Bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device and method based on flower bud coil

Abstract

The invention relates to the technical field of electromagnetic ultrasonic excitation devices, in particular to a bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device and method based on a flower bud coil. The coil is located above the surface of an object to be detected, the magnet is arranged above the coil, the magnetic field shielding body covers the magnet, and the magnet is located in the magnetic field shielding body; the coils are single-turn or multi-turn flower bud coils, are symmetrical about the central axis, and are progressively arranged layer by layer from outside to inside; the magnet is a periodic permanent magnet with alternating polarities, and the magnet is composed of eight strip-shaped magnets with SN poles arranged alternately; the magnetic field shielding body is composed of an electromagnetic shielding shell. The device can generate bidirectional horizontal shear guided waves and reduce side lobes, is mainly used for detecting defects in a certain direction on the surface or near surface of a material under the conditions of high temperature, non-coupling, non-contact, high speed and the like, performs detection, quantitative evaluation and evaluation on the material, and has a wide application prospect in some specific nondestructive detection scenes.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic ultrasonic excitation devices, and in particular to a bidirectional horizontal shear waveguide electromagnetic ultrasonic excitation device based on a flower bud coil. Background Art

[0002] In the process of building production, some metal products are often needed, such as the sewer pipes laid underground in the city, the U-rib plates used in the cross-river bridges, and the buildings built with steel structures. In the production process of these metal materials, the quality of the products varies. Some metal products such as flat materials such as steel plates may have some small defects on the surface or near the surface, and it is impossible to judge whether they meet the standards at a glance with the naked eye. Some metal products such as pipes and U-rib plates involve welds between plates. The defects of welds are also difficult to judge by the integrity of the appearance. The conventional detection method for these defects is sampling detection, using chemical and physical detection methods. Sampling for wave damage detection, although this method can fully detect the quality of metal materials, it is time-consuming and labor-intensive, and cannot guarantee that every product in the same batch can have the same quality as the sample. Therefore, the advantages of non-destructive testing are highlighted. Non-destructive testing has the characteristics of non-destructive, comprehensive detection, and fast speed.

[0003] It has been widely used in the current industry. The most commonly used one in the current industry is ultrasonic testing, that is, using ultrasonic testing to generate ultrasonic waves through piezoelectric sensors for detection. However, the use of ultrasonic waves to detect object defects also has great limitations. During the propagation process, ultrasonic waves will be affected by changes in the thickness of the object, the deposits on the surface of the object, and the shape of the object. In addition, the detection of some defects is not suitable for ultrasonic waves with large vibration energy. In recent years, horizontal shear waveguides are often used to achieve nondestructive testing to solve such problems. Horizontal shear waveguides (SH0 waves) have no dispersion phenomenon, and their wave velocity does not change with the change of plate thickness and excitation frequency. This horizontal shear waveguide (SH waveguide) has the ability to detect tiny damage. When using horizontal shear waveguides for weld defect detection, since the vibration direction of the horizontal shear waveguide is perpendicular to the columnar grains of the weld, this can make the horizontal shear waveguide pass through the weld metal-parent material interface without reflection, avoiding the characteristics of traditional ultrasonic testing for austenitic weldments, such as ultrasonic beam path bending, contour distortion and high attenuation along certain propagation directions. In the current research on this type of electromagnetic horizontal shear waveguide sensors, there are mainly two types: bidirectional SH-EMAT and omnidirectional SH-EMAT. Summary of the invention

[0004] The object of the present invention is to solve the disadvantages existing in the prior art, and a bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device and method based on a bud coil are proposed. By finely adjusting the coil size, it is ensured to generate SH waves of a specified mode on the plane of the object to be detected, and the side lobes can be effectively reduced to generate a purer bidirectional horizontal shear guided wave. The horizontal shear guided wave generated by this electromagnetic ultrasonic excitation device can be used in special scenarios with bidirectional SH guided wave non-destructive testing requirements, and can also be used in non-destructive testing scenarios of unidirectional SH waves.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on a bud coil, comprising a coil, a magnet and a magnetic field shielding body; the coil is located above the surface of the object to be detected, the magnet is arranged above the coil, the magnetic field shielding body covers the magnet, and the magnet is located inside the magnetic field shielding body;

