Temperature, strain and acoustic emission measuring method and device based on tilted fiber bragg grating

Abstract

The invention provides a temperature, strain and acoustic emission measurement method and device based on a tilted fiber bragg grating. The method comprises the following steps: carrying out cladding mode and Ghost mode demodulation on a transmission spectrum of a tilted fiber grating to obtain cladding mode wavelength shift and Ghost mode wavelength shift; wherein the tilted fiber bragg grating is mounted on a target structure; the cladding mode wavelength shift and the Ghost mode wavelength shift are substituted into the two-parameter matrix and solved, and the temperature variation and the strain variation of the target structure are obtained; wherein the two-parameter matrix comprises cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity and Ghost mode-strain sensitivity of the tilted fiber bragg grating; and the Bragg reflection spectrum of the tilted fiber grating is demodulated and analyzed to obtain an acoustic emission signal of the target structure. According to the invention, simultaneous measurement of temperature, strain and acoustic emission signals can be realized only by using a single fiber bragg grating.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing, and in particular, to a method and device for measuring temperature, strain, and acoustic emission based on a tilted fiber Bragg grating. Background Art

[0002] With the continuous development of science and technology, fiber optic sensing technology has been widely applied in industries, medical treatment, aerospace and other fields due to its advantages of high precision, strong real-time performance, electromagnetic interference resistance and corrosion resistance. As an important branch, fiber Bragg grating sensing technology has attracted much attention for its high sensitivity, strong multiplexing ability and other advantages.

[0003] However, when traditional fiber Bragg gratings are subjected to signals such as temperature, strain, and acoustic emission, the central wavelength will drift, making it difficult to accurately separate a certain signal. However, in actual application scenarios, it is often necessary to simultaneously measure multiple parameters. For example, in structural health monitoring, especially in large-scale projects such as high-rise buildings, bridges, and tunnels, it is necessary to monitor the temperature to confirm the state of materials, and also monitor the strain signals and acoustic emission signals received by the structure to confirm whether cracks and damages occur inside the structure, realize early diagnosis and warning of faults, and ensure the long-term stable operation of the structure.

[0004] Currently, by combining fiber Bragg gratings with different temperature, strain, and acoustic emission sensitivities, the problem of cross-sensitivity in multi-parameter measurement of fiber Bragg gratings can be solved, but different types of fiber Bragg gratings need to be prepared, resulting in complex sensor structures and deployment processes. Summary of the Invention

[0005] Embodiments of the present invention provide a method and device for measuring temperature, strain, and acoustic emission based on a tilted fiber Bragg grating to solve the problem of multi-parameter measurement that requires different types of fiber Bragg gratings.

[0006] In a first aspect, embodiments of the present invention provide a method for measuring temperature, strain, and acoustic emission based on a tilted fiber Bragg grating, including:

[0007] Demodulating the cladding mode and Ghost mode of the transmission spectrum of the tilted fiber Bragg grating to obtain the cladding mode wavelength shift and Ghost mode wavelength shift; wherein, the tilted fiber Bragg grating is installed on the target structure;

[0008] Substitute the cladding mode wavelength shift and Ghost mode wavelength shift into the two-parameter matrix and solve to obtain the temperature change and strain change of the target structure; wherein, the two-parameter matrix includes the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber Bragg grating;

[0009] Demodulate and analyze the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure.

[0010] In one possible implementation, demodulating and analyzing the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure includes:

[0011] Demodulate the Bragg reflection spectra of the tilted fiber grating at multiple moments to obtain multiple phase change amounts and form a phase change sequence;

[0012] Perform frequency-domain filtering on the phase change sequence to obtain the acoustic emission signal of the target structure.

[0013] In one possible implementation, demodulating the Bragg reflection spectra of the tilted fiber grating at multiple moments to obtain multiple phase change amounts and form a phase change sequence includes:

[0014] Calculate the ambient temperature based on the temperature change amount of the target structure;

[0015] Extract the Bragg reflection spectra of the tilted fiber grating at multiple moments for demodulation based on the Bragg-phase sensitivity corresponding to the ambient temperature to obtain multiple phase change amounts and form a phase change sequence.

