Device for measuring magnetic field

Abstract

The utility model relates to a device for measuring a magnetic field, which comprises a light source module, a light splitting module, a three-path optical fiber transmission assembly and a calculation processing module which are connected with one another, and is characterized in that the light source module provides laser beams for the light splitting module; the light splitting module splits the laser beams and irradiates the laser beams to three paths of optical fiber transmission assemblies respectively; the structures of the three optical fiber transmission assemblies are the same, and the magnetic field sensing module in each optical fiber transmission assembly deforms under the action of an external magnetic field and obtains an interference image through processing; and the calculation processing module processes the interference image to obtain a magnetic field value in the magnetic field sensing module. According to the device, the magnetic field is measured based on optical sensing measurement of the Bragg grating and the magnetostrictive material, the influence of electrical noise on magnetic field measurement can be effectively reduced, the cost of the device is relatively low, and the size and direction of the magnetic field can be conveniently measured.

Description

Technical Field

[0001] This utility model belongs to the field of magnetic field detection technology, specifically relating to a device for measuring magnetic fields. Background Technology

[0002] Existing technologies for measuring magnetic fields mainly include the following methods: Electrical measurement methods, which are based on Faraday's law of electromagnetic induction, the Hall effect, etc., utilizing electromagnetic interactions or magnetosensitive electrical materials to convert magnetic field strength into electrical quantities. The magnitude of the magnetic field is determined by measuring changes in voltage or current in the circuit. Commonly used methods include the electromagnetic induction coil method, the Hall effect method, the fluxgate method, and the magnetoresistive effect method. Optical measurement methods rely primarily on the interaction between light and magnetic fields. Especially under certain materials and phenomena, the magnetic field significantly affects the propagation characteristics of light. Changes in optical quantities are obtained through optical observation, thereby determining the magnitude of the magnetic field. Common optical measurement methods include the magneto-optical effect (Faraday effect) and laser scanning microscopy (LSM).

[0003] Microscopic measurement methods are sophisticated techniques and approaches used to detect the distribution and intensity of magnetic fields at microscales (such as nanoscale, atomic scale, or surface scale). Microscopic magnetic field measurements typically require in-depth research into the magnetic behavior of magnetic materials, micro-magnetic source systems, and nanostructures. However, these methods suffer from several drawbacks: significant environmental noise impacts measurement methods, particularly electrical noise, which can drastically affect circuit stability and lead to substantial errors; optical methods often require high-precision instruments such as spectrometers and lens combinations, which are often expensive and bulky, severely limiting the scope of convenient and rapid detection. Utility Model Content

[0004] In order to overcome the above-mentioned problems in the prior art, the present invention provides a device for measuring magnetic fields, which is used to solve the above-mentioned problems in the prior art.

[0005] A device for measuring magnetic fields, the device comprising a light source module, a beam splitting module, a three-way fiber optic transmission assembly, and a computing processing module connected to each other, wherein the light source module provides a laser beam to the beam splitting module;

[0006] The beam splitting module splits the laser beam and directs it onto the three fiber optic transmission components respectively;

[0007] The three optical fiber transmission components have the same structure, and the magnetic field sensing module in each optical fiber transmission component deforms under the action of an external magnetic field and is processed to obtain an interference image.

[0008] The calculation and processing module processes the interference image to obtain the magnetic field value in the magnetic field sensing module.

[0009] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the light source module is a 50mW laser in the visible light band.

[0010] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the beam splitting module is composed of two beam splitters with a beam splitting ratio of 1:1 arranged at a certain angle.

[0011] In addition to the aspects and any possible implementations described above, a further implementation is provided in which each optical fiber transmission component further includes a lens, an optical fiber, a collimating lens, an interferometer, and an image acquisition module connected in sequence, wherein the magnetic field sensing module is fixed on the optical fiber, the lens focuses the received split beam and transmits it in sequence through the optical fiber to the magnetic field sensor module, the collimating lens, and the interferometer, and the image acquisition module captures the image formed by the interferometer and transmits the captured image to the computing processing module.