[0007] The shape of the coil is similar to a bud, called a bud coil; the coil is a single-turn or multi-turn bud coil, the coil is symmetric about the central axis, and progresses layer by layer from the outside to the inside;

[0008] The magnet is a periodic permanent magnet with alternating polarities, and the magnet is composed of eight bar magnets with alternating SN poles;

[0009] The magnetic field shielding body is a frame made of an electromagnetic shielding housing material, which can control the magnetic field distribution. The magnetic field shielding body has a hollow structure, and the magnetic field shielding body is a cuboid with five faces and an open bottom; its overall size needs to be slightly larger than the magnet, specifically about 1.2 times the size of the magnet;

[0010] The coil is located in a uniform magnetic field perpendicular to the coil plane generated by the combined action of the magnet and the magnetic field shielding body, and the magnetic field direction has the characteristic of periodic change.

[0011] Preferably, the folding angle of the coil is θ = 45°, and the relationship between the coil pitch β and the width ω of a single bar magnet is as follows: β = ω.

[0012] Preferably, the sizes of each bar magnet are the same, and on the side facing the coil, the S pole and the N pole are alternately distributed. The relationship between the width of a single bar magnet and the wavelength of the SH wave is: λ = 2×ω, where ω is the width of a single magnet and λ is the wavelength of the SH wave.

[0013] Preferably, the magnetic field direction generated by the magnet points from the N pole to the S pole of the magnet, and the surfaces of the N pole and the S pole of the magnet are parallel to the coil; the coil is very close to the magnet, and the magnetic field direction is perpendicular to the coil.

[0014] Among them, the magnetic field generated by the magnet, under the action of the magnetic field shielding body, forms a uniform magnetic field perpendicular to the plane of the coil. The direction of the magnetic field changes periodically. The magnetic field shielding body changes the magnetic field direction and magnetic field intensity outside the magnet, so that the magnetic field intensity and magnetic field direction received by the coil located below the outside of the magnet are consistent with those at the center of the magnet, thereby creating an ideal uniform magnetic field environment perpendicular to the plane of the coil with an alternating direction.

[0015] Preferably, the current input and output of the coil are relatively close, there is no magnet coverage above, and it is perpendicular to the magnet; the relationship between the coil length l and the coil spacing β at the current input and output of the coil is: l = β.

[0016] Preferably, an alternating current is passed through the coil, and the current frequency is jointly determined by the characteristics of the object to be detected and the wavelength of the horizontal shear guided wave to be generated. The specific relationship is as follows: In the formula, v is the propagation speed of the shear wave on the surface to be measured, and f is the alternating current frequency.

[0017] Preferably, the relationship between the wavelength λ of the horizontal shear guided wave generated by the electromagnetic ultrasonic excitation device and the coil spacing β is:

[0018] Preferably, after an alternating current is passed through the coil, eddy currents are generated on the surface of the object to be detected, and the magnetic induction intensity directly below the S pole of the magnet is B S = TB, and the magnetic induction intensity directly below the N pole of the magnet is B N = -TB. The eddy currents on the surface of the object to be detected are excited by the Lorentz force in the magnetic field.

[0019] Preferably, the resultant force of the Lorentz force generated by the eddy currents generated by the coil on the surface of the object to be detected in the magnetic field is 0 in the propagation direction of the SH wave, and has F y+ = 4TBJαcosθ and F y- = -4TBJαcosθ, two forces with equal magnitudes and opposite directions, and the resultant force is also 0; that is, the amplitudes generated on both sides perpendicular to the propagation direction of the SH wave are the same, and there is no amplitude in the propagation direction of the SH wave.