[0016] In one possible implementation, after demodulating and analyzing the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure, it further includes:

[0017] Form a strain change amount sequence with multiple strain change amounts of the target structure;

[0018] Remove the acoustic emission signal of the target structure from the strain change amount sequence to obtain a corrected strain change amount sequence.

[0019] In one possible implementation, before substituting the cladding mode wavelength shift and Ghost mode wavelength shift into the two-parameter matrix and solving to obtain the temperature change amount and strain change amount of the target structure, it further includes:

[0020] Calibrate the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber grating through experiments.

[0021] In one possible implementation, the tilted fiber grating is obtained by line-by-line femtosecond laser writing. During the writing process, the transmission spectrum and reflection spectrum of the tilted fiber grating are observed in real time, and the writing parameters are adjusted based on the observation results.

[0022] In a second aspect, an embodiment of the present invention provides a temperature, strain, and acoustic emission measurement device based on a tilted fiber grating, including:

[0023] A first demodulation module is used to demodulate the transmission spectrum of the tilted fiber Bragg grating (FBG) in terms of cladding mode and ghost mode to obtain the cladding mode wavelength shift and the ghost mode wavelength shift; wherein the tilted fiber Bragg grating is installed on the target structure;

[0024] A solution module is used to substitute the cladding mode wavelength shift and the ghost mode wavelength shift into a dual-parameter matrix and solve it to obtain the temperature change and strain change of the target structure; wherein the dual-parameter matrix includes the cladding mode-temperature sensitivity, ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and ghost mode-strain sensitivity of the tilted fiber Bragg grating;

[0025] The second demodulation module is used to demodulate and analyze the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure.

[0026] In a third aspect, an embodiment of the present invention provides a terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method described in the first aspect or any possible implementation of the first aspect are implemented.

[0027] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the steps of the method described in the first aspect or any possible implementation of the first aspect.

[0028] The embodiment of the present invention provides a temperature, strain, and acoustic emission measurement method and device based on a tilted fiber Bragg grating. The method utilizes the characteristics that the cladding mode and Ghost mode of the tilted fiber Bragg grating have different sensitivities to temperature and strain. A matrix is constructed by constructing four pre-measured sensitivities. After actual measurement, the demodulated cladding mode wavelength offset and Ghost mode wavelength offset are substituted into a two-parameter matrix and solved. In this way, the temperature change and strain change of the target structure can be separated. At the same time, the acoustic emission signal of the target structure is extracted through the Bragg reflection spectrum. The temperature, strain, and acoustic emission signals can be simultaneously measured using only a single fiber Bragg grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1It is an application scenario diagram of a temperature, strain, and acoustic emission measurement method based on a tilted fiber Bragg grating provided by an embodiment of the present invention;

[0031] Figure 2 It is an implementation flowchart of a temperature, strain, and acoustic emission measurement method based on a tilted fiber Bragg grating provided by an embodiment of the present invention;

[0032] Figure 3 It is a schematic diagram of the implementation principle of a temperature, strain, and acoustic emission measurement method based on a tilted fiber Bragg grating provided by an embodiment of the present invention;

[0033] Figure 4 It is a schematic structural diagram of a tilted fiber Bragg grating writing device provided by an embodiment of the present invention;

[0034] Figure 5 It is a schematic structural diagram of a temperature, strain, and acoustic emission measurement device based on a tilted fiber Bragg grating provided by an embodiment of the present invention;

[0035] Figure 6 It is a schematic diagram of a terminal provided by an embodiment of the present invention. Detailed implementation manners

[0036] In the following description, specific details such as specific system structures and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will be described through specific embodiments with reference to the accompanying drawings.

