Large-strain fiber Bragg grating sensor based on desensitization ring

Abstract

A large-strain fiber Bragg grating sensor based on a desensitization ring mainly consists of a fiber Bragg grating, a desensitization ring, a fixing block, and a support column. The desensitization ring is tightened and fixed to the fixing block by applying pretension, and the support column is assembled and connected to the desensitization ring through the fixing block. Installing a grating on the desensitization ring allows for arbitrary desensitization. When subjected to external tension or compression, the desensitization ring deforms, causing strain in the fiber Bragg grating mounted on it. This strain causes a shift in the center wavelength of the fiber Bragg grating. The product of the center wavelength shift and the desensitized sensitivity coefficient is the measured strain value in the x-axis direction. This sensor's desensitization ring responds to strain in a single direction through geometric deformation, exhibiting a large deformation range. By adjusting the angle between the fiber Bragg grating and the strain application direction, large strain measurements within different strain ranges can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic grating sensing technology, and in particular, it applies large strain desensitization measurement of fiber optic gratings. Background Technology

[0002] Fiber Bragg gratings (FBGs), as wavelength modulation devices, have garnered widespread attention in the field of fiber optic sensing. Compared to intensity-modulated fiber optic sensors, they are unaffected by light source fluctuations and are advantageous for wavelength division multiplexing (WDM). Compared to phase-modulated fiber optic sensors, they offer advantages such as simpler components, smaller size, and ease of multiplexing. Compared to polarization-modulated fiber optic sensors, they are easier to demodulate and multiplex. Compared to traditional electrical sensors, FBG sensors offer advantages such as simple structure, small size, resistance to electromagnetic interference, and good multiplexing, making them widely applicable in harsh working environments such as aerospace, civil engineering health monitoring, and petroleum engineering. However, conventional FBGs have limited strain tolerance, making it impossible to measure signals under high strain conditions. Therefore, researching high-strain FBG sensors based on desensitization rings to achieve desensitization and realize the measurement of external signals under high strain is of great significance.

[0003] Currently, fiber Bragg gratings are mainly packaged in substrate, tubular, and embedded forms. For large-strain fiber Bragg grating sensors, desensitizing tubes are primarily used to encapsulate the fiber Bragg grating to achieve desensitization, as in "A Packaging Method for a Fiber Bragg Grating Sensitivity-Increasing / Desensitizing Strain Sensor" (Ren Liang, Li Hongnan, Patent Application No.: CN200710157591.3). This sensor is prone to lateral displacement of the desensitizing tube relative to the fixed support point under external forces, leading to inaccurate measurement results. Another example is the "Large-Strain Fiber Bragg Grating Sensor" (Li Chuan, Wu Kun, Ye Xiaoping, Patent Application No.: CN201020123871.X), which expands the strain detection range by encapsulating the fiber Bragg grating with a multi-layered mechanical structure. However, this sensor suffers from limitations such as limited material design and insufficient desensitization effect. Summary of the Invention

[0004] A large-strain fiber Bragg grating sensor based on an attenuation ring mainly consists of a fiber Bragg grating, an attenuation ring, a fixing block, and a support column. Under large strain conditions, i.e., strain exceeding the strain range that a conventional fiber Bragg grating can withstand, the support column mounted on the object under test is displaced by the strain of the object under test. This displacement causes the attenuation ring to undergo irregular deformation through the fixing block. Let the strain axis be the x-axis. If the attenuation ring is subjected to tension in the x-axis direction, it will contract in the y-axis direction; conversely, if the attenuation ring is subjected to compression in the x-axis direction, it will stretch in the y-axis direction. Therefore, when subjected to tension in the x-direction, if the fiber grating is mounted on the desensitizing ring along the x-axis, the fiber grating is in a tensile state, generating the maximum positive strain. When mounted along the y-axis, the fiber grating is in a compressed state, generating the maximum negative strain. Conversely, when subjected to compression in the x-direction, if the fiber grating is mounted on the desensitizing ring along the x-axis, the fiber grating is in a compressed state, generating the maximum negative strain. When mounted along the y-axis, the fiber grating is in a tensile state, generating the maximum positive strain. If the fiber grating is mounted between the x-axis and y-axis, regardless of whether tension or compression is applied in the x-axis direction, the strain generated on the fiber grating will be between the maximum positive strain and the maximum negative strain. Furthermore, there is a specific angular direction between the x-axis and y-axis where the strain always remains zero; this direction can be called the zero-strain direction. When a grating is installed between the x-axis and the zero-strain direction, its strain sensitivity gradually decreases as the angle between the grating and the x-axis increases. When a grating is installed between the zero-strain direction and the y-axis, its strain sensitivity gradually decreases to 0 as the angle between the grating and the y-axis increases. Therefore, arbitrary desensitization can be achieved by installing a grating on a desensitization ring. When the desensitization ring is subjected to external tension or compression, it deforms, causing strain in the fiber grating installed on the ring. This strain causes a shift in the center wavelength of the fiber grating. The product of the center wavelength shift and the desensitized sensitivity coefficient is the measured value of the strain in the x-axis direction.

