CN110152964B - Directional magnetic concentrator type lamb wave electromagnetic acoustic transducer - Google Patents
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- CN110152964B CN110152964B CN201910459551.7A CN201910459551A CN110152964B CN 110152964 B CN110152964 B CN 110152964B CN 201910459551 A CN201910459551 A CN 201910459551A CN 110152964 B CN110152964 B CN 110152964B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
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- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/0207—Driving circuits
- B06B1/0215—Driving circuits for generating pulses, e.g. bursts of oscillations, envelopes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
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- B06B1/04—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with electromagnetism
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B2201/00—Indexing scheme associated with B06B1/0207 for details covered by B06B1/0207 but not provided for in any of its subgroups
- B06B2201/50—Application to a particular transducer type
- B06B2201/52—Electrodynamic transducer
- B06B2201/54—Electromagnetic acoustic transducers [EMAT]
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Abstract
The invention discloses a pointing magnetic concentrator type lamb wave electromagnetic acoustic transducer, which comprises a rectangular rubidium iron boron magnet, a multi-cluster inflection coil and a magnetic concentrator. And placing the multi-cluster inflection coil on the surface of the aluminum plate to be detected, and fixing the rubidium-iron-boron magnet and the magnetic concentrator right above the multi-cluster inflection coil. Tests prove that the developed directional magnetic concentrator type lamb wave electromagnetic acoustic transducer can excite single S in an aluminum plate0The mode guides the waves, and verifies that the developed directional magnetic concentrator type lamb wave electromagnetic acoustic transducer has better frequency response characteristics; through an omnidirectional test experiment, the developed directional magnetic concentrator type lamb wave electromagnetic acoustic transducer has higher normalized amplitude in the range of 75-105 degrees. The developed directional magnetic concentrator type lamb wave electromagnetic acoustic transducer can be used for realizing large-range and high-efficiency defect detection on the plate structure, and has great application value and potential in the field of plate structure health monitoring and nondestructive evaluation.
Description
Technical Field
The invention relates to a pointing magnetic concentrator type lamb wave electromagnetic acoustic transducer, which belongs to the field of ultrasonic nondestructive testing, namely, a magnetic concentrator is added on the basis of the traditional electromagnetic acoustic transducer to guide and concentrate a magnetic field generated by a magnet, so that the modal unity of the transducer is improved, and the sensor is utilized to excite the S with the single mode and the consistent circumferential direction on an aluminum plate0Modal guided waves.
Background
The electromagnetic acoustic transducer is composed of a magnet and a coil, has simple structure, convenient use and strong designability, namely, the structure of the magnet and the coil is designed and changed in various forms to excite ultrasonic waves in various forms and various modes. For magnets providing a static magnetic field in an electromagnetic acoustic transducer, neodymium iron boron permanent magnets are currently commonly used. However, since the magnetic field of the permanent magnet has non-changeability and non-uniformity, the electromagnetic acoustic transducer can generate other unwanted modes, which affects the modal unity of the signal.
In order to solve the problems, the invention adds a magnetic concentrator on the basis of the traditional electromagnetic acoustic transducer, the material is ferrite with high magnetic permeability, and the traditional electromagnetic acoustic transducer is easy to generate unnecessary modes due to the non-uniformity of the magnetic field distribution of a common magnet, so that the electromagnetic acoustic transducer is more dependent on the value of the excitation frequency and the design of a coil structure. The magnetic concentrator type lamb wave electromagnetic acoustic transducer researched by the invention adopts the magnetic concentrator to guide and concentrate the magnetic field generated by the magnet, so that the generated mode is purer, and the mode singleness of signals is further improved. Therefore, the research on the magnetic concentrator type lamb wave electromagnetic acoustic transducer for detecting the aluminum alloy plate has important theoretical significance and practical value.
