A pressure and temperature dual-parameter sensing method and device based on fiber forward Brillouin scattering

Abstract

The present invention provides a method and device for dual-parameter sensing of pressure and temperature based on forward Brillouin scattering in optical fibers. This method is based on the linear relationship between the change in the forward Brillouin scattering frequency shift of an optical fiber and the changes in pressure and temperature in the external environment. By utilizing the different responses of the forward Brillouin scattering frequency shift changes caused by two different transverse acoustic modes to pressure and temperature changes, and by simultaneously measuring two forward Brillouin scattering frequency shift changes, the changes in the external environment temperature and pressure can be resolved. The sensing device of the present invention has excellent mechanical strength and high temperature resistance and can be applied to harsh environments. Moreover, the structure of the present invention is simple, the measurement is stable, and the cross-sensitivity problem between pressure and temperature can be effectively eliminated, and it is expected to become a simple, accurate, durable, and stable sensing method for simultaneously measuring pressure and temperature. It has great potential in practical applications in fields such as aerospace, medicine, and environmental monitoring.

Description

Technical Field:

[0001] The present invention belongs to the technical field of fiber optic sensing, and particularly relates to a pressure and temperature dual-parameter sensing method and device based on fiber optic forward Brillouin scattering. Background Art:

[0002] With the development of technology, common sensing technologies have gradually evolved from traditional sensing technologies such as mechanical and piezoelectric to all-fiberized fiber optic sensing technologies. All-fiberized fiber optic sensors have excellent characteristics such as low cost, large measurement range, good linearity, multi-parameter, high reliability, and anti-electromagnetic interference. Therefore, they are very suitable for applications in oil and gas exploration and production, extreme harsh environment monitoring, aerospace engineering structural health monitoring, biomedical applications, etc., for long-term accurate synchronous measurement of parameters such as pressure, temperature, strain, vibration, and acoustic impedance at the same measurement point.

[0003] During the operation of various mechanical equipment, sudden failures may occur due to the adverse effects of vibration, shock, high heat, and humidity, affecting the task execution. Therefore, by long-term monitoring parameters such as pressure, temperature, and strain during operation, predicting their health status in advance, and performing targeted preventive maintenance before sudden failures are exposed, effective health management can be achieved. Developing a fiber optic pressure and temperature sensing and monitoring system that is applied to the ship use environment and can obtain high-precision and low-error measurement and feedback signals of pressure and temperature dual-parameters at the same measurement point is of great significance.

[0004] Typical fiber optic-based pressure and temperature dual-parameter sensing methods include fiber Bragg grating (FBG), stimulated Brillouin scattering (SBS), optical microcavity (Micro-cavity), and Fabry-Perot interferometer (FPI), etc. Sensors based on the above methods have been able to effectively achieve discriminative sensing of pressure and temperature, but there are still certain defects. For example, the pressure and temperature dual-parameter sensing method based on FBG is one of the most widely used pressure and temperature dual-parameter sensing methods in practical applications at present, but generally at least two sensors are required to achieve synchronous measurement of pressure and temperature, resulting in increased use costs; while the pressure measurement range of the sensing method based on optical microcavity is generally relatively narrow (less than 1 MPa), and in practical applications, a measurement range of at least 20 MPa is required, resulting in limited application scenarios; at the same time, many sensing methods cannot eliminate the cross-sensitivity problem between pressure and temperature, resulting in problems such as large measurement errors and low sensitivity. These inherent defects limit their applications in practical engineering. Therefore, an ideal pressure and temperature dual-parameter sensing technology should have characteristics such as simple structure, long-term stability, wide measurement range, low measurement error, and effective elimination of the cross-sensitivity problem between pressure and temperature.

[0005] The present invention is directed to fiber optic sensing technology, and designs a pressure and temperature dual-parameter sensing method and device based on forward Brillouin scattering in optical fibers. By making full use of the acousto-optic characteristics and the characteristics of multi-mode participation of forward Brillouin scattering in optical fibers, as well as the linear relationship between forward Brillouin frequency shift and pressure and temperature, and the characteristics that different modes have different pressure and temperature sensitivities, the simultaneous measurement of pressure and temperature with a simple structure, long-term stability, low error, and elimination of cross-sensitivity problems is achieved. Summary of the Invention:

[0006] The object of the present invention is to provide a pressure and temperature dual-parameter sensing method and device based on forward Brillouin scattering in optical fibers in view of the deficiencies of the prior art, which have the advantages of simple structure, long-term stability, low error, elimination of cross-sensitivity, etc.

