Magnetic flux focusing type multi-mode guided wave transducer and pipeline detection method

Abstract

The invention discloses a magnetic flux focusing type multi-mode guided wave transducer which comprises the components of a magnet assembly (1) which comprises an axial magnetizing annular permanent magnet (3) and a magnetic flux focusing ring (4) which are arranged on a supporting framework (5); wherein the magnetic flux focusing ring (4) is clamped between the axial magnetizing annular permanent magnets (3) with the same magnetic poles and is used for converging magnetic flux and forming a radial static magnetic field on the periphery of the magnetic flux focusing ring (4); the flexible printed circuit coil module (2) wraps and is fixed on the outer surface of the magnet assembly (1); when the FPC coil module (2) is electrified, eddy current is induced on the surface of the pipeline (6) to be detected, and the eddy current interacts with the radial static magnetic field to excite or receive guided waves. According to the transducer, through magnetic circuit design and a modular structure, the problems of low energy conversion efficiency and single mode can be solved at the same time.

Description

Technical Field

[0001] This invention relates to the field of pipeline non-destructive testing equipment technology, specifically to a flux-focusing multimode guided wave transducer and a pipeline testing method. Background Technology

[0002] In modern industrial sectors such as petrochemicals, nuclear power, and aerospace, pipeline systems are core infrastructure ensuring safe and stable production operations. They undertake critical functions such as fluid transport and energy transfer. However, during long-term operation, pipelines are susceptible to defects caused by corrosion, fatigue, stress damage, and complex operating conditions. If these defects are not detected and addressed in a timely manner, they can easily lead to major safety accidents, threatening personnel lives and company property. Therefore, developing efficient and convenient non-destructive testing technologies for pipelines is crucial. Among these, pipelines represented by densely packed tube bundles, such as tube bundle heat exchangers, suffer from extremely limited external operating space due to their dense arrangement and external covering by insulation layers, protective structures, or other equipment. Traditional testing methods are not applicable, necessitating the use of other technologies for effective testing.

[0003] Ultrasonic guided wave testing technology has become an important means of monitoring the health of pipeline structures due to its long propagation distance, high sensitivity, and superior ability to achieve full cross-section coverage. The excitation methods of ultrasonic guided waves mainly include the piezoelectric effect and the electromagnetic acoustic (EMAT) effect. Among them, the electromagnetic acoustic (EMAT) effect, due to its non-contact advantage, has been widely studied and applied in the field of pipeline inspection. The physical mechanisms of EMAT technology are mainly divided into two categories: Lorentz force and magnetostriction. Although the transduction efficiency of the magnetostrictive effect is high, its application is limited to ferromagnetic materials, thus limiting its applicability. In contrast, EMAT based on the Lorentz force effect, because its principle is applicable to all conductive materials, has a wider range of engineering application prospects.

[0004] In piping systems, such as those with tube bundle heat exchangers, where external inspection is limited, waveguide-based in-pipe technology is crucial for efficient in-service inspection. However, existing in-pipe technologies have fundamental limitations: traditional in-pipe piezoelectric transducers, due to their dependence on coupling agents, suffer from reliability issues in the narrow and potentially contaminated environment of pipes; while in-pipe magnetostrictive transducers, although highly efficient, rely on ferromagnetic materials, rendering them ineffective for non-ferromagnetic pipes made of materials like stainless steel, copper, and aluminum, severely limiting their applicability. In contrast, in-pipe electromagnetic acoustic (EMAT) transducers, with their non-contact operating principle, fundamentally solve the coupling problem within pipes. Furthermore, their Lorentz force-based mechanism is applicable to all conductive materials, making them a viable technology for in-pipe inspection.

[0005] In confined space pipeline inspection, such as heat exchanger tube bundles, traditional in-pipe EMAT transducers suffer from two major technical bottlenecks: insufficient energy conversion efficiency and limited functional modes. Magnetic flux leakage caused by defects in the magnet structure design results in insufficient effective magnetic field strength in the coil's working area, leading to low transduction efficiency. Furthermore, existing EMAT probes employ an integrated structure design, with each probe supporting only a single guided wave mode excitation, failing to meet the multi-modal collaborative detection requirements for complex defects.

[0006] Therefore, there is an urgent need in this field for a novel transducer structure that can significantly improve transducer efficiency and flexibly excite multimode guided waves. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a flux-focusing multimode guided wave transducer and a pipeline inspection method to address the shortcomings of the prior art. The transducer, through magnetic circuit design and modular structure, can simultaneously solve the problems of low energy conversion efficiency and single mode.

