Dual-f-p cavity hollow core fiber magnetic field and temperature dual-parameter sensor and method

Abstract

The application discloses a kind of double F-P cavity hollow core fiber magnetic field temperature dual parameter sensor and method, the sensor includes light source, optical circulator, sensing probe and signal processing unit.Sensing probe is formed by single-mode optical fiber and hollow core fiber fusion to form two series F-P cavities, the outer wall of first cavity is provided with magnetostrictive material layer, the outer wall of second cavity is coated with high thermal expansion coefficient elastic polymer layer, so that two cavities produce differential response to magnetic field and temperature.Signal processing unit monitors the drift amount of two cavity characteristic spectrum wavelength, substitutes into the coefficient matrix of pre-calibration, simultaneously solves magnetic field intensity and temperature value.The application realizes the high-precision synchronous distinction measurement of magnetic field and temperature, compact structure, strong anti-interference ability, suitable for multi-parameter monitoring in complex environment.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a dual-parameter sensor and method for magnetic field and temperature in a dual-FP cavity hollow fiber. Background Technology

[0002] Magnetic field detection technology has significant application value in military defense, geological exploration, food safety testing, and environmental monitoring. Compared with traditional magnetic field measurement techniques, fiber optic sensing technology has advantages such as resistance to electromagnetic interference, small size, ease of multiplexing, and distributed measurement. Currently, fiber optic sensing technologies used for magnetic field measurement are mainly based on the magnetostrictive effect, Faraday magneto-optical effect, and magnetohydrodynamic refractive index modulation effect. Among these, the scheme based on combining magnetostrictive materials with fiber gratings (FBGs) or fiber interferometers (such as FP cavities and MZ interferometers) suffers from severe limitations in measurement accuracy due to its inherent temperature cross-sensitivity. To address this issue, existing technologies typically employ parallel reference fibers or complex algorithms for decoupling. However, these methods still have limitations: the reference fiber method increases system complexity and cost, and the inconsistency between the environment of the reference path and the sensing path introduces decoupling errors; simple algorithmic decoupling relies on accurate mathematical models and lacks robustness in complex and variable environments.

[0003] The applicant's research revealed that Fabry-Perot interferometers (FPIs) are widely used for sensing various physical quantities due to their flexible structure, high sensitivity, and ease of fabrication. Hollow-core photonic crystal fibers (HC-PCFs) possess the characteristic of light propagation within an air core, exhibiting an extremely low effective thermo-optical coefficient, which significantly suppresses temperature-induced optical phase noise. Simultaneously, magnetostrictive materials (such as Terfenol-D) can convert magnetic fields into mechanical strain, and polymer materials with high thermal expansion coefficients (such as PDMS) can amplify temperature changes into significant mechanical deformation. Therefore, this invention, based on these advantageous materials and combined with an innovative fiber optic interferometric structure, constructs a compact, high-performance sensor that can naturally decouple multiple parameters. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-parameter sensor and method for magnetic field and temperature in a dual-FP cavity hollow fiber optic cable, in order to solve the problem of temperature cross-sensitivity that is common in existing fiber optic magnetic field sensors, and to achieve high-precision, synchronous, and distinguishable measurement of magnetic field and temperature, while maintaining a compact sensor structure and strong anti-interference capability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A dual-FP cavity hollow fiber magnetic field and temperature dual-parameter sensor includes: a light source, an optical circulator, an optical fiber sensing probe, and a signal processing unit.

[0007] The light source is connected to the first port of the optical circulator, the fiber optic sensing probe is connected to the second port of the optical circulator, and the signal processing unit is connected to the third port of the optical circulator.

[0008] The fiber optic sensing probe includes a first single-mode fiber, a section of hollow fiber and a second single-mode fiber connected sequentially along the optical path.

[0009] A first Fabry-Perot interferometer cavity is formed between the end face of the first single-mode fiber and the first end face of the hollow fiber.

[0010] A second Fabry-Perot interferometer cavity is formed between the second end face of the hollow fiber and the end face of the second single-mode fiber.

[0011] The hollow optical fiber has a magnetostrictive material layer bonded to the outer surface of the first Fabry-Perot interferometer cavity.

[0012] The hollow optical fiber has an elastic polymer material layer bonded to the outer surface of the second Fabry-Perot interferometer cavity;

[0013] The signal processing unit is used to acquire the reflection spectrum of the fiber optic sensing probe, and calculate the cavity length change of the two interferometer cavities by tracking the wavelength drift of the characteristic spectral peaks of the first and second Fabry-Perot interferometer cavities. Based on the differential response brought about by the magnetostrictive material layer and the elastic polymer material layer, the independent magnetic field strength and temperature values ​​are calculated simultaneously.

