High-precision optical fiber geomagnetic measurement probe, device and method

Abstract

The invention relates to a high-precision optical fiber geomagnetic measurement probe, device and method, the probe comprises a magnetostriction rod and a detection assembly, the detection assembly comprises a transmission assembly, the transmission assembly comprises a pair of parallel and opposite first rods, the two adjacent ends of the pair of first rods are connected through a first deformation rod and a second deformation rod respectively, and the first deformation rod is connected with the second deformation rod; each of the first deformation rod and the second deformation rod is formed by bending the middle part of a vertical rod; the sensing optical fiber is wound in the circumferential direction of the first deformation rod and the second deformation rod; the magnetostriction rod is arranged in the middle of the transmission assembly, and the two ends of the magnetostriction rod are connected with the middles of the pair of first rods correspondingly. Through the arrangement, the manufacturing difficulty and cost are reduced, the introduction of noise is reduced, and the magnetic field measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic measuring devices, and in particular to a high-precision optical fiber geomagnetic measuring probe, device and method. Background Art

[0002] The geomagnetic field is one of the Earth's fundamental physical fields. As an inherent physical property of the Earth, it contains rich and important information about the Earth's interior and exterior. As an ancient discipline, geomagnetism has broad applications in many fields, including navigation and communications, resource exploration, near-Earth space and deep Earth research, and earthquake prediction and forecasting, contributing to the national economy and national defense. Furthermore, geomagnetism is of great significance to understanding the Earth and the human environment. Over the past two decades, with the advancement of optical information technology and the gradual reduction in the price of optical information products, fiber-optic sensing technology has also seen significant progress. Compared to traditional dynamic measurement techniques based on electrical quantities, fiber-optic sensors offer advantages such as high sensitivity, immunity to electromagnetic interference, corrosion resistance, light weight, and low power consumption.

[0003] Existing sensors that measure weak magnetic fields through optical fibers require complex optical path systems and special materials such as NV color center diamonds and alkali metal gas chambers, which increases the difficulty and cost of production, limits the sensor's usage environment and makes it impossible to measure various geomagnetic elements. Summary of the Invention

[0004] In order to solve the above-mentioned defects, the present invention proposes a high-precision fiber-optic geomagnetic measurement probe, device and method. Without relying on complex optical path systems and special materials, a shorter fiber-optic interferometer arm can be used to amplify and enhance the sensitivity of the magnetostrictive rod deformation. Furthermore, a push-pull structure design is adopted, which greatly improves the magnetic field measurement accuracy while greatly reducing the number of probe structures, increasing the stability of the probe while greatly reducing the production difficulty and cost. It has a wide range of applications and can realize the measurement of various geomagnetic elements.

[0005] The technical solution adopted by the present invention is a high-precision optical fiber geomagnetic measurement probe, comprising a magnetostrictive rod and a detection assembly, wherein the detection assembly comprises:

[0006] The transmission assembly includes a pair of parallel and opposite first rods, with adjacent ends of the pair of first rods connected by a deformable rod 1 and a deformable rod 2, respectively. The deformable rod 1 and the deformable rod 2 are each formed by a vertical rod bent in the middle;

[0007] a sensing optical fiber, which is wound along the circumference of the first deformable rod and the second deformable rod;

[0008] The magnetostrictive rod is arranged in the middle of the transmission assembly, and both ends of the magnetostrictive rod are respectively connected to the middle of a pair of first rods.

[0009] Preferably, the middle portions of the deformable rod 1 and the deformable rod 2 are bent toward the inside of the transmission assembly, and the sensing optical fiber is wound circumferentially along the bending points of the deformable rod 1 and the deformable rod 2.

[0010] Preferably, the sensing optical fiber is wound around the circumference of the deformable rod 1 and the deformable rod 2 in a state with a certain prestress.

[0011] Preferably, the detection assembly further includes a pair of optical fiber winding parts, the optical fiber winding parts including a connecting end and a winding end, the outer sides of the bending points of the deformable rod 1 and the deformable rod 2 are respectively connected to a connecting end of the optical fiber winding part, the winding end has a groove along the circumference of the deformable rod 1 and the deformable rod 2, and the sensing optical fiber is wound around the circumference of a pair of optical fiber winding parts through the groove.

[0012] Preferably, the groove forms an arc shape along its extension direction, and the transmission assembly is an integrated structure obtained by cutting a titanium alloy plate.

[0013] Preferably, it comprises a base and a pair of detection assemblies, wherein the pair of detection assemblies are connected via an adjacent pair of parallel and opposite first rods, and the other pair of first rods are respectively fixed on the base; the magnetostrictive rod is arranged in the middle of one of the transmission assemblies in the pair of transmission assemblies.

[0014] The present invention also provides a high-precision optical fiber geomagnetic measurement device, comprising three of the above-mentioned high-precision optical fiber geomagnetic measurement probes, wherein the three magnetostrictive rods are perpendicular to each other.

