A Magnetic Field Testing Method for MNF Coated with Fe-MoS2

Abstract

The present invention provides a method for testing the MNF magnetic field based on Fe-MoS₂ coating. The present invention adopts the evanescent field enhanced Mach-Zehnder principle, and senses through Fe-MoS₂ two-dimensional nanomaterials coated on MNF. The light output by the broadband light source interferes in the sensing unit. When the magnetic field changes, the refractive index of the Fe-MoS₂ two-dimensional nanomaterials changes, resulting in an optical path difference and thus generating interference. The least squares method is used to fit the wave valleys, and the average sensitivity is defined and obtained by the microprocessor to achieve real-time monitoring of the magnetic field. The present invention aims at magnetic field detection and effectively solves the problems of hysteresis, flammability, large volume, and difficult operation of traditional magnetic field sensors. As a two-dimensional material, Fe-MoS₂ has good optical properties and is a direct bandgap material. Therefore, Fe-MoS₂ can be used as a magnetic sensitive material to detect the magnetic field in combination with optical fibers and can achieve real-time detection of the magnetic field.

Description

Technical Field

[0001] This invention patent relates to a method for testing the MNF magnetic field coated with Fe-MoS2, belonging to the field of fiber optic sensing technology. Background Art

[0002] Magnetic field is one of the most common physical quantities and is increasingly widely used in fields such as biology, medicine, and education. Especially in the field of underwater magnetic detection, it can make up for the errors caused by underwater noise in traditional sonar detection.

[0003] Most traditional magnetic field detection methods mainly rely on detecting electrical signals. However, the devices carrying electrical signals are mostly made of metal materials, and such devices themselves will cause certain changes in the magnetic field, resulting in large errors. In addition, there is oil in some large magnetic field environments, especially in current transformers themselves. Detection mainly based on electrical signals leads to risks such as flammability and explosiveness in the magnetic field environment; moreover, there are also demagnetization and hysteresis phenomena, which greatly affect the measurement results and cause large errors.

[0004] Compared with traditional electronic sensors, fiber optic sensors have high signal-to-noise ratio, can be remotely monitored, are not affected by electromagnetic interference, have high sensitivity, and have high flexibility in use. At present, many fiber optic sensors related to temperature, stress, magnetic field, etc. have been developed. Fiber optic sensors for magnetic field detection mostly use magnetostriction and magnetic fluid as sensitive materials, and have the defect of weak detection ability for weak magnetic fields. Although the MoS2 material itself has weak magnetism, doping with transition metals will increase its magnetism. And Fe-MoS2 is a two-dimensional material with good optical properties, being a direct bandgap material, having good thermal conductivity, extremely strong anti-wear performance, and strong modifiability. Therefore, it can be used as a magnetic sensitive material to detect the magnetic field in combination with optical fibers, and the existence of the evanescent field can effectively improve the detection sensitivity.

[0005] Tao Yu et al. (Tao Yu. Design and Application of Fiber Optic Magnetic Field Sensor Based on Magnetic Materials [D]. Chongqing University of Technology, 2021.) proposed a design and application of a fiber optic magnetic field sensor based on magnetic materials. However, the method selected magnetic fluid as the sensitive material and filled the magnetic fluid into the hollow fiber. Since the core diameter of the hollow fiber is in the micron range, there are great difficulties in the preparation of filling the magnetic fluid, and the same traditional magnetic sensitive materials and traditional wavelength drift determination methods are used; Jia Lingyan et al. (Jia Lingyan. Research on Novel Fiber Optic Magnetic Field Sensor [D]. Hebei University of Technology, 2022.) proposed a novel fiber optic magnetic field sensor, but the same traditional magnetic fluid and magnetostrictive materials are used, which is just a continuation of the tradition. And the novel two-dimensional magnetic material used in this method can replace the traditional magnetic sensitive materials, and there are essential differences in the determination of wavelength drift; Peng J et al. (Peng J, Zhang S, Jia S, et al. A highly sensitive magnetic field sensor based on FBG and magnetostrictive composite with oriented magnetic domains [J]. Measurement, 2022, 189: 110667.) proposed a highly sensitive magnetic field sensor based on FBG and magnetostrictive composite with oriented magnetic domains. This research uses traditional magnetostrictive composite for coating, and the sensitivity determination method is the intensity change at a certain point. Therefore, this research is essentially different from it; Luo Y et al. (Luo Y, Lei X, Shi F, et al. A novel optical fiber magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid [J]. Optik, 2018.) A novel fiber optic magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid.

