An array-type planar eddy current sensor based on Koch curve

Abstract

The present invention provides an array-type planar eddy current sensor based on the Koch curve. Through the arrayed excitation coils and signal pickup coils, it can not only microscopically expand the detection space of traditional eddy current detection technology and improve its detection sensitivity, but also macroscopically expand the detection space, which helps to detect defects such as cracks and corrosion over a large area and improve its detection speed. At the same time, the present invention uses a complex Koch curve coil structure to distribute the eddy currents generated on the metal surface in more directions in a local area, increasing the probability and intensity of interaction between eddy currents and cracks, thereby effectively improving the planar sensor's crack detection capability, thereby compensating for the shortcomings of traditional sensors in detecting tiny cracks and complex component defects, providing a new solution for defect detection in actual engineering structures, and playing an important role in the field of intelligent manufacturing.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent manufacturing and the category of electromagnetic eddy current detection technology in the field of non-destructive testing, and in particular relates to an array-type planar eddy current sensor based on the Koch curve. Background Art

[0002] Flexible planar eddy current sensors, as a new type of planar eddy current sensor, offer advantages over traditional three-dimensional rigid eddy current sensors, including adaptability to complex surface areas, ease of manufacturing, maximum surface contact with parts, high reliability and sensitivity, and effective suppression of lift-off noise. Eddy current sensors can be categorized as absolute or differential based on their coil winding method. Absolute eddy current sensors have the simplest coil winding, enabling signal acquisition using a single coil. Cracks or other defects in the test piece can cause changes in the magnetic field within the coil.

[0003] The paper "Planar Coil-Excited Eddy Current Sensor Based on Fractal Theory" proposes a planar eddy current sensor based on a Koch snowflake pattern excitation device, a self-similar structure based on fractal theory. This sensor can effectively increase the local eddy current energy density and improve the eddy current distribution, thereby enhancing the ability to detect small crack defects. However, arraying of such sensors has not yet been achieved, and non-arrayed sensors still have significant shortcomings in detecting cracks in large areas and complex surfaces. They are also susceptible to measurement noise, resulting in low defect classification accuracy. Summary of the Invention

[0004] To solve the above problems, the present invention provides an array-type planar eddy current sensor based on the Koch curve, which changes the spatial distribution of the excitation field through the Koch curve and realizes arraying, effectively improving the detection capability and detection speed of small cracks in different directions.

[0005] A Koch curve-based array planar eddy current sensor includes an array of overlapping excitation coils and signal pickup coils. The excitation coils are formed by connecting mutually symmetrical upper and lower coils in series. The series connection is carried out in the following manner: the right endpoint of the upper coil is connected in series with the right endpoint of the lower coil, and the left endpoints of the upper and lower coils serve as the input and output terminals of the excitation signal, respectively; or the right endpoint of the upper coil is connected in series with the left endpoint of the lower coil, and the remaining left and right endpoints serve as the input and output terminals of the excitation signal, respectively.

[0006] The upper half coil and the lower half coil are each obtained by sequentially connecting three or more Koch curve segments in series, wherein the Koch curve segments are sequentially connected by connecting four fractal line segments in series, wherein each fractal line segment is sequentially connected by connecting the first line segment to the fourth line segment, wherein the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°, and the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°;

[0007] The signal pickup coil array is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two Koch curve segments in series in a vertically symmetrical manner, and the series starting point and series end point of each signal pickup coil serve as output terminals of two induction signals respectively.

[0008] An array-type planar eddy current sensor based on a Koch curve includes an array of overlapping excitation coils and signal pickup coils, wherein the excitation coil is formed by connecting a mutually symmetrical upper half coil and a lower half coil in series, and the series connection is carried out in such a way that the right endpoint of the upper half coil and the right endpoint of the lower half coil are connected in series, and the left endpoints of the upper half coil and the lower half coil serve as the input terminal and output terminal of the excitation signal, respectively.

