent with a dropper, stir evenly clockwise with a glass rod while adding curing agent, stir until there is no floccules and bubbles in the mixed liquid, and fully mix the two solutions to obtain a silica gel liquid mixture; Sensor packaging: slowly pour the prepared silica gel liquid mixture into the middle axis position of the soil pressure sensor mold and stop, then embed the pre-treated fiber Bragg grating into the slot reserved on the middle axis of the soil pressure sensor mold, apply prestress to the optical fiber, arrange the position of the fiber Bragg grating, and continue to slowly pour the silica gel mixed solution to the top of the soil pressure sensor mold; The sensor is demoulded and cured at room temperature for 8 hours before taking out the cured earth pressure sensor from the earth pressure sensor mold.

2. A method for manufacturing a novel flexible earth pressure sensor according to claim 1, characterized in that: The mass ratio of the silica gel solution to the curing agent is 100:

3.

3. The method for manufacturing a novel flexible earth pressure sensor according to claim 1 is characterized in that: The soil pressure sensor mold is cylindrical and includes an upper box device and a lower box device; the side walls of the upper box device and the lower box device are respectively provided with 4 card slots for fixing optical fibers; the top of the upper box device is provided with a circular glue injection port for injecting a silicone liquid mixture.

4. A method for manufacturing a novel flexible earth pressure sensor according to claim 3, characterized in that: The four card retention slots of the upper box device are arranged in an array with the center position of the side wall of the upper box device as the center; the four card retention slots of the lower box device are arranged in an array with the center position of the side wall of the lower box device as the center.

5. The method for manufacturing a novel flexible earth pressure sensor according to claim 1 is characterized in that: The maximum operating time of the sensor package does not exceed 10 minutes.

6. A novel flexible earth pressure sensor, manufactured by the method for manufacturing a novel flexible earth pressure sensor according to any one of claims 1 to 5, characterized in that: include: Fiber Bragg grating and a flexible conductive substrate; the fiber Bragg grating is arranged in the middle of the flexible conductive substrate, and the fiber Bragg grating is arranged in two groups and is cross-arranged with each other.

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