CN112014777B - Space magnetic gradient tensor measurement system based on optical fiber magnetic field sensor and working method thereof - Google Patents
Space magnetic gradient tensor measurement system based on optical fiber magnetic field sensor and working method thereof Download PDFInfo
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Abstract
The invention relates to a space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor and a working method thereof, wherein the system comprises an external feedback compensation unit, an internal optical fiber magnetic sensing unit and an integral structure fixing component unit; the internal optical fiber magnetic sensing unit comprises a plurality of magnetic sensing optical fibers, a modulation sensing structure and three optical fiber fixing circular plates, wherein the plurality of magnetic sensing optical fibers are arranged and fixed on the three optical fiber fixing circular plates, each magnetic sensing optical fiber is provided with two modulation sensing structures, the modulation of the modulation sensing structure is realized by winding a modulation coil at the periphery, applying two different modulation frequencies on the two modulation sensing structures, and obtaining magnetic induction intensity information measured at two different positions near the different modulation frequencies of an output spectrum. The invention has higher magnetic measurement sensitivity, can effectively shield external electromagnetic interference, is convenient for integrated installation and test with structures such as a small-sized pressure-bearing cabin and the like due to the light and handy design, and is suitable for magnetic field detection in a complex physical environment.
Description
Technical Field
The invention relates to a space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor and a working method thereof, and belongs to the technical field of optical fiber sensing.
Background
With the continuous development of magnetic measurement technology, the magnetic measurement sensor is continuously optimized, and has profound significance in the fields of space magnetic detection, military industry, electric power, medical treatment and the like. The magnetic detection greatly facilitates the life production and scientific research of people.
The traditional magnetic field sensor converts a magnetic field into an electric field by using an electronic element, an electric signal is easy to be interfered by electromagnetic waves, and the transmission efficiency is not high. Magnetometers such as a fluxgate, a magnetic resistance effect and an optical pump mostly have the defects of large volume, complex structure, small monitoring range and the like, and are limited in application in many fields.
With the development of optical fiber sensing technology, magnetic field sensing by using optical fibers gradually becomes a key research direction of various countries, the optical fibers are not sensitive enough to a magnetic field, and a proper magnetic sensitive material is selected to be combined with the optical fibers, so that the problems that the traditional magnetic field sensor is easily limited by electromagnetic interference, low sensitivity, small measurement range and the like can be solved, the synchronous detection network in a large space volume is easily realized due to the light structure and the characteristic of easy distributed multiplexing, and the modulation and demodulation technology matched with the magnetic field sensor can enable information to be collected at a high speed. Therefore, the optical fiber magnetic field sensor has wider application range and higher reliability.
The characteristics that optical fibers are easy to multiplex and network are utilized, the measurement of the space magnetic gradient tensor is realized through the optical fiber magnetic field sensor, the limitation requirements of space volumes of an underwater pressure bearing cabin, a space cabin and the like can be effectively met, the anti-interference capacity to a complex environment is good, the measurement sensitivity can also meet the measurement requirement, and the sensor technology is a sensing technology with huge application potential.
The detection of the magnetic gradient tensor needs to use a plurality of sensors for synchronous measurement, and the magnetic gradient tensor is obtained by collecting and operating the measurement results of the sensors at different positions. At present, a full tensor magnetic gradiometer with higher measurement precision consists of a low-temperature superconducting quantum interferometer, but has the defects of large volume, high manufacturing cost and strict requirement on working temperature, and is not suitable for general application. The magnetic gradient tensor instrument based on the triaxial fluxgate sensor is widely applied at present and comprises four fluxgate sensors, and a feedback coil needs to be designed outside to enable the fluxgate to work in a near-zero magnetic environment so as to improve the measurement precision and reduce the interference.
Disclosure of Invention
In order to solve the defects of the prior art, the applicability of the magnetic field sensor and the comprehensive integrity of the measurement information are improved. The invention provides a space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor, which can adapt to measurement requirements under multiple environments and realize tensor information acquisition.
The invention also provides a working method of the spatial magnetic gradient tensor measurement system.
The technical scheme of the invention is as follows:
a space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor comprises an external feedback compensation unit, an internal optical fiber magnetic sensing unit and an integral structure fixing component unit;
the internal optical fiber magnetic sensing unit is fixedly arranged in the external feedback compensation unit through the integral structure fixing part unit, and the external feedback compensation unit is also stably arranged through the integral structure fixing part unit;
the external feedback compensation unit is a spherical structure with a coil wound on the surface; the external feedback compensation unit can generate a feedback magnetic field inside, shield environment interference fields such as external invalid geomagnetism and the like, and enable the internal optical fiber sensing unit to work in a near-zero magnetic environment, so that the measurement responsivity and the sensitivity of the low-frequency magnetic field to be measured are improved.
The internal optical fiber magnetic sensing unit comprises a plurality of magnetic sensing optical fibers, a modulation sensing structure and three optical fiber fixing circular plates, wherein the three optical fiber fixing circular plates comprise an upper optical fiber fixing circular plate, a middle optical fiber fixing circular plate and a lower optical fiber fixing circular plate, and the upper optical fiber fixing circular plate, the middle optical fiber fixing circular plate and the lower optical fiber fixing circular plate are arranged in the external feedback compensation unit in parallel from top to bottom;
the magnetic sensing optical fibers are arranged and fixed on the three optical fiber fixing circular plates, and the magnetic sensing optical fibers are spatially arranged to take the three optical fiber fixing circular plates as a placing platform to fix the internal optical fiber magnetic sensing unit; the magnetic sensing optical fiber is a single-wire double-sensing-part structure, each magnetic sensing optical fiber is provided with two modulation sensing structures, in order to realize simultaneous and independent measurement, the modulation sensing structures are wound with modulation coils at the peripheries, the modulation sensing structures realize modulation by winding the modulation coils at the peripheries, and two different modulation frequencies are applied to the two modulation sensing structures respectively, so that the two modulation sensing structures obtain the intensity and the frequency of magnetic field signals measured at two different positions near the different modulation frequencies of an output spectrum. Because the two modulation frequencies and the relative difference value are larger than the frequency of the external low-frequency magnetic field, the modulation magnetic field crosstalk between the two modulation frequencies can be effectively removed.
