Electromagnetic tomography sensing device and method for small-size metal detection

Abstract

The invention discloses an electromagnetic tomography sensing device and method for small-size metal detection. The device comprises an electromagnetic tomography sensor, a multi-channel eddy current instrument and a computer end which are connected in sequence, the electromagnetic tomography sensor comprises a plurality of coils and a plurality of PCBs (Printed Circuit Board); a plurality of groups of contacts are arranged at two ends of the PCB, the plurality of groups of contacts at one end of the PCB are correspondingly connected with the coil, and the plurality of groups of contacts at the other end of the PCB are connected with a channel of the multi-channel eddy current instrument. According to the invention, accurate position detection and size distinguishing can be carried out on small-size conductive or magnetic conductive materials, and contributions are made to research and application of small-size target detection in industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic tomography, and in particular to an electromagnetic tomography sensing device and method for small-size metal detection. Background Art

[0002] Due to its non-invasive, radiation-free, low-cost and non-contact characteristics, electromagnetic tomography technology is being widely studied and applied in many fields. It is particularly suitable for scenarios involving material conductivity and magnetic permeability. For example, electromagnetic tomography technology can be used for metal defect detection in industrial processes, ion water monitoring, analysis of multiphase flow in pipelines, and separation of ferrite powder. Electromagnetic tomography technology can also be applied to the fields of medicine and biological imaging, including analysis of biological tissues and monitoring of human stroke. Electromagnetic tomography technology is based on the principle of electromagnetic induction. Multiple electrical signals are generated by coupling between multiple electromagnetic coils and conductive materials, and images are obtained after signal reconstruction algorithms. Compared with other non-contact imaging methods, such as acoustic imaging, thermal imaging and visible light imaging, electromagnetic tomography methods take into account the characteristics of fast time and high accuracy, greatly improving measurement efficiency.

[0003] A study proposed a design of a parallel electromagnetic tomography sensor, in which a large-sized excitation coil surrounds the object space and generates a uniform parallel excitation magnetic field. This design improves the detectability of the center of the imaging space, but the number of independent measurements is limited and accurate imaging images cannot be obtained. Some scholars have mentioned and analyzed multi-pole geometry. The measurement signal is enhanced by inserting a ferrite core into the coil to concentrate the magnetic flux. However, the above studies mainly focus on the application of relatively large-sized targets, and the monitoring research of small targets (such as small-sized steel bars and copper wires) is still insufficient.

[0004] Electromagnetic tomography is widely used in nondestructive testing of metal materials due to its fast response, non-contact, and high sensitivity to electromagnetic properties. Electromagnetic reconstruction algorithms can be divided into two categories: non-iterative algorithms and iterative algorithms. Non-iterative algorithms, such as linear back projection and Tikhonov regularization, have the advantages of simplicity and fast response speed and are suitable for real-time imaging. Iterative algorithms, such as conjugate gradient method and Landweber iteration method, generally provide higher quality images. Different electromagnetic reconstruction algorithms produce imaging images of different qualities. Although existing research has developed and improved different algorithms to improve accuracy and response speed, they are still not effective in distinguishing objects of different sizes. Summary of the invention

[0005] The purpose of the present invention is to provide an electromagnetic tomography sensing device and method for small-sized metal detection, which can accurately detect the position and distinguish the size of small-sized conductive or magnetic materials, and contribute to the research and application of small-sized target detection in industrial production.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] An electromagnetic tomography sensing device for small-size metal detection comprises an electromagnetic tomography sensor, a multi-channel eddy current instrument and a computer terminal connected in sequence;

[0008] The electromagnetic tomography sensor comprises a circular imaging area, N coils and a plurality of PCB boards; a plurality of groups of contacts are arranged at both ends of the PCB board, the plurality of groups of contacts at one end of the PCB board are correspondingly connected to the coils, and the plurality of groups of contacts at the other end of the PCB board are connected to channels of a multi-channel eddy current instrument; among the N coils, (N-2) coils are evenly distributed around the circular imaging area and are located in the same plane, and two horizontally parallel coils are wound up and down on the plane where the (N-2) coils are located, wherein N is a positive integer greater than 2.

[0009] Preferably, N=10, and the multiple coils include a first coil, a second coil, a third coil, a fourth coil, a fifth coil, a sixth coil, a seventh coil, an eighth coil, a ninth coil, and a tenth coil; the first to eighth coils are evenly distributed around the circular imaging area, and the ninth and tenth coils are wound up and down in parallel with the horizontal direction on the plane where the first to eighth coils are located.