[0012] In addition to the aspects described above and any possible implementations, a further implementation is provided in which each optical fiber transmission assembly further includes an optical fiber adjustment frame, one end of the optical fiber being connected to the optical fiber adjustment frame and the other end being connected to the collimating lens.

[0013] In addition to the aspects described above and any possible implementation, a further implementation is provided in which the magnetic field sensing module includes a Bragg grating and a magnetostrictive material, the Bragg grating being etched onto the optical fiber at a location, and the magnetostrictive material being fixed to the two side regions of the Bragg grating.

[0014] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the magnetostrictive material is a terbium-dysprosium-iron alloy.

[0015] In addition to the aspects and any possible implementations described above, a further implementation is provided in which each of the magnetic field sensing modules is fixed on a fixed bracket along the x, y, z directions according to the grating axis to form a three-dimensional probe module, wherein the x, y, z directions conform to the right-hand rule.

[0016] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the angle is 90°.

[0017] In addition to the aspects described above and any possible implementations, a further implementation is provided in which the interferometer is a Fabry-Perot etalon.

[0018] Beneficial effects of this utility model

[0019] This invention discloses a magnetic field measuring device, comprising a light source module, a beam splitting module, a three-way fiber optic transmission assembly, and a computing processing module connected to each other. The light source module provides a laser beam to the beam splitting module; the beam splitting module splits the laser beam and illuminates each of the three fiber optic transmission assemblies separately; the three fiber optic transmission assemblies have identical structures, and the magnetic field sensing module in each fiber optic transmission assembly deforms under the influence of an external magnetic field, and the deformation is processed to obtain an interference image; the computing processing module processes the interference image to obtain the magnetic field value in the magnetic field sensing module. It has the following advantages:

[0020] (1) The device of this utility model is based on optical fiber path. The main physical quantity measured is the wavelength of the optical fiber output end that reflects the external magnetic field. It is less susceptible to electrical interference and can effectively improve the measurement accuracy in strong interference environment. It can also reduce the impact of environmental noise on measurement.

[0021] (2) The device in this utility model includes a laser, a Bragg grating, a terbium-dysprosium-iron alloy (magnetostrictive material) and a Fabry-Perot etalon, etc. Compared with large instruments such as spectrometers, it has a lower cost, is easy to integrate, has a smaller size, and is convenient to use, thereby reducing the cost of magnetic field detection equipment.

[0022] (3) By combining the sensing parts in three dimensions and designing the three-dimensional probe module, this utility model can realize the measurement of the magnetic field direction of the external magnetic field in three-dimensional space. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the device structure of this utility model;

[0024] Figure 2 This is a schematic diagram of the magnetic field sensing module structure of this utility model;

[0025] Figure 3 This is a schematic diagram of the three-dimensional probe module structure of this utility model;

[0026] Figure 4 Interference fringe pattern formed by the device of this utility model;

[0027] Figure 5 This is a modular schematic diagram of the device of this utility model;

[0028] Figure 6 This is a schematic diagram of the Bragg grating spectrum. Detailed Implementation

[0029] To better understand the technical solution of this utility model, the content of this utility model includes, but is not limited to, the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of this utility model. To make the technical problem to be solved, the technical solution, and the advantages of this utility model clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0030] It should be understood that the embodiments described in this utility model are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0031] The terminology used in the embodiments of this utility model is for the purpose of describing particular embodiments only and is not intended to be limiting of the utility model. The singular forms “a,” “the,” and “the” used in the embodiments of this utility model and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0032] This invention provides a device for measuring magnetic fields. The device includes a light source module, a beam splitting module, a three-way fiber optic transmission assembly, and a computing processing module connected to each other. The light source module provides a laser beam to the beam splitting module.

[0033] The beam splitting module splits the laser beam and directs it onto the three fiber optic transmission components respectively;

[0034] The three optical fiber transmission components have the same structure, and the magnetic field sensing module in each optical fiber transmission component deforms under the action of an external magnetic field and is processed to obtain an interference image.

[0035] The calculation and processing module processes the interference image to obtain the magnetic field value in the magnetic field sensing module.