[0008] To achieve the above objectives, according to one aspect of the present invention, a flux-focusing multimode guided wave transducer is provided, comprising: The magnet assembly (1) includes at least two magnet units disposed on the support frame (5). Each magnet unit includes two axially magnetized annular permanent magnets (3) with the same magnetic poles and the same size and a flux focusing ring (4). The flux focusing ring (4) is sandwiched between the axially magnetized annular permanent magnets (3) with the same magnetic poles and is used to focus the magnetic flux and form a radial static magnetic field on its outer periphery. The support frame (5) is attached to the pipe to be tested (6) and has a support plate on its upper part that is parallel to the axial magnetic pole direction of the axially magnetized annular permanent magnets (3). The magnet assembly (1) is disposed on the support plate. The flexible printed circuit coil module (2) is wrapped and fixed to the outer surface of the magnet assembly (1); when the FPC coil module (2) is energized, eddy currents are induced on the surface of the pipe to be tested (6), and interact with the radial static magnetic field to excite or receive guided waves.

[0009] In the above scheme, the transducer can serve as both a transmitter and a receiver. The transmitter is used to excite longitudinal (L) wave or torsional (T) wave guided wave modes, and the receiver is used to receive the echo signal of the corresponding mode. The flexible printed circuit coil module (2) and the magnet assembly (1) are detachably connected. By replacing the flexible printed circuit coil module (2) with different excitation mode waveforms, the transducer can be excited in longitudinal wave (L wave) and transverse wave (T wave) modes and receive the corresponding echo signals.

[0010] In the above scheme, the magnet assembly (1) includes at least two magnet units, forming a periodic permanent magnet (PPM) array; The magnetic poles of adjacent magnet units have the same direction, and the adjacent magnet units maintain a preset distance.

[0011] In the above scheme, the preset spacing is an odd multiple of the half wavelength of the target longitudinal waveguide mode.

[0012] In the above scheme, the center-to-center distance between adjacent conductors of the coil in the flexible printed circuit (FPC) coil module (2) is adapted to half the wavelength of the target guided wave mode; the adaptation specifically includes: two magnetic units consisting of "axially magnetized ring permanent magnet (3) - flux focusing ring (4) - axially magnetized ring permanent magnet (3)" form a PPM array. The PPM array needs to be set according to the half wavelength of the target guided wave mode in order to enhance the signal through the constructive interference of the guided wave. The working area of ​​the flux focusing ring 4 in the two magnetic units needs to overlap with that of the flexible printed circuit coil module 2. Therefore, the center-to-center distance between adjacent conductors of the coil in the flexible printed circuit coil module (2) needs to be adapted to half the wavelength of the target guided wave mode.

[0013] In the above scheme, the axial length of the magnetic flux focusing ring (4) is the same as the width of the working area of ​​the flexible printed circuit coil module (2); the working area of ​​the flexible printed circuit coil module (2) is the area where the flexible printed circuit coil module (2) and the support frame (5) intersect perpendicularly in the length direction. The magnetic unit composed of the axially magnetized annular permanent magnet (3), the flux focusing ring (4), and the axially magnetized annular permanent magnet (3) has a total length of axially magnetized annular permanent magnet (3) at both ends, and the total length of the axially magnetized annular permanent magnet (3) is 3 times the width of the working area of ​​the flexible printed circuit coil module (2).

[0014] In the above scheme, the working area of ​​the flexible printed circuit (FPC) coil module (2) covers the outer peripheral surface of the flux focusing ring (4).

[0015] In the above scheme, the flux focusing ring (4) is made of a soft magnetic material with high permeability and is used to guide the magnetic lines of force of the axially magnetized annular permanent magnet (3) to form a closed magnetic circuit. The flux focusing ring (4) concentrates the magnetic flux to the working area of ​​the flexible printed circuit (FPC) coil module (2) to form a high-intensity radial magnetic field and reduce axial leakage magnetic field.

[0016] In the above scheme, a cylindrical structure is provided below the support plate of the support frame (5), which can fit tightly against the inner wall of the pipe (6) to be tested; The axial length of the support frame (5) is determined according to the design requirements of the periodic permanent magnet (PPM) array.

