A serial flexible hinge fiber Bragg grating acceleration seismic geophone
Through the design of the series-connected flexible hinged structure, the problem of poor anti-interference capability of the hinged fiber grating acceleration seismic detector is solved, and high sensitivity and wide band measurement performance are achieved, with a simple structure and low cost.
Patent Information
- Application Number
- CN202210756374.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-06-29
- Publication Date
- 2025-08-19
- Estimated Expiration
- 2042-06-29
AI Technical Summary
The existing hinged fiber grating acceleration seismic detector has poor anti-interference ability and is difficult to meet the actual working requirements.
A series-connected flexible hinge structure is designed, including an L-shaped base, a first and a second flexible hinge, a first and a second mass, and is formed by 3D printing, and the optical fiber grating is suspended in a suspended state, optimizing the size and connection mode of the flexible hinge and mass.
It achieves high sensitivity, wide band and strong anti-interference capability, has a large measurement range, simple structure and low cost.
Smart Images
Figure CN115015999B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a serial flexible hinge type optical fiber Bragg grating acceleration seismic geophone. Background Art
[0002] In seismic geophone technology used in oil and gas exploration, the performance of the detector has a significant impact on exploration accuracy. Traditional electromagnetic geophones are susceptible to electromagnetic interference and are not resistant to high temperatures. Fiber-optic geophones, on the other hand, offer numerous advantages, including high sensitivity, enhanced safety, and a long service life. Fiber Bragg grating (FBG) geophones, as wavelength-modulating passive components, are not affected by light source stability. They also feature a simple, easy-to-process structure and can be applied to distributed measurements. They have a wide range of applications and hold promising prospects.
[0003] The main body of a fiber Bragg grating (FBG) acceleration geophone generally consists of an elastic structure, an inertial mass, and a fiber Bragg grating (FBG). When the geophone receives an acceleration signal, the mass displaces due to inertia, causing the elastic structure to deform. This in turn causes the grating to deform and generate strain, shifting its center wavelength. This change in center wavelength is then measured using a demodulation system to measure the acceleration signal.
[0004] Currently, fiber Bragg grating acceleration geophones primarily include beam, hinge, diaphragm, and elastic cylinder structures. Hinge structures, with their wide measurement range, high precision, and ease of fabrication, have been a research hotspot in recent years. However, hinge structures suffer from poor anti-interference capabilities. Therefore, to meet practical operational requirements, it is necessary to design geophones with wide bandwidths, strong anti-interference capabilities, and high sensitivity. Summary of the Invention
[0005] The technology to be solved by the present invention is to provide a series flexible hinge type fiber Bragg grating acceleration seismic detector with simple structure, high sensitivity, strong anti-interference ability and large measurement range.
[0006] The technical solution adopted to solve the above technical problems is: a serial flexible hinge type fiber Bragg grating acceleration seismic detector, a first flexible hinge is provided on the inner side of the L-shaped base side arm, a first mass block is provided at the end of the first flexible hinge, a second flexible hinge is provided on the other side of the first mass block opposite to the first flexible hinge, a second mass block is provided at the end of the second flexible hinge, the first flexible hinge, the first mass block, the second flexible hinge and the second mass block are connected as a whole and are in a suspended state, the top of the first mass block is lower than the top of the side arm of the base, the top of the side arm of the base is flush with the top of the second mass block, an optical fiber with a grating engraved is provided at the center of the top of the side arm of the base and the top of the second mass block, and the grating part on the optical fiber is in a suspended state.
[0007] As a preferred technical solution, the center lines of the first flexible hinge, the first mass block, the second flexible hinge and the second mass block coincide.
[0008] As a preferred technical solution, the first flexible hinge and the second flexible hinge have the same structure as an elliptical flexible hinge.
[0009] As a preferred technical solution, the long axis of the first flexible hinge and the second flexible hinge is 2 to 3 mm, and the short axis is 1 to 1.5 mm.
[0010] As a preferred technical solution, the minimum thickness t of the first flexible hinge and the second flexible hinge at the recess is 0.5 to 1.2 mm.