[0038] Figure 1 It is an application scenario diagram of a temperature, strain, and acoustic emission measurement method based on a tilted fiber Bragg grating provided by an embodiment of the present invention. As Figure 1As shown in the figure, the tilted fiber Bragg grating is pasted on the aluminum plate. A piezoelectric ceramic sensor is placed near the tilted fiber Bragg grating. The excitation signal of the piezoelectric ceramic sensor is the acoustic emission source. The light emitted by the broadband light source 1 enters the tilted fiber Bragg grating 3 after passing through the 2×2 coupler 2. The transmitted light of the tilted fiber Bragg grating is monitored by the spectral analyzer 4 to measure the wavelength changes of the cladding mode and the Ghost mode in real time, and obtain temperature and strain information. The reflected light of the tilted fiber Bragg grating 3 enters the 3×3 coupler 7 through the isolator 5 and the circulator 6, and is incident on the Faraday rotator mirror 9 through the delay fiber 8. The signal reflected back by the Michelson interferometer interferes at the 3×3 coupler 7. The three output lights are photoelectrically converted by the photodetector 10 and are analog-to-digital converted by the data acquisition card 11. The obtained signal is sent to the computer 12, and through the corresponding program processing, the acoustic emission signal is extracted, so as to realize the simultaneous measurement of multiple parameters.

[0039] In the preparation process, the femtosecond laser line-by-line writing technology is used to prepare a high-quality tilted fiber Bragg grating, so that it can simultaneously excite the cladding mode, the Ghost mode and the Bragg mode.

[0040] Before measurement, the transmitted spectrum signal of the tilted fiber Bragg grating is obtained through the spectral analyzer. Different temperatures and strains are applied to the tilted fiber Bragg grating in turn, and the wavelength shifts of the cladding mode and the Ghost mode are analyzed. The temperature and strain sensitivities of different modes of the tilted fiber Bragg grating are calibrated. In actual measurement, the corresponding temperature and strain information can be obtained by solving the two-parameter matrix.

[0041] The phase change information of the Bragg mode wavelength in the reflected spectrum of the tilted fiber Bragg grating is demodulated by the 3×3 coupler and the Michelson interferometer, and the acoustic emission signal is extracted, so as to realize the measurement of temperature, strain and acoustic emission multi-parameter signals.

[0042] See Figure 2 , which shows the implementation flowchart of the temperature, strain, and acoustic emission measurement method based on the tilted fiber Bragg grating provided by the embodiment of the present invention, and is described in detail as follows:

[0043] In step 201, the cladding mode and the Ghost mode of the transmitted spectrum of the tilted fiber Bragg grating are demodulated to obtain the wavelength shift of the cladding mode and the wavelength shift of the Ghost mode; wherein, the tilted fiber Bragg grating is installed on the target structure.

[0044] In this embodiment, as Figure 3 shown, the core function of the Bragg grating is based on the Bragg scattering principle. When the Bragg condition is satisfied, that is, the wavelength of the light is equal to twice the effective refractive index of the grating period divided by the sine of the incident angle (for the TFBG, it is the cosine of the tilt angle), the self-backward propagation coupling of the core mode will occur, forming the Bragg mode or the core mode resonance. It refers to the light mode that leaks from the core to the fiber cladding and propagates therein.

[0045] In the TFBG, due to the tilt of the grating plane, in addition to the core mode, a large number of cladding mode resonances are excited.

[0046] The Ghost mode can also be called the phantom mode or the ghost mode. It is composed of a group of low-order cladding modes. Its mode field radius is slightly larger than that of the core mode, and its characteristics are similar to those of the core mode. The low-order cladding modes cover the interface between the core and the cladding.

[0047] The target structure can be an object that needs to be health monitored, such as a composite material, a metal structure, or a bridge structure.

[0048] In step 202, the cladding mode wavelength shift and the Ghost mode wavelength shift are substituted into the two-parameter matrix and solved to obtain the temperature change and the strain change of the target structure; among them, the two-parameter matrix includes the cladding mode-temperature sensitivity, the Ghost mode-temperature sensitivity, the cladding mode-strain sensitivity, and the Ghost mode-strain sensitivity of the tilted fiber Bragg grating.