[0017] According to another aspect of the present invention, a pipeline inspection method is provided, the method comprising the following steps: S1. Two identical guided wave transducers are set at both ends of a conductive pipe to be tested, serving as the transmitter and receiver. The guided wave transducer is a flux-focusing multimode guided wave transducer as described above. S2. A high-frequency alternating current and an appropriate voltage are passed into the waveguide transducer, which serves as the transmitting end. Based on the principle of electromagnetic induction, eddy currents of the same frequency are induced on the surface of the pipe under test. The radial static magnetic field generated by the magnet component of the waveguide transducer at the transmitting end and the orthogonal interaction with the eddy current are used to excite the guided wave propagating longitudinally along the pipe under test. S3. The guided wave transducer, acting as the receiving end, detects the reflected or scattered guided wave signals and converts the pipe vibration into an electrical signal through the principle of electromagnetic induction. The received signal is amplified, filtered, and data is acquired. The guided wave propagation characteristics are analyzed to locate and quantify the defects in the pipe under test.

[0018] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: This invention provides a flux-focusing multimode guided wave transducer. By introducing a "flux-focusing ring," the magnetic circuit is greatly optimized, significantly increasing the radial magnetic field strength in the coil's working area. This enhances the Lorentz force effect, improves energy conversion efficiency, and yields a detection signal with higher amplitude and better signal-to-noise ratio. Combining a PPM array design with wavelength matching of the coil spacing, this invention can excite pure target guided wave modes and further enhance the signal through constructive interference, improving detection reliability and accuracy. The modular design, separating the magnet core from the functional coils, allows for flexible switching between longitudinal and torsional waves by replacing low-cost FPC coil modules, meeting the multimode detection requirements of complex defects while significantly reducing equipment costs and operational complexity. The adjustable size of the support frame allows the transducer to adapt to a range of pipe diameters, and its Lorentz force-based working principle makes it suitable for pipes made of all conductive materials, resulting in a wide range of applications. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a front view of a flux-focusing multimode guided wave transducer according to Embodiment 1 of the present invention.

[0020] Figure 2This is a full view of a flux-focusing multimode guided wave transducer installed on a pipeline according to Embodiment 1 of the present invention.

[0021] Figure 3 This is a schematic diagram of the excitation principle of a single array in Embodiment 1 of the present invention.

[0022] Figure 4 This is a circuit board design diagram of the flexible printed circuit coil module in Embodiment 1 of the present invention.

[0023] Figure 5 This is a schematic diagram of the magnetic field line distribution of a conventional magnet structure without soft iron elements in Embodiment 1 of the present invention.

[0024] Figure 6 This is a schematic diagram of the magnetic field lines distribution of the magnet core using soft iron elements in Embodiment 1 of the present invention.

[0025] Figure 7 This is a schematic diagram of the experimental results of the guided wave signal received when using a traditional transducer without a magnetic flux focusing ring (soft iron element) in Embodiment 1 of the present invention.

[0026] Figure 8 This is a schematic diagram of the experimental results of the guided wave signal received when using a transducer with a flux focusing ring (soft iron element) in Embodiment 1 of the present invention.

[0027] Figure 9 This is a schematic diagram illustrating the definition of key geometric dimensions of a single excitation unit in Embodiment 1 of the present invention.

[0028] Figure 10 This is a schematic diagram showing the relationship between the magnitude of the Lorentz force and the length ratio of the magnet to the soft iron in Embodiment 1 of the present invention.

[0029] Explanation of the labels in the diagram: 1. Magnet assembly; 2. Flexible printed circuit coil module; 3. Axially magnetized annular permanent magnet; 4. Flux focusing ring; 5. Support frame; 6. Pipe under test. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Example 1 This application provides a flux-focusing multimode guided wave transducer, such as... Figure 1-10As shown, the flux-focusing multimode guided wave transducer provided in this embodiment includes: The magnet assembly 1 includes at least two magnet units disposed on the support frame 5. Each magnet unit includes two axially magnetized annular permanent magnets 3 with the same magnetic poles and the same size and a flux focusing ring 4. The flux focusing ring 4 is sandwiched between the axially magnetized annular permanent magnets 3 with the same magnetic poles and is used to focus the magnetic flux and form a radial static magnetic field on its outer periphery. The support frame 5 is attached to the pipe 6 to be tested, and its upper part has a support plate parallel to the axial magnetic pole direction of the axially magnetized annular permanent magnets 3. The magnet assembly (1) is disposed on the support plate. A flexible printed circuit (FPC) coil module 2 is wrapped around and fixed to the outer surface of the magnet assembly 1. When energized, the FPC coil module 2 induces eddy currents on the surface of the pipe under test 6, which interact with the radial static magnetic field to excite or receive guided waves. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 The diagram shown is a three-dimensional structure of the transducer of the present invention.

