Active source magnetic susceptibility imaging method for buried object detection in emergency search and rescue

Abstract

The invention discloses an active source magnetic susceptibility imaging method for buried object detection in emergency search and rescue. Comprising the following steps: 1) electrifying an exciting coil to generate a strong magnetic field, magnetizing underground metal in a detection area to generate a secondary induced magnetic field, controlling attenuation of the secondary induced magnetic field, changing magnetic flux in a pair of receiving coils along with the attenuation of the secondary induced magnetic field, and respectively generating induced electromotive force; acquiring the difference between the induced electromotive forces of one pair of receiving coils as data; 2) after a plurality of groups of electromotive force difference data are obtained, realizing inversion imaging of three-dimensional magnetic susceptibility by solving a target function, and accurately positioning an area of a buried person or a key object; the magnetic signals can effectively penetrate through the blindage in the mode that the electrified coil actively excites the magnetic field, the magnetic signals serve as targets, the shielding effect of the complex blindage environment on other signals is avoided, and it is ensured that search and rescue have high sensitivity and resolution by means of the large magnetic susceptibility difference between the sediment or water flow blindage and the target to be searched and rescued.

Description

Technical Field

[0001] This invention belongs to the technical field of systems that utilize the reflection or re-radiation of radio waves, such as radar systems; similar systems that utilize the reflection or re-radiation of waves whose properties or wavelengths are irrelevant or unspecified; and particularly relates to an active source magnetic susceptibility imaging method for high-precision locating and positioning of buried objects in the field of emergency search and rescue. Background Technology

[0002] my country is one of the countries most severely affected by natural disasters in the world. Frequent natural disasters place high demands on emergency search and rescue technologies. Searching for buried persons and objects is the primary task of post-disaster emergency rescue operations. Geological disasters, earthquakes, and floods often result in people being buried by landslides, mudslides, building rubble, and mudslides. However, factors such as collapsed buildings and mudslide erosion cause complex coverings over search targets, making the detection environment complex and traditional search methods difficult to accurately and promptly determine the location of buried objects. Existing search and rescue methods mainly include manual search, search dogs, and life radar detection. Instruments such as radar and infrared detectors are used; however, the actual use of these methods has obvious limitations: manual search is inefficient, has low accuracy, and is highly dangerous; search dogs mainly rely on their sense of smell, are easily affected by environmental factors, and have limited effective search depth; radar detectors have too shallow a search depth; infrared detectors cannot penetrate the surface covering medium; the above methods are difficult to play an effective role in actual search and rescue. The inefficiency of the search and rescue methods for buried persons may not only lead to missing the best search and rescue opportunity, but also increase the difficulty and danger of the search and rescue for front-line rescuers. The above methods are difficult to play an efficient search and rescue role in actual rescue.

[0003] Commonly used detection methods are introduced as follows: First, acoustic / vibration detectors were first used in the 1972 Farmington Mine Disaster in the United States. The principle of this method is to use microphones or detectors to detect the sound and vibration signals emitted by trapped personnel, and analyze the signal characteristics to determine the location of the trapped personnel. The advantage of this method is that the measurement technology is relatively mature, the sensor has high sensitivity to sound and vibration signals, and can effectively detect weak signals. In addition, low-frequency vibration waves attenuate slowly in solid media such as walls, so the detection depth of this method is relatively large compared with other methods. The disadvantage of this method is that the rescue scene may be accompanied by secondary disasters such as aftershocks and floods, and the resulting vibrations will seriously interfere with the detection of effective signals. In addition, due to the extremely complex environment of the ruins, the vibration wave propagation process is accompanied by reflection, refraction and scattering, which seriously affects the positioning accuracy of the triangulation method for trapped personnel.

