A transceiver coil mutual inductance type magnetic detection method and system

Abstract

This invention discloses a method and system for magnetic detection based on mutual inductance between transmitting and receiving coils, belonging to the field of magnetic induction detection technology. The detection method includes: applying an alternating excitation voltage signal to the transmitting coil, and obtaining a preset proportion in which the received signal power of the receiving coil decreases to its maximum value. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth; when the absolute value of the difference between the detection bandwidth and the corresponding reference bandwidth is less than or equal to a preset threshold, it is determined that there is no metal target in the area to be detected; otherwise, it is determined that there is a metal target in the area to be detected. Since the bandwidth is not a single point value, but a range characteristic of the resonant response under certain attenuation conditions, it can comprehensively reflect the combined effects of environmental background, coil coupling, loss changes, and metal target disturbances on the system frequency response, and has strong anti-fluctuation ability. Based on this, the present invention improves the accuracy of target detection.

Description

Technical Field

[0001] This invention belongs to the field of magnetic induction detection technology, and more specifically, relates to a magnetic detection method and system based on mutual inductance of transceiver coils. Background Technology

[0002] Magnetic detection technology typically utilizes the electromagnetic coupling between an alternating magnetic field and a metallic target to achieve target detection. When a metallic target enters an alternating magnetic field region, eddy currents are generated inside the target. These eddy currents, in turn, alter the distribution of the surrounding magnetic field and the circuit parameters of the coil circuit. Therefore, the impact on the target can be characterized by induced voltage, equivalent impedance, resonant frequency, or power response. This technology exhibits excellent anti-interference capabilities, signal penetration, and multi-directional radiation characteristics in complex electromagnetic environments, and has been widely used in underground and underwater detection scenarios in recent years.

[0003] Existing single-coil self-inductive magnetic detection methods typically require a transmitting coil. Target detection is performed by determining whether the resonant point of the transmitting coil has shifted. Although the system structure is relatively simple, this method is difficult to fully characterize the influence of metallic targets. It is also difficult to simultaneously consider the combined effects of changes in the environmental background, changes in coil coupling state, changes in losses, and additional disturbances from metallic targets on the system response. As a result, it has weak anti-fluctuation capability and low target detection accuracy. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a transceiver coil mutual inductance magnetic detection method and system to solve the technical problem of low target detection accuracy in the prior art.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a transceiver coil mutual inductance magnetic detection method, applied to a transceiver coil mutual inductance magnetic detection device including a transmitting coil and a receiving coil; The above-mentioned magnetic detection methods include: An alternating excitation voltage signal is applied to the transmitting coil, causing the transmitting coil to generate an alternating magnetic field in the region to be detected; Obtain a preset ratio of the received signal power of the receiving coil decreasing to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ; Determine the detection bandwidth With the corresponding reference bandwidth If the absolute value of the difference is less than or equal to a preset threshold, then it is determined that there is no metal target in the area to be detected; otherwise, it is determined that there is a metal target in the area to be detected. Among them, the reference bandwidth This is a preset ratio by which the received signal power of the receiving coil decreases to its maximum value under a reference state where no metallic target is present. p The frequency range corresponding to the time.

[0006] More preferably, the preset ratio at which the received signal power of the receiving coil decreases to the maximum value of the received signal power is obtained. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ,include: The intrinsic impedance of the transmitting coil The impedance of the receiving coil Equivalent impedance of metallic targets Angular frequency of the excitation voltage signal and voltage value Mutual inductance between the transmitting coil and the receiving coil and the equivalent current of the transmitting coil and the equivalent current of the receiving coil Substituting the values ​​into the three-loop coupled equivalent circuit model and solving it, we obtain the mutual inductance between the transmitting coil and the metallic target. And the mutual inductance between the receiving coil and the metal target Then the equivalent impedance of the transmitting coil can be calculated. ; Based on the equivalent impedance of the transmitting coil The equivalent self-inductance of the transmitting coil was calculated. The resonant frequencies of the transmitting coils were calculated respectively. and quality factors ; Based on resonant frequency and quality factors Calculate the preset ratio by which the received signal power of the receiving coil decreases to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ; The above-mentioned three-loop coupled equivalent circuit model is a set of equations composed of KVL equations established for the transmitting coil and receiving coil, the transmitting coil and the metal target, and the receiving coil and the metal target, respectively.