The method comprises the steps of arranging 5 same-kind magnetic sensing optical fibers, wherein each magnetic sensing optical fiber is provided with two sections of modulation sensing structures which are spaced at a certain distance, the two sections of modulation sensing structures of each magnetic sensing optical fiber are symmetrically arranged around a center, each section of modulation sensing structure can measure magnetic induction component values of the position of the modulation sensing structure along the axial direction of the modulation sensing structure, the two sections of modulation sensing structures on the same magnetic sensing optical fiber measure two magnetic field signal intensity values, the ratio of the difference value to the fixed position distance of the two modulation sensing structures on the magnetic sensing optical fiber approximates to obtain a group of gradient values at the center of an origin, so that 5 groups of gradient values of different magnetic induction components in different directions and different magnetic induction components can be obtained by the 5 magnetic sensing optical fibers, and the gradient tensor of an external field to be measured can be obtained after the 5 independent gradient elements of the tensor are respectively corresponding.
According to the invention, the internal optical fiber magnetic sensing unit comprises 5 magnetic sensing optical fibers; each magnetic sensing optical fiber is distributed along the coordinate axis of the rectangular coordinate system, the origin o of the rectangular coordinate system is superposed with the circle center of the middle-layer optical fiber fixing circular plate, the plane of the middle-layer optical fiber fixing circular plate is parallel to the xoy plane of the rectangular coordinate system, the x axis and the y axis are any two straight lines which pass through the origin o and are perpendicular to each other on the xoy plane, the z axis passes through the origin o and is perpendicular to the xoy plane, and the directions of the x axis, the y axis and the z axis accord with the right-hand rule;
three magnetic sensing optical fibers are distributed on the xoy plane, wherein a first magnetic sensing optical fiber is placed along the x axis, two modulation sensing structures on the first magnetic sensing optical fiber are symmetrical relative to the original point, and the direction of the modulation sensing structures is the same as the x axis; the second magnetic sensing optical fiber is placed along the y axis, two modulation sensing structures on the second magnetic sensing optical fiber are symmetrical about the origin, and the direction of the modulation sensing structures is the same as the y axis; the third magnetic sensing optical fiber is arranged along the y axis, the third magnetic sensing optical fiber is symmetrical about the x axis, a bulge is bent at the position close to the x axis, the direction of the bulge is opposite to the x axis, and two modulation sensing structures arranged at the bent position are symmetrical about the x axis; to achieve vertical placement, the optical fibers are placed in bends.
The fourth magnetic sensing optical fiber is arranged on a yoz plane, is placed along the z axis, is arranged on the plane where the upper layer optical fiber fixing circular plate is located, is parallel to the y axis, is bent to vertically penetrate through the middle layer optical fiber fixing circular plate to the plane where the lower layer optical fiber fixing circular plate is located, and the two arranged modulation sensing structures are symmetrical about the y axis; the fifth magnetic sensing optical fiber is arranged on the xoz plane, is placed along the z axis, is arranged on the plane where the upper layer optical fiber fixing circular plate is located, is parallel to the x axis, is bent to vertically penetrate through the middle layer optical fiber fixing circular plate to the plane where the lower layer optical fiber fixing circular plate is located, and the two arranged modulation sensing structures are symmetrical about the x axis; the remaining two magnetic sensing optical fibers are distributed on the z axis, the two sections of magnetic sensing structures of the magnetic sensing optical fibers are perpendicular to the z axis, the magnetic sensing optical fibers are placed on the upper surface of the upper layer circular plate and the upper surface of the lower layer circular plate, and the distance between the two surfaces is consistent with the distance between the sensing structures. Two groups of sensing structures of two optical fibers arranged along the z axis are arranged along the directions of the x axis and the y axis respectively, and the tail ends of the magnetic sensing structures are arranged above the z axis.
Each modulation sensing structure on each magnetic sensing optical fiber can respond to the change of the magnetic field along the axial direction, and is converted into a light intensity signal to be observed. Therefore, the difference value of the two measured intensity measurements and the distance between the two sensing structures can be used as a ratio by using a difference method, and the gradient value of the magnetic induction component at the central origin point is approximately obtained. Specifically, at the arrangement position of the magnetic sensing optical fiber, the magnetic induction intensity component B along the x-axis direction at two positions is obtained through two modulation sensing structures on the x-axisxx1And Bxx2The distance between the two modulation sensing structures is Deltax, so the B at the origin can be approximatedxGradient in the direction of the x-axis, i.e.
In a similar way, according to the placing position, B can be obtainedx、ByThe gradient along the y-axis and along the z-axis, so that 5 different components at the origin and gradients in different directions are obtained.
According to the present invention, preferably, the center distance between the two modulation sensing structures on each of the magnetic sensing fibers is equal, and the center distance between the two modulation sensing structures on each of the magnetic sensing fibers is 2 times that of each modulation sensing structure. Since the distance is used when the gradient value is obtained, and according to the concept of gradient, the gradient value is closer to the exact value at the origin when the distance is smaller, but the design of the mechanical structure needs to be considered at the same time, and therefore, it is necessary to optimally obtain the smallest distance while satisfying the installation requirement. The external feedback compensation unit needs to be designed according to the requirement of completely containing the sensing part, and the diameter of the external feedback compensation unit can be 3-4 times of the length of the modulation sensing structure.
According to the invention, the integral structure fixing part unit comprises a concave base, a plurality of screw rods and a plurality of nuts; the bottom of the external feedback compensation unit is fixed on the concave base through a plurality of screw rods and nuts in a matched mode, three optical fiber fixing circular plates penetrate through the plurality of screw rods and fix the positions of the three optical fiber fixing circular plates through the nuts, and a hole in the top of the external feedback compensation unit extends out of the plurality of screw rods and is fastened through the nuts.