[0049] In this embodiment, the sensitivity refers to the degree of change in the grating wavelength with temperature or strain. When temperature and strain change simultaneously, the wavelength is affected by both factors and changes, making it difficult to directly distinguish the temperature change and the strain change based on the change in wavelength.

[0050] Since the cladding modes and Ghost modes of the grating correspond to different sensitivities, a sensitivity matrix can be constructed using the four sensitivities: the cladding mode-temperature sensitivity, the Ghost mode-temperature sensitivity, the cladding mode-strain sensitivity, and the Ghost mode-strain sensitivity. Then, using the following relationship, substituting the cladding mode wavelength shift and the Ghost mode wavelength shift, the temperature change and the strain change can be solved:

[0051]

[0052] Among them, Δλ1 is the cladding mode wavelength shift, Δλ2 is the Ghost mode wavelength shift, K T1 is the cladding mode-temperature sensitivity, K T2 is the Ghost mode-temperature sensitivity, K ε1 is the cladding mode-strain sensitivity, K ε2 is the Ghost mode-strain sensitivity, ΔT is the temperature change, and Δε is the strain change.

[0053] After transforming the above formula, the solution formula is as follows:

[0054]

[0055] In step 203, the Bragg reflection spectrum of the tilted fiber grating is demodulated and analyzed to obtain the acoustic emission signal of the target structure.

[0056] In this embodiment, light waves are emitted by a broadband light source, enter the tilted fiber grating through a 2×2 coupler, the spectral analyzer monitors the change of the transmission spectrum, the reflected light enters the photodetector through a 3×3 coupler and an unbalanced Michelson interferometer, and after the optoelectronic signal conversion, it is sent to a computer by a data acquisition card to complete data processing, obtain the phase change information of the interference signal, and measure the acoustic emission signal of the tilted fiber grating according to this information.

[0057] The acoustic emission signal is obtained by demodulating the phase information through a 3×3 coupler and a Michelson interferometer. The output phase of the interferometer can be expressed as:

[0058]

[0059] In the formula, λ is the Bragg wavelength of the tilted fiber grating, n is the core refractive index, d is the optical path difference of the interferometer, and Δλ is the change of the Bragg wavelength. The larger d is, the more sensitive the interferometer is to the change of the light source wavelength. However, when the line width is certain, the contrast of the output fringes is worse. According to the interference condition of two light beams: the optical path difference d is less than the coherence length Δc of the light source, that is, d < Δc = λ 2 / Δλ. For the tilted fiber grating in the present invention, d can be taken as 5 mm.

[0060] In the embodiment of the present invention, by using the characteristics that the cladding mode and the Ghost mode of the tilted fiber grating have different sensitivities to temperature and strain, a matrix is constructed through four pre-measured sensitivities. After actual measurement, the wavelength shift of the cladding mode and the wavelength shift of the Ghost mode obtained by demodulation are substituted into the two-parameter matrix and solved, so that the temperature change amount and the strain change amount of the target structure can be separated. At the same time, the acoustic emission signal of the target structure is extracted through the Bragg reflection spectrum, and the simultaneous measurement of temperature, strain and acoustic emission signal can be realized by using only a single fiber grating.

[0061] In a possible implementation manner, demodulating and analyzing the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure includes:

[0062] Demodulating the Bragg reflection spectra of the tilted fiber grating at multiple moments to obtain multiple phase change amounts and forming a phase change sequence;

[0063] Performing frequency-domain filtering on the phase change sequence to obtain the acoustic emission signal of the target structure.

[0064] In this embodiment, the strain change of the structure is usually caused by slow deformation of the structure or static load, which manifests as a low-frequency signal (such as less than 1kHz), and the acoustic emission signal is a high-frequency elastic wave (usually tens of kHz to MHz) generated by transient events inside the material (such as crack extension).