[0007] More preferably, the equivalent circuit model of the three-loop coupling is as follows:

[0008] in, Represents the imaginary number symbol; This represents the eddy current equivalent in the metallic target.

[0009] More preferably, the equivalent impedance of the transmitting coil for: .

[0010] More preferably, the resonant frequency and quality factors They are respectively:

[0011]

[0012] in, This is the matching resonant capacitor for the transmitting coil; This is the resistance value of the transmitting coil.

[0013] More preferably, equivalent self-inductance for:

[0014] in, Represents the imaginary number symbol; This is the equivalent impedance of the transmitting coil; express The imaginary part.

[0015] More preferably, the above-mentioned resonant frequency-based and quality factors Calculate the preset ratio by which the received signal power of the receiving coil decreases to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ,include: When coupling factor When the value is less than 1, the magnetic detection device is determined to be in an undercoupled state, and the detection bandwidth is [value missing]. ; When coupling factor When the value equals 1, the magnetic detection device is determined to be in a critical coupling state, and the detection bandwidth is [value missing]. ; When coupling factor When the value is greater than 1, the magnetic detection device is determined to be in an overcoupled state, and the detection bandwidth is [value missing]. ; Wherein, coupling coefficient .

[0016] More preferably, a preset ratio p It is 1 / 2 or 1 / 10.

[0017] More preferably, the above magnetic detection method further includes: when a metallic target exists in the area to be detected, determining the location of the metallic target based on the current bandwidth characteristics. Obtain the pre-collected sample set; The K feature samples most similar to the current bandwidth feature are selected from the sample set to form a candidate sample set; ; The label that appears most frequently in the candidate sample set is taken as the current location of the metal target in the area to be detected; The aforementioned sample set was obtained through the following methods: Obtain a metal sample that is identical in size and material type to the metal target; The area to be detected is divided into voxel grids; The center point of each voxel grid is taken as the position of the metal sample, and the bandwidth feature corresponding to the metal sample at that position is obtained; a sample set is constructed with the bandwidth feature as the feature sample and the corresponding position as the label; The bandwidth characteristics mentioned above are: preset ratio p The absolute value of the corresponding difference Or, each preset ratio in the preset ratio set p' The vector formed by the absolute values ​​of the corresponding differences; the preset ratio set includes preset ratios p ; for and The absolute value of the difference.

[0018] More preferably, the KNN algorithm is used to obtain the K feature samples that are most similar to the current bandwidth features from the sample set.

[0019] In a second aspect, the present invention provides a transceiver coil mutual inductance magnetic detection system, comprising: a transceiver coil mutual inductance magnetic detection device and a control module; wherein the transceiver coil mutual inductance magnetic detection device comprises: a transmitting coil and a receiving coil; the control module is used to execute the transceiver coil mutual inductance magnetic detection method provided in the first aspect of the present invention.

[0020] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a method for magnetic detection using mutual inductance of transmitting and receiving coils, which involves applying an alternating excitation voltage signal to the transmitting coil and obtaining a preset ratio in which the received signal power of the receiving coil decreases to its maximum value. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth When the detection bandwidth With the corresponding reference bandwidth When the absolute value of the difference is less than or equal to a preset threshold, it is determined that there is no metal target in the area to be detected; otherwise, it is determined that there is a metal target in the area to be detected. Since the bandwidth is not a single point value, but a range characteristic of the resonant response under certain attenuation conditions, it can comprehensively reflect the combined effects of the environmental background, coil coupling, loss changes, and metal target disturbances on the system frequency response, and has strong anti-fluctuation ability. Based on this, the present invention improves the accuracy of target detection.