According to the present invention, preferably, the upper optical fiber fixing circular plate, the middle optical fiber fixing circular plate and the lower optical fiber fixing circular plate are parallel to the ground, the middle optical fiber fixing circular plate passes through a sphere center of the external feedback compensation unit, the upper optical fiber fixing circular plate and the lower optical fiber fixing circular plate are symmetrically disposed, and a distance between two modulation sensing structures on each of the magnetic sensing fibers is equal to a distance between the upper optical fiber fixing circular plate and the lower optical fiber fixing circular plate.
The setting of above-mentioned position has guaranteed that two magnetism sensing structures on each magnetism sensing optical fiber can both have same distance value, because the gradient value of seeking is relevant with the difference and the distance of magnetic induction intensity component, and the distance keeps the same, can ensure that the gradient size is only determined by the magnetic induction intensity in the external magnetic field that awaits measuring, reduces the error, improves measurement accuracy.
According to the invention, preferably, grooves and small holes in rows are arranged at positions where the modulation sensing structures are arranged on the three optical fiber fixing circular plates, the grooves are used for integrally placing the modulation sensing structures, and the small holes in rows are used for penetrating and winding fastening belts or providing screw fixing holes for fastening clamps, so that the modulation sensing structures are fixed on the optical fiber fixing circular plates.
According to the invention, preferably, the external feedback compensation unit, the concave base, the screw rod and the nut are made of nonmagnetic materials.
Further preferably, the external feedback compensation unit and the concave base are made of PLA or ABS 3D printing materials; the screw rod and the nut are made of nylon materials.
According to the invention, preferably, the surface of the external feedback compensation unit is provided with a plurality of through holes for guiding the input and the output of the plurality of magnetic sensing optical fibers.
According to the optimization of the invention, the modulation sensing structure is based on an optical fiber sensing structure, a conical structure is drawn by removing a small segment of bare optical fiber of a cladding, magnetic fluid is filled outside and sealed, and a coil is wound outside a thin glass tube for sealing the magnetic fluid. The alternating magnetic field is generated when alternating current is introduced into the coil, the modulation sensing structure is modulated, the magnetic induction intensity and the magnetic induction intensity component along the axial direction of the magnetic sensing structure are mainly modulated, the low-frequency magnetic fields in other directions can be concentrated near low frequency, and the signals of the external low-frequency magnetic field to be detected which are consistent with the axial direction of the sensing structure can be modulated near modulation frequency, so that the directions of the collected magnetic field signals are ensured to be distinguished, and after different modulation frequencies are applied to the two modulation sensing structures, the magnetic field detection at two positions can be realized without mutual crosstalk.
The working method of the space magnetic gradient tensor measurement system based on the optical fiber magnetic field sensor comprises the following steps that each magnetic sensing optical fiber is connected with a light source outside the space magnetic gradient tensor measurement system, and a receiving end of each magnetic sensing optical fiber is connected with a photoelectric detector:
(1) after light passes through the modulation sensing structure, a light intensity signal modulated by a magnetic field is output, data acquisition and processing analysis are carried out at a receiving end of the magnetic sensing optical fiber, measurement signals acquired near two modulation frequencies on the same magnetic sensing optical fiber are obtained, and therefore the magnetic induction intensity at two positions is obtained;
(2) according to a theoretical method for calculating and obtaining magnetic gradient tensors, 5 groups of magnetic induction intensity values obtained by 5 magnetic sensing fibers are subjected to approximate gradient calculation through difference processing, and gradient values in 5 independent tensor matrixes are obtained; and substituting gradient values in 5 independent tensor matrixes into tensor operation to obtain the spatial magnetic gradient tensor.
Preferably, according to the present invention, in the step (2),
A. the gradient calculation of the approximation of difference processing is carried out on 5 groups of magnetic induction intensity values acquired by 5 magnetic sensitive fibers, and gradient values in 5 independent tensor matrixes are obtained
As shown in formulas (I) to (V):
in the formula (I), Bxx1、Bxx2The magnetic induction intensity component along the x-axis direction is measured by two modulation sensing structures on a first magnetic sensing optical fiber on the x-axis at the same time, and delta x is the distance between the two modulation sensing structures on the first magnetic sensing optical fiber; b isxxMeans the magnetic induction intensity component measured on the x-axis along the x-axisA magnitude;
in the formula (II), Bxy1、Bxy2The magnetic induction intensity component along the x-axis direction is measured by two modulation sensing structures on a third magnetic sensing optical fiber on the y-axis at the same time, and delta y is the distance between the two modulation sensing structures on the third magnetic sensing optical fiber; b isxyRefers to the magnetic induction component value measured on the y-axis along the x-axis direction;
in the formula (III), Bxz1、Bxz2The component of the magnetic induction intensity along the x-axis direction is measured by two modulation sensing structures on a fifth magnetic sensing optical fiber on the z-axis at the same time, and the delta z is the distance between the two modulation sensing structures on the fifth magnetic sensing optical fiber; b isxzRefers to the magnetic induction component value measured on the z-axis along the x-axis direction;
in the formula (IV), Byy1、Byy2The component of the magnetic induction intensity along the y-axis direction is measured by two modulation sensing structures on a second magnetic sensing optical fiber on the y-axis at the same time, and delta y is the distance between the two modulation sensing structures on the second magnetic sensing optical fiber; b isyyThe magnetic induction component value measured on the y axis along the y axis direction is referred to;
in the formula (V), Byz1、Byz2The magnetic induction intensity component along the y-axis direction is measured by two modulation sensing structures on the fourth magnetic sensing optical fiber on the z-axis at the same time, and the delta z is the distance between the two modulation sensing structures on the fourth magnetic sensing optical fiber; b isyzRefers to the magnetic induction component value measured on the z-axis along the y-axis direction;
B. the gradient values in 5 independent tensor matrixes are brought into tensor operation to obtain a spatial magnetic gradient tensor T, the spatial magnetic gradient tensor T is the spatial change rate of three components of a magnetic field vector in three mutually orthogonal directions, a magnetic field B is a vector field, and the spatial magnetic gradient tensor T is a form of multiplying two matrixes, and is shown in a formula (VI):
the derivation of formula (VI) is as follows:
The spatial magnetic gradient tensor T comprises 9 elements in total, no conduction current exists in a passive field, the divergence and the rotation of the magnetic induction intensity are zero,
and
namely:
only 5 elements are independent from each other, so the tensor can be obtained as long as 5 groups of independent gradient values are measured.