[0004] Secondly, optical observation equipment was first used in the 1982 Stratford apartment building rescue in the United States. This method works by inserting industrial fiber optic endoscopes or optical cameras underground to visualize the rescue space and thus determine the location of trapped personnel. The advantage of this method is its accurate location of trapped personnel, and the ability to rationally formulate rescue plans based on the visualized underground structure. However, the disadvantages are that, on the one hand, it requires scanning through gaps in the rubble, resulting in low efficiency; and on the other hand, it is ineffective in rescue scenarios without gaps, such as mudslides and floods.

[0005] Third, infrared detectors were first used in the 1995 Great Hanshin Earthquake in Japan. The principle behind this method is that the difference in temperature between buried individuals and surrounding shelters results in different infrared radiation frequencies; the location of buried individuals is achieved by detecting the infrared spectrum. The advantage of this method is that it does not require contact with the rubble and can be remotely controlled for large-area infrared detection, improving the safety and efficiency of search and rescue operations. However, the disadvantages of this method are that infrared light has poor penetration through solid media. When survivors are buried under walls, soil, or metal plates several meters thick, the infrared detectors will fail. Furthermore, the temperature difference indicators required for infrared detection may be difficult to discern due to high summer temperatures or rain erosion, rendering them ineffective.

[0006] Fourth, gas detectors were also first used in the 1995 Great Hanshin Earthquake in Japan. The principle behind this method is that human respiration causes changes in the concentration of oxygen and carbon dioxide in a confined space, and the location of survivors is determined by detecting abnormal carbon dioxide concentrations. The advantage of this method is that, compared to sound wave and vibration wave detection, it does not depend on the consciousness of the buried person, as even in a coma, there will be changes in carbon dioxide concentration. However, the disadvantage of this method is that there is a lot of interference. The decomposition of organic matter and animal respiration can all cause changes in carbon dioxide concentration, which seriously interferes with the search and rescue of buried persons. In addition, the measurement of gas concentration in weather conditions such as strong winds and rain will deviate significantly from the actual situation, resulting in unsatisfactory results in locating buried persons.

[0007] Fifth, radar life detectors were first used in the 2001 Gujarat earthquake in India. The principle of this method is to emit electromagnetic waves into the ground. When the electromagnetic waves pass through different media, some of their energy is reflected. If there are physiological activities such as breathing and heartbeat underground, the reflected electromagnetic wave signals will show regular changes, indicating life signals. The advantage of this method is that it has strong anti-interference ability. The regular life signals are not affected by vibration or environmental noise and can still play a role in complex environments. However, the disadvantage of this method is that the electromagnetic waves cannot penetrate metal plates, reinforced concrete and other metal shelters. In humid environments, the electromagnetic wave energy is easily absorbed by water, which greatly reduces the effective detection range of this method.

[0008] In summary, given the complex and non-uniform shelter environment, severe weather conditions, and frequent secondary disasters in actual rescue scenarios, existing search and rescue technologies have their own shortcomings, making it difficult to complete efficient and scientific emergency rescue and life-saving tasks. In view of the many defects and deficiencies in the existing search and detection technologies for buried personnel, there is an urgent need to develop new and effective emergency search and rescue technologies for buried personnel. Summary of the Invention

[0009] This invention provides an active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue. This method aims to overcome the technical bottleneck of difficulty in locating buried targets during post-disaster emergency rescue, and also improves upon the shortcomings of infrared detectors and radar life detectors in the field of emergency search and rescue. This invention proposes an active source magnetic susceptibility detection and imaging technology. By exciting a strong electromagnetic field in the detection area, the buried metal object is magnetized, generating a secondary induced magnetic field. The magnetic flux of a pair of receiving coils changes with the decay of the secondary induced magnetic field, generating induced electromotive forces. The difference in induced electromotive forces between the pair of receiving coils is collected as data. By solving an objective function, three-dimensional magnetic susceptibility inversion imaging is achieved, thereby realizing the location and imaging of buried metal objects. This allows for the precise location of buried personnel or key objects in complex environments.