[0036] like Figures 1-5 As shown, the light source module uses a laser light source, specifically a 50mW visible light laser. Excessive laser power, such as 200mW, poses a risk of burning out the components; this power level ensures good experimental results while maintaining safety.

[0037] The beam splitting module is implemented using a combination beam splitter 3, which consists of two beam splitters with a beam splitting ratio of 1:1 placed at a certain angle, such as 90°, to split a laser beam into three beams.

[0038] The three fiber optic transmission components have the same structure. In addition to the magnetic field sensing module, each fiber optic transmission component also includes a lens 2, an optical fiber 5, a collimating lens 7, an interferometer, and an image acquisition module connected in sequence. The interferometer is implemented using a Fabry-Perot etalon 8, which is used to perform multi-beam interference on the three sets of outgoing light to form three sets of interference fringes. The image acquisition module is implemented using a camera or other imaging equipment, which consists of a high-resolution CCD or CMOS element and a lens group, and is used to acquire the interference fringe image formed by the Fabry-Perot etalon 8.

[0039] The magnetic field sensing module is fixed on the optical fiber 5. The lens 2 focuses the received split beam and transmits it sequentially to the magnetic field sensing module, the collimating lens 7, and the Fabry-Perot etalon 8 through the optical fiber 5. The image acquisition module captures the image formed by the Fabry-Perot etalon 8 and transmits the captured image to the computing and processing module. The computing and processing module is implemented using an existing computer or other computing device, and the calculation method or program is implemented using an existing algorithm or program. This utility model does not impose any limitations.

[0040] Each optical fiber transmission component also includes an optical fiber adjustment frame 4, one end of the optical fiber 5 is connected to the optical fiber adjustment frame 4, and the other end is connected to the collimating lens 7.

[0041] The magnetic field sensing module includes a Bragg grating 10 and a magnetostrictive material 11. The Bragg grating 10 is etched onto the optical fiber 5 at the location of the magnetostrictive material 11. The period of the grating 10 is a multiple of the center wavelength of the laser 1, thus allowing interference to occur and enabling the device to detect the corresponding signal. The magnetostrictive material 11 is fixed to the two side regions of the Bragg grating 10 using an adhesive 12 or similar fixation. The etched area between the two side regions of the Bragg grating 10 is not fixed to the magnetostrictive material 11. The deformation of the Bragg grating 10 is caused by the deformation of the magnetostrictive material portion between its fixing point and the magnetostrictive material 11. Since the two ends of the Bragg grating 10 and the magnetostrictive material 11 are bonded together, if the magnetostrictive material 11 elongates, the grating 10 elongates along with it. If the etched area of ​​the Bragg grating 10 is also fixed to the magnetostrictive material 11, the deformation of the Bragg grating 10 will be greatly inhibited by the glue adhering to the magnetostrictive material 11, since the glue itself does not have good deformation characteristics, thus leading to a decrease in the effect. Therefore, this invention only fixes the two sides of the etched area of ​​the Bragg grating 10, which can ensure that the deformation of the magnetostrictive material 11 is not affected by the glue.

[0042] The magnetostrictive material 11 is a terbium-dysprosium-iron alloy. In this invention, the magnetic strain direction of the magnetostrictive material 11 can be the same as or different from the grating axis of the Bragg grating 10; the relationship between the two is not limited. When the magnetic strain direction is the same as the Bragg grating axis, the direction of the force generated by the strain is kept consistent with the grating axis, so that the deformation generated by the strain is transmitted to the grating with maximum efficiency, causing deformation of the grating axis, thereby changing the grating period.

