A crack sensor employing an elastic sheet and a fiber optic grating and its application method

Abstract

This invention discloses a crack sensor employing an elastic sheet and a fiber Bragg grating, and its usage method. The elastic sheet includes an arc portion and two supporting legs. The arc portion is a symmetrical variable curvature arc, with both ends extending to form supporting legs. The two supporting legs are respectively used to fix the arc portion to both sides of the crack, allowing the arc portion to span over the crack. The fiber Bragg grating includes a grating segment and a transmission segment. A portion of the grating segment is attached to the arc portion, while the remaining portion is separated from the arc portion. The output port of the transmission segment is used to output the sensor signal. This invention uses only a single fiber Bragg grating to simultaneously measure crack displacement and current temperature, saving costs, facilitating installation, and avoiding the influence of temperature on the grating's measurement of crack displacement, resulting in more accurate measurement results.

Description

Technical Field

[0001] This invention relates to the field of sensing and measuring displacement and temperature of building cracks, and more particularly to a crack sensor employing an elastic sheet and a fiber optic grating, and its method of use. Background Technology

[0002] Compared with traditional electronic temperature and strain sensors, fiber Bragg grating sensors have advantages such as no need for power supply to the sensing unit, small size, long-distance signal transmission, multi-point multiplexing, and resistance to electromagnetic interference. Fiber Bragg grating temperature and strain sensors have broad application prospects in the field of civil engineering.

[0003] Monitoring surface cracks or structural deformation in buildings plays a crucial role in assessing the health and safety of buildings and their structures. Existing electronic and other types of crack or displacement sensors suffer from drawbacks such as large size, inconvenient installation, difficulty in multi-point multiplexing, and susceptibility to electromagnetic interference. Therefore, a method using fiber optic gratings to measure crack displacement changes has been proposed. However, in practical applications, changes in ambient temperature affect the center wavelength of the fiber optic grating, necessitating compensation for the sensor's temperature characteristics. A common compensation method is to use two fiber optic gratings: one to measure crack displacement, and the other to respond only to temperature. However, this method increases system cost, installation difficulty, and the two fiber optic gratings may not be at the same temperature point. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that existing sensors using fiber Bragg gratings require two fiber Bragg gratings for temperature compensation. This invention utilizes the chirp characteristics of the fiber Bragg grating spectrum under non-uniform strain, enabling simultaneous measurement of crack displacement and temperature using only a single fiber Bragg grating.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: A crack sensor using an elastic sheet and a fiber optic grating is provided. The elastic sheet includes an arc portion and two supporting legs. The arc portion is a left-right symmetrical variable curvature arc, and both ends of the arc portion extend to form supporting legs. The two supporting legs are respectively used to fix the arc portion to both sides of the crack, so that the arc portion spans over the crack. The fiber optic grating includes a grating segment and a transmission segment. A portion of the grating segment is attached to the arc portion, and the remaining portion of the grating segment is separated from the arc portion. The output port of the transmission segment is used to output sensor signals.

[0006] Preferably, a portion of the grating segment is welded to the arc portion.

[0007] Preferably, half of the grating segment is pasted onto the arc portion, and the midpoint of the grating segment coincides with the midpoint of the arc portion.

[0008] Preferably, the grating segment is attached to the upper surface of the arc portion.

[0009] Preferably, the elastic sheet is Ω-shaped.

[0010] The present invention also provides a method for using a crack sensor based on any one of the above claims, comprising the following steps:

[0011] S1, fix the two legs of the crack sensor to the two sides of the crack respectively, so that the arc portion spans over the crack, and the line connecting the midpoint of the arc portion and the midpoint of the crack coincides with the axis of symmetry of the arc portion.

[0012] S2 continuously receives sensor signals and generates spectral curves based on the sensor signals;

[0013] S3. Based on the sensor signal at the initial moment, generate a spectral curve as the initial spectrum, and record the crack displacement and ambient temperature at this time as the initial crack displacement and initial temperature, respectively.

[0014] S4. Based on the real-time received sensor signals and the initial spectrum, initial crack displacement, and initial temperature, the current crack displacement and current temperature are calculated.