[0021] 2. Furthermore, in the transceiver coil mutual inductance magnetic detection method provided by this invention, the detection bandwidth is calculated through a three-loop coupling model. The three-loop coupling equivalent circuit model is a set of equations composed of KVL equations established for the transmitting coil and receiving coil, the transmitting coil and the metal target, and the receiving coil and the metal target, respectively. It can simultaneously characterize the influence of the three types of coupling relationships—transmission and reception, transmission and target, and reception and target—on the equivalent impedance of the transmitting coil, thereby making the bandwidth change more sensitive to environmental changes and further improving the accuracy of target detection. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the generator coil mutual inductance magnetic detection device provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the actual device for mutual inductance magnetic detection of the hair coil provided in an embodiment of the present invention; Figure 3 This is a three-dimensional distribution diagram showing the 10dB bandwidth variation of a metal target located in different voxel grids, provided as an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Example 1 This embodiment provides a transceiver coil mutual inductance magnetic detection method, applied to a transceiver coil mutual inductance magnetic detection device including a transmitting coil and a receiving coil; such as Figure 1 and Figure 2 As shown, the receiving coil and the transmitting coil are spaced apart; when there is a metal target in the area to be detected, the receiving coil, the transmitting coil and the metal target in the area to be detected are coupled together.

[0025] The above-mentioned magnetic detection methods include: An alternating excitation voltage signal is applied to the transmitting coil, causing the transmitting coil to generate an alternating magnetic field in the region to be detected; Obtain a preset ratio of the received signal power of the receiving coil decreasing to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ; Determine the detection bandwidth With the corresponding reference bandwidth If the absolute value of the difference is less than or equal to a preset threshold, then it is determined that there is no metal target in the area to be detected; otherwise, it is determined that there is a metal target in the area to be detected. Among them, the reference bandwidth This is a preset ratio by which the received signal power of the receiving coil decreases to its maximum value under a reference state where no metallic target is present. p The frequency range corresponding to the time.

[0026] It should be noted that the reference bandwidth The reference bandwidth can be measured by applying an alternating excitation voltage signal to the transmitting coil in a reference state where no metallic target is present, or it can be obtained through simulation calculation; no limitation is made here. It can also be updated periodically in a preset metal-free target environment. In one optional implementation, the reference bandwidth... Obtained through the following methods: Taking the case where the transmitting and receiving coils are identical, under the baseline condition of the absence of a metallic target, the equivalent circuit between the transmitting and receiving coils can be considered as a transformer-coupled resonant circuit, and its transfer function can be expressed as:

[0027] in, and These are the output voltage and input voltage of the transformer-coupled resonant circuit, respectively. The reference angular frequency; This refers to the mutual inductance between the transmitting coil and the receiving coil; This is the equivalent impedance of the transmitting coil; This is the equivalent impedance of the receiving coil.

[0028] Further introduce the reference coupling coefficient Benchmark quality factor and define the benchmark coupling factor. and normalized offset frequency Then the normalized frequency response of the coupled resonant circuit can be written as: ; ω is the angular frequency of the sweep signal; L is the coil inductance; R is the coil resistance.

[0029] by The bandwidth is defined by the amount of attenuation relative to the peak value; where, when At that time, the corresponding reference bandwidth .

[0030] When coupling factor When the value is less than 1, the magnetic detection device is determined to be in an undercoupled state, and the detection bandwidth is [value missing]. ; When coupling factor When the value equals 1, the magnetic detection device is determined to be in a critical coupling state, and the detection bandwidth is [value missing]. ; When coupling factor When the value is greater than 1, the magnetic detection device is determined to be in an overcoupled state, and the detection bandwidth is [value missing]. ; in, As the reference frequency, This is the reference quality factor for the coil.

[0031] It should be noted that the detection bandwidth It can be measured or calculated through simulation; no limitation is made here. Preferably, in one optional implementation, the preset ratio of the received signal power of the receiving coil decreasing to the maximum value of the received signal power is used to obtain the above-mentioned acquisition of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ,include: The intrinsic impedance of the transmitting coil The impedance of the receiving coil Equivalent impedance of metallic targets Angular frequency of the excitation voltage signal and voltage value Mutual inductance between the transmitting coil and the receiving coil and the equivalent current of the transmitting coil and the equivalent current of the receiving coil Substituting the values ​​into the three-loop coupled equivalent circuit model and solving it, we obtain the mutual inductance between the transmitting coil and the metallic target. And the mutual inductance between the receiving coil and the metal target Then the equivalent impedance of the transmitting coil can be calculated. ; Based on the equivalent impedance of the transmitting coil The equivalent self-inductance of the transmitting coil was calculated. The resonant frequencies of the transmitting coils were calculated respectively. and quality factors ; Based on resonant frequency and quality factors Calculate the preset ratio by which the received signal power of the receiving coil decreases to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ; The above-mentioned three-loop coupled equivalent circuit model is a set of equations composed of KVL equations obtained based on Kirchhoff's voltage law for transmitting coil and receiving coil, transmitting coil and metal target, and receiving coil and metal target, respectively.

