Novel small-sized receiving coil group electromagnetic ultrasonic sensor and method for detecting submillimeter-level tiny defects at high resolution

Abstract

The invention relates to a novel small-sized receiving coil group electromagnetic ultrasonic sensor and a method for high-resolution detection of submillimeter-level tiny defects. The sensor comprises a permanent magnet, an exciting coil and a receiving coil group, the receiving coil group comprises at least two independent preset small coils; the receiving coil group is arranged above the effective receiving area of the exciting coil; the permanent magnet is placed above the effective receiving area of the receiving coil assembly, and the magnetic pole direction is perpendicular to the plane of the receiving coil assembly. The invention aims to solve the technical problems that an existing electromagnetic ultrasonic sensor is low in signal-to-noise ratio, depends on complex signal processing and is difficult to give consideration to high-resolution and high-reliability detection when detecting submillimeter-level tiny defects, and provides a small-sized receiving coil group electromagnetic ultrasonic sensor which is compact in structure and high in signal-to-noise ratio and a detection method. Under the condition of not depending on complex post-processing, high-resolution recognition of submillimeter-level tiny defects in the metal material can be achieved.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a novel small-sized electromagnetic ultrasonic sensor with a receiving coil assembly and a method for high-resolution detection of sub-millimeter-level micro-defects. Background Technology

[0002] Electromagnetic ultrasonic transducers (EMATs) operate in a non-contact, coupling agent-free manner, generating and receiving ultrasonic waves in conductive specimens through the principles of eddy currents and Lorentz forces. They are particularly suitable for industrial online testing scenarios such as high-temperature and high-speed applications.

[0003] However, existing EMAT technology still has significant shortcomings in meeting the high-resolution detection requirements of sub-millimeter-level micro-defects. In recent years, researchers have proposed various improvement schemes. For example, Chinese patent CN119643715 A discloses a Fresnel coil electromagnetic ultrasonic transducer and detection method for defect and stress detection. By designing a Fresnel coil, it solves the problems of low efficiency, poor accuracy, and corrosion of the surface of large precision rotating equipment caused by traditional ultrasonic methods, reflecting the continuous exploration in this field to improve detection performance and applicability.

[0004] Despite these shortcomings, such approaches still fail to fundamentally overcome the core bottleneck of EMAT in micro-defect detection: the primary problem lies in the inherent contradiction between signal-to-noise ratio (SNR) and spatial resolution. While large receiving coils can improve signal strength, their low spatial resolution makes it difficult to identify the weak echoes of tiny defects; conversely, small coils, while improving resolution, suffer from a significantly reduced SNR due to their limited sensing area and weak energy capture, making the signal susceptible to noise interference. Submillimeter-level defects exhibit random morphology and orientation, easily causing ultrasonic scattering and dispersing echo energy. Traditional single receiving coils have fixed and relatively large sensing areas, making it difficult to accurately obtain high SNR reflections from tiny defects. Currently, improving SNR largely relies on signal averaging or noise reduction algorithms, which not only increases system complexity and cost but also fails to meet real-time detection requirements. Although array-based approaches have been attempted, they primarily focus on excitation arrays, offering limited improvement in receiving SNR; furthermore, the low SNR of small coils prevents receiving arrays from fully realizing their high-resolution potential.

[0005] Therefore, there is an urgent need to develop a new type of EMAT sensor that can balance signal-to-noise ratio and resolution in its structural design, and achieve high sensitivity and high reliability detection of sub-millimeter level defects without relying on complex signal processing. Summary of the Invention

[0006] In view of the shortcomings of the aforementioned background technology, the present invention aims to solve the technical problems of existing electromagnetic ultrasonic sensors in detecting sub-millimeter-level micro-defects, such as low signal-to-noise ratio, reliance on complex signal processing, large size, and inability to meet online monitoring requirements. The present invention provides a compact, high-signal-to-noise-ratio small-sized electromagnetic ultrasonic sensor with a receiver coil assembly and a detection method, aiming to achieve high-resolution, high-reliability identification of sub-millimeter-level (especially diameters greater than 0.1 mm) pore defects in metallic materials without the need for complex post-processing.