[0006] All the above-mentioned studies currently use traditional magnetic sensitive materials for coating, and still judge the sensitivity by the drift at a certain point. Therefore, there are essential differences from this method. Summary of the Invention

[0007] In view of the above problems, the present invention proposes an MNF magnetic field testing method based on Fe-MoS2 coating, which solves the problems that the current magnetic field detection is vulnerable to environmental influence and it is difficult to achieve weak magnetic field detection, and realizes the detection of the magnetic field.

[0008] A method for testing the magnetic field of MNF coated with Fe-MoS2, characterized in that it includes a broadband light source (1), a magnetic field testing device (2), a photoelectric conversion module (3), an ADC module (4), a microprocessor (5), and a computer (6);

[0009] The central wavelength of the broadband light source (1) is 1550 nm, which is used to generate an optical signal;

[0010] The magnetic field testing device (2) includes a rotating magnetic seat (2-1), an N-level magnet (2-2), an S-level magnet (2-3), a magnetic seat power supply device (2-4), and a sensing unit (2-5), where:

[0011] The N-level magnet (2-2) and the S-level magnet (2-3) are respectively placed at both ends of the rotating magnetic seat (2-1), and the magnetic force of the N-level magnet (2-2) and the S-level magnet (2-3) can be adjusted through the magnetic seat power supply device (2-4). In addition, the sensing unit (2-5) is placed on the rotating magnetic seat (2-1);

[0012] The sensing unit (2-5) is composed of a single-mode optical fiber 1 (2-5-1), an MNF (2-5-2), and a single-mode optical fiber 2 (2-5-4) fused to form a Mach-Zehnder structure. In addition, the Fe-MoS2 nanomaterial (2-5-3) is coated on the waist cone center of the MNF (2-5-2);

[0013] The specific preparation process of the sensing unit (2-5) includes the production and dimension of the Mach-Zehnder structure, and the production and coating of the Fe-MoS2 nanomaterial (2-5-3), where:

[0014] The length of the single-mode optical fiber 1 (2-5-1) is 10 cm, the core diameter is 9 μm, the MNF (2-5-2) is a multi-mode optical fiber taper, the core diameter is 62.5 μm, the length is 3 cm, the transition zone (2-5-2-1) length is 1.1 cm, the waist cone (2-5-2-2) length is 0.9 cm, and the waist cone diameter is 20 μm. First, use a hydrogen-oxygen flame taper machine to taper the central part of the multi-mode optical fiber until the length is 9 mm. Secondly, one end of the MNF (2-5-2) and the single-mode optical fiber 1 (2-5-1) are fused by a fusion splicer until the loss is 0. Finally, the other end of the MNF (2-5-2) and the single-mode optical fiber 2 (2-5-4) are fused by a fusion splicer until the loss is 0;

[0015] The preparation of the Fe-MoS2 nanomaterial (2-5-3) selects the hydrothermal method. First, measure 60 mL of deionized water and add it to a beaker, and measure 0.425 g of (NH4)6Mo7O 24Add 4H2O to a beaker, measure 2.5 g of CN2H4S and add it to the beaker, measure 0.01 g of Fe(NO3)3·9H2O and add it to the beaker; place the beaker on a magnetic stirrer and stir for 60 min to disperse it evenly. Then, after stirring, pour the dispersion into a reaction kettle, place the reaction kettle in a drying oven, heat it at 120 °C for 12 h, remove the clear liquid on the surface and wash it with alcohol. Put the washed suspension into a centrifuge and centrifuge it at 6000 rmp / min for 20 min. After washing again, centrifuge it at 6000 rmp / min for 20 min to obtain a Fe-MoS2 suspension;