[0007] To achieve the above technical object, the present invention adopts the following technical solutions:

[0008] (1) The present invention provides a pressure and temperature dual-parameter sensing method based on forward Brillouin scattering in an optical fiber. This method utilizes the linear relationships that exist between the forward Brillouin frequency shifts of two different transverse acoustic modes in the sensing optical fiber and pressure, and between the forward Brillouin frequency shift and temperature. By measuring the changes in the forward Brillouin frequency shifts corresponding to the two acoustic modes, the pressure and temperature are calculated using these linear relationships. By changing the pressure and temperature of the environment around the sensing optical fiber, the forward Brillouin scattering peak frequency shift-pressure coefficient and the frequency shift-temperature coefficient of different acoustic modes are calibrated. According to the error calculation formula, the optimal combination of two acoustic modes with the lowest measurement error is obtained as the sensing mode combination. When the external pressure and temperature change, the changes in the external pressure and temperature are obtained through the sensing matrix calculation formula based on the forward Brillouin scattering frequency shift of the sensing mode combination, thereby realizing the simultaneous sensing of pressure and temperature using the forward Brillouin scattering frequency shift. Specifically, it includes the following steps:

[0009] Step S1: Obtain the forward Brillouin scattering spectrum excited by the transverse acoustic mode of the sensing optical fiber in the initial state, where the spectrum of the m-th scattering peak is R 0,m Forward Brillouin scattering spectrum excited by the acoustic mode, and obtain the center frequency position of each R 0,m acoustic mode; select the mode suitable for sensing according to the signal-to-noise ratio and sensitivity;

[0010] Step S2: Perform temperature and pressure variation processing on the sensing optical fiber to obtain the forward Brillouin scattering spectrum diagram excited by the transverse acoustic mode of the sensing optical fiber. By performing Lorentz fitting on the forward Brillouin scattering peaks of each mode, the variation of the forward Brillouin frequency shift of the scattering peaks in different states and different transverse acoustic modes after temperature and pressure variation can be obtained, that is, the variation of the central frequency of the forward Brillouin scattering peak. Utilize the linear relationships between the forward Brillouin frequency shifts of two different transverse acoustic modes in the sensing optical fiber and pressure, and between the forward Brillouin frequency shift and temperature, thereby obtaining the frequency shift-pressure sensitivity and frequency shift-temperature sensitivity of the two different transverse acoustic modes. Screen out the mode combination with the minimum measurement error as the sensing mode combination;

[0011] Step S3: Measure the variation of the forward Brillouin frequency shift of the sensing mode combination screened in Step S2 after temperature and pressure variation, calculate the variation of the ambient pressure and the variation of the temperature, and achieve the measurement.

[0012] Further, in Step S2, substitute the frequency shift-pressure sensitivity and frequency shift-temperature sensitivity corresponding to each mode into Formula (1) for calculation, and screen out the mode combination with the minimum measurement error;

[0013]

[0014] where, δν is the measurement error of the forward Brillouin frequency shift of different transverse acoustic modes; C ν-P is the frequency shift-pressure sensitivity, C ν-T is the frequency shift-temperature sensitivity; δP is the pressure measurement error, δT is the temperature measurement error; the subscripts all represent the mode numbers m = i or j, i ≠ j.

[0015] Further, in Step S3, substitute the variation of the forward Brillouin frequency shift of the sensing mode combination after temperature and pressure variation into Formula (2), and the variation of the ambient pressure and the variation of the temperature can be solved;

[0016]

[0017] where, Δν is the variation of the forward Brillouin frequency shift of the sensing mode combination after temperature and pressure variation; ΔP is the variation of the pressure, and ΔT is the variation of the temperature.

