A flexible soil stress sensor

Abstract

The utility model relates to flexible sensor technical field, specifically disclose a kind of flexible soil stress sensor, comprising: fiber bragg grating, connecting wire and flexible conductive matrix, the middle part of flexible conductive matrix is provided with fiber bragg grating, fiber bragg grating is set to two groups and mutually cross-shaped and is set;The utility model is to realize the accurate perception to soil stress, according to the characteristics that fiber bragg grating is sensitive to axial strain, not sensitive to radial strain, design into "cross" type sensing unit, the purpose of arranging two fiber bragg gratings is to obtain the average value of the wavelength change of both in data processing process to reduce the error caused by loading eccentricity, when there is normal stress on the upper surface of flexible conductive matrix, flexible conductive matrix is deformed, cause internal optical fiber to produce corresponding axial strain, by detecting the wavelength change of fiber bragg grating, the axial strain is calculated, and the normal stress value to be measured is calculated.

Description

Technical Field

[0001] This utility model belongs to the field of flexible sensor technology, specifically relating to a flexible soil stress sensor. Background Technology

[0002] A fiber Bragg grating (FBG) is a passive optical device, belonging to the category of uniform short-period fiber gratings. It features a uniform axial refractive index distribution, a fixed-size core, and a fixed refractive index. Compared to other types of fiber gratings such as chirped fiber gratings, apodized fiber gratings, and phase-shifted fiber gratings, it is more suitable for sensing changes in parameters such as pressure, strain, and temperature. The fiber used in FBGs is germanium-doped silica fiber. During fabrication, the ultraviolet photosensitivity of the fiber is utilized, and an ultraviolet laser is used to create an optical waveguide structure with a periodically changing refractive index on the fiber core, similar in principle to a narrowband filter.

[0003] According to fiber coupled-mode theory, a broadband light source transmits light with a certain bandwidth into the fiber core through a circulator. When the broadband light is transmitted through the fiber Bragg grating, the light that satisfies the fiber Bragg condition will be reflected, while the other part will be transmitted back in the original direction. This specific wavelength that is reflected back is called the Bragg wavelength. By receiving the corresponding reflected light signal, the center wavelength shift of the Bragg grating can be demodulated, thereby detecting changes in external physical quantities.

[0004] The encapsulation material used in the manufacturing process of fiber Bragg grating sensors is crucial, as it protects the optical fiber and enhances sensitivity. Therefore, the manufacturing process of the encapsulation material should be as simple as possible to avoid damaging the optical fiber, and the encapsulation material should effectively transfer strain to the optical fiber to reduce loss. Currently, there are three main encapsulation methods for fiber Bragg grating sensors: two-end clamping, substrate, and embedded.

[0005] Sensors fabricated using the two-end clamping encapsulation method have clamping components placed at both ends of the sensor, and structural strain is transferred to the fiber Bragg grating through these clamping components. Two-end clamping sensors can be embedded inside the structure being measured or attached to its surface, offering simple installation and easy replacement and reuse. However, due to the short lifespan and susceptibility to corrosion of the adhesive used to bond the clamping components to the sensor, two-end clamping sensors have poor durability.

[0006] Sensors fabricated using the substrate packaging method involve attaching a fiber Bragg grating to a groove in a substrate, forming a single testing unit with the substrate. Structural strain is transferred from the substrate to the fiber Bragg grating, which is simple and convenient. However, substrate packaging has poor interface compatibility and significant losses during strain transfer, resulting in lower testing accuracy.

[0007] Sensors fabricated using embedded packaging methods encapsulate fiber Bragg gratings within composite materials, which reduces strain transmission loss to some extent; however, this method places high demands on packaging equipment and conditions, and the choice of composite material also affects the sensor's sensitivity. Utility Model Content

[0008] The purpose of this invention is to provide a flexible soil stress sensor to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, this utility model provides the following technical solution:

[0010] A flexible soil stress sensor, comprising:

[0011] The fiber Bragg grating, connecting wires, and a flexible conductive substrate are provided. The fiber Bragg grating is disposed in the middle of the flexible conductive substrate. The fiber Bragg grating is connected to the connecting wires. The fiber Bragg grating is configured in two groups and is arranged in a cross shape with each other.

[0012] Preferably, the flexible conductive substrate is a cylinder with a diameter of 40 mm.

[0013] Preferably, the flexible conductive substrate is configured as a cylinder with a height of 10 mm.

[0014] Preferably, the flexible conductive substrate is silicone rubber, which consists of two parts: silicone and a curing agent.

[0015] Preferably, the fiber Bragg grating is parallel to the bottom surface of the flexible conductive substrate and is 5 mm away from the bottom surface of the flexible conductive substrate.

