CN-122018015-A - Magnetic detection method based on scalar gradient

CN122018015ACN 122018015 ACN122018015 ACN 122018015ACN-122018015-A

Abstract

The invention provides a magnetic detection method based on scalar gradients, relates to the technical field of magnetic positioning, and solves the problems that the traditional scalar magnetic detection has large positioning error, the effective detection distance of tensor magnetic detection is short, and the magnetic moment direction and the geomagnetic field direction are strictly coincident as required by the traditional scalar gradient method. The invention adopts the magnetic sensor array to collect the scalar intensity of the magnetic field and obtain the scalar gradient, equivalent the remote magnetic target as the magnetic dipole deduction modeling, solves the unit direction vector of the target pointing to the sensor, solves the distance by the dual-measuring point simultaneous geometric equation, determines the target position by pseudo-solving and screening, does not need the magnetic moment to be in the same direction as the geomagnetic field, and takes the detection distance and the positioning precision into account. The invention effectively gives consideration to the effective distance and positioning precision of magnetic detection, overcomes the contradiction of large error of the traditional scalar method and short detection distance of tensor method, does not need strict same direction of magnetic moment and geomagnetic field, ensures positioning precision by means of pseudo-screening, and improves robustness and practical detection applicability in complex magnetic field environment.

Inventors

LIN SHENGXIN
SUN LEYANG
LIU YUNTAO
LI GE
JIN YINXI
PAN DONGHUA
LI LIYI

Assignees

哈尔滨工业大学

Dates

Publication Date: 20260512
Application Date: 20260408

Claims (10)

1. A magnetic detection method based on scalar gradients, comprising the steps of: S1, acquiring magnetic scalar intensities of magnetic field at multiple points on a coordinate axis by utilizing a magnetic sensor array, and acquiring magnetic scalar gradient information by using difference instead of differentiation; S2, based on the scalar gradient information of the magnetic field, decomposing the position information of the magnetic target into direction information and distance information, and resolving to obtain a unit direction vector which points to the magnetic sensor array from the magnetic target; S3, moving the magnetic sensor array to another measuring point, repeating the step S2, obtaining two groups of unit direction vectors, solving the distance between the magnetic target and the sensor array by using a simultaneous geometrical equation, and determining the space position coordinates of the magnetic target by combining the unit direction vectors and the distance; And S4, screening the pseudo solution generated by the solution to obtain a true and effective solution, and then completing positioning.
2. The scalar gradient-based magnetic detection method according to claim 1, wherein in S1, when the detection distance is greater than 3 times of the size of the magnetic target itself, the magnetic target is equivalent to a magnetic dipole, a space rectangular coordinate system is established with the magnetic dipole as an origin, and the magnetic induction intensity B o of the magnetic target is calculated according to a magnetic dipole model: (1) Wherein B o is a magnetic induction vector generated by a magnetic dipole model at a detection point, mu 0 is vacuum magnetic permeability, the value of the vacuum magnetic permeability is 4pi× -7 H/M, M is a magnetic moment vector of the magnetic dipole, r is a position vector pointing to the detection point from the magnetic dipole, r is a distance from the magnetic dipole to the detection point, Taking a mould of the formula (1) to obtain: (2) wherein M is the magnitude of the magnetic moment vector M, and the vector angle phi is the angle between the magnetic moment vector M and the position vector r.
3. The scalar gradient-based magnetic detection method according to claim 2, wherein in S1, the total magnetic field B t measured by the magnetic sensor array during magnetic target detection in the presence of the geomagnetic field background is the result of superposition of the magnetic dipole magnetic field vector B o and the geomagnetic field vector B e , (3) And simultaneously taking the modulus value of two sides to obtain: (4) taylor expansion is performed on the formula (4) to obtain: (5) the modulus of the geomagnetic field vector B e is about 0.5-0.6 Gauss, which is far greater than the magnetic field strength of the magnetic dipole.
4. A scalar gradient based magnetic detection method according to claim 3, wherein in S1, the third term in equation (5) is ignored while the second term is expanded to obtain: (6) Wherein ,r 0 =(r x ,r y ,r z ) T 、m 0 =(m x ,m y ,m z ) T 、e 0 =(e x ,e y ,e z ) T are the unit vector of the detection position vector, the unit vector of the magnetic dipole moment and the unit vector of the geomagnetic field respectively, The magnetic moment direction in the formula (6) is approximated to the geomagnetic field direction, and is simplified as: (7) And (3) making: (8) wherein θ is the included angle between the direction of the magnetic target and the geomagnetic field direction.
5. The scalar gradient-based magnetic detection method according to claim 4, wherein in S2, the formula (7) and the formula (8) are combined, and the formula (7) is derived: (9) (10) Wherein T represents the magnetic field gradient of the spatial position of the magnetic target, The direction vector r 0 is obtained by changing the formula (10): (11)。
6. The scalar gradient-based magnetic detection method according to claim 5, wherein in S3, the sum of the left and right of equation (11) and the geomagnetic field direction unit vector e 0 is obtained by: (12) Equation (12) is a nonlinear equation containing only one unknown amount cos theta, wherein alpha is the included angle between the gradient vector T and the geomagnetic field vector e, the value range of cos alpha is [ -1,1], when the value of cos alpha changes, the nonlinear equation has three solutions in the range and corresponds to three different cos theta values respectively, the three solutions are replaced to equation (11) to obtain three corresponding direction vectors r 0 pointing to the magnetic sensor array, wherein two solutions have no practical meaning in physics, belong to pseudo solutions and need to be removed through proper mathematical or physical constraint, In addition, a single measuring point is solved to obtain a direction vector of a magnetic target, the magnetic sensor is moved to another measuring point in space, the calculation flow is repeated, another group of direction vectors corresponding to the measuring point is solved to obtain, and then an equation set is constructed as follows: (13) Based on the two sets of direction vectors, constructing a geometric relation shown in the formula (13), solving the distance between the magnetic target and the sensor array, and combining the distance with the corresponding direction vector, namely determining the spatial position coordinate r 1 of the magnetic target by taking the magnetic sensor array as an origin: (14) Wherein r 1 is the distance from the first measuring point to the magnetic target in the formula (13), and u 10 is the unit direction vector pointing from the magnetic target to the first measuring point of the sensor in the formula (11).
7. The scalar gradient based magnetic detection method of claim 6, wherein in S4, for the existing pseudo solution problem in equation (11), the pseudo solution screening mechanism is: Firstly, substituting three results solved by the formula (12) into the formula (11), solving to obtain three unit direction vectors r 0 , and extracting the z coordinate component of each vector; At this time, the number of vectors N with the z coordinate smaller than 0 is only two, namely N=1 or N=2, if N=1, the unit direction vector is directly determined as an effective solution, if N=2, the two-point positioning method is first expanded into a track positioning method, distance data sets A and B are constructed, standard deviations sigma 1 and sigma 2 of the two sets of data are respectively calculated, and the unit direction vector corresponding to a data set with smaller standard deviation is selected as a correct solution; Finally, based on the correct direction vector obtained by screening, the final positioning calculation is completed by combining the formula (13) and the formula (14), Wherein, the data set A, B = { r 12 ,r 23 ,r 34 ,…,r ij }, j = i+1}, i represents the ith magnetic sensor array measurement point, j represents the (i+1) th magnetic sensor array measurement point, and r ij represents the magnetic target distance obtained by the combined measurement of the ith magnetic sensor array measurement point and the jth magnetic sensor array measurement point.
8. A computer program product comprising computer program/instructions which, when executed by a processor, implements the scalar gradient based magnetic detection method of any of claims 1-7.
9. A storage medium having stored thereon a computer program, which when executed by a processor implements the scalar gradient based magnetic detection method of any of claims 1-7.
10. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor executing the program to implement the scalar gradient based magnetic detection method of any of claims 1-7.