[0020] The present invention also provides a non-destructive testing method for bidirectional horizontal shear guided waves based on a bud coil. Using the above-mentioned electromagnetic ultrasonic excitation device for bidirectional horizontal shear guided waves based on a bud coil, the non-destructive testing method includes the following steps: By placing the bud coil in a uniform magnetic field with an alternating direction perpendicular to the plane of the coil under the combined action of the magnet and the magnetic field shielding body, passing an alternating current, and generating bidirectional horizontal shear guided waves on the plane of the surface of the object to be detected.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. In the present invention, the bud coil is placed in a uniform magnetic field with an alternating direction perpendicular to the coil plane under the combined action of a magnet and a magnetic field shield, and an alternating current is applied to generate bidirectional horizontal shear guided waves on the plane of the detected object's surface.

[0023] 2. The present invention can generate bidirectional horizontal shear waves and reduce side lobes. Compared with the existing electromagnetic ultrasonic transducers for generating bidirectional SH waves, due to the unique bud coil design, each segment of the coil is exposed to the specified magnetic field, ensuring that no extra coil segments are exposed to the magnetic field, and to a certain extent, avoiding the influence of side lobes generated by the extra coils.

[0024] 3. The coil design of the present invention effectively limits the excitation of ultrasonic guided waves in the direction perpendicular to the propagation direction of the SH wave, and the specified mode of shear horizontal guided waves can be generated on the plane to be measured by fine-tuning some dimensions. In specific bidirectional non-destructive testing scenarios, such as detecting minute defects on fuel delivery pipelines, straight seam welds of U-rib plates, etc., it has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of the present invention;

[0026] Figure 2 is a schematic side view of the present invention and a diagram of the direction of generating SH waves;

[0027] Figure 3 is a schematic diagram of the bud coil in the present invention;

[0028] Figure 4 is a schematic diagram of the spatial distribution of the coil and the magnet in the present invention;

[0029] Figure 5 is a schematic diagram of the principle of generating bidirectional horizontal shear guided waves in the present invention;

[0030] Figure 6 is a schematic diagram of the local force analysis in the present invention;

[0031] Figure 7 is a schematic diagram of the modeling in the COMSOL simulation of the embodiment of the present invention;

[0032] Figure 8 is for the embodiment of the present invention in the COMSOL simulation and Figure 1 the corresponding magnetic field distribution diagram;

[0033] Figure 9 is for the embodiment of the present invention in the COMSOL simulation and Figure 2 the corresponding magnetic field distribution diagram;

[0034] Figure 10 The figure shows the displacement effect diagram of the embodiment of the present invention in COMSOL simulation.

[0035] In the figure: 1 - magnetic field shield, 2 - magnet, 3 - coil, 4 - object to be detected, 5 - current (direction perpendicular to the plane and inward), 6 - current (direction perpendicular to the plane and outward). Specific embodiments

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, so that those skilled in the art can better understand the advantages and features of the present invention, and thus make a clearer definition of the protection scope of the present invention. The embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0037] Refer to Figures 1-10 , a bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on a bud coil, comprising a coil 3, a magnet 2 and a magnetic field shield 1; the coil 3 is located above the surface of the object to be detected 4, the magnet 2 is arranged above the coil 3, the magnetic field shield 1 covers the magnet 2, and the magnet 2 is located within the magnetic field shield 1;

[0038] The shape of the coil 3 is similar to a bud, called a bud coil; the coil 3 is a single-turn or multi-turn bud coil, the coil 3 is symmetric about the central axis, and progresses layer by layer from the outside to the inside; as Figure 3 shown, Figure 3 is a single-turn bud coil. Among them, the folding angle of the coil 3 is θ = 45°, and the relationship between the spacing β of the coil 3 and the width ω of a single bar magnet is as follows: β = ω.

[0039] The magnet 2 is a periodic permanent magnet with alternating polarities, and the magnet 2 is composed of eight bar magnets with alternating SN poles; the specific placement method is as Figure 4 shown.