[0010] To address the aforementioned technical problems, this invention provides an active-source magnetic susceptibility imaging method for detecting buried objects during emergency search and rescue operations. The method includes the following steps: 1) When the coil is energized, a strong magnetic field is generated. The magnetization caused by the strong magnetic field generates a secondary induced magnetic field in the underground metal in the detection area. The attenuation of the secondary induced magnetic field is controlled. The magnetic flux in the pair of receiving coils changes with the attenuation of the secondary induced magnetic field and generates induced electromotive force respectively. The difference of induced electromotive force between the pair of receiving coils is collected as data. 2) After obtaining multiple sets of electromotive force difference data, the three-dimensional magnetic susceptibility is inverted and imaged by solving the objective function, so as to accurately locate the area of ​​buried personnel or key objects.

[0011] Furthermore, in step 1), the energized coil is a large coil formed by winding enameled copper wire. Given the copper wire diameter D and the number of turns N, the height h of the top of the coil from the ground is: (1) One pair of receiving coils consists of receiving coil I and receiving coil II, both concentric with the excitation coil and connected in series. Receiving coil I and receiving coil II have identical specifications: a wire diameter of d, N1 turns, a coil area of ​​S, and a coil height of [missing information]. The receiving coil I is fixed to the top of the large coil and its upper surface is flush with the top of the excitation coil. It is wound in a clockwise direction. The receiving coil II is fixed to the bottom of the excitation coil and its lower surface is flush with the bottom of the excitation coil. It is wound in a counterclockwise direction.

[0012] Furthermore, in step 1), let the coordinates of any point P in space be... When a direct current of strength I is supplied to the excitation coil, the magnetic field strength H generated by the excitation coil at point P is: (2) Where B0 is the magnetic flux density, μ0 is the free permeability, and Bρ and Bz are the radial and vertical components of the magnetic flux density, respectively. The specific calculation formula is as follows: (3) (4) in: The above formula and These represent the first and second kind of complete elliptic integrals, respectively; Exploration of underground space If a key, cell phone, belt buckle, or vehicle is buried at a location, it will be magnetized by a magnetic field H. The effective magnetization M produced by the buried object is: (5) If buried magnetic metal objects can be considered as magnetic dipoles, then... The magnetic flux density generated by the secondary induced magnetic field produced by the magnetization of the buried metal object along the axial direction at the location of the receiving coil is: (6) The buried magnetic metal body is considered as a magnetic dipole, and its volume V is taken as unit 1; z is the height difference between the buried object and the small coil. After the excitation coil is de-energized, the formula for the decay of the magnetic induction intensity B over time is: (7) in The magnetic flux density is , and the magnetic flux density of the secondary induced magnetic field is . , Let be the decay time constant; the rate of change of the secondary field magnetic induction intensity at any decay time t is: (8) but The change in the secondary induced magnetic field of the buried magnetic metal object causes the induced electromotive force generated in receiving coil I and receiving coil II. and for: (9) The difference in induced electromotive force between the two small coils is: (10).

[0013] Furthermore, in step 1), a series of observation points are set at different locations in the detection area. At time intervals of 0.01s, the electromotive force difference after power failure is measured sequentially at each observation point, thus obtaining electromotive force difference data vectors at different times and locations. The underground space of the detection area is divided into a series of small cubes, and the difference in induced electromotive force at any point is... All of these are the sum of the electromotive force differences generated by all the cubes, that is: (11) With vectors Let represent the magnetic susceptibility of the underground cube. Then, according to formula (10), the vector... sum vector Satisfying the relation: (12) in express A dimensional kernel matrix, Indicates the underground The attenuation of the secondary induced magnetic field of the cube affects the detection area. The contribution of the induced electromotive force difference of the coil at each observation point can be calculated using formula (10): (13) Electromotive force difference data at all observation points at different times were obtained through measurement. At this point, formula (12) can be regarded as a linear inversion problem. By using a regularization strategy to minimize the objective function, the underground magnetic susceptibility can be achieved. The objective function is: (14) The first term in the above equation represents the data fitting term, the second term represents the model constraint term, and the third term represents the logarithmic barrier function; where For regularization parameters, As the initial reference model, The weighting matrix of the model constrains the model to have physical meaning; and The upper and lower limits of magnetic susceptibility are respectively used to ensure that the physical property values ​​of the inversion results are consistent with the actual situation. The objective function of formula (14) is solved by the stationary point method to realize underground three-dimensional magnetic susceptibility imaging, thereby locating the underground spatial location of buried metal or personnel.

