An electromagnetic acoustic transducer that concentrates magnetic field strength to enhance lorentz forces

Abstract

The application belongs to the technical field of ultrasonic nondestructive testing, and discloses a kind of electromagnetic acoustic transducer of concentrated magnetic field intensity enhancement Lorentz force, including magnetic ring type permanent magnet, for providing horizontal direction static magnetic field;Magnetic core type permanent magnet is located inside magnetic ring type permanent magnet, and magnetic core type permanent magnet is used to provide vertical direction static magnetic field;Pure iron is located in the bottom of magnetic ring type permanent magnet;Spiral coil is located between magnetic ring type permanent magnet and the sample to be tested, for inducing out eddy current opposite to current direction and periodic distribution;Through the magnetic gathering effect of pure iron, the horizontal direction and vertical direction static magnetic field interact with eddy current, and the ultrasonic wave of vertical incidence into the sample to be tested is coupled out.The application concentrates the magnetic field intensity by the matching structure of magnetic ring, magnetic core and pure iron, enhances Lorentz force, effectively improves the signal-to-noise ratio and detection accuracy of electromagnetic acoustic transducer, has better advantages in defect detection, and can be used for rapid, non-contact nondestructive testing of pipeline structure.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic nondestructive testing technology, and particularly relates to an electromagnetic acoustic transducer that concentrates magnetic field strength to enhance Lorentz force. Background Technology

[0002] Hydrogen pipelines are widely used in hydrogen production and transportation companies. During their service life, hydrogen pipelines are prone to defects such as cracks, corrosion, and porosity. To ensure the safe use of hydrogen pipelines, it is necessary to perform non-destructive testing and structural health monitoring. Ultrasonic non-destructive testing (NDT) is widely used in various industrial fields because of its advantages such as fast testing speed, low cost, and strong ability to detect internal defects. It can perform rapid and wide-range NDT on hydrogen pipelines. Electromagnetic acoustic transducers (EMAT) achieve the excitation and reception of ultrasonic waves based on the electromagnetic coupling mechanism. Its working mechanism includes Lorentz force, magnetization force, and magnetostrictive effect, and it can work effectively in low-temperature, normal-temperature, and high-temperature environments. Therefore, designing high signal-to-noise ratio ETAs is crucial for hydrogen pipeline inspection.

[0003] Traditional electromagnetic transducers use a single permanent magnet as a static magnetic field source. Their inherent structural limitations result in severe magnetic field divergence and rapid attenuation, as well as a small effective focusing area. This leads to low Lorentz force coupling efficiency, ultimately resulting in low excitation signal amplitude and poor signal-to-noise ratio, making it difficult to meet the requirements of high-precision and high-stability non-destructive testing.

[0004] Therefore, there is an urgent need for an electromagnetic acoustic transducer structure that concentrates magnetic field strength to enhance the Lorentz force, in order to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide an electromagnetic acoustic transducer that concentrates magnetic field strength to enhance Lorentz force, thereby solving the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: The present invention provides an electromagnetic acoustic transducer with concentrated magnetic field strength to enhance the Lorentz force, comprising: Magnetic ring permanent magnets are used to provide a static magnetic field in the horizontal direction; A core-type permanent magnet is located inside the ring-type permanent magnet, and the core-type permanent magnet is used to provide a static magnetic field in the vertical direction; Pure iron is located at the bottom of the inner ring-type permanent magnet and is fixedly connected to the bottom end of the core-type permanent magnet. A spiral coil is located between the magnetic ring permanent magnet and the test sample. The spiral coil is used to induce eddy currents that are opposite to the direction of the current and are periodically distributed. Through the magnetic focusing effect of the pure iron, the static magnetic fields in the horizontal and vertical directions interact with the eddy currents, coupling out ultrasonic waves that are vertically incident into the test sample.

[0007] Preferably, both the magnetic ring permanent magnet and the magnetic core permanent magnet have circular cross-sectional shapes.

[0008] Preferably, the polarization direction of the magnetic ring permanent magnet is radial, and the polarization direction of the magnetic core permanent magnet is axial.

[0009] Preferably, the ratio of the area of ​​the magnetic ring permanent magnet to the area of ​​the magnetic core permanent magnet is 1:1.

