A sensor and method for crack detection in metal structures

Abstract

The present application relates to the technical field of precision sensing electrode design, and particularly relates to a sensor and method for metal structure crack detection, comprising: a substrate; an excitation wiring assembly, the excitation wiring assembly comprising an upper excitation trace layer and a lower excitation trace layer, the upper excitation trace layer and the lower excitation trace layer being electrically connected through a metal via; a signal pickup wiring assembly, comprising an upper pickup trace layer and a lower pickup trace layer, the upper pickup trace layer and the lower pickup trace layer being electrically connected through a metal via, a single excitation wiring assembly and a single signal pickup wiring assembly forming a detection cycle unit, and the number of detection cycle units being multiple. The present application adopts a double-layer symmetrical differential excitation architecture, can widen the dynamic range of the sensor signal, effectively weaken the background noise caused by the lift-off distance fluctuation in the detection process, has a faster response speed to the slight change of the eddy current field, has a stronger real-time defect capturing capability, and is suitable for continuous scanning imaging of large-area metal members.

Description

Technical Field

[0001] This invention relates to the field of precision sensing electrode design technology, and in particular to a sensor and method for detecting cracks in metal structures. Background Technology

[0002] Eddy current testing is a non-destructive testing technique based on the principle of electromagnetic induction. It induces an eddy current field on the surface of the metal component being tested by an excitation coil, and uses a receiving coil to pick up the magnetic field changes caused by defect disturbances in the eddy current field to achieve defect detection. It has advantages such as being non-contact, having a fast detection speed, and requiring no coupling medium, and is widely used for surface and near-surface defect detection in critical metal components such as oil pipelines, aerospace components, pressure vessels, and bridge steel structures. Printed circuit board (PCB) planar coils, due to their high process precision, good consistency, ease of integration, and mass production capabilities, have become the mainstream implementation form of eddy current sensors.

[0003] Existing PCB planar eddy current sensors mostly adopt traditional rectangular, circular, or square regular geometric configurations. However, existing PCB planar eddy current sensors have prominent inherent defects: the magnetic field distribution is extremely uneven, the magnetic fields generated by the current elements in straight segments cancel each other out, and only local magnetic field peaks are formed at the corners, resulting in low magnetic field excitation efficiency. On the other hand, if flexible eddy current sensors are used to adapt to complex curved surfaces, miniaturization design is often required, which severely limits the wiring space and severely restricts the sensitivity and signal-to-noise ratio.

[0004] Therefore, there is a need for a sensor and method for crack detection that can effectively detect microcracks and has high sensitivity in identifying multi-orientation defects. Summary of the Invention

[0005] The main objective of this invention is to provide a sensor and method for detecting cracks in metal structures, aiming to solve the problems of poor microcrack detection and insufficient sensitivity for multi-orientation defect identification in existing PCB eddy current sensors.

[0006] To achieve the above objectives, the present invention proposes a sensor for detecting cracks in metal structures, comprising:

[0007] Base;

[0008] An excitation routing assembly is disposed on the substrate. The excitation routing assembly includes an upper excitation routing layer and a lower excitation routing layer, which are electrically connected through metal vias.

[0009] A signal pickup wiring assembly is disposed on the substrate. The signal pickup wiring assembly includes an upper pickup routing layer and a lower pickup routing layer. The upper pickup routing layer and the lower pickup routing layer are electrically connected through metal vias. A single excitation wiring assembly and a single signal pickup wiring assembly form a detection loop unit. The number of detection loop units is multiple.

[0010] The trace profiles of both the excitation wiring component and the signal pickup wiring component are Hilbert curves that have undergone closed-loop truncation processing.

[0011] Preferably, the iteration order of the Hilbert curve ranges from 3 to 6, and the single-cell reference size is 2 mm to 10 mm.

[0012] Preferably, the upper excitation trace layer is wound counterclockwise from the outside to the inside along the Hilbert curve contour to a predetermined number of turns, and then connected to the lower excitation trace layer through a metal via. After that, the same number of turns are wound clockwise from the inside to the outside. The excitation coil assembly leads out excitation input leads and excitation output leads.

[0013] Preferably, the upper pickup trace layer winds along the Hilbert curve profile from the outside to the inside to the target number of turns, and then connects to the lower pickup trace layer through a metal via. The winding direction of the lower pickup trace layer is the same as that of the upper pickup trace layer. The signal pickup coil assembly leads out signal lead one and signal lead two.