Under the arrangement of 5 magnetic sensing fibers, 5 groups of gradient values of different components in different directions can be obtained according to difference approximation.
Substituting 5 groups of gradient values obtained according to the arrangement of the magnetic sensing fibers into the tensor to obtain a magnetic gradient tensor of the space to be measured, wherein the magnetic gradient tensor represents the following steps:
the elements in the tensor matrix are obtained by measurement and calculation of the magnetic sensing structures on the arranged magnetic induction optical fibers, so that gradient tensor measurement can be realized.
The invention has the beneficial effects that:
1. the space magnetic gradient tensor measurement system based on the optical fiber magnetic field sensor is simple and convenient in structure and low in manufacturing cost. The whole structure is compact and fixed, the invention is based on the modulation sensing structure of the combination of the magnetic fluid and the optical fiber, is different from the structure formed by the exciting coil, the induction coil and the magnetic core in the fluxgate, only a small segment of cladding of the optical fiber is removed, the optical fiber is processed into a conical structure, and the magnetic fluid is wrapped and encapsulated at the periphery, so that the weight and the size are greatly improved, the weight and the size of the whole set of device are light, the size is small, and the device can be effectively integrated in most measuring and monitoring equipment.
2. The internal optical fiber magnetic sensing unit realizes the distribution multiplexing of optical fiber measurement, is convenient to construct a measurement network and can realize multi-point synchronous monitoring.
3. The external optical fiber magnetic field sensor has the advantages of electromagnetic interference resistance, good insulativity, high measurement sensitivity and the like, and the external feedback compensation part can effectively shield geomagnetic interference and can be suitable for magnetic field measurement in a complex environment.
4. The magnetic field measurement at two positions of the invention can be simultaneously measured by two sections of conical structures with different distances on the same optical fiber, and only different modulation frequencies are applied to the outer parts of the two sections to separate two measurement signals on a frequency domain. And the two fluxgate sensors are used for realizing magnetic field measurement at different positions, so that more output signals are output, multi-channel acquisition is required, the power consumption of the system is increased, and the effectiveness is reduced.
5. The fluxgate sensor works based on the electrical principle and transmits the measured magnetic induction intensity signal through the electric signal, so that the fluxgate sensor is easily interfered by external strong electromagnetic, the integrity of the signal is damaged, and the readability of the signal is reduced.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a spatial magnetic gradient tensor measurement system based on a fiber-optic magnetic field sensor according to the present invention;
FIG. 2 is a schematic structural diagram of a modulation sensing structure in a magnetic sensing optical fiber according to the present invention;
fig. 3 is a frequency modulation effect diagram of the modulation sensing structure of the present invention.
1. The device comprises an external feedback compensation unit 2, an optical fiber fixing circular plate 3, a magnetic sensing optical fiber 4, a modulation sensing structure 5, a nut 6, a screw rod 7 and a concave base.
Detailed Description
The invention is further defined in the following, but not limited to, the figures and examples in the description.
Example 1
A space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor is shown in figure 1 and comprises an external feedback compensation unit 1, an internal optical fiber magnetic sensing unit and an integral structure fixing component unit;
the internal optical fiber magnetic sensing unit is fixedly arranged in the external feedback compensation unit 1 through the integral structure fixing part unit, and the external feedback compensation unit 1 is also stably arranged through the integral structure fixing part unit;
the external feedback compensation unit 1 is a spherical structure with a coil wound on the surface; the method comprises the following steps that an existing magnetic field feedback ball is adopted, and three enamelled wire winding grooves which are parallel to a Cartesian coordinate system in the direction, are vertically crossed, are equal in width, unequal in depth and equal in spacing distribution are formed in the outer surface of a spherical non-conductive material; the external feedback compensation unit 1 can generate a feedback magnetic field inside, shield environment interference fields such as external invalid geomagnetism and the like, and enable the internal optical fiber sensing unit to work in a near-zero magnetic environment, so that the measurement responsivity and the sensitivity of the low-frequency magnetic field to be measured are improved.
The internal optical fiber magnetic sensing unit comprises a plurality of magnetic sensing optical fibers 3, a modulation sensing structure 4 and three optical fiber fixing circular plates 2, wherein the three optical fiber fixing circular plates 2 comprise an upper optical fiber fixing circular plate, a middle optical fiber fixing circular plate and a lower optical fiber fixing circular plate, and the upper optical fiber fixing circular plate, the middle optical fiber fixing circular plate and the lower optical fiber fixing circular plate are arranged in the external feedback compensation unit 1 in parallel from top to bottom;
the upper optical fiber fixing circular plate, the middle optical fiber fixing circular plate and the lower optical fiber fixing circular plate are parallel to the ground, the middle optical fiber fixing circular plate penetrates through the spherical center of the external feedback compensation unit 1, the upper optical fiber fixing circular plate and the lower optical fiber fixing circular plate are symmetrically arranged, and the distance between the two modulation sensing structures 4 on each magnetic sensing optical fiber 3 is equal to the distance between the upper optical fiber fixing circular plate and the lower optical fiber fixing circular plate.
The setting of above-mentioned position has guaranteed that two magnetism sensing structures on each magnetism sensing optical fiber 3 can both have same distance value, because the gradient value of seeking is relevant with the difference and the distance of magnetic induction intensity component, and the distance keeps the same, can ensure that the gradient size is only determined by the magnetic induction intensity in the external magnetic field that awaits measuring, reduces the error, improves measurement accuracy.