[0014] Furthermore, the hollow optical fiber is a hollow photonic crystal fiber or a capillary tube, and its internal air channels may be selectively filled with magnetic fluid.

[0015] Furthermore, the magnetostrictive material layer is a thin film or sheet of Terfenol-D, FeGa alloy, or FeCoV alloy, which is bonded to the outer wall of the hollow optical fiber by bonding or plating.

[0016] Furthermore, the elastic polymer material layer is polydimethylsiloxane, silicone rubber, or polyurethane, and is formed on the outer wall of the hollow optical fiber by coating and curing.

[0017] Furthermore, the signal processing unit includes a spectral acquisition module and a data processing module. The spectral acquisition module is used to acquire the reflection spectrum in real time, and the data processing module is used to perform wavelength peak tracking, drift calculation, and magnetic field strength and temperature value calculation based on the calibration coefficient matrix.

[0018] A method for measuring a dual parameter of magnetic field and temperature based on the sensor includes the following steps:

[0019] The initial reflection spectrum of the fiber optic sensing probe under no magnetic field and reference temperature is obtained to determine the center wavelength of the characteristic interference peak of the first Fabry-Perot interferometer cavity. and the center wavelength of the characteristic interference peak of the second Fabry-Perot interferometer cavity And take these two center wavelengths as the initial reference values;

[0020] The reflection spectrum of the fiber optic sensing probe is acquired in real time, and the center wavelengths of the characteristic interference peaks of the first and second Fabry-Perot interferometers are tracked in real time. and The wavelength drift is calculated based on the determined initial reference value. , ;

[0021] Obtain the pre-calibrated wavelength sensitivity coefficients of the first Fabry-Perot interferometer cavity to magnetic fields and temperature. , The wavelength sensitivity coefficients of the second Fabry-Perot interferometer cavity to magnetic fields and temperature. , And satisfy >> , >> ; will be obtained and Substitute into the following system of equations: ;

[0022] Solve the equations simultaneously to obtain the current magnetic field strength H and temperature T.

[0023] Furthermore, the sensitivity coefficient is calibrated through the following steps:

[0024] At a constant temperature, a standard magnetic field with a known gradient is applied, and the results are recorded. and The slopes of the curves relating to magnetic field strength are determined as follows: and ;

[0025] Under a constant magnetic field, a standard temperature with a known gradient is applied, and the temperature is recorded. and The slopes of the curves relating to temperature are determined as follows: and .

[0026] Furthermore, the simultaneous solution specifically involves: ... , and calibration coefficients , , , The matrix equations are constructed, and the separated magnetic field strength H and temperature T are output through matrix inversion or linear equation solving algorithms.

[0027] Furthermore, the internal air channel of the hollow optical fiber is filled with magnetic fluid, and the refractive index of the magnetic fluid is changed by a magnetic field to further modulate the optical path and enhance the magnetic field response sensitivity.

[0028] Furthermore, the real-time value of the center wavelength of the tracking feature interference peak is obtained using a peak-finding algorithm.

[0029] The beneficial effects of this invention are:

[0030] (1) By using the dual FP cavity spatial separation structure and different cavity external materials, the response mechanisms and coefficients of the two FP cavities to magnetic field and temperature are fundamentally different, thus avoiding signal aliasing from a physical mechanism perspective and achieving efficient and reliable decoupling.

[0031] (2) The entire sensing probe is made of standard single-mode fiber and hollow fiber fusion spliced ​​together. It does not require complex optical splitting devices or multiple discrete sensors. It has a simple, robust, and compact structure, and is easy to package and deploy.

[0032] (3) By selecting magnetostrictive materials with different properties (such as Terfenol-D for high sensitivity and FeGa for large range) and adjusting the thickness and material of the polymer layer, the magnetic field sensitivity, temperature sensitivity and range of the sensor can be flexibly designed to meet different application requirements.

[0033] (4) All-fiber passive sensor head, suitable for working in harsh environments such as strong electromagnetic fields, flammable and explosive environments. Attached Figure Description

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0035] Figure 1 This is a schematic diagram of the overall structure of the sensor system provided in an embodiment of the present invention.

[0036] Figure 2 This is a detailed cross-sectional view of the sensing probe in an embodiment of the present invention.