[0014] Furthermore, in step 2), a generalized cross-validation method is used to determine the regularization parameters. Take the depth-weighted matrix as To improve the skin effect and ambiguity of the magnetic susceptibility in the inversion results; specifically in the form of: (15) The three-dimensional spatial magnetic susceptibility is solved iteratively using the Gauss-Newton method. The formula for calculating the model update amount in each iteration is as follows: (16) in and It is a diagonal matrix. , , .

[0015] The beneficial effects of this invention are as follows: 1. This invention provides an active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue. By exciting a strong electromagnetic field in the detection area, the buried metal object is magnetized to generate a secondary induced magnetic field. The magnetic flux of a pair of receiving coils changes with the decay of the secondary induced magnetic field and generates induced electromotive force. The difference between the induced electromotive forces of the pair of receiving coils is collected as data. By solving the objective function, the three-dimensional magnetic susceptibility is inverted and imaged, thereby realizing the location and imaging of the buried metal object. This allows for the accurate location of buried personnel or key objects in complex environments.

[0016] 2. The active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue can detect the magnetic susceptibility distribution within a certain spatial range. Compared with the prior art, it has higher sensitivity and greater detection depth, effectively overcoming key technical challenges in emergency search and rescue and powerfully safeguarding the lives and safety of the people.

[0017] 3. The present invention provides an active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue. By performing three-dimensional magnetic susceptibility imaging on the target area, it enables the location and search and rescue of buried objects and buried personnel in complex rescue environments, providing reliable technical support for finding missing persons and seizing the "golden 72 hours" for disaster relief. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the structure of the excitation coil and the receiving coil in the active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue according to the present invention. Figure 2 is a detection status diagram of an active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue according to the present invention. Figure 3 is a structural diagram of an active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue according to the present invention.

[0019] Figure 4 This is a schematic diagram of the imaging results when the present invention is applied to an example of a mobile phone to be detected.

[0020] Reference numerals: 1-Excitation coil; 2-Receiver coil II; 3-Receiver coil I; 4-Housing shell. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] like Figure 1-4 This invention presents a schematic diagram of an active source magnetic susceptibility imaging method for detecting buried objects in emergency search and rescue. The method includes the following steps: 1) An energized excitation coil generates a strong magnetic field. The strong magnetic field magnetizes the underground metal in the detection area, causing a secondary induced magnetic field. The attenuation of the secondary induced magnetic field is controlled. The magnetic flux in a pair of receiving coils changes with the attenuation of the secondary induced magnetic field, generating induced electromotive forces respectively. The difference in induced electromotive forces between the pair of receiving coils is collected as data. 2) After obtaining multiple sets of electromotive force difference data, the three-dimensional magnetic susceptibility is inverted and imaged by solving the objective function, so as to accurately locate the area of ​​buried personnel or key objects.

[0023] In emergency rescue scenarios, buried individuals typically carry keys, mobile phones, and ferromagnetic belts, while the buried objects may be cars washed away by mud and sand. Ferromagnetic objects exhibit a significant difference in magnetic susceptibility compared to silt and other burial materials.