[0010] Preferably, the end face radius of the pure iron is the same as the end face radius of the magnetic core permanent magnet.

[0011] Preferably, the sum of the heights of the core permanent magnet and the pure iron is the same as the height of the ring permanent magnet, the top surface of the ring permanent magnet is aligned with the top surface of the core permanent magnet, and the bottom surface of the ring permanent magnet is aligned with the bottom surface of the pure iron.

[0012] Preferably, the spiral coil has a single-layer wiring structure, and the outer diameter of the spiral coil is no greater than 80% of the diameter of the magnetic ring permanent magnet.

[0013] Preferably, the center-to-center distance between two adjacent wires in the spiral coil is equal to half the wavelength of the target ultrasonic wave.

[0014] Preferably, the center-to-center distance between adjacent conductors in the spiral coil is l=0.52mm, and the center frequency of the electromagnetic transducer is f=3MHz.

[0015] Preferably, the test sample is an aluminum block or a hydrogen pipeline.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides an electromagnetic acoustic transducer that concentrates magnetic field strength to enhance the Lorentz force. A magnetic ring-type permanent magnet provides a horizontal static magnetic field, laying the foundation for subsequent synthesis of a vector magnetic field with the vertical magnetic field. A magnetic core-type permanent magnet provides a vertical static magnetic field, orthogonal to the horizontal static magnetic field, together forming a two-dimensional magnetic field distribution, enhancing the controllability of the Lorentz force. Pure iron, utilizing its high permeability, concentrates magnetic field lines onto the surface of the test sample, reducing magnetic leakage and enhancing the local magnetic field strength. When a high-frequency current is passed through a helical coil, alternating eddy currents are generated within the skin depth layer of the test sample. The static magnetic field and eddy currents, under the effect of magnetic focusing, form vertically incident ultrasonic waves, achieving non-contact ultrasonic excitation and improving the stability and signal-to-noise ratio of the detection. This invention, through the combined structure of the magnetic ring, magnetic core, and pure iron, concentrates the magnetic field strength, enhances the Lorentz force, and effectively improves the signal-to-noise ratio and detection accuracy of the electromagnetic acoustic transducer. It can be used for rapid, non-contact, non-destructive testing of structures such as pipelines. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a schematic diagram of the electromagnetic acoustic transducer of the present invention; Figure 2 This is a two-dimensional front view of the electromagnetic acoustic transducer of the present invention; Figure 3 This is a two-dimensional top view of the electromagnetic acoustic transducer of the present invention; Figure 4 This is a schematic diagram of the spiral coil of the present invention; Figure 5 The simulation results of the displacement amplitude excited by the electromagnetic acoustic transducer in the aluminum block are shown in the figure. Figure 6 The simulated magnetic flux density distribution of the static bias magnetic field; Figure 7 The simulated magnetic flux density distribution of the alternating dynamic magnetic field; Figure 8 The graph shows the simulated values ​​of the y-component of the magnetic flux density. Among them: 1. Magnetic ring permanent magnet; 2. Magnetic core permanent magnet; 3. Pure iron; 4. Spiral coil; 5. Test sample. Detailed Implementation

[0019] 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.

[0020] 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.

[0021] Reference Figures 1-8 This invention provides an electromagnetic acoustic transducer that concentrates magnetic field strength to enhance Lorentz force, comprising: Magnetic ring permanent magnet 1, used to provide a static magnetic field in the horizontal direction; The core-type permanent magnet 2 is located inside the ring-type permanent magnet 1. The core-type permanent magnet 2 is used to provide a static magnetic field in the vertical direction. Pure iron 3 is located at the bottom of the magnetic ring permanent magnet 1 and is fixedly connected to the bottom of the magnetic core permanent magnet 2; The spiral coil 4 is located between the magnetic ring permanent magnet 1 and the test sample 5. The spiral coil 4 is used to induce eddy currents that are opposite to the direction of the current and are periodically distributed. Through the magnetic focusing effect of pure iron 3, the static magnetic fields in the horizontal and vertical directions interact with the eddy currents, coupling out ultrasonic waves that are vertically incident into the test sample 5.