A plurality of magnetic sensing optical fibers 3 are arranged and fixed on the three optical fiber fixing circular plates 2, and the magnetic sensing optical fibers 3 are spatially arranged and use the three optical fiber fixing circular plates 2 as a placing platform to fix the internal optical fiber magnetic sensing unit; the magnetic sensing optical fiber 3 is a single-wire double-sensing-part structure, two modulation sensing structures 4 are arranged on each magnetic sensing optical fiber 3, in order to realize simultaneous and independent measurement, a modulation coil is wound on the periphery of each modulation sensing structure 4, the modulation sensing structures 4 realize modulation by winding the modulation coil on the periphery, and two different modulation frequencies are respectively applied to the two modulation sensing structures 4, so that the two modulation sensing structures 4 obtain the intensity and the frequency of magnetic field signals measured at two different positions near the different modulation frequencies of an output spectrum. Because the two modulation frequencies and the relative difference value are larger than the frequency of the external low-frequency magnetic field, the modulation magnetic field crosstalk between the two modulation frequencies can be effectively removed.
5 same-kind magnetic sensing optical fibers 3 are arranged, two sections of modulation sensing structures 4 with certain distance are arranged on each magnetic sensing optical fiber 3, the two sections of modulation sensing structures 4 of each magnetic sensing optical fiber 3 are symmetrically arranged around the center, each section of modulation sensing structure 4 can measure the magnetic induction component value along the axial direction of the modulation sensing structure 4 at the position, two sections of modulation sensing structures 4 on the same magnetic sensing optical fiber 3 measure two magnetic field signal intensity values, the ratio of the difference value to the position distance of the two modulation sensing structures 4 on the magnetic sensing optical fiber 3 after being fixed is approximate to obtain a gradient value at the center of a group of origin points, therefore, 5 magnetic sensing fibers 3 can respectively obtain 5 groups of gradient values of magnetic induction components in different directions and different magnetic induction intensity components, and the gradient tensor of the external field to be measured can be obtained after the gradient values respectively correspond to 5 independent gradient elements of the tensor.
The internal optical fiber magnetic sensing unit comprises 5 magnetic sensing optical fibers 3; each magnetic sensing fiber 3 is distributed along the coordinate axis of the rectangular coordinate system, the origin o of the rectangular coordinate system coincides with the center of the middle layer fiber fixed circular plate, and the plane of the middle layer fiber fixed circular plate is parallel to the xoy plane of the rectangular coordinate system, as shown in fig. 1. The x axis and the y axis are any two straight lines which pass through the original point o on the xoy plane and are perpendicular to each other, the z axis passes through the original point o and is perpendicular to the xoy plane, and the directions of the x axis, the y axis and the z axis accord with the right-hand rule;
three magnetic sensing optical fibers 3 are arranged on the xoy plane, wherein a first magnetic sensing optical fiber is arranged along the x axis, two modulation sensing structures 4 on the first magnetic sensing optical fiber are symmetrical relative to the original point, and the direction of the modulation sensing structures 4 is the same as the x axis; the second magnetic sensing optical fiber is placed along the y axis, the two modulation sensing structures 4 on the second magnetic sensing optical fiber are symmetrical about the origin, and the direction of the modulation sensing structures 4 is the same as the y axis; the third magnetic sensing optical fiber is arranged along the y axis, the third magnetic sensing optical fiber is symmetrical about the x axis, a bulge is bent at the position close to the x axis, the direction of the bulge is opposite to the x axis, and the two modulation sensing structures 4 arranged at the bent position are symmetrical about the x axis; to achieve vertical placement, the optical fibers are placed in bends.
The fourth magnetic sensing optical fiber is arranged on a yoz plane, is arranged along the z axis, is arranged on the plane where the upper layer optical fiber fixing circular plate is located, is parallel to the y axis, is bent to vertically penetrate through the middle layer optical fiber fixing circular plate to the plane where the lower layer optical fiber fixing circular plate is located, and is provided with two modulation sensing structures 4 which are symmetrical about the y axis; the fifth magnetic sensing optical fiber is arranged on the xoz plane, is placed along the z-axis, is arranged on the plane where the upper layer optical fiber fixing circular plate is located, is parallel to the x-axis, is bent to vertically penetrate through the middle layer optical fiber fixing circular plate to the plane where the lower layer optical fiber fixing circular plate is located, and the two arranged modulation sensing structures 4 are symmetrical about the x-axis; the remaining two magnetic sensing fibers 3 are distributed on the z-axis, the two sections of magnetic sensing structures of the magnetic sensing fibers are perpendicular to the z-axis direction, the magnetic sensing structures are placed on the upper surface of the upper layer circular plate and the upper surface of the lower layer circular plate, and the distance between the two surfaces is consistent with the distance between the sensing structures. Two groups of sensing structures of two optical fibers arranged along the z axis are arranged along the directions of the x axis and the y axis respectively, and the tail ends of the magnetic sensing structures are arranged above the z axis.
Each modulation sensing structure 4 on each magnetic sensing fiber 3 can respond to the change of the magnetic field along the axial direction and is converted into a light intensity signal to be observed. Therefore, the magnitude of the magnetic induction component along the axial direction of the modulation sensing structure 4 is obtained, and the two modulation sensing structures 4 on one magnetic sensing optical fiber 3 can measure magnetic field signals at two different positions but with the same magnetic induction component direction, so that a difference value of the two measured intensity components can be used by using a difference method, and a ratio can be made between the difference value and the distance between the two sensing structures, and the gradient value of the magnetic induction component at the central origin point is approximately obtained. Specifically, at the arrangement position of the magnetic sensing fiber 3, the magnetic induction intensity component B along the x-axis direction at two positions is obtained through two modulation sensing structures 4 on the x-axisxx1And Bxx2The distance between the two modulation sensing structures 4 is Δ x, so that the original point B can be approximatedxGradient in the direction of the x-axis, i.e.
In a similar way, according to the placing position, B can be obtainedx、ByThe gradient along the y-axis and along the z-axis, so that 5 different components at the origin and gradients in different directions are obtained.