[0024] The working principle of this invention is as follows: Multiple detectors are placed in the detection area. Inside the detector housing 4, there are excitation coils 1 and receiving coils of different diameters. According to the magnetic induction effect of current, a strong current flowing through the large coil of excitation coil 1 will generate a strong magnetic field around it. The underground medium and buried metal objects are magnetized by the strong magnetic field and generate an induced magnetic field. After the large coil of excitation coil stops being energized, the induced magnetic field will decay over time. The decay of the magnetic field causes a change in the magnetic flux in the small coil of receiving coil, thereby generating an induced electromotive force. The underground or underwater space is discretized into a series of small cubes. At a certain moment, the induced electromotive force generated by the small coil is the superposition effect of the magnetic flux change caused by the attenuation of the magnetic field of all the cubes. Since the induced electromotive force of the coil is linearly related to the magnetic induction intensity, and the magnetic induction intensity is proportional to the magnetic susceptibility of the medium; Therefore, by measuring the induced electromotive force at different times and locations, the magnetic susceptibility of each cube can be obtained by inversion, thus realizing three-dimensional magnetic susceptibility imaging.

[0025] In a preferred embodiment, in step 1), the energized coil is a large coil formed by winding enameled copper wire. Given the copper wire diameter D and the number of turns N, the height h of the top of the coil from the ground is: (1) One pair of receiving coils consists of receiving coil I3 and receiving coil II2, which are concentric with and connected in series with the excitation coil. Receiving coils I and II have the same specifications: a wire diameter of d, a number of turns of N1, a coil area of ​​S, and a coil height of [missing information]. The receiving coil I is fixed to the top of the large coil and its upper surface is flush with the top of the excitation coil. It is wound in a clockwise direction. The receiving coil II is fixed to the bottom of the excitation coil and its lower surface is flush with the bottom of the excitation coil. It is wound in a counterclockwise direction.

[0026] This embodiment uses a detector to generate a magnetic field and observe the induced electromotive force difference data. The detector mainly includes a power stage circuit and an integrated component of an electromagnetic excitation coil and a receiving coil. The power stage circuit mainly consists of a power supply and transmitting and receiving control circuit elements. The power supply mainly provides a stable DC power to the large coil. The transmitting and receiving control circuit elements control the current transmission and de-energization and protect the power supply and circuit safety.

[0027] For the integrated electromagnetic transmitting and receiving coil component, both the large and small coils are wound on a fiberglass skeleton. A large coil, 1m in diameter and 270mm high, is formed by single-layer winding of 150 turns using 1.8mm diameter enameled copper wire, with an inductance of 40mH and a resistance of 2.11Ω. Two small coils, 0.4m in diameter and 10mm high, are formed by single-layer winding of 500 turns using 0.02mm diameter enameled copper wire, each with a resistance of 336Ω, but wound in opposite directions. In actual search and rescue scenarios, the excitation coil is designed to be energized for 0.05s with a current intensity of 20A DC. The 0.05s energization time ensures the current is approximately DC. The subsequent power-off time is designed to be 0.15s, balancing detection efficiency and power consumption, ensuring the coil's maximum operating temperature does not exceed 40℃. Experiments show that if the large coil has a diameter of 1 meter and 150 turns, and the small coil has a diameter of 0.4m and 100 turns, the results are satisfactory. With a meter, 500 turns, and a DC current of 20 A, it can detect induced electromotive force within 2 microvolts.