[0015] Preferably, it also includes a fiber optic interferometer, an optical cable, a 3X3 coupler and a reflector, wherein the two ends of the optical cable are respectively connected to the fiber optic interferometer and one end of the 3X3 coupler, and the two ends of the sensing optical fiber are respectively connected to the reflector and the other end of the 3X3 coupler.

[0016] The present invention also proposes a high-precision optical fiber geomagnetic measurement method, which comprises:

[0017] S100, placing the high-precision fiber-optic geomagnetic measurement device at a location to be measured, and aligning the three magnetostrictive rods in the geographic north, geographic east, and vertically downward directions, respectively;

[0018] S200, calibrate the initial magnetic field intensity E0 in the three directions of geographic north, geographic east and vertical downward;

[0019] S300, measuring the demodulated voltage signals v(t) in three directions: geographic north, geographic east, and vertically downward;

[0020] S400, based on E0 and v(t), obtain the change ΔE of the magnetic field intensity in the three directions of geographic north, geographic east and vertical downward;

[0021] S500. Solve the seven elements of geomagnetism.

[0022] Preferably, the S400 specifically includes:

[0023] Substitute E0 and v(t) into the formula Solving for ΔE,

[0024] Among them, A R 、A S 、A M 、A d 、A N 、A D is a constant, n is the refractive index of the sensing fiber, υ0 is the central wavelength of the interference light signal, c0 is the speed of light in vacuum, K is the conversion coefficient between the change in the magnetostrictive rod and the sensing fiber, N is the number of windings of the sensing fiber on the optical fiber winding component, l is the strain distance of one circle of the sensing fiber on the optical fiber winding component, C is the magnetostrictive coefficient, and d is the initial length of the magnetostrictive rod.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The relatively simple structure eliminates the need for specialized, expensive materials, reducing the need for specialized materials and complex optical path construction, lowering both manufacturing complexity and cost. The optical fiber sensor offers a long sensing distance and avoids magnetic field interference from current flow, paving the way for a wide range of applications and enabling measurement of various geomagnetic elements. The transmission assembly's structural design amplifies the small extension and contraction of the magnetostrictive rod into a change in the length of the optical fiber sensor, minimizing noise and improving magnetic field measurement accuracy.

[0027] Through a streamlined mechanical push-pull amplification structure, the magnetostriction of each dimension of the magnetostrictive rod is amplified and temperature compensated, which increases the measurement accuracy and sensitivity of the geomagnetic measurement device while greatly reducing the number of structural parts and process difficulty of the probe. While ensuring the measurement function, it reduces the instability factors caused by the complex structure, reduces the production cost, and improves the overall stability of the probe. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is described in detail below with reference to the embodiments and accompanying drawings, in which:

[0029] Figure 1 It is a structural diagram of the transmission component;

[0030] Figure 2 It is a schematic diagram of the structure of the transmission component and the optical fiber winding component;

[0031] Figure 3 It is a schematic diagram of the structure of the transmission assembly, the optical fiber winding component and the magnetostrictive rod;

[0032] Figure 4 is a schematic structural diagram of a pair of detection components;

[0033] Figure 5 It is a schematic structural diagram of an optical fiber winding component;

[0034] Figure 6 It is a structural diagram of the base;

[0035] Figure 7 is a schematic structural diagram of a high-precision optical fiber geomagnetic measurement device in one embodiment;

[0036] Figure 8 is a schematic structural diagram of a high-precision optical fiber geomagnetic measurement device in another embodiment;

[0037] Figure 9 It is a demodulation principle diagram based on 3X3 coupler.

[0038] 1. Transmission assembly; 2. Magnetostrictive rod; 3. Housing; 4. Optical cable; 5. Gland connector; 6. Sensing fiber; 7. 3X3 coupler; 8. Reflector; 9. Base; 10. Optical fiber winding; 11. Optical fiber interferometer. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar components or components having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0040] In one embodiment, a high-precision fiber optic geomagnetic measurement probe includes a magnetostrictive rod 2 and a detection assembly. The magnetostrictive rod 2 is the core component of magnetic field sensing. It uses the magnetostrictive effect. When the external magnetic field changes, its own length will change accordingly. The detection assembly includes a transmission assembly 1 and a sensing optical fiber 6. The transmission assembly 1 includes a pair of parallel and opposite first rods. The adjacent ends of the pair of first rods are connected by a deformable rod 1 and a deformable rod 2. The deformable rod 1 and the deformable rod 2 are both formed by bending a vertical rod in the middle. The bending direction of the deformable rod 1 and the deformable rod 2 can be in any direction. This special structural design provides a basis for the subsequent winding of the sensing optical fiber 6 and the transmission of mechanical deformation. The deformable rod 1 and the deformable rod 2 can be bent into two straight rods or into an arc-shaped structure. The adjacent ends of the pair of first rods are connected by a pair of deformable rods to form a closed frame structure, and the structure has a certain degree of flexibility and deformability.