[0032] The transducer of this invention can serve as both a transmitter and a receiver. The transmitter is used to excite longitudinal (L) wave or torsional (T) wave guided wave modes, and the receiver is used to receive the echo signals of the corresponding modes. The flexible printed circuit (FPC) coil module 2 and the magnet assembly 1 are detachably connected. By replacing the flexible printed circuit coil module 2 that excites different mode waveforms, the transducer can be excited in longitudinal (L) wave and transverse (T) wave modes and receive the corresponding echo signals.

[0033] In this embodiment, the magnet assembly 1 includes two magnet units consisting of "axially magnetized annular permanent magnet 3 - flux focusing ring 4 - axially magnetized annular permanent magnet 3"; the magnetic pole directions of adjacent magnet units are the same, and a preset distance is maintained between adjacent magnet units to form a periodic permanent magnet (PPM) array.

[0034] Specifically, in this embodiment, the transducer mainly consists of a general-purpose PPM array magnet assembly 1 and an interchangeable set of flexible printed circuit coil modules 2. The magnet assembly 1 consists of an axially magnetized annular permanent magnet 3, a soft iron element with high magnetic permeability serving as a flux focusing ring 4, and a support frame 5. The flux focusing ring 4 is placed between the axially magnetized annular permanent magnet portions 3 with the same magnetic pole direction, providing an optimized radial static magnetic field for the transducer to operate. The FPC coil module 2 is wrapped around and fixed on the outer surface of the magnet assembly 1, wherein the working area of ​​the FPC coil module 2 fits onto the upper surface of the flux focusing ring 4, providing a dynamic magnetic field for the transducer to operate.

[0035] The transducer in this embodiment is assembled according to... Figure 1 and Figure 2The operator wraps and fixes the selected flexible printed circuit (FPC) coil module 2 onto the outer surface of the magnet assembly 1. The working coil area of ​​the FPC coil module 2 is fitted to the upper surface of the flux focusing ring 4. This is based on the following technical principle: the working coil area needs to fit into the area where the flux focusing ring 4 is located because this area is the ideal working area for obtaining a radial static magnetic field according to the "magnetic flux focusing" effect. The main function of the FPC coil module 2 is to induce eddy currents in the pipe 6 under test, providing a dynamic magnetic field for the transducer to operate. This matching maximizes the generated Lorentz force, thereby greatly improving the energy conversion efficiency of the transducer.

[0036] like Figure 3 As shown, the transduction process of a single excitation unit is as follows: The working area of ​​the FPC coil module 2 is precisely aligned with the upper surface of the soft iron element. When the high-frequency alternating current passes through the conductive circuit of the FPC coil module 2, according to the principle of electromagnetic induction, eddy currents of the same frequency will be induced on the surface of the pipe under test 6. At the same time, the magnet assembly 1, composed of the axially magnetized annular permanent magnet 3 and the magnetic flux focusing ring 4, forms a highly concentrated radial static magnetic field through the magnetic flux focusing effect. According to the Lorentz force principle, the eddy current density vector and the radial static magnetic field vector interact orthogonally on the surface of the pipe wall, generating a Lorentz force perpendicular to both. When the eddy current is distributed circumferentially, it will excite longitudinal waves; when the eddy current is distributed axially, it will excite torsional waves. The precise alignment design of the FPC coil module 2 and the magnetic flux focusing ring 4 ensures the spatial matching of the dynamic magnetic field and the static magnetic field, thereby maximizing the Lorentz force effect. The core physical relationship followed by the entire transduction process can be expressed by the following formula (1): (1) In the formula, The Lorentz force is the force acting on a unit volume of the pipe wall of the pipe under test. The vector representing the current density of the eddy current. Given the magnetic flux density vector of a static magnetic field, the Lorentz force in a specific direction can be obtained.

[0037] One of the core innovations of this invention, the magnet component 1, lies in its fundamental optimization of the magnetic circuit design through the introduction of a magnetic flux focusing ring 4. Its technological superiority can be demonstrated through comparison. Figure 5 and Figure 6 A detailed explanation will be provided.

