Optical fiber mine magnetic detection sensor and system based on magnetic composite sheath and FPI

Abstract

The invention discloses an optical fiber mine magnetic detection sensor and system based on a magnetic composite sheath and an FPI, and belongs to the technical field of optical fiber sensing and mineral resource detection. The magnetic composite sheath optical fiber sensor comprises an optical fiber core, a Fabry-Perot interference cavity inscribed in the fiber core, a wrapping layer wrapping the outer side of the fiber core, a coating layer wrapping the outer side of the wrapping layer, and a magnetic composite sheath wrapping the outer side of the coating layer. And the magnetostrictive composite sheath is prepared by compounding Terfenol-D / Metglas and novolac epoxy resin. The optical fiber detection sensing system comprises a laser light source, an acousto-optic modulator, an erbium-doped optical fiber amplifier, a beam splitter, a circulator, a magnetic composite sheath optical fiber sensor, a reference optical fiber sensor, a beam combiner, a detector and a data processor. The optical fiber mine magnetic detection sensor and system are widely applied to underground mineral magnetic field detection, and have the advantages of high sensitivity, high environmental adaptability, low cost and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing and mineral resource exploration, and particularly relates to an optical fiber mineral magnetic detection sensor and system based on a magnetostrictive composite sheath and FPI. Background Art

[0002] With the continuous growth of the global demand for mineral resources, traditional underground mineral detection technologies (such as electromagnetic methods and magnetic prospecting) face challenges such as low resolution, poor anti-interference ability, and bulky equipment in complex geological environments. Especially for the positioning of deep or weakly magnetic ore bodies, existing methods often suffer from a decrease in signal-to-noise ratio due to environmental noise (such as electromagnetic interference and temperature drift), which restricts the detection accuracy and efficiency. Optical fiber sensing technology provides a new idea for underground mineral detection with its advantages of high sensitivity, anti-electromagnetic interference, corrosion resistance, and the ability to achieve long-distance distributed monitoring. However, there is still room for optimization in the integration of magnetic field-sensitive materials and structural design.

[0003] When existing mineral magnetic field detection technologies face deep weak magnetic anomalies, the sensitivity of traditional magnetoresistive or Hall sensors is insufficient (usually Hall sensors with a sensitivity better than 1 μT are difficult to meet the requirements), and electronic devices are easily affected by harsh environments such as strong electromagnetic interference and high temperature and humidity in mines (for example, traditional electronic components may fail or drift severely at temperatures > 150 °C), which restricts their detection accuracy and reliability. Although superconducting quantum interference devices (SQUIDs) have extremely high sensitivity, their strict cryogenic working conditions and high costs make it difficult to promote them in mine sites. Currently, in optical fiber magnetic sensing technology, the fiber Bragg grating (FBG)-based solutions are mostly single-point measurements, which are difficult to meet the requirements for resolving the spatial magnetic field gradient of large-scale geological structures. Moreover, some magnetic-sensitive coating layers have problems such as poor long-term stability, chemical corrosion, and mechanical wear; for distributed sensing technologies based on Rayleigh or Raman scattering, although they can monitor over long distances, the magnetic field sensitivity is generally low (usually > 10 μT). Existing methods of combining a single magnetostrictive material (such as TbDyFe alloy) by winding or combining with EFPI can convert magnetic field signals, but there is still room for improvement in the coupling efficiency between the material and the optical fiber, long-term stability, and performance consistency in a wide temperature range (such as -40 to 150 °C).

[0004] Traditional solutions have technical problems that need to be solved urgently in the accurate calculation of the magnetic field direction, mode coupling effect, amplification of signals, and replacing complex resonators, as well as significantly reducing costs and simplifying the packaging process while ensuring high performance. Even for the multi-channel array system proposed by Huazhong University of Science and Technology, although the spatial resolution has been improved, it also faces problems such as complex structure, large volume, and high cost.

[0005] When the magnetostrictive material is coated on the entire optical fiber cladding, it will convert the magnetic field sensing into overall telescopic deformation along the axial direction of the optical fiber core, resulting in a low spatial resolution of the magnetic field magnetic source and being unable to calculate the magnetic field orientation. Moreover, it requires that the magnetic field direction must be parallel to the optical fiber axis, which limits its application.

[0006] Terfenol-D (terbium dysprosium iron alloy), as a magnetostrictive functional material with good performance, can generate very significant physical deformations under the excitation of an external magnetic field and becomes a key sensitive component in high-sensitivity magnetic field sensing applications. The huge magnetostrictive strain exhibited by this material is much higher than that of traditional magnetic materials, enabling it to effectively convert weak magnetic field signals into measurable stresses, providing the possibility for detecting deep, hidden or target bodies with weak magnetic signals themselves.

