Single-magnet inclined winding coil electromagnetic ultrasonic transducer for high-frequency SH wave detection
By designing a single-magnet tilted meandering coil electromagnetic ultrasonic transducer, the processing difficulties and signal distortion problems of traditional EMAT in high-frequency detection are solved, enabling precise excitation and flexible detection of high-frequency SH waves, and reducing costs.
Patent Information
- Application Number
- CN202511346445.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-19
- Publication Date
- 2025-11-28
AI Technical Summary
Traditional piezoelectric sensors are susceptible to environmental influences in complex structures and are difficult to efficiently excite single-mode SH waves. Periodic permanent magnet EMATs are difficult to manufacture and have poor magnetic field uniformity during high-frequency detection, resulting in signal distortion and decreased detection accuracy.
It adopts a single magnet tilted meandering coil design, combined with a double-layer out-of-phase meandering coil and a vertically magnetized permanent magnet, and uses Lorentz force to synthesize a vertical alternating force field to excite high-frequency SH waves, thereby reducing the probe size to improve flexibility and accuracy.
It achieves high accuracy and flexibility in high-frequency SH wave detection, reduces magnet manufacturing costs, enhances signal stability and detection accuracy, and supports the integration of multi-modal sensors.
Smart Images
Figure CN121027306A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a transducer, in particular to a single-magnet tilted serpentine coil electromagnetic ultrasonic transducer for high-frequency SH wave detection. BACKGROUND
[0002] As a core means in the field of structural health monitoring (SHM), ultrasonic guided wave technology has significant engineering value in industrial non-destructive evaluation (NDE) due to its non-contact detection characteristics. Traditional piezoelectric sensors (PZTs) are susceptible to environmental temperature and humidity due to their dependence on physical coupling agents, and signal attenuation occurs easily in curved surface / high temperature working conditions, which seriously restricts their detection ability in complex structures. In contrast, electromagnetic acoustic transducers (EMATs) directly excite ultrasonic guided waves based on the Lorentz force or magnetostrictive mechanism, freeing them from the constraints of coupling agents and providing an innovative solution for high-robustness detection in harsh environments.
[0003] In plate defect detection, the technical advantages of EMATs are particularly prominent. They can precisely excite horizontal shear waves (SH waves) through customized coil design and excitation parameter control, and are widely used due to their easily controlled modalities and sensitivity to surface defects. In particular, the non-dispersive fundamental horizontal shear mode (SH0) exhibits excellent modal purity and low attenuation characteristics in thin plate structures. On the other hand, piezoelectric transducers are difficult to efficiently excite single-mode SH waves due to the limitations of electromechanical coupling coefficients, and multi-modal aliasing phenomena can significantly increase signal analysis complexity. Traditional SH wave generation based on Lorentz force electromagnetic ultrasonic transducers are composed of coils and periodically arranged permanent magnets. Periodic permanent magnet EMATs (PPM EMATs) excite SH waves with a fixed wavelength to achieve interference enhancement, where the distance between adjacent magnets is λ / 2. When high-frequency horizontal shear waves need to be excited, the magnet geometry of the periodic permanent magnet structure must be reduced to match the wavelength, which not only poses challenges for magnet processing but also exacerbates the magnetic pole edge effect and reduces the uniformity of the magnetic field, thereby affecting the transduction efficiency and signal stability.
[0004] In contrast, wavelength modulation through electromagnetic coil structure can effectively avoid the above processing limitations, reduce the manufacturing cost of assembling multiple magnets, and improve the flexibility of high-frequency response. In addition, the lateral size of existing EMATs is usually around 25-50 mm, which results in only part of the wave front interacting with the defect when detecting small defects, causing signal distortion. Therefore, it is necessary to further reduce the lateral size of EMATs to accurately capture the complete signal of the defect, avoid wave distortion by bypassing the defect edge, and truly reflect the local defect characteristics. SUMMARY
[0005] Aiming at the above-mentioned deficiencies in the prior art, the application provides a single-magnet inclined meander coil electromagnetic ultrasonic transducer for high-frequency SH wave detection.
[0006] In order to achieve the above-mentioned application purposes, the application adopts the technical scheme that: A single-magnet inclined meander coil electromagnetic ultrasonic transducer for high-frequency SH wave detection, characterized in that it comprises: A vertically magnetized permanent magnet for generating a vertical static magnetic field; A double-layer out-of-phase meander coil located below the permanent magnet, containing a top layer coil and a bottom layer coil staggered in spatial position, conductors of the top layer coil and the bottom layer coil being periodically and oppositely distributed and symmetrically arranged at an inclined angle θ; A test piece located below the double-layer out-of-phase meander coil for propagating SH guided waves excited by Lorentz force; Wherein, when the top layer coil and the bottom layer coil are supplied with opposite high-frequency currents, horizontal direction Lorentz force components generated under the action of the vertical static magnetic field are offset to each other, and longitudinal components are superimposed to form a periodic alternating force field perpendicular to the surface of the test piece.