[0038] In contrast, first refer to Figure 5 The figure schematically illustrates the magnetic field distribution of a conventional magnet structure without soft iron components. The magnetic field lines generated by the permanent magnet start directly from the N pole, pass through the air, and return to the S pole, resulting in severe magnetic flux leakage and insufficient effective magnetic field strength.

[0039] In comparison, refer to Figure 6In this embodiment, the magnet assembly 1 greatly optimizes the magnetic circuit by introducing soft iron elements. The principle can be explained by magnetic circuit theory. The core relationship in the magnetic circuit can be expressed by the following equations (2) and (3): (2) (3) In the formula, For magnetic flux, It is a magnetomotive force. For magnetic reluctance, The length of the magnetic circuit. The magnetic permeability of the material, This represents the cross-sectional area of ​​the magnetic circuit.

[0040] The soft iron element in the embodiments of this application uses high magnetic permeability ( >>1) is made of soft magnetic material, and according to formula (3), its magnetic resistance Extremely low, therefore, according to equation (2), the vast majority of magnetic flux It will preferentially choose to propagate via soft iron paths. (Refer to...) Figure 6 This magnetic flux focusing effect effectively guides the magnetic field lines, thereby obtaining a high-intensity, high-purity radial static magnetic field in the working area of ​​the flexible printed circuit coil.

[0041] Reference Figure 9 The figure schematically defines the key geometric dimensions in a single excitation unit, including the total length of the axially magnetized annular permanent magnet 3. With FPC coil width The ratio is This directly affects the efficiency of Lorentz force generation. Simultaneously, the working area of ​​the FPC coil module 2 needs to perfectly cover the flux focusing ring 4; therefore, the axial length of the flux focusing ring 4 is exactly equal to... Typically, this ratio should be matched to the transducer's operating conditions so that the Lorentz force effect can effectively excite the ultrasonic guided wave. This application's embodiments, through finite element simulation and experimental verification, have determined an optimal length ratio between the two components to obtain a high-efficiency signal. The relationship is given by the following equation (4): (4) Figure 10 This demonstrates how the magnitude of the Lorentz force varies with the length ratio, as obtained through finite element simulation. Typical relationship curves of change. When When the value is less than 3, the magnitude of the Lorentz force increases proportionally; however, when... When the value is greater than 3, its growth rate begins to slow down significantly. The value tends to stabilize at >4. When the ratio is 3, the transducer achieves the optimal performance balance between magnetic field uniformity, force generation efficiency, and structural compactness, ensuring that each individual transducer unit operates at maximum efficiency. Therefore, under the premise of meeting the overall size constraints of the PPM array, this invention preferably adopts... Design principles of 3. The distance between magnet units was determined based on the PPM principle, and the lengths of the flux focusing ring 4 and the axially magnetized annular permanent magnet 3 were selected accordingly. While meeting the requirements of PPM, their ratio was made as close to 3 as possible to ensure that each independent transducer unit can operate with the highest efficiency.

[0042] To further enhance signal strength and ensure the highest detection sensitivity, this application first optimizes the intrinsic transduction efficiency of a single transducer magnet unit, and then optimizes the cooperative working mode between multiple magnet units through the configuration of a periodic permanent magnet (PPM) array.

[0043] Figure 1 Multiple optimized transducer magnet units are combined into a PPM array to achieve secondary signal enhancement through constructive interference of waves. The relationship between propagation wavelength and frequency; wavelength of ultrasonic guided waves. With the speed of propagation and frequency The relationship between them is: (5) in, The propagation speed depends on the longitudinal (L) mode or the torsional (T) mode, which is related to the material of the pipe under test (6) and the waveguide mode.

[0044] In this embodiment, the entire magnet assembly 1 comprises two aforementioned "flux-focusing" magnet units, with the second magnet unit having the same magnetic pole direction relative to the first magnet unit, thus forming a periodic permanent magnet (PPM) array. To enhance the signal through constructive interference of guided waves, the structure of this PPM array follows the following design principles: (6) In the formula, The center-to-center distance between adjacent transducer units. The wavelength of the target guided wave. This is a constant. This means that the array spacing must be an odd multiple of half the wavelength of the target longitudinal guided wave mode, so that the guided wave signal of the target mode can be enhanced to the maximum extent through the principle of wave superposition.

