Electromagnetic ultrasonic transducer for generating single-mode Lamb wave and design method thereof

Abstract

The present invention relates to the field of electromagnetic ultrasonic technology, and provides an electromagnetic ultrasonic transducer for generating a single-mode Lamb wave and a design method thereof, wherein the electromagnetic ultrasonic transducer comprises: a permanent magnet, a metal coil unit and an ester solid glue; an arc-shaped groove is provided on the bottom surface of the permanent magnet, and after the arc-shaped groove is provided, the permanent magnet presents an arched structure, and a metal coil unit is arranged inside the arc-shaped groove of the permanent magnet; the metal coil unit comprises: a plurality of layers of parallel zigzag coils; the number of bends of the zigzag coils gradually decreases from the bottom layer to the upper layer; the zigzag coil of the next layer is connected to the zigzag coil of the upper layer; the ester solid glue fills the gap between the permanent magnet and the zigzag coil; the zigzag coil does not contact the tested object; and the zigzag coil is arranged above the tested object. The present invention can avoid the multi-modal phenomenon of exciting guided waves, and excite a single-modal guided wave, and the conversion efficiency is significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic ultrasonic technology, and in particular to an electromagnetic ultrasonic transducer for generating a single-mode Lamb wave and a design method thereof. Background Art

[0002] With the rapid development of the national economy, metal sheets are widely used in all walks of life. However, in the process of metal sheet production, processing and use, various defects will inevitably appear, such as metal surface scratches, internal cracks, etc. Therefore, non-destructive testing, as a technology that detects surface and internal defects of the tested piece without destroying the tested piece and provides specific information of the defects, is widely used in defect detection of metal sheets. In the field of non-destructive testing, electromagnetic ultrasonic testing technology makes detection simpler and easier due to its advantages such as wide detection range, high detection accuracy, no need for coupling agent and complex pretreatment technology, and greatly improves production efficiency.

[0003] However, the low conversion efficiency of the electromagnetic ultrasonic transducer in the existing technology, the dispersion characteristics of the waveguide and the multi-modal characteristics lead to messy signals and low detection efficiency during detection. Therefore, how to improve the detection efficiency of electromagnetic ultrasonic detection technology has become a hot issue. Summary of the invention

[0004] The present invention mainly solves the technical problem that the multi-modal characteristics of the electromagnetic ultrasonic Lamb wave transducer in the prior art lead to chaotic signals and low detection efficiency during detection, and proposes an electromagnetic ultrasonic transducer that generates a single-mode Lamb wave and a design method thereof, so as to improve the efficiency of non-destructive testing and significantly improve the conversion efficiency.

[0005] The present invention provides an electromagnetic ultrasonic transducer for generating a single-mode Lamb wave, comprising: a permanent magnet 1, a metal coil unit 2 and an ester solid glue 4;

[0006] An arc-shaped groove is formed on the bottom surface of the permanent magnet 1. After the arc-shaped groove is formed, the permanent magnet 1 presents an arched structure. A metal coil unit 2 is disposed in the arc-shaped groove of the permanent magnet 1.

[0007] The metal coil unit 2 comprises: multiple layers of parallel zigzag coils; the number of bends of the zigzag coils gradually decreases from the bottom layer to the upper layer; the zigzag coils of the next layer are connected to the zigzag coils of the previous layer;

[0008] The ester solid glue 4 fills the gap between the permanent magnet 1 and the zigzag coil; the zigzag coil is not in contact with the tested object 3; and the zigzag coil is arranged above the tested object 3.

[0009] Preferably, the metal coil unit 2 is provided with three layers of zigzag coils, the bottom layer zigzag coil has five bends, the middle layer zigzag coil has three bends, and the upper layer zigzag coil has one bend.