Example 2
The system for measuring the spatial magnetic gradient tensor based on the optical fiber magnetic field sensor in the embodiment 1 is characterized in that:
the center distance between the two modulation sensing structures 4 on each magnetic sensing fiber 3 is equal, and the center distance between the two modulation sensing structures 4 on each magnetic sensing fiber 3 is 2 times that of each modulation sensing structure 4. Since the distance is used when the gradient value is obtained, and according to the concept of gradient, the gradient value is closer to the exact value at the origin when the distance is smaller, but the design of the mechanical structure needs to be considered at the same time, and therefore, it is necessary to optimally obtain the smallest distance while satisfying the installation requirement. The external feedback compensation unit 1 needs to be designed according to the requirement of completely containing the sensing part, and the diameter of the external feedback compensation unit can be 3-4 times of the length of the modulation sensing structure 4.
Example 3
The system for measuring the spatial magnetic gradient tensor based on the optical fiber magnetic field sensor in the embodiment 2 is characterized in that:
the whole structure fixing part unit comprises a concave base 7, a plurality of screw rods 6 and a plurality of nuts 5; the bottom of the external feedback compensation unit 1 is fixed on the concave base 7 through the matching of a plurality of screws 6 and nuts 5, the three optical fiber fixing circular plates 2 are inserted through the plurality of screws 6 and the positions of the three optical fiber fixing circular plates 2 are fixed through the nuts 5, and the top opening of the external feedback compensation unit 1 extends out of the plurality of screws 6 and is fastened through the nuts 5.
Example 4
A system for fiber optic magnetic field sensor based spatial magnetic gradient tensor measurement according to embodiments 1-3, the difference being that:
the position department that is provided with modulation sensing structure 4 on three optic fibre fixed circular plate 2 is provided with the recess and arranges the aperture to, and the recess is used for wholly placing modulation sensing structure 4, arranges the aperture to be used for wearing around the fastening band or provide the screw fixed orifices for the fastening clamp, makes modulation sensing structure 4 be fixed in on optic fibre fixed circular plate 2.
The external feedback compensation unit 1, the concave base 7, the screw 6 and the nut 5 are made of nonmagnetic materials. The external feedback compensation unit 1 and the concave base 7 are made of PLA or ABS 3D printing materials; the screw rod 6 and the nut 5 are made of nylon materials.
The surface of the external feedback compensation unit 1 is provided with a plurality of through holes for guiding the input and the output of a plurality of magnetic sensing optical fibers 3.
As shown in fig. 2, the modulation sensing structure 4 is manufactured by removing a small segment of bare fiber from a cladding, drawing a tapered structure, filling and sealing a magnetic fluid outside, and winding a coil outside a thin glass tube for sealing the magnetic fluid, based on the optical fiber sensing structure. Produce alternating magnetic field when the coil lets in the alternating current, modulate modulation sensing structure 4, mainly be along magnetic induction and the magnetic induction component of magnetic sensing structure axial modulate, this can concentrate the low frequency magnetic field of other directions near the low frequency, and the signal of the external low frequency magnetic field that awaits measuring that is unanimous with sensing structure axial can be modulated near modulation frequency, consequently, the direction of the magnetic field signal of ensureing to distinguish the collection, and behind two modulation sensing structure 4 applys different modulation frequencies, can realize the magnetic field of two positions and survey and can not crosstalk each other. As shown in fig. 3, the abscissa represents the modulation signal in Hz and the ordinate represents the output power; the modulation sensing structure 4 can respond to the change of a magnetic field, converts the change into a light intensity signal, transmits the light intensity signal through the magnetic sensing optical fiber 3, is connected to a detector for displaying, a modulation coil of the modulation sensing structure 4 can apply different frequency modulations f1 and f2 to two signals detected by two sections of modulation sensing structures 4 on the same magnetic sensing optical fiber 3 respectively, can perform modulation frequency shift on magnetic field frequencies fc1 and fc2 detected by the two sections of modulation sensing structures respectively, can distinguish the two detection signals at a detection end conveniently, analyzes and calculates the magnitude of two magnetic field strengths, and obtains a ratio of a difference value to the placement distance of the two modulation sensing structures 4 to obtain an approximate gradient value of a magnetic induction component.
Example 5
Embodiment 1-4 is a working method of a space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor, where each magnetic sensing optical fiber 3 is connected to a light source outside the space magnetic gradient tensor measurement system, and a receiving end of each magnetic sensing optical fiber 3 is connected to a photodetector, including the steps of:
(1) after light passes through the modulation sensing structure 4, a light intensity signal modulated by a magnetic field is output, data acquisition and processing analysis are carried out at a receiving end of the magnetic sensing optical fiber 3, measurement signals acquired near two modulation frequencies on the same magnetic sensing optical fiber 3 are obtained, and therefore magnetic induction intensities at two positions are obtained;
(2) according to a theoretical method for calculating and obtaining the magnetic gradient tensor, 5 groups of magnetic induction intensity values obtained by 5 magnetic sensitive fibers 3 are subjected to approximate gradient calculation of difference processing to obtain gradient values in 5 independent tensor matrixes; and substituting gradient values in 5 independent tensor matrixes into tensor operation to obtain the spatial magnetic gradient tensor.