[0018] (2) The present invention also provides a sensing device for implementing the pressure and temperature dual-parameter sensing method of the above-mentioned forward Brillouin scattering in optical fibers, including a light source, an optical isolator, a first polarization controller, a Sagnac loop, a photodetector, and a data processing system. The Sagnac loop is sequentially composed of an optical coupler, a second polarization controller, and a sensing optical fiber. The light source generates continuous laser light that passes through the optical isolator and the first optical polarization controller, and is evenly divided into two beams by the optical coupler and enters the Sagnac loop. They are transmitted clockwise and counterclockwise in the loop respectively. The light wave transmitted clockwise passes through the second polarization controller and the sensing optical fiber in sequence, and the light wave transmitted counterclockwise passes through the sensing optical fiber and the second polarization controller in sequence. In the sensing optical fiber, the incident light excites a vibration sound field to form a refractive index density grating, which generates a phase modulation on the incident light wave. The two light waves transmitted clockwise and counterclockwise in the loop interfere in the optical coupler, converting the phase modulation into an intensity modulation, generating a coherent light wave signal, which is converted into an electrical signal for analysis and processing by the photodetector, and finally received and analyzed by the data processing system.

[0019] Further, the light source is a narrow-linewidth semiconductor laser that can generate a stable continuous light wave with a wavelength of 1550 nm.

[0020] Further, the sensing optical fiber is a single-mode optical fiber with a double cladding layer.

[0021] Further, the optical coupler is a 2×2 optical coupler.

[0022] Advantages of the present invention:

[0023] Compared with the traditional FBG-based pressure and temperature dual-parameter sensor, the solution of the present invention has the characteristic that the pressure and temperature dual-parameters can be measured simultaneously only through one optical fiber, with a simple structure and low cost. Compared with the optical microcavity-based pressure and temperature dual-parameter sensor, the solution of the present invention has a wider pressure measurement range, higher robustness, and is applicable to more application scenarios. At the same time, the solution of the present invention effectively eliminates the problem of cross-sensitivity between pressure and temperature, and can realize simple, accurate, durable, and stable simultaneous measurement of pressure and temperature, and can be effectively used in the pressure and temperature dual-parameter simultaneous monitoring system. Description of the drawings:

[0024] Figure 1 It is a schematic structural diagram of an embodiment of the present invention;

[0025] Figure 2 It is an FBS spectrogram of the sensing optical fiber at normal temperature and unpressurized state;

[0026] Figure 3 It is the frequency shift-pressure sensitivity (C ν-P ) and frequency shift-temperature sensitivity (Cν-T ) Figure;

[0027] Figure 4 is R 0,8 Schematic diagram of the relationship between frequency shift and pressure in the acoustic mode;

[0028] Figure 5 are the pressure measurement error and temperature measurement error of different acoustic mode combinations;

[0029] Figure 6 are the experimental measurement errors of pressure and temperature obtained from the verification experiment;

[0030] Figure 7 is R 0,6 and R 0,8 Schematic diagram of the time stability of the frequency shift of the acoustic mode.

[0031] The reference signs in the drawings are:

[0032] 1. Light source; 2. Optical isolator; 3. First polarization controller; 4. Optical coupler; 5. Second polarization controller; 6. Sensing optical fiber; 7. Photoelectric detector; 8. Data processing system. Specific implementation mode:

[0033] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Embodiment 1

[0035] Referring to Figure 1 , the embodiment of the present invention provides a pressure and temperature dual-parameter sensing device based on fiber optic forward Brillouin scattering, including a light source 1, an optical isolator 2, a first polarization controller 3, a Sagnac loop, a photoelectric detector 7 and a data processing system 8. The Sagnac loop is composed of an optical coupler 4, a second polarization controller 5 and a sensing optical fiber 6 connected in sequence.

[0036] The light source 1 generates continuous laser light that passes through the optical isolator 2 and the first optical polarization controller 3, and is evenly divided into two beams by the optical coupler 4 and enters the Sagnac loop, where they are transmitted in the clockwise and counterclockwise directions respectively. The optical coupler 4 can be used to prevent the light reflected from the Sagnac loop from interfering with the light source 1.