[0011] As a preferred technical solution, the weight of the first mass block is less than the weight of the second mass block, and both the first mass block and the second mass block are rectangular parallelepiped structures.
[0012] As a preferred technical solution, the widths of the first mass block and the second mass block are equal, the height of the first mass block is less than the height of the second mass block, and the length of the first mass block is less than the length of the second mass block.
[0013] As a preferred technical solution, the length e1 of the first mass block is 5 mm, the width is 15-20 mm, and the height h1 is 6.2-8.2 mm; the length e2 of the second mass block is 7.5 mm, the width is 15-20 mm, and the height h2 is 16.5-18.2 mm.
[0014] As a preferred technical solution, both ends of the optical fiber are fixed to the top of the L-shaped base side arm and the top of the second mass block with glue, and a certain prestress is applied before fixation.
[0015] As a preferred technical solution, the base, the first flexible hinge, the first mass block, the second flexible hinge and the second mass block are integrally formed by 3D printing.
[0016] The beneficial effects of the present invention are as follows:
[0017] The first flexible hinge, the first mass block, the second flexible hinge and the second mass block of the present invention are connected as one, which makes the processing simple, the overall structure small in size and the cost low. Through simulation experiments, it can be seen that the resonant frequency in the main vibration direction of the present invention is 690.87 Hz, indicating that the detector has a large measurement range, and the lateral interference direction frequency is 7151.3 Hz, which is much larger than the main vibration direction frequency, indicating that the present invention has strong anti-interference ability. The sensitivity of the present invention is 40.3 pm / g in the frequency range of 0 to 300 Hz, indicating that it has high sensitivity in this frequency band. The optical fiber of the present invention adopts a two-point packaging method to effectively avoid chirp. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is a structural schematic diagram of the present invention.
[0019] Figure 2 It is a structural parameter diagram of the present invention.
[0020] Figure 3 It is a mechanical model diagram of the present invention after being subjected to acceleration.
[0021] Figure 4 This is the main vibration direction frequency diagram of Example 1 of the present invention.
[0022] Figure 5 This is the lateral interference direction frequency diagram of Example 1 of the present invention.
[0023] Figure 6 This is a diagram showing the relationship between the displacement of a point on the optical fiber and the frequency in Example 1 of the present invention in the main vibration direction.
[0024] Wherein: base 1; first flexible hinge 2; second flexible hinge 3; first mass block 4; second mass block 5; grating 6; optical fiber 7. DETAILED DESCRIPTION
[0025] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the present invention is not limited to the following embodiments.
[0026] Example 1
[0027] exist Figure 1 、 2 In the embodiment, the serial flexible hinge type fiber Bragg grating acceleration seismic detector is composed of a base 1, a first flexible hinge 2, a second flexible hinge 3, a first mass block 4, a second mass block 5, and an optical fiber 7.
[0028] A first flexible hinge 2 is processed on the inner side of the side arm of the L-shaped base 1, a first mass block 4 is processed on the end of the first flexible hinge 2, a second flexible hinge 3 is processed on the other side of the first mass block 4 opposite to the first flexible hinge 2, and a second mass block 5 is processed on the end of the second flexible hinge 3. The first flexible hinge 2, the first mass block 4, the second flexible hinge 3 and the second mass block 5 are connected as a whole and the center lines coincide with each other in a suspended state. The first flexible hinge 2 and the second flexible hinge 3 have the same structure as an elliptical flexible hinge, with a long axis of 2.5 mm, a short axis of 1 mm, and a minimum thickness t of 1 mm at the notch. The weight of the first mass block 4 is less than the weight of the second mass block 5, and the first mass block 4 and the second mass block 5 are connected as a whole. Both mass blocks 5 are rectangular structures. The length e1 of the first mass block 4 is 5 mm, the width is 20 mm, and the height h1 is 7 mm. The length e2 of the second mass block 5 is 7.5 mm, the width is 20 mm, and the height h2 is 17 mm. The top of the first mass block 4 is lower than the top of the side arm of the base 1, and the top of the side arm of the base 1 is flush with the top of the second mass block 5. The optical fiber 7 with the engraved grating 6 is fixed to the center of the top of the side arm of the base 1 and the top of the second mass block 5 with glue. A certain prestress is applied to the optical fiber 7 before fixation to improve the sensitivity. The grating area length of the grating 6 is 10 mm and the central wavelength is 1551.787 nm. The grating 6 part of the optical fiber 7 is in a suspended state.