[0041] The sensing optical fiber 6 is wound around the deformable rod 1 and the deformable rod 2. This winding method enables the sensing optical fiber 6 to closely follow the deformation of the deformable rod and produce a change in length, thereby causing a change in the optical path difference. Figure 3 The magnetostrictive rod 2 is positioned in the middle of the transmission assembly 1, with its ends connected to the middle of a pair of first rods. This connection allows changes in the length of the magnetostrictive rod 2 to be directly and effectively transmitted to the transmission assembly 1, thereby driving corresponding changes in the sensing fiber 6.

[0042] The transmission assembly 1 can be composed of connected rods or plates. That is, the first rod, deformable rod 1, and deformable rod 2 can also be strips of plate material. The transmission assembly 1 must be constructed of a non-magnetic material with a relative magnetic permeability close to 1 to ensure that the Earth's magnetic field fully acts on the magnetostrictive rod 2. The specific parameters can be adjusted based on actual conditions. The magnetostrictive rod 2 and transmission assembly 1 can be connected using methods such as gluing, converting the magnitude of the Earth's magnetic field to the length of the magnetostrictive rod 2, thereby varying the distance between the two ends of the transmission assembly 1. The specific parameters of the magnetostrictive rod 2 can be adjusted based on actual conditions.

[0043] When the geomagnetic field changes, the magnetostrictive rod 2 changes length due to the magnetostrictive effect. Due to the connection between the magnetostrictive rod 2 and the transmission assembly 1, the distance between the first rods of the transmission assembly 1 increases, causing deformation (stretching or compressing) of the first and second deformable rods. The sensing fiber 6 is wound circumferentially around the deformable rods, and the deformation of the deformable rods is directly transmitted to the sensing fiber 6, causing the length of the sensing fiber 6 to change, resulting in a change in the optical path difference and a phase difference in the fiber interference signal. By demodulating this phase difference and other processing, relevant elements of the geomagnetic field can be calculated.

[0044] The structure of this embodiment is relatively simple and does not rely on special expensive materials. This reduces the reliance on special materials and the complex optical path construction process during the manufacturing process, thereby reducing the difficulty and cost of manufacturing. The sensing fiber 6 has a long sensing distance and does not generate interference magnetic fields due to current. It has a wide range of applications and can measure various elements of the geomagnetic field. The structural design of the transmission assembly 1 can amplify the small expansion and contraction of the magnetostrictive rod 2 into a change in the length of the sensing fiber 6, reducing the introduction of noise and improving the accuracy of magnetic field measurement. The structure is relatively streamlined, while ensuring the measurement function, it reduces the instability factors caused by the complex structure and improves the overall stability of the probe.

[0045] In one embodiment, see Figure 1The middle portions of both deformable rods 1 and 2 bend toward the interior of transmission assembly 1, forming an I-shaped structural component. This compact design facilitates the miniaturization of the probe and facilitates installation and use in various scenarios. The sensing fiber 6 can be effectively wound within a relatively compact space, avoiding the introduction of increased environmental noise caused by overly long interferometer arms and providing more stable winding.

[0046] In one embodiment, the sensing fiber 6 is wrapped around the deformable rods 1 and 2 with a certain prestress. When the magnetostrictive rod 2 and the deformable rods undergo a slight deformation due to changes in the local magnetic field, the sensing fiber 6 responds more quickly and significantly to this deformation, resulting in a greater length change. This prestress ensures a tight fit between the sensing fiber 6 and the deformable rods, reducing looseness or relative displacement between the sensing fiber 6 and the deformable rods caused by factors such as environmental vibration and temperature fluctuations.

[0047] In one embodiment, see Figure 2 The detection assembly also includes a pair of optical fiber winding members 10, each of which includes a connection end and a winding end. The outer sides of the bending points of the deformable rod 1 and the deformable rod 2 are respectively connected to a connection end of the optical fiber winding member 10. Specifically, the connection between the deformable rod 1 and the deformable rod 2 and their corresponding optical fiber winding members 10 can be achieved by plugging, bonding, welding, etc. Figure 5 The winding end is provided with grooves along the circumference of the deformable rod 1 and the deformable rod, and the sensing optical fiber 6 is wound around the circumference of a pair of optical fiber winding members 10 through the grooves. The grooves provide a winding path for the sensing optical fiber 6, reducing the displacement of the sensing optical fiber 6.

[0048] The optical fiber winding component 10 is mainly used to connect the transmission component 1 and the sensing optical fiber 6. When the distance between the two ends of the transmission component 1 changes, the distance of the optical fiber winding component 10 located in the middle of the transmission component 1 will change, thereby causing the sensing optical fiber 6 fixedly wound on it to change in length, resulting in a change in the optical interference signal. The specific parameters of the optical fiber winding component 10 can be adjusted according to actual conditions.