[0007] Metglas (iron-based amorphous alloy), as a magnetostrictive material with unique advantages, its main characteristics include good magnetostrictive response, excellent mechanical flexibility, high magnetic permeability, low coercivity, and low loss due to high resistivity.

[0008] Novolac Epoxy Resin, as an important high-performance thermosetting polymer, usually has a very high glass transition temperature (Tg), endowing it with excellent high-temperature resistance characteristics and the ability to maintain mechanical properties at high temperatures. Good dimensional stability and adhesion properties to various materials.

[0009] Therefore, there is an urgent need for a new technical solution in the existing technology to solve this problem. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide an optical fiber ore magnetic detection sensor and system based on a magnetostrictive composite sheath and FPI, which is used to solve the comprehensive deficiencies of the existing technology in terms of sensitivity, environmental tolerance, multi-dimensional information acquisition, sensing mechanism innovation, and system integration and cost-effectiveness.

[0011] The technical solution adopted by the present invention is to provide an optical fiber ore magnetic detection sensor based on a magnetostrictive composite sheath and FPI, including an optical fiber core, a reflective grating inscribed on the core, a cladding coated on the outside of the core, a coating coated on the outside of the cladding, and a magnetostrictive composite sheath coated on the outside of the coating.

[0012] The reflective grating is a Fabry-Perot interferometer.

[0013] The magnetostrictive composite sheath is prepared by compounding a magnetostrictive material and a flexible polymer.

[0014] The magnetostrictive material used is Terfenol-D / Metglas, and the flexible polymer used is phenolic epoxy resin.

[0015] Another technical solution adopted by the present invention is to provide a preparation method of an optical fiber mine magnetic detection sensor based on a magnetostrictive composite sheath and FPI, including the following steps:

[0016] Step 1: Prepare the magnetostrictive composite material;

[0017] Mix Terfenol-D particles, Metglas powder, and liquid phenolic epoxy resin evenly according to a mass ratio of 3:1:1 to form a coatable composite slurry.

[0018] Step 2: Prepare and process the optical fiber;

[0019] Select a single-mode optical fiber as the base of the sensing optical fiber. Make a Fabry-Perot interference structure at a position 8 ± 0.5 mm from the end face of the single-mode optical fiber. Make two reflective surfaces on the optical fiber to form an F-P cavity. By writing a fiber Bragg grating (FBG), the reflectivity of the grating in the cavity length of the F-P cavity will be sensitive to external strain.

[0020] Step 3: Coating process of the composite sheath material;

[0021] Coat the magnetostrictive composite material slurry prepared in Step 1 evenly on the outside of the core of the sensing optical fiber processed in Step 2. Phenolic epoxy resin is a thermosetting polymer and is cured at a temperature of 60 ± 2 °C for 12 ± 0.5 hours to crosslink the resin. The Terfenol-D and Metglas particles will be firmly fixed around the optical fiber to form a strong and stable magnetostrictive sheath layer with a thickness of 200 ± 5 μm and a uniformity error of ≤ ± 5 μm.

[0022] Another technical solution adopted by the present invention is to provide an optical fiber mine magnetic detection sensor system based on a magnetostrictive composite sheath and FPI, including the above sensor, and also including a laser light source, an acousto-optic modulator, an erbium-doped fiber amplifier, a beam splitter, a circulator, a reference fiber sensor, a combiner, a detector, and a data processor. The light emitted by the laser light source is incident on the beam splitter through a single-mode optical fiber, an acousto-optic modulator, and an erbium-doped fiber amplifier, and is split into two beams of light. One beam enters through port 1 of the circulator and exits from port 2 and enters the sensor. The other beam enters through port 1 of another circulator and exits from port 2 and enters the reference fiber sensor. Both the sensor and the reference fiber sensor adopt Fabry-Perot interferometers. The interference signals of the sensor and the reference fiber sensor respectively return to the combiner through their respective circulators. The optical signals are combined by the combiner, and finally are transmitted to the data processor of the monitoring system through the return optical fiber of the detector.

[0023] The detector is a photodiode.

[0024] Through the above design, the present invention can bring the following beneficial effects:

[0025] ‌1. Metglas is used as an auxiliary material for Terfenol-D and is combined with phenolic epoxy resin. The unique properties of Metglas are fully utilized to optimize and enhance the magnetic sensing performance with Terfenol-D as the core: The high magnetic permeability of Metglas plays a role in guiding magnetic flux and concentrating magnetic flux, more effectively guiding the external weak magnetic field to Terfenol-D, thereby improving the magnetic field response sensitivity of Terfenol-D.