[0009] The upper half coil and the lower half coil are each obtained by sequentially connecting three or more Koch curve segments in series, wherein the Koch curve segments are sequentially connected by connecting four fractal line segments in series, wherein each fractal line segment is sequentially connected by connecting the first line segment to the fourth line segment, wherein the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°, and the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°;

[0010] The signal pickup coil array is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two rectangular coils obtained in a cross-winding manner in series in a vertically symmetrical manner, wherein one of the long sides of the rectangular coil is composed of a Koch curve segment, and the winding starting point and winding end point of each signal pickup coil respectively serve as output terminals of two induction signals.

[0011] An array-type planar eddy current sensor based on a Koch curve comprises an array of overlapping excitation coils and an array of signal pickup coils, wherein the array of excitation coils is obtained by connecting three or more excitation coils in series, and the two ends of the series connection serve as input terminals and output terminals of the excitation signal, respectively;

[0012] Each excitation coil is obtained by connecting two symmetrical Koch curve segments in parallel, and the Koch curve segments are sequentially obtained by connecting four fractal line segments in series, wherein each fractal line segment is sequentially obtained by connecting the first line segment to the fourth line segment in series, and the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°; the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°;

[0013] The signal pickup coil array is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two Koch curve segments in series in a vertically symmetrical manner, and the series starting point and series end point of each signal pickup coil serve as output terminals of two induction signals respectively.

[0014] Furthermore, the output terminals of each signal pickup coil are connected to a multiplexer controlled by a 51 single-chip microcomputer. When the sensor detects a defect in the component to be tested, the corresponding signal pickup coil with an induction signal output is selected by the multiplexer, and the induction signal output by it is studied separately.

[0015] Furthermore, the first to fourth line segments of each fractal line segment have the same length.

[0016] Furthermore, the excitation coil and the signal pickup coil are both arranged on the flexible circuit board, and the excitation coil and the signal pickup coil are arranged on different layers. At the same time, the input terminal and output terminal of the excitation coil and the output terminal of the signal pickup coil are all connected to the pads on the flexible circuit board.

[0017] Furthermore, each signal pickup coil has multiple turns of coil wound inside according to its own outer envelope.

[0018] Beneficial effects:

[0019] 1. The present invention provides an array-type planar eddy current sensor based on the Koch curve. Through the arrayed excitation coils and signal pickup coils, it can not only microscopically expand the detection space of traditional eddy current detection technology and improve its detection sensitivity, but also macroscopically expand the detection space, which is helpful for detecting defects such as cracks and corrosion over a large area and improving its detection speed. At the same time, the present invention uses a complex Koch curve coil structure to distribute the eddy currents generated on the metal surface in more directions in a local area, increasing the probability and intensity of interaction between eddy currents and cracks, thereby effectively improving the planar sensor's crack detection capability, and further compensating for the shortcomings of traditional sensors in detecting tiny cracks and complex component defects, providing a new solution for defect detection in actual engineering structures, and playing an important role in the field of intelligent manufacturing.

[0020] 2. The present invention provides an array-type planar eddy current sensor based on the Koch curve, wherein the excitation coil and signal pickup coil are arranged in an array on a flexible circuit board. The excitation coil based on the Koch curve can effectively detect tiny cracks in different directions, and its array arrangement facilitates the detection of defects such as cracks and corrosion over a large area. The array rear coil is arranged on the flexible circuit board, which can closely fit complex curved surfaces, fully utilizing the characteristics of flexibility, improving the ability to detect defects on complex curved surfaces, and compensating for the shortcomings of rigid eddy current sensors. At the same time, because the excitation coil of the present invention is composed of two symmetrical parts connected in series, this series-type eddy current sensor has differential excitation characteristics, which can effectively reduce the output signal of the planar eddy current sensor when there are no cracks and can effectively suppress the influence of lift-off noise.