[0049] In one embodiment, the groove at the winding end of the optical fiber winding member 10 forms an arc along its extension direction, which reduces the sudden change in direction of the sensing optical fiber 6 during winding. The optical fiber moves more smoothly in the groove when stretched or contracted, reducing the wear and breakage of the sensing optical fiber 6.

[0050] In one embodiment, the transmission assembly 1 is a one-piece structure formed by cutting titanium alloy plates. This not only ensures structural strength but also reduces gaps and loosening risks between components. The stable structure effectively resists external interference such as vibration and impact, ensuring the accuracy and reliability of measurements in complex environments. More specifically, the transmission assembly 1 can be made of TA2 titanium alloy. The one-piece structure is obtained by laser cutting a TA2 titanium alloy plate with a length of 55 mm, a width of 110 mm, and a thickness of 20 mm. This ensures that the Earth's magnetic field fully acts on the magnetostrictive rod 2 while maintaining the required structural strength.

[0051] In one embodiment, see Figure 4 The high-precision fiber-optic geomagnetic measurement probe includes a base 9 and a pair of detection assemblies. The detection assemblies are connected by a pair of adjacent, parallel, and opposing first rods. The other pair of first rods is fixed to the base 9. The magnetostrictive rod 2 is positioned in the middle of one of the pair of transmission assemblies 1. The pair of detection assemblies form a mechanical push-pull amplification structure. The base 9 fixes the positions of the two detection assemblies at both ends along their arrangement, allowing for compression between the two detection assemblies.

[0052] When the magnetostrictive rod 2 changes length due to a changing magnetic field, this length change is transmitted to the fiber winding member 10 via the transmission assembly 1, causing the length of the optical fiber wound thereon to change. Simultaneously, the other transmission assembly 1, which does not contain the magnetostrictive rod 2, is squeezed, causing the length of the optical fiber wound thereon to change as well. In this way, the deformation of the magnetostrictive rod 2 is amplified. That is, a small change in the length of the magnetostrictive rod 2 can cause a larger difference in the length of the two sensing optical fibers 6.

[0053] In actual application environments, temperature changes will affect the length of the sensing fiber 6, thereby interfering with the magnetic field measurement results. However, this push-pull amplification structure has a temperature compensation function to a certain extent. Because the two sensing fibers 6 in a pair of detection components are in similar temperature environments, when the temperature changes, the two sensing fibers 6 will be affected by the temperature at the same time and produce the same length change trend (simultaneous extension or shortening). However, when calculating the magnetic field change, it is determined by the difference in the length change of the two sensing fibers 6. These length changes caused by the same temperature trend will partially offset each other when calculating the difference, thereby reducing the impact of temperature on the measurement results and achieving temperature compensation.

[0054] Through a unique mechanical push-pull amplification structure, the tiny deformation of the magnetostrictive rod 2 is amplified into a significant difference in the length of the two sensing fibers 6. This produces a more significant optical interference signal change when measuring weak magnetic field changes, improving measurement accuracy and sensitivity. Compared to some complex geomagnetic measurement structures, this solution uses a streamlined mechanical push-pull amplification structure, reducing the number of structural components, lowering manufacturing difficulty and cost, and increasing the probe's test stability.

[0055] In one embodiment, a high-precision fiber-optic geomagnetic measurement device, see Figure 7 The apparatus comprises three of the high-precision fiber optic geomagnetic measurement probes described in the above embodiments, with the three magnetostrictive rods 2 positioned perpendicular to each other. The three perpendicularly arranged magnetostrictive rods 2 can independently sense changes in the geomagnetic field in three orthogonal directions (which can be considered as the X, Y, and Z axes), thereby achieving precise geomagnetic measurement.

[0056] In one embodiment, the high-precision fiber-optic geomagnetic measurement device also includes a fiber-optic interferometer 11, an optical cable 4, a 3X3 coupler 7 and a reflector 8, the two ends of the optical cable 4 are respectively connected to the fiber-optic interferometer 11 and one end of the 3X3 coupler 7, and the two ends of the sensing optical fiber 6 are respectively connected to the reflector 8 and the other end of the 3X3 coupler 7.