[0010] Correspondingly, the present invention also provides a design method for an electromagnetic ultrasonic transducer that generates a single-mode Lamb wave, comprising the following process:

[0011] Step 100, obtaining electromagnetic ultrasonic transducer parameters input by a user, wherein the electromagnetic ultrasonic transducer parameters include the width and height of the arc-shaped groove in the arch structure;

[0012] Step 200, determine the relationship between the width, height and radius of the arc-shaped groove in the arch structure according to the following formula:

[0013]

[0014] Wherein, w represents the width of the arc-shaped groove in the arch structure, h represents the height of the arc-shaped groove in the arch structure, and R represents the radius of the arc-shaped groove in the arch structure;

[0015] Step 300, determine the coordinates of any point a on the permanent magnet 1 by the following formula:

[0016]

[0017] Using the relationship between the width, height and radius of the arc groove in the arch structure, the following formula is obtained:

[0018]

[0019] Step 400, determine the distance from any point b to point a of the ester solid glue 4 in the arc-shaped groove of the permanent magnet 1 by the following formula:

[0020]

[0021] Its unit vector is:

[0022]

[0023] Step 500, determine the magnetic field strength of the permanent magnet 1 to point b according to the magnetic field strength formula:

[0024]

[0025] Where μ0 represents the magnetic permeability in vacuum; q m Indicates the value of magnetic charge; The unit vector representing the position of the magnetic charge and the line connecting the position at a distance r from the magnetic charge;

[0026] Step 600, based on the same permanent magnet 1, the magnetic charge value at each location is the same, and using formula (2), formula (3), and formula (6), the magnetic field strength of the permanent magnet 1 at point b is obtained as:

[0027]

[0028] Right now:

[0029]

[0030] Step 700: Decompose the magnetic field intensity into horizontal components H according to formula (5) and formula (6): bx and the vertical component H by :

[0031]

[0032] Step 800: Since it is required to generate a vertical magnetic field strength, H bx Set it to 0, and get the following formula:

[0033]

[0034] Step 900, mathematical operation is performed using formula (10) to obtain the multiple coefficient of the width and height of the arc-shaped groove in the arch structure:

[0035]

[0036] Wherein, k represents the multiple coefficient of the width and height of the arc groove in the arch structure;

[0037] Step 1000, by determining the multiple coefficients of the width and height of the arc-shaped groove in the arch structure, an electromagnetic ultrasonic transducer that generates a single-mode Lamb wave is obtained.

[0038] The electromagnetic ultrasonic transducer and design method for generating a single-mode Lamb wave of the present invention are provided with an arched structure, which can not only avoid the multi-mode phenomenon of exciting guided waves and stimulate a single-mode guided wave, but also has low cost and a wide application prospect. Compared with a single-layer zigzag coil, the multi-layer parallel zigzag coil used has a significantly improved conversion efficiency, enhanced received echo signals, and is not easily disturbed by noise, which greatly improves detection efficiency and is conducive to the development of detection technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic structural diagram of an electromagnetic ultrasonic transducer capable of generating a single-mode Lamb wave provided by the present invention;

[0040] Figure 2 is a schematic structural diagram of a metal coil unit provided by the present invention;

[0041] Figure 3 is a top view of the metal coil unit provided by the present invention;

[0042] Figure 4 It is a physical model diagram of the arch structure provided by the present invention;

[0043] Figure 5 This is the working principle diagram of a common electromagnetic ultrasonic transducer;

[0044] Figure 6 It is a working principle diagram of the optimized electromagnetic ultrasonic transducer of the present invention;

[0045] Figure 7 It is a comparison diagram of the magnetic fields formed by ordinary square permanent magnets and the arched structure permanent magnets of the present invention;

[0046] Figure 8 It is a finite element model and structural parameter diagram of the electromagnetic ultrasonic transducer of the present invention;

[0047] Fig. 9 is a pulse excitation voltage signal diagram of the coil of the present invention;

[0048] Fig.10 is a Lamb wave signal diagram excited by the electromagnetic ultrasonic transducer of the present invention;

[0049] Fig.11 is a model and structural parameter diagram of the electromagnetic ultrasonic transducer of the comparison group of the present invention;

[0050] Fig.12 It is a comparison diagram of Lamb waves excited by the comparison group of the present invention and the optimized transducer. DETAILED DESCRIPTION

[0051] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all the contents.