[0045] Specifically, to verify the actual performance of the transducer of this invention, this embodiment uses a defect-free nickel-copper alloy pipe with a length of 1700 mm, an outer diameter of 16 mm, and a wall thickness of 1.75 mm as the test object (test pipe 6). 177 kHz is selected as the excitation frequency to efficiently excite the target longitudinal wave L(0,2) mode near this frequency. The wavelength of the L(0,2) mode at this frequency is calculated. Approximately 74.3 mm. First, a comparative experiment was conducted: two identical PPM array transducers without pure iron components were constructed for "one-to-one" transmission and reception testing. The axially magnetized annular permanent magnet 3 of each transducer's magnet unit consisted of multiple N52-grade permanent magnet stacks with an outer diameter of 12 mm, an inner diameter of 5.5 mm, and a thickness of 1 mm. The total length of each axially magnetized annular permanent magnet 3 was 9 mm. According to the design guidelines for PPM arrays, the center-to-center distance d between the two magnet units was set to 37.15 mm. Finally, the FPC coil module 2 was assembled onto the outer surfaces of the two transducers. Figure 7 As shown, it illustrates the guided wave signal received using a conventional transducer structure, which has a low amplitude and poor signal-to-noise ratio. Subsequently, a performance verification experiment of this embodiment was conducted. A pair of identical PPM array transducers of this invention, integrating a flux focusing ring 4 (pure iron element), were constructed. Except for the addition of a pure iron element with an axial width of 5 mm, all other parameters were completely identical to the conventional transducer in the comparative experiment. This pair of transducers of this invention were deployed at both ends of a pipe in the same "one transmits, one receives" mode and tested. (Refer to...) Figure 8 It shows the signal received when using the transducer according to the embodiments of this application.

[0046] The results of this comparative experiment show that, under identical conditions, by adding the innovative design of the flux focusing ring 4, the transducer in this embodiment can efficiently excite a pure L(0,2) mode guided wave, with a clear received signal and a wave velocity that highly matches the theoretical calculation. Figure 7 and Figure 8 The comparison clearly shows that the transducer used in the embodiment of this application ( Figure 8 The received signal has a higher amplitude than that of a traditional structure. Figure 7 The signal was clearly observed, with multiple clear end-face reflection echoes and minimal signal noise. This directly demonstrates the significant improvement in energy conversion efficiency and signal quality caused by the magnetic flux focusing effect, indicating that the transducer of this invention has strong practical applicability in real-world applications.

[0047] This embodiment also provides a pipeline inspection method, which includes the following steps: S1. Two identical waveguide transducers are set at both ends of a conductive pipe under test as the transmitter and receiver. The waveguide transducer is a flux-focusing multimode waveguide transducer in this embodiment. S2. A high-frequency alternating current and an appropriate voltage are passed into the waveguide transducer, which serves as the transmitting end. Based on the principle of electromagnetic induction, eddy currents of the same frequency are induced on the surface of the pipe under test. The radial static magnetic field generated by the magnet component of the waveguide transducer at the transmitting end and the orthogonal interaction with the eddy current are used to excite the guided wave propagating longitudinally along the pipe under test. S3. The guided wave transducer, acting as the receiving end, detects the reflected or scattered guided wave signals and converts the pipe vibration into an electrical signal through the principle of electromagnetic induction. The received signal is amplified, filtered, and data is acquired. The guided wave propagation characteristics are analyzed to locate and quantify the defects in the pipe under test.

[0048] The specific steps of the above pipeline inspection method are as follows: (1) Transmitter (excitation end) operation procedure: Based on the target frequency of the guided wave to be excited, the center-to-center spacing of adjacent conductors in the flexible printed circuit coil module 2 is calculated and designed to ensure that the spacing is accurately matched with the half-wavelength of the target guided wave mode. The coil module is then wrapped around and fixed to the outer surface of the magnet assembly 1, completing the waveguide transducer assembly. The assembled waveguide transducer is inserted into one end of the pipe 6 to be tested and fixed, ensuring a tight fit with the inner wall of the pipe, and that the working area of ​​the coil module completely covers the outer periphery of the flux focusing ring 4. A high-frequency alternating current and an appropriate voltage are set by a signal generator. The high-frequency alternating current is amplified by a power amplifier and then connected to the flexible printed circuit coil module 2. According to the principle of electromagnetic induction, eddy currents of the same frequency will be induced on the surface of the pipe under test 6 after the coil is energized. At the same time, the magnet assembly 1, which consists of an axially magnetized annular permanent magnet 3 and a magnetic flux focusing ring 4, forms a highly concentrated radial static magnetic field through the magnetic flux focusing effect. According to the Lorentz force principle, the eddy current density vector on the surface of the pipe wall of the pipe under test 6 interacts orthogonally with the radial static magnetic field vector, generating a directional Lorentz force perpendicular to both. When the eddy current is distributed circumferentially, it excites a longitudinal wave, and when it is distributed axially, it excites a torsional wave. The guided wave propagates longitudinally along the pipe.

