Fiber bragg grating soil pressure sensor and manufacturing method thereof

Abstract

The application discloses a fiber Bragg grating soil pressure sensor and a manufacturing method thereof, and solves the problems of small range, poor dynamic matching with the rock-soil medium and insufficient high-frequency signal capturing capacity of the existing sensor. A linear groove is arranged on the inner bottom of a circular box-shaped shell, a first single-mode optical fiber with a fiber Bragg grating is arranged in the linear groove, and protection and sealing are performed on the first single-mode optical fiber. When a dynamic impact soil pressure acts on the circular box-shaped shell, elastic deformation occurs according to the small deflection plate shell theory. The deformation is transmitted to the fiber Bragg grating, and the center wavelength of the FBG is shifted. Through the establishment of a linear mapping relationship between the pressure and the wavelength shift of the FBG, the wide frequency response characteristic is ensured while the large-range dynamic impact soil stress measurement is realized, and the high-frequency signal capturing capacity of the FBG is greatly improved.

Description

Technical Field

[0001] This invention relates to sensors and their manufacturing methods, specifically to a fiber Bragg grating earth pressure sensor and its manufacturing method. Background Technology

[0002] In fields such as explosion impact and protective engineering, measuring dynamic pressure propagating in soil is of great significance. Traditional electrical sensors (such as piezoelectric and resistance strain gauge sensors) are susceptible to strong electromagnetic interference in extreme environments and have inherent drawbacks such as short signal transmission distances. Fiber Bragg grating (FBG) sensors, due to their advantages such as resistance to electromagnetic interference, corrosion resistance, and the ability to achieve long-distance distributed measurement, provide a new solution for stress measurement in the aforementioned extreme environments. Existing technologies already include various FBG-based pressure or stress sensors; for example, there are FBG sensors employing thin diaphragms, large-size flexible structures, or special sensitivity-enhancing configurations. These designs primarily aim to improve the sensor's sensitivity, making it suitable for static or quasi-static, low-to-medium range pressure monitoring scenarios such as bridge health monitoring and oil and gas well pressure measurement.

[0003] However, existing FBG sensor designs still have significant shortcomings when measuring dynamic stress in soil under extreme environments such as explosive impacts. These shortcomings are mainly reflected in the following aspects:

[0004] (1) Small range: The thin diaphragm or large flexible structure adopted in pursuit of high sensitivity improves the sensitivity, but seriously sacrifices the sensor’s load-bearing capacity and inherent frequency, making it unable to accurately measure the impact signal under a large range of hundreds of megapascals.

[0005] (2) Poor dynamic matching with soil and rock media: If the sensor structure is not specially designed according to the characteristics of soil and rock media (e.g., the height-to-diameter ratio is too large), it will introduce significant dynamic matching error, resulting in distortion of the measurement waveform and failure to truly reflect the stress state in the soil.

[0006] (3) Insufficient high-frequency signal capture capability: The inherent frequency of the existing sensor structure is limited, and it is often used in conjunction with a demodulation system with insufficient sampling rate, making it difficult to fully capture the high-frequency details in the impact stress signal.

[0007] Therefore, the existing technology lacks a dynamic soil stress sensor that can simultaneously meet the requirements of high range, wide frequency response, and electromagnetic environment resistance, which severely restricts the accurate measurement of dynamic soil pressure under transient extreme conditions such as explosions and impacts. Summary of the Invention

[0008] To address the technical problems of existing sensors, such as small measurement range, poor dynamic matching with soil and rock media, and insufficient high-frequency signal acquisition capability, this invention provides a fiber Bragg grating soil pressure sensor and its fabrication method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A fiber Bragg grating earth pressure sensor is characterized by comprising a cylindrical housing, a first single-mode optical fiber, a first loose tube, a first armored protective sleeve, and a main connector.

[0011] The inner bottom of the circular box-shaped shell is provided with a linear groove, and the side wall is provided with a mounting hole. The axis of the mounting hole is parallel to the linear groove and corresponds to one end of the linear groove.