[0052] Embodiment 1

[0053] like Figure 1-3 As shown, an electromagnetic ultrasonic transducer for generating a single-mode Lamb wave provided by an embodiment of the present invention comprises: a permanent magnet 1, a metal coil unit 2 and an ester solid glue 4;

[0054] An arc-shaped groove is formed on the bottom surface of the permanent magnet 1 . After the arc-shaped groove is formed, the permanent magnet 1 presents an arched structure. A metal coil unit 2 is disposed in the arc-shaped groove of the permanent magnet 1 .

[0055] The metal coil unit 2 includes: multiple layers of parallel zigzag coils; the number of bends of the zigzag coils gradually decreases from the bottom layer to the upper layer, that is, the width of the zigzag coil gradually decreases from the bottom layer to the upper layer, and the cross-section of the multiple layers of zigzag coils is in a "pyramid" shape. The zigzag coils in the top layer are in a "U" shape, and the zigzag coils in other layers are in a serpentine shape, and the spacing between adjacent parallel sides in the zigzag coils is the same. For example, three layers of zigzag coils are provided, the zigzag coil in the bottom layer has five bends, the zigzag coil in the middle layer has three bends, and the zigzag coil in the upper layer has one bend. Its structural diagram is shown as follows Figure 2 As shown, the top view is Figure 3 The zigzag coils of the next layer are connected to the zigzag coils of the previous layer. The input and output directions of the zigzag coils of different layers are the same. The zigzag coils of multiple layers in parallel are connected to the current through the input end of the bottom layer. The current can enter the zigzag coils of each layer in turn and then be output at the output end of the zigzag coil of the bottom layer.

[0056] The ester solid glue 4 fills the gap between the permanent magnet 1 and the zigzag coil; the zigzag coil is not in contact with the tested object 3; and the zigzag coil is arranged above the tested object 3.

[0057] In the electromagnetic ultrasonic transducer of this embodiment, the permanent magnet 1 adopts a magnetic field focusing design, and the zigzag coil is placed in an arc-shaped groove below the permanent magnet 1, so that the magnetic field in the area below the arched structure is uniformly perpendicular to the test piece 3 in the form of an aluminum plate.

[0058] The permanent magnet 1 of this embodiment is provided with arc grooves and has an arched structure. Since the magnetic field strength in the vertical direction of the arched structure increases and the magnetic field strength in the horizontal direction decreases, a static magnetic field in the vertical direction is provided. The coil passing high-frequency alternating current provides an alternating magnetic field. The metal coil unit 2 induces eddy currents on the test piece 3. The eddy currents cause the test piece 3 to generate Lorentz force under the action of the magnetic field generated by the permanent magnet. Due to the action of the Lorentz force, Lamb waves are generated in the test piece 3. The test piece 3 is a non-ferromagnetic test piece. In order to make full use of the internal space of the arched structure, the metal coil unit 2 performs a "pyramid" optimization design on the multi-layer zigzag coil according to the permanent magnet distribution law and the Huygens superposition principle, so that the number of folded coil layers decreases from the middle to both sides.

[0059] The present invention adopts electromagnetic ultrasonic detection technology. As a kind of ultrasonic detection technology, electromagnetic ultrasonic detection technology is widely used in various detection processes because it does not need to pre-treat the surface of the test piece, does not need to add coupling agent between the sensor and the test piece, and has high sensitivity to tiny defects. In order to generate a horizontal magnetic field and then excite a single A0 mode Lamb wave or enhance the Lamb wave A0 mode, a U-shaped permanent magnet structure and an "SNS" structure composite permanent magnet structure are often used; in order to generate a vertical magnetic field and then excite a single S0 mode Lamb wave, a double permanent magnet structure with opposite polarities placed above and below the test piece is often used.