[0014] This invention also discloses a method for fabricating a sensor for detecting cracks in metal structures. The fabrication method, applied to the sensor described in any of the above technical solutions, includes the following steps:

[0015] First-order Hilbert basic units are etched on the excitation trace layer and the pickup trace layer of the PCB board, respectively. The first-order Hilbert basic unit is formed by splicing four straight lines of equal length end to end. The angle between two adjacent straight lines is 90°, and the first and last straight lines are located on the same horizontal straight line.

[0016] Replace the traces at each 90° corner of the first-order Hilbert basic unit with a Hilbert unit of the same structure that is reduced by 1 / 2 to complete one single-order iteration. Perform this step multiple times according to preset requirements until multi-order iterations are completed to obtain multi-order Hilbert curves.

[0017] On the excitation trace layer and the pickup trace layer of the PCB board, the line segments between the start and end points of the multi-order Hilbert curve are respectively cut out, and the start and end points are electrically connected through conductive traces so that the multi-order Hilbert curve forms a closed conductive loop, and all 90° orthogonal corners are retained, and the outer contour is constrained to a rectangle.

[0018] Metal vias are fabricated between the closed conductive loop of the excitation trace layer and the closed conductive loop of the pickup trace layer to make the upper and lower layers electrically connected, thereby obtaining the sensor.

[0019] Preferably, the preset iteration order is 3 to 6.

[0020] Preferably, in the step of etching first-order Hilbert basic units on the excitation trace layer and the pickup trace layer of the PCB board respectively, the overall length and width dimensions of the first-order Hilbert basic unit on the excitation trace layer are larger than the overall length and width dimensions of the first-order Hilbert basic unit on the pickup trace layer.

[0021] Preferably, in the step of constraining the outer contour to a rectangle, the aspect ratio of the rectangle is the same as the aspect ratio of the overall outer frame of the first-order Hilbert basic unit.

[0022] This invention provides a sensor and method for detecting cracks in metal structures. The invention employs a dual-layer symmetrical differential excitation architecture, which broadens the dynamic range of the sensor signal and effectively reduces background noise caused by lift-off distance fluctuations during detection. The excitation and pickup circuits uniformly adopt fourth-order Hilbert fractal wiring, resulting in faster response to minute changes in the eddy current field and stronger real-time defect capture capability. Simultaneously, the overall outer contour of the coil is a regular rectangle, suitable for continuous scanning imaging of large-area metal components. The integrated structure and low manufacturing cost balance adaptability to curved and planar component detection with industrial practicality. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the processes shown in these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the upper excitation trace layer of the sensor for detecting cracks in metal structures provided in Embodiment 1 of the present invention.

[0025] Figure 2 This is a schematic diagram of the lower excitation trace layer of the sensor for detecting cracks in metal structures provided in Embodiment 2 of the present invention.

[0026] Figure 3 This is a schematic diagram of the upper pickup trace layer of the sensor for detecting cracks in metal structures provided in Embodiment 1 of the present invention.

[0027] Figure 4This is a schematic diagram of the lower pickup trace layer of the sensor for detecting cracks in metal structures provided in Embodiment 2 of the present invention.

[0028] Figure 5 This is a schematic diagram illustrating the generation of a closed fourth-order Hilbert curve according to an embodiment of the present invention;

[0029] Figure 6 This is the three-dimensional eddy current density distribution surface of the sensor used for detecting cracks in metal structures in this invention;

[0030] Figure 7 This is a schematic flowchart illustrating the fabrication method of the sensor for detecting cracks in metal structures according to the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0033] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0034] Eddy current testing (ECT) is a core technology in the field of electromagnetic nondestructive testing. However, existing industrial eddy current testing methods have inherent defects: the magnetic field distribution is uneven, the magnetic fields of current elements in straight sections cancel each other out, and only local magnetic field peaks are formed at corners; the excited eddy currents have a single polarization direction, and when the crack and the eddy current direction are approximately parallel, the eddy current disturbance is weak, resulting in a significant blind zone for angle detection; due to the skin effect, the detection sensitivity for deep and subsurface defects decays rapidly, making it difficult to meet the modern testing requirements of omnidirectional, high sensitivity, and deep penetration.