[0026] 2. The excellent mechanical flexibility of Metglas can improve the mechanical properties of the entire composite sheath layer, help alleviate the brittleness problem of Terfenol-D, improve the anti-bending and processing adaptability of the sensing optical fiber, and ensure stable performance within a wide temperature range of -40~150°C.

[0027] 3. When phenolic epoxy resin is combined with Terfenol-D with giant magnetostrictive effect, the sensitive magnetic response characteristics of Terfenol-D can be effectively combined with the stability advantages of the resin, which is suitable for harsh environments such as high temperature and high humidity in mines.

[0028] 4. The integrated design of the composite material avoids the traditional complex packaging process, and the cost is greatly reduced. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of the magneto-induced sheath optical fiber of an optical fiber mine magnetic detection sensor and system based on magneto-induced composite sheath and FPI according to the present invention;

[0030] Figure 2 It is a schematic working principle diagram of an optical fiber mine magnetic detection sensor and system based on magneto-induced composite sheath and FPI according to the present invention;

[0031] Figure 3 It is a schematic optical path structure diagram of an optical fiber mine magnetic detection sensor and system based on magneto-induced composite sheath and FPI according to the present invention;

[0032] Figure 4 It is a schematic working scenario diagram of an optical fiber mine magnetic detection sensor and system based on magneto-induced composite sheath and FPI according to the present invention.

[0033] In the figure, 1 - fiber core, 2 - cladding, 3 - reflective grating, 4 - coating layer, 5 - magnetostrictive composite sheath, 6 - laser light source, 7 - single - mode fiber, 8 - acousto - optic modulator, 9 - erbium - doped fiber amplifier, 10 - beam splitter, 11 - circulator, 12 - sensor, 13 - reference fiber sensor, 14 - combiner, 15 - detector, 16 - data processor. Detailed implementation mode

[0034] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation modes:

[0035] As Figure 1 shown, the fiber - optic mineral magnetic detection sensor of the present invention based on a magnetostrictive composite sheath and FPI includes a fiber - optic core 1, a reflective grating 3 inscribed on the core 1, a cladding 2 coated outside the core 1, a coating layer 4 coated outside the cladding 2, and a magnetostrictive composite sheath 5 coated outside the coating layer 4. The core 1 and the cladding 2 are the main optical transmission channels, and the cladding 2 realizes the function of light - wave conduction through the refractive - index difference. The Bragg wavelength of the reflective grating 3 is determined by the grating period and the effective refractive index of the core.

[0036] Preferably, the magnetostrictive composite sheath 5 is prepared by compounding Terfenol - D, Metglas and phenolic epoxy resin.

[0037] A preparation method of a fiber - optic mineral magnetic detection sensor based on a magnetostrictive composite sheath and FPI:

[0038] Step 1: Prepare the magnetostrictive composite material.

[0039] Mix Terfenol - D particles, Metglas powder and liquid phenolic epoxy resin evenly according to a mass ratio of 3:1:1 to form a coatable composite slurry.

[0040] Step 2: Fiber preparation and treatment.

[0041] Select a single - mode fiber as the base of the sensing fiber, and make a Fabry - Perot interference structure at a distance of 8 ± 0.5 mm from the end face of the single - mode fiber. Make two reflective surfaces on the fiber to form an F - P cavity. By inscribing a fiber Bragg grating (FBG), the reflectivity of the grating in the cavity length of the F - P cavity will be sensitive to external strain.

[0042] Step 3: Coating process of the composite - sheath material.

[0043] The magneto-responsive composite material slurry prepared in Step 1 is evenly coated on the outer core of the sensing optical fiber after being processed in Step 2. Phenolic epoxy resin is a thermosetting polymer and is cured at a temperature of 60 ± 2°C for 12 ± 0.5 hours to crosslink the resin. The Terfenol-D and Metglas particles will be firmly fixed around the optical fiber, forming a strong and stable magneto-responsive sheath layer with a thickness of 200 ± 5 μm and a uniformity error of ≤ ±5 μm.

[0044] Principle of sensor operation:

[0045] As Figure 2 shown, when the sensor is exposed to an external magnetic field (H), the magneto-responsive composite sheath 5 that wraps the optical fiber core 1, composed of the magneto-sensitive element Terfenol-D, Metglas that aids in enhancing and improving flexibility, and phenolic epoxy resin that provides environmental stability and structural support, will respond. Terfenol-D undergoes magnetostrictive deformation due to the magnetic field. This deformation is amplified under the magnetic permeability enhancement of Metglas and is efficiently transmitted to the Bragg grating (FBG) within the optical fiber core 1 through the phenolic epoxy resin matrix.