[0021] 3. The present invention provides an array-type planar eddy current sensor based on the Koch curve. After alternating current is passed through the excitation coil, an induced magnetic field is generated, and induced eddy currents are generated in the test piece. When there are no defects in the test piece, since the upper and lower parts of the signal pickup coil are symmetrically connected in reverse, the induced voltages will cancel each other out using the differential measurement principle, and there will be no output. Once a defect appears in the test piece, the induced voltages in the upper and lower parts of the signal pickup coil change, and a signal is output. It can be seen that the differential measurement-type Koch fractal array eddy current sensor provided by the present invention can improve the detection capability of crack defects, and while increasing the density of the excitation eddy current field, it can quickly detect tiny cracks and complex cracks, and effectively suppress common-mode interference signals such as temperature and lift-off effects.

[0022] 4. The present invention provides an array-type planar eddy current sensor based on the Koch curve. By adopting a rectangular array of Koch curve excitation coils to change the spatial distribution of the excitation field, defects can be quantified without the need for differential analysis. The sensor is not easily affected by measurement noise and can also improve the sensor's ability to detect microcracks in different directions and effectively extract the changes in the magnetic field caused by the eddy current disturbance caused by the cracks. At the same time, the array arrangement helps to detect defects such as cracks and corrosion over a large area. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic structural diagram of an array-type planar eddy current sensor based on a Koch curve provided by the present invention;

[0024] Figure 2 A schematic diagram of the structure of an excitation coil provided by the present invention;

[0025] Figure 3 A schematic diagram of a Koch curve segment provided by the present invention;

[0026] Figure 4 A schematic diagram of a fractal line segment provided by the present invention;

[0027] Figure 5 A schematic diagram of the Koch curve generation process provided by the present invention;

[0028] Figure 6 A schematic diagram of the signal pickup coil structure provided by the present invention;

[0029] Figure 7 A schematic diagram of the planar eddy current sensor provided by the present invention scanning a crack on a test piece;

[0030] Figure 8 A schematic structural diagram of another array-type planar eddy current sensor based on the Koch curve provided by the present invention;

[0031] Figure 9 A schematic structural diagram of another excitation coil provided by the present invention;

[0032] Figure 10 A schematic structural diagram of another signal pickup coil provided by the present invention;

[0033] Figure 11 The present invention provides Figure 10 Schematic diagram of the winding method of the signal pickup coil shown;

[0034] Figure 12 A schematic structural diagram of another excitation coil provided by the present invention;

[0035] Figure 13 The present invention provides Figure 12 Schematic diagram of the direction of the excitation current of the excitation coil shown;

[0036] Figure 14 A schematic diagram of the magnetic field direction when the test piece provided by the present invention has no cracks;

[0037] Figure 15 This is a schematic diagram of the magnetic field direction when the test piece provided by the present invention has cracks. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0039] Example 1

[0040] This embodiment proposes an absolute Koch array sensor based on the planar eddy current sensor of the Koch snowflake, realizes its arraying, and generates an absolute coil structure after the array, thereby improving the detection speed of the sensor. Figure 1As shown, an array-type planar eddy current sensor based on the Koch curve is characterized by comprising an array of overlapping excitation coils and signal pickup coils, wherein, as Figure 2 As shown, the excitation coil is obtained by connecting the upper half coil and the lower half coil in series, and the series connection method is: the right end point of the upper half coil and the right end point of the lower half coil are connected in series, and the left end points of the two serve as the input terminal and output terminal of the excitation signal respectively.

[0041] The upper coil and the lower coil are both obtained by serially connecting three or more Koch curve segments, where Figure 3 As shown, the Koch curve segment is obtained by connecting four fractal segments in series, where Figure 4 As shown, each fractal line segment is obtained by serially connecting the first to fourth line segments, and the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°. The first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°.

[0042] It should be noted that the Koch curve is generated by Figure 5 As shown:

[0043] 1. Given a straight line segment, divide it into three equal parts to generate three line segments;

[0044] 2. Use the middle line segment as one side of the equilateral triangle, and the other two sides of the equilateral triangle are automatically generated;

[0045] 3. Then delete the middle line segment of the three line segments in step 1;

[0046] 4. Treat each line segment generated by the above steps as a line segment and repeat steps 1, 2, and 3.