[0012] The first loose tube and the first armored protective sleeve are sequentially fitted onto the first single-mode optical fiber from the inside out, and the two ends of the first single-mode optical fiber are exposed outside the first loose tube and the first armored protective sleeve, respectively, forming a first exposed section and a second exposed section. A fiber Bragg grating is engraved on the outside of the first exposed section. The first exposed section extends into the circular box-shaped housing from the mounting hole and is bonded to the linear groove. The second exposed section is used to connect to an external signal receiving device.

[0013] The main connector is fitted outside the first armored protective sleeve at one end near the first exposed section;

[0014] The first loose sleeve end near the first exposed section, the first armored protective sleeve end near the first exposed section, and the main connector end near the first exposed section are all embedded in the mounting hole, and the outer wall of the main connector is connected to the inner wall of the mounting hole.

[0015] Furthermore, the cylindrical shell and the main connector are wrapped with a cement mortar envelope that matches the impedance of the soil and rock medium in the area to be tested.

[0016] Furthermore, the outer diameter of the circular box-shaped shell ranges from 27mm to 33mm, the inner diameter ranges from 12mm to 17mm, and the ratio of its height to its outer diameter ranges from 0.32 to 0.34.

[0017] The linear groove is provided along the diameter of the circular box-shaped shell.

[0018] Furthermore, the circular box-shaped shell is made of titanium alloy and includes a cylindrical shell body with a closed bottom and a circular cover.

[0019] The inner wall of the shell body is a first-level stepped inner wall, including a small-diameter circular inner wall near the inner bottom of the shell body, a large-diameter circular inner wall away from the inner bottom of the shell body, and a circular stepped inner wall located between the small-diameter circular inner wall and the large-diameter circular inner wall and parallel to the inner bottom of the shell body.

[0020] The cover is installed inside the shell body, its circumferential sidewall is threadedly connected to the inner wall of the large-diameter ring, its bottom surface is in contact with the inner wall of the ring step surface, and its top surface is flush with the top surface of the shell body.

[0021] The linear groove is provided on the inner bottom of the shell body;

[0022] The mounting hole is located on the side wall of the shell body.

[0023] Furthermore, an annular groove is provided on the inner wall of the annular stepped surface inside the shell body;

[0024] An annular sealing ring is provided inside the annular groove.

[0025] Furthermore, it also includes a second single-mode optical fiber, a second loose tube, a second armored protective sleeve, and a heat shrink tubing;

[0026] The second loose tube and the second armored protective sleeve are sequentially fitted onto the second single-mode optical fiber from the inside out, and the two ends of the second single-mode optical fiber are exposed outside the second loose tube and the second armored protective sleeve, respectively, forming the third exposed section and the fourth exposed section.

[0027] The second exposed section of the first single-mode fiber and the third exposed section of the second single-mode fiber are fused together to form a fusion splice section.

[0028] The heat shrink tubing is fitted onto the welded section and the outside of the first and second loose tubing near the welded section;

[0029] The fourth exposed section of the second single-mode fiber is used to connect to an external signal receiving device.

[0030] Furthermore, it also includes protective sleeves;

[0031] Note: The assembly formed by the first single-mode fiber, the first loose tube, and the first armored protective sleeve is the first fiber assembly A; the assembly formed by the second single-mode fiber, the second loose tube, and the second armored protective sleeve is the second fiber assembly B.

[0032] The end of the first optical fiber assembly A near the heat shrink tubing, the end of the second optical fiber assembly B near the heat shrink tubing, the heat shrink tubing, and the fusion splice section inside the heat shrink tubing are all installed inside the protective sleeve.

[0033] Rubber sealing blocks are provided between the inner walls of both ends of the protective sleeve and the outer walls of the first optical fiber assembly A and the second optical fiber assembly B.