[0032] It should be noted that, in the state to be detected, if a metallic target enters the detection area, the metallic target will generate eddy currents under the action of an alternating magnetic field. After equating the metallic target with an eddy current equivalent circuit, a three-loop coupling model is formed between the transmitting coil, the receiving coil, and the metallic target eddy current equivalent circuit. In one optional implementation, the three-loop coupling equivalent circuit model is as follows:

[0033] in, Represents the imaginary number symbol; This represents the eddy current equivalent in the metallic target.

[0034] Solving the equivalent circuit model of the three-loop coupling yields the mutual inductance between the transmitting coil and the metallic target. And the mutual inductance between the receiving coil and the metal target Then the equivalent impedance of the transmitting coil can be calculated. for: .

[0035] Then the equivalent self-inductance is calculated. for:

[0036] in, Represents the imaginary number symbol; This is the equivalent impedance of the transmitting coil; express The imaginary part.

[0037] The equivalent self-inductance of the transmitting coil is calculated based on its equivalent impedance. The resonant frequencies of the transmitting coils were calculated respectively. and quality factors :

[0038]

[0039] in, This is the matching resonant capacitor for the transmitting coil; This is the resistance value of the transmitting coil.

[0040] In this embodiment, the equivalent circuit between the transmitting coil and the receiving coil can be regarded as a transformer-coupled resonant circuit, and its transfer function can be expressed as:

[0041] in, The angular frequency after frequency offset occurs; and These are the output voltage and input voltage of the transformer-coupled resonant circuit, respectively. This refers to the mutual inductance between the transmitting coil and the receiving coil; This is the equivalent impedance of the transmitting coil; This is the equivalent impedance of the receiving coil. A coupling coefficient is further introduced. Quality Factor and define the coupling factor. and normalized offset frequency Then the normalized frequency response of the coupled resonant circuit can be written as: ; ω is the angular frequency of the sweep signal.

[0042] by The bandwidth is defined by the amount of attenuation relative to the peak value; where, when At that time, the corresponding detection bandwidth It should be noted that the above preset ratio... p It can be 1 / 2, 1 / 5, 1 / 10, etc., and there is no limitation here. Preferably, p It can be 1 / 2 or 1 / 10. (Preset ratio) p A value of 1 / 2 corresponds to a 3dB bandwidth; when the preset ratio is used... p A bandwidth of 1 / 10 corresponds to 10dB. It should be noted that a 3dB bandwidth is more suitable for characterizing response changes near the peak region, while a 10dB bandwidth is more beneficial for characterizing response broadening over a wider dynamic range. Therefore, this embodiment can strike a balance between sensitivity, robustness, and discriminative power depending on different detection scenarios. (Based on the coupling factor...) Select the appropriate bandwidth formula for the given interval. For undercoupling, For critical coupling, This is overcoupling.

[0043] In one alternative implementation, the above-mentioned resonant frequency-based approach... and quality factors Calculate the preset ratio by which the received signal power of the receiving coil decreases to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ,include: When coupling factor When the value is less than 1, the magnetic detection device is determined to be in an undercoupled state, and the detection bandwidth is [value missing]. When the preset ratio p When it is 1 / 2, This corresponds to a 3dB bandwidth; when the preset ratio is used... p When it is 1 / 10, This corresponds to a 10dB bandwidth.

[0044] When coupling factor When the value equals 1, the magnetic detection device is determined to be in a critical coupling state, and the detection bandwidth is [value missing]. When the preset ratio p When it is 1 / 2, This corresponds to a 3dB bandwidth; when the preset ratio is used... p When it is 1 / 10, This corresponds to a 10dB bandwidth.

