A horizontal shear wave excitation device based on a diamond window coil

Abstract

This invention discloses a horizontal shear wave guided excitation device based on a rhombus-shaped coil, comprising an electromagnetic shielding shell, a permanent magnet, and a rhombus-shaped coil. The rhombus-shaped coil is suspended directly above the surface of the object to be tested, and the permanent magnet is located directly above the rhombus-shaped coil, which is covered by the electromagnetic shielding shell. By precisely designing the physical structure and geometric parameters of the excitation coil, a steady-state elastic wave conforming to preset conditions is excited on the surface of the metal workpiece under test. This device can effectively improve the signal-to-noise ratio of the sensing signal and effectively improve the detection probability and detection rate of surface microcrack defects, showing broad application prospects in non-destructive testing in various fields. By applying an AC excitation signal to the rhombus-shaped coil, a time-varying magnetic field is generated in the adjacent space; the eddy currents in the magnetic field environment are subjected to the Lorentz force, exciting SH waves propagating horizontally along the workpiece surface; this can significantly improve the signal-to-noise ratio of the sensing signal, which is beneficial for further defect processing and analysis.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, and particularly relates to a horizontal shear waveguide excitation device based on a rhombus-shaped coil. Background Technology

[0002] With the continuous advancement of science and technology, metallic materials have been widely used in industrial production, playing an irreplaceable role. However, due to the high chemical activity of most metals, they are prone to oxidation and corrosion when exposed to air for extended periods, leading to defects such as cracks and pits, ultimately adversely affecting the structural safety and the safety of personnel and property.

[0003] In the field of electromagnetic nondestructive testing, commonly used methods include fiber optic sensing technology, magnetic flux leakage detection systems, and eddy current testing. While these methods are effective for rail engineering and ground pipelines, fiber optic sensing systems are susceptible to environmental factors such as temperature, humidity, and mechanical vibration. Especially in high-temperature, high-humidity, or strong-vibration environments, measurement stability and accuracy can easily decrease. Magnetic flux leakage detection typically requires a strong magnetization system, resulting in bulky and heavy equipment, which is unsuitable for testing complex structures or confined spaces. Eddy current signals are easily affected by changes in material conductivity and permeability; inhomogeneous material structure or parameter fluctuations can introduce additional interference. These methods suffer from insufficient environmental adaptability and low signal-to-noise ratios, making it difficult to meet the testing requirements under complex working conditions. Summary of the Invention

[0004] Objective: This invention addresses the problem of low signal-to-noise ratio (SNR) in existing nondestructive testing (NDT) applications by proposing a horizontal shear wave guided excitation device based on a rhombus-shaped coil. Through precise design of the physical structure and geometric parameters of the excitation coil, a steady-state elastic wave conforming to preset conditions is excited on the surface of the metal workpiece under test. This device effectively improves the SNR of the sensing signal and significantly increases the detection probability and speed of surface microcracks, showing broad application prospects in various NDT fields. By applying an AC excitation signal to the rhombus-shaped coil, a time-varying magnetic field is generated in the adjacent space. When the object to be tested is placed in this alternating magnetic field, eddy currents are generated on its surface due to electromagnetic induction. These eddy currents are subjected to Lorentz force in the magnetic field environment, exciting horizontal SH waves propagating along the workpiece surface. These SH waves significantly improve the SNR of the sensing signal, facilitating further defect processing and analysis.

[0005] Technical solution: The present invention provides a horizontal shear waveguide excitation device based on a rhombus-shaped coil, comprising an electromagnetic shielding shell, a permanent magnet and a rhombus-shaped coil; the rhombus-shaped coil is suspended directly above the surface of the object to be detected, the permanent magnet is located directly above the rhombus-shaped coil, and the permanent magnet is covered by the electromagnetic shielding shell.

[0006] Furthermore, the electromagnetic shielding shell is a hollow rectangular box with an opening at the bottom; the permanent magnet is an array of eight strip permanent magnets, and each strip permanent magnet has the same geometric specifications; the coil is a rhombus-shaped coil, which, along with the eddy currents it generates, is symmetrical about both the horizontal and vertical central axes; the angle of retraction of the rhombus-shaped coil is the same as the angle between the horizontal plane and the horizontal plane. for: =45°.