[0035] Based on this, such as Figures 1-6 As shown, this invention proposes a sensor for detecting cracks in metal structures, comprising: a substrate; an excitation wiring assembly disposed on the substrate, the excitation wiring assembly including an upper excitation wiring layer and a lower excitation wiring layer electrically connected through metal vias; and a signal pickup wiring assembly disposed on the substrate, the signal pickup wiring assembly including an upper pickup wiring layer and a lower pickup wiring layer electrically connected through metal vias, wherein a single excitation wiring assembly and a single signal pickup wiring assembly form a detection loop unit, and the number of detection loop units is multiple; wherein the wiring profiles of both the excitation wiring assembly and the signal pickup wiring assembly are Hilbert curves that have undergone closed-loop truncation processing.

[0036] Understandably, existing planar PCB eddy current probes generally suffer from poor microcrack detection and insufficient sensitivity in identifying multi-orientation defects. This invention employs a double-layer series planar eddy current sensing structure based on multi-order Hilbert fractal routing for both the excitation and signal pickup circuits. By relying on multiple 90° orthogonal corners, a multi-directional eddy current vector field is generated on the surface of the metal specimen, significantly increasing the probability of eddy currents coupling with cracks at any angle. Simultaneously, double-layer via series routing increases the total number of coil turns, amplifying the defect-induced voltage output and significantly improving the ability to identify microcracks and buried cracks.

[0037] In this invention, the substrate is an FR4 double-layer PCB substrate with a thickness of 0.8mm. Metallized vias are provided on the substrate to achieve electrical conduction between the two wiring layers. It is understood that a flexible substrate can also be used.

[0038] The sensor principle in this invention, taking a rectangular planar coil as an example, allows for quantitative analysis of the magnetic field distribution based on the Biot-Savart law, the expression of which is:

[0039] ;

[0040] in, For current elements, The differential vector of the generated magnetic field strength, The position vector of the current element to the target point. Let I be the magnitude of the position vector, I be the constant current, and the overall magnetic field strength of the coil is the vector superposition of the magnetic fields of the four straight-side conductors.

[0041] The Hilbert curve involved in this invention is a typical fractal space-filling curve. Its core mathematical essence is to achieve high-density filling of a two-dimensional plane with a low-dimensional curve by recursively iterating through all regions of a square plane using a continuous, non-self-intersecting polygonal line. The recursive generation logic of the nth-order Hilbert curve can be represented by a mathematical formula, and its iterative core expression is:

[0042]

[0043] in, Perform rotation transformations of 0°, 90°, 180°, and 270° on the (n-1)th order Hilbert curve. This refers to the short connecting line segments that link the four quadrant sub-curves. This iterative process endows the curve with four core characteristics: extremely strong space-filling ability, maximizing linear density within a finite plane; continuous 90° right-angle turns throughout, with the number of corners increasing exponentially with the iteration order; strict self-similarity, maintaining a high degree of consistency between the local topology and the overall structure; and no intersections or breaks in the path, ensuring continuous and stable current conduction. Combined with the above formula, the magnetic field vectors of the current elements at the right-angle corners are superimposed in the same direction, which can significantly enhance the local magnetic field, providing core theoretical support for the topology optimization of eddy current coils.

[0044] In this embodiment, the multi-order Hilbert fractal is preferably fourth-order. The coil wiring topology is the core carrier for eddy current excitation and defect magnetic field pickup, and its assembly configuration and winding method directly determine the signal-to-noise ratio and defect resolution capability of this sensor. In this invention, the excitation coil first uses a fourth-order Hilbert fractal pattern that has undergone closed-loop interception as the wiring outline. Relying on the high-density orthogonal corner characteristics of the fractal structure, a frontal orthogonal eddy current field is constructed to eliminate the blind zone of crack detection angle that exists in traditional coils.

[0045] In one embodiment, the upper pickup trace layer winds along the Hilbert curve profile from the outside in to the target number of turns, and then connects to the lower pickup trace layer through a metal via. The winding direction of the lower pickup trace layer is the same as that of the upper pickup trace layer. The signal pickup coil assembly leads out signal lead one and signal lead two.

[0046] In this embodiment, the complete winding of the excitation coil is as follows: the operator first runs the wire counterclockwise along the upper Hilbert contour, and then winds it from the outside to the inside at a fixed equal interval to the preset number of turns; the lower coil is connected through the PCB metal via, and the same number of turns are wound clockwise from the inside to the outside. After the wiring is completed, the excitation input and output leads are led out.

[0047] The signal pickup coil also adopts a closed-loop interception of the fourth-order Hilbert fractal profile, matching the orthogonal eddy current distribution characteristics at the excitation end, to capture the multi-directional alternating magnetic field generated by crack distortion from all directions, thereby improving the pickup sensitivity of weak magnetic field changes.