[0045] When coupling factor When the value is greater than 1, the magnetic detection device is determined to be in an overcoupled state, and the detection bandwidth is [value missing]. When the preset ratio p When it is 1 / 2, This corresponds to a 3dB bandwidth; when the preset ratio is used... p When it is 1 / 10, This corresponds to a 10dB bandwidth.

[0046] Wherein, coupling coefficient ; As can be seen from the above expression, under the same coupling state, the amplitude decrease range corresponding to 10dB bandwidth is greater than that of 3dB bandwidth, the feature dynamic range is larger, and it is more sensitive to weak coupling disturbances caused by metallic targets. Therefore, it is preferable to take the 10dB bandwidth change as the main inversion feature.

[0047] Preferably, in an optional embodiment, the above magnetic detection method further includes: when a metallic target exists in the area to be detected, determining the location of the metallic target based on the current bandwidth characteristics. Obtain the pre-collected sample set; The K feature samples most similar to the current bandwidth feature are selected from the sample set to form a candidate sample set; ; The label that appears most frequently in the candidate sample set is taken as the current location of the metal target in the area to be detected; The aforementioned sample set was obtained through the following methods: Obtain a metal sample that is identical in size and material type to the metal target; The area to be detected is divided into voxel grids; The center point of each voxel grid is taken as the position of the metal sample, and the bandwidth feature corresponding to the metal sample at that position is obtained; a sample set is constructed with the bandwidth feature as the feature sample and the corresponding position as the label; The bandwidth characteristics mentioned above are: preset ratio p The absolute value of the corresponding difference Or, each preset ratio in the preset ratio set p' The vector formed by the absolute values ​​of the corresponding differences; the preset ratio set includes preset ratios p ; for and The absolute value of the difference.

[0048] It should be noted that the similarity metric used to obtain the K most similar feature samples to the current bandwidth feature from the sample set can be cosine similarity, Manhattan distance, Euclidean distance, etc., and is not limited here. Preferably, clustering algorithms such as KNN and K-means can also be used to obtain the K most similar feature samples to the current bandwidth feature from the sample set.

[0049] In one specific implementation, the input current is set to 1A, the radius of both the transmitting and receiving coils is 0.1m, the size of the metal target is 0.01m, and the default conductivity is 10. 6 S / m, default relative permeability is 1, default resonant frequency is 450kHz, number of turns is 1 turn, wire diameter is 1mm.

[0050] When collecting the sample set, obtain metal samples that are the same size and material type as the metal target; A mapping relationship between the location of the metal sample and its bandwidth features is established beforehand. The location of the metal sample includes the radial offset of the metal target relative to the axes of the transmitting and receiving coils, and its axial distance relative to the coil plane; the bandwidth feature is preferably a 10dB bandwidth variation, but can also be further combined with a 3dB bandwidth variation. When collecting the sample set, the bandwidth features corresponding to the metal sample at different voxel center positions are used as training samples, and the corresponding positions are used as labels to construct the collected sample set; the K-nearest neighbor classification algorithm is used to classify the measured bandwidth features, thereby obtaining the location of the metal target.

[0051] In a specific embodiment corresponding to the simulation results, a three-dimensional spatial coordinate system is established: with the direction of the line connecting the centers of the transmitting coil and the receiving coil as the x-axis, the transmitting coil is located on the left and the receiving coil is located on the right, arranged coaxially and spaced apart; the center coordinates of the transmitting coil are (…). The center coordinates of the receiving coil are (0, 0), and the center coordinates of the receiving coil are ( ,0,0), where This is the center-to-center distance between the transmitting and receiving coils. In this embodiment, The radius of the transmitting and receiving coils is set to 0.50m, the number of coil turns is set to 1, and the wire diameter is set to 1mm. The reference resonant frequency of the transmitting coil detection circuit is set to 450kHz, and the matching capacitor is determined so that the transmitting detection circuit is in a matched resonant state under the reference condition of no metal target.