[0015] Preferably, the specific operation of S2 is as follows: the output port of the fiber Bragg grating is connected to the fiber Bragg grating demodulator, and the fiber Bragg grating demodulator receives the sensor signal emitted from the fiber Bragg grating and generates a spectral curve.

[0016] Preferably, S4 includes:

[0017] S41, the spectral curve generated by the sensor signal has obvious double peaks. The peak corresponding to the grating segment pasted on the elastic sheet is the moving peak, and the peak corresponding to the grating segment not pasted on the elastic sheet is the reference peak. When the crack displacement changes by ΔS and the temperature changes by ΔT, the wavelength response of the moving peak to pressure and temperature, Δλ1, is expressed as Δλ1=A. S1 ΔS+A T1 The wavelength response Δλ2 of the reference peak wavelength to displacement and temperature is expressed as Δλ2=A S2 ΔS+A T2 ΔT, where A s1 A T1 A S2 and A T2 This is the sensitivity response factor coefficient, which is related to the sensor's materials and manufacturing process.

[0018] S42, construct the following displacement and temperature equations:

[0019]

[0020] S43, compare the wavelength response of the currently detected moving peak and reference peak with that of the moving peak and reference peak in the initial spectrum, and obtain the crack displacement change ΔS and temperature change ΔT according to the displacement and temperature equation;

[0021] S44, based on the initial crack displacement and the initial temperature, the current crack displacement S and the current temperature T can be obtained.

[0022] Preferably, the support legs are fixed to both sides of the crack using expansion screws.

[0023] The present invention has the following beneficial effects:

[0024] The present invention provides a crack sensor using an elastic sheet and a fiber optic grating, which can monitor crack displacement and changes in ambient temperature in real time, while avoiding the influence of temperature on crack displacement measurement.

[0025] This invention discloses a crack sensor that uses an elastic sheet and a fiber optic grating. It requires only one fiber optic grating, has a simple structure, saves costs, and makes installation more convenient.

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments. Attached Figure Description

[0027] Figure 1 The image shows the spectral curves of a fiber optic grating under non-uniform strain conditions.

[0028] Figure 2 This is a perspective view of an embodiment of the present invention;

[0029] Figure 3 This is a left view of an embodiment of the present invention;

[0030] Figure 4 This is a cross-sectional view along the AA direction of an embodiment of the present invention;

[0031] Figure 5 This is a graph showing the spectrum of the present invention at different displacements and the initial spectrum. Detailed Implementation

[0032] To address the problems in design, fabrication, and installation of existing crack displacement sensors, this embodiment proposes a crack sensor employing an elastic sheet and a fiber Bragg grating. The fiber Bragg grating is welded or glued to the surface of the bent elastic sheet. Due to thermal expansion and contraction, uneven strain occurs within the fiber Bragg grating. Under uniform strain, the fiber Bragg grating's spectral curve is a single-peak curve; under uneven strain, its spectrum shifts to the left. Therefore, the fiber Bragg grating portion welded or glued to the elastic sheet experiences a leftward shift in its spectrum, resulting in a distinct double-peak spectral curve for the entire fiber Bragg grating. Figure 1 As shown. When a fiber Bragg grating is bonded to the surface of an elastic sheet, the relationship between the strain ∈ of the fiber Bragg grating and its curvature ρ is: K is related to the parameters of the optical fiber and the elastic sheet (Zhou Jinlong, Dong Xiaopeng, Shi Zhidong, Theoretical and experimental study on the bending sensitivity of Bragg gratings in D-shaped optical fibers, Acta Photonica Sinica, 2006, 35(11): 1734-1737). Because the oscillation period and wavelength of the peak / valley positions of the fiber grating have different responses to the stress and temperature, the crack displacement and current temperature can be measured simultaneously by utilizing the spectral chirp characteristics of the fiber grating under non-uniform strain conditions. During the measurement, the two ends of the elastic sheet are fixed to the two ends of the crack, so that the fiber grating in contact with the sheet is subjected to a non-uniform strain field equivalent to that of the elastic sheet during the crack displacement process, while the fiber grating not in contact with the sheet is not subjected to the non-uniform strain field. Therefore, the changes in crack displacement and external temperature will cause changes in the spectral curve of the fiber grating. By studying the variation of the oscillation period and specific peak / valley wavelengths of the spectral curve with crack displacement and temperature, and solving the equations simultaneously, it is possible to simultaneously measure crack displacement and current temperature, thus overcoming the influence of ambient temperature changes on crack measurement results.