[0065] Both will cause the wavelength shift of the tilted fiber Bragg grating, but since there is a large difference in their frequencies, this feature can be used to set a reasonable baseline and perform high-pass filtering in the frequency domain to eliminate the phase change caused by static strain. The remaining signal is the acoustic emission signal.

[0066] In a possible implementation, the Bragg reflection spectra of the tilted fiber Bragg grating at multiple moments are demodulated to obtain multiple phase changes and form a phase change sequence, including:

[0067] Calculate the ambient temperature based on the temperature change of the target structure;

[0068] Based on the Bragg-phase sensitivity corresponding to the ambient temperature, the Bragg reflection spectra of the tilted fiber Bragg grating at multiple moments are extracted and demodulated to obtain multiple phase changes and form a phase change sequence.

[0069] In this embodiment, Bragg-phase sensitivity refers to the degree to which the Bragg mode phase varies with the acoustic emission signal. Because temperature changes can affect the Bragg wavelength and phase, temperature measurement is typically performed separately with an additional sensor. Temperature compensation is then performed based on the measured temperature to extract the acoustic emission signal from the Bragg phase variation.

[0070] In this embodiment, the Bragg-phase sensitivity at different ambient temperatures is pre-calibrated. The temperature variation calculated in the previous steps is used to select the corresponding sensitivity. The phase variation can be directly calculated based on the sensitivity, achieving temperature compensation. This improves computational efficiency and reduces the amount of computation required during actual measurement. Specifically, the number of Bragg-phase sensitivities can be set based on how the Bragg-phase sensitivity changes with ambient temperature, with each Bragg-phase sensitivity corresponding to an ambient temperature range.

[0071] In a possible implementation, after demodulating and analyzing the Bragg reflection spectrum of the tilted fiber Bragg grating to obtain the acoustic emission signal of the target structure, the method further includes:

[0072] Combining multiple strain variations of the target structure into a strain variation sequence;

[0073] The acoustic emission signal of the target structure is removed from the strain variation sequence to obtain a corrected strain variation sequence.

[0074] In this embodiment, the strain variation obtained in step 202 may be a superposition of the strain and the acoustic emission signal. Therefore, after determining the acoustic emission signal, the acoustic emission signal is removed from the strain variation to correct the strain variation.

[0075] In one possible implementation, before the cladding mode wavelength shift and the ghost mode wavelength shift are brought into the dual-parameter matrix and solved to obtain the temperature change and strain change of the target structure, the following steps are further included:

[0076] The cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity and Ghost mode-strain sensitivity of tilted fiber Bragg grating are calibrated experimentally.

[0077] In this embodiment, the two ends of the prepared tilted fiber Bragg grating are connected to a broadband light source and a spectrum analyzer respectively, and the tilted fiber Bragg grating is placed in an electric constant temperature drying oven for temperature calibration to obtain the temperature sensitivity K of the cladding mode λ1 and the ghost mode λ2 respectively. T1 and K T2 Furthermore, one end of the tilted fiber Bragg grating was glued to the fiber fixture using epoxy structural adhesive, and the fixture at the other end was placed on a one-dimensional translation stage. A certain prestress was applied to ensure that the tilted fiber Bragg grating was in a taut state. The end was fixed to the fixture using epoxy structural adhesive, and the strain sensitivity K of the tilted fiber Bragg grating cladding mode and Ghost mode was calibrated. ε1 and K ε2 .

[0078] When temperature and strain change simultaneously, the temperature and strain information can be obtained by extracting the central wavelengths of the cladding mode and Ghost mode in the transmission spectrum, calculating the offset, and solving the equations.

[0079] In one possible implementation, a tilted fiber Bragg grating is obtained by line-by-line writing using a femtosecond laser. During the writing process, the transmission spectrum and reflection spectrum of the tilted fiber Bragg grating are observed in real time, and the writing parameters are adjusted based on the observation results.