[0047] Furthermore, if Figure 6 As shown, the signal pickup coil array of this embodiment is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two Koch curve segments in series in a vertically symmetrical manner, and the series starting point and series end point of each signal pickup coil serve as output terminals of two induction signals respectively.

[0048] It can be seen that this embodiment will Figure 3 The obtained Koch curve segments are arrayed along the X direction, and the current flows in and out along the left lead, and we get Figure 2The excitation coil of the loop shown in the figure; the signal pickup coil array is composed of a single closed signal pickup coil, and there is a certain distance between each signal pickup coil. The lead part of each signal pickup coil is connected to the multi-way switch selector. In addition, the Koch fractal curve of the signal pickup coil must coincide with the fractal curve of the excitation coil, as shown in Figure 2. Figure 1 shown.

[0049] Furthermore, the crack detection method of the absolute Koch array sensor proposed in this embodiment is as follows:

[0050] 1. The proposed excitation coil and signal pickup coil are processed onto a flexible printed circuit board, and the signal pickup coil is bonded to the device under test;

[0051] 2. Pass a certain amount of alternating current through the excitation coil;

[0052] 3. By controlling the multiplexer, the output signal of a certain channel of the signal pickup coil is determined to enter the signal conditioning circuit;

[0053] 4. Scan the cracks on the test piece. The scanning diagram is as follows: Figure 7 shown.

[0054] In summary, this embodiment proposes an absolute Koch array sensor based on fractal geometry, which realizes the arraying of Koch sensors and improves the detection speed on the basis of the original ones.

[0055] Example 2

[0056] Based on the above embodiments, this embodiment provides a series-type flexible array eddy current sensor based on the Koch curve. Due to its flexibility, this sensor can fit tightly to complex curved surfaces. At the same time, due to its array arrangement, it can quickly detect tiny cracks in a large area.

[0057] like Figure 8 As shown, an array-type planar eddy current sensor based on the Koch curve is characterized by comprising an array of overlapping excitation coils and signal pickup coils, wherein the excitation coil is obtained by connecting mutually symmetrical upper and lower half coils in series, and the series connection is as follows: the right end point of the upper half coil and the left end point of the lower half coil are connected in series, and the remaining left end point and right end point serve as the input terminal and output terminal of the excitation signal, respectively. Figure 9 shown.

[0058] That is to say, in the excitation coil of this embodiment, the Koch curve segments are connected end to end, forming half of the excitation coil, and then the upper half of the coil is arranged horizontally symmetrically, and then the end of the line segment is connected to the beginning of the symmetrical line segment to form a series excitation coil.

[0059] The signal pickup coil is the same as that in the first embodiment, and the signal pickup coil is arranged directly below the excitation coil, and each signal pickup coil is arranged independently. The structure of the signal pickup coil after the array is as follows: Figure 6 shown.

[0060] It should be noted that the excitation coil and the signal pickup coil are arranged on the flexible circuit board, wherein the excitation coil and the pickup coil are arranged on the same layer, and the leads of the excitation coil and the pickup coil are both connected to the pads.

[0061] Furthermore, the input end of the excitation coil is arranged on one side, and due to the series structure, the output end is arranged on the other side, that is, the input end and the output end are arranged on two sides in completely opposite directions and connected to the pads on the flexible circuit board.

[0062] Furthermore, the pickup coils are individually arranged, with leads from each coil extending from the bottom and connected to pads on the flexible circuit board. It should be noted that the individual pickup coils, with their leads extending from the same side and a small distance between them, do not affect the pickup of the measured signal.

[0063] Furthermore, the two horizontally symmetrical parts of the excitation coil are connected in series, and the excitation currents on the two parts of the excitation coil are in opposite directions.