[0007] To achieve the above objectives, the present invention provides the following solution: A novel miniature electromagnetic ultrasonic sensor with receiving coil assembly includes: a permanent magnet, an excitation coil, and a receiving coil assembly; The receiving coil group includes at least two independent preset miniature coils; wherein the diameter of the preset miniature coil is smaller than that of the excitation coil, and the preset miniature coil is located within the range of the excitation coil; The receiving coil group is positioned directly above the effective receiving portion of the excitation coil, and the ineffective portion of the receiving coil group is staggered from the excitation coil. The permanent magnet is placed directly above the effective receiving area of ​​the receiving coil group, with its magnetic pole direction perpendicular to the plane of the receiving coil group.

[0008] Optionally, the excitation coil is made of copper enameled wire of a preset diameter wound with a preset number of turns to form an effective excitation region with a preset length and width.

[0009] Optionally, the receiving coil group is composed of copper enameled wire of a preset diameter wound with a preset number of turns to form an effective receiving area with a preset length and width.

[0010] Optionally, the preset small coils in the receiving coil group are arranged in a way that the coils are arranged closely or partially overlapped along the length direction with either side of the coil as the effective part, forming a compact array unit, and are encapsulated and fixed with insulating tape, with the lead of each coil being led out independently.

[0011] Optionally, both the excitation coil and the receiving coil group are racetrack-shaped coils.

[0012] A method for high-resolution detection of sub-millimeter-scale micro-defects includes: A novel small receiving coil electromagnetic ultrasonic sensor is placed above the surface of the test piece. A pulsed current is passed through the excitation coil to generate ultrasonic waves; When an ultrasonic wave propagates in the test piece and encounters a defect, it generates a reflected echo. The reflected echo signal is received synchronously or in stages using a receiving coil group. The signals received by the receiving coil group are acquired and processed synchronously or in stages, and defects are identified based on the characteristics of the echo signals.

[0013] The beneficial effects of this invention are as follows: This invention provides a miniature receiving coil electromagnetic ultrasonic sensor and a high-resolution detection method, which have the following outstanding advantages: First, high signal-to-noise ratio and high-resolution detection capability: By adopting a structural design in which several independent miniature receiving coils are tightly arranged in an array, the sensing area of ​​each coil is significantly reduced, effectively suppressing the interference of spatial electromagnetic background noise, while greatly improving the spatial resolution of the sensor. It can accurately capture weak reflection signals from sub-millimeter-level tiny defects, achieving high signal-to-noise ratio signal acquisition. Second, compact structure and applicability to online monitoring: The sensor adopts a unique layout in which the receiving coil group is stacked on one side directly above the excitation coil, and combined with manual or machine precision winding and layered encapsulation with insulating tape, it achieves miniaturization, compactness, and good insulation of the overall structure. This design not only makes the sensor easy to manufacture and integrate, but is also very suitable for installation and use in complex or confined spaces in industrial environments, providing a hardware foundation for online real-time monitoring. Third, simplified detection process and improved real-time performance: Since this invention fundamentally improves the signal-to-noise ratio at the hardware level, the detection method does not need to rely on complex software noise reduction algorithms for signal post-processing, and the received echo signal can be directly analyzed and identified. This significantly simplifies the configuration of the detection system, reduces data processing costs, and greatly improves detection efficiency and real-time performance, meeting the stringent speed and efficiency requirements of industrial online monitoring. The results show that this invention, through innovative sensor structure design and manufacturing process, successfully solves key problems of traditional electromagnetic ultrasonic technology in detecting sub-millimeter-level defects, such as low signal-to-noise ratio, reliance on post-processing, and large size. It provides a high-performance, low-cost, and online-suitable solution for detecting minute defects, possessing significant application value and promising prospects in the field of industrial non-destructive testing. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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 these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a novel small-sized receiving coil electromagnetic ultrasonic sensor and detection system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a 0.1mm defect specimen according to an embodiment of the present invention; Figure 3This is a physical diagram of the electromagnetic ultrasonic sensor detection device according to an embodiment of the present invention; Figure 4 This is a graph showing the test results of the signal amplitude and signal-to-noise ratio of the small array coil in an embodiment of the present invention; Figure 5 This is a diagram showing the results of detecting non-positional defects in a small array coil according to an embodiment of the present invention. Detailed Implementation