[0010] Preferably, the diameters of the first coil, the second coil, the third coil, the fourth coil, the fifth coil, the sixth coil, the seventh coil and the eighth coil are smaller than those of the ninth coil and the tenth coil.

[0011] Preferably, the multiple PCB boards include a first PCB board and a second PCB board, the first coil, the second coil, the third coil, the fourth coil, and the tenth coil are connected to multiple groups of contacts on the first PCB board, and the fifth coil, the sixth coil, the seventh coil, the eighth coil, and the ninth coil are connected to multiple groups of contacts on the second PCB board.

[0012] Preferably, the electromagnetic tomography sensor further comprises a plurality of iron cores, which are respectively arranged in the first coil, the second coil, the third coil, the fourth coil, the fifth coil, the sixth coil, the seventh coil and the eighth coil.

[0013] An electromagnetic tomography sensing method for small-sized metal detection, applied to any one of the above-mentioned electromagnetic tomography sensing devices for small-sized metal detection, comprising:

[0014] The object to be tested is placed vertically in the imaging area of ​​the electromagnetic tomography sensor. The multi-channel eddy current instrument generates an alternating current which is passed into each coil in turn to generate an excitation magnetic field. The object to be tested induces eddy currents under the action of the excitation magnetic field, and the eddy currents will generate a secondary magnetic field.

[0015] The coil generates an induced voltage under the action of the excitation magnetic field and the secondary magnetic field; in each working cycle, the multi-channel eddy current instrument collects the induced voltage of the coil and transmits the collected data to the computer end, and the program on the computer end processes the collected data to realize the detection and size distinction of the object to be measured.

[0016] Preferably, in one working cycle, the first coil to the eighth coil are alternately fed with alternating current to serve as excitation coils to generate an excitation magnetic field, and the remaining coils serve as induction coils to generate an induced voltage.

[0017] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0018] (1) The present invention reduces the overall size of the electromagnetic tomography sensor, especially reduces the imaging area diameter to 7.5 mm, thereby ensuring that the magnetic field of each excitation coil can act on each induction coil, so that it can sensitively capture the weak signal generated by small objects. Therefore, compared with existing detection technologies, the sensor has higher accuracy in detecting small objects.

[0019] (2) The sensor designed by the present invention adopts a new coil arrangement and adds a horizontal coil that is not available in traditional sensors. The vertical magnetic field generated by the horizontal coil is more sensitive to the cross-sectional size of the object placed in the detection area. The size of the detected object can be directly reflected in the measurement value of the horizontal coil, which further standardizes the judgment of the object size in the reconstructed image and makes up for the deficiency of traditional electromagnetic tomography sensors that are difficult to distinguish the size of objects. At the same time, since the vertical magnetic field generated by the horizontal coil is approximately evenly distributed in the detection area, the measurement value can remain relatively stable when the object is placed in different positions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 A structural diagram of an electromagnetic tomography sensing device for small-size metal detection provided by the present invention;

[0022] Figure 2This is a structural connection diagram of the electromagnetic tomography sensor of the present invention;

[0023] Among them, 1-first coil, 2-second coil, 3-third coil, 4-fourth coil, 5-fifth coil, 6-sixth coil, 7-seventh coil, 8-eighth coil, 9-ninth coil, 10-tenth coil, 11-first PCB board, 12-second PCB board;

[0024] Figure 3 A three-dimensional view of the spatial distribution of electromagnetic tomography sensor coils of the present invention;

[0025] Figure 4 This is a principle block diagram of the electromagnetic tomography sensor device of the present invention;

[0026] Figure 5 Reconstructed images of copper wires of different diameters according to an embodiment of the present invention;

[0027] Among them, (a) is the reconstructed image of the copper wire with a diameter of 1 mm, (b) is the reconstructed image of the copper wire with a diameter of 1.5 mm, and (c) is the reconstructed image of the copper wire with a diameter of 3 mm.

[0028] Figure 6 These are the horizontal coil measurement values ​​corresponding to 1mm, 1.5mm and 3mm copper wires at different positions in the embodiment of the present invention;

[0029] Figure 7 Reconstructed images of steel rods of different diameters according to an embodiment of the present invention;

[0030] Among them, (a) is the reconstructed image of a steel rod with a diameter of 1.6 mm, (b) is the reconstructed image of a steel rod with a diameter of 2.46 mm, and (c) is the reconstructed image of a steel rod with a diameter of 4 mm.