[0037] The following labels are used in the diagram: 1-Light source, 2-Optical circulator, 3-Sensing probe, 4-Signal processing unit, 3-1-First single-mode fiber, 3-2-Hollow fiber segment, 3-3-Second single-mode fiber, 3-4-Magnetostrictive material layer, 3-5-Elastic polymer material layer, 3-6-Air channel (can be filled with magnetic fluid), FP1-First Fabry-Perot interferometer cavity, FP2-Second Fabry-Perot interferometer cavity. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0039] See Figure 1 This invention provides a fiber optic sensor for measuring magnetic field and temperature dual parameters based on a hollow fiber dual FP cavity, comprising a light source 1, an optical circulator 2, a sensing probe 3, and a signal processing unit 4.

[0040] The light source 1 is connected to the first port of the optical circulator 2; the sensing probe 3 is connected to the second port of the optical circulator 2; and the signal processing unit 3 is connected to the third port of the optical circulator 2.

[0041] The sensing probe 3 includes a first single-mode fiber 3-1, a hollow fiber 3-2, and a second single-mode fiber 3-3, which are connected sequentially along the optical path. A first Fabry-Perot interference cavity FP1 is formed between the end face of the first single-mode fiber 3-1 and the first end face of the hollow fiber 3-2. A second Fabry-Perot interference cavity FP2 is formed between the second end face of the hollow fiber 3-2 and the end face of the second single-mode fiber. A magnetostrictive material layer 3-4 is bonded to the outer surface of the hollow fiber 3-2 corresponding to the first Fabry-Perot interference cavity 3-1. An elastic polymer material layer 3-5 is bonded to the outer surface of the hollow fiber 3-2 corresponding to the second Fabry-Perot interference cavity FP2.

[0042] The signal processing unit 4 is used to acquire the reflection spectrum of the fiber optic sensing probe 3. By tracking the wavelength drift of the characteristic spectral peaks of the first Fabry-Perot interferometer FP1 and the second Fabry-Perot interferometer FP2, the change in cavity length of the two interferometer cavities is calculated. Based on the differential response brought about by the magnetostrictive material layer 3-4 and the elastic polymer material layer 3-5, the independent magnetic field strength and temperature value are calculated simultaneously.

[0043] See Figure 2The fabrication method of the sensing probe 3 is as follows: A section of hollow photonic crystal fiber 3-2 is selected, and its two ends are aligned with the first single-mode fiber 3-1 and the second single-mode fiber 3-3 in a fusion splicer. By optimizing the splicing parameters (such as low discharge power), a small air gap is formed, thereby constituting the first FP cavity (FP1) and the second FP cavity (FP2). A Terfenol-D sheet is pasted on the outer wall of the FP1 region as a magnetostrictive material layer 3-4. PDMS is coated and cured on the outer wall of the FP2 region to form an elastic polymer material layer 3-5. Optionally, magnetic fluid is injected into the air channels (3-6) of the hollow photonic crystal fiber 3-2.

[0044] When light emitted from the broadband light source enters the sensing probe through the optical circulator, it interferes and is reflected between the reflective surfaces of the first FP cavity (FP1) and the second FP cavity (FP2). The reflected light from the two cavities superimposes in the optical fiber, forming a composite reflection spectrum containing two interference fringes of different frequencies. The intensity of this composite spectrum can be expressed as the superposition of the reflection spectra of the two cavities. This reflection spectrum is acquired using a spectrometer, and a peak-finding algorithm can be used to identify and track the center wavelength of a characteristic interference peak from each of FP1 and FP2. and Under the influence of an external magnetic field (H) and temperature (T), the cavity length change of FP1, which incorporates a magnetostrictive material layer, is mainly affected by the magnetostrictive strain induced by the magnetic field and the thermal expansion of the material. For FP2, which incorporates a polymer material layer with a high coefficient of thermal expansion, the cavity length change is mainly governed by the stress caused by the thermal expansion of the polymer layer, and its response to the magnetic field is extremely weak. Therefore, the drift of the two characteristic wavelengths... and They can be represented as:

[0045] ;

[0046] ;

[0047] in, and Especially the wavelength response sensitivity coefficient of FP1 to magnetic fields and temperature, and These are the wavelength response sensitivity coefficients of FP2 to magnetic fields and temperature, respectively, and they satisfy... >> , >> After obtaining these four sensitivity coefficients through preliminary calibration, the real-time measured values ​​will be... and By substituting the above equations into the solution, the simultaneous measurement of magnetic field and temperature can be achieved.