[0060] The "arch bridge" structure of the present invention can not only avoid the multi-modal phenomenon of exciting guided waves, but also stimulate single-mode guided waves, and is low-cost and has a wide range of application prospects. Compared with single-layer zigzag coils, the multi-layer parallel zigzag coils used have significantly improved conversion efficiency, enhanced received echo signals, and are less susceptible to noise interference, greatly improving detection efficiency and facilitating the development of detection technology.

[0061] Embodiment 2

[0062] In order to generate a uniform magnetic field in the vertical direction and thus excite a single S0 mode, the common electromagnetic ultrasonic transducer (EMAT) was improved and a new EMAT consisting of an "arch bridge" structure permanent magnet, a "pyramid" zigzag coil, a lipid solid filling gel and a test piece was designed. Figure 4 As shown, in order to generate a uniform magnetic field, a two-dimensional model of a permanent magnet with an "arch bridge" structure is constructed. A design method of an electromagnetic ultrasonic transducer for generating a single-mode Lamb wave provided by an embodiment of the present invention includes the following process:

[0063] Step 100: Acquire electromagnetic ultrasonic transducer parameters input by a user, wherein the electromagnetic ultrasonic transducer parameters include the width and height of the arc-shaped groove in the arch structure.

[0064] Step 200, determine the relationship between the width, height and radius of the arc-shaped groove in the arch structure according to the following formula:

[0065]

[0066] Wherein, w represents the width of the arc-shaped groove in the arch structure, h represents the height of the arc-shaped groove in the arch structure, and R represents the radius of the arc-shaped groove in the arch structure.

[0067] Step 300, determine the coordinates of any point a on the permanent magnet 1 by the following formula:

[0068]

[0069] Using the relationship between the width, height and radius of the arc groove in the arch structure, the following formula is obtained:

[0070]

[0071] Step 400, determine the distance from any point b to point a of the ester solid glue 4 in the arc-shaped groove of the permanent magnet 1 by the following formula:

[0072]

[0073] Its unit vector is:

[0074]

[0075] Step 500, determine the magnetic field strength of the permanent magnet 1 to point b according to the magnetic field strength formula:

[0076]

[0077] Where μ0 represents the magnetic permeability in vacuum; q m Indicates the value of magnetic charge; Represents the unit vector of the line connecting the position of the magnetic charge and the distance r from the magnetic charge.

[0078] Step 600, based on the same permanent magnet 1, the magnetic charge value at each location is the same, and using formula (2), formula (3), and formula (6), the magnetic field strength of the permanent magnet 1 at point b is obtained as:

[0079]

[0080] Right now:

[0081]

[0082] Step 700: Decompose the magnetic field intensity into horizontal components H according to formula (5) and formula (6): bx and the vertical component H by :

[0083]

[0084] Step 800: Since it is required to generate a vertical magnetic field strength, H bx Set it to 0, and get the following formula:

[0085]

[0086] Step 900, mathematical operation is performed using formula (10) to obtain the multiple coefficient of the width and height of the arc-shaped groove in the arch structure:

[0087]

[0088] Wherein, k represents a multiple coefficient of the width and height of the arc-shaped groove in the arch structure.

[0089] Step 1000, by determining the multiple coefficients of the width and height of the arc-shaped groove in the arch structure, an electromagnetic ultrasonic transducer that generates a single-mode Lamb wave is obtained.

[0090] The electromagnetic ultrasonic transducer is mainly composed of a permanent magnet 1, a metal coil unit 2, and an ester solid glue 4. The permanent magnet 1 provides a static magnetic field in a vertical direction, and the coil passing a high-frequency alternating current provides an alternating magnetic field. The magnetic field and the current interact to generate ultrasonic guided waves in the test piece. Its working principle is as follows: Figure 5 shown.

[0091] In non-ferromagnetic materials, the ultrasonic guided waves excited by EMAT in the specimen are mainly based on the Lorentz force mechanism. The Lorentz force (component) perpendicular to the specimen plane produces the A0 mode (transverse wave), and the Lorentz force (component) parallel to the specimen plane produces the S0 mode (longitudinal wave). Therefore, controlling the direction of the Lorentz force generated in time can achieve the excitation of a single S0 mode.