[0064] It should be noted that the excitation coil of the series flexible array eddy current sensor of this embodiment has the advantage of being able to induce mutually perpendicular eddy currents on the sensor scanning axis, thereby improving the detection capability of the planar eddy current sensor for microcracks in different directions; in addition, since the excitation coil of this embodiment is composed of two symmetrical parts connected in series, the eddy current sensor with this series structure has a differential excitation characteristic, which can effectively reduce the output signal of the planar eddy current sensor when there is no crack, and can suppress the influence of lift-off noise; finally, this embodiment arranges the excitation coil and the signal pickup coil in an array and processes them in a flexible circuit board, which is more suitable for defect detection on complex curved surfaces and effectively reduces the missed detection rate.

[0065] Example 3

[0066] Based on the above embodiments, this embodiment provides another differential measurement Koch fractal array eddy current sensor, which needs to significantly improve the detection capability of crack defects, increase the density of the excitation eddy current field, while achieving large-area and rapid detection of tiny cracks and complex cracks, and effectively suppress common-mode interference signals such as temperature and lift-off effects.

[0067] The excitation coil of this embodiment adopts Figure 2 The excitation coil is shown, and the signal pickup coil is as shown Figure 10As shown, it is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two rectangular coils obtained in a cross-winding manner in series in a vertically symmetrical manner, wherein one of the long sides of the rectangular coil is composed of a Koch curve segment, and the winding starting point and winding end point of each signal pickup coil respectively serve as the output terminals of two induction signals.

[0068] It can be seen that the signal pickup coil of this embodiment is composed of two rectangular coils connected in series. The two rectangular coils are distributed up and down. The upper rectangular coil only performs Koch fractal on the upper side, and the lower rectangular coil only performs Koch fractal on the lower side. At the same time, the cross winding direction of the signal pickup coil is as follows: Figure 11 As shown, the cross-winding intersection on the left is located on different layers of the flexible circuit board, that is, the upper and lower layers of coils are separated from each other.

[0069] Furthermore, the excitation coil of this embodiment further includes an excitation current input section and an excitation current output section, wherein, as Figure 2 As shown, the excitation current input section is the upper half of the Koch fractal excitation coil, and the excitation current output section is the lower half of the Koch fractal excitation coil, and the wire leads are all at the left end of the coil, with the excitation current input at the top and the output at the bottom; the signal pickup coils all have wire leads, and the wires led out of each signal pickup coil are at the lower end of the coil and close to the left.

[0070] It should be noted that when the excitation coil and the signal pickup coil are arranged on the flexible circuit board, the excitation coil is at the bottom and the signal pickup coil is at the top; based on the differential measurement principle, a sinusoidal AC signal is input into the excitation current input section of the excitation coil, and the excitation coil will generate an alternating magnetic field. When it approaches the test piece, induced eddy currents are generated in the test piece, and the induced voltages generated in the upper and lower symmetrical parts of each signal pickup coil cancel each other out. At this time, there is no signal output. However, when a defect in the test piece is detected, the induced voltages generated in the upper and lower symmetrical parts of the signal pickup coil are broken from the mutual cancellation, and a signal is output.

[0071] The leads of the signal pickup coil are connected to a multiplexer, which is controlled by a 51-bit single-chip microcomputer. When a defect is detected in the DUT, the circuit containing the corresponding signal pickup coil with a signal output is selected by the multiplexer, and its output signal can be studied separately.

[0072] It can be seen that this embodiment provides a differential measurement Koch fractal array eddy current sensor, which can improve the detection capability of crack defects, increase the density of the excitation eddy current field, and realize large-area and rapid detection of small cracks and complex cracks, and effectively suppress common-mode interference signals such as temperature and lift-off effects.

[0073] Example 4

[0074] Based on the above embodiments, this embodiment provides another array-type planar eddy current sensor based on the Koch curve, which changes the spatial distribution of the excitation field by adopting a rectangular array of Koch curve excitation coils, so that defects of the test piece can be quantified without differential.