[0046] This strain precisely transmitted by the magnetic field through the magneto-responsive composite sheath 5 will change the grating period of the FBG and the effective refractive index of the core, thereby causing a drift in the Bragg wavelength in its reflection spectrum. By accurately monitoring this wavelength drift and combining it with the calibrated magnetic response characteristics of the sensor (which benefit from the high strain coefficient of Terfenol-D, the optimized design of the sheath layer, and the performance stability ensured by phenolic epoxy resin in the range of -40 to 150°C and in the harsh mining environment), the magnetic field intensity can be calculated to achieve highly sensitive detection of mine magnetic anomalies.

[0047] As Figure 3 shown, an optical fiber mine magnetic detection sensing system based on a magneto-responsive composite sheath and FPI according to the present invention includes a laser light source 6, an acousto-optic modulator 8, an erbium-doped fiber amplifier 9, a beam splitter 10, a circulator 11, a reference fiber sensor 13, a beam combiner 14, a detector 15, and a data processor 16. The laser light source 6 generates light with specific spectral characteristics and is a broadband light source for interference demodulation. The erbium-doped fiber amplifier 9 amplifies the optical power of the light source to ensure sufficient light is injected into the FPI sensing unit and a strong enough reflected interference signal is obtained. The light emitted by the laser light source 6 enters the beam splitter 10 through a single-mode fiber 7, an acousto-optic modulator 8, and an erbium-doped fiber amplifier 9 and is split into two beams of light. One beam enters through port 1 of the circulator 11 and exits through port 2 and enters the sensor 12, and the other beam enters through port 1 of another circulator 11 and exits through port 2 and enters the reference fiber sensor 13.

[0048] The sensor 12 uses a Fabry - Perot interferometer (FPI). The cavity length of the FPI cavity or the refractive index of the medium inside the cavity will change because the magnetostrictive sheath material wrapped around it expands, contracts or deforms under the action of an external magnetic field, resulting in the drift of the FPI reflection spectrum or the change of the interference fringe phase. The reference fiber optic sensor 13 has a similar structure to the sensor 12 but is placed in an environment that is not affected by the magnetic field or has a known magnetic field response. The reference fiber optic sensor 13 is used to compensate for the influence of common - mode noises such as light source fluctuations and temperature changes on the sensor 12, thereby improving the accuracy and stability of magnetic field measurement.

[0049] The interference signals of the sensor 12 and the reference fiber optic sensor 13 respectively pass through their respective circulators 11 and return to the beam combiner 14. The optical signals are combined by the beam combiner 14 and finally transmitted to the data processor 16 of the monitoring system through the return fiber of the detector 15. Using differential measurement, the combined optical signal contains the information on the change of FPI characteristics caused by magnetic field changes and environmental factors. Due to the interference effect of the FPI, its reflected light intensity will change significantly with the tiny change of the cavity length. Through a specific FPI demodulation algorithm, the data processor 16 can analyze the cavity length change or phase change of the sensor 12 relative to the reference fiber optic sensor 13 from the interference signal. Combining the magnetostrictive coefficient of the magnetostrictive sheath material and the sensing characteristics of the FPI, the intensity information of the magnetic field to be measured is finally calculated, and distributed or quasi - distributed magnetic field measurement along the optical fiber is realized.

[0050] As Figure 4 shown, the working process of an optical fiber mine magnetic detection and sensing system based on a magnetostrictive composite sheath and FPI of the present invention: The components of the required optical sensors are integrated in the spherical housing A of the sensor. During detection, the sensing optical fiber C is led out from the device maintenance port B and inserted into the pre - drilled hole, thereby detecting the magnetic field distribution of metal minerals in the soil and determining the mining location.