[0028] In a preferred embodiment, in step 1), it is assumed that the coordinates of any point P in space are... When a direct current of strength I is supplied to the excitation coil, the magnetic field strength H generated by the excitation coil at point P is: (2) Where B0 is the magnetic flux density, μ0 is the free permeability, and Bρ and Bz are the radial and vertical components of the magnetic flux density, respectively. The specific calculation formula is as follows: (3) (4) in: The above formula and These represent the first and second kind of complete elliptic integrals, respectively; Exploration of underground space If a key, cell phone, belt buckle, or vehicle is buried at a location, it will be magnetized by a magnetic field H. The effective magnetization M produced by the buried object is: (5) If buried magnetic metal objects can be considered as magnetic dipoles, then... The magnetic flux density generated by the secondary induced magnetic field produced by the magnetization of the buried metal object along the axial direction at the location of the receiving coil is: (6) The buried magnetic metal body is regarded as a magnetic dipole, and its volume V is taken as unit 1. z is the height difference between the buried object and the small coil. The height difference Z between the buried object and the receiving coil I and the receiving coil II are not the same. After the excitation coil is de-energized, the formula for the decay of the magnetic induction intensity B over time is: (7) in The magnetic flux density is , and the magnetic flux density of the secondary induced magnetic field is . , Let be the decay time constant; the rate of change of the secondary field magnetic induction intensity at any decay time t is: (8) but The change in the secondary induced magnetic field of the buried magnetic metal object causes the induced electromotive force generated in receiving coil I and receiving coil II. and for: (9) The difference in induced electromotive force between the two small coils is: (10).

[0029] In a preferred embodiment, in step 1), a series of observation points are set at different locations in the detection area. At time intervals of 0.01s, the electromotive force difference after power failure is measured sequentially at each observation point, thus obtaining electromotive force difference data vectors at different times and locations. The underground space of the detection area is divided into a series of small cubes, and the difference in induced electromotive force at any point is... All of these are the sum of the electromotive force differences generated by all the cubes, that is: (11) With vectors Let represent the magnetic susceptibility of the underground cube. Then, according to formula (10), the vector... sum vector Satisfying the relation: (12) in express A dimensional kernel matrix, Indicates the underground The attenuation of the secondary induced magnetic field of the cube affects the detection area. The contribution of the induced electromotive force difference of the coil at each observation point can be calculated using formula (10): (13) Electromotive force difference data at all observation points at different times were obtained through measurement. At this point, formula (12) can be regarded as a linear inversion problem. By using a regularization strategy to minimize the objective function, the underground magnetic susceptibility can be achieved. The objective function is: (14) The first term in the above equation represents the data fitting term, the second term represents the model constraint term, and the third term represents the logarithmic barrier function; where For regularization parameters, As the initial reference model, The weighting matrix of the model constrains the model to have physical meaning; and These represent the upper and lower limits of magnetic susceptibility; referencing the passive source magnetic susceptibility inversion problem, the upper and lower limits are... and Set them to 0SI and 1SI respectively to ensure that the physical property values ​​of the inversion results match the actual situation; The weights of the barrier function are typically set to large initial values ​​during calculation, gradually approaching 0 with iteration.

[0030] The objective function of formula (14) can be solved by using the stationary point method to achieve three-dimensional magnetic susceptibility imaging of the underground, thereby locating the underground spatial location of buried metal objects or personnel.

[0031] When a buried magnetic object is magnetized by a primary field, generating a secondary induced magnetic field, the current supplied to the large coil is stopped. After the power is turned off, both the primary and secondary magnetic fields decay over time, causing changes in the magnetic flux within the two smaller coils and generating induced electromotive forces (EMFs). For the primary magnetic field, since both coils are concentric with the large coil, the changes in magnetic flux within the two smaller coils are the same, resulting in identical induced EMF values. Furthermore, because the two smaller coils are wound in opposite directions, the total induced EMF after they are connected in series under the influence of the primary magnetic field is 0V. For the secondary magnetic field, due to the different vertical distances between the buried object and the two coils, the decay of the secondary field leads to different changes in magnetic flux within the two smaller coils, resulting in differences in the magnitude of the induced EMFs. Using the difference in induced EMFs between the two smaller coils as data, three-dimensional magnetic susceptibility imaging of the underground can be achieved.