[0057] The 3x3 coupler 7 is primarily used to connect the sensing fiber 6 and the optical cable 4. This 3x3 coupler 7 splits the three optical signals, each with a phase difference of 120 degrees. It splits the sensing light signal output by the fiber interferometer 1111 into two interferometer arms and combines and splits the two reflected optical signals, generating three optical signals, each with a phase difference of 120 degrees, for demodulation by the fiber interferometer 11. The parameters of the 3x3 coupler 7 can be adjusted according to actual needs. The sensing fiber 6 is primarily used to connect the 3x3 coupler 7, the reflector 8, and the fiber winding assembly 10. The sensing fiber 6 serves as the two interferometer arms of the Michelson interferometer. Both ends of the sensing fiber 6 are glued to the fiber winding assembly 10, ensuring a certain prestressed state. The specific parameters of the sensing fiber 6 can be adjusted according to actual needs. The reflector 8 is primarily used to connect the sensing fiber 6 and reflect the sensing light signal from the sensing fiber 6. The specific parameters of the reflector 8 can be adjusted according to actual needs. The fiber optic interferometer 11 is mainly used to connect the optical cable 4, output the sensing light signal to the geomagnetic probe through the optical cable 4, and demodulate the phase difference of the reflected light interference signal. The seven elements of geomagnetism are calculated through relevant formulas to realize geomagnetic measurement. The specific parameters of the fiber optic interferometer 11 can be adjusted according to actual conditions.

[0058] See also Figure 8The optical signal emitted by the fiber optic interferometer 11 reaches the 3X3 coupler 7 via the optical cable 4. The 3X3 coupler 7 distributes the optical signal to the two sensing optical fibers 6. When the magnetic field changes, the magnetostrictive rod 2 drives the transmission assembly 1 to change the length of the sensing optical fiber 6, thereby changing the optical path difference. The reflector 8 reflects the optical signal back, which then passes through the sensing optical fiber 6 and returns to the 3X3 coupler 7. The 3X3 coupler 7 combines and splits the reflected light signals to form optical signals with specific phase differences, which are then transmitted back to the fiber optic interferometer 11 via the optical cable 4. The fiber optic interferometer 11 demodulates the phase difference of these optical signals and calculates them based on relevant formulas to ultimately obtain relevant information about the Earth's magnetic field.

[0059] The 3x3 coupler 7 splits the optical signal into multiple signals with specific phase differences. Leveraging the principle of interference, it enhances the ability to detect changes in the optical path difference of the sensing fiber 6. Even if the optical path difference caused by magnetic field changes is very small, the interference and processing of these multiple signals allows for more precise measurement of the phase difference change, thereby improving the accuracy of magnetic field measurement. In weak magnetic field measurement scenarios, this allows for more accurate capture of subtle changes in the magnetic field.

[0060] In one embodiment, the high-precision fiber-optic geomagnetic measurement device further includes a housing 3 and a gland connector 5. The housing 3 is connected to the base 9 to form a closed area, and the three high-precision fiber-optic geomagnetic measurement probes in the above-mentioned embodiments are located in this closed area. The high-precision fiber-optic geomagnetic measurement probes are isolated from the external space to ensure the stability of the magnetic field measurement environment. The housing 3 must be made of non-magnetic material with a relative magnetic permeability close to 1 to ensure that the geomagnetic field fully acts on the magnetostrictive rod 2. The specific parameters can be adjusted according to actual conditions. The gland connector 5 is mainly used to connect the optical cable 4 and the housing 3, so that the optical fiber in the optical cable 4 enters the interior of the sealed geomagnetic probe and is connected to the 3X3 coupler 7. The specific parameters of the gland connector 5 can be adjusted according to actual conditions. The optical cable 4 is mainly used to connect the gland connector 5 and the optical fiber interferometer 11, so that the optical signal between the optical fiber interferometer 11 and the geomagnetic probe can be stably transmitted. The specific parameters of the optical cable 4 can be adjusted according to actual conditions.

[0061] See also Figure 6-7 The base 9 is primarily used to connect the transmission assembly 1, 3x3 coupler 7, reflector 8, and housing 3, securing the three high-precision fiber-optic geomagnetic measurement probes perpendicular to each other. The 3x3 coupler 7 and reflector 8 must also be securely fastened to the base 9 to prevent loosening of the optical components and affecting the measurement results. The housing 3 is secured to the base 9 with screws. The base 9 must be made of a non-magnetic material with a relative magnetic permeability close to 1 to ensure that the geomagnetic field fully acts on the magnetostrictive rod 2. Specific parameters can be adjusted based on actual conditions.

[0062] In a more specific embodiment, the magnetostrictive rod is made of a terbium-dysprosium-iron alloy with a saturation magnetostriction coefficient greater than 1500 ppm. Its specific dimensions are a cylinder with a diameter of 1 cm and a length of 10 cm. The outer casing is made of plastic-steel material with outer dimensions of 30 cm in length, 30 cm in width, 30 cm in height, and 1 cm in thickness. The optical cable has an 8 mm diameter and contains three-core single-mode optical fibers that comply with the ITU-TG.652 standard. The gland connector is made of all-PVC plastic, with M20x1.5 threads, a 12 mm opening, and a length of 22.7 mm. The sensing fiber uses Corning's bend-resistant optical fiber with a minimum bend diameter of 3 cm. The 3x3 coupler has a splitting ratio of 33:33:33, with a phase difference of 120 degrees. Its specific dimensions are a cylinder with a diameter of 3 mm and a length of 6 cm. The reflector has a reflectivity of 99.9% and its specific dimensions are a cylinder with a diameter of 3 mm and a length of 1.5 cm. The base is made of plastic-steel material, 28cm long, 28cm wide, and 28cm high. Three mutually perpendicular square holes on the base are 6cm wide, 21.8cm high, and 2cm deep, just enough to fit two detection components to form a one-dimensional geomagnetic probe. The fiber optic winding part is made of plastic-steel, and the groove for winding the sensing fiber is a semicircle with a diameter of 3cm. The minimum recognizable phase change of the fiber optic interferometer is 1X10 -5 rad, sensitivity greater than 50dB, chassis dimensions are 45cm long, 43cm wide and 18cm high.