[0016] Compared with the prior art, the beneficial effects of this utility model are:

[0017] To achieve accurate sensing of soil stress, this invention utilizes the characteristic of fiber Bragg gratings being sensitive to axial strain but insensitive to radial strain. A "cross"-shaped sensing unit is designed, with two fiber Bragg gratings arranged to calculate the average wavelength change of both during data processing, thus reducing errors caused by load eccentricity. When normal stress is applied to the upper surface of the flexible conductive substrate, the substrate deforms, causing corresponding axial strain in the internal optical fibers. By detecting the wavelength change of the fiber Bragg gratings, the axial strain is calculated, thereby deducing the value of the normal stress to be measured. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0019] Figure 2 This is a side sectional view of the present invention;

[0020] In the diagram: 10. Fiber Bragg grating;

[0021] 20. Connect the wires;

[0022] 30. Flexible conductive substrate. Detailed Implementation

[0023] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model. Example

[0024] Please see Figures 1-2 As shown, a flexible soil stress sensor includes:

[0025] The fiber Bragg grating 10, the connecting wire 20, and the flexible conductive substrate 30 are provided. The fiber Bragg grating 10 is disposed in the middle of the flexible conductive substrate 30. The fiber Bragg grating 10 is connected to the connecting wire 20. The fiber Bragg grating 10 is configured in two sets and is arranged in a cross shape with each other.

[0026] To achieve accurate sensing of soil stress, based on the characteristics of fiber Bragg grating 10 being sensitive to axial strain but insensitive to radial strain, a "cross"-shaped sensing unit was designed. The purpose of arranging two fiber Bragg gratings 10 is to calculate the average wavelength change of the two during data processing to reduce the error caused by loading eccentricity.

[0027] refer to Figures 1-2 As shown, the flexible conductive substrate 30 is configured as a cylinder with a diameter of 40 mm.

[0028] refer to Figures 1-2 As shown, the flexible conductive substrate 30 is configured as a cylinder with a height of 10 mm.

[0029] refer to Figures 1-2 As shown, the flexible conductive substrate 30 is silicone rubber, which consists of two parts: silicone and curing agent.

[0030] Common encapsulation materials include polymers, metals, and alloys. According to the theory of materials mechanics, when a fiber Bragg grating is encapsulated in an elastic material with a low elastic modulus, the resulting composite has an elastic modulus much smaller than that of the fiber Bragg grating itself, achieving a sensitivity enhancement effect. To ensure that the elastic modulus of the encapsulated sensor is much smaller than that of the soil, polymers are chosen as the encapsulation material. Generally, resin-based and rubber-based polymers are suitable for encapsulating fiber Bragg gratings. Resin-based materials have high load-bearing capacity, strength, and heat resistance, but their pressure sensitivity is low. Rubber-based materials have a low coefficient of thermal expansion and a low elastic modulus, making them more sensitive to pressure but less sensitive to temperature; they are mostly used for encapsulating pressure sensors.

[0031] After investigating the parameters of various polymers, silica gel solution (xSiO2) was selected due to its flexible texture, environmental friendliness, non-toxicity, non-irritating properties, and lack of allergic reactions. YH2O) is used as the sensor's sensitizing material to encapsulate a bare fiber Bragg grating. Specifically, this involves mixing and curing a silicone rubber solution and a curing agent to form a flexible conductive substrate 30. Further, the silicone rubber is prepared according to a mass ratio of 100:3 between the silicone rubber solution and the curing agent. First, 40g of silicone rubber solution is poured into a clean, peeled beaker. Then, 1.2g of curing agent is slowly added using a dropper while simultaneously stirring clockwise with a glass rod until the mixture is free of flocculation and bubbles, ensuring thorough mixing. The mixture is then cured at room temperature for 8 hours. Furthermore, the entire encapsulation process should be completed within 10 minutes to prevent the mixture from curing exothermically in the beaker.

[0032] refer to Figures 1-2 As shown, the fiber Bragg grating 10 is parallel to the bottom surface of the flexible conductive substrate 30, and the distance between the fiber Bragg grating 10 and the bottom surface of the flexible conductive substrate 30 is 5mm.

[0033] When a normal stress is applied to the upper surface of the flexible conductive substrate 30, the flexible conductive substrate 30 deforms, causing the internal optical fiber to generate a corresponding axial strain. By detecting the wavelength change of the fiber Bragg grating 10, the axial strain is calculated, thereby deducing the value of the normal stress to be measured.

[0034] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flexible soil stress sensor, characterized in that, include: The fiber Bragg grating (10), connecting wire (20) and flexible conductive substrate (30) are provided in the middle of the flexible conductive substrate (30). The fiber Bragg grating (10) is connected to the connecting wire (20). The fiber Bragg grating (10) is provided in two sets and is arranged in a cross shape with each other. The flexible conductive substrate (30) is silicone rubber; The fiber Bragg grating (10) is parallel to the bottom surface of the flexible conductive substrate (30) and is 5 mm away from the bottom surface of the flexible conductive substrate (30).

2. The flexible soil stress sensor according to claim 1, characterized in that: The flexible conductive substrate (30) is configured as a cylinder with a diameter of 40 mm.

3. A flexible soil stress sensor according to claim 2, characterized in that: The flexible conductive substrate (30) is configured as a cylinder with a height of 10 mm.

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