[0007] Furthermore, the rhombus-shaped coil is placed in a uniform magnetic field environment formed by the combined action of a permanent magnet and an electromagnetic shielding shell; the magnetic poles of the permanent magnet facing the rhombus-shaped coil are arranged alternately with S poles and N poles.

[0008] Furthermore, the bottom surface of the permanent magnet is parallel to the plane of the rhombus-shaped coil, and the permanent magnet is located inside the electromagnetic shielding shell; that is, the surface above the object to be tested consists of: the rhombus-shaped coil, the permanent magnet, and the electromagnetic shielding shell.

[0009] Furthermore, the horizontal or vertical distance between two adjacent turns of the diamond-shaped coil... The width of a single bar permanent magnet in the permanent magnet satisfy And the wavelength of the excited SH wave The relationship is .

[0010] Furthermore, the rhomboid-shaped coil operates under the action of an AC excitation signal, thereby generating a time-varying magnetic field. According to Faraday's law of electromagnetic induction, the density of the induced current is proportional to the rate of change of the magnetic field, satisfying the following: ,in, eddy current density, The electrical conductivity of the material, It represents the magnetic flux density. denoted as the rate of change of the magnetic field over time.

[0011] Furthermore, when an AC excitation signal is applied to the rhomboid-shaped coil, eddy currents are generated on the surface of the object to be detected; the permanent magnet is placed directly above the surface of the object to be detected, thereby providing a static magnetic field perpendicular to the surface of the object to be detected. , Represents magnetic field exist Components in direction, The vector represents the unit vector in the z-direction of a spatial rectangular coordinate system; therefore, the eddy current generated by the rhombus-shaped coil can be expressed as... or , and They represent eddies. exist and Components in direction, and These represent the unit vectors in the x and y directions in a spatial rectangular coordinate system, respectively.

[0012] Furthermore, the eddy currents induced on the surface of the object to be detected by the rhomboid coil will be subjected to a Lorentz force under the action of a magnetic field, and satisfy the following: In the formula, The Lorentz force acting on the surface of the object to be tested; due to the unique coil structure of the rhomboid-shaped coil, the actual Lorentz force acting on the surface of the object to be tested, derived through force analysis, can be expressed as: In other words, the horizontal component of the Lorentz force on the surface of the object to be tested is canceled out, and it is only subjected to the periodically changing vertical force, thus generating a relatively pure horizontal SH wave.

[0013] Furthermore, the rhomboid-shaped coil can generate a horizontal SH wave on the surface of the object to be detected, and the wave velocity of the SH wave can be expressed as: ,in, Let be the shear modulus of the material to be tested. The density of the material is given; when the SH wave propagates to the defect location, due to the change in the shear stress boundary conditions at the defect, reflected echo signals will be generated at the front and rear ends of the defect.

[0014] Furthermore, the application of this device includes the following steps: placing the rhomboid coil in a magnetic field generating structure composed of a permanent magnet and an electromagnetic shielding shell, applying an AC excitation signal to the rhomboid coil, and under the action of the uniform magnetic field of the permanent magnet, the surface of the object to be detected will be subjected to a vertical Lorentz force, thereby generating a horizontally propagating SH wave; the SH wave can significantly improve the signal-to-noise ratio of the sensing signal, which is beneficial for further processing and analysis of defects.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0016] 1. The present invention provides a horizontal shear waveguide excitation device based on a rhombus-shaped coil, wherein the rhombus-shaped coil is composed of two parts, left and right, with the current flowing in opposite directions. The current in the left coil flows first to the upper left and then to the lower left; the current in the right coil flows first to the lower right and then to the upper right. The two currents converge and cross at a symmetrical angle in the central region. Due to the superposition effect of the symmetrical crossing current path and the magnetic field, the Lorentz force density in the central region is significantly enhanced and gradually attenuates outward, so most of the energy is concentrated in the central region, and the generated SH wave energy is relatively concentrated with small side lobes.