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] See Figures 2 to 4The diagram shown is a structural diagram of an embodiment of the present invention. The crack sensor includes a fiber optic grating 1 and an elastic sheet 2. The elastic sheet 2 is Ω-shaped, including an arc portion 21 and two support portions 22. The arc portion 21 is a left-right symmetrical variable curvature arc, and the two ends of the arc portion 21 extend into the two support portions 22. The support portions 22 are used to fix the arc portion 21 to both sides of the crack, so that the arc portion 21 spans over the crack. The fiber optic grating 1 includes a grating segment 11 and a transmission segment 12, with a length of 1 cm. Half of the grating segment 11 is welded or glued to the arc portion 21, and the other half of the grating segment 11 is separated from the arc portion 21. The midpoint of the grating segment 11 coincides with the midpoint of the arc portion 21 at point M. The output port of the transmission segment 12 is used to output sensor signals.

[0035] In this embodiment, the steps are as follows:

[0036] S1, fix the two legs 22 of the crack sensor to the two sides of the crack respectively, so that the arc part 21 spans over the crack, and the line connecting the midpoint of the arc part 21 and the midpoint of the crack coincides with the axis of symmetry of the arc part 21.

[0037] S2 continuously receives sensor signals and generates spectral curves based on the sensor signals;

[0038] S3. Based on the sensor signal at the initial moment, generate a spectral curve as the initial spectrum, and record the crack displacement and ambient temperature at this time as the initial crack displacement and initial temperature, respectively.

[0039] S4. Based on the real-time received sensor signals and the initial spectrum, initial crack displacement, and initial temperature, the current crack displacement and current temperature are calculated.

[0040] Specifically, the operation of S2 is as follows: the output port of the fiber Bragg grating 1 is connected to the fiber Bragg grating demodulator, and the fiber Bragg grating demodulator receives the sensor signal emitted from the fiber Bragg grating 1 and generates a spectral curve.

[0041] Specifically, S4 includes:

[0042] S41, the spectral curve generated by the sensor signal has obvious double peaks. The peak corresponding to the grating segment 11 welded or glued to the elastic sheet is the moving peak, and the peak corresponding to the grating segment 11 not welded or glued to the elastic sheet is the reference peak. When the crack displacement changes by ΔS and the temperature changes by ΔT, the wavelength response of the moving peak to pressure and temperature, Δλ1, is expressed as Δλ1=A. S1 ΔS+A T1 The wavelength response Δλ2 of the reference peak wavelength to displacement and temperature is expressed as Δλ2=A S2 ΔS+A T2 ΔT, where As1 A T1 A S2 and A T2 This is the sensitivity response factor coefficient, which is related to the sensor's materials and manufacturing process.

[0043] S42, construct the following displacement and temperature equations:

[0044]

[0045] S43, compare the wavelength response of the currently detected moving peak and reference peak with that of the moving peak and reference peak in the initial spectrum, and obtain the crack displacement change ΔS and temperature change ΔT according to the displacement and temperature equation;

[0046] S44. Based on the initial crack displacement and the initial temperature, the current crack displacement S and the current temperature T can be obtained.

[0047] Specifically, the support leg 22 is fixed to both sides of the crack by expansion screws.