[0007] Further, the conductor inclined angle θ of the double-layer out-of-phase meander coil satisfies the relationship: Lorentz force generated by the top layer coil , Lorentz force generated by the bottom layer coil , Total Lorentz force synthesized by the current unit ; Lorentz force synthesized by the next unit
[0008] In the above formula, is the Lorentz force, are direction vectors respectively.
[0009] Further, the permanent magnet is a rectangular magnetic steel, the magnetization direction of which is perpendicular to the surface of the test piece, and the pole area completely covers the projection area of the double-layer out-of-phase meander coil.
[0010] Further, the test piece is an aluminum plate, the thickness of which and the excitation frequency satisfy the SH1 mode cutoff frequency constraint relationship The application has the following beneficial effects: The design uses double-layered out-of-phase meander coils to synthesize dynamic Lorentz force field, which ensures the detection accuracy while improving the operation flexibility and miniaturization of the probe. In addition, the single magnet design enables quick switching of detection frequency by replacing the modular coil under certain conditions, thereby reducing the manufacturing and assembly cost of the magnet. Notably, the single magnet structure can integrate the coil for generating Lamb waves, thereby constructing a dual-mode sensor, which provides a new idea for more comprehensive defect detection. BRIEF DESCRIPTION OF DRAWINGS
[0011] Figure 1 A schematic diagram of a single-magnet inclined meander coil electromagnetic ultrasonic transducer structure for high-frequency SH wave detection according to the present application.
[0012] Figure 2 A design principle diagram according to the present application.
[0013] Figure 3 A SH wave dispersion curve diagram in a 1mm aluminum plate according to an embodiment of the present application.
[0014] Figure 4 A synthesized Lorentz force spatial distribution diagram according to an embodiment of the present application.
[0015] Figure 5 A spatial Fourier transform diagram of the Lorentz force according to an embodiment of the present application.
[0016] Figure 6 A spatial Fourier transform diagram of the Lorentz force according to an embodiment of the present application.
[0017] Figure 7 A time-domain Fourier transform diagram of the current according to an embodiment of the present application.
[0018] Figure 8 A working area diagram of the EMAT according to an embodiment of the present application. DETAILED DESCRIPTION
[0019] The specific embodiments of the present application are described below to facilitate understanding of the present application by those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments. For those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application as defined in the appended claims, and all applications utilizing the concept of the present application are included in the protection.
[0020] A single-magnet inclined meander coil electromagnetic ultrasonic transducer for high-frequency SH wave detection, as shown in Figure 1 , comprising: a vertically magnetized permanent magnet for generating a vertical static magnetic field; The double-layered out-of-phase meander coil below the permanent magnet comprises a top layer coil and a bottom layer coil staggered in spatial position, conductors of the top layer coil and the bottom layer coil being periodically reversed and symmetrically arranged at an oblique angle θ; The tested piece below the double-layered out-of-phase meander coil is used to propagate SH guided waves excited by Lorentz force; Wherein, when the top layer coil and the bottom layer coil are connected to reversed high-frequency currents, horizontal Lorentz force components generated under the action of a vertical static magnetic field are offset to each other, and longitudinal components are superimposed to form a periodic alternating force field perpendicular to the surface of the test piece.
[0021] In this embodiment, according to different materials of the test piece, the EMAT transduction mechanisms mainly include: Lorentz force mechanism, magnetostriction mechanism and magnetization force mechanism. For non-ferromagnetic materials such as copper and aluminum, the mechanism of ultrasonic waves is Lorentz force. For ferromagnetic materials such as iron, cobalt, nickel and steel, the above three working mechanisms are included. In this work, aluminum is chosen as the measured sample, which belongs to non-ferromagnetic material, so only the Lorentz force mechanism is considered. The single-magnet periodic meander coil EMAT (SM-PMC EMAT) proposed in this study is composed of a vertically magnetized permanent magnet and an inclined out-of-phase meander coil. Figure 1 The principle of the synthesis of Lorentz force generated by the meander coil on the surface of the test piece is given.
[0022] According to Figure 2 The dispersion curve shown in the figure shows that the cutoff frequency of the SH1 mode in the 1mm thick aluminum plate is 1564kHz. In order to realize the effective excitation of the horizontal shear wave (SH wave) SH0 mode, the excitation frequency needs to be lower than this value. The spatial period of the coil is precisely matched with the guided wave characteristics of the SH0 mode. The coil is wound in double layers and out of phase, and the current distribution of the top layer and the bottom layer presents a periodic reverse feature. The top layer and the bottom layer are connected to modulated high-frequency currents, and the current directions of the top layer and the bottom layer are different and the spatial positions are different. Combined with the vertical static magnetic field provided by the permanent magnet, Lorentz force is generated, and the Lorentz forces of the upper and lower layers are synthesized to obtain the final Lorentz force. The specific derivation process is as follows: For a single wire, the coil is connected to a high-frequency alternating current The excitation current of the coil induces an alternating magnetic field with the same frequency as the excitation current in the steel pipe, and eddy currents with the same frequency as the coil excitation current and opposite direction are induced in the skin depth layer on the surface of the steel pipe.