[0017] 2. The electromagnetic ultrasonic excitation device based on a rhombus-shaped coil provided by this invention can significantly improve the signal-to-noise ratio of the sensing signal. When a defect exists on the surface of the object being detected, the excited SH wave will produce obvious reflected echoes at the front and rear edges of the defect. Because the rhombus-shaped coil can excite SH waves with high purity and concentrated energy, the defect reflection echo characteristics are more significant, which is beneficial for subsequent signal extraction and analysis, and has good engineering applicability and broad application prospects. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0019] Figure 2 This is a schematic diagram showing the spatial relative position of the current direction of the rhomboid-shaped coil and the permanent magnet in this invention;

[0020] Figure 3 This is a schematic diagram of the magnetic field after adding an electromagnetic shielding shell when the present invention is implemented in COMSOL simulation software;

[0021] Figure 4 This is a schematic diagram of the eddy currents induced on the surface of the object to be detected by the rhomboid coil when the present invention is implemented in the COMSOL simulation software;

[0022] Figure 5 This is a schematic diagram illustrating the principle of generating SH waves on the surface of the object to be detected in this invention.

[0023] Figure 6 This is a schematic diagram of the local force analysis of the rhomboid-shaped coil in this invention;

[0024] Figure 7 This is a schematic diagram of the Lorentz force acting on the surface of the object to be detected when the present invention is implemented in the COMSOL simulation software;

[0025] Figure 8 This is a schematic diagram of the SH wave generated on the surface of the object to be tested by the rhomboid coil when the present invention is implemented in the COMSOL simulation software.

[0026] In the diagram: 1. Electromagnetic shielding shell; 2. Permanent magnet; 3. Diamond-shaped coil; 4. Object to be tested. Detailed Implementation

[0027] The technical solutions of the present invention are described in detail with reference to the specific embodiments shown in the accompanying drawings, so that those skilled in the art can fully understand the technical content, technical advantages, and innovative characteristics of the present invention, thereby reasonably defining the scope of patent protection of the present invention. The embodiments described in this invention are only for illustrating the technical solutions of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any equivalent transformations, modifications, or extensions made by those skilled in the art based on the technical concept of the present invention without creative effort should be covered within the scope of protection of the present invention.

[0028] Example 1:

[0029] Reference Figures 1-8 A horizontal shear waveguide excitation device based on a rhombus-shaped coil includes an electromagnetic shielding shell 1, a permanent magnet 2, and a rhombus-shaped coil 3. The rhombus-shaped coil 3 is suspended directly above the surface of the object to be measured, and the permanent magnet 2 is located directly above the rhombus-shaped coil 3. The permanent magnet 2 is partially covered by the electromagnetic shielding shell. The coil approximates a rhombus-shaped structure. The permanent magnet 2 is an array of eight strip permanent magnets arranged in a periodic alternation of SN polarities. The electromagnetic shielding shell 1 is a cover-type structure with an open bottom. The eddy currents induced by the rhombus-shaped coil 3 on the surface of the object to be measured are symmetrical about both the horizontal and vertical axes. Figure 4 As shown; the rhombus-shaped coil 3 can generate SH waves with relatively concentrated energy propagating horizontally on the surface of the object under test 4, such as... Figure 8 As shown;

[0030] In this embodiment, the coil is a rhombus-shaped coil, and the angle between the folding angle of the rhombus-shaped coil 3 and the horizontal plane is... for: = 45°.

[0031] In this embodiment, the electromagnetic shielding shell 1 is a hollow rectangular box with an opening at the bottom; the permanent magnet 2 is an array of eight strip-shaped permanent magnets, and each strip-shaped permanent magnet has the same geometric specifications, such as... Figure 2 As shown; the rhomboid-shaped coil 3 and the eddy currents it generates are symmetrical about both the horizontal and vertical central axes, as shown. Figure 4 As shown; the bottom surface of the permanent magnet 2 is parallel to the plane where the rhombus-shaped coil 3 is located, and the permanent magnet 2 is located inside the electromagnetic shielding shell 1; that is, the surface above the object to be detected 4 consists of: the rhombus-shaped coil 3, the permanent magnet 2, and the electromagnetic shielding shell 1, in sequence. Figure 1 As shown.