[0080] In this embodiment, if Figure 3As shown in the figure, after the femtosecond laser S1 completes pumping, pulse broadening, amplification, and compression in the power supply box, it outputs high-quality and high-power Gaussian light. The light enters the beam expander S3 through the first mirror S2. The output power of the laser can be flexibly adjusted through the electric laser power attenuator S4. The light beam is sent into the polarization controller S6 and the polarization converter S7 through the second mirror S5 to realize the control of the polarization state of the light beam. Then it enters the objective lens S11 through the third mirror S9 and is focused on the fiber core by the objective lens S11. The fiber is placed on the X-Y displacement stage S13 through the fixture S12. The objective lens focusing and fiber movement are realized by controlling the Z-axis displacement stage S10 and the X-Y displacement stage S13 through the computer S15. The CCD S8 and the LED S14 assist in monitoring the structure during the fiber processing. The broadband light source S16, the spectral analyzer S17, the 2×2 coupler S18, and the spectral analyzer S19 are respectively used to monitor the reflection spectrum and transmission spectrum of the tilted fiber grating, and the writing parameters are adjusted in real time to realize the writing of high-performance tilted fiber gratings. The center wavelength of the Bragg mode is 1550 nm, the reflectivity > 90%, and the 3 dB bandwidth < 0.2 nm. Due to the certain tilt angle between the grating lines and the fiber axis of the tilted fiber grating, the cladding mode, the Ghost mode, and the Bragg mode are simultaneously excited. The sensitivities of the three to temperature, strain, and acoustic emission signals are different. The simultaneous measurement of temperature and strain is realized by demodulating the cladding mode and the Ghost mode among them.

[0081] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The order of execution of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0082] The following is an apparatus embodiment of the present invention. For the details not described in detail therein, reference may be made to the corresponding method embodiment above.

[0083] Figure 5 The structural schematic diagram of the temperature, strain, and acoustic emission measurement device based on the tilted fiber grating provided by the embodiment of the present invention is shown. For the convenience of description, only the parts related to the embodiment of the present invention are shown and are described in detail as follows:

[0084] As Figure 5 shown, the temperature, strain, and acoustic emission measurement device 5 based on the tilted fiber grating includes:

[0085] The first demodulation module 51 is used to demodulate the cladding mode and the Ghost mode of the transmission spectrum of the tilted fiber grating to obtain the wavelength shift of the cladding mode and the wavelength shift of the Ghost mode; wherein, the tilted fiber grating is installed on the target structure;

[0086] A solution module 52, configured to substitute the cladding mode wavelength shift and the Ghost mode wavelength shift into a two-parameter matrix and solve to obtain the temperature change and strain change of the target structure; wherein, the two-parameter matrix includes the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber Bragg grating;

[0087] A second demodulation module 53, configured to demodulate and analyze the Bragg reflection spectrum of the tilted fiber Bragg grating to obtain the acoustic emission signal of the target structure.

[0088] In a possible implementation, the second demodulation module 53 is specifically configured to:

[0089] Demodulate the Bragg reflection spectra of the tilted fiber Bragg grating at multiple moments to obtain multiple phase change amounts and form a phase change sequence;

[0090] Perform frequency domain filtering on the phase change sequence to obtain the acoustic emission signal of the target structure.

[0091] In a possible implementation, the second demodulation module 53 is specifically configured to:

[0092] Calculate the ambient temperature based on the temperature change of the target structure;

[0093] Based on the Bragg-phase sensitivity corresponding to the ambient temperature, extract the Bragg reflection spectra of the tilted fiber Bragg grating at multiple moments for demodulation to obtain multiple phase change amounts and form a phase change sequence.

[0094] In a possible implementation, the second demodulation module 53 is further configured to:

[0095] After demodulating and analyzing the Bragg reflection spectrum of the tilted fiber Bragg grating to obtain the acoustic emission signal of the target structure, form a strain change amount sequence from multiple strain change amounts of the target structure;

[0096] Remove the acoustic emission signal of the target structure from the strain change amount sequence to obtain a corrected strain change amount sequence.