[0029] In this embodiment, the base 1, the first flexible hinge 2, the first mass block 4, the second flexible hinge 3 and the second mass block 5 are integrally formed by 3D printing.
[0030] The working principle of the present invention is as follows:
[0031] The external acceleration signal generates inertial force on the first mass block 4 and the second mass block 5, which in turn generates strain in the sensitive structures of the first flexible hinge 2 and the second flexible hinge 3. This in turn generates axial strain in the fiber Bragg grating (FBG), causing the center wavelength of the FBG to change. The center wavelength change is obtained through the demodulation system, enabling the detection of the acceleration signal. The relationship between the center wavelength drift of the FBG and strain can be expressed as:
[0032]
[0033] Among them, λ B is the central wavelength of grating 6, Δλ B is the center wavelength shift, ε is the strain of grating 6, P e is the effective elastic-optical coefficient of optical fiber 7.
[0034] Under the action of the acceleration signal, the first mass block 4 and the second mass block 5 swing slightly around the first flexible hinge 2 under the action of the inertial force, and the second mass block 5 swings slightly around the second flexible hinge 3 at the same time. Figure 3 , the dynamic equation of the entire detector is:
[0035]
[0036] θ is the hinge rotation angle, so the resonant frequency of the detector is:
[0037]
[0038] Where J is the moment of inertia of the entire mass about the central axis of rotation, k f is the elastic stiffness of the fiber, K s is the rotational stiffness of the flexible hinge, expressed as:
[0039]
[0040] Where E is the elastic modulus of the flexure hinge material, ω is the thickness of the flexure hinge, t is the minimum thickness at the flexure hinge notch, a is the major axis of the elliptical flexure hinge, and u is a parameter related to the ratio of the semi-minor axis of the flexure hinge to the minimum thickness at the hinge notch.
[0041] The elastic stiffness of the optical fiber 7 is expressed as:
[0042]
[0043] Among them, E f is the elastic modulus of optical fiber 7, A f is the cross-sectional area of optical fiber 7, and l is the effective length of optical fiber 7.
[0044] When the inertial mass is stimulated by external forces and the hinge rotates, the wavelength drift of the grating 6 is:
[0045]
[0046] a is the external acceleration value, ξ is the damping ratio of the detector, and γ=ω / ω0 is the frequency ratio of the detector.
[0047] In the working flat area, the sensitivity of the detector is expressed as:
[0048]
[0049] like Figures 4-6 Shown are the simulation results of Example 1. Figure 4 is the resonant frequency of the detector in the main vibration direction, which is 690.87 Hz, indicating that the detector has a large measurement range; Figure 5 is the frequency of the detector in the lateral interference direction, which is 7151.3 Hz, much larger than the frequency in the main vibration direction, indicating that the detector has strong anti-interference ability. Figure 6When vibrating in the main vibration direction, the relationship between the displacement of a point on the optical fiber and the frequency is shown. It can be calculated that in the flat area of 0 to 300 Hz, the sensitivity of the detector is 40.3 pm / g, indicating that the detector has a high sensitivity in this frequency band.
[0050] Example 2
[0051] In this embodiment, a first flexible hinge 2 is provided on the inner side of the side arm of the L-shaped base 1. A first mass 4 is machined at the end of the first flexible hinge 2. A second flexible hinge 3 is machined on the other side of the first flexible hinge 4 opposite the first flexible hinge 2. A second mass 5 is machined at the end of the second flexible hinge 3. The first and second flexible hinges 2 and 3 have the same elliptical structure, with a major axis of 2 mm and a minor axis of 1 mm. The minimum thickness t at the notch of the first and second flexible hinges 2 and 3 is 0.5 mm. The first and second mass blocks 4 and 5 are both rectangular parallelepiped structures. The first mass block 4 has a length of 5 mm, a width of 15 mm, and a height of 6.5 mm. The second mass block 5 has a length of 7.5 mm, a width of 15 mm, and a height of 16.5 mm. Other components, their connection relationships, and parameters are the same as those in Example 1.