[0048] In this invention, the pickup coil and the excitation coil use Hilbert fractal units with the same iteration order. The design parameters for the trace width and spacing are kept uniform, but the overall length and width of the single-channel pickup unit are smaller than those of the excitation coil. The pickup coil adopts a single-wire continuous series wiring form, with the signal lead-out terminal one and the excitation input lead-out terminal one arranged on the same side. The wire is wound in a single layer along the Hilbert contour from the outside to the inside to the target number of turns, and then connected to the lower pickup coil through a vertical via. The winding direction of the upper and lower pickup traces is completely consistent, and the multi-layer series superposition of induced electromotive force completes the signal output at the end of the signal lead-out terminal two. The closed-loop truncation fourth-order Hilbert pattern used in this invention is obtained from the standard fourth-order Hilbert iterative curve. The basic fractal unit consists of four straight lines of equal length connected end to end. The included angle between two adjacent straight lines is fixed at 90°. The first and last straight lines are on the same horizontal straight line. The start and end points of the original complete Hilbert curve are diagonally distributed and the loop is not closed. This invention truncates the close-range line segments at the start and end to form a closed conductive loop. All right-angle corners are completely preserved. The overall outer contour of the coil is constrained to a standard rectangle, which is convenient for splicing multi-channel arrays. Among them, the input and output leads of the excitation loop are uniformly arranged on the same side of the outermost trace of the upper excitation coil.

[0049] like Figure 7 As shown, this invention also discloses a method for fabricating a sensor for detecting cracks in metal structures. The fabrication method, applied to the sensor described in any of the above technical solutions, includes the following steps:

[0050] Step S10: Etch first-order Hilbert basic units on the excitation trace layer and the pick-up trace layer of the PCB board respectively. The first-order Hilbert basic unit is formed by splicing four straight lines of equal length end to end. The angle between two adjacent straight lines is 90° and the first and last straight lines are located on the same horizontal straight line.

[0051] Step S20: Replace the traces at each 90° corner of the first-order Hilbert basic unit with a Hilbert unit of the same structure that is reduced by 1 / 2 to complete one single-order iteration. Perform this step multiple times according to the preset requirements until multi-order iteration is completed to obtain multi-order Hilbert curves.

[0052] Step S30: On the excitation trace layer and the pick trace layer of the PCB board, the line segments between the start and end points of the multi-order Hilbert curve are respectively cut out, and the start and end points are electrically connected through conductive traces so that the multi-order Hilbert curve forms a closed conductive loop, and all 90° orthogonal corners are retained, and the outer contour is constrained to a rectangle.

[0053] Step S40: A metal via is fabricated between the closed conductive loop of the excitation trace layer and the closed conductive loop of the pickup trace layer to make the upper and lower layers electrically connected, thereby fabricating the sensor.

[0054] In one embodiment, in step S10, the first-order Hilbert basic unit is etched on the excitation trace layer and the pick-up trace layer of the PCB board, respectively. The overall length and width of the first-order Hilbert basic unit on the excitation trace layer is larger than the overall length and width of the first-order Hilbert basic unit on the pick-up trace layer.

[0055] In one embodiment, in step S30, where the outer contour constraint is a rectangle, the aspect ratio of the rectangle is the same as the aspect ratio of the overall outer frame of the first-order Hilbert basic unit.

[0056] The sensor prepared by this invention is a basic industrial general-purpose double-layer Hilbert sensor, which only uses side external vias and a four-channel pickup array. It has low processing difficulty and low production cost, and is suitable for the detection of conventional flat steel structures and pressure vessel plates.

[0057] This invention provides a sensor and method for detecting cracks in metal structures. The invention employs a double-layer symmetrical differential excitation architecture, which broadens the dynamic range of the sensor signal and effectively reduces background noise caused by lift-off distance fluctuations during detection. The excitation and pickup circuits uniformly utilize fourth-order Hilbert fractal wiring, forming a bidirectional orthogonal eddy current field on the specimen surface. Cracks with different orientations can generate significant eddy current distortion, comprehensively improving the sensitivity for identifying multi-angle defects. The double-layer series wiring significantly increases the effective number of winding turns within a limited PCB board area, amplifying the induced voltage output and significantly reducing the probability of missing short micro-cracks and weld-buried cracks. The superposition of multiple fractal coils forms a high-intensity alternating excitation magnetic field, resulting in faster response to minute changes in the eddy current field and stronger real-time defect capture capability. Simultaneously, the overall outer contour of the coil is a regular rectangle, allowing for linear arraying of small pickup units, suitable for continuous scanning imaging of large-area metal components. The entire sensor system is mass-produced using mature PCB etching technology, featuring an integrated structure, low processing cost, and balancing adaptability to curved and planar component detection with industrial practicality. The differential symmetrical wiring structure can cancel the static background magnetic flux when there are no defects, further improving the signal-to-noise ratio of the test and meeting the high-precision non-destructive testing requirements of bridge steel structures, pressure vessels, and aerospace metal components.