[0052] In this embodiment, the space to be detected between the transmitting and receiving coils is divided into multiple cubic voxel grids with sides of 5 cm. Using the direction of the line connecting the transmitting and receiving coils as the x-axis, the x-direction can be divided within the effective detection range between the transmitting and receiving coils, while the y-direction and z-direction can be divided within the effective sensing range near the coil radius. Each voxel grid uses its center point as a candidate target location for a metal sample. Metal samples are sequentially placed at the center points of each voxel, and the bandwidth characteristics corresponding to each voxel center point are calculated or calibrated, thus forming a calibration library (i.e., a sample set) of "voxel position-bandwidth characteristics". For cases where a single transmitting coil and a single receiving coil are arranged coaxially, due to the system's axial symmetry, prior position information can be further combined to filter the candidate voxel position set. Each voxel number can also be used as a category label for subsequent K-nearest neighbor spatial classification.

[0053] When establishing the calibration library, for the first... Individual center point Based on the three-loop coupled equivalent circuit, the mutual inductance between the transmitting and receiving coils is calculated when the metal sample is located at the center point of the voxel. Mutual inductance between the transmitting coil and the metallic target Mutual inductance between the receiving coil and the metal target Then the equivalent impedance of the transmitting coil can be calculated. Then by The equivalent self-inductance of the transmitting coil is obtained, and the quality factor is calculated accordingly. Then, the corresponding bandwidth characteristics are calculated. ; The total number of voxels. Construct a sample set with bandwidth features as feature samples and corresponding positions as labels, as the calibration library.

[0054] In this embodiment, a preset ratio is taken. pA value of 1 / 10 corresponds to a 10dB bandwidth. The 10dB bandwidth change essentially represents the difference in broadening of the resonant response curve at the current voxel location relative to the reference environment; therefore, it directly reflects the degree of environmental disturbance at that voxel location. For example... Figure 3 The above is a three-dimensional distribution diagram of the 10dB bandwidth variation when the metal target is located in different voxel grids, as provided in this embodiment.

[0055] During actual detection, the voltage, current, or sweep frequency response of the transmitting end is acquired, the measured bandwidth features are extracted, and these are input into a K-nearest neighbor classifier built based on calibration samples. The classifier outputs the candidate location of the target. When the confidence of the classification result is lower than a preset threshold, it is determined that the target is not located in the current calibration space or needs to be recalibrated. Specifically, the Euclidean distance between the feature to be measured and each calibration sample can be calculated, K nearest neighbor samples can be selected, and the candidate location can be determined based on the majority voting result. K is preferably any odd number of 3, 5, or 7.

[0056] In this implementation, when a metallic target exists within the detection area, based on the current bandwidth characteristics... The specific process of determining the location of a metallic target includes: Step 1: Locate the center point of each calibrated voxel. Record the location of the metal sample at the center point of the voxel. At that time, the corresponding bandwidth characteristic quantity and assign location labels To form a sample set .

[0057] Step two: Analyze the bandwidth features in the sample set and the current bandwidth features. Perform normalization processing, which can be done by range normalization or standard deviation normalization, so that the bandwidth characteristics can participate in distance calculation on the same numerical scale.

[0058] Step 3: Calculate the current bandwidth characteristics The distance between the sample and each labeled sample in the sample set. The distance is calculated using Euclidean distance by default, i.e.:

[0059] in, Current bandwidth characteristics The j Normalized components, For the first i The first calibration sample jThe normalized component is n, where n is the number of feature dimensions. When the probe feature uses only a single bandwidth variation, n = 1. In another embodiment, Manhattan distance or weighted Euclidean distance can also be used to accommodate situations where different feature dimensions contribute unevenly to the classification results; in weighted Euclidean distance, the weight of each dimension can be preset according to the contribution of that feature dimension to the class discrimination ability in the calibration experiment.

[0060] Step four, according to distance Sort the samples from smallest to largest and select the top K nearest neighbors to form a nearest neighbor set. In this embodiment, K is taken as an odd number to reduce the probability of a tie in voting, preferably K is 3, 5 or 7.

[0061] Step 5: Analyze the nearest neighbor set. The category labels in the middle perform majority voting to select the nearest neighbor set. The label that appears most frequently is used as the current location of the metal target in the area to be detected; in another embodiment, the nearest neighbor samples can also be weighted according to the inverse of the distance, so that the closer the sample is, the greater the weight is when voting.