[0051] Working principle: When the FPI sensing unit is exposed to an external magnetic field, the main magnetostrictive material in the magnetostrictive sheath material fusion layer undergoes magnetostrictive deformation under the combined action of the magnetic permeability enhancement of the auxiliary material and the mechanical synergy of the polymer. This deformation directly acts on the FPI cavity, causing a precise change in its optical cavity length. According to the Fabry-Perot interference principle, the change in the FPI cavity length causes the interference fringes of its reflection spectrum to shift or the phase to change, and this change amount is directly related to the external magnetic field strength. The other beam of light split by the beam splitter enters the reference optical fiber, which also constitutes a reference FPI unit for compensating common-mode noises such as light source fluctuations and temperature changes. The reflected interference light signals from the sensing FPI and the reference FPI return through their respective optical path designs and are combined in the combiner for differential measurement. The combined interference light signal is detected by a photodiode, and the light intensity or phase information is converted into an electrical signal. Finally, the data processor analyzes the change in the interference signal of the sensing FPI relative to the reference FPI using a specific FPI demodulation algorithm, and precisely resolves the change amount of the cavity length caused by the magnetic field. Combining the pre-calibrated magnetostrictive coefficient of the magnetostrictive sheath material and the sensing characteristics of the FPI, the intensity information of the magnetic field to be measured is finally calculated, thereby achieving high-sensitivity and high-precision detection of mine magnetic anomalies.

[0052] The implementation modes of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A fiber optic mine magnetic detection sensor based on a magnetostrictive composite sheath and an FPI, characterized in that: It includes an optical fiber core (1), a reflective grating (3) inscribed on the core (1), a cladding (2) coated on the outside of the core (1), a coating layer (4) coated on the outside of the cladding (2), and a magnetostrictive composite sheath (5) coated on the outside of the coating layer (4).

2. The fiber optic ore magnetic detection sensor based on the magnetostrictive composite sheath and FPI according to claim 1, characterized in that: The reflective grating (3) is a Fabry - Perot interferometer.

3. The fiber optic mine magnetic detection sensor based on the magnetostrictive composite sheath and FPI according to claim 1, wherein: The magnetostrictive composite sheath (5) is prepared by compounding a magnetostrictive material and a flexible polymer.

4. The fiber optic ore magnetic detection sensor based on the magnetostrictive composite sheath and FPI according to claim 3, characterized in that: The magnetostrictive material uses Terfenol - D / Metglas, and the flexible polymer uses phenolic epoxy resin.

5. Preparation method of an optical fiber mine magnetic detection sensor based on a magnetostrictive composite sheath and an FPI, characterized in that: It includes the following steps: Step 1: Prepare the magnetostrictive composite material; Mix Terfenol - D particles, Metglas powder, and liquid phenolic epoxy resin evenly according to a mass ratio of 3:1:1 to form a coatable composite slurry; Step 2: Fiber preparation and treatment; Select a single - mode fiber as the substrate of the sensing fiber. Make a Fabry - Perot interference structure at a position 8 ± 0.5 mm from the end face of the single - mode fiber. Make two reflective surfaces on the fiber to form an F - P cavity. By inscribing a fiber Bragg grating (FBG), the reflectivity of the grating in the cavity length of the F - P cavity will be sensitive to external strain; Step 3: Coating process of the composite sheath material; Coat the magnetostrictive composite material slurry prepared in Step 1 evenly on the outside of the core of the sensing fiber processed in Step 2. Phenolic epoxy resin is a thermosetting polymer. Cure it at a temperature of 60 ± 2 °C for 12 ± 0.5 hours to crosslink the resin. The Terfenol - D and Metglas particles will be firmly fixed around the fiber, forming a strong and stable magnetostrictive sheath layer with a thickness of 200 ± 5 μm and a uniformity error of ≤ ± 5 μm.

6. A fiber optic ore magnetic detection sensor system based on a magnetostrictive composite sheath and an FPI, comprising the sensor (12) according to any one of claims 1-4, further comprising a laser light source (6), an acousto-optic modulator (8), an erbium-doped fiber amplifier (9), a beam splitter (10), a circulator (11), a reference fiber optic sensor (13), a beam combiner (14), a detector (15), and a data processor (16), characterized in that: The light emitted by the laser light source (6) passes through the single - mode fiber (7), the acousto - optic modulator (8), and the erbium - doped fiber amplifier (9) and is incident on the beam splitter (10), where it is split into two beams of light. One beam enters through port 1 of the circulator (11) and exits from port 2 and enters the sensor (12). The other beam enters through port 1 of another circulator (11) and exits from port 2 and enters the reference fiber sensor (13). Both the sensor (12) and the reference fiber sensor (13) use Fabry - Perot interferometers. The interference signals of the sensor (12) and the reference fiber sensor (13) respectively return to the beam combiner (14) through their respective circulators (11). The optical signals are combined by the beam combiner (14), and finally, they are transmitted to the data processor (16) of the monitoring system through the return fiber of the detector (15).

7. The fiber optic mine magnetic detection sensor system based on the magnetostrictive composite sheath and FPI according to claim 6, characterized in that: The detector (15) is a photodiode.

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