[0043] Preferably, the device of this utility model integrates three magnetic field sensing modules to form a three-dimensional probe module 13. The three-dimensional probe consists of the sensing modules distributed along the x, y, and z directions and the fixed bracket. The fixed bracket is not connected to other devices. Specifically, a solid support is set up, and three sets of sensing modules are placed on the solid support along the x, y, and z directions according to the grating axis. During placement, the material is not directly connected to the solid support. The fiber segment with the grating and the extensible material are connected together in the above manner to form a sensing module. The direction of the sensing module is pointing to the axis of the Bragg grating 10, which is also the magnetic strain direction of the magnetostrictive material 11. The x, y, and z directions are mutually perpendicular, satisfying the right-hand rule. The three sets of sensing modules connected to the optical fiber are placed on the solid support according to the above x, y, and z directions. The placement method involves designing a groove on the solid support that is slightly larger than the outline of the sensing module and has the same shape as its outline. After the sensing module is placed in the groove, a cover plate is fixed on the top of the groove, so that the sensing module is placed in a fully enclosed cavity. The cavity has a small hole to allow the optical fiber connected to the sensing module to pass through, leaving a certain space margin of 1-2 mm to allow for material deformation. For example, if the sensor module size is 2mm*10mm*4mm, then the cavity size is 3mm*11mm*5mm. Because the magnetostrictive material 11 will deform under the action of a magnetic field, if the cavity size is exactly the same as the sensor module size, the magnetostrictive material will be compressed during the deformation process. The pressure generated by the compression on the magnetostrictive material leads to a decrease in deformation efficiency. The x, y, and z directions are mutually perpendicular. The Bragg gratings in the three sensor modules are connected by optical fibers. The optical fiber output end is placed on the adjustment frame according to the design of the optical fiber adjustment frame used. The light from the output end passes through the collimating lens 7.

[0044] In this invention, the light emitted from the grating 10 is interfered with by the Fabry-Perot etalon 8, forming interference fringes. The principle of the Fabry-Perot etalon 8 is Fabry-Perot interference, and the specific formation principle is described below in the Fabry-Perot interference principle description. By observing the diameter change of the dark rings under the influence of the magnetic field, the magnitude of the magnetic field can be calculated.

[0045] As an embodiment of the present utility model, the present utility model also discloses a measurement method for a magnetic field measuring device, including the following steps: S1. Turn on the light source module and adjust its laser emission angle, the position and angle of the beam splitter of the beam splitter module and the fiber adjustment frame of each fiber transmission component, so that the fiber input end coincides with the lens focus of each fiber transmission component, so that the three laser beams split by the beam splitter module are coupled into the fibers of the three fiber transmission components respectively, so that the brightness of the fiber output end reaches the maximum.

[0046] S2. Align the image acquisition modules of the three-way fiber optic transmission components with the three outgoing beam interferometers, so that the three image acquisition modules can capture the images formed by the corresponding interferometers. Process the images to obtain the first wavelengths selected by the fiber optic grating in the x, y, and z directions.

[0047] S3. Place the device in an unknown or undetected external magnetic field and calculate the second wavelength selected by the fiber optic gratings at the locations of the three magnetic field sensing modules in the three-dimensional probe module in the x, y, and z directions, respectively.

[0048] S4. Obtain the change in the selected wavelength of the fiber optic grating from the first wavelength and the second wavelength, obtain the grating deformation of the Bragg grating of the magnetic field sensing module from the change in wavelength, and obtain the initial value of the magnetic field measurement and the magnetic field correction coefficient of the magnetic field sensing module in the x, y, and z directions with respect to the unknown or measured external magnetic field from the grating deformation.

[0049] S5. Repeat S3 and S4 to perform multiple measurements, and finally obtain the final magnetic field measurement values ​​and / or corresponding magnetic field directions of the magnetic field sensing module in the x, y, and z directions.

[0050] The specific process is as follows: When using this device to measure an unknown external magnetic field, the following steps are taken: (1) Turn on the laser 1, adjust the laser emission angle, the position and angle of the beam splitter 3 and the fiber optic adjustment frame 4, and try to make the fiber optic input end coincide with the focal point of the focusing lens 2, so that the three laser beams are coupled into the three optical fibers 5 respectively. When the brightness of the fiber optic output end reaches the maximum, the optical path has been adjusted to the optimal state.