Description

Magnetic detection method based on scalar gradient Technical Field The invention relates to the technical field of magnetic positioning, in particular to a magnetic detection method based on scalar gradient. Background The magnetic detection method is a target detection technology based on magnetic field measurement, has the advantages of high sensitivity, quick response, non-contact measurement and the like, and has unique value and application potential in multiple fields of national defense safety, resource exploration, environment monitoring and the like. When the underwater vehicle or the underground unexplosive object is detected, compared with acoustic detection and optical detection, the magnetic detection method is not easy to be interfered by a medium and has stronger concealment. When mineral distribution or archaeological remains are explored, compared with the traditional drilling and magnetotelluric methods, the magnetic detection mode is more efficient, the cost is lower, and the damage to detection targets is small. The magnetic detection algorithm is taken as a core component in a magnetic detection system, and is important to the accuracy and reliability of a detection result of the system. An efficient magnetic detection system not only needs to have excellent signal acquisition capability and noise filtering capability, but also needs to rely on a proper and precise logic calculation method, and the three components complement each other to jointly determine the advantages and disadvantages of detection performance. The signal acquisition capability determines the effectiveness of the system in capturing weak magnetic field signals under different environmental conditions, and even advanced algorithms can not provide accurate results if the signal acquisition is insufficient or is interfered by serious noise. Meanwhile, the noise filtering capability can effectively inhibit background noise, improve the definition of signals and lay a good foundation for subsequent data processing. The magnetic detection method bears the important responsibility of extracting magnetic anomaly information from complex interference signals and establishing connection with a detection target, rounding and truncation errors in numerical calculation in the detection method and unavoidable simplification and approximation of a physical model to complex reality, nonlinear transmission and amplification can occur in the iterative inversion process of an algorithm, and the reliability and the accuracy of a positioning result are reduced. The following problems exist in the current magnetic detection method: 1. The magnetic detection method based on the scalar has larger positioning error, while the magnetic detection method based on the magnetic tensor has higher precision but shorter detectable distance. The scalar-based magnetic detection method is to detect the total magnetic field intensity by acquiring the mode information of the magnetic field vector to realize target detection. The method has relatively simple measurement principle and strong system robustness, and the signal decays slowly along with the distance under the uniform geomagnetic field background, so that the method has a far effective detection distance and is suitable for large-range rapid scanning. However, it is limited in that a single scalar observation cannot uniquely determine the vector characteristics of the magnetic field source, resulting in the inversion problem having serious non-uniqueness, which ultimately manifests as a large positioning error. In contrast, magnetic gradient tensor detection acquires higher-dimensional magnetic field structure information by synchronously measuring the rate of change of the magnetic field in the spatially orthogonal directions. The method has the remarkable advantages that the background field inhibition capability is that the partial abnormal gradient caused by the target can be directly extracted by tensor measurement because the spatial gradient of the uniform background magnetic field is zero, so that the signal to noise ratio is greatly improved. However, the cost is that the decay of the magnetic gradient field with distance is much faster than the total field strength. This sharp signal attenuation severely constrains its effective range, typically maintaining a high signal-to-noise ratio only over a few times the target feature size, limiting its application in long range detection. 2. Traditional magnetic detection methods based on scalar gradients require that the magnetic moment direction be exactly coincident with the geomagnetic field direction. In order to establish an analytical link between total field strength and gradient magnitude, the most common method is to derive based on an ideal model of the magnetic dipole. When the magnetic moment direction of the target is consistent with the geomagnetic field direction, the disturbance magnetic field vector generated by the target