The step (2) comprises the following steps:
A. the gradient calculation of the approximation of difference processing is carried out on 5 groups of magnetic induction intensity values acquired by 5 magnetic sensitive fibers 3, and gradient values in 5 independent tensor matrixes are obtained
As shown in formulas (I) to (V):
in the formula (I), Bxx1、Bxx2The magnetic induction intensity component along the x-axis direction is measured by two modulation sensing structures 4 on a first magnetic sensing optical fiber on the x-axis at the same time, and deltax is the distance between the two modulation sensing structures 4 on the first magnetic sensing optical fiber; b isxxRefers to the magnetic induction component value measured on the x-axis along the x-axis direction;
in the formula (II), Bxy1、Bxy2Is measured by two modulation sensing structures 4 on the third magnetic sensing optical fiber on the y axis simultaneouslyThe magnetic induction intensity component along the x-axis direction, and Δ y is the distance between the two modulation sensing structures 4 on the third magnetic sensing fiber; b isxyRefers to the magnetic induction component value measured on the y-axis along the x-axis direction;
in the formula (III), Bxz1、Bxz2The component of the magnetic induction intensity along the x-axis direction is measured by two modulation sensing structures 4 on a fifth magnetic sensing optical fiber on the z-axis at the same time, and Δ z is the distance between the two modulation sensing structures 4 on the fifth magnetic sensing optical fiber; b isxzRefers to the magnetic induction component value measured on the z-axis along the x-axis direction;
in the formula (IV), Byy1、Byy2The component of the magnetic induction intensity along the y-axis direction is measured by two modulation sensing structures 4 on a second magnetic sensing optical fiber on the y-axis at the same time, and Δ y is the distance between the two modulation sensing structures 4 on the second magnetic sensing optical fiber; b isyyThe magnetic induction component value measured on the y axis along the y axis direction is referred to;
in the formula (V), Byz1、Byz2The magnetic induction intensity component along the y-axis direction is measured by two modulation sensing structures 4 on the fourth magnetic sensing optical fiber on the z-axis at the same time, and the delta z is the distance between the two modulation sensing structures 4 on the fourth magnetic sensing optical fiber; b isyzRefers to the magnetic induction component value measured on the z-axis along the y-axis direction;
B. the gradient values in 5 independent tensor matrixes are brought into tensor operation to obtain a spatial magnetic gradient tensor T, the spatial magnetic gradient tensor T is the spatial change rate of three components of a magnetic field vector in three mutually orthogonal directions, a magnetic field B is a vector field, and the spatial magnetic gradient tensor T is a form of multiplying two matrixes, and is shown in a formula (VI):
the derivation of formula (VI) is as follows:
The spatial magnetic gradient tensor T comprises 9 elements in total, no conduction current exists in a passive field, the divergence and the rotation of the magnetic induction intensity are zero,
and
namely:
only 5 elements are independent from each other, so the tensor can be obtained as long as 5 groups of independent gradient values are measured.
With the arrangement of 5 magnetically sensitive fibers 3, 5 sets of gradient values of different components in different directions can be derived from the difference approximation.
Substituting 5 groups of gradient values obtained by the arrangement of the magnetic sensing optical fibers 3 into the tensor to obtain a magnetic gradient tensor of the space to be measured, wherein the magnetic gradient tensor represents the following steps:
the elements in the tensor matrix are obtained by measurement and calculation of the magnetic sensing structures on the arranged magnetic induction optical fibers, so that gradient tensor measurement can be realized.
Claims (11)
1. A space magnetic gradient tensor measurement system based on an optical fiber magnetic field sensor is characterized by comprising an external feedback compensation unit, an internal optical fiber magnetic sensing unit and an integral structure fixing component unit;
the internal optical fiber magnetic sensing unit is fixedly arranged in the external feedback compensation unit through the integral structure fixing part unit, and the external feedback compensation unit is also stably arranged through the integral structure fixing part unit;
the external feedback compensation unit is a spherical structure with a coil wound on the surface;
the internal optical fiber magnetic sensing unit comprises a plurality of magnetic sensing optical fibers, a modulation sensing structure and three optical fiber fixing circular plates, wherein the three optical fiber fixing circular plates comprise an upper optical fiber fixing circular plate, a middle optical fiber fixing circular plate and a lower optical fiber fixing circular plate, and the upper optical fiber fixing circular plate, the middle optical fiber fixing circular plate and the lower optical fiber fixing circular plate are arranged in the external feedback compensation unit in parallel from top to bottom; the magnetic sensing optical fibers are arranged and fixed on the three optical fiber fixing circular plates, two modulation sensing structures are arranged on each magnetic sensing optical fiber, modulation coils are wound on the peripheries of the modulation sensing structures, the modulation sensing structures realize modulation by winding the modulation coils on the peripheries, and two different modulation frequencies are applied to the two modulation sensing structures respectively, so that the two modulation sensing structures obtain the intensity and the frequency of magnetic field signals measured at two different positions near the different modulation frequencies of the output spectrum.
2. The system according to claim 1, wherein the internal fiber magnetic sensing unit comprises 5 magnetic sensing fibers; each magnetic sensing optical fiber is distributed along the coordinate axis of the rectangular coordinate system, the origin o of the rectangular coordinate system is superposed with the circle center of the middle-layer optical fiber fixing circular plate, the plane of the middle-layer optical fiber fixing circular plate is parallel to the xoy plane of the rectangular coordinate system, the x axis and the y axis are any two straight lines which pass through the origin o and are perpendicular to each other on the xoy plane, and the z axis passes through the origin o and is perpendicular to the xoy plane;
three magnetic sensing optical fibers are distributed on the xoy plane, wherein a first magnetic sensing optical fiber is placed along the x axis, two modulation sensing structures on the first magnetic sensing optical fiber are symmetrical relative to the original point, and the direction of the modulation sensing structures is the same as the x axis; the second magnetic sensing optical fiber is placed along the y axis, two modulation sensing structures on the second magnetic sensing optical fiber are symmetrical about the origin, and the direction of the modulation sensing structures is the same as the y axis; the third magnetic sensing optical fiber is arranged along the y axis, the third magnetic sensing optical fiber is symmetrical about the x axis, a bulge is bent at the position close to the x axis, the direction of the bulge is opposite to the x axis, and two modulation sensing structures arranged at the bent position are symmetrical about the x axis;
the fourth magnetic sensing optical fiber is arranged on a yoz plane, is placed along the z axis, is arranged on the plane where the upper layer optical fiber fixing circular plate is located, is parallel to the y axis, is bent to vertically penetrate through the middle layer optical fiber fixing circular plate to the plane where the lower layer optical fiber fixing circular plate is located, and the two arranged modulation sensing structures are symmetrical about the y axis; and the fifth magnetic sensing optical fiber is arranged on the xoz plane, is placed along the z axis, is arranged on the plane where the upper-layer optical fiber fixing circular plate is located, is parallel to the x axis, is bent to vertically penetrate through the middle-layer optical fiber fixing circular plate to the plane where the lower-layer optical fiber fixing circular plate is located, and is symmetrical about the x axis.