[0040] The magnetic field shield 1 is a frame made of an electromagnetic shielding housing material, which can control the magnetic field distribution. The magnetic field shield has a hollow structure. The magnetic field shield 1 is a cuboid with five faces and an open bottom; its overall size needs to be slightly larger than the magnet, specifically about 1.2 times the size of the magnet;

[0041] As Figure 8 , Figure 9 shown, Figure 8 is Figure 1 the corresponding magnetic field. The magnetic field shield 1 clearly changes the magnetic field distribution, leaving most of the magnetic field within the frame.Figure 9 For Figure 2 the corresponding magnetic field, it can be clearly seen that the coil 3 is located in a uniform magnetic field perpendicular to the plane of the coil generated by the combined action of the magnet 2 and the magnetic field shield 1, and the direction of the magnetic field has the characteristic of periodic change.

[0042] Among them, the magnetic field shield 1 changes the direction and intensity of the magnetic field outside the magnet, so that the magnetic field intensity and direction received by the coil located below the outside of the magnet are the same as those at the center of the magnet, thereby creating a relatively ideal uniform magnetic field environment in the same direction. The positional relationship between the coil 3 and the object to be detected 4 is as Figure 1 shown. The coil 3 is parallel to the surface of the object to be detected 4, and non-contact detection is used. The detailed spatial distribution of the coil 3, the magnet 2, and the magnetic field shield 1 is as Figure 7 shown. The coil 3 is about 0.2 mm above the surface of the object to be detected 4, the magnet 2 is about 2 mm above the coil 3, the magnet 2 is located inside the magnetic field shield 1, and the magnetic field shield 1 is entirely above the magnet 2. As Figure 8 shown, the present invention can generate SH waves with less sidelobes and two-way propagation in an aluminum plate with a thickness of 5 mm, and the wavelength is 8 mm.

[0043] Specifically, the sizes of each of the bar magnets are the same, and on the side facing the coil, the S poles and N poles are alternately distributed. The relationship between the width of a single bar magnet and the wavelength of the SH wave is: λ = 2×ω, where ω is the width of a single magnet and λ is the wavelength of the SH wave.

[0044] Specifically, the direction of the magnetic field generated by the magnet 2 points from the N pole to the S pole of the magnet, and the surfaces of the N pole and S pole of the magnet 2 are parallel to the coil; the coil 3 is very close to the magnet 2, and the magnetic field direction is perpendicular to the coil.

[0045] Among them, the magnetic field generated by the magnet 2, under the action of the magnetic field shield, forms a uniform magnetic field perpendicular to the plane of the coil, and the direction of the magnetic field changes periodically. The magnetic field shield changes the direction and intensity of the magnetic field outside the magnet, so that the magnetic field intensity and direction received by the coil located below the outside of the magnet are the same as those at the center of the magnet, thereby creating a relatively ideal uniform magnetic field environment perpendicular to the plane of the coil and with alternating directions.

[0046] Specifically, the current input and output ends of the coil 3 are relatively close, there is no magnet covering above, and it is perpendicular to the magnet; the relationship between the coil length l of the current input and output ends of the coil and the coil spacing β is: l = β.

[0047] Specifically, an alternating current is passed through the coil 3, and the current frequency is jointly determined by the characteristics of the object to be detected and the wavelength of the horizontal shear guided wave to be generated. The specific relationship is as follows: Wherein, v is the propagation speed of the shear wave on the surface to be measured, and f is the alternating current frequency.

[0048] Specifically, the relationship between the wavelength λ of the horizontally polarized shear wave generated by the electromagnetic ultrasonic excitation device and the coil pitch β is:

[0049] Specifically, after the coil 3 is energized with alternating current, eddy currents are generated on the surface of the object to be detected. The magnetic induction intensity directly below the S pole of the magnet is B S = TB, and the magnetic induction intensity directly below the N pole of the magnet is B N = -TB. The eddy currents on the surface of the object to be detected are excited by the Lorentz force in the magnetic field.