[0058] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A sensor for detecting cracks in metal structures, characterized in that, include: Base; An excitation routing assembly is disposed on the substrate. The excitation routing assembly includes an upper excitation routing layer and a lower excitation routing layer, which are electrically connected through metal vias. A signal pickup wiring assembly is disposed on the substrate. The signal pickup wiring assembly includes an upper pickup routing layer and a lower pickup routing layer. The upper pickup routing layer and the lower pickup routing layer are electrically connected through metal vias. A single excitation wiring assembly and a single signal pickup wiring assembly form a detection loop unit. The number of detection loop units is multiple. The trace profiles of both the excitation wiring component and the signal pickup wiring component are Hilbert curves that have undergone closed-loop truncation processing.

2. The sensor for detecting cracks in metal structures as described in claim 1, characterized in that, The iteration order of the Hilbert curve ranges from 3 to 6, and the reference size of a single cell is from 2 mm to 10 mm.

3. The sensor for detecting cracks in metal structures as described in claim 2, characterized in that, The upper excitation trace layer is wound counterclockwise from the outside to the inside along the Hilbert curve contour to a preset number of turns, and then connected to the lower excitation trace layer through a metal via. The same number of turns are then wound clockwise from the inside to the outside. The excitation coil assembly leads out excitation input leads and excitation output leads.

4. The sensor for detecting cracks in metal structures as described in claim 2, characterized in that, The upper pickup trace layer winds along the Hilbert curve profile from the outside in to the target number of turns, and then connects to the lower pickup trace layer through a metal via. The winding direction of the lower pickup trace layer is the same as that of the upper pickup trace layer. The signal pickup coil assembly leads out signal lead one and signal lead two.

5. A method for fabricating a sensor for detecting cracks in metal structures, characterized in that, The preparation method, when applied to the sensor as described in any one of claims 1 to 4, includes the following steps: First-order Hilbert basic units are etched on the excitation trace layer and the pickup trace layer of the PCB board, respectively. The first-order Hilbert basic unit is formed by splicing four straight lines of equal length end to end. The angle between two adjacent straight lines is 90°, and the first and last straight lines are located on the same horizontal straight line. Replace the traces at each 90° corner of the first-order Hilbert basic unit with a Hilbert unit of the same structure that is reduced by 1 / 2 to complete one single-order iteration. Perform this step multiple times according to preset requirements until multi-order iterations are completed to obtain multi-order Hilbert curves. On the excitation trace layer and the pickup trace layer of the PCB board, the line segments between the start and end points of the multi-order Hilbert curve are respectively cut out, and the start and end points are electrically connected through conductive traces so that the multi-order Hilbert curve forms a closed conductive loop, and all 90° orthogonal corners are retained, and the outer contour is constrained to a rectangle. Metal vias are fabricated between the closed conductive loop of the excitation trace layer and the closed conductive loop of the pickup trace layer to make the upper and lower layers electrically connected, thereby obtaining the sensor.

6. The method for preparing a sensor for detecting cracks in metal structures as described in claim 5, characterized in that, The preset iteration order is 3 to 6.

7. The method for preparing a sensor for detecting cracks in metal structures as described in claim 5, characterized in that, In the step of etching first-order Hilbert basic units on the excitation routing layer and the pickup routing layer of the PCB board respectively, the overall outer frame length and width of the first-order Hilbert basic unit on the excitation routing layer is larger than the overall outer frame length and width of the first-order Hilbert basic unit on the pickup routing layer.

8. The method for preparing a sensor for detecting cracks in metal structures as described in claim 5, characterized in that, In the step of constraining the outer contour to a rectangle, the aspect ratio of the rectangle is the same as the aspect ratio of the overall outer frame of the first-order Hilbert basic unit.

Images