[0032] In this embodiment, the horizontal or vertical distance between two adjacent turns of the wire in the rhombus-shaped coil 3 is... The width of a single bar permanent magnet in the permanent magnet 2 satisfy And the wavelength of the excited SH wave The relationship is .

[0033] In this embodiment, the magnetic field generated by the permanent magnet 2 is distributed along the direction from its N pole to its S pole, and the lift-off height of its N and S pole surfaces from the plane where the rhombus-shaped coil 3 is located is small, making the magnetic field direction basically perpendicular to the plane where the rhombus-shaped coil 3 is located, that is, the magnetic field direction is consistent with the normal direction of the plane. The electromagnetic shielding shell 1 is used to guide and constrain the magnetic field generated by the permanent magnet 2, forming a periodically alternating vertical uniform magnetic field at the plane where the rhombus-shaped coil 3 is located, such as... Figure 3 As shown, this ensures that the magnetic field strength distribution and direction within the area where the rhombus-shaped coil 3 is located are consistent with the magnetic field in the central region of the permanent magnet 2.

[0034] In this embodiment, when the rhomboid coil 3 is subjected to an AC excitation signal, eddy currents are generated on the surface of the object to be detected 4. According to Faraday's law of electromagnetic induction, the density of the induced current is proportional to the rate of change of the magnetic field, and the induced eddy currents satisfy the following: ,in, eddy current density, The electrical conductivity of the material, It represents the magnetic flux density. The magnetic field changes over time. The permanent magnet 2 is placed directly above the surface of the object 4 to be tested, thereby providing a static magnetic field perpendicular to the surface of the object 4 to be tested. Therefore, the eddy current generated by the rhombus-shaped coil 3 can be expressed as: or .

[0035] In this embodiment, the eddy currents induced on the surface of the object 4 by the rhomboid coil 3 will be subjected to a Lorentz force under the action of a magnetic field, and satisfy the following: In the formula, The Lorentz force acting on the surface of the object to be tested is given by: Due to the unique coil structure of the rhomboid coil 3, the actual Lorentz force acting on the surface of the object to be tested 4 can be expressed as follows through force analysis: That is, the horizontal component of the Lorentz force on the surface of the object to be tested 4 is canceled out, and it is only subjected to a periodically varying vertical force, such as Figure 5 As shown; thus, relatively pure horizontal SH waves can be generated, such as Figure 8 As shown;

[0036] In this embodiment, the rhomboid-shaped coil 3 can generate a horizontal SH wave on the surface of the object 4 to be detected, and the wave velocity of the SH wave can be expressed as: ,in, Let be the shear modulus of the material of the object 4 to be tested. The density of its material.

[0037] In this embodiment, when the rhombus-shaped coil 3 is subjected to an AC excitation signal, it can induce eddy currents on the surface of the object to be detected 4 and generate horizontal SH waves under the action of a magnetic field. When the SH waves propagate to the defect location, due to the change in the shear stress boundary conditions at the defect, reflected echo signals will be generated at the front and rear ends of the defect.

[0038] In this invention, the rhombus-shaped coil 3, after being energized with alternating current, induces eddy currents on the surface of the object 4 under the influence of the skin effect, primarily forming a surface-level eddy current distribution. These eddy currents generate Lorentz forces under the magnetic field of the permanent magnet 2. Due to the structural characteristics of the rhombus-shaped coil 3, the horizontal Lorentz force components cancel each other out, leaving only the vertical Lorentz force component. Figure 5 As shown; this excites the generation of SH waves propagating along the direction perpendicular to the Lorentz force, such as Figure 8 As shown, when there is a defect on the surface of the object 4 to be tested, the SH wave will generate obvious reflected echo signals at the leading and trailing edges of the defect when it propagates to the defect location.