[0048] Signal processing and demodulation methods include:

[0049] (1) Initialization calibration: In a standard temperature-controlled magnetic field environment, the wavelength sensitivity coefficients of FP1 and FP2 to magnetic field H and temperature T are calibrated. , , , And record the initial characteristic wavelength. , .

[0050] (2) Real-time measurement and demodulation:

[0051] S1. The spectrometer acquires the reflectance spectrum in real time.

[0052] S2. Determine the center wavelength of the current characteristic peaks of FP1 and FP2 using a peak-finding algorithm. and .

[0053] S3. Calculate the wavelength shift: , .

[0054] S4. Will , And the calibration coefficients are substituted into the system of equations:

[0055] The real-time magnetic field strength H and temperature T are obtained by solving.

[0056] The demodulation method of the present invention will be further explained below with reference to a specific theoretical calculation example.

[0057] In this example, the sensor is set to have the following calibration parameters (these calibration values ​​can be obtained through a standard calibration procedure under laboratory conditions, as shown in Table 1):

[0058] Table 1

[0059]

[0060] In the absence of a magnetic field ( ), reference temperature ( Under these conditions, the initial center wavelengths of the characteristic peaks of the two cavities were recorded as follows: = 1550.00 nm = 1550.00 nm.

[0061] Assuming the sensor is located in a measured environment with a true magnetic field strength H = 5.00 mT and a true temperature T = 35.00 °C, the wavelength shift of the characteristic peaks of the two cavities can be theoretically calculated using the following formula:

[0062] Then the real-time center wavelength output by the sensor at this time is: =1550.080 nm, =1550.400 nm.

[0063] Substituting the wavelength shift mentioned above into the demodulation equations:

[0064] 80.00 = 12.00 × H + 2.00 × (T - 25)

[0065] 400.00≈0×H+40.00×(T-25)

[0066] Solving the second equation, we get T - 25 = 10.00 °C, which means T = 35.00 °C. Substituting this into the first equation, we get 80.00 = 12.00 × H + 20.00, which gives H = 5.00 mT.

[0067] Calculation results show that, using the sensor structure and demodulation method proposed in this invention, the magnetic field strength H=5.00 mT and temperature T=35.00 °C, which are completely consistent with the preset values, can be accurately deduced from the measured wavelength drift. This example theoretically proves that the technical solution of this invention can achieve simultaneous and differentiated measurement of magnetic field and temperature.

[0068] Compared with the prior art, the present invention has the following characteristics and effects:

[0069] High-precision dual-parameter decoupled measurement: By employing two spatially separated Fabry-Perot interferometer cavities, and combining a magnetostrictive material layer (sensitive to magnetic fields) and a high thermal expansion coefficient elastic polymer material layer (sensitive to temperature) on the outer walls of the two cavities respectively, the response mechanisms and sensitivity coefficients of the two cavities to magnetic fields and temperatures are fundamentally different. >> , >> This physically avoids signal aliasing, eliminating the need for complex reference optical paths or algorithms relying on precise mathematical models. It enables efficient and reliable synchronous decoupled measurement of magnetic fields and temperatures by solving a system of simultaneous equations.

[0070] Compact structure and strong environmental adaptability: The sensing probe is composed of only a single-mode fiber and a section of hollow fiber fused together, eliminating the need for discrete sensors or additional beam splitters. The overall structure is robust, compact, and easy to package and deploy. At the same time, the all-fiber passive design enables it to operate stably in harsh environments such as strong electromagnetic fields and flammable and explosive environments.

[0071] High flexibility and customizability: By selecting magnetostrictive materials with different properties (such as high-sensitivity Terfenol-D or large-range FeGa alloy) and adjusting the material type and thickness of the polymer layer, the magnetic field sensitivity, temperature sensitivity and measurement range of the sensor can be designed as needed to meet the differentiated needs of various application scenarios such as power equipment monitoring and industrial process control.