[0052] Example 3
[0053] In this embodiment, a first flexible hinge 2 is provided on the inner side of the side arm of the L-shaped base 1. A first mass 4 is machined at the end of the first flexible hinge 2. A second flexible hinge 3 is machined on the other side of the first flexible hinge 4 opposite the first flexible hinge 2. A second mass 5 is machined at the end of the second flexible hinge 3. The first and second flexible hinges 2 and 3 have the same elliptical structure, with a major axis of 3 mm and a minor axis of 1.5 mm. The minimum thickness t at the notch of the first and second flexible hinges 2 and 3 is 1.2 mm. The first and second mass 4 and 5 are both rectangular parallelepiped structures. The first mass 4 has a length of 5 mm, a width of 18 mm, and a height of 8.2 mm, while the second mass 5 has a length of 7.5 mm, a width of 18 mm, and a height of 18.2 mm. Other components, their connection relationships, and parameters are the same as those in Example 1.
Claims
1. A serial flexible hinge fiber Bragg grating acceleration seismic geophone, characterized by: A first flexible hinge is provided on the inner side of the L-shaped base side arm, a first mass block is provided at the end of the first flexible hinge, a second flexible hinge is provided on the other side of the first mass block opposite to the first flexible hinge, and a second mass block is provided at the end of the second flexible hinge. The first flexible hinge, the first mass block, the second flexible hinge and the second mass block are connected as a whole and are in a suspended state. The top of the first mass block is lower than the top of the base side arm, and the top of the base side arm is flush with the top of the second mass block. An optical fiber with a grating is provided at the center of the top of the base side arm and the top of the second mass block, and the grating portion on the optical fiber is in a suspended state. The weight of the first mass block is less than the weight of the second mass block, and both the first mass block and the second mass block are rectangular parallelepiped structures; The widths of the first mass block and the second mass block are equal, the height of the first mass block is less than the height of the second mass block, and the length of the first mass block is less than the length of the second mass block.
2. The serial flexible hinge fiber Bragg grating acceleration geophone according to claim 1, characterized in that: The center lines of the first flexible hinge, the first mass, the second flexible hinge and the second mass coincide with each other.
3. The serial flexible hinge fiber Bragg grating acceleration geophone according to claim 1, characterized in that: The first flexible hinge and the second flexible hinge have the same structure as each other, that is, an elliptical flexible hinge.
4. The serial flexible hinge fiber Bragg grating acceleration geophone according to claim 3, characterized in that: The long axis of the first flexible hinge and the second flexible hinge is 2-3 mm, and the short axis is 1-1.5 mm.
5. The serial flexible hinge fiber Bragg grating acceleration geophone according to any one of claims 1 to 3, characterized in that: The minimum thickness t of the first flexible hinge and the second flexible hinge at the notch is 0.5-1.2 mm.
6. The serial flexible hinge fiber Bragg grating acceleration geophone according to claim 1, characterized in that: The length e1 of the first mass block is 5 mm, the width is 15-20 mm, and the height h1 is 6.2-8.2 mm; the length e2 of the second mass block is 7.5 mm, the width is 15-20 mm, and the height h2 is 16.5-18.2 mm.
7. The serial flexible hinge fiber Bragg grating acceleration geophone according to claim 1, characterized in that: The two ends of the optical fiber are fixed to the top of the L-shaped base side arm and the top of the second mass block by glue, and a certain prestress is applied before fixation.
8. The serial flexible hinge fiber Bragg grating acceleration geophone according to claim 1, characterized in that: The base, the first flexible hinge, the first mass block, the second flexible hinge and the second mass block are integrally formed by 3D printing.