[0048] See Figure 5 The figure shows the simulation results of this embodiment. The figure records the curves of the initial crack displacement S0 (i.e., the initial spectrum), crack displacement S1, and crack displacement S2. Each spectral curve has obvious double peaks, where the left peak is the moving peak and the right peak is the reference peak. As shown in the figure, based on the wavelength response Δλ1 between the moving peak of the crack displacement S1 curve and the moving peak of the initial spectrum, and based on the wavelength response Δλ2 between the reference peak of the crack displacement S1 curve and the reference peak of the initial spectrum, the crack displacement change ΔS1 relative to S0 and the temperature change ΔT1 at displacement S1 relative to the initial temperature can be obtained by substituting them into the displacement and temperature calculation formulas. Then, combining the initial crack displacement S0 and the initial temperature T0, the displacement S1 and the temperature T1 at displacement S1 can be obtained. The calculation steps for displacement S2 and the temperature T2 at displacement S2 are the same as described above.

[0049] As can be seen, the crack sensor and its usage method proposed in this invention, which uses an elastic sheet and a fiber optic grating, can simultaneously measure crack displacement and current temperature using only one fiber optic grating, saving costs, facilitating installation, and avoiding the influence of temperature on the grating's measurement of crack displacement, thus making the measurement results more accurate.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for using a crack sensor employing an elastic sheet and a fiber optic grating, characterized in that, The elastic sheet includes an arc portion and two support portions. The arc portion is a variable curvature arc that is symmetrical from left to right. The two ends of the arc portion extend to form support portions. The two support portions are used to fix it to both sides of the crack, so that the arc portion spans over the crack. The fiber optic grating includes a grating segment and a transmission segment. A portion of the grating segment is attached to the arc portion, and the remaining portion of the grating segment is separated from the arc portion. The output port of the transmission segment is used to output sensor signals. The method of using the crack sensor includes the following steps: S1, fix the two legs of the crack sensor to the two sides of the crack respectively, so that the arc portion spans over the crack, and the line connecting the midpoint of the arc portion and the midpoint of the crack coincides with the axis of symmetry of the arc portion. S2 continuously receives sensor signals and generates spectral curves based on the sensor signals; S3. Based on the sensor signal at the initial moment, generate a spectral curve as the initial spectrum, and record the crack displacement and ambient temperature at this time as the initial crack displacement and initial temperature, respectively. S4. Based on the real-time received sensor signals and the initial spectrum, initial crack displacement, and initial temperature, the current crack displacement and current temperature are obtained. S4 includes: S41, the spectral curve generated by the sensor signal has obvious double peaks. The peak corresponding to the grating segment pasted on the elastic sheet is the moving peak, and the peak corresponding to the grating segment not pasted on the elastic sheet is the reference peak. When the crack displacement changes by ΔS and the temperature changes by ΔT, the wavelength response of the moving peak to pressure and temperature, Δλ1, is expressed as Δλ1=A. S1 ΔS+A T1 The wavelength response Δλ2 of the reference peak wavelength to displacement and temperature is expressed as Δλ2=A S2 ΔS+A T2 ΔT, where A s1 A T1 A S2 and A T2 This is the sensitivity response factor coefficient, which is related to the sensor's materials and manufacturing process. S42, construct the following displacement and temperature equations: S43, compare the wavelength response of the currently detected moving peak and reference peak with that of the moving peak and reference peak in the initial spectrum, and obtain the crack displacement change ΔS and temperature change ΔT according to the displacement and temperature equation; S44, based on the initial crack displacement and the initial temperature, the current crack displacement S and the current temperature T can be obtained.

2. The method of using the crack sensor according to claim 1, characterized in that, A portion of the grating segment is welded to the arc portion.

3. The method of using the crack sensor according to claim 1, characterized in that, Half of the grating segment is pasted onto the arc portion, and the midpoint of the grating segment coincides with the midpoint of the arc portion.

4. The method of using the crack sensor according to claim 1, characterized in that, The grating segment is attached to the upper surface of the arc portion.

5. The method of using the crack sensor according to claim 1, characterized in that, The elastic sheet is shaped like an "Ω".

6. The method of using the crack sensor according to claim 1, characterized in that, The specific operation of S2 is as follows: the output port of the fiber Bragg grating is connected to the fiber Bragg grating demodulator, and the fiber Bragg grating demodulator receives the sensor signal emitted from the fiber Bragg grating and generates a spectral curve.

7. The method of using the crack sensor according to claim 1, characterized in that, The support legs are fixed to both sides of the crack with expansion bolts.

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