[0049] (2) Receiver operation procedure: A waveguide transducer identical to the excitation end is inserted at the other end of the pipe under test 6, ensuring its installation posture and fixing method are synchronized with the excitation end to guarantee consistent signal reception. When the guided wave generated by the excitation end propagates inside the pipe, it will cause the pipe wall to vibrate slightly when it encounters a defect or a reflected echo from the pipe end face. At this time, the flexible printed circuit coil module 2 of the receiving transducer is in the radial static magnetic field provided by the magnet assembly 1. The vibration of the pipe wall 6 under test causes the coil to move relative to the magnetic field, resulting in a change in the magnetic flux passing through the coil. According to the principle of electromagnetic induction, the change in magnetic flux will induce a corresponding alternating electromotive force signal in the flexible printed circuit coil module 2. Then, the flexible printed circuit coil module 2 of the receiving transducer is connected to a preamplifier to initially amplify the weak electrical signal induced by the coil, while suppressing environmental electromagnetic interference, equipment circuit noise, and other noise, thereby improving the signal-to-noise ratio. Subsequently, the output of the preamplifier is connected to a data acquisition card, which transmits the processed electrical signal to a computer for subsequent data analysis. Finally, the signal recording and analysis were completed using a data acquisition card and a computer, enabling the location and quantification of defects in the pipeline under test.

[0050] In summary, this application provides a flux-focusing multimode guided wave transducer (EMAT) that can excite and receive longitudinal and torsional waves by replacing interchangeable flexible coils, adapting to the detection needs of different types of defects and thus improving the comprehensiveness and accuracy of detection. The transducer employs a stable and efficient magnetic field design, providing an optimized radial static magnetic field through the "flux-focusing" effect and PPM array, enhancing the Lorentz force effect and improving signal quality and detection stability. Structurally, the modular magnet core and interchangeable FPC flexible coil design not only improve the transducer's performance and maintainability but also greatly simplify the detection operation process. Furthermore, this invention achieves flexible switching between different ultrasonic guided wave modes through a modular switching mechanism, avoiding the need to design and install multiple transducers for different modes, thereby reducing the investment cost of detection equipment. Since the EMAT based on the Lorentz force effect is suitable for various complex working conditions, its engineering adaptability is significantly improved, expanding its application scope in fields such as petrochemicals, nuclear industry, and aerospace. This invention has broad application prospects in pipeline health monitoring, providing an efficient and low-cost non-destructive testing solution for pipeline structural safety assessment and maintenance.

[0051] Example 2 This application provides a flux-focusing multimode guided wave transducer, which is basically the same as the method in embodiment 1, except that the flux-focusing ring 4 in this embodiment is made of nickel-iron alloy.

[0052] It should be noted that, depending on the implementation needs, the various steps described in this application can be broken down into more steps, or two or more steps or parts of the steps can be combined into new steps to achieve the purpose of this invention.

[0053] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A magnetic flux focusing multimodal guided wave transducer, comprising: The application relates to a transducer for detecting defects in a pipeline, comprising: a magnet assembly (1) comprising at least two magnet units arranged on a support skeleton (5), each magnet unit comprising two axially magnetized annular permanent magnets (3) with the same magnetic pole and the same size and a magnetic flux focusing ring (4), wherein the magnetic flux focusing ring (4) is arranged between the two axially magnetized annular permanent magnets (3) with the same magnetic pole to converge the magnetic flux and form a radial static magnetic field on the outer periphery of the magnetic flux focusing ring (4); the support skeleton (5) is attached to the pipeline (6) to be detected, and the upper part of the support skeleton (5) is provided with a support plate parallel to the axial magnetic pole direction of the axially magnetized annular permanent magnet (3); a flexible printed circuit coil module (2) wrapped around and fixed to the outer surface of the magnet assembly (1); the FPC coil module (2) generates eddy current on the surface of the pipeline (6) to be detected when energized, and the eddy current interacts with the radial static magnetic field to excite or receive the guided wave.