[0031] Figure 8 These are the horizontal coil measurement values ​​corresponding to different positions of 1.6 mm, 2.46 mm and 4 mm steel bars in the embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Reference Figure 1 As shown, the present invention discloses an electromagnetic tomography sensing device for small-size metal detection, which includes an electromagnetic tomography sensor, a multi-channel eddy current instrument and a computer terminal connected in sequence.

[0034] like Figure 2 As shown, the electromagnetic tomography sensor includes a circular imaging area, N coils and multiple PCB boards; multiple groups of contacts are provided at both ends of the PCB board, the multiple groups of contacts at one end of the PCB board are correspondingly connected to the coils, and the multiple groups of contacts at the other end of the PCB board are connected to the channels of the multi-channel eddy current instrument; among the N coils, (N-2) coils are evenly distributed around the circular imaging area and are located in the same plane, and two horizontally parallel coils are wound up and down on the plane where the (N-2) coils are located, wherein N is a positive integer greater than 2.

[0035] Specifically, N=10, and the electromagnetic tomography sensor includes a circular imaging area, 8 small-sized coils evenly distributed around the imaging area, and 2 large coils wound horizontally. The imaging area of ​​the sensor has a diameter of 7.5 mm. The 8 small coils are placed in 8 small holes around the imaging area. The total number of turns of each small coil is 200. Its outer radius and inner radius are 0.7 mm and 0.4 mm respectively, and the axial length is 2.4 mm. A core with a length of 7.5 mm and a radius of 0.35 mm is inserted into each small coil to enhance the magnetic flux density generated by the coil and the degree of coupling between the coils. In addition, two large coils parallel to the horizontal direction are wound up and down on the plane where the 8 small coils are located. Each large coil has a total number of turns of 30, an axial length of 2 mm, an inner diameter of 8.5 mm, and is located in two horizontal grooves respectively.

[0036] Furthermore, the plurality of coils include a first coil 1 , a second coil 2 , a third coil 3 , a fourth coil 4 , a fifth coil 5 , a sixth coil 6 , a seventh coil 7 , an eighth coil 8 , a ninth coil 9 , and a tenth coil 10 ; and the PCB board includes a first PCB board 11 and a second PCB board 12 .

[0037] Furthermore, the diameters of the first coil 1 , the second coil 2 , the third coil 3 , the fourth coil 4 , the fifth coil 5 , the sixth coil 6 , the seventh coil 7 , and the eighth coil 8 are smaller than those of the ninth coil 9 and the tenth coil 10 .

[0038] Furthermore, the first coil 1, the second coil 2, the third coil 3, the fourth coil 4, and the tenth coil 10 are connected to multiple groups of contacts of the first PCB board 11, and the fifth coil 5, the sixth coil 6, the seventh coil 7, the eighth coil 8, and the ninth coil 9 are connected to multiple groups of contacts of the second PCB board 12.

[0039] Furthermore, the first coil 1 to the eighth coil 8 are evenly distributed around the circular imaging area, and the ninth coil 9 and the tenth coil 10 are wound up and down in parallel in the horizontal direction on the plane where the first coil 1 to the eighth coil 8 are located.

[0040] Furthermore, the electromagnetic tomography sensor further includes a plurality of iron cores, which are respectively arranged in the first coil 1, the second coil 2, the third coil 3, the fourth coil 4, the fifth coil 5, the sixth coil 6, the seventh coil 7, and the eighth coil 8. The spatial distribution of the coils and the iron cores is as follows: Figure 3 shown.

[0041] An electromagnetic tomography sensing method for small-sized metal detection, applied to any one of the above-mentioned electromagnetic tomography sensing devices for small-sized metal detection, comprising:

[0042] The object to be measured is placed vertically in the imaging area of ​​the electromagnetic tomography sensor. The multi-channel eddy current instrument generates an alternating current which is passed into each coil in turn to generate an excitation magnetic field. The object to be measured induces eddy currents under the action of the excitation magnetic field, and the eddy currents will generate a secondary magnetic field.

[0043] The coil generates an induced voltage under the action of the excitation magnetic field and the secondary magnetic field; in each working cycle, the multi-channel eddy current instrument collects the induced voltage of the coil and transmits the collected data to the computer end, and the program on the computer end processes the collected data to realize the detection and size distinction of the object being measured.