[0092] In order to excite a single S0 mode Lamb wave, an arched structure is used for the permanent magnet 1 of the EMAT, so that the magnetic field has the ability to gather magnetic field under the "arch bridge", even if the direction of the static magnetic field is perpendicular to the direction of waveguide propagation. Since the static magnetic field distribution has the characteristics of unevenness, the closer to the magnetic center line, the more uniform the magnetic field distribution and the greater the magnetic field intensity, so the multi-layer parallel zigzag coil of the EMAT is designed with a "pyramid" structure to improve the energy conversion efficiency of the EMAT for the S0 mode. The working principle of the optimized electromagnetic ultrasonic transducer is as follows: Figure 6 shown.

[0093] In order to illustrate the effect of the present invention, the method of the present invention is verified below:

[0094] Step 1: A two-dimensional multi-physics field finite element simulation model was established based on COMSOL software, and the modeling parameters were defined; the parameters included specimen thickness, specimen Young's modulus, specimen Poisson's ratio, specimen density, specimen conductivity, permanent magnet residual flux density, permanent magnet relative magnetic permeability and coil conductivity.

[0095] In this step, the two-dimensional multi-physics field includes electric field, acoustic field, and structural field. The parameters required for modeling are defined as shown in the following table:

[0096]

[0097] The parameters include the thickness of the specimen (aluminum), the Young's modulus of the specimen (aluminum), the Poisson's ratio of the specimen (aluminum), the density of the specimen (aluminum), the conductivity of the specimen (aluminum), the residual magnetic flux density of the permanent magnet, the relative magnetic permeability of the permanent magnet and the conductivity of the coil;

[0098] Step 2: According to formula (11), take w = 28mm, and get:

[0099] h=2.69mm (12)

[0100] In order to verify the magnetic field gathering effect of the "arch bridge" structure permanent magnet, the magnetic field formed by the ordinary square permanent magnet (h = 0) and the "arch bridge" type permanent magnet (h = 2.7) is simulated as follows: Figure 7 shown.

[0101] Step 3: Establish a geometric model including a permanent magnet, a metal coil, a test piece and an air layer. The permanent magnet (1) adopts a magnetic field concentration design, and the contact point between the permanent magnet and the folded coil is an "arch bridge" structure. The coil is a "pyramid" optimized design of an ordinary multi-layer folded coil, so that the number of folded coil layers decreases from the middle to the sides. The finite element model and structural parameters are as follows Figure 8 As shown;

[0102] Step 4: In order to excite the Lamb wave S0 mode with maximum efficiency, the optimal excitation S0 mode frequency can be known based on the phase matching condition and dispersion curve:

[0103]

[0104] Where: v so is the SO mode plate wave group velocity; D is the wire spacing. Therefore, a pulse excitation voltage signal with a frequency of 657KHz is applied to the coil, such as Fig. 9 The guided wave signal based on the Lorentz force mechanism is received at a distance of 0.5m from the electromagnetic ultrasonic transducer. In order to avoid the influence of the end face reflection on the simulation results, the end face is set as a soft sound field and low reflection boundary;

[0105] Step 5: The ultrasonic guided waves excited by the optimized electromagnetic ultrasonic transducer still have the S0 mode, such as Fig.10 As shown, there are two main reasons: First, due to the uneven distribution of the static magnetic field generated by the permanent magnet, the magnetic field formed by the "arch bridge" type magnet is not absolutely uniform in the area below the "arch bridge". Second, the interaction between the alternating magnetic field formed by the coil and the eddy current will produce a Lorentz force component perpendicular to the aluminum plate, thus generating A0 mode guided waves;