[0051] (2) Align the three cameras 9 with the three beams of light separated by a Fabry-Perot datum 8, and adjust the datum 8 to be parallel so that the three cameras can each capture images as shown. Figure 4As shown, due to the influence of the external magnetic field, the radius of the dark ring in the interference pattern also changes. The processing module processes the received interference pattern to obtain either a first wavelength or a second wavelength. The first wavelength corresponds to the first-order fringe, and the second wavelength corresponds to the second-order fringe, thus forming multi-order interference fringes. In one interference pattern of this invention, many orders of fringes can be seen simultaneously. For ease of representation, they are referred to from the inside out as the first-order, second-order, and third-order fringes. The diameters corresponding to the dark ring 14 are respectively...

[0052] D x1 D x2 ;D y1 D y2 ;D z1 D z2 Using the known information, the cavity length h of the Fabry-Perot etalon 8 and the focal length f of the lens of the camera 9 can be obtained. According to the formula...

[0053]

[0054] In the formula, i can be x, y, or z. The three wavelengths corresponding to the three optical fibers are calculated from this formula as λ. xB1 , λ yB1 , λ zB1 In this step, when the laser passes through the fiber grating, without the application of an external magnetic field, the entire device selects a wavelength λ that matches the current fiber grating constant. xB1 , λ yB1 , λ zB1 In the following steps, when an external magnetic field is applied, the grating in the 3D probe module is stretched due to the magnetic field, causing its parameters to change. This allows the device to select a matching wavelength, thereby forming a waveform as shown below. Figure 4 The movement of the dark rings in the fringe image reflects a change in the position of the depression in the spectrum of the light incident on the etalon. The reason for the change in the position of the depression is that the magnetostrictive material deforms under the action of the magnetic field, which causes the grating to deform, resulting in a change in the fiber grating constant. This causes a change in the wavelength that matches the grating, which in turn causes a change in the center wavelength of the grating interference, thus changing the position of the depression and the diameter.

[0055] (3) Preferably, before measuring the unknown external magnetic field, the three-dimensional probe module is placed in an alternating magnetic field to demagnetize the magnetostrictive material therein. An alternating magnetic field of 0.1 to 0.2 mT is built using a 3-18V / 50Hz transformer and a Helmholtz coil to demagnetize the magnetostrictive material. The purpose of demagnetization is to make the measurement results more accurate. Alternatively, a certain amount of time can be waited for the three-dimensional probe module to demagnetize automatically. Therefore, this step is optional.

[0056] (4) Preferably, the three-dimensional probe module can also be calibrated or corrected before applying an external magnetic field. Specifically, the three-dimensional probe module after demagnetization in step (3) is placed in a known constant magnetic field. At this time, the diameter D′ corresponding to the three sets of dark rings 14 of the first and second levels is recorded. x1 、D′ x2 ;D′ y1 、D′ y2 ;D′ z1 、D′ z2 According to the formula λ is calculated xB2 , λ yB2 , λ zB2 Then λ xB2 , λ yB2 , λ zB2 Substitute into the formula respectively

[0057]

[0058] The initial values ​​B′ of the magnetic field measurement in each direction can be obtained by calculation. x B′ y B′ z B, which was measured beforehand with the known magnetic field x B y B z Correction factor for ratio value The correction coefficient function is obtained by repeating measurements multiple times. The purpose of repeated measurements is to obtain different correction coefficient values ​​corresponding to different Bi' values. By fitting the numerical values, the functional relationship between Bi' and B is obtained, and the final measured values ​​of the magnetic field in each direction are then obtained.

[0059]

[0060] i = x, y, z, L is the grating length of the grating in the magnetic field sensing module, l is the effective magnetostrictive material length in the magnetic field sensing module, and a and c are the coefficients relating the magnetostrictive effect coefficient to the magnitude of the magnetic induction intensity, respectively.

[0061] This step is a calibration process used to ensure the accuracy of instrument measurements. This step should be performed based on the actual situation.