3. The system for measuring the spatial magnetic gradient tensor based on the fiber-optic magnetic field sensor as recited in claim 1, wherein the modulation sensing structure is manufactured by removing a small segment of bare fiber of a cladding to draw a conical structure, filling and sealing a magnetic fluid outside the conical structure, and winding a coil outside a thin glass tube for sealing the magnetic fluid;
the central distance between the two modulation sensing structures on each magnetic sensing optical fiber is equal, and the central distance between the two modulation sensing structures on each magnetic sensing optical fiber is 2 times that of each modulation sensing structure.
4. The system for measuring the spatial magnetic gradient tensor based on the fiber-optic magnetic field sensor is characterized in that the integral structure fixing component unit comprises a concave base, a plurality of screw rods and a plurality of nuts; the bottom of the external feedback compensation unit is fixed on the concave base through a plurality of screw rods and nuts in a matched mode, three optical fiber fixing circular plates penetrate through the plurality of screw rods and fix the positions of the three optical fiber fixing circular plates through the nuts, and a hole in the top of the external feedback compensation unit extends out of the plurality of screw rods and is fastened through the nuts.
5. The system according to claim 1, wherein the upper, middle and lower optical fiber fixing circular plates are parallel to the ground, the middle optical fiber fixing circular plate passes through a center of sphere of the external feedback compensation unit, the upper and lower optical fiber fixing circular plates are symmetrically disposed, and a distance between two modulation sensing structures on each magnetic sensing fiber is equal to a distance between the upper and lower optical fiber fixing circular plates.
6. The system according to claim 1, wherein a groove and a pair of small holes are formed at a position where the modulation sensing structure is disposed on three optical fiber fixing circular plates, the groove is used for integrally placing the modulation sensing structure, and the pair of small holes are used for penetrating a fastening belt or providing screw fixing holes for a fastening clip, so that the modulation sensing structure is fixed on the optical fiber fixing circular plates.
7. The system of claim 1, wherein the external feedback compensation unit, the concave base, the screw and the nut are made of nonmagnetic materials.
8. The system according to claim 7, wherein the external feedback compensation unit and the concave base are made of PLA or ABS 3D printing materials; the screw rod and the nut are made of nylon materials.
9. The system for measuring the spatial magnetic gradient tensor based on the optical fiber magnetic field sensor as recited in claim 1, wherein a plurality of through holes for guiding the input and the output of a plurality of magnetic sensing optical fibers are arranged on the surface of the external feedback compensation unit.
10. The method for operating the system for measuring the spatial magnetic gradient tensor based on the fiber-optic magnetic field sensor as recited in any one of claims 2 to 9, wherein each magnetic sensing fiber is connected with a light source outside the system for measuring the spatial magnetic gradient tensor, and a receiving end of each magnetic sensing fiber is connected with a photoelectric detector, comprising the following steps:
(1) after light passes through the modulation sensing structure, a light intensity signal modulated by a magnetic field is output, data acquisition and processing analysis are carried out at a receiving end of the magnetic sensing optical fiber, measurement signals acquired near two modulation frequencies on the same magnetic sensing optical fiber are obtained, and therefore the magnetic induction intensity at two positions is obtained;
(2) according to a theoretical method for calculating and obtaining magnetic gradient tensors, 5 groups of magnetic induction intensity values obtained by 5 magnetic sensing fibers are subjected to approximate gradient calculation through difference processing, and gradient values in 5 independent tensor matrixes are obtained; and substituting gradient values in 5 independent tensor matrixes into tensor operation to obtain the spatial magnetic gradient tensor.
11. The method for operating the fiber-optic magnetic field sensor-based spatial magnetic gradient tensor measurement system according to claim 10, wherein the step (2) includes the steps of:
A. the gradient calculation of the approximation of difference processing is carried out on 5 groups of magnetic induction intensity values acquired by 5 magnetic sensitive fibers, and gradient values in 5 independent tensor matrixes are obtained
As shown in formulas (I) to (V):
in the formula (I), Bxx1、Bxx2The magnetic induction intensity component along the x-axis direction is measured by two modulation sensing structures on a first magnetic sensing optical fiber on the x-axis at the same time, and delta x is the distance between the two modulation sensing structures on the first magnetic sensing optical fiber; b isxxRefers to the magnetic induction component value measured on the x-axis along the x-axis direction;
in the formula (II), Bxy1、Bxy2The magnetic induction intensity component along the x-axis direction is measured by two modulation sensing structures on a third magnetic sensing optical fiber on the y-axis at the same time, and delta y is the distance between the two modulation sensing structures on the third magnetic sensing optical fiber; b isxyRefers to the magnetic induction component value measured on the y-axis along the x-axis direction;
in the formula (III), Bxz1、Bxz2The component of the magnetic induction intensity along the x-axis direction is measured by two modulation sensing structures on a fifth magnetic sensing optical fiber on the z-axis at the same time, and the delta z is the distance between the two modulation sensing structures on the fifth magnetic sensing optical fiber;Bxzrefers to the magnetic induction component value measured on the z-axis along the x-axis direction;
in the formula (IV), Byy1、Byy2The component of the magnetic induction intensity along the y-axis direction is measured by two modulation sensing structures on a second magnetic sensing optical fiber on the y-axis at the same time, and delta y is the distance between the two modulation sensing structures on the second magnetic sensing optical fiber; b isyyThe magnetic induction component value measured on the y axis along the y axis direction is referred to;
in the formula (V), Byz1、Byz2The magnetic induction intensity component along the y-axis direction is measured by two modulation sensing structures on the fourth magnetic sensing optical fiber on the z-axis at the same time, and the delta z is the distance between the two modulation sensing structures on the fourth magnetic sensing optical fiber; b isyzRefers to the magnetic induction component value measured on the z-axis along the y-axis direction;
B. the gradient values in 5 independent tensor matrixes are brought into tensor operation to obtain a spatial magnetic gradient tensor T, the spatial magnetic gradient tensor T is the spatial change rate of three components of a magnetic field vector in three mutually orthogonal directions, a magnetic field B is a vector field, and the spatial magnetic gradient tensor T is a form of multiplying two matrixes, and is shown as a formula (VI):
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