[0032] In a preferred embodiment, in step 2), a generalized cross-validation method is used to determine the regularization parameter. Take the depth-weighted matrix as To improve the skin effect and ambiguity of the magnetic susceptibility in the inversion results; specifically in the form of: (15) In the formula, each element of vector z is the depth value of the cube, and z0 is the height difference between the upper and lower interfaces of the cube. The three-dimensional spatial magnetic susceptibility is solved iteratively using the Gauss-Newton method. Model update size in each iteration The calculation formula is as follows: (16) in and It is a diagonal matrix. , , , To sense the electromotive force difference data, using It can achieve iterative updates of magnetic susceptibility in three-dimensional space.

[0033] To verify the effectiveness of the present invention, assuming that there is a mobile phone to be detected at a depth of 2m underground, the following simulation experiment was conducted.

[0034] The specific implementation steps of the detection capability analysis method are as follows: 1) Input: Location coordinates of all ground observation points The induced electromotive force difference data obtained at each observation point Coordinates of the center points of each cube in the space to be probed Upper and lower limits of magnetic susceptibility in the detection area and Maximum number of iterations ; Step 1: Calculate the kernel matrix required for imaging and model weighting matrix The specific steps are as follows: Step 1.1: Based on the combined coil parameters and different decay times, calculate the core matrix according to formulas (2)-(5) and (13). , of which elements The decay time is represented by t. k At time s, the j-th underground cube For the i-th observation point on the Earth's surface The contribution of the induced electromotive force difference; Step 1.2: Based on the cube depth The model weighting matrix is ​​calculated according to formula (15). ; Step 2: Determine the regularization parameters : Plot the correlation curve between data item and model item, and select the inflection point corresponding to As a regularization parameter, it balances the weights of data fitting terms and model constraint terms; Step 3: Initialize the magnetic susceptibility model vector Initialize the number of iterations Initialize the barrier function weight coefficients ; Step 4: Integrate observation data nuclear matrix Model weighting matrix upper and lower limits of magnetic susceptibility and Weighting coefficient and The magnetic susceptibility model vector is solved by iterative calculation with equal parameters. The specific steps are as follows: Step 4.1: Number of Update Iterations 1; Step 4.2: Update the matrix form of the model's upper and lower bounds: and ; Step 4.3: Solve formula (16) based on the conjugate gradient algorithm (CG) to obtain the magnetic susceptibility model update amount of the k-th iteration compared to the previous iteration; Step 4.4: Update the magnetic susceptibility model vector: Step length ; Step 4.5: Determine whether to terminate the iterative operation: If the condition is met, the iteration terminates; otherwise, the next step of the calculation continues. Step 4.6: Update the regularization weight coefficients and : , ; Step 4.7: Return to Step 4.1 and repeat the calculation; Step 5: Obtain the three-dimensional magnetic susceptibility imaging results of the space to be detected (e.g., ... Figure 4 ).

[0035] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An active source magnetic susceptibility imaging method for buried object detection in emergency search and rescue, characterized in that: The method comprises the following steps: 1) energizing the coil to generate a strong magnetic field, magnetizing the underground metal in the detection area to generate a secondary induction magnetic field, controlling the decay of the secondary induction magnetic field, and changing the magnetic flux in the receiving coil to generate an induced electromotive force; collecting the difference between the induced electromotive forces of the receiving coil as data; 2) after obtaining a plurality of sets of electromotive force difference data, solving the objective function to realize three-dimensional magnetic susceptibility inversion imaging, and accurately positioning the buried personnel or key object area.

2. The active source magnetic susceptibility imaging method for buried object detection in emergency search and rescue according to claim 1, characterized in that: In step 1), the energized coil is a large coil wound by enameled copper wire, the diameter of the copper wire is D, and the number of turns is N, then the height h of the top of the coil from the ground is: （1） 1 The receiving coil is the receiving coil I and the receiving coil II which are both concentric with the excitation coil and connected in series. The receiving coil I and the receiving coil II are of the same specification, and the wire diameter of both is d, the number of turns is N1, the coil area is S, and the coil height is The receiving coil I is fixed on the top of the large coil and the upper surface is flush with the top of the excitation coil, and the wire is wound in the clockwise direction. The receiving coil II is fixed on the bottom of the excitation coil and the lower surface is flush with the bottom of the excitation coil, and the wire is wound in the counterclockwise direction.