[0005] The purpose of this invention is to provide a large-strain fiber Bragg grating sensor based on a desensitization ring, which has advantages such as small size and simple structure. Unlike traditional sensors that use desensitization tubes for desensitization, this invention is based on the principle that the desensitization ring has a compensating effect on the large strain generated by the external test signal, thereby achieving desensitization of the fiber Bragg grating sensor under large strain, and the desensitization effect is significant. Under the action of the external test signal, the desensitization ring is subjected to uniform stress and its shape undergoes regular changes, causing the center wavelength of the fiber Bragg grating to drift, which enables the measurement of the external test signal under large strain conditions.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a large strain fiber grating sensor based on a desensitizing ring, mainly composed of a fiber grating, a desensitizing ring, a fixing block, and a support column; the desensitizing ring and the fixing block are tightened and fixed by applying pretension; the support column is assembled and connected to the desensitizing ring through the fixing block; the fiber grating is installed on the desensitizing ring.

[0007] When the included angle between the fiber Bragg grating and the strain axis is changed, different desensitization effects can be achieved, and the desensitization principle is as follows:

[0008] When strain is applied to the strain axis, the distance between the two support pillars elongates or shortens. Since the desensitization ring is mounted on the support pillars via fixing blocks, under large strain conditions, the support pillars drive the fixing blocks to displace along the strain direction, thereby driving the desensitization ring to produce irregular deformation. The deformation of the desensitization ring is affected by the contact area among the support pillars, the fixing blocks and the desensitization ring. The deformed desensitization ring stretches or retracts the fiber Bragg grating fixed thereon, and transmits the strain information of the object to be measured under the support pillars to the fiber Bragg grating. Since the direction of the fiber Bragg grating is inconsistent with the strain direction of the object to be measured, the deformation amount of the desensitization ring in the direction of the fiber Bragg grating is smaller than the deformation amount of the object to be measured, thereby realizing desensitization of strain sensing.

[0009] The desensitization ring is annular, with an outer diameter D and an inner diameter d. The fiber Bragg grating is mounted on the desensitization ring with a spacing a (d < a < D), and the included angle between the fiber Bragg grating and the strain axis is defined as θ. Under large strain conditions, for different included angles θ, the relationship curve between the strain amount applied on the strain axis and the strain amount generated by the fiber Bragg grating takes the strain amount applied along the strain axis as the horizontal axis and the strain amount generated by the fiber Bragg grating as the vertical axis, and the slope is the desensitization coefficient of the sensor. The desensitization coefficient of the sensor is determined by the included angle θ, and the desensitization coefficient gradually decreases to zero as the included angle θ increases, and the strain sensitivity also gradually decreases to zero. If the included angle θ continues to increase, the desensitization coefficient becomes negative, its absolute value gradually increases from zero, the strain sensitivity is also negative, and its absolute value gradually increases from zero. Therefore, different sensitivities can be obtained by adjusting the included angle θ between the fiber Bragg grating and the strain axis, so as to realize measurement of different strain ranges. The strain measurement range is determined by the elastic deformation range of the desensitization ring material, which can be far larger than the maximum strain range of the fiber Bragg grating, and is no longer constrained by the elastic range of the fiber Bragg grating.