[0044] Specifically, in one working cycle, the first coil to the eighth coil are alternately fed with alternating current as excitation coils to generate an excitation magnetic field, and the remaining coils are used as induction coils to generate an induced voltage;

[0045] All coils are connected to the multi-channel eddy current instrument through two PCB boards to realize signal transmission. The multi-channel eddy current instrument performs IQ demodulation processing on the measured data and then transmits it to the computer. The new sensor designed by the present invention adopts multiple sets of "excitation-reception" working modes. The excitation signal is generated by the multi-channel eddy current instrument. In one working cycle, alternating current is passed into each small coil in turn as an excitation coil, and the remaining 7 small coils are used as induction coils. For example, when the first coil 1 is excited, the induced voltage values ​​of the second coil 2, the third coil 3, ..., the eighth coil 8 are collected. When the second coil 2 is excited, the induced voltage values ​​of the third coil 3, the fourth coil 4, ..., the eighth coil 8 are collected. In this way, the signal can be obtained from the small coils. A set of independent measurement values ​​is used for subsequent image reconstruction. In addition, the two large horizontal coils form an independent excitation-receiving pair. The ninth coil 9 on the top is excited to generate a vertical and uniform magnetic field, and the tenth coil 10 on the bottom generates an induced voltage, thereby obtaining an additional set of measurement values ​​for object size differentiation. Therefore, the sensor will generate 28+1=29 sets of independent measurement values ​​in one working cycle. These 29 sets of measurement values ​​are used to achieve image reconstruction and size differentiation of the measured object. The workflow of the entire system is as follows: Figure 4 shown.

[0046] The multi-channel eddy current instrument collects the induced voltages of 28 groups of small coils and 1 group of horizontal coils, and transmits the collected data to the computer.

[0047] The corresponding program on the computer will process the collected data. The first 28 sets of measurement values ​​obtained by the small coils are used to obtain a two-dimensional distribution image of the electromagnetic characteristics of the measured object through an inversion algorithm, and the last set of measurement values ​​generated by the horizontal coils are used to further distinguish the sizes of different measured objects.

[0048] In specific embodiment 1 (image reconstruction and size distinction of copper wires of different sizes):

[0049] The implementation process of this embodiment is as follows Figure 4 As shown, at an excitation frequency of 20kHz, three representative conductive materials of different sizes: copper wires with a diameter of 1mm, 1.5mm and 3mm are placed vertically in various positions in the imaging area, and the measurement values ​​of all coils are extracted and processed on the computer using the corresponding program. The Landweber iteration method is used here for image reconstruction. The execution steps of the algorithm are shown in Algorithm 1, and the configuration of the relevant parameters of the iteration algorithm is shown in Table 1.

[0050] Algorithm 1: Landweber Iteration Method

[0051] Input: small coil measurement vector V, sensitivity matrix S, number of iterations, calculation step α error tolerance ∈

[0052] Output: electromagnetic characteristic distribution vector g

[0053] 1: Initialization: g 1 =(S T S-αI)S T V,k=1

[0054] 2: while(k <iteration)do

[0055] 3:g k+1 =g k +αS T (V-Sg k )

[0056] 4:if

[0057] 5:Break;

[0058] 6:end if

[0059] 7: end while

[0060] Table 1

[0061]

[0062] Figure 5 Several representative reconstructed images are shown, and the black dotted line represents the actual position of the copper wire. It can be seen that this sensor can detect the existence of the small-sized copper wire and accurately reflect its location. However, the image is difficult to reflect the size of the copper wire, and copper wires of different sizes are also difficult to distinguish in the reconstructed image. The bar graph drawn using the real part, imaginary part and amplitude of the horizontal coil measurement value is shown in Figure 1. Figure 6 As shown in the figure, when copper wires of different sizes are placed at different positions in the imaging area: lower left corner, lower right corner, upper right corner, upper left corner and center, their corresponding horizontal coil measurements can remain relatively uniform. However, there is still a certain degree of fluctuation in the measurements at different positions, which may be caused by the incomplete uniformity of the magnetic field and the slight deviation of the copper wire placement angle from the vertical direction. In general, each size of copper wire can correspond to a unique set of horizontal coil measurements. By analyzing the measurements of the horizontal coil, copper wires of different sizes can be intuitively distinguished.