[0097] In a possible implementation, the solution module 52 is further configured to:

[0098] Before substituting the cladding mode wavelength shift and the Ghost mode wavelength shift into the two-parameter matrix and solving to obtain the temperature change and strain change of the target structure, calibrate the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber Bragg grating through experiments.

[0099] In a possible implementation, the tilted fiber grating is written line by line based on femtosecond laser. During the writing process, the transmission spectrum and reflection spectrum of the tilted fiber grating are observed in real time, and the writing parameters are adjusted based on the observation results.

[0100] In the embodiments of the present invention, by utilizing the characteristics that the cladding modes and Ghost modes of the tilted fiber grating have different sensitivities to temperature and strain, a matrix is constructed through four pre-measured sensitivities. After actual measurement, the wavelength shifts of the demodulated cladding modes and Ghost modes are substituted into the two-parameter matrix and solved, so that the temperature change and strain change of the target structure can be separated. At the same time, the acoustic emission signal of the target structure is extracted through the Bragg reflection spectrum, and the simultaneous measurement of temperature, strain and acoustic emission signal can be realized by using only a single fiber grating.

[0101] Figure 6 It is a schematic diagram of the terminal provided by the embodiments of the present invention. As Figure 6 shown, the terminal 6 of this embodiment includes: a processor 60, a memory 61, and a computer program 62 stored in the memory 61 and operable on the processor 60. When the processor 60 executes the computer program 62, the steps in the above-mentioned embodiments of the temperature, strain, and acoustic emission measurement methods based on the tilted fiber grating are implemented, such as Figure 2 the steps 201 to 203 shown. Alternatively, when the processor 60 executes the computer program 62, the functions of each module / unit in the above-mentioned device embodiments are implemented, such as Figure 5 the functions of the modules / units 51 to 53 shown.

[0102] Exemplarily, the computer program 62 can be divided into one or more modules / units. The one or more modules / units are stored in the memory 61 and executed by the processor 60 to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing specific functions, and these instruction segments are used to describe the execution process of the computer program 62 in the terminal 6. For example, the computer program 62 can be divided into Figure 5 the modules / units 51 to 53 shown.

[0103] The terminal 6 can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The terminal 6 may include, but is not limited to, a processor 60 and a memory 61. Those skilled in the art can understand that Figure 6 this is only an example of the terminal 6 and does not constitute a limitation on the terminal 6. It may include more or fewer components than shown in the figure, or combine some components, or different components. For example, the terminal may further include input / output devices, network access devices, a bus, etc.

[0104] The so-called processor 60 may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0105] The memory 61 may be an internal storage unit of the terminal 6, such as the hard disk or memory of the terminal 6. The memory 61 may also be an external storage device of the terminal 6, such as a plug-in hard disk equipped on the terminal 6, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, etc. Further, the memory 61 may also include both the internal storage unit of the terminal 6 and the external storage device. The memory 61 is used to store the computer program and other programs and data required by the terminal. The memory 61 may also be used to temporarily store data that has been output or is to be output.

[0106] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above division of each functional unit and module is used as an example. In actual applications, the above functions can be allocated to different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiments can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction and do not limit the protection scope of this application. The specific working processes of the units and modules in the above system can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0107] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0108] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in connection with the embodiments disclosed herein can be implemented in electronic hardware, or in a combination of computer software and electronic hardware. Whether these functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. A person skilled in the art can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the present invention.

[0109] In the embodiments provided by the present invention, it should be understood that the disclosed device / terminal and method can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For example, the division of the modules or units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect coupling or communication connection of the device or unit can be in an electrical, mechanical or other form.