[0010] When a fixed strain is applied along the strain axis, the relationship curve of the strain generated by the fiber Bragg grating varying with θ takes the included angle θ between the fiber Bragg grating and the strain axis as the horizontal axis and the strain amount generated by the fiber Bragg grating as the vertical axis. Wherein, curve 1, curve 2 and curve 3 are respectively the strain response curves of the fiber Bragg grating when the applied fixed strain values are 15952με, 10695με and 6013με, and curve 4 and curve 5 are respectively the strain response curves of the fiber Bragg grating when the applied fixed strain values are -2498με and -6317με. Under tension, as the included angle θ increases, the strain generated by the fiber Bragg grating gradually decreases, drops to zero when θ is approximately 40°, and when the angle exceeds this value, the fiber Bragg grating generates negative strain, and the strain magnitude increases as the angle increases; under compression, as the included angle θ increases, the fiber Bragg grating generates negative strain, and the strain magnitude gradually decreases, drops to zero when θ is approximately 40°, and when the angle exceeds this value, the fiber Bragg grating generates positive strain, and the strain magnitude increases as the angle increases.

[0011] x represents the direction of applied strain, and y represents the orthogonal direction of applied strain. If the fiber grating is installed on regions I1 and I2 symmetrical to the x-axis, it will produce positive strain when stretched along the x-axis and negative strain when compressed. Similarly, if the fiber grating is installed on regions II1 and II2 symmetrical to the y-axis, it will produce negative strain when stretched along the x-axis and positive strain when compressed. Furthermore, within regions I and II, there are installation points where the strain generated by the fiber grating is equal in magnitude but opposite in sign. If a fiber grating is installed in two directions with opposite strain directions and the same sensitivity, and their strain signals are directly subtracted, the influence of external temperature changes can be compensated, and the sensor sensitivity will be doubled. In summary, the large-strain fiber grating sensor based on the desensitization ring can achieve large-strain measurement of different strain ranges by adjusting the angle between the fiber grating and the strain application axis.

[0012] Compared with existing inventions, the advantages of this invention are:

[0013] Conventional fiber Bragg gratings have limited strain tolerance. By installing a grating on a desensitization ring, arbitrary desensitization can be achieved. The desensitization ring of this sensor responds to strain in a single direction through geometric deformation, and has the characteristic of a large deformation range. By adjusting the angle between the fiber Bragg grating and the strain application direction, large strain measurements of different strain ranges can be achieved. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A top view of a large strain fiber Bragg grating sensor structure based on a desensitization ring;

[0016] Figure 2 The curves show the relationship between the strain applied along the strain axis and the strain generated by the fiber grating under different included angles θ under large strain conditions.

[0017] Figure 3 The curve showing the relationship between strain generated by the fiber grating and θ when a fixed strain is applied along the strain axis;

[0018] Figure 4 A schematic diagram showing the different effects of strain when the fiber Bragg grating is installed in different areas.

[0019] Figure 5This is a three-dimensional structural diagram of the desensitizing ring of the present invention when the cross-section is circular;

[0020] Figure 6 This is a three-dimensional structural diagram of the desensitizing ring when its cross-section is rectangular.

[0021] Figure 7 This is a three-dimensional structural diagram of the desensitizing ring when its cross-section is a regular hexagon.

[0022] Figure 8 A three-dimensional structural diagram of the desensitizing ring when its cross-section is trapezoidal;

[0023] Figure 9 This is an installation diagram illustrating how this fiber Bragg grating installation method, such as FBG-1 and FBG-2, can compensate for temperature and double the sensitivity of the sensor.

[0024] In the figure: (1) is a fiber optic grating, (2) is a desensitization ring, (3) is a fixing block, and (4) is a support column. Detailed Implementation

[0025] The following are three specific examples of the present invention. These examples are only used to further analyze the present invention in detail, but are not intended to limit the scope of the present invention. Specific Implementation Example 1:

[0027] The fiber grating in this example is as follows: Figure 5 As shown in Figure (1), the fiber optic grating is mounted on the desensitization ring at a certain angle to the strain axis.

[0028] The desensitizing ring in this example is as follows: Figure 5 As shown in (3), the desensitizing ring has a circular cross-section and is placed on both sides of the fixing block. It is tightened and fixed by applying pretension.

[0029] The supporting column in this example is as follows: Figure 5 As shown in (4), the support column is assembled and connected to the desensitizing ring through a fixing block.

[0030] In this example, the fiber grating, desensitization ring, fixing block, and support column are all made of elastic materials.