[0039] Figure 6 This is a schematic diagram illustrating the local force analysis of the eddy currents induced on the surface of the object 4 by the rhomboid-shaped coil 3. Since the rhomboid-shaped coil 3 is symmetrical in both the horizontal and vertical directions, therefore... Figure 6 The localized force situation shown can represent the force characteristics of the eddy currents induced in other corresponding parts of the coil. For ease of analysis, [the following is omitted as it is not part of the original text]. Figure 6 The eddy currents shown are divided into four regions: A, B, C, and D. The eddy currents within each region are numbered sequentially from the outside in using the rhomboid coil, namely, turn 1, turn 2, turn 3, and turn 4. Let the Lorentz force on the eddy current induced in the nth turn of the coil within region X (where X is A, B, C, or D) be: The Lorentz force on the induced eddy currents on the surface of the object to be detected 4 can be expressed in four regions as follows:

[0040] Area A: ;

[0041] Area B: , ;

[0042] Area C: , , ;

[0043] Area D: , , ,

[0044] .

[0045] in and Let X represent the eddy current induced in the nth turn of the coil and the magnetic field it experiences, respectively. Due to the unique folded structure and structural symmetry of the rhomboid coil 3, the horizontal components of the Lorentz force on each small portion of the eddy current cancel each other out. Therefore, the effective Lorentz force on the eddy current mainly manifests as the vertical component, the magnitude of which can be expressed as: ,in This is the angle between the folding angle of the rhombus-shaped coil 3 and the horizontal plane. If using... Let represent the effective value of the Lorentz force on the eddy current induced in the nth turn of the coil in region X. Then:

[0046] Area A: ;

[0047] Area B: ; ;

[0048] Area C: ; ;

[0049] ;

[0050] Area D: ; ;

[0051] ; ;

[0052] The effective value of the Lorentz force mentioned above Only retained Vertical components, such as Figure 5 As shown, relatively pure SH waves in the horizontal direction can be excited; when there are defects on the surface of the object to be detected 4, when the SH waves propagate to the defect location, due to the change in the shear stress boundary conditions of the defect region, the front and rear ends of the defect will generate reflected echo signals respectively.

[0053] In summary, this invention achieves efficient excitation of horizontal SH waves through a special coil structure design. The generated SH waves exhibit excellent sidelobe suppression and high energy concentration, effectively reducing interference from invalid wave modes on the detection signal, improving the signal-to-noise ratio and stability, and contributing to subsequent signal extraction and analysis, thereby enhancing the reliability of the detection results. This invention is simple in structure, easy to implement, and requires no coupling agent, making it suitable for non-destructive testing of defects in industrial equipment and possessing significant engineering application value.

[0054] Example 2:

[0055] This embodiment provides a horizontal shear waveguide excitation device based on a rhombus-shaped coil, including the following steps: placing the rhombus-shaped coil 3 inside a magnetic field generating device composed of a permanent magnet 2 and an electromagnetic shielding shell 1, so that the plane where the rhombus-shaped coil 3 is located is subjected to a uniform magnetic field that periodically alternates along the normal direction.

[0056] When an AC excitation signal is applied to the rhomboid coil 3, the uniform magnetic field generated by the permanent magnet 2 causes the surface of the object under test 4 to experience a vertical Lorentz force, thereby generating a horizontally propagating SH wave. The SH wave is relatively pure with few sidelobes, resulting in a high sensing signal-to-noise ratio. When there are defects on the surface of the object under test 4, the reflected echo signal generated by the SH wave at the defect can be acquired.

[0057] The technical solutions and specific embodiments disclosed in this invention are clear and explicit, facilitating understanding and implementation by those skilled in the art. Without departing from the technical concept and basic principles of this invention, those skilled in the art can make various adjustments, modifications, or equivalent substitutions to the technical solutions. All reasonable changes, improvements, or equivalent solutions made based on the technical concept of this invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A horizontal shear waveguide excitation device based on a rhombus-shaped coil, characterized in that, It includes an electromagnetic shielding shell (1), a permanent magnet (2) and a diamond-shaped coil (3); the diamond-shaped coil (3) is suspended directly above the surface of the object to be tested (4), the permanent magnet (2) is located directly above the diamond-shaped coil (3), and the permanent magnet (2) is covered by the electromagnetic shielding shell (1).