[0022] In one embodiment of the present invention, pure iron 3 is fixed to the bottom end of the magnetic core permanent magnet 2 by magnetic attraction, and a spiral coil 4 is arranged at the coupling gap between the magnetic ring permanent magnet 1 and the test sample 5. The magnetic ring permanent magnet provides a horizontal static magnetic field, laying the foundation for subsequent synthesis of a vector magnetic field with the vertical magnetic field. The magnetic core permanent magnet provides a vertical static magnetic field, which is orthogonal to the horizontal static magnetic field, together forming a two-dimensional magnetic field distribution, enhancing the controllability of the Lorentz force. Pure iron utilizes its high permeability to concentrate magnetic lines of force to the surface of the test sample, reducing magnetic leakage and enhancing the local magnetic field strength. After a high-frequency current is passed through the spiral coil, alternating eddy currents are generated in the skin depth layer of the test sample. The static magnetic field and eddy currents form vertically incident ultrasonic waves under the action of magnetic focusing, realizing non-contact ultrasonic excitation and improving the stability and signal-to-noise ratio of the detection.

[0023] As an optional implementation, both the magnetic ring permanent magnet 1 and the magnetic core permanent magnet 2 have a circular cross-sectional shape.

[0024] In one embodiment of the present invention, the circular cross-section ensures the axial symmetry of the magnetic field, making the magnetic field distribution of the transducer uniform in the working area and avoiding biased magnetization and localized weak magnetic fields.

[0025] As an optional implementation, the polarization direction of the magnetic ring permanent magnet 1 is radial, and the polarization direction of the magnetic core permanent magnet 2 is axial.

[0026] In one embodiment of the present invention, radial polarization and axial polarization generate horizontal and vertical static magnetic fields, respectively. The two are orthogonal to each other, which facilitates obtaining the optimal Lorentz force direction through vector superposition and improves energy conversion efficiency.

[0027] As an optional implementation, the area ratio of the magnetic ring permanent magnet 1 to the area of ​​the magnetic core permanent magnet 2 is 1:1.

[0028] In one embodiment of the present invention, the 1:1 area ratio maximizes the static magnetic induction intensity B on the surface of the test sample without exceeding the saturation limit, thus ensuring a strong magnetic field while avoiding nonlinear distortion caused by magnetic saturation.

[0029] As an optional implementation, the end face radius of the pure iron 3 is the same as the end face radius of the magnetic core permanent magnet 2.

[0030] In one embodiment of the present invention, the same radius structure enables the pure iron and the magnetic core permanent magnet to form a continuous, low magnetic resistance magnetic circuit, further concentrating the magnetic lines of force and enhancing the magnetic focusing effect.

[0031] As an optional implementation, the total height of the core permanent magnet 2 and the pure iron 3 is the same as the height of the ring permanent magnet 1, the top surface of the ring permanent magnet 1 is aligned with the top surface of the core permanent magnet 2, and the bottom surface of the ring permanent magnet 1 is aligned with the bottom surface of the pure iron 3.

[0032] In one embodiment of the present invention, height alignment ensures the coaxial closed magnetic circuit of the magnetic ring and the magnetic core-pure iron assembly, reducing magnetic leakage. By adjusting the height of the pure iron, the height of the magnetic core can be changed without changing the total height of the magnetic ring, thereby flexibly adjusting the magnetic field concentration in the pure iron region. As an optional implementation, the spiral coil 4 has a single-layer wiring structure, and the outer diameter of the spiral coil 4 is no greater than 80% of the diameter of the magnetic ring permanent magnet 1.

[0033] In one embodiment of the present invention, single-layer wiring reduces the parasitic capacitance and resistance of the coil, reduces energy loss, and controls the outer diameter to within 80% of the magnetic ring diameter, ensuring that the coil is always in the strongest and most uniform static magnetic field region, thereby improving excitation efficiency.

[0034] As an optional implementation, the center-to-center distance between two adjacent wires in the helical coil 4 is equal to half the wavelength of the target ultrasonic wave.

[0035] In one embodiment of the present invention, following the half-wavelength principle, the sound waves excited by each coil are superimposed in phase in the propagation direction to achieve coherent enhancement, thereby maximizing the amplitude of the ultrasonic wave.