[0031] The results of the case study in large strain are as follows:

[0032] When the fiber Bragg grating is mounted on the desensitization ring along the x-axis, the fiber Bragg grating is in a tensile state, generating the maximum positive strain. When it is encapsulated along the y-axis, the fiber Bragg grating is in a compressed state, generating the maximum negative strain. When the fiber Bragg grating is mounted between the x-axis and y-axis, the strain generated on the grating is between the maximum positive strain and the maximum negative strain. At a specific angle between the x-axis and y-axis, the strain always remains at 0. Specific Implementation Example 2:

[0034] This example Figure 6 As shown, the desensitizing ring has a rectangular cross-section. It is tightened and fixed by applying pretension. The support column is assembled and connected to the desensitizing ring through a fixing block. The fiber grating is installed on the desensitizing ring at the optimal desensitization angle with the strain axis. Specific Implementation Example 3:

[0036] This example Figure 7 As shown, the desensitizing ring has a regular hexagonal cross-section. The desensitizing ring is tightened and fixed by applying pretension. The support column is assembled and connected to the desensitizing ring through a fixing block. The fiber grating is installed on the desensitizing ring at the optimal desensitization angle with the strain axis. Specific Implementation Example 4:

[0038] This example Figure 8 As shown, the desensitizing ring has a trapezoidal cross-section. The desensitizing ring is tightened and fixed by applying pretension. The support column is assembled and connected to the desensitizing ring through a fixing block. The fiber grating is installed on the desensitizing ring and forms the optimal desensitization angle with the strain axis. Specific Implementation Example 5:

[0040] This example Figure 9 As shown, by installing a fiber Bragg grating (FBG-1) and FBG-2 in two directions with opposite strain directions and the same sensitivity, and directly subtracting their strain signals, the influence of external temperature changes can be compensated, and the sensor sensitivity will be doubled. The same effect can be achieved by installing a fiber Bragg grating in a corresponding region symmetrical to the strain application axis.

[0041] The specific examples above are only used to further illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can still make various changes without departing from the main idea of ​​the present invention. Therefore, all equivalent technical implementations fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A large-strain fiber grating sensor based on a desensitizing ring, which consists of a fiber grating (1), a desensitizing ring (2), a fixing block (3) and a supporting column (4), characterized in that, The desensitizing ring (2) is installed on both sides of the fixing block (3). The desensitizing ring (2) and the fixing block (3) are tightened and fixed by pretension. The support column (4) is assembled and connected to the desensitizing ring (2) through the fixing block (3). The fiber optic grating (1) is installed on the desensitizing ring (2). The strain sensitivity and strain measurement range of the sensor are adjusted by changing the angle between the fiber optic grating (1) and the line connecting the two fixing blocks (3).

2. The adjustment of the strain sensitivity and strain measurement range of a sensor according to claim 1, characterized in that When the fiber optic grating (1) coincides with the line connecting the two fixed blocks (3), the sensor has the highest sensitivity and the smallest strain measurement range. When the angle between the fiber optic grating (1) and the line connecting the two fixed blocks (3) is about 40°, the strain is as low as zero. At angles smaller than this zero strain, the sensor has extremely low sensitivity and extremely high strain measurement range.

3. The adjustment of the strain sensitivity and strain measurement range of a sensor according to claim 1, characterized in that, The desensitization ring has installation areas where the strain generated by the fiber Bragg grating is equal in magnitude but opposite in sign. If a fiber Bragg grating is installed in two directions with opposite strain directions and the same sensitivity, and their strain signals are directly subtracted, the influence of external temperature changes can be compensated, and the sensitivity of the sensor will be doubled.

4. The adjustment of the strain sensitivity of a sensor according to claim 2, characterized in that The angle between the fiber grating (1) and the line connecting the two fixed blocks (3) is between 0° and zero strain. The larger the angle, the lower the sensitivity.

5. The strain measurement range adjustment of a sensor according to claim 2, wherein, The angle between the fiber grating (1) and the line connecting the two fixed blocks (3) is between 0° and zero strain. The larger the angle, the larger the measurement range.

6. The reduced sensitivity ring based large strain fiber grating sensor of claim 1, wherein, The shape of the desensitization ring (2) can be a circular ring or an elliptical ring.

7. The reduced sensitivity ring based large strain fiber grating sensor of claim 1, wherein, The cross-sectional shape of the desensitization ring (2) can be circular, elliptical, square, rectangular, trapezoidal and other polygonal.

8. A method of strain adjustment of a desensitizing ring based large strain fiber grating sensor according to any one of claims 1 to 7, characterized in that, Under large strain conditions, the support column causes the fixed block to displace along the strain direction, which in turn causes the desensitizing ring to deform. The deformed desensitizing ring stretches or retracts the fiber grating fixed on it. By adjusting the angle between the fiber grating and the strain application direction, large strain measurement of different strain ranges can be achieved.

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