[0062] (5) Place the entire device in an unknown external magnetic field, which is the unknown magnetic field to be measured. Use the device of this invention to perform the measurement, and use the same measurement method as in step (4) to measure B″. x B″ y B″ z , B″ x B″ y B″ z Substituting into formula (3), the measured magnetic field value P of the magnetic field to be measured can be obtained.x终 P y终 B z终 B

[0063] (6) Determining the direction of the magnetic field: Through a single measurement, the angles α, β, and γ are calculated. A three-dimensional rectangular coordinate system is established based on the x, y, and z directions of the three-dimensional sensing module. The azimuth angles of the magnetic field direction under this coordinate system are the angles α, β, and γ, which can determine eight possible directions (one for each octant). For example, for the sensing module in the x direction, regardless of whether the magnetic field is along the positive or negative x-axis, the deformation of the magnetostrictive material 11 in the sensing module is a deformation of increasing length. Therefore, regardless of the direction of the magnetic field along the x-axis, the observed final phenomenon is the same, so one phenomenon corresponds to two directions. Similarly, the observed phenomena along the y and z axes each correspond to two directions. Therefore, the final direction of the magnetic field, combined with the directions of the x, y, and z axes, has a total of 2*2*2 = 8 directions. Then, a known magnetic field with a direction along the x, y, and z axes is introduced. The three-dimensional probe module is placed in this magnetic field. By changing the direction of the known magnetic field, two sets of values ​​are measured. The direction of the known magnetic field in the larger set forms an acute angle with the magnetic field under test. According to the knowledge of vector composition, if two vectors of constant magnitude are continuously changed in their included angle, the combined vector magnitude is largest when the included angle is 0 degrees, smaller when the included angle is larger, and smallest when the included angle is 180 degrees. For example, given a known magnetic field and a magnetic field to be measured along the x-axis, if the x-axis magnetic field direction is changed, the x-axis magnetic field direction before and after the change will differ by 180 degrees. Therefore, one direction will form an acute angle with the direction of the magnetic field to be measured, and the other will form an obtuse angle. By measuring the combined magnetic field vector magnitude of the magnetic field to be measured and the known magnetic field before and after the x-axis direction change, according to the aforementioned method, the x-axis magnetic field direction corresponding to the larger measured vector magnitude forms an acute angle with the direction of the magnetic field to be measured. From this, it can be deduced that the direction of the x-axis component of the magnetic field to be measured is consistent with the direction of the known magnetic field along the x-axis. Repeat the above measurement three times: the first time to determine the direction of the x-axis component of the magnetic field to be measured, and the second and third times to determine the directions of the magnetic field components along the y and z axes, respectively. After all three directions are determined, the magnetic field direction can be determined according to the orthogonal vector addition rule, thus determining the magnetic field direction of the magnetic field to be measured.

[0064] The following is a description of the principle of this device.

[0065] The magnetostrictive material used in this invention exhibits the following magnetostrictive effect characteristics: Ferromagnetic materials possess a crystal-like structure. Adjacent atoms generate elementary magnetic moments due to electron spin, and these elementary magnetic moments interact with each other, driving them to align parallel to each other in the same direction, forming magnetic domains. When an external magnetic field is applied, these magnetic domains rotate, causing a slight change in the material's length or volume. This phenomenon is called the magnetostrictive effect. Introducing the magnetostrictive effect coefficient τ, the expression is:

[0066] Where Δl is the deformation of the magnetostrictive material.

[0067] Ferromagnetic materials exhibiting magnetostriction show a linear relationship between the magnetostriction effect (Δl) and the magnitude of the magnetic field within a specific range. Based on this linear relationship, a linear curve can be fitted by measurement, and the magnetostriction coefficient can then be measured for application in magnetic field measurement.

[0068] Bragg grating: A Bragg grating is a fiber optic or optical material structure with a periodic change in refractive index. When light propagates through a Bragg grating, laser light of a specific wavelength of 532 nm is strongly reflected due to the Bragg condition being satisfied.

[0069] The grating equation of a Bragg grating:

[0070] kλ B =2n eff Λ (5)

[0071] λ B n is the center wavelength where interference occurs; eff Λ represents the effective refractive index of the grating; Λ represents the grating period.