[0110] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place, or they can be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0111] In addition, the functional units in each embodiment of the present invention can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0112] When the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, to implement all or part of the processes in the above-described embodiment methods of the present invention, it can also be completed by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above-described various embodiments of the temperature, strain, and acoustic emission measurement methods based on tilted fiber gratings. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the content included in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0113] The above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for measuring temperature, strain, and acoustic emission based on an inclined fiber grating, characterized in that Including: Demodulating the cladding mode and Ghost mode of the transmission spectrum of the tilted fiber grating to obtain the cladding mode wavelength shift and the Ghost mode wavelength shift; wherein, the tilted fiber grating is installed on the target structure; Substituting the cladding mode wavelength shift and the Ghost mode wavelength shift into a two-parameter matrix and solving to obtain the temperature change and strain change of the target structure; wherein, the two-parameter matrix includes the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber grating; Demodulating and analyzing the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure.

2. The temperature, strain, and acoustic emission measurement method based on an inclined fiber grating according to claim 1, wherein The demodulating and analyzing the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure includes: Demodulating the Bragg reflection spectra of the tilted fiber grating at multiple moments to obtain multiple phase change amounts and forming a phase change sequence; Performing frequency-domain filtering on the phase change sequence to obtain the acoustic emission signal of the target structure.

3. The temperature, strain, and acoustic emission measurement method based on an inclined fiber grating according to claim 2, characterized in that The demodulating the Bragg reflection spectra of the tilted fiber grating at multiple moments to obtain multiple phase change amounts and forming a phase change sequence includes: Calculating the ambient temperature based on the temperature change of the target structure; Extracting the Bragg reflection spectra of the tilted fiber grating at multiple moments based on the Bragg-phase sensitivity corresponding to the ambient temperature for demodulation to obtain multiple phase change amounts and forming a phase change sequence.

4. The temperature, strain, and acoustic emission measurement method based on an inclined fiber grating according to claim 2, characterized in that After the demodulating and analyzing the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure, it further includes: Forming a strain change amount sequence from multiple strain change amounts of the target structure; Removing the acoustic emission signal of the target structure from the strain change amount sequence to obtain a corrected strain change amount sequence.

5. The temperature, strain, and acoustic emission measurement method based on an inclined fiber grating according to claim 1, characterized in that Before substituting the cladding mode wavelength shift and the Ghost mode wavelength shift into the two-parameter matrix and solving to obtain the temperature change and strain change of the target structure, it further includes: Calibrating the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber grating through experiments.

6. The temperature, strain, and acoustic emission measurement method based on an inclined fiber grating according to claim 1, wherein The tilted fiber grating is obtained by line-by-line writing based on femtosecond laser. During the writing process, the transmission spectrum and reflection spectrum of the tilted fiber grating are observed in real time, and the writing parameters are adjusted based on the observation results.

7. A temperature, strain, and acoustic emission measurement device based on an inclined fiber Bragg grating, characterized in that, Including: A first demodulation module for demodulating the cladding mode and Ghost mode of the transmission spectrum of the tilted fiber grating to obtain the cladding mode wavelength shift and the Ghost mode wavelength shift; wherein, the tilted fiber grating is installed on the target structure; A solving module for substituting the cladding mode wavelength shift and the Ghost mode wavelength shift into a two-parameter matrix and solving to obtain the temperature change and strain change of the target structure; wherein, the two-parameter matrix includes the cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity, and Ghost mode-strain sensitivity of the tilted fiber grating; The second demodulation module is used to demodulate and analyze the Bragg reflection spectrum of the tilted fiber grating to obtain the acoustic emission signal of the target structure.

8. The temperature, strain, and acoustic emission measurement device based on an inclined fiber grating according to claim 7, wherein Specifically, the second demodulation module is used for: Demodulating the Bragg reflection spectra of the tilted fiber grating at multiple moments to obtain a plurality of phase change amounts and forming a phase change sequence; Performing frequency-domain filtering on the phase change sequence to obtain the acoustic emission signal of the target structure.

9. A terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 above are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, the steps of the method according to any one of claims 1 to 6 above are implemented.

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