[0072] The embodiments of the present invention, through innovative dual-cavity structure and material modification, combined with a simple dual-wavelength demodulation method, effectively achieve high-precision and synchronous measurement of magnetic field and temperature, which has important practical value.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-FP cavity hollow fiber magnetic field and temperature dual-parameter sensor, characterized in that, include: Light source (1), optical circulator (2), fiber optic sensing probe (3) and signal processing unit (4); The light source (1) is connected to the first port of the optical circulator (2), the fiber optic sensing probe (3) is connected to the second port of the optical circulator (2), and the signal processing unit (4) is connected to the third port of the optical circulator (2). The fiber optic sensing probe (3) includes a first single-mode fiber (3-1), a section of hollow fiber (3-2), and a second single-mode fiber (3-3) connected sequentially along the optical path. A first Fabry-Perot interferometer cavity (FP1) is formed between the end face of the first single-mode fiber (3-1) and the first end face of the hollow fiber (3-2). A second Fabry-Perot interferometer (FP2) is formed between the second end face of the hollow fiber (3-2) and the end face of the second single-mode fiber (3-3). The hollow optical fiber (3-2) has a magnetostrictive material layer (3-4) bonded to the outer surface of the first Fabry-Perot interferometer cavity (FP1). The hollow fiber (3-2) has an elastic polymer material layer (3-5) bonded to the outer surface of the second Fabry-Perot interferometer cavity (FP2). The signal processing unit (4) is used to collect the reflection spectrum of the fiber optic sensing probe (3), and calculate the cavity length change of the two interferometers by tracking the wavelength drift of the characteristic spectral peaks of the first Fabry-Perot interferometer (FP1) and the second Fabry-Perot interferometer (FP2). Based on the differential response brought about by the magnetostrictive material layer (3-4) and the elastic polymer material layer (3-5), the independent magnetic field strength and temperature value are calculated simultaneously.

2. The sensor according to claim 1, characterized in that: The hollow fiber (3-2) is a hollow photonic crystal fiber or a capillary, and its internal air channel (3-6) may be selectively filled with magnetic fluid.

3. The sensor according to claim 1, characterized in that: The magnetostrictive material layer (3-4) is a thin film or sheet-like Terfenol-D, FeGa alloy or FeCoV alloy, which is bonded to the outer wall of the hollow optical fiber (3-2) by bonding or plating.

4. The sensor according to claim 1, characterized in that: The elastic polymer material layer (3-5) is polydimethylsiloxane, silicone rubber or polyurethane, and is formed on the outer wall of the hollow optical fiber (3-2) by coating and curing.

5. The sensor according to claim 1, characterized in that: The signal processing unit (4) includes a spectrum acquisition module and a data processing module. The spectrum acquisition module is used to acquire the reflection spectrum in real time, and the data processing module is used to perform wavelength peak tracking, drift calculation, and magnetic field strength and temperature value calculation based on the calibration coefficient matrix.

6. A method for measuring a dual parameter of magnetic field and temperature based on the sensor according to any one of claims 1 to 5, characterized in that, Includes the following steps: The initial reflection spectrum of the fiber optic sensing probe (3) under no magnetic field and reference temperature is obtained to determine the center wavelength of the characteristic interference peak of the first Fabry-Perot interferometer (FP1). The center wavelength of the characteristic interference peak of the second Fabry-Perot interferometer (FP2) And take these two center wavelengths as the initial reference values; The reflection spectrum of the fiber optic sensing probe (3) is acquired in real time, and the center wavelength values ​​of the characteristic interference peaks of the first Fabry-Perot interferometer (FP1) and the second Fabry-Perot interferometer (FP2) are tracked in real time. and The wavelength drift is calculated based on the determined initial reference value. , ; Obtain the pre-calibrated wavelength sensitivity coefficients of the first Fabry-Perot interferometer cavity (FP1) to magnetic fields and temperature. , The wavelength sensitivity coefficients of the second Fabry-Perot interferometer (FP2) to magnetic fields and temperature. , And satisfy >> , >> ; will be obtained and Substitute into the following system of equations: ; Solve the equations simultaneously to obtain the current magnetic field strength H and temperature T.

7. The method according to claim 6, characterized in that, The sensitivity coefficient is calibrated through the following steps: At a constant temperature, a standard magnetic field with a known gradient is applied, and the results are recorded. and The slopes of the curves relating to magnetic field strength are determined as follows: and ; Under a constant magnetic field, a standard temperature with a known gradient is applied, and the temperature is recorded. and The slopes of the curves relating to temperature are determined as follows: and .

8. The method according to claim 6, characterized in that, The simultaneous solution specifically involves: [The following is a list of steps / methods / etc.] , and calibration coefficients , , , The matrix equations are constructed, and the separated magnetic field strength H and temperature T are output through matrix inversion or linear equation solving algorithms.

9. The method according to claim 6, characterized in that: Magnetic fluid is filled in the internal air channel (3-6) of the hollow optical fiber (3-2). The refractive index of the magnetic fluid is changed by the magnetic field to further modulate the optical path and enhance the magnetic field response sensitivity.

10. The method according to claim 6, characterized in that: The real-time value of the center wavelength of the tracking feature interference peak is obtained using a peak-finding algorithm.

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