[0072] From the above formula, it can be seen that the wavelength λ of the grating satisfies the condition. B When interference enhancement occurs at the reflecting end of the grating, a dip appears in the spectrum at the corresponding projection end, λ. B The corresponding light intensity decreases significantly, from Figure 6 The left-hand diagram shows that transmission occurs through the grating. Because the spectral width of the grating's enhanced interference is narrower than the spectral width of the light source, most wavelengths corresponding to the enhanced interference are reflected, resulting in low transmission. Wavelengths outside the enhanced interference region are still transmitted normally. The peaks in the reflection spectrum in the right-hand diagram represent the wavelengths of light reflected due to enhanced interference. Fiber Bragg gratings are essentially similar to filters. When light waves pass through a Bragg grating, only phase-matched light is strongly reflected, while phase-mismatched light is weakly reflected. The grating acts like a mirror; the incident light wave must satisfy the Bragg condition to be reflected; otherwise, it continues to propagate along the optical path.

[0073] Differentiating both sides of equation (5) yields:

[0074] kdλ B =2n eff dΛ sorting results:

[0075] At the same time, according to formula (5), we get

[0076] Therefore, by combining equations (5') and (5”), we obtain... Simplifying the formula yields

[0077] Assuming there are N periods in the Bragg grating, then from the above equation, we can obtain...

[0078]

[0079] This process is linear; the derivative is replaced with a change in quantity.

[0080]

[0081] The change in a single period ΔΛ multiplied by the number of periods N equals the change in grating length, and the length of a single period Λ multiplied by the number of periods N equals the grating length. Therefore, we can obtain...

[0082] Further simplification of the expression yields

[0083] ΔL is the grating area deformation, and L is the grating area length.

[0084] Therefore, the grating undergoes axial deformation caused by the deformation of the magnetostrictive material. This deformation is applied by the magnetostrictive material itself, through a magnetic field that causes deformation. Since the Bragg grating's axis is aligned with the magnetic strain direction of the magnetostrictive material, the force generated by the material deformation is transmitted to the grating, and the direction of this force is consistent with the grating's axis, causing axial deformation. This results in a corresponding displacement of the depression at the projected spectrum. Since the light wavelength is mostly in the nanometer range, this method can be used to measure minute deformations. By combining the grating with the magnetostrictive material and measuring the wavelength λ... B The amount of displacement can be used to deduce the material deformation, and thus the magnitude of the magnetic field to be measured.

[0085] Fabry Perrault Intervention:

[0086] Fabry-Perot interferometry is an optical phenomenon based on multi-beam interference. The Fabry-Perot interferometer etalon 8 of this invention consists of two parallel mirrors forming an optical cavity between them. When light enters this cavity, some light is reflected at the mirror surfaces, while some penetrates the cavity and continues its journey. Multiple reflections form multiple reflected beams, which interfere with each other, producing interference fringe patterns. By analyzing these fringes, the spectral information of the transmitted light from the grating can be obtained. Due to the interference of multiple reflected beams, the optical cavity of the Fabry-Perot etalon 8 achieves very fine wavelength selectivity, significantly improving resolution compared to two-beam interferometry, and producing bright and sharp fringes.

[0087] Therefore, when the transmitted light from the grating interferes and forms interference fringes through the Fabry-Perot etalon 8, the wavelength of the transmitted light λ BSince the intensity of the grating-modulated light is significantly reduced in a certain area, this should also be reflected in the interference fringes, such as... Figure 4 As shown, the transmitted light from the grating, i.e., light with significantly reduced intensity, forms an interference pattern in the Fabry-Perot etalon 8. The wavelength corresponding to the dark ring can be calculated using the aforementioned formula. The measurement logic of this invention lies in observing the movement of the dark ring in the interference fringes of the measuring etalon, calculating the wavelength shift of the Bragg grating using formulas (1) and (2), and then calculating the periodic change and grating area deformation of the Bragg grating using formula (6). Since the grating is bonded to the magnetostrictive material, the grating area deformation can be considered equal to the magnetostrictive material deformation. Given the original length of the magnetostrictive material, the magnetostrictive effect coefficient can be obtained from formula (4). By fitting the coefficient to the magnitude of the magnetic induction intensity, the magnetic induction intensity of the sensing area can be obtained.