[0016] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] This embodiment proposes a novel small electromagnetic ultrasonic sensor with receiving coil assembly, comprising: a permanent magnet or electromagnet, an excitation coil, and a receiving coil assembly; The receiving coil group includes at least two independent preset miniature coils; wherein the size of the preset miniature coil is smaller than that of the excitation coil, and the preset miniature coil is located within the range of the excitation coil; The receiving coil group is positioned above the effective receiving portion of the excitation coil, and the ineffective portion of the receiving coil group is staggered from the excitation coil. The permanent magnet is placed directly above the effective receiving area of ​​the receiving coil group, with its magnetic pole direction perpendicular to the plane of the receiving coil group.

[0019] Furthermore, the excitation coil is composed of copper enameled wire of a preset diameter wound with a preset number of turns, forming an effective excitation region with a preset length and width.

[0020] Furthermore, the receiving coil group is composed of copper enameled wire of a preset diameter wound with a preset number of turns, forming an effective receiving area with a preset length and width.

[0021] Furthermore, the preset small coils in the receiving coil group use any side of the coil as the effective receiving part. The effective receiving parts are arranged in a way that is closely arranged or partially overlapped along the length direction to form a compact array unit, and are encapsulated and fixed with insulating tape. The lead of each coil is led out independently.

[0022] Specifically, in this embodiment, the effective excitation area of ​​the excitation coil located directly below or diagonally below the permanent magnet or electromagnet is larger than the effective receiving area of ​​a single receiving coil; the small receiving coil group consists of at least two independent small coils arranged in a closely spaced or partially overlapping manner, and the independent small coils can also be connected in series; the ineffective part of the receiving coil group is staggered from the excitation coil, so that the ineffective sensing area of ​​the receiving coil is far away from the excitation coil.

[0023] In this embodiment, the miniature coil is smaller than the excitation coil, so that multiple miniature receiving coils can be located within the range of the excitation coil simultaneously.

[0024] This embodiment uses the detection of micro-through-hole defects in an aluminum sheet as an example. Figure 1 As shown, a cylindrical through-hole with a diameter of 0.1 mm and a depth of 30 mm was pre-placed inside the plate as an artificial defect to verify the performance of this sensor.

[0025] 1. Sensor fabrication: (1). Excitation coil fabrication: Select copper enameled wire with a diameter of 0.1mm as the raw material. On a layer of polyimide insulating tape with a thickness of approximately 0.05mm, manually wind 30 turns counterclockwise to form a racetrack-shaped coil, ensuring that its effective receiving area is 3mm × 10mm. After winding, cover it with another layer of the same polyimide tape for encapsulation and fixation, and lead out the positive and negative leads.

[0026] (2) Fabrication of the receiving coil assembly: Copper enameled wire with a diameter of 0.06mm was selected as the raw material. Using the same process as the excitation coil, eight miniature racetrack-shaped coils were independently fabricated. Each coil had 15 turns, ensuring its effective receiving area was 1mm × 8mm. The eight encapsulated miniature receiving coils were arranged closely along their length with their right-side racetrack-shaped effective receiving surfaces, leaving no gaps between them, forming a compact array unit (total size approximately 8mm × 8mm), and then completely encapsulated and fixed using insulating tape. The leads of each coil were led out independently.

[0027] (3) Sensor Assembly: Stack the packaged receiving coil assembly and attach it directly above the effective receiving area (left track) of the excitation coil, ensuring that their center lines are aligned. Then, place a neodymium iron boron (N52) permanent magnet directly above the effective receiving area of ​​the coil assembly, with the magnetic pole direction perpendicular to the coil plane, to provide a static bias magnetic field of approximately 0.5T (e.g., ...). Figure 2 (As shown).