[0037] Inside the Sagnac loop, the light wave propagating in the clockwise direction sequentially passes through the second polarization controller 5 and the sensing optical fiber 6, and the light wave propagating in the counterclockwise direction sequentially passes through the sensing optical fiber 6 and the second polarization controller 5. Inside the sensing optical fiber 6, the incident light excites a vibration sound field to form a refractive index density grating, which generates a phase modulation on the incident light wave. The two light waves propagating in the clockwise and counterclockwise directions respectively in the loop interfere in the optical coupler 4, converting the phase modulation into an intensity modulation, generating a coherent light wave signal, which is converted into an electrical signal for analysis and processing by the photodetector 7, and finally received and analyzed by the data processing system 8.

[0038] In this embodiment, the light source 1 is a narrow linewidth semiconductor laser, which can generate a stable continuous light wave with a wavelength of 1550 nm; the sensing optical fiber 6 is a single-mode optical fiber with a double coating layer; the optical coupler 4 is a 2×2 optical coupler.

[0039] Embodiment 2

[0040] The embodiment of the present invention provides a pressure and temperature dual-parameter sensing method based on fiber forward Brillouin scattering, which specifically includes the following steps:

[0041] Step S1: When the sensing optical fiber is at room temperature and not pressurized, the light wave enters the sensing optical fiber 6 to excite the sound field, and the participating transverse acoustic mode is the R 0,m acoustic mode, generating the forward Brillouin scattering spectrum corresponding to each R 0,m acoustic mode, as Figure 2 shown; then perform Lorentz fitting on the forward Brillouin scattering peaks of each R 0,m acoustic mode, and the center frequency position of each acoustic mode can be obtained; select the mode with a signal-to-noise ratio higher than 3 dB and a better sensing sensitivity for sensing. In this embodiment, the selected modes are R 0,5 ~R 0,9 ;

[0042] Step S2: Use a water bath and a hydraulic press to pressurize (0 MPa to 15 MPa) and heat (20 °C to 60 °C) the sensing optical fiber 6 respectively. By performing Lorentz fitting on the forward Brillouin scattering peaks of each mode, the forward Brillouin frequency shift changes of the scattering peaks of different modes in different states can be obtained, that is, the center frequency change of the forward Brillouin scattering peak. Utilize the linear relationships between the forward Brillouin frequency shifts of two different transverse acoustic modes in the sensing optical fiber and pressure, and between the forward Brillouin frequency shift and temperature, so as to obtain the frequency shift-pressure sensitivity (C ν-P ) and the frequency shift-temperature sensitivity (C ν-T ), as Figure 3 shown. Taking the R 0,8 acoustic mode as an example, the relationship between the frequency shift and pressure is asFigure 4 as shown

[0043] Substitute the frequency shift - pressure sensitivity (C ν-P ) and the frequency shift - temperature sensitivity (C ν-T ) corresponding to each mode into formula (1) for calculation, and screen out the mode combination with the smallest measurement error;

[0044]

[0045] where δν is the forward Brillouin frequency shift measurement error of different transverse acoustic modes; C ν-P is the frequency shift - pressure sensitivity, C ν-T is the frequency shift - temperature sensitivity; δP is the pressure measurement error, and δT is the temperature measurement error; the subscripts all represent the mode numbers m = i or j, i ≠ j.

[0046] In this embodiment, the selected (R 0,6 , R 0,8 ) mode combination is used as the sensing mode combination, and the pressure measurement error and the temperature measurement error are 0.05 MPa and 0.08 °C respectively, as Figure 5 shown

[0047] Step S3: Measure the change in the forward Brillouin frequency shift of the sensing mode combination screened in step S2 after the temperature and pressure change. Substitute the change in the forward Brillouin frequency shift (Δν6, Δν8) of the sensing mode combination (R 0,6 , R 0,8 ) after the temperature and pressure change into formula (2), and then the change in the ambient pressure ΔP and the change in the temperature ΔT can be solved to achieve the measurement.

[0048]

[0049] Through verification experiments, it is proved that the method of the present invention can achieve the simultaneous measurement of the two parameters of pressure and temperature, and the measurement errors of pressure and temperature are 0.05 MPa and 0.13 °C respectively in the range of 0 - 18 MPa for the pressure and 20 - 60 °C for the temperature of the sensor, as Figure 6 shown

[0050] As Figure 7 shown, within 120 minutes, the measurement stability of the sensor is tested at an interval of 20. It is found that the standard deviation of the center frequency is less than 0.01%, indicating that the pressure - temperature dual - parameter sensing method and device based on forward Brillouin scattering of the present invention has measurement stability and is suitable for long - term operation.