[0050] Specifically, the resultant force of the Lorentz force generated by the eddy currents generated by the coil 3 on the surface of the object to be detected in the magnetic field is 0 in the propagation direction of the SH wave, and has F y+ = 4TBJαcosθ and F y- = -4TBJαcosθ, two forces with equal magnitudes and opposite directions, and the resultant force is also 0; that is, the amplitudes generated on both sides perpendicular to the propagation direction of the SH wave are the same, and there is no amplitude in the propagation direction of the SH wave.

[0051] Among them, electromagnetic ultrasonic is one of the types of ultrasonic sensors and can be used for non-destructive evaluation of materials. In the excitation and reception of guided waves, EMAT mainly works using two different mechanisms: the Lorentz force mechanism and the magnetostrictive mechanism.

[0052] The Lorentz force mechanism is only applicable to conductive materials, and the magnetostrictive mechanism is only applicable to materials attached with high magnetostrictive patches. For any material, as long as the surface of the object to be detected 4 is in the form of a plate or a tube structure, the present invention can be used to generate horizontally polarized shear waves.

[0053] The horizontally polarized shear wave is a type of ultrasonic guided wave. The vibration direction of the SH guided wave is perpendicular to the propagation direction and parallel to the surface of the propagation medium.

[0054] The specific principle of generating bidirectional horizontally polarized shear waves by the present invention is as Figure 5 、 Figure 6As shown: In the bud coil 3, the direction of the current is like a winding line. When an alternating current is passed through the coil, an eddy current effect is generated on the conductive surface of the object 4 to be detected. Through the combined action of the magnet 2 and the magnetic field shield 1, a periodic permanent magnet with alternating polarity is applied to the coil 3 along the z direction. This event leads to the development of the Lorentz force perpendicular to both the eddy current and the magnetic field. This generates an elastic wave perpendicular to the direction of the Lorentz force, dividing the bud coil 3 into four parts: the upper left half, the lower left half, the lower right half, and the upper right half of the coil 3. In the upper left half of the coil under the magnet 2, except for the two coils parallel to the width of the magnet, the Lorentz forces generated in the two directions are parallel and opposite to each other, and the two un-canceled coils cancel each other out with the two coils symmetric to the upper right half. The same applies to the lower left half and the lower right half. All these Lorentz forces act at a V-shaped angle in a specific direction, which can be decomposed into two components: longitudinal and transverse. All the transverse components of the Lorentz force cancel each other out, while the longitudinal components of the Lorentz force act in the transverse direction at a certain interval along the reverse direction. This results in the superposition of the influential Lorentz forces in the long axis direction. The direction of the longitudinal component of the Lorentz force changes by 180 degrees every other along the transverse direction, as Figure 2 shown. This phenomenon causes longitudinal vibration on the surface of the specimen and causes waves in the transverse direction, that is, generates horizontal shear guided waves (SH waves). The local force analysis is as Figure 6 shown. In Figure 6 , eight coil segments are selected for analysis: The magnetic induction intensity at the coil directly below the S pole of the magnet is B S = TB, and the magnetic induction intensity at the coil directly below the N pole of the magnet is B N = -TB. As Figure 6 shown, the eddy currents generated by the eight coil segments are:

[0055]

[0056] The eddy currents of other coil segments are the same. The eddy currents generated by the coil on the surface of the object 4 to be detected generate a resultant force of 0 in the propagation direction of the SH wave under the action of the magnetic field. The coil is divided into 9 regions according to Figure 6 , from top to bottom. The forces on the first two regions from top to bottom are as follows:

[0057]

[0058] Combining the above Lorentz forces, we can get

[0059] In region 1, F 1 = 2TBJαcosθ, and the direction is perpendicular to the x-axis;

[0060] In region 2, F 2 = 0;

[0061] Similarly for other regions; in region 3, F 3 = 2TBJαcosθ, with the direction perpendicular to the x-axis;

[0062] In region 4, F 4 = 0;

[0063] In region 5, F 5 = 0;

[0064] In region 6, F 6 = 0;

[0065] In region 7, F 7 = -2TBJαcosθ, with the direction perpendicular to the x-axis;

[0066] In region 8, F 8 = 0;

[0067] In region 9, F 9 = -2TBJαcosθ, with the direction perpendicular to the x-axis.