[0075] Specifically, an array-type planar eddy current sensor based on the Koch curve includes an array of excitation coils and an array of signal pickup coils placed in overlapping positions, wherein, as Figure 12 As shown, the excitation coil array is obtained by connecting three or more excitation coils in series, and the two ends of the series connection serve as the input terminal and output terminal of the excitation signal respectively;

[0076] Each excitation coil is obtained by connecting two symmetrical Koch curve segments in parallel, and the Koch curve segments are sequentially obtained by connecting four fractal line segments in series, wherein each fractal line segment is sequentially obtained by connecting the first line segment to the fourth line segment in series, and the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°; the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°;

[0077] The signal pickup coil array is as follows Figure 6 As shown, it is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two Koch curve segments in series in a symmetrical manner, and the series starting point and series end point of each signal pickup coil serve as the output terminals of the two induction signals respectively.

[0078] Through the above connection method, such as Figure 13 As shown, the direction of the excitation current is explained as follows: the excitation current enters the input terminal and is separated at the left connection of the first excitation coil, so that the excitation current directions of the upper and lower branches are opposite, and the excitation currents of the upper and lower branches flow into the upper Koch curve segment and the lower Koch curve segment respectively, and the current flow directions on the upper Koch curve segment and the lower Koch curve segment are the same. Finally, the excitation current enters the upper and lower branches at the right connection of the first excitation coil, converges at the intersection, and flows out from the output terminal. Since the excitation coils of this embodiment are obtained through an array, the flow direction of the excitation current in each rectangular Koch snowflake diagram is similar. It should be noted that since the excitation coils are axially symmetrical, the line segments have the same length and shape.

[0079] Furthermore, the signal pickup coil array is as follows Figure 6As shown, its outline is similar to that of the excitation coil, the upper Koch curve segment and the lower Koch curve segment are open and opposite to each other and are connected in series to form an open structure, and the open Koch snowflake rectangular structure is the same as the Koch snowflake rectangular structure of the excitation coil.

[0080] It should be noted that the direction of the rotating eddy current at the measured point on the test piece at each instant is fixed. To illustrate the problem, the part of the rotating eddy current in the sensing area can be simplified as a straight line current, such as Figure 14 and Figure 15 shown. Figure 14 and Figure 15 The rectangle formed by the dotted line represents the signal pickup coil with the y-axis as the symmetry axis, the black line segment with an arrow is a simplified eddy current, and the symbols on both sides of the eddy current represent the normal magnetic field in the positive and negative directions perpendicular to the sensing surface. Figure 14 As shown in , when the eddy current is undisturbed, it can be seen from the symmetry in the figure that the contribution of the eddy current to the magnetic flux of the signal pickup coil is zero; Figure 15 As shown in Figure 2, when the eddy current is disturbed by the presence of cracks, Figure 14 The symmetry in the circuit is broken, and the magnetic flux in the signal pickup coil is no longer zero, thus outputting a crack signal.

[0081] It can be seen that this embodiment provides an array-type planar eddy current sensor based on the Koch curve. The advantage of its excitation coil is that it can induce mutually perpendicular eddy currents in the planar eddy current sensor, thereby improving the detection capability of the planar eddy current sensor for microcracks in different directions; the advantage of its signal pickup coil is that it has basically the same contour shape as the excitation coil, and the area enclosed by itself is the largest measurement area, which can effectively extract the changes in the magnetic field caused by the eddy current disturbance caused by the crack; in addition, the planar eddy current sensor composed of the excitation coil and the signal pickup coil of this embodiment also has a differential excitation characteristic, which can effectively reduce the output signal of the planar eddy current sensor when there is no crack, and can suppress the influence of lift-off noise.