[0034] Furthermore, it also includes fiber optic connectors;

[0035] The fiber optic connector is connected to the fourth exposed section of the second single-mode fiber, enabling the second single-mode fiber to be connected to an external signal receiving device through the fiber optic connector.

[0036] The fiber optic connector is either an APC fiber optic connector or an FC fiber optic connector.

[0037] A method for fabricating a fiber Bragg grating earth pressure sensor, used to fabricate the aforementioned fiber Bragg grating earth pressure sensor, is characterized by including the following steps:

[0038] Step 1: Insert the first bare section of the first single-mode fiber into the round box-shaped housing through the mounting hole on the side wall of the round box-shaped housing, and bond it into the linear groove, while making the fiber Bragg grating on the outer wall of the first bare section located at the center of the linear groove.

[0039] Step 2: Slide the first loose tube and the first armored protective sleeve onto the first single-mode optical fiber from the inside out, and insert the ends of the two near the first exposed section into the mounting hole;

[0040] Step 3: Fit the main connector onto the outside of the first armored protective sleeve, so that the end closest to the first exposed section extends into the mounting hole and connects with the inner wall of the mounting hole. Then, apply glue to the connection point to complete the fabrication of the fiber Bragg grating earth pressure sensor.

[0041] Furthermore, step 1 specifically includes:

[0042] Step 1.1: Insert the first exposed section of the first single-mode fiber into the round box-shaped housing through the mounting hole on the side wall of the housing body, and install it in the linear groove.

[0043] Step 1.2: Inject UV adhesive evenly into the linear groove to bond the first exposed section to the linear groove, while ensuring that the fiber Bragg grating on the outer wall of the first exposed section is located at the center of the linear groove.

[0044] Step 3 specifically includes:

[0045] Step 3.1: Fit the main connector over the first armored protective sleeve, so that the end closest to the first exposed section extends into the mounting hole and connects with the inner wall of the mounting hole. Inject AB glue at the connection point to make the two firmly connected.

[0046] Step 3.2: Place the annular sealing ring into the annular groove;

[0047] Step 3.3: Apply 703 glue evenly to the inner wall of the large diameter ring of the shell body, and then screw the cover into it to press the cover tightly against the annular sealing ring.

[0048] Step 3.4: Wrap the shell body, cover body and main joint with a cement mortar envelope that matches the impedance of the soil medium in the area to be measured through the mold. After the cement mortar envelope solidifies, remove the mold to complete the fabrication of the fiber Bragg grating soil pressure sensor.

[0049] The beneficial effects of this invention are:

[0050] 1. This invention provides a fiber Bragg grating earth pressure sensor and its fabrication method. A linear groove is provided at the bottom of a cylindrical shell. A first single-mode fiber, inscribed with a fiber Bragg grating, is placed within the linear groove and protected and sealed. When dynamic impact earth pressure acts on the cylindrical shell, it undergoes elastic deformation according to the small deflection plate and shell theory. This deformation is transmitted to the fiber Bragg grating, causing a shift in the FBG's center wavelength. By establishing a linear mapping relationship between pressure and FBG wavelength shift, a wide-range dynamic impact earth stress measurement can be achieved while maintaining broadband response characteristics, greatly improving the FBG's ability to capture high-frequency signals.

[0051] 2. The fiber Bragg grating earth pressure sensor of the present invention uses a cylindrical housing made of titanium alloy, with its outer diameter ranging from 27mm to 33mm and its height-to-diameter ratio ranging from 0.32 to 0.34, forming a titanium alloy diaphragm-type sensor body. The high elastic modulus (approximately 110 GPa) and high yield strength of the titanium alloy diaphragm, combined with the diaphragm-type design, ensure that the sensor can maintain a high natural frequency of over 54.88 kHz while withstanding pressures up to 100 MPa, thereby meeting the measurement requirements of high-frequency dynamic signals.