[0088] The following experimental demonstration proves the method for obtaining angle α: A weak magnetic field is provided using a Helmholtz coil. The theoretical value of the field strength inside the coil is calculated based on the magnitude of the current applied to the coil. Measurement experiments are then conducted according to the aforementioned steps, and the data shown in Table 1 are obtained. The percentage difference = 100% * |Measured field strength value - Theoretical field strength value| / theoretical value is used to measure the reliability of the measurement of the device involved.

[0089] Table 1. Experimental data for one-dimensional measurement

[0090]

[0091] A Helmholtz coil is used to provide the magnetic field to be measured. The theoretical value of the field strength inside the coil is calculated based on the magnitude of the current applied to the coil. The measurement experiment is carried out according to the aforementioned steps, and the three-dimensional measurement test data in Table 2 are obtained. The data in Table 2 are obtained according to the steps of this utility model. The measured field strength values ​​(mT), (mT), and (mT) of the x-field strength are vector-added to obtain the measured field strength value (mT). The theoretical field strength value is calculated based on the current applied to the Helmholtz coil and is a known value.

[0092] Table 2. Three-dimensional measurement test data

[0093]

[0094] Data analysis shows that the z-axis of the 3D probe module is almost perpendicular to the magnetic field direction. The magnetic field direction angle α measured by the 3D probe module is obtained using the following formula:

[0095]

[0096] The angle error β′ is:

[0097] The 35.00° is the theoretical angle value of the magnetic field direction. Therefore, it can be seen that the accuracy of the magnetic field direction angle measured by the method of this invention is very high.

[0098] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or related technical or knowledge. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be protected within the scope of the appended claims.

Claims

1. A device for measuring magnetic fields, characterized in that, The device includes a light source module, a beam splitting module, a three-way fiber optic transmission assembly, and a computing processing module connected to each other, wherein the light source module provides a laser beam to the beam splitting module; The beam splitting module splits the laser beam and directs it onto the three fiber optic transmission components respectively; The three optical fiber transmission components have the same structure, and the magnetic field sensing module in each optical fiber transmission component deforms under the action of an external magnetic field and is processed to obtain an interference image. The calculation and processing module processes the interference image to obtain the magnetic field value in the magnetic field sensing module.

2. The apparatus according to claim 1, characterized in that, The light source module is a 50mW laser in the visible light band.

3. The apparatus according to claim 1 or 2, characterized in that, The beam splitting module is composed of two beam splitters with a beam splitting ratio of 1:1 arranged at a certain angle.

4. The apparatus according to claim 1, characterized in that, Each fiber optic transmission component further includes a lens, an optical fiber, a collimating lens, an interferometer, and an image acquisition module connected in sequence. The magnetic field sensing module is fixed on the optical fiber. The lens focuses the received split beam and transmits it sequentially to the magnetic field sensor module, the collimating lens, and the interferometer through the optical fiber. The image acquisition module captures the image formed by the interferometer and transmits the captured image to the computing and processing module.

5. The apparatus according to claim 4, characterized in that, Each optical fiber transmission assembly also includes an optical fiber adjustment frame, with one end of the optical fiber connected to the optical fiber adjustment frame and the other end connected to the collimating lens.

6. The apparatus according to claim 4, characterized in that, The magnetic field sensing module includes a Bragg grating and a magnetostrictive material. The Bragg grating is etched onto the optical fiber at the location, and the magnetostrictive material is fixed to the two side regions of the Bragg grating.

7. The apparatus according to claim 6, characterized in that, The magnetostrictive material is a terbium-dysprosium-iron alloy.

8. The apparatus according to claim 7, characterized in that, Each of the magnetic field sensing modules is fixed on a fixed bracket along the x, y, z directions according to the grating axis, forming a three-dimensional probe module, wherein the x, y, z directions conform to the right-hand rule.

9. The apparatus according to claim 3, characterized in that, The specified angle is 90°.

10. The apparatus according to claim 3, characterized in that, The interferometer is a Fabry-Perot etalon.

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