[0028] This embodiment also proposes a method for high-resolution detection of sub-millimeter-level micro-defects, including: A novel small receiving coil electromagnetic ultrasonic sensor is placed above the surface of the test piece. A pulsed current is passed through the excitation coil to generate ultrasonic waves; When an ultrasonic wave propagates in the test piece and encounters a defect, it generates a reflected echo. The reflected echo signal is received synchronously or in stages using a receiving coil group. The signals received by the receiving coil group are acquired and processed synchronously or in stages, and defects are identified based on the characteristics of the echo signals.

[0029] The method in this embodiment also includes: positioning based on the time when each receiving coil receives the signal; and evaluating the defect size or equivalent size based on the characteristics such as the amplitude of the signal received by each coil.

[0030] The receiving coil group can effectively capture ultrasonic echo signals that are located in areas directly below or diagonally below the excitation coil. Even if the defect reflection source is several millimeters away from the excitation center area, it can still be effectively captured by one or more receiving coils.

[0031] Specifically, in this embodiment, such as Figure 3 As shown, the assembled sensor is connected to the electromagnetic ultrasonic excitation and receiving system. The excitation section generates a high-peak pulse current; the receiving section is connected to an oscilloscope. The sensor is fixed to the surface of the aluminum specimen, with its coil center directly above the area to be tested.

[0032] An excitation unit was set up to generate a pulse excitation signal with a peak current of 35A and a center frequency of 3MHz. This excitation signal passed through the excitation coil to excite ultrasonic waves, which were mainly transverse waves, in the aluminum specimen. The ultrasonic waves were reflected after encountering a 0.1mm diameter through-hole defect during propagation. The reflected ultrasonic waves were captured by the receiving coil group above. The signals from the eight receiving coils were sequentially connected to an oscilloscope, and the oscilloscope's average frequency was set to 64 cycles to further suppress random noise.

[0033] The collected signals are as follows Figure 4As shown in the figure. Measurements showed that the peak voltage of the defect echo signal 1 mm to the left of the defect was 0.47 mV, but this was not the optimal signal-to-noise ratio (SNR). At 2 mm to the left of the defect, with a peak voltage of 0.36 mV, the maximum background noise voltage was 0.11 mV. Based on this, the SNR was calculated to be 3.2 (approximately 10.4 dB). This SNR is significantly higher than that of conventional single large-coil sensors (whose SNR is typically <2:1 when detecting similar sub-millimeter defects) under the same conditions. This superior performance is not only due to the high SNR inherent in the small coil unit itself, but also fundamentally stems from the spatial acquisition advantage provided by the array-type receiving structure employed in this invention. Thus, the high spatial resolution of the small receiving coil is effectively utilized to detect defects as small as 0.1 mm with a resolution of up to 2 mm. To further verify the detection capability of the new EMAT for sub-millimeter defects, defects were processed at depths of 25 mm, 30 mm, 35 mm, and 40 mm from the sample surface. The detection results are as follows. Figure 5 As shown, this fully demonstrates the sensor's superior performance in detecting sub-millimeter defects in samples with a thickness of up to 40 mm.

[0034] Although a regular through-hole was used in this embodiment, the result fully verifies the sensor's excellent ability to capture weak signals. For irregularly shaped micro-defects in reality (such as microcracks, pits, etc.), their reflected echoes often exhibit multi-directional scattering characteristics, with highly uncertain energy distribution. The receiving coil array used in this invention, through its distributed sensing unit layout, constitutes a wide-area, sensitive signal acquisition network, which can effectively cope with the uncertainty of the spatial distribution of the echo, significantly improving the detection probability and reliability of randomly oriented micro-defects—a key advantage that a single large coil sensor cannot achieve.

[0035] This embodiment confirms that by using the sensor structure and preferred parameters provided by the present invention (excitation coil: 0.1mm wire diameter, 30 turns; receiving coil: 0.06mm wire diameter, 15 turns; excitation current: 35A), it is possible to effectively achieve high signal-to-noise ratio and high resolution detection of sub-millimeter (0.1mm) minute defects in aluminum materials, thus verifying the effectiveness and superiority of the present invention.