[0052] 3. The fiber Bragg grating earth pressure sensor of the present invention sets the height-to-diameter ratio of the circular box-shaped shell to be 0.32-0.34, and uses cement mortar with the impedance of the soil medium in the area to be measured to make the enclosure, which ensures the wave propagation matching between the sensor and the soil medium and effectively controls the measurement error of the sensor. Attached Figure Description

[0053] Figure 1 This is a three-dimensional structural schematic diagram of an embodiment of a fiber Bragg grating earth pressure sensor according to the present invention;

[0054] Figure 2 This is a cross-sectional view of a circular box-shaped housing, main connector, annular sealing ring, part of the first single-mode optical fiber, part of the first loose tube, and part of the first armored protective sleeve in an embodiment of a fiber Bragg grating earth pressure sensor of the present invention.

[0055] Figure 3 This is an exploded view of the circular housing and main connector in an embodiment of a fiber Bragg grating earth pressure sensor according to the present invention;

[0056] Figure 4 This is a half-sectional view of the protective sleeve and its internal components in an embodiment of a fiber Bragg grating earth pressure sensor of the present invention.

[0057] Figure 5 This is an exploded view of the protective sleeve and its internal components in an embodiment of a fiber Bragg grating earth pressure sensor according to the present invention.

[0058] Figure 6 This is a schematic diagram of step 3.4 of an embodiment of the manufacturing method of a fiber Bragg grating earth pressure sensor of the present invention, in which a cement mortar encapsulation is wrapped around the cylindrical shell and the main connector using a mold.

[0059] The attached figures are labeled as follows:

[0060] 1. Circular box-shaped shell; 11. Linear groove; 12. Mounting hole; 13. Shell body; 131. Inner wall of small-diameter circular ring; 132. Inner wall of large-diameter circular ring; 133. Inner wall of circular ring stepped surface; 14. Cover; 15. Annular groove; 16. Annular sealing ring; 2. First single-mode optical fiber; 21. First exposed section; 3. First loose tube; 4. First armored protective sleeve; 5. Main connector; 6. Cement mortar enclosure; 7. Second loose tube; 8. Heat shrink tubing; 9. Protective sleeve; 91. Rubber sealing block; 10. Optical fiber connector; 101. Mold; A. First optical fiber assembly; B. Second optical fiber assembly. Detailed Implementation

[0061] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] This invention provides a fiber Bragg grating earth pressure sensor, combined with... Figures 1 to 5 As shown, it includes a circular box-shaped housing 1, a first single-mode optical fiber 2, a first loose tube 3, a first armored protective sleeve 4, a main connector, a second single-mode optical fiber, a second loose tube 7, a second armored protective sleeve, a heat shrink tubing 8, a protective sleeve 9, and an optical fiber connector 10.

[0063] like Figure 2 and Figure 3As shown, the outer diameter of the circular box-shaped shell 1 ranges from 27mm to 33mm, the inner diameter ranges from 12mm to 17mm, and the ratio of its height to its outer diameter ranges from 0.32 to 0.34. In this embodiment, the outer diameter of the circular box-shaped shell 1 is 30mm, the inner diameter is 15mm (i.e., the diameter of the inner wall 131 of the small diameter annulus), and the ratio of its height to its outer diameter is 0.33. The circular box-shaped shell 1 is made of titanium alloy and includes a cylindrical shell body 13 with a closed bottom and a circular cover 14. A linear groove 11 is provided on the inner bottom of the shell body 13, and a mounting hole 12 is provided on its side wall. The axis of the mounting hole 12 is parallel to the linear groove 11 and corresponds to one end of the linear groove 11. The linear groove 11 is set along the diameter of the shell body 13. The inner wall of the shell body 13 is a stepped inner wall, including a small diameter annulus inner wall 131 near the inner bottom of the shell body 13, a large diameter annulus inner wall 132 away from the inner bottom of the shell body 13, and a small diameter annulus inner wall 132 located at the inner bottom of the shell body 13. An inner wall 133 of a circular stepped surface is formed between the inner wall 131 of the large-diameter ring and the inner wall 132 of the large-diameter ring, and is parallel to the inner bottom of the shell body 13. An annular groove 15 is provided in the inner wall 133 of the circular stepped surface inside the shell body 13. An annular sealing ring 16 is provided in the annular groove 15. The cover 14 is installed inside the shell body 13, and its circumferential sidewall is threadedly connected to the inner wall 132 of the large-diameter ring. Its bottom surface contacts the inner wall 133 of the circular stepped surface and the annular sealing ring 16, and its top surface is flush with the top surface of the shell body 13, forming a circular box-shaped diaphragm-type sensor body.