[0063] In one embodiment, a high-precision optical fiber geomagnetic measurement method comprises:

[0064] S100. Place the high-precision fiber-optic geomagnetic measurement device described in claim 7 or 8 at the location to be measured, and align the three magnetostrictive rods in the directions of geographic north, geographic east, and vertically downward, respectively. This step is essential for subsequent accurate measurement. Only by ensuring that the orientation of the magnetostrictive rods aligns with the target measurement direction can the geomagnetic field components in the corresponding direction be measured. For example, during field geological exploration, tools such as a compass are used to assist in the device's orientation, ensuring that the magnetostrictive rods accurately align with the geographic direction.

[0065] S200: Calibrate the initial magnetic field strength E0 in the three directions of geographic north, geographic east, and vertical downward. Specifically, Method 1: Align another three-component magnetometer with the three measurement directions of the high-precision fiber-optic geomagnetic measurement device to be calibrated, and then measure the initial magnetic field strength E0 in the three directions. Method 2: Place the magnetostrictive material in a zero magnetic space using a magnetic field shielding device to calibrate E0 to 0.

[0066] S300 measures the demodulated voltage signals v(t) in the three directions of geographic north, geographic east, and vertical downward. When the geomagnetic field changes, the magnetostrictive rod changes length accordingly, which is transmitted to the sensing fiber through the transmission assembly, causing a change in the optical path difference. This change is ultimately demodulated in the fiber interferometer to produce the voltage signal v(t). This voltage signal carries information about geomagnetic field changes and is key data for subsequent calculations of changes in magnetic field strength.

[0067] S400, based on E0 and v(t), obtain the magnetic field intensity change ΔE in the three directions of geographic north, geographic east, and vertical downward.

[0068] S500. Solve the seven elements of geomagnetism.

[0069] The high-precision fiber-optic geomagnetic measurement device described in the above embodiment reduces the sources of measurement error. Furthermore, using the demodulated voltage signal and precise calculation formulas, the change in magnetic field intensity and the seven geomagnetic elements can be accurately calculated, providing users with comprehensive geomagnetic field information.

[0070] In one embodiment, the S400 specifically includes:

[0071] Substitute E0 and v(t) into the formula Solving for ΔE,

[0072] Among them, A R 、A S 、A M 、A d 、A N 、A D is a constant, n is the refractive index of the sensing fiber, υ0 is the central wavelength of the interference light signal, c0 is the speed of light in vacuum, K is the conversion coefficient between the change in the magnetostrictive rod and the sensing fiber, N is the number of windings of the sensing fiber on the optical fiber winding component, l is the strain distance of one circle of the sensing fiber on the optical fiber winding component, C is the magnetostrictive coefficient, and d is the initial length of the magnetostrictive rod.

[0073] In a more specific embodiment, the specific calculation method is as follows.

[0074] The geomagnetic field is a vector field with both magnitude and direction, and is generally represented by the vector F (Jerzy Jankowski, 1999). F is generally described by its various components, which are called geomagnetic elements. The geomagnetic elements mainly include the horizontal component (H), the north component (X), the east component (Y), the vertical component (Z), the magnetic declination (D), the magnetic inclination (I) and the total field strength (F). Among them, X, Y, and Z are more commonly used in theoretical research, H, Z, and D are more commonly used in geomagnetic relative records, and F, D, and I are more commonly used in absolute observations. F, H, X, Y, and Z are called intensity components, and D and I are called angle components. The relationship between the components is as follows:

[0075] Z=FsinI........................ (1-1)

[0076] Y=HsinD........................ (1-2)

[0077] F=H 2 +Z 2 =X 2 +Y 2 +Z 2 ...... (1-3)

[0078] When a magnetic field acts on a magnetostrictive material, the magnetic atoms within it will arrange themselves in an orderly manner along the direction of the magnetic field, causing the magnetostrictive material to expand and contract in volume along the direction of the magnetic field. This is the magnetostrictive effect. However, this volume deformation and the trend of change in the direction or magnitude of the magnetic field are different because the magnetostrictive materials themselves are composed of different materials, specifically metal alloys such as iron-nickel alloys, iron-aluminum alloys, iron-cobalt alloys, and rare earth metal alloys such as terbium-dysprosium-iron alloys. Therefore, the degree of expansion and contraction caused by their magnetostrictive effect is also different. In the linear working region, the relationship between the magnetostriction coefficient and the axial strain ε can be expressed as:

[0079] C(E0+ΔE)=Δd / d=ε.............(1-4)

[0080] In the above formula, C is the magnetostriction coefficient, E0 is the initial magnetic field intensity, ΔE is the change in magnetic field intensity, Δd is the change in material length caused by the magnetic field direction, and d is the initial length of the telescopic material.