[0068] From this, it can be obtained that the coil has no force in the x-axis direction and has two forces on the y-axis, F y+ = 4TBJαcosθ and F y- = -4TBJαcosθ, which are equal in magnitude and opposite in direction, and the resultant force is 0. That is, the amplitudes generated in the positive and negative directions of the y-axis are the same and propagate along the x-axis, while there is no amplitude in the x-axis direction and no SH wave propagating along the y-axis is generated. From this, the theoretical basis for generating bidirectional horizontal shear guided waves in the present invention, as well as the theoretical basis for effectively reducing side lobes, can be obtained.

[0069] Using the above principle, a schematic diagram of applying the present invention on an aluminum plate is as shown in Figure 7 The magnetic field jointly generated by the magnetic field shielding body 1 and the magnet 2 is as shown in Figure 8 , Figure 9 The bidirectional SH waves excited on the aluminum plate are as shown in Figure 10 It can be clearly seen that the alternating displacements propagate to both sides. The horizontal shear guided waves generated by the present invention have the function of reducing side lobes and restricting the propagation of ultrasonic guided waves in the vertical direction.

[0070] Among them, SH-EMAT has the following advantages compared with piezoelectric ceramic ultrasonic technology:

[0071] (1) It has the characteristics of strong adaptability and high efficiency;

[0072] (2) The SH0 wave has no dispersion characteristics and is not affected by the geometric shape of the medium;

[0073] (3) It has a wide detection range and is suitable for the detection of metal plates or pipes;

[0074] (4) High sensitivity, non-contact detection, and relatively stable signals;

[0075] (5) No coupling agent is required, making it convenient and fast to use.

[0076] The SH-EMAT technology can be used for tomography of tubular structures, detection of transverse, bidirectional defects or metal loss in pipelines, and also for defect detection of metal plates, etc.

[0077] SH wave mode control: The design of the present invention can adjust the coil spacing according to the transverse wave propagation characteristics of the surface to be detected, the alternating current frequency or the specified SH wavelength. The following formula shows the relationship between the coil spacing, the width of a single magnet, the transverse wave propagation characteristics of the surface to be detected, the guided wave wavelength, and the alternating current frequency. The mode of the excited SH wave, including SH0, SH1, SH2, SH3, SH4, etc., can be controlled by adjusting the coil spacing, the width of a single magnet, or the alternating current frequency.

[0078] v = λ × f = 2 × β × f = 2 × ω × f = (ω + β) × f

[0079] In the formula, the coil spacing is β, the width of a single magnet is ω, the theoretical velocity of the target SH mode guided wave of the material to be detected is v, the alternating current frequency is f, and the wavelength of the SH wave is λ.

[0080] In summary, the present invention can generate bidirectional horizontal shear guided waves and reduce side lobes. It is mainly used to detect defects with a certain direction on the surface or near the surface of materials under high temperature, non-coupling, non-contact, high-speed, etc. conditions, and can detect, quantitatively evaluate, and assess materials. It has broad application prospects in some specific non-destructive testing scenarios.