2. The horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 1, characterized in that, The electromagnetic shielding shell (1) is a hollow rectangular box with an open bottom; the permanent magnet (2) is an array of eight strip permanent magnets, and each strip permanent magnet has the same geometric specifications; the coil is a rhombus-shaped coil, and it and the eddy currents it generates are symmetrical about the horizontal and vertical central axes; the angle of the rhombus-shaped coil (3) is the angle between the folding angle and the horizontal plane. for: = 45°.

3. The horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 1, characterized in that, The rhombus-shaped coil (3) is placed in a uniform magnetic field environment formed by the combined action of the permanent magnet (2) and the electromagnetic shielding shell (1); the magnetic poles of the permanent magnet (2) facing the rhombus-shaped coil (3) are arranged alternately with the S pole and the N pole.

4. The horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 1, characterized in that, The bottom surface of the permanent magnet (2) is parallel to the plane of the rhombus-shaped coil (3), and the permanent magnet (2) is inside the electromagnetic shielding shell (1); that is, the surface above the object to be tested (4) consists of the rhombus-shaped coil (3), the permanent magnet (2) and the electromagnetic shielding shell (1).

5. A horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 1, characterized in that, The horizontal or vertical distance between two adjacent turns of the diamond-shaped coil (3) The width of a single bar permanent magnet in the permanent magnet (2) satisfy And the wavelength of the excited SH wave The relationship is .

6. A horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 5, characterized in that, The rhomboid-shaped coil (3) operates under the action of an AC excitation signal, thereby generating a time-varying magnetic field. According to Faraday's law of electromagnetic induction, the density of the induced current is proportional to the rate of change of the magnetic field, satisfying the following: ,in, eddy current density, The electrical conductivity of the material, It represents the magnetic flux density. denoted as the rate of change of the magnetic field over time.

7. A horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 6, characterized in that, When the rhomboid coil (3) is subjected to an AC excitation signal, eddy currents are generated on the surface of the object to be tested (4); the permanent magnet (2) is placed directly above the surface of the object to be tested (4), thereby providing a static magnetic field perpendicular to the surface of the object to be tested (4): , Represents magnetic field exist Components in direction, The vector in the z-direction represents the unit vector in the spatial rectangular coordinate system; therefore, the eddy current generated by the rhombus-shaped coil (3) can be expressed as: or , and They represent eddies. exist and Components in direction, and These represent the unit vectors in the x and y directions in a spatial rectangular coordinate system, respectively.

8. A horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 7, characterized in that, The eddy currents induced on the surface of the object to be tested (4) by the rhomboid-shaped coil (3) will be subjected to Lorentz force under the action of the magnetic field, and satisfy the following: In the formula, The Lorentz force on the surface of the object to be tested is given by the following formula: Due to the unique coil structure of the rhomboid coil (3), the actual Lorentz force on the surface of the object to be tested (4) can be expressed as follows through force analysis: That is, the horizontal component of the Lorentz force on the surface of the object to be tested (4) is canceled out, and it is only subjected to the periodically changing vertical force, thus generating a relatively pure horizontal SH wave.

9. A horizontal shear waveguide excitation device based on a rhombus-shaped coil according to claim 8, characterized in that, The rhomboid-shaped coil (3) can generate a horizontal SH wave on the surface of the object to be detected (4), and the wave velocity of the SH wave can be expressed as: ,in, The shear modulus of the material of the object to be tested (4) is given. The density of the material is given; when the SH wave propagates to the defect location, due to the change in the shear stress boundary conditions at the defect, reflected echo signals will be generated at the front and rear ends of the defect.

10. A horizontal shear waveguide excitation device based on a rhombus-shaped coil according to any one of claims 1 to 9, characterized in that, The application of this device includes the following steps: placing the diamond-shaped coil (3) in a magnetic field generating structure composed of a permanent magnet (2) and an electromagnetic shielding shell (1), applying an AC excitation signal to the diamond-shaped coil (3), and under the action of the uniform magnetic field of the permanent magnet (2), the surface of the object to be detected (4) will be subjected to a vertical Lorentz force, thereby generating a horizontally propagating SH wave; the SH wave can significantly improve the signal-to-noise ratio of the sensing signal, which is beneficial for further processing and analysis of defects.

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