[0082] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may of course make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. An array-type planar eddy current sensor based on the Koch curve, characterized in that: The invention comprises an array of overlapping excitation coils and signal pickup coils, wherein the excitation coil is formed by connecting a symmetrical upper half coil and a lower half coil in series, and the series connection is carried out in the following manner: the right end point of the upper half coil is connected in series with the right end point of the lower half coil, and the left end points of the upper half coil and the lower half coil serve as the input terminal and output terminal of the excitation signal, respectively; or the right end point of the upper half coil and the left end point of the lower half coil are connected in series, and the remaining left end point and right end point serve as the input terminal and output terminal of the excitation signal, respectively. The upper half coil and the lower half coil are each obtained by sequentially connecting three or more Koch curve segments in series, wherein the Koch curve segments are sequentially connected by connecting four fractal line segments in series, wherein each fractal line segment is sequentially connected by connecting the first line segment to the fourth line segment, wherein the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°, and the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°; The signal pickup coil array is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two Koch curve segments in series in a vertically symmetrical manner, and the series starting point and series end point of each signal pickup coil serve as output terminals of two induction signals respectively.

2. An array-type planar eddy current sensor based on the Koch curve, characterized in that: The invention comprises an array of overlapping excitation coils and signal pickup coils, wherein the excitation coil is formed by connecting a symmetrical upper half coil and a lower half coil in series, and the series connection is as follows: the right end point of the upper half coil is connected in series with the right end point of the lower half coil, and the left end points of the upper half coil and the lower half coil serve as the input terminal and output terminal of the excitation signal respectively; The upper half coil and the lower half coil are each obtained by sequentially connecting three or more Koch curve segments in series, wherein the Koch curve segments are sequentially connected by connecting four fractal line segments in series, wherein each fractal line segment is sequentially connected by connecting the first line segment to the fourth line segment, wherein the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°, and the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°; The signal pickup coil array is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two rectangular coils obtained in a cross-winding manner in series in a vertically symmetrical manner, wherein one of the long sides of the rectangular coil is composed of a Koch curve segment, and the winding starting point and winding end point of each signal pickup coil respectively serve as output terminals of two induction signals.

3. An array-type planar eddy current sensor based on the Koch curve, characterized in that: It includes an overlapping excitation coil array and a signal pickup coil array, wherein the excitation coil array is obtained by connecting three or more excitation coils in series, and the two ends of the series connection serve as input terminals and output terminals of the excitation signal respectively; Each excitation coil is obtained by connecting two symmetrical Koch curve segments in parallel, and the Koch curve segments are sequentially obtained by connecting four fractal line segments in series, wherein each fractal line segment is sequentially obtained by connecting the first line segment to the fourth line segment in series, and the first line segment and the fourth line segment are located on the same straight line, and the angle between the second line segment and the third line segment is 60°; the first fractal line segment and the fourth fractal line segment are located on the same straight line, and the angle between the second fractal line segment and the third fractal line segment is 60°; The signal pickup coil array is obtained by arranging more than three signal pickup coils, and the outer envelope of the signal pickup coil array is the same as the outer envelope of the excitation coil; the signal pickup coil is obtained by connecting two Koch curve segments in series in a vertically symmetrical manner, and the series starting point and series end point of each signal pickup coil serve as output terminals of two induction signals respectively.

4. The array-type planar eddy current sensor based on the Koch curve according to any one of claims 1 to 3, characterized in that: The output terminals of each signal pickup coil are connected to a multiplexer controlled by a 51 single-chip microcomputer. When the sensor detects a defect in the component to be tested, the corresponding signal pickup coil with an induction signal output is selected by the multiplexer, and its output induction signal is studied separately.

5. The array-type planar eddy current sensor based on the Koch curve according to any one of claims 1 to 3, characterized in that: The lengths of the first to fourth segments of each fractal segment are the same.

6. The array-type planar eddy current sensor based on the Koch curve according to any one of claims 1 to 3, characterized in that: The excitation coil and the signal pickup coil are both arranged on the flexible circuit board, and the excitation coil and the signal pickup coil are arranged on different layers. At the same time, the input terminal and output terminal of the excitation coil and the output terminal of the signal pickup coil are all connected to the pads on the flexible circuit board.

7. The array-type planar eddy current sensor based on the Koch curve according to any one of claims 1 to 3, characterized in that: Each signal pickup coil has multiple turns of coil wound inside according to its own outer envelope.

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