[0016] The Fe-MoS2 nanomaterial (2-5-3) is coated on the center of the waist cone of MNF (2-5-2) by the drop-casting method. First, use a pipette to suck the prepared Fe-MoS2 nanomaterial (2-5-3) suspension and drop it on the center of the waist cone of MNF (2-5-2). After the alcohol evaporates, the Fe-MoS2 nanomaterial (2-5-3) is evenly coated on the center of the waist cone of MNF (2-5-2);

[0017] The light beam emitted by the broadband light source (1) is transmitted to the magnetic field testing device (2). The refractive index of the Fe-MoS2 nanomaterial (2-5-3) on the waist cone of MNF (2-5-2) changes with the change of the magnetic field. When the emitted light is transmitted to MNF (2-5-2) by the single-mode optical fiber 1 (2-5-1), a part of it continues to be transmitted in the core of MNF (2-5-2), while the light that penetrates into the cladding causes the optical path to change due to the reaction of the Fe-MoS2 nanomaterial (2-5-3) to the magnetic field. When it is transmitted to the single-mode optical fiber 2 (2-5-4), the light in the cladding and the core interferes. With the change of the magnetic field, the spectrum in the sensing unit (2-1) drifts. The optical signal is converted into an electrical signal by the photoelectric conversion module (3) and transmitted to the ADC module (4) to convert the continuous analog signal into a discrete digital signal and perform data acquisition. The collected data is processed by the microprocessor (5);

[0018] Step 1: Perform positioning and fitting processing on the sensing trough in the range of 1540 - 1550 nm:

[0019] The fiber optic spectrum is represented by a Gaussian function, and the trough position is determined by fitting and positioning, that is

[0020]

[0021] Take the logarithm of both sides:

[0022]

[0023] Let lnI(λ) = y, Substitute a, b, and c into formula (2) to obtain

[0024] y = aλ 2 + bλ + c (3)

[0025]

[0026] Where I(λ) represents the light intensity corresponding to different wavelengths, λ dip represents the wavelength value corresponding to the wave trough, Δλ represents the wavelength change amount, A represents a constant. Substituting the collected wavelength data into formulas (3) and (4) can obtain the central wavelength value corresponding to the wave trough. Formula (3) is in the form of quadratic polynomial fitting. Therefore, the least squares method is used to fit the data;

[0027] Step 2: Change the magnetic field intensity and scan the wavelengths corresponding to different magnetic field intensities. When the magnetic field intensity increases, the sensing wave trough drifts towards the long-wavelength direction, and the microprocessor collects the changing wavelengths;

[0028] Step 3: Take points from the collected drift wavelength group. I dip represents the spectral intensity value corresponding to the wave trough. Taking 5 intersection points centered on I dip ±0.5n, where n = 0, 1, 2 for marking. A total of 5 groups are taken, denoted as L1, L2, L3, L4, L5. Each group corresponds to a wavelength sensitivity. Due to the wavelength fitting error at each point and the spectral deformation at each part, the average sensitivity is defined to represent the response of the sensor to the magnetic field change;

[0029] Step 4: Define the average sensitivity formula as:

[0030]

[0031] Where λ1, λ2, λ3, λ4, λ5 are the wavelengths at the 5 groups of L1, L2, L3, L4, L5 respectively, s1, s2, s3, s4, s5 are the wavelength sensitivities of the 5 groups of L1, L2, L3, L4, L5 respectively, I1, I2, I3, I4, I5 are different magnetic field intensities, and b1, b2, b3, b4, b5 are the wavelengths corresponding to the 5 groups of L1, L2, L3, L4, L5 when the magnetic field intensity is 0, This is the average sensitivity of the sensor. After the microprocessor processes the collected data, the final average sensitivity is obtained The final average sensitivity is displayed by the computer

[0032] The beneficial effects of the present invention are:

[0033] 1. Compared with the invention patent "A Method and Device for MNF Magnetic Field Testing Based on NSiV Double Color Centers" applied by the same inventor on the same day, although both methods are applicable to magnetic field detection, the method mentioned in "A Method and Device for MNF Magnetic Field Testing Based on NSiV Double Color Centers" focuses on the detection of weak magnetic fields, belonging to the nT magnitude, and uses excited fluorescence to change the optical path difference. This method focuses on the detection of relatively weak magnetic fields, belonging to the mT magnitude, and uses the evanescent field principle to change the optical path difference. Therefore, the application environments of the two methods are different, and the sensing principles are also different.