[0063] In specific embodiment 2 (image reconstruction and size distinction of steel bars of different sizes):

[0064] The operation process and related configuration of this embodiment are the same as those of embodiment 1. Three representative ferromagnetic materials of different sizes: steel rods with a diameter of 1.6 mm, 2.46 mm, and 4 mm were placed vertically at various positions within the imaging area. The representative reconstructed images thus obtained are shown in FIG. Figure 7 As shown in the figure, the white dotted line represents the location of the steel rod. It can be seen that the steel rod has the opposite polarity (i.e., opposite pixel value) to the copper wire in the reconstructed image, reflecting the difference in electromagnetic properties between the two. Similarly, these steel rods are placed in the lower left corner, lower right corner, upper right corner, upper left corner and center of the imaging area, and the horizontal coil measurement values ​​are obtained as follows Figure 8 Compared to copper wire, the steel rod can obtain more stable and uniform measurements, and the steel rods of different sizes can be easily distinguished by the corresponding horizontal coil measurements.

[0065] The present invention designs a new type of small electromagnetic tomography sensor, which is suitable for small target detection and has the ability to distinguish sizes. The sensor arranges eight small-sized coils around the measuring pipe (imaging area) for target imaging, and wraps two horizontal coils around the entire measuring pipe, which can generate a nearly uniform vertical magnetic field to distinguish target objects of different sizes. The target is imaged by eight small coils, and the image is reconstructed by the electromagnetic characteristic distribution obtained by the inversion algorithm to obtain the position information of the target. Further, according to the measurement value of the horizontal coil, the relevant information of the target size is obtained to standardize the judgment of the object size in the reconstructed image.

[0066] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0067] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An electromagnetic tomography sensing device for small-size metal detection, characterized in that: It includes an electromagnetic tomography sensor, a multi-channel eddy current instrument and a computer terminal connected in sequence; The electromagnetic tomography sensor includes a circular imaging area, N coils and multiple PCB boards; multiple groups of contacts are provided at both ends of the PCB board, the multiple groups of contacts at one end of the PCB board are correspondingly connected to the coils, and the multiple groups of contacts at the other end of the PCB board are connected to the channels of a multi-channel eddy current instrument; among the N coils, (N-2) coils are evenly distributed around the circular imaging area and are located in the same plane, and two horizontally parallel coils are wound up and down on the plane where the (N-2) coils are located, wherein N is a positive integer greater than 2.

2. The electromagnetic tomography sensing device for small-size metal detection according to claim 1, characterized in that: The N=10, and the plurality of coils include a first coil, a second coil, a third coil, a fourth coil, a fifth coil, a sixth coil, a seventh coil, an eighth coil, a ninth coil, and a tenth coil; the first to eighth coils are evenly distributed around the circular imaging area, and the ninth and tenth coils are wound up and down in parallel in the horizontal direction on the plane where the first to eighth coils are located.

3. The electromagnetic tomography sensing device for small-size metal detection according to claim 2, characterized in that: The diameters of the first coil, the second coil, the third coil, the fourth coil, the fifth coil, the sixth coil, the seventh coil, and the eighth coil are smaller than the diameters of the ninth coil and the tenth coil.

4. The electromagnetic tomography sensing device for small-size metal detection according to claim 3, characterized in that: The multiple PCB boards include a first PCB board and a second PCB board. The first coil, the second coil, the third coil, the fourth coil, and the tenth coil are connected to multiple groups of contacts on the first PCB board. The fifth coil, the sixth coil, the seventh coil, the eighth coil, and the ninth coil are connected to multiple groups of contacts on the second PCB board.

5. The electromagnetic tomography sensing device for small-size metal detection according to claim 4, characterized in that: The electromagnetic tomography sensor further includes a plurality of iron cores, which are respectively arranged in the first coil, the second coil, the third coil, the fourth coil, the fifth coil, the sixth coil, the seventh coil, and the eighth coil.

6. An electromagnetic tomography sensing method for small-size metal detection, applied to an electromagnetic tomography sensing device for small-size metal detection as claimed in any one of claims 1 to 5, characterized in that: include: The object to be measured is placed vertically in the imaging area of ​​the electromagnetic tomography sensor, and the multi-channel eddy current instrument generates an alternating current which is sequentially passed into each coil to generate an excitation magnetic field; the object to be measured induces eddy currents under the action of the excitation magnetic field, and the eddy currents will generate a secondary magnetic field; The coil generates an induced voltage under the action of the excitation magnetic field and the secondary magnetic field; in each working cycle, the multi-channel eddy current instrument collects the induced voltage of the coil and transmits the collected data to the computer end, and the program on the computer end processes the collected data to realize the detection and size distinction of the object to be measured.

7. The electromagnetic tomography sensing method for small-size metal detection according to claim 6, characterized in that: In a working cycle, the first coil to the eighth coil are alternately fed with alternating current to serve as excitation coils to generate an excitation magnetic field, and the remaining coils serve as induction coils to generate an induced voltage.

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