[0062] Step 6: Calculate the classification confidence based on the percentage of votes received by the winning category among its K nearest neighbors, or based on the weighted voting and its proportion of the total weight. When the confidence is lower than a preset threshold, it can be determined that the current sample is located in the category boundary region, and trigger recalibration, expansion of the candidate category set, or introduction of prior location information for secondary discrimination.

[0063] Through the above process, the K-nearest neighbor classification algorithm uses the similarity relationship between the test sample and a set of neighboring labeled samples in the local feature space to complete the classification decision, and then uses the bandwidth feature to invert the location of the metal target.

[0064] It should be noted that the aforementioned voxel mesh calibration library can be obtained either by calculation using a three-loop coupled equivalent circuit or by finite element simulation or actual measurement calibration. When using actual measurement calibration, metal targets of known size and material can be placed at the center of each voxel sequentially, and the corresponding bandwidth characteristics can be recorded and stored as a calibration library. In practical applications, the 5cm mesh can be replaced with a smaller or larger mesh size according to the required detection accuracy, or the initially matched candidate voxels can be further subdivided to balance positioning accuracy and computational load.

[0065] In one optional implementation, the baseline bandwidth characteristics of the system are first obtained under the condition of no metal target to describe the background response of the environment to be detected. Then, under the condition of a metal target, the metal target is equivalent to an eddy current loop, which together with the transmitting coil and the receiving coil forms a three-loop coupled system. The equivalent impedance and bandwidth change after the target is introduced are solved. Then, a labeled sample library is established based on the bandwidth change corresponding to different voxel positions. Finally, the sample library is used to perform position determination on the measured bandwidth characteristics to realize the target presence judgment and position parameter inversion.

[0066] This embodiment uses bandwidth as the core detection feature, highlighting its sensitivity to environmental changes, configurable measurement sensitivity, and comprehensive characterization ability of the original environmental features and the additional features of metal obstacles, thereby improving the practicality of detection and inversion in complex environments.

[0067] This embodiment does not simply record the response at a certain frequency point, but uses the similarity relationship between the sample under test and a set of calibration samples in the local feature space for classification and decision-making. Therefore, it is more suitable for small-range fluctuations caused by temperature drift, device error, environmental disturbance and measurement noise in actual engineering.

[0068] Example 2 This embodiment provides a transceiver coil mutual inductance magnetic detection system, including: a transceiver coil mutual inductance magnetic detection device and a control module; wherein, the transceiver coil mutual inductance magnetic detection device includes: a transmitting coil and a receiving coil; the control module is used to execute the transceiver coil mutual inductance magnetic detection method provided in Embodiment 1 of the present invention.

[0069] This embodiment can be applied to scenarios such as underground exploration and underwater exploration. The target to be explored is equipped with a device containing a metal target, and it is explored by a transceiver coil mutual inductance magnetic detection system.

[0070] The relevant technical solutions are the same as the transceiver coil mutual inductance magnetic detection method provided in Embodiment 1 of the present invention, and will not be described in detail here.

[0071] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A magnetic detection method based on mutual inductance of transceiver coils, characterized in that, It is applied to a transceiver coil mutual inductance magnetic detection device that includes a transmitting coil and a receiving coil; The magnetic detection method includes: An alternating excitation voltage signal is applied to the transmitting coil, causing the transmitting coil to generate an alternating magnetic field in the region to be detected; Obtain a preset ratio of the received signal power of the receiving coil decreasing to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ; Determine the detection bandwidth With the corresponding reference bandwidth If the absolute value of the difference is less than or equal to a preset threshold, then it is determined that there is no metal target in the area to be detected; otherwise, it is determined that there is a metal target in the area to be detected. Among them, the reference bandwidth This is a preset ratio by which the received signal power of the receiving coil decreases to its maximum value under a reference state where no metallic target is present. p The frequency range corresponding to the time.