[0036] As an optional implementation, the center-to-center distance between adjacent wires in the spiral coil 4 is l=0.52mm, and the center frequency of the electromagnetic transducer is f=3MHz.

[0037] In one embodiment of the present invention, for a typical detection frequency of 3MHz, the coil spacing is optimized to 0.52mm. Setting it to 0.52mm at a center frequency of 3MHz enables the in-phase superposition of the sound waves excited by each coil, thereby maximizing the energy conversion efficiency.

[0038] As an optional implementation, the test sample 5 is an aluminum block or a hydrogen pipeline.

[0039] In one embodiment of the present invention, the transducer has excellent detection capabilities for non-ferromagnetic metal materials and hydrogen pipelines, and can be extended to the field of non-destructive testing of light metals and pipelines.

[0040] In one embodiment of the present invention, the object to be detected is a solid aluminum cylinder with a radius of 25 mm and a height of 25 mm; The magnetic ring permanent magnet 1 provides a horizontal bias static magnetic field with the following dimensions: outer diameter 30mm, inner diameter 15mm, and height 20mm.

[0041] The magnetic core permanent magnet 2 provides a vertically biased static magnetic field with dimensions of 15mm in diameter and 19mm in height.

[0042] Pure iron 3 provides a magnetic focusing effect, with dimensions of 15mm in diameter and 1mm in height.

[0043] The spiral coil 4 uses a single-layer wiring method with 22 turns and a wire diameter of 0.2mm. The total effective coil width is 23mm, ensuring that the coil is always in a static magnetic field region with maximum magnetic field strength and uniform distribution. The spacing between two adjacent conductors is determined according to the wavelength of the target transverse wave, following the half-wavelength principle, i.e., λ / 2. The center-to-center spacing between adjacent conductors of this transducer is l=0.52mm, corresponding to a theoretical center frequency f of 3MHz for the electromagnetic ultrasonic transducer.

[0044] Reference Figure 5 The displacement amplitude simulation results are shown in the COMSOL finite element simulation time-domain waveform diagram of the electromagnetic acoustic transducer with a 25mm thick aluminum block. The simulation waveforms show that three clear received waves appear sequentially at approximately 4.5μs, 12.5μs, and 20.5μs, with the amplitude of a single received echo reaching 6.77. mm, the amplitude of the secondary and tertiary received echoes decreases sequentially.

[0045] Reference Figure 6 Simulated magnetic flux density distribution of static bias magnetic field shows that the magnetic field is highly concentrated at the sharp corner of the lower edge of the pure iron, forming a distinct red high magnetic flux density region (peak value close to 2T); the magnetic field inside the magnetic core permanent magnet is mainly vertically downward, uniform in direction, and the magnetic circuit is stable; in the internal region of the aluminum block, the magnetic field decays rapidly from the surface of the test sample to the interior, which is consistent with the skin effect of static magnetic field, and the surface magnetic field is stronger.

[0046] Reference Figure 7 Simulated magnetic flux density distribution of alternating dynamic magnetic field: Simulation results show that the peak amplitude of alternating dynamic magnetic field of coil can reach 40. 10 -8 T, the magnetic field energy is highly concentrated on the surface of the sample under test directly below the transducer, which directly corresponds to stronger eddy currents and generates a larger Lorentz force.

[0047] Reference Figure 8The simulated magnetic flux density values ​​of the y-component are shown. The simulation results show that the two positive peaks are located at approximately 5 mm and 35 mm, with a peak value of approximately 0.5 T; the two negative peaks are located at approximately 13 mm and 27 mm, with a valley value of approximately -0.95 T; and the middle negative peak is located at approximately 20 mm, with an amplitude of approximately -0.45 T. The curves are completely symmetrically distributed, indicating that the transducer structure is symmetrically designed, the magnetic field is uniformly distributed, and there is no obvious magnetic leakage, which can ensure the consistency and stability of ultrasonic excitation.