[0106] Step 6: In order to fully verify the optimization effect of the new EMAT structure and eliminate the influence of the difference in the distance between the permanent magnet and the aluminum plate specimen, three groups of comparative simulation experiments were established based on the simulation verification of the new EMAT to compare the effect of the optimized EMAT with the ordinary EMAT, the EMAT that only optimizes the permanent magnet, and the EMAT that only optimizes the coil structure to excite a single S0 mode. The finite element models and structural parameters of the three groups of EMAT are as follows: Fig.11 As shown;

[0107] Step 7: Use comparative experiments to conduct simulation verification and comparison with ordinary transducers and partially optimized transducers. The comparison results are as follows: Fig.12 As shown. It can be seen that both the "arch bridge" permanent magnet and the "pyramid" folded coil can suppress the A0 modal waveguide excited by the transducer, but do not affect the S0 modal waveguide excited by the transducer. The experimental group using the "arch bridge" permanent magnet and the "pyramid" folded coil can basically eliminate the A0 modal waveguide.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that modifying the technical solutions described in the aforementioned embodiments, or replacing some or all of the technical features therein by equivalents, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for an electromagnetic ultrasonic transducer for generating a single-mode Lamb wave, characterized in that: The process includes: Step 100, obtaining electromagnetic ultrasonic transducer parameters input by a user, wherein the electromagnetic ultrasonic transducer parameters include the width and height of the arc-shaped groove in the arch structure; The electromagnetic ultrasonic transducer comprises: a permanent magnet (1), a metal coil unit (2) and an ester solid glue (4); an arc-shaped groove is provided on the bottom surface of the permanent magnet (1); after the arc-shaped groove is provided, the permanent magnet (1) presents an arched structure; the metal coil unit (2) is arranged in the arc-shaped groove of the permanent magnet (1); the metal coil unit (2) comprises: multiple layers of parallel zigzag coils; the number of bends of the zigzag coils gradually decreases from the bottom layer to the upper layer; the zigzag coil of the lower layer is connected to the zigzag coil of the upper layer; the ester solid glue (4) fills the gap between the permanent magnet (1) and the zigzag coil; the zigzag coil does not contact the test piece (3); the zigzag coil is arranged above the test piece (3); the metal coil unit (2) is provided with three layers of zigzag coils, the zigzag coil of the bottom layer has five bends, the zigzag coil of the middle layer has three bends, and the zigzag coil of the upper layer has one bend; Step 200, determine the relationship between the width, height and radius of the arc-shaped groove in the arch structure according to the following formula: Wherein, w represents the width of the arc-shaped groove in the arch structure, h represents the height of the arc-shaped groove in the arch structure, and R represents the radius of the arc-shaped groove in the arch structure; Step 300, determine the coordinates of any point a on the permanent magnet 1 by the following formula: Using the relationship between the width, height and radius of the arc groove in the arch structure, the following formula is obtained: Step 400, determine the distance from any point b to point a of the ester solid glue 4 in the arc-shaped groove of the permanent magnet 1 by the following formula: Its unit vector is: Step 500, determine the magnetic field strength of the permanent magnet 1 to point b according to the magnetic field strength formula: Where μ0 represents the magnetic permeability in vacuum; q m Indicates the value of magnetic charge; The unit vector representing the position of the magnetic charge and the line connecting the position at a distance r from the magnetic charge; Step 600, based on the same permanent magnet 1, the magnetic charge value at each location is the same, and using formula (2), formula (3), and formula (6), the magnetic field strength of the permanent magnet 1 at point b is obtained as: Right now: Step 700: Decompose the magnetic field intensity into horizontal components H according to formula (5) and formula (6): bx and the vertical component H by : Step 800: Since it is required to generate a vertical magnetic field strength, H bx Set it to 0, and get the following formula: Step 900, mathematical operation is performed using formula (10) to obtain the multiple coefficient of the width and height of the arc-shaped groove in the arch structure: Wherein, k represents the multiple coefficient of the width and height of the arc groove in the arch structure; Step 1000, by determining the multiple coefficients of the width and height of the arc-shaped groove in the arch structure, an electromagnetic ultrasonic transducer that generates a single-mode Lamb wave is obtained.

Images