[0081] When the external magnetic field changes, the length of the magnetostrictive material changes, thereby changing the spacing between the pair of first rods of the transmission assembly and the outer diameter of the optical fiber winding member. This in turn causes an optical path difference (i.e., an interference arm length difference) between the two sensing optical fibers wound on the optical fiber winding member. The relationship between the change in the length of the magnetostrictive material and the interference arm length difference Δr can be expressed as:

[0082] Δr=KNlΔd.............(1-5)

[0083] In the above formula, K is the conversion coefficient between the magnetostrictive material and the sensing optical fiber variation, N is the number of windings of the sensing optical fiber on the optical fiber winding component, and l is the strain distance of one winding of the sensing optical fiber on the optical fiber winding component.

[0084] The difference in the length of the interference arm of the fiber optic interferometer system causes a phase difference in the fiber optic interference signal. The arm length difference Δr is related to the phase change signal. The relationship can be expressed as:

[0085]

[0086] In the above formula, n is the refractive index of the optical fiber, υ0 is the center wavelength of the interference light signal, and c0 is the speed of light in a vacuum.

[0087] When the fiber interference signal is transmitted back to the fiber interferometer, the fiber interference signal u detected by the three-way photodetector (PD) i (t) in the following form:

[0088]

[0089] In the above formula, A is the DC amplitude of the interference signal, B is the AC amplitude of the interference signal, B = A·V, where V is the fringe contrast of the interference signal.

[0090] Multiply the sum of the three received PD signals by -1 / 3 to get

[0091]

[0092] Add -A to the three received PD signals respectively, and set the gain to A1, and we can get:

[0093]

[0094]

[0095] Then pass the result of the above formula (1-9) through three identical differentiators and set the gain to A. d , we can get

[0096]

[0097] Using trigonometric relationships

[0098] sin(α+β)-sin(α-β)=2cosαsinβ............(1-11)

[0099] Multiply the result of each signal in formula (1-9) by the difference of the differential signals of the other two signals in formula (1-10), and set the multiplier gain to A. M , combined with the trigonometric function relationship (1-11), we can get

[0100]

[0101] Using mathematical relationships

[0102]

[0103] Add the three signals in equation (1-12) and set the multiplier gain to A. s ,get

[0104]

[0105] Square the three signals in equation (1-9) and add them together, and set the multiplier gain to A. D ,available

[0106]

[0107] Divide equation (1-12) by equation (1-9) and set the divider gain to A. R , and then integrate the result over time to get the following formula

[0108]

[0109] Where, Is the phase signal to be measured; A R 、A S 、A M 、A d 、A N 、A D They are all constants and can be freely set in the demodulation program. The overall demodulation principle diagram is as follows Figure 9 shown.

[0110] Combining formulas (1-4), (1-5), (1-6), and (1-16) yields

[0111]

[0112] Among them, π, n, v0, K, N, l, C, d, c0, v(t), E0, A R 、A S 、A M 、A d 、A N 、A D When all are known quantities, the phase change can be demodulated by the interferometer and the change in magnetic field intensity ΔE in the measurement direction can be calculated.

[0113] Substituting the calibration value E0 of each axis into formula (1-17) can calculate the magnitude of the geomagnetic field intensity components on the north component (X component), east component (Y component) and vertical component (Z component).

[0114] The horizontal component (H), magnetic declination (D), magnetic inclination (I) and total field strength (F) can be calculated using formulas (1-1), (1-2) and (1-3).

[0115] The high-precision fiber optic geomagnetic measurement probe, device and method of the present invention are mainly used for earth magnetic field measurement, mineral resource exploration, engineering and environmental exploration, underground buried object detection and high-precision measurement of material magnetism.

[0116] In this specification, the use of terms such as "Embodiment 1," "this embodiment," and "in one embodiment" indicates that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in the invention or at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example; furthermore, the specific features, structures, materials, or characteristics described may be appropriately combined in any one or more embodiments or examples.

[0117] In the description of this specification, the terms "connect," "install," "fix," "dispose," and "have" are to be understood in a broad sense. For example, "connect" can mean a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0118] In the description of this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising the element.