[0034] 2. Compared with the invention patent "A Method and Device for Testing Dual Parameters of Magnetic Field and Temperature of NSiV Double Color Centers" applied by the same inventor on the same day, although both methods can detect magnetic fields, the method mentioned in "A Method and Device for Testing Dual Parameters of Magnetic Field and Temperature of NSiV Double Color Centers" focuses on the magnetic field detection under the influence of temperature. This method focuses on the magnetic field detection in a single environment.

[0035] 3. Compared with the invention patent "A Method and Device for Dual Parameter Testing of Magnetic Field and Stress Coated with MoSFe" applied by the same inventor on the same day, although both methods can detect magnetic fields and both use MoSFe as the magnetosensitive material. However, the method mentioned in "A Method and Device for Dual Parameter Testing of Magnetic Field and Stress Coated with MoSFe" focuses on the magnetic field detection under the influence of stress, such as in strong wind weather. This method focuses on the magnetic field detection in a single environment.

[0036] 4. Compared with the invention patent "SPR-Based D-Type Photonic Crystal Fiber Magnetic Field Sensitive Sensing Device and Method" applied by the same inventor on November 19, 2020, although both methods can detect magnetic fields, the method mentioned in "SPR-Based D-Type Photonic Crystal Fiber Magnetic Field Sensitive Sensing Device and Method" focuses on the SPR principle. This method focuses on the Mach-Zehnder principle, with the evanescent field added to improve the sensitivity, and this method uses the average sensitivity for determination. Therefore, there are essential differences in the determination methods of the two methods. Description of the Drawings

[0037] For ease of explanation, the present invention will be described in detail by the following specific embodiments and drawings.

[0038] Figure 1 It is a flowchart of a method for MNF magnetic field testing based on Fe-MoS2 coating;

[0039] Figure 2 It is a diagram of a testing device for a method for MNF magnetic field testing based on Fe-MoS2 coating;

[0040] Figure 3Structural diagram of a sensing unit for a Fe-MoS2 coated MNF magnetic field testing method

[0041] Figure 4 Interference spectrum of a Fe-MoS2 coated MNF magnetic field testing method Detailed implementation mode

[0042] To make the objectives, technical solutions, and advantages of this invention patent clearer, the following describes this invention patent through specific implementation examples shown in the attached drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of this invention patent. In addition, in the following description, the description of some well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts of this invention patent.

[0043] Implementation examples are as Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 shown. The following technical solutions are adopted in this detailed implementation mode: A Fe-MoS2 coated MNF magnetic field testing method, and the specific implementation process of the method is as follows:

[0044] As Figure 1 shown, this invention adopts a direct-through optical path diagram, which is sequentially connected to a broadband light source (1), a magnetic field testing device (2), a photoelectric conversion module (3), an ADC module (4), a microprocessor (5), and a computer (6);

[0045] As Figure 2 shown, the light emitted by the broadband light source (1) is transmitted to the sensing unit (2-5), where Mach-Zehnder interference occurs. By adjusting the magnitude of the magnetic base power supply device (2-4), the magnitude of the magnetic field generated by the N-pole magnet (2-2) and the S-pole magnet (2-3) is changed. The change in the magnetic field causes a drift in the interference spectrum transmitted by the sensing unit (2-5);