2. The magnetic flux focusing multi-modal guided wave transducer of claim 1, wherein, The transducer can be used as a transmitting end and a receiving end; the transmitting end is used for exciting the longitudinal wave or torsional wave guided wave mode, and the receiving end is used for receiving the echo signal of the corresponding mode; The flexible printed circuit coil module (2) is detachably connected with the magnet assembly (1), and by replacing the flexible printed circuit coil module (2) for exciting different mode waveforms, the transducer can be used for exciting the longitudinal wave and transverse wave mode and receiving the corresponding echo signal.

3. The magnetic flux focusing multi-modal guided wave transducer of claim 1, wherein, The magnet assembly (1) comprises at least two magnet units, and forms a periodic permanent magnet array. The magnetic pole directions of adjacent magnet units are the same, and a preset interval is kept between the adjacent magnet units.

4. The magnetic flux focusing multi-modal guided wave transducer of claim 3, wherein, The preset interval is an odd multiple of the half wavelength of the target longitudinal guided wave mode.

5. The magnetic flux focusing multi-modal guided wave transducer of claim 1, wherein, The center distance between adjacent wires of the coil in the flexible printed circuit coil module (2) is adapted to the half wavelength of the target guided wave mode. The adaptation includes that two magnet units composed of the axially magnetized annular permanent magnet (3)-the magnetic flux focusing ring (4)-the axially magnetized annular permanent magnet (3) form the periodic permanent magnet array, the distance of the periodic permanent magnet array needs to be set according to the half wavelength of the target guided wave mode so as to enhance the signal through the constructive interference of the guided wave, and the working area of the magnetic flux focusing ring 4 and the flexible printed circuit coil module 2 needs to be overlapped in the two magnet units, therefore, the center distance between adjacent wires of the coil in the flexible printed circuit coil module (2) needs to be adapted to the half wavelength of the target guided wave mode.

6. The magnetic flux focusing multi-modal guided wave transducer of claim 1, wherein, The axial length of the magnetic flux focusing ring (4) is the same as the width of the working area of the flexible printed circuit coil module (2); the working area of the flexible printed circuit coil module (2) is the area where the flexible printed circuit coil module (2) and the support skeleton (5) are vertically intersected in the length direction. The length sum of the two axially magnetized annular permanent magnets (3) at the two ends of the magnet unit composed of the axially magnetized annular permanent magnet (3)-the magnetic flux focusing ring (4)-the axially magnetized annular permanent magnet (3) is the total length of the axially magnetized annular permanent magnet (3), and the total length of the axially magnetized annular permanent magnet (3) is 3 times the width of the working area of the flexible printed circuit coil module (2).

7. The magnetic flux focusing multi-modal guided wave transducer of claim 1, wherein, The working area of the flexible printed circuit coil module (2) covers the outer peripheral surface of the magnetic flux focusing ring (4).

8. The magnetic flux focusing multi-modal guided wave transducer of claim 2, wherein, The magnetic flux focusing ring (4) is made of high magnetic permeability soft magnetic material, and is used for guiding the magnetic force lines of the axial magnetized ring-shaped permanent magnet (3) to form a closed magnetic circuit.

9. The magnetic flux focusing multi-modal guided wave transducer of claim 1, wherein, A cylindrical structure is arranged below the support plate of the support framework (5), and can be tightly attached to the inner wall of the pipeline (6) to be measured; The axial length of the support framework (5) is determined according to the design requirements of the periodic permanent magnet array.

10. A method of pipeline inspection, characterized by, The method comprises the following steps: S1, two same waveguide transducers are arranged as a transmitting end and a receiving end at two ends of a conductive pipeline to be measured, and the waveguide transducer is a magnetic flux focusing type multi-modal waveguide transducer according to any one of claims 1-9; S2, high-frequency alternating current and adaptive voltage are input to the waveguide transducer as the transmitting end, and according to the electromagnetic induction principle, eddy current of the same frequency is induced on the surface of the pipeline to be measured; the orthogonal action of the radial static magnetic field generated by the magnet assembly of the transmitting end waveguide transducer and the eddy current excites the waveguide propagating along the longitudinal direction of the pipeline to be measured; S3, the waveguide transducer as the receiving end detects the reflected or scattered waveguide signal, and converts the pipeline vibration into an electric signal through the electromagnetic induction principle; the received signal is amplified, filtered and data collected, the waveguide propagation characteristics are analyzed, and the positioning and quantization of the defects of the pipeline to be measured are realized.

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