2. The transceiver coil mutual inductance magnetic detection method according to claim 1, characterized in that, The preset ratio at which the received signal power of the receiving coil drops to its maximum value. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ,include: The intrinsic impedance of the transmitting coil The impedance of the receiving coil Equivalent impedance of metallic targets Angular frequency of the excitation voltage signal and voltage value Mutual inductance between the transmitting coil and the receiving coil and the equivalent current of the transmitting coil and the equivalent current of the receiving coil Substituting the values ​​into the three-loop coupled equivalent circuit model and solving it, we obtain the mutual inductance between the transmitting coil and the metallic target. And the mutual inductance between the receiving coil and the metal target Then the equivalent impedance of the transmitting coil can be calculated. ; Based on the equivalent impedance of the transmitting coil The equivalent self-inductance of the transmitting coil was calculated. The resonant frequencies of the transmitting coils were calculated respectively. and quality factors ; Based on resonant frequency and quality factors Calculate the preset ratio by which the received signal power of the receiving coil decreases to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ; The three-loop coupled equivalent circuit model is a set of equations consisting of KVL equations established for the transmitting coil and receiving coil, the transmitting coil and the metal target, and the receiving coil and the metal target, respectively.

3. The transceiver coil mutual inductance magnetic detection method according to claim 2, characterized in that, The equivalent circuit model of the three-loop coupling is as follows: in, Represents the imaginary number symbol; This represents the eddy current equivalent in the metallic target.

4. The transceiver coil mutual inductance magnetic detection method according to claim 2, characterized in that, The equivalent impedance of the transmitting coil for: 。 5. The transceiver coil mutual inductance magnetic detection method according to claim 2, characterized in that, The resonant frequency and the aforementioned quality factors They are respectively: in, This is the matching resonant capacitor for the transmitting coil; This is the resistance value of the transmitting coil.

6. The transceiver coil mutual inductance magnetic detection method according to claim 2, characterized in that, The equivalent self-inductance for: in, Represents the imaginary number symbol; This is the equivalent impedance of the transmitting coil; express The imaginary part.

7. The transceiver coil mutual inductance magnetic detection method according to claim 2, characterized in that, Based on resonant frequency and quality factors Calculate the preset ratio by which the received signal power of the receiving coil decreases to the maximum value of the received signal power. p The frequency range corresponding to the time is used as a preset ratio. p The corresponding detection bandwidth ,include: When coupling factor When the value is less than 1, the magnetic detection device is determined to be in an undercoupled state, and the detection bandwidth is [value missing]. ; When coupling factor When the value equals 1, the magnetic detection device is determined to be in a critical coupling state, and the detection bandwidth is [value missing]. ; When coupling factor When the value is greater than 1, the magnetic detection device is determined to be in an overcoupled state, and the detection bandwidth is [value missing]. ; Wherein, coupling coefficient .

8. The transceiver coil mutual inductance magnetic detection method according to any one of claims 1-7, characterized in that, The preset ratio p It is 1 / 2 or 1 / 10.

9. The transceiver coil mutual inductance magnetic detection method according to any one of claims 1-7, characterized in that, Also includes: When a metallic target is present in the area to be detected, the location of the metallic target is determined based on the current bandwidth characteristics: Obtain the pre-collected sample set; Select the K feature samples that are most similar to the current bandwidth feature from the sample set to form a candidate sample set; ; The label that appears most frequently in the candidate sample set is taken as the current location of the metal target in the area to be detected; The sample set is obtained in the following way: Obtain a metal sample that is identical in size and material type to the metal target; The area to be detected is divided into voxel grids; The center point of each voxel grid is taken as the position of the metal sample, and the bandwidth feature corresponding to the metal sample at that position is obtained; a sample set is constructed with the bandwidth feature as the feature sample and the corresponding position as the label; The bandwidth characteristic is: preset ratio. p The absolute value of the corresponding difference Or, each preset ratio in the preset ratio set p' The vector formed by the absolute values ​​of the corresponding differences; The preset ratio set includes preset ratios p ; for and The absolute value of the difference.

10. A transceiver coil mutual inductance magnetic detection system, characterized in that, include: A transceiver coil mutual inductance magnetic detection device and a control module; wherein the transceiver coil mutual inductance magnetic detection device includes: a transmitting coil and a receiving coil; the control module is used to execute the transceiver coil mutual inductance magnetic detection method according to any one of claims 1-9.

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