[0064] The first loose tube 3 and the first armored protective sleeve 4 are sequentially fitted onto the first single-mode optical fiber 2 from the inside out, with both ends of the first single-mode optical fiber 2 exposed outside the first loose tube 3 and the first armored protective sleeve 4, forming a first exposed section 21 and a second exposed section. A fiber Bragg grating is engraved on the outside of the first exposed section 21. The first exposed section 21 extends from the mounting hole 12 into the round box-shaped housing 1 and is bonded to the linear groove 11. The other end of the first single-mode optical fiber 2 is used to connect to an external signal receiving device. The main connector 5 is fitted onto the outside of the first armored protective sleeve 4 near the first exposed section 21. The ends of the first loose tube 3, the first armored protective sleeve 4, and the main connector 5 near the first exposed section 21 are all embedded in the mounting hole 12, and the outer wall of the main connector 5 is connected to the inner wall of the mounting hole 12.

[0065] The round box-shaped shell 1 and the main connector 5 are wrapped with a cement mortar envelope 6 that matches the impedance of the soil and rock medium in the area to be tested.

[0066] The second loose tube 7 and the second armored protective sleeve are sequentially fitted onto the second single-mode optical fiber from the inside out, with both ends of the second single-mode optical fiber exposed outside the second loose tube 7 and the second armored protective sleeve, forming the third exposed section and the fourth exposed section; the second exposed section of the first single-mode optical fiber 2 and the third exposed section of the second single-mode optical fiber are fused together to form a fusion section; the heat shrink tube 8 is fitted onto the fusion section and the first loose tube 3 and the second loose tube 7 near the fusion section.

[0067] Note: The assembly formed by the first single-mode fiber 2, the first loose tube 3, and the first armored protective sleeve 4 is the first fiber assembly A, and the assembly formed by the second single-mode fiber 2, the second loose tube 7, and the second armored protective sleeve is the second fiber assembly B.

[0068] like Figure 4 and Figure 5 As shown, the end of the first optical fiber assembly A near the heat shrink tubing, the end of the second optical fiber assembly B near the heat shrink tubing 8, the heat shrink tubing 8, and the fusion splice section inside the heat shrink tubing 8 are all installed inside the protective sleeve 9; rubber sealing blocks 91 are provided between the inner walls of both ends of the protective sleeve 9 and the outer walls of the first optical fiber assembly A and the second optical fiber assembly B.

[0069] The fiber optic connector 10 is connected to the fourth exposed section of the second single-mode fiber, enabling the second single-mode fiber to be connected to an external signal receiving device through the fiber optic connector 10; the fiber optic connector 10 is selected from APC fiber optic connectors or FC fiber optic connectors.

[0070] This invention provides a method for fabricating a fiber Bragg grating earth pressure sensor, which includes the following steps:

[0071] Step 1 specifically includes:

[0072] Step 1.1: Insert the first exposed section 21 of the first single-mode fiber 2 into the shell body 13 through the mounting hole 12 on the side wall of the shell body 13, and install the first exposed section 21 in the linear groove 11, so that the fiber Bragg grating (FBG grating) on ​​the outer wall of the first exposed section 21 is located at the center of the linear groove 11.