3. The active source magnetic resonance method for buried object detection in emergency search and rescue according to claim 2, characterized in that: In step 1), let the coordinates of any point P in space be When a direct current with intensity I is supplied to the excitation coil, the magnetic field intensity H of the magnetic field generated by the excitation coil at point P is: （2） where B0is the magnetic induction, μ0is the vacuum permeability, B ρ and B z are the radial and vertical components of the magnetic induction, respectively, and the specific formula is as follows: wherein: , the above formula and represent the first and second kinds of complete elliptic integrals, respectively; Underground space of a detection area When the buried object exists, the key, the mobile phone, the metal head of the belt or the vehicle is magnetized by the magnetic field, and the effective magnetization M generated by the buried object is: （5） The underground buried magnetic metal object can be regarded as a magnetic dipole, and then The magnetic induction intensity generated by the secondary induction magnetic field of the buried metal object magnetized by the magnetic field in the axial direction at the position of the receiving coil is: （6） Where the buried magnetic metal body is regarded as a magnetic dipole, its volume V is taken as 1, and z is the height difference between the buried object and the small coil; After the excitation coil is powered off, the decay formula of the magnetic induction intensity B with time after power-off is: （7） wherein is the magnetic induction, and the secondary field magnetic induction is , is the decay time constant; the rate of change of the secondary field magnetic induction at any decay time t is: （8） Then The secondary induction magnetic field change caused by the magnetic buried metal object causes the receiving coil I and the receiving coil II to generate an induced electromotive force And Is: （9） The difference between the induced electromotive forces of the two small coils is: （10）。 4. The active source magnetic resonance method for buried object detection in emergency search and rescue according to claim 3, characterized in that: In step 1), a series of observation points are set at different positions of the detection area, and the electromotive force difference after power-off is measured at each observation point in turn at a time interval of 0.01 s, so as to obtain electromotive force difference data vectors at different times and different positions ; the underground space of the detection area is divided into a series of small cubes, and the difference of induced electromotive force at any point is the sum of the electromotive force differences generated by all the cubes, that is: （11） The vector representing the susceptibility of the subsurface cube, then according to equation (10), the vector and the vector satisfy the relationship: （12） wherein denotes a nuclear matrix of dimension denotes the contribution of the th cubic secondary magnetic field decay to the difference of the induced electromotive forces of the th observation point coil of the detection region, which can be calculated by formula (10) as follows: （13） The measured potential difference data at different times and all observation points are used At this time, formula (12) can be regarded as a linear inversion problem, and the solution of the underground magnetization can be realized by minimizing the objective function using the regularization strategy, and the objective function is: （14） The first term of the formula represents a data fitting term, the second term represents a model constraint term, and the third term is a logarithmic barrier function; wherein is a regularization parameter, is an initial reference model, is a model weighting matrix, is a barrier function weight; and are upper and lower limits of magnetic susceptibility, respectively; solving the objective function of formula (14) by using a stationary point method can achieve three-dimensional magnetic susceptibility imaging of the underground, and further locate the underground space position of the buried metal or personnel.

5. The active source magnetic resonance method for buried object detection in emergency search and rescue according to claim 4, characterized in that: In step 2), the generalized cross-validation method is used to determine the regularization parameter The depth weighting matrix is taken as To improve the skin effect and the multi-solution of the inversion result magnetization, the specific form is: （15） Gauss-Newton method is used to solve the magnetization in three-dimensional space The formula for calculating the model update amount in each iteration is as follows: (16) wherein and is a diagonal matrix, , , , is the induced electromotive force difference data.

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