[0048] This invention proposes an electromagnetic acoustic transducer with concentrated magnetic field strength to enhance the Lorentz force. The transducer consists of a magnetic ring permanent magnet, a magnetic core permanent magnet, pure iron, and a helical coil within a flexible circuit board. When the transducer is operational, the magnetic ring permanent magnet provides a radial static magnetic field, the magnetic core permanent magnet provides an axial static magnetic field, and the pure iron optimizes the overall magnetic circuit distribution. The helical coil, carrying a high-frequency current, induces eddy currents in opposite directions and periodically alternating distributions. The generated static magnetic field and the induced eddy currents work together to couple a vertically incident, periodically alternating Lorentz force according to the left-hand rule. This vertically incident Lorentz force serves as a vertically incident ultrasonic sound source. Finite element simulation results verify that the developed electromagnetic acoustic transducer with enhanced Lorentz force solves the problems of severe magnetic field divergence, rapid attenuation, and small effective focusing area in traditional single-permanent-magnet-excited ultrasonic transverse waves, thus enhancing the signal-to-noise ratio and detection capability of the electromagnetic acoustic transducer. This invention, based on a single-core permanent magnet, tightly arranges pure iron beneath it and coaxially nests a magnetic ring permanent magnet around its outer side. This enhances the axial symmetry of the magnetic field, the magnetic focusing effect, and the superposition and coupling efficiency of the magnetic fields of the core and ring. Finite element simulation analysis verifies that the developed electromagnetic acoustic transducer with concentrated magnetic field strength enhancing Lorentz force exhibits good signal-to-noise ratio and detection capability. Using this designed electromagnetic acoustic transducer with concentrated magnetic field strength enhancing Lorentz force, health monitoring of test samples can be achieved. It has significant application value and potential in the fields of structural health monitoring and non-destructive testing.

[0049] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0050] 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 by those skilled in the art to the technical solutions of the present invention 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. An electromagnetic acoustic transducer that concentrates magnetic field strength to enhance Lorentz force, characterized in that, include: A magnetic ring permanent magnet (1) is used to provide a static magnetic field in the horizontal direction; A core-type permanent magnet (2) is located inside the ring-type permanent magnet (1), and the core-type permanent magnet (2) is used to provide a static magnetic field in the vertical direction; Pure iron (3) is located at the bottom of the magnetic ring permanent magnet (1) and is fixedly connected to the bottom end of the magnetic core permanent magnet (2); A spiral coil (4) is located between the magnetic ring permanent magnet (1) and the test sample (5). The spiral coil (4) is used to induce eddy currents that are opposite to the direction of the current and are periodically distributed. Through the magnetic focusing effect of the pure iron (3), the static magnetic fields in the horizontal and vertical directions interact with the eddy currents, coupling out ultrasonic waves that are vertically incident into the test sample (5).

2. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: Both the magnetic ring permanent magnet (1) and the magnetic core permanent magnet (2) have circular cross-sectional shapes.

3. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: The polarization direction of the magnetic ring permanent magnet (1) is radial, and the polarization direction of the magnetic core permanent magnet (2) is axial.

4. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: The ratio of the area of ​​the magnetic ring permanent magnet (1) to the area of ​​the magnetic core permanent magnet (2) is 1:

1.

5. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: The end face radius of the pure iron (3) is the same as the end face radius of the magnetic core permanent magnet (2).

6. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: The sum of the total heights of the magnetic core permanent magnet (2) and the pure iron (3) is the same as the height of the magnetic ring permanent magnet (1). The top surface of the magnetic ring permanent magnet (1) is aligned with the top surface of the magnetic core permanent magnet (2), and the bottom surface of the magnetic ring permanent magnet (1) is aligned with the bottom surface of the pure iron (3).

7. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: The spiral coil (4) has a single-layer wiring structure, and the outer diameter of the spiral coil (4) is no greater than 80% of the diameter of the magnetic ring permanent magnet (1).

8. The electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 7, characterized in that: The center-to-center distance between two adjacent wires in the spiral coil (4) is equal to half the wavelength of the target ultrasonic wave.

9. An electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 8, characterized in that: The center-to-center distance between adjacent conductors in the spiral coil (4) is l=0.52mm, and the center frequency of the electromagnetic transducer is f=3MHz.

10. An electromagnetic acoustic transducer with concentrated magnetic field strength to enhance Lorentz force according to claim 1, characterized in that: The test sample (5) is an aluminum block or a hydrogen pipeline.

Images