[0046] As Figure 3As shown, the evanescent field is used to enhance the Mach-Zehnder effect of the sensing unit (2-5), thereby improving the sensitivity of magnetic field testing. Specifically, when the light beam emitted by the broadband light source (1) is transmitted from the single-mode optical fiber 1 (2-5-1) to the MNF (2-5-2), part of the light is transmitted in the cladding, and the other part of the light is directly transmitted in the core. When the light transmitted in the cladding reaches the waist cone (2-5-2-2), the optical path of the light transmitted in the cladding changes due to the magnetic field sensitivity of the Fe-MoS2 nanomaterial (2-5-3), and the evanescent field will cause a greater optical path difference between the light in the cladding and the core. When the light transmitted in the cladding and the light transmitted in the core reach the single-mode optical fiber 2 (2-5-4), they will be recoupled into the core, and at this time, the Mach-Zehnder interference phenomenon occurs. When the magnetic field changes, the interference spectrum drifts.

[0047] As Figure 4 shown, it is the interference spectrum. When the magnetic field changes, the interference spectrum drifts. Since the peaks of each interference spectrum converge at a point, the drift degrees of the troughs are different, and there are errors during fitting. Therefore, taking I dip ±0.5n, where n = 0, 1, 2 as the center, 5 intersection points are marked horizontally, a total of 5 groups are taken, and the average sensitivity is used to define the response of the sensor to the magnetic field change. Therefore, this invention patent proposes a new sensitivity determination method, namely the average sensitivity. According to formulas (5) and (6), the average sensitivity of the magnetic field sensor can be calculated.