[0023] The permanent magnet provides a vertical downward static magnetic field:
[0024] Lorentz force is generated by the bias magnetic field B and the eddy current The interaction results in:
[0025] The Lorentz force is decomposed into two parts, the top coil:
[0026] The bottom coil:
[0027] The total Lorentz force is:
[0028] The resultant Lorentz force after the next unit is
[0029] The tested sample is isotropic and satisfies the assumptions of linear elasticity and continuity. The tested sample undergoes elastic deformation under the action of the Lorentz force , and the motion equation of the tested sample is:
[0030] wherein, is the stress tension; u is the displacement matrix; is the bulk density of the tested sample; is or .
[0031] Considering the relationship between and u, equation (7) can be expressed in displacement, that is,
[0032] It is assumed that h (x) is the spatial distribution of the EMAT after synthesis. Under the ideal array, h (x) is a square wave with a period of λ, and the direction is represented by positive and negative. Therefore, the spatial distribution h (x) is given by the square wave function shown in Figure 4 , which takes the starting point of the coil as the zero point and x axis as the displacement variable. As Figure 5 shown in , the Fourier transform of h (x) gives the spatial bandwidth of the transducer:
[0033] The current flowing through the coil is a five-period sine signal modulated by a Hanning window, and the time-domain waveform and the frequency-domain waveform are as shown in Figure 6 and 7 , wherein:
[0034] The working area of EMAT distribution on the phase velocity-frequency plane can be obtained using the equation as shown in Figure 8
[0035]
[0036] where k is the spatial angular frequency (or wave number), T is the period of the time signal, and are the time and spatial frequencies, respectively.
[0037] When the EMAT acts as a receiver, the ultrasonic wave on the surface of the material induces the particle vibration, drives the free charge in the conductive material to move in the static bias magnetic field, generates eddy current, induces the voltage on the receiving coil, and then the received ultrasonic wave signal can be measured to characterize the structural features or internal defects of the test piece.
[0038] The principles and implementation manners of the present application are described by using specific embodiments in the present application, and the above embodiment descriptions are only used to help understand the method of the present application and its core idea; meanwhile, for the ordinary skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges can be changed, and the above descriptions should not be understood as the limitation of the present application.
[0039] The person skilled in the art will understand that the embodiments described herein are used to help the reader understand the principles of the present application and should be understood as the protection scope of the present application not being limited to such specific descriptions and embodiments. The person skilled in the art can make various other specific modifications and combinations according to the technical inspirations disclosed in the present application without departing from the essence of the present application, and these modifications and combinations are still within the protection scope of the present application.
Claims
1. A single-magnet tilted meandering coil electromagnetic ultrasonic transducer for high-frequency SH wave detection, characterized in that, include: Perpendicularly magnetized permanent magnets are used to generate vertical static magnetic fields; The double-layered out-of-phase meandering coil located below the permanent magnet includes a top coil and a bottom coil with spatially staggered positions. The conductors of the top coil and the bottom coil are periodically distributed in opposite directions and arranged symmetrically with an inclination angle θ. The test piece, located below the double-layered out-of-phase meandering coil, is used to propagate SH guided waves excited by the Lorentz force; When the top coil and bottom coil are supplied with reverse high-frequency current, the horizontal Lorentz force components generated under the action of the vertical static magnetic field cancel each other out, and the longitudinal components are superimposed to form a periodic alternating force field perpendicular to the surface of the specimen.
2. The transducer according to claim 1, characterized in that, The conductor tilt angle θ of the double-layer out-of-phase meandering coil satisfies the following relationship: Lorentz force generated by the top coil , Lorentz force generated by the bottom coil , Total Lorentz force of current unit synthesis ; The Lorentz force after the next unit synthesis In the above formula, For Lorentz force, These are the direction vectors.
3. The transducer according to claim 1, characterized in that, The permanent magnet is a rectangular neodymium iron boron magnet with its magnetization direction perpendicular to the surface of the specimen, and the magnetic pole area completely covers the projection area of the double-layer out-of-phase meandering coil.
4. The transducer according to claim 1, characterized in that, The test piece is a non-ferromagnetic metal plate, and its thickness and excitation frequency satisfy the SH1 mode cutoff frequency constraint relationship.