[0073] Step 1.2: Using an automated dispensing system, UV adhesive is evenly injected into the linear groove 11 along the channel. The UV adhesive should fill the linear groove 11 and be slightly higher than the opening of the linear groove 11 but not overflow. After dispensing, UV light source is used to irradiate for about 30 seconds to allow the UV adhesive to fully cure, thereby bonding the first exposed section 21 to the linear groove 11 and firmly attaching the FBG grid to the central area of ​​the linear groove 11, that is, the central area of ​​the inner bottom of the shell body 13, so as to sensitively sense the maximum radial strain generated by the sensor under pressure.

[0074] To ensure that the FBG grid is accurately located at the center of the linear groove 11, the length of the first exposed section 21 of the first single-mode fiber 2 needs to be determined and trimmed according to the distance from the fiber insertion hole to the center of the linear groove 11, so that the FBG grid is aligned with the central area of ​​the linear groove 11 after insertion.

[0075] Step 2: Place the first loose tube 3 and the first armored protective sleeve 4 onto the outside of the first single-mode optical fiber 2 from the inside out, and insert the end of the two near the first exposed section 21 into the mounting hole 12.

[0076] Step 3 specifically includes:

[0077] Step 3.1: Fit the main connector 5 onto the outside of the first armored protective sleeve 4, so that one end of it near the first exposed section 21 extends into the mounting hole 12 and connects with the inner wall of the mounting hole 12. Then inject AB glue at the connection to fix it.

[0078] Step 3.2: Place the annular sealing ring 16 into the annular groove 15;

[0079] Step 3.3: Apply 703 glue evenly to the inner wall 132 of the large diameter ring of the shell body 13, and then screw in the cover body 14 to press the cover body 14 tightly against the annular sealing ring 16.

[0080] Step 3.4, as follows Figure 6 As shown, a cement mortar package 6 is wrapped around the outside of the circular box-shaped housing 1 and the main connector 5 using a mold 101. After the cement mortar package 6 solidifies, the mold 101 is removed, thus completing the fabrication of the fiber Bragg grating earth pressure sensor.

[0081] To ensure good contact between the sensor and the soil medium and to reduce dynamic matching errors caused by uneven contact, a cement mortar enclosure 6 needs to be fabricated on the outside of the sensor body (i.e., the cylindrical housing 1, its internal components, and the main connector 5) after its fabrication. The steps for fabricating the cement mortar enclosure 6 are as follows:

[0082] First, the lower and upper molds are combined to form a cylindrical mold with an inner diameter of 50 mm and a height of 25 mm. The encapsulated sensor body is placed in the center of the mold. Then, pre-mixed cement mortar, consistent with the impedance of the soil medium, is poured into the mold and vibrated to ensure that the mortar completely covers the cylindrical shell 1 and the main connector 5 without any air bubbles. Afterward, the cement mortar is allowed to fully solidify, and then the mold is removed. The solidified cement mortar enclosure 6 is then cut and surface-polished as necessary to ensure a smooth outer surface and uniform thickness, ultimately forming a sensor body that matches the mechanical impedance of the surrounding soil. This cement mortar enclosure 6 effectively transmits soil stress and protects the sensor body.

[0083] Regarding the connection between the first single-mode fiber 2 and the second single-mode fiber:

[0084] First, the second exposed section of the first single-mode fiber 2 and the third exposed section of the second single-mode fiber are fused together using a fiber optic fusion splicer to form a fusion section. Then, a heat shrink tube 8 is installed outside the fusion section for protection. The two ends of the heat shrink tube 8 are respectively pressed onto the outside of the first loose tube 3 and the second loose tube 7, rather than the outside of the second and third exposed sections. Then, rubber sealing blocks 91 are installed on the outside of the first armored protective sleeve 4 and the end of the second armored protective sleeve closest to the heat shrink tube 8. Finally, with the heat shrink tube 8 as the center, a protective sleeve 9 is installed outside it, and the two rubber sealing blocks 91 are embedded in the grooves at both ends of the inner wall of the protective sleeve 9. Then, 703 glue is evenly applied to the joint of the rubber sealing blocks 91.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fiber Bragg grating earth pressure sensor, characterized in that: It includes a round box-shaped housing (1), a first single-mode optical fiber (2), a first loose tube (3), a first armored protective sleeve (4), and a main connector (5); The inner bottom of the round box-shaped shell (1) is provided with a linear groove (11), and the side wall is provided with a mounting hole (12). The axis of the mounting hole (12) is parallel to the linear groove (11) and corresponds to one end of the linear groove (11). The first loose tube (3) and the first armored protective sleeve (4) are sequentially fitted onto the outside of the first single-mode optical fiber (2) from the inside to the outside, and the two ends of the first single-mode optical fiber (2) are exposed outside the first loose tube (3) and the first armored protective sleeve (4) respectively, forming a first exposed section (21) and a second exposed section. The first exposed section (21) is engraved with a fiber Bragg grating. The first exposed section (21) extends into the round box-shaped housing (1) from the mounting hole (12) and is bonded to the linear groove (11). The second exposed section is used to connect to an external signal receiving device. The main connector (5) is fitted onto the outside of the first armored protective sleeve (4) near the first exposed section (21); The first loose sleeve (3) is fitted into the first exposed section (21) at one end, the first armored protective sleeve (4) is fitted into the first exposed section (21) at one end, and the main connector (5) is fitted into the first exposed section (21) at one end. The outer wall of the main connector (5) is connected to the inner wall of the mounting hole (12).

2. The fiber Bragg grating earth pressure sensor according to claim 1, characterized in that: The circular shell (1) and the main connector (5) are wrapped with a cement mortar envelope (6) that matches the impedance of the soil and rock medium in the area to be tested.

3. The fiber Bragg grating earth pressure sensor according to claim 2, characterized in that: The outer diameter of the circular box-shaped shell (1) ranges from 27 mm to 33 mm, the inner diameter ranges from 12 mm to 17 mm, and the ratio of its height to its outer diameter ranges from 0.32 to 0.

34. The linear groove (11) is provided along the diameter of the circular box-shaped shell (1).

4. The fiber Bragg grating earth pressure sensor according to any one of claims 1-3, characterized in that: The circular box-shaped shell (1) is made of titanium alloy and includes a cylindrical shell body (13) with a closed bottom and a circular cover (14). The inner wall of the shell body (13) is a first-level stepped inner wall, including a small-diameter circular inner wall (131) near the inner bottom of the shell body (13), a large-diameter circular inner wall (132) away from the inner bottom of the shell body (13), and a circular stepped inner wall (133) located between the small-diameter circular inner wall (131) and the large-diameter circular inner wall (132) and parallel to the inner bottom of the shell body (13). The cover (14) is installed inside the shell body (13), its circumferential sidewall is threadedly connected to the inner wall (132) of the large diameter ring, its bottom surface is in contact with the inner wall (133) of the ring step surface, and its top surface is flush with the top surface of the shell body (13). The linear groove (11) is provided on the inner bottom of the shell body (13); The mounting hole (12) is provided on the side wall of the shell body (13).

5. The fiber Bragg grating earth pressure sensor according to claim 4, characterized in that: An annular groove (15) is provided on the inner wall (133) of the annular stepped surface of the shell body (13). An annular sealing ring (16) is provided inside the annular groove (15).

6. The fiber Bragg grating earth pressure sensor according to claim 5, characterized in that: It also includes a second single-mode fiber, a second loose tube (7), a second armored protective sleeve, and a heat shrink tubing (8); The second loose tube (7) and the second armored protective sleeve are sequentially fitted onto the second single-mode optical fiber from the inside to the outside, and the two ends of the second single-mode optical fiber are exposed outside the second loose tube (7) and the second armored protective sleeve, respectively, forming the third exposed section and the fourth exposed section. The second exposed section of the first single-mode fiber (2) and the third exposed section of the second single-mode fiber are fused together to form a fusion section; The heat shrink tubing (8) is sleeved on the outside of the weld section and the first loose tubing (3) and the second loose tubing (7) near the weld section; The fourth exposed section of the second single-mode fiber is used to connect to an external signal receiving device.