Claims

1. A magnetic field testing method for MNF coated with Fe-MoS2, characterized in that: It includes a broadband light source (1), a magnetic field testing device (2), a photoelectric conversion module (3), an ADC module (4), a microprocessor (5), and a computer (6); The center wavelength of the broadband light source (1) is 1550 nm, which is used to generate optical signals; The magnetic field testing device (2) includes a rotating magnetic seat (2-1), an N-level magnet (2-2), an S-level magnet (2-3), a magnetic seat power supply device (2-4), and a sensing unit (2-5), where: The N-level magnet (2-2) and the S-level magnet (2-3) are respectively placed at both ends of the rotating magnetic seat (2-1). The magnetic force of the N-level magnet (2-2) and the S-level magnet (2-3) can be adjusted through the magnetic seat power supply device (2-4). In addition, the sensing unit (2-5) is placed on the rotating magnetic seat (2-1); The sensing unit (2-5) is composed of a single-mode optical fiber 1 (2-5-1), an MNF (2-5-2), and a single-mode optical fiber 2 (2-5-4) fused to form a Mach-Zehnder structure. In addition, the Fe-MoS2 nanomaterial (2-5-3) is coated on the waist cone center of the MNF (2-5-2); The specific preparation process of the sensing unit (2-5) includes the fabrication and dimensions of the Mach-Zehnder structure, and the fabrication and coating of the Fe-MoS2 nanomaterial (2-5-3), where: The length of the single-mode optical fiber 1 (2-5-1) is 10 cm, and the core diameter is 9 μm. The MNF (2-5-2) is a tapered multimode optical fiber with a core diameter of 62.5 μm and a length of 3 cm. The length of the transition region (2-5-2-1) is 1.1 cm, and the length of the waist cone (2-5-2-2) is 0.9 cm, and the waist cone diameter is 20 μm. First, use a hydrogen-oxygen flame taper machine to taper the central part of the multimode optical fiber until the length is 9 mm. Secondly, one end of the MNF (2-5-2), the single-mode optical fiber 1 (2-5-1), is fused using a fusion splicer until the loss is 0. Finally, use a fusion splicer to fuse the other end of the MNF (2-5-2) with the single-mode optical fiber 2 (2-5-4) until the loss is 0; The hydrothermal method is selected for the preparation of the Fe-MoS2 nanomaterial (2-5-3). First, 60 mL of deionized water is measured and added to a beaker. 0.425 g of (NH4)6Mo7O 24 ·4H2O is measured and added to the beaker. 2.5 g of CN2H4S is measured and added to the beaker. 0.01 g of Fe(NO3)3·9H2O is measured and added to the beaker. The beaker is placed on a magnetic stirrer and stirred for 60 min to make it evenly dispersed. Secondly, after the stirring is completed, the dispersion is poured into a reaction kettle. The reaction kettle is placed in an oven and heated at 120 °C for 12 h. After removing the clear liquid on the surface, it is washed with alcohol. The washed suspension is put into a centrifuge and centrifuged at 6000 rmp / min for 20 min. After washing again, it is centrifuged at 6000 rmp / min for 20 min to obtain the Fe-MoS2 suspension; The Fe-MoS2 nanomaterial (2-5-3) is coated on the waist cone center of the MNF (2-5-2) by the drop coating method. First, use a pipette to suck the prepared Fe-MoS2 nanomaterial (2-5-3) suspension and drop it on the waist cone center of the MNF (2-5-2). After the alcohol volatilizes, the Fe-MoS2 nanomaterial (2-5-3) is evenly coated on the waist cone center of the MNF (2-5-2); The light beam emitted by the broadband light source (1) is transmitted to the magnetic field testing device (2). The refractive index of the Fe-MoS2 nanomaterial (2-5-3) on the waist cone of the MNF (2-5-2) changes with the change of the magnetic field. When the emitted light is transmitted from the single-mode fiber 1 (2-5-1) to the MNF (2-5-2), a part of it continues to be transmitted in the core of the MNF (2-5-2), while the light penetrating into the cladding causes the optical path to change due to the reaction of the Fe-MoS2 nanomaterial (2-5-3) to the magnetic field. When it is transmitted to the single-mode fiber 2 (2-5-4), the light in the cladding and the core interferes. With the change of the magnetic field, the spectrum in the sensing unit (2-5) drifts. The optical signal is converted into an electrical signal by the optoelectronic conversion module (3), and is transmitted to the ADC module (4) to convert the continuous analog signal into a discrete digital signal and perform data acquisition. The collected data is processed by the microprocessor (5); Step 1: Perform positioning and fitting processing on the sensing trough in the range of 1540 - 1550 nm: The fiber optic spectrum is represented by a Gaussian function, and the trough position is determined through fitting and positioning, that is Take the logarithm on both sides: Let Substituting a, b, and c into formula (2) gives y = aλ 2 + bλ + c (3) where I(λ) represents the light intensity corresponding to different wavelengths, and λ dip represents the wavelength value corresponding to the wave trough, Δλ represents the wavelength change, A represents a constant. Substituting the collected wavelength data into formulas (3) and (4), the central wavelength value corresponding to the wave trough can be obtained. Formula (3) is in the form of quadratic polynomial fitting, so the least squares method is adopted to fit the data; Step 2: Change the magnetic field intensity and scan the wavelengths corresponding to different magnetic field intensities. When the magnetic field intensity increases, the sensing trough drifts towards the long-wavelength direction, and the microprocessor collects the changing wavelengths; Step 3: Take points from the collected drift wavelength group, I dip represents the spectral intensity value corresponding to the wave trough. Taking 5 intersection points horizontally with I dip ±0.5n, where n = 0, 1, 2 as the center and mark them. A total of 5 groups are taken, denoted as L1, L2, L3, L4, L5. Each group corresponds to a wavelength sensitivity. Due to the wavelength fitting error at each point and the deformation of the spectrum everywhere, the average sensitivity is adopted to define the response of the sensor to the magnetic field change; Step 4: Define the average sensitivity formula as: Where λ1, λ2, λ3, λ4, and λ5 are the wavelengths at the five groups of L1, L2, L3, L4, and L5 respectively, s1, s2, s3, s4, and s5 are the wavelength sensitivities of the five groups of L1, L2, L3, L4, and L5 respectively, I1, I2, I3, I4, and I5 are different magnetic field intensities, and b1, b2, b3, b4, and b5 are the wavelengths corresponding to the five groups of L1, L2, L3, L4, and L5 when the magnetic field intensity is 0. This is the average sensitivity of the sensor, and the microprocessor processes the collected data to obtain the final average sensitivity. The computer displays the final average sensitivity.

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