[0036] This invention provides a miniature receiving coil electromagnetic ultrasonic sensor and a high-resolution detection method, which has the following outstanding advantages: First, high signal-to-noise ratio and high-resolution detection capability: By adopting a structural design of eight independent miniature receiving coils tightly arranged in an array, the sensing area of ​​each coil is significantly reduced (the effective receiving area of ​​a single coil is only 1mm × 8mm), effectively suppressing the interference of spatial electromagnetic background noise, while greatly improving the spatial resolution of the sensor. It can accurately capture weak reflected signals from sub-millimeter-level (as small as 0.1mm) defects, achieving high signal-to-noise ratio signal acquisition. Second, compact structure and applicability to online monitoring: The sensor adopts a unique layout in which the receiving coil group is stacked on one side directly above the excitation coil, and combined with manual or machine precision winding and layered encapsulation with insulating tape, it achieves miniaturization, compactness, and good insulation of the overall structure. This design not only makes the sensor easy to manufacture and integrate, but is also very suitable for installation and use in complex or confined spaces in industrial environments, providing a hardware foundation for online real-time monitoring. Third, the detection process is simplified and real-time performance is improved: Because this invention fundamentally improves the signal-to-noise ratio at the hardware level, the detection method does not require complex software noise reduction algorithms for signal post-processing. The received echo signals can be directly analyzed and identified. This significantly simplifies the configuration of the detection system, reduces data processing costs, and greatly improves detection efficiency and real-time performance, meeting the stringent speed and efficiency requirements of industrial online monitoring. The results show that this invention, through innovative sensor structure design and manufacturing process, successfully solves the key problems of low signal-to-noise ratio, reliance on post-processing, and large size in traditional electromagnetic ultrasonic technology for detecting sub-millimeter-level defects. It provides a high-performance, low-cost, and online-suitable solution for detecting minute defects, possessing significant application value and promising prospects in the field of industrial non-destructive testing.

[0037] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A novel miniature electromagnetic ultrasonic sensor with a receiving coil assembly, characterized in that, include: Permanent magnet, excitation coil and receiving coil assembly; The receiving coil group includes at least two independent preset miniature coils; wherein the size of the preset miniature coil is smaller than that of the excitation coil, and the preset miniature coil is located within the range of the excitation coil; The receiving coil group is positioned above the effective receiving portion of the excitation coil, and the ineffective portion of the receiving coil group is staggered from the excitation coil. The permanent magnet is placed above the effective receiving area of ​​the receiving coil group, with its magnetic pole direction perpendicular to the plane of the receiving coil group.

2. The novel miniature receiving coil electromagnetic ultrasonic sensor according to claim 1, characterized in that, The excitation coil is made of copper enameled wire of a preset diameter wound with a preset number of turns, forming an effective excitation region with a preset length and width.

3. The novel miniature receiving coil electromagnetic ultrasonic sensor according to claim 1, characterized in that, The receiving coil group is composed of copper enameled wire of a preset diameter wound with a preset number of turns, forming an effective receiving area with a preset length and width.

4. The novel miniature receiving coil electromagnetic ultrasonic sensor according to claim 1, characterized in that, The preset small coils in the receiving coil group are arranged with either side of the coil as the effective receiving part. The effective receiving parts are arranged in a way that is closely arranged or partially overlapped along the length direction to form a compact array unit, and are fixed as a whole with insulating material. The lead of each coil is led out independently.

5. The novel miniature receiving coil electromagnetic ultrasonic sensor according to claim 1, characterized in that, Both the excitation coil and the receiving coil group adopt racetrack-shaped coils.

6. A method for high-resolution detection of sub-millimeter-level micro-defects using the novel miniature receiving coil electromagnetic ultrasonic sensor according to any one of claims 1-5, characterized in that: The method includes: A novel small receiving coil electromagnetic ultrasonic sensor is placed above the surface of the test piece. A pulsed current is passed through the excitation coil to generate ultrasonic waves; When an ultrasonic wave propagates in the test piece and encounters a defect, it generates a reflected echo. The reflected echo signal is received synchronously or in stages using a receiving coil group. The signals received by the receiving coil group are acquired and processed synchronously or in stages, and defects are identified based on the characteristics of the echo signals.

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