[0051] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. Any technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should be regarded as within the protection scope of the present invention.

Claims

1. A pressure and temperature dual-parameter sensing method based on forward Brillouin scattering of optical fiber, characterized in that, This method utilizes the linear relationships between the forward Brillouin frequency shifts of two different transverse acoustic modes in a sensing optical fiber and pressure, as well as between the forward Brillouin frequency shifts and temperature. By measuring the changes in the forward Brillouin frequency shifts corresponding to the two acoustic modes, the pressure and temperature are calculated using the above linear relationships, and the method includes the following steps: Step S1: Obtain the forward Brillouin scattering spectrum diagram excited by the transverse acoustic mode of the sensing optical fiber in the initial state, where the spectrum of the m-th scattering peak is R 0,m Forward Brillouin scattering spectrum excited by the acoustic mode to obtain each R 0,m Central frequency position of the acoustic mode; Step S2: Perform temperature and pressure variation processing on the sensing optical fiber to obtain the forward Brillouin scattering spectrum diagram excited by the transverse acoustic modes of the sensing optical fiber, and obtain the changes in the forward Brillouin frequency shifts of the scattering peaks in different states and different transverse acoustic modes after temperature and pressure variation. Utilize the linear relationships between the forward Brillouin frequency shifts of two different transverse acoustic modes in the sensing optical fiber and pressure, as well as between the forward Brillouin frequency shifts and temperature, so as to obtain the frequency shift-pressure sensitivity and frequency shift-temperature sensitivity of the two different transverse acoustic modes, and screen out the mode combination with the minimum measurement error as the sensing mode combination; Step S3: Measure the changes in the forward Brillouin frequency shifts of the sensing mode combination screened in Step S2 after temperature and pressure variation, and calculate the changes in the ambient pressure and temperature; In Step S2, by substituting the frequency shift-pressure sensitivity and frequency shift-temperature sensitivity corresponding to each mode into formula (1) for calculation, the mode combination with the minimum measurement error is screened out; where δν is the measurement error of the forward Brillouin frequency shift of different transverse acoustic modes; C ν-P is the frequency shift-pressure sensitivity, C ν-T is the frequency shift-temperature sensitivity; δP is the pressure measurement error, δT is the temperature measurement error; the subscripts all represent the mode numbers m = i or j, where i ≠ j; In Step S3, substitute the changes in the forward Brillouin frequency shifts of the sensing mode combination after temperature and pressure variation into formula (2), and the changes in the ambient pressure and temperature can be solved; Wherein, Δν is the change in the forward Brillouin frequency shift of the sensing mode combination after temperature and pressure variation; ΔP is the change in pressure, and ΔT is the change in temperature.

2. A sensing device for implementing the pressure and temperature dual-parameter sensing method of forward Brillouin scattering of an optical fiber according to claim 1, characterized in that it includes a light source (1), an optical isolator (2), a first polarization controller (3), a Sagnac loop, a photodetector (7) and a data processing system (8). The Sagnac loop is sequentially composed of an optical coupler (4), a second polarization controller (5) and a sensing optical fiber (6); The light source (1) generates continuous laser light that passes through the optical isolator (2) and the first polarization controller (3), and is evenly divided into two beams by the optical coupler (4) and enters the Sagnac loop, where they are transmitted clockwise and counterclockwise respectively in the loop. The light wave transmitted clockwise sequentially passes through the second polarization controller (5) and the sensing optical fiber (6), and the light wave transmitted counterclockwise sequentially passes through the sensing optical fiber (6) and the second polarization controller (5). The two light waves interfere in the optical coupler (4), converting the phase modulation into intensity modulation, generating a coherent light wave signal that is converted into an electrical signal by the photodetector (7) and received and analyzed by the data processing system (8).

3. The sensing device according to claim 2, characterized in that the light source (1) is a narrow linewidth semiconductor laser.

4. The sensing device according to claim 2, characterized in that the sensing optical fiber (6) is a single-mode optical fiber with a double coating layer.

5. The sensing device according to claim 2, characterized in that The optical coupler (4) is a 2×2 optical coupler.

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