[0119] The above description of the embodiments is to facilitate ordinary technicians in this technical field to understand and apply the technology of this case. People familiar with the technology in this field can obviously make various modifications to these examples easily and apply the general principles described here to other embodiments without having to go through creative work. Therefore, this case is not limited to the above embodiments. Modifications to the following situations should all be within the scope of protection of this case: ① A new technical solution implemented based on the technical solution of the present invention and combined with existing common knowledge, the technical effect produced by the new technical solution does not exceed the technical effect of the present invention; ② The equivalent replacement of some features of the technical solution of the present invention with the known technology, the technical effect produced is the same as the technical effect of the present invention; ③ The technical solution of the present invention is expandable, and the substantive content of the expanded technical solution does not exceed the technical solution of the present invention; ④ The equivalent transformation made by the content of the description and drawings of the present invention is directly or indirectly applied to other related technical fields.

Claims

1. A high-precision fiber optic geomagnetic measurement probe, characterized in that: It includes a magnetostrictive rod and a detection assembly, and the detection assembly includes: The transmission assembly includes a pair of parallel and opposite first rods, with adjacent ends of the pair of first rods connected by a deformable rod 1 and a deformable rod 2, respectively. The deformable rod 1 and the deformable rod 2 are each formed by a vertical rod bent in the middle; a sensing optical fiber, which is wound along the circumference of the first deformable rod and the second deformable rod; The magnetostrictive rod is arranged in the middle of the transmission assembly, and both ends of the magnetostrictive rod are respectively connected to the middle of a pair of first rods.

2. The measuring probe according to claim 1, characterized in that The middle parts of the deformable rod 1 and the deformable rod 2 are both bent toward the inside of the transmission assembly, and the sensing optical fiber is wound around the circumference of the bending points of the deformable rod 1 and the deformable rod 2.

3. The measuring probe according to claim 2, characterized in that The sensing optical fiber is wound around the circumference of the first deformable rod and the second deformable rod in a state with a certain prestress.

4. The measuring probe according to claim 2, characterized in that The detection assembly also includes a pair of optical fiber winding parts, which include connecting ends and winding ends. The outer sides of the bending points of the deformable rod 1 and the deformable rod 2 are respectively connected to a connecting end of the optical fiber winding part, and the winding ends are provided with grooves along the circumference of the deformable rod 1 and the deformable rod 2. The sensing optical fiber is wound around the circumference of the pair of optical fiber winding parts through the grooves.

5. The measuring probe according to claim 4, characterized in that The groove forms an arc shape along its extending direction, and the transmission component is an integrated structure obtained by cutting a titanium alloy plate.

6. The measuring probe according to any one of claims 1 to 5, characterized in that The invention comprises a base and a pair of detection assemblies, wherein the pair of detection assemblies are connected via a pair of adjacent parallel and opposite first rods, and the other pair of first rods are respectively fixed on the base; the magnetostrictive rod is arranged in the middle of one of the transmission assemblies in the pair of transmission assemblies.

7. A high-precision optical fiber geomagnetic measurement device, characterized in that: The invention comprises three high-precision optical fiber geomagnetic measurement probes according to any one of claims 1 to 6, wherein the three magnetostrictive rods are perpendicular to each other.

8. The measuring device according to claim 7, characterized in that It also includes a fiber optic interferometer, an optical cable, a 3X3 coupler and a reflector, wherein the two ends of the optical cable are respectively connected to the fiber optic interferometer and one end of the 3X3 coupler, and the two ends of the sensing optical fiber are respectively connected to the reflector and the other end of the 3X3 coupler.

9. A high-precision optical fiber geomagnetic measurement method, characterized in that: The method comprises: S100, placing the high-precision fiber-optic geomagnetic measurement device according to claim 7 or 8 at a location to be measured, and aligning the three magnetostrictive rods in the geographic north, geographic east, and vertically downward directions, respectively; S200, calibrate the initial magnetic field intensity E0 in the three directions of geographic north, geographic east and vertical downward; S300, measuring the demodulated voltage signals v(t) in three directions: geographic north, geographic east, and vertically downward; S400, based on E0 and v(t), obtain the change ΔE of the magnetic field intensity in the three directions of geographic north, geographic east and vertical downward; S500. Solve the seven elements of geomagnetism.

10. The measuring method according to claim 9, characterized in that The S400 specifically includes: Substitute E0 and v(t) into the formula Solving for ΔE, Among them, A R 、A S 、A M 、A d 、A N 、A D is a constant, n is the refractive index of the sensing fiber, υ0 is the central wavelength of the interference light signal, c0 is the speed of light in vacuum, K is the conversion coefficient between the change in the magnetostrictive rod and the sensing fiber, N is the number of windings of the sensing fiber on the optical fiber winding component, l is the strain distance of one circle of the sensing fiber on the optical fiber winding component, C is the magnetostrictive coefficient, and d is the initial length of the magnetostrictive rod.

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