[0081] The descriptions and practices disclosed in the present invention are easy to think about and understand for ordinary technical personnel in the technical field. Without departing from the principle of the present invention, several improvements and refinements can also be made. Therefore, the modifications or improvements made without departing from the spirit of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A bidirectional horizontal shear waveguide electromagnetic ultrasonic excitation device based on a flower bud coil, characterized in that: It includes a coil, a magnet and a magnetic field shielding body; the coil is located above the surface of the object to be detected, the magnet is arranged above the coil, the magnetic field shielding body is covered on the magnet, and the magnet is located inside the magnetic field shielding body; The coil is a single-turn or multi-turn bud coil, and the coil is symmetrical about the central axis and progresses layer by layer from the outside to the inside; The magnet is a periodic permanent magnet with alternating polarity, and the magnet is composed of eight bar magnets with S-N poles placed alternately; The magnetic field shielding body is composed of an electromagnetic shielding shell, the magnetic field shielding body is a hollow structure, and the magnetic field shielding body is a rectangular parallelepiped with an opening at the bottom; The coil is located in a uniform magnetic field perpendicular to the coil plane generated by the combined action of the magnet and the magnetic field shielding body.

2. According to the bud coil-based bidirectional horizontal shear waveguide electromagnetic ultrasonic excitation device according to claim 1, it is characterized in that: The folding angle of the coil is θ=45°, and the relationship between the spacing β of the coil and the width ω of a single bar magnet is as follows: β=ω.

3. A bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on a flower bud coil according to claim 2, characterized in that: Each of the bar magnets has the same size, and on the side facing the coil, the S pole and the N pole are alternately distributed. The relationship between the width of a single bar magnet and the wavelength of the SH wave is: λ=2×ω, where ω is the width of a single magnet and λ is the wavelength of the SH wave.

4. A bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on a flower bud coil according to claim 1, characterized in that: The direction of the magnetic field generated by the magnet is from the N pole of the magnet to the S pole, and the N pole and S pole surfaces of the magnet are parallel to the coil.

5. According to the bud coil-based bidirectional horizontal shear waveguide electromagnetic ultrasonic excitation device of claim 1, it is characterized in that: The relationship between the coil length l at the current input and current output of the coil and the coil spacing β is: l=β.

6. A bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on a flower bud coil according to claim 3, characterized in that: The coil is fed with an alternating current, and the current frequency is determined by the characteristics of the object to be detected and the wavelength of the horizontal shear waveguide to be generated. The specific relationship is as follows: Where v is the propagation velocity of the shear wave on the surface of the object to be detected, and f is the frequency of the alternating current.

7. A bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on a flower bud coil according to claim 3, characterized in that: The relationship between the wavelength λ of the horizontal shear waveguide generated by the electromagnetic ultrasonic excitation device and the coil spacing β is:

8. The bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on the flower bud coil according to claim 1 is characterized in that: When the coil is supplied with alternating current, eddy current is generated on the surface of the object to be detected. The magnetic induction intensity directly below the S polarity of the magnet is B. S =TB, the magnetic induction intensity directly below the N-polarity magnet is B N =-TB, the eddy current on the surface of the object to be detected excites the Lorentz force under the magnetic field.

9. The bidirectional horizontal shear guided wave electromagnetic ultrasonic excitation device based on the flower bud coil according to claim 1 is characterized in that: The eddy current generated by the coil on the surface of the object to be detected generates a Lorentz force under the action of the magnetic field, which is 0 in the direction of SH wave propagation and has F in the direction perpendicular to the SH wave propagation. y+ =4TBJαcosθ and F y- =-4TBJαcosθ Two forces of equal magnitude and opposite direction, the resultant force is also 0; that is, the amplitudes generated on both sides perpendicular to the propagation direction of the SH wave are the same, and there is no amplitude in the propagation direction of the SH wave.

10. A non-destructive testing method of bidirectional horizontal shear waveguide based on a flower bud coil, using the bidirectional horizontal shear waveguide electromagnetic ultrasonic excitation device based on a flower bud coil as claimed in any one of claims 1 to 9, characterized in that: The nondestructive testing method comprises the following steps: placing the flower bud coil in a uniform magnetic field that alternately changes in a direction perpendicular to the coil plane under the joint action of a magnet and a magnetic field shield, passing an alternating current, and generating a bidirectional horizontal shear waveguide on the plane of the surface of the object to be tested.

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