7. The fiber Bragg grating earth pressure sensor according to claim 6, characterized in that: It also includes a protective sleeve (9); Note: The first single-mode fiber (2), the first loose tube (3) and the first armored protective sleeve (4) form the first fiber assembly A, and the second single-mode fiber, the second loose tube (7) and the second armored protective sleeve form the second fiber assembly B. The first optical fiber assembly A, the end of the heat shrink tubing (8), the second optical fiber assembly B, the heat shrink tubing (8), and the fusion splice section inside the heat shrink tubing (8) are all installed inside the protective sleeve (9). Rubber sealing blocks (91) are provided between the inner walls of both ends of the protective sleeve (9) and the outer walls of the first optical fiber assembly A and the second optical fiber assembly B.

8. The fiber Bragg grating earth pressure sensor according to claim 7, characterized in that: It also includes fiber optic connectors (10); The fiber optic connector (10) is connected to the fourth exposed section of the second single-mode fiber, so that the second single-mode fiber can be connected to an external signal receiving device through the fiber optic connector (10). The fiber optic connector (10) is an APC fiber optic connector or an FC fiber optic connector.

9. A method for fabricating a fiber Bragg grating earth pressure sensor, used to fabricate the fiber Bragg grating earth pressure sensor according to any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Insert the first bare section (21) of the first single-mode fiber (2) into the round box-shaped housing (1) through the mounting hole (12) on the side wall of the round box-shaped housing (1) and attach it to the linear groove (11). At the same time, make the fiber Bragg grating on the outer wall of the first bare section (21) located at the center of the linear groove (11). Step 2: Place the first loose tube (3) and the first armored protective sleeve (4) onto the outside of the first single-mode optical fiber (2) from the inside out, and insert the end of the two near the first exposed section (21) into the mounting hole (12); Step 3: Fit the main connector (5) onto the outside of the first armored protective sleeve (4), so that one end of it close to the first exposed section (21) extends into the mounting hole (12) and connects with the inner wall of the mounting hole (12). Then inject glue at the connection to complete the fabrication of the fiber Bragg grating earth pressure sensor.

10. The method for manufacturing the fiber Bragg grating earth pressure sensor according to claim 9, characterized in that: Step 1 specifically includes: Step 1.1: Insert the first exposed section (21) of the first single-mode fiber (2) into the round box-shaped housing (1) through the mounting hole (12) on the side wall of the housing body (13) and install it in the linear groove (11). Step 1.2: Inject UV glue evenly into the linear groove (11) so that the first exposed section (21) is bonded to the linear groove (11), and at the same time, make the fiber Bragg grating on the outer wall of the first exposed section (21) located in the center of the linear groove (11). Step 3 specifically includes: Step 3.1: Fit the main connector (5) onto the outside of the first armored protective sleeve (4), so that one end of it close to the first exposed section (21) extends into the mounting hole (12) and connects with the inner wall of the mounting hole (12). Inject AB glue at the connection point to make the two firmly connected. Step 3.2: Place the annular sealing ring (16) into the annular groove (15); Step 3.3: Apply 703 glue evenly to the inner wall (132) of the large diameter ring of the shell body (13), and then screw in the cover (14) to press the cover (14) tightly against the annular sealing ring (16). Step 3.4: Wrap the shell body (13), cover body (14) and main connector (5) with cement mortar (6) that is consistent with the impedance of the soil and rock medium in the area to be measured through the mold (101). After the cement mortar (6) solidifies, remove the mold (101) to complete the fabrication of the fiber Bragg grating soil pressure sensor.

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