In this subject, the magnetic concentrator mainly functions as a magnetic conductor and a magnetic collector, and changes the direction of a magnetic field provided by the permanent magnet to shield an unnecessary mode and improve the singleness of a signal mode. The induction heating process was simulated to evaluate the effect of the flux concentrator on the temperature profile of the inner surface of the injection molding barrel. Different magnetic flux concentrator intervals are applied, the uniform heating capacity of the induction heating system is researched through commercial software ANSYS, then experiments are carried out, and the experimental results and the simulation results form better contrast. Simulation results show that changing the barrel diameter or changing the operating frequency had no effect on the temperature profile of the barrel inner surface. Liu et al discloses an electrostatic field concentrator that uses a shell with an anisotropic dielectric constant to concentrate an electrostatic field to a core region to achieve an enhanced electrostatic field while maintaining an external field. Research shows that the device has certain application value in nondestructive detection, energy transfer and other static electricity related fields. Predrag et al studied the sensitivity of hall devices using planar magnetic concentrators of different shapes, optimizing the shape, magnification and linear working range of the magnetic separator. Songchang et al simulated the static magnetic field strength of 80A/m using COMSOL Multiphysics finite element software, and investigated the effect of various parameters of the magnetic concentrator, including the dimensions and permeability of the magnetic concentrator and Hall elements, on the simulation results after the magnetic concentrator was added to the static magnetic field.
Disclosure of Invention
The invention relates to a pointing type magnetic concentrator lamb wave electromagnetic acoustic transducer, which is characterized in that a magnetic concentrator is added on the basis of the traditional electromagnetic acoustic transducer to guide and concentrate a magnetic field generated by a magnet, so that the generated mode is purer, and the mode singleness of signals is further improved. Therefore, the research on the magnetic concentrator type lamb wave electromagnetic acoustic transducer for detecting the aluminum alloy plate has important theoretical significance and practical value.
In order to achieve the purpose, the invention adopts the following design scheme:
a pointing magnetic concentrator type lamb wave electromagnetic acoustic transducer comprises a rubidium-iron-boron magnet 1, a multi-cluster inflection coil 2 in a flexible circuit board and a magnetic concentrator 3. The method is characterized in that: the rubidium iron boron magnet 1 is arranged at the uppermost end of the structure; the magnetic concentrator 3 is arranged at the lower end of the rubidium-iron-boron magnet 1; a plurality of clusters of inflection coils 2 in the flexible circuit board are arranged at the lower end of a magnetic concentrator 3, and each cluster region of the plurality of clusters of inflection coils corresponds to the tooth-shaped rectangular region of the magnetic concentrator structure one by one.
The directional magnetic concentrator type lamb wave electromagnetic acoustic transducer is characterized in that: the cross section of the rubidium iron boron magnet 1 is rectangular and is polarized along the vertical direction; the length of the rectangular magnet is l1Width of l2Thickness of h1And providing an offset static magnetic field perpendicular to the surface of the test piece.
The pointing type magnetic concentrator lamb wave electromagnetic acoustic transducer is characterized in that: the flexible circuit board is provided with a plurality of clusters of the inflection coils 2, and a double-layer wiring mode is adopted, so that the performance of the sensor is improved. The flexible circuit board is provided with a plurality of clusters of the inflection coils 2, each cluster of the inflection coils has five coils, the current direction of each coil is the same, and the current directions of the coils of adjacent clusters are opposite. The distance between two adjacent and opposite clusters of wires is L1Equal to the half wavelength lambda/2 corresponding to the theoretical center frequency of the designed directional magnetic concentrator lamb wave electromagnetic acoustic transducer and the theoretical center frequency fc＝Vp/2L1。
The pointing type magnetic concentrator lamb wave electromagnetic acoustic transducer is characterized in that: the magnetic concentrator 3 in the flexible circuit board has four dentate rectangular areas in total, and the dentate rectangular areas correspond to each cluster of areas of the multi-cluster inflection coil one by one. Each toothed rectangular area has a length l3Width of l2(same as the width of the magnet) and a height h2. Overall height h of the magnetic concentrator3Length is l1(corresponding to the length of the magnet) and a width of l2(corresponding to the magnet width). The distance between adjacent teeth is equal to the distance L between two clusters of wires1。
The invention can obtain the following beneficial effects:
1. the rectangular rubidium iron boron magnet 1 is polarized along the vertical direction, and a static magnetic field distributed in the vertical direction is generated near the surface of the aluminum plate test piece;
2. the flexible circuit board is provided with a plurality of clusters of the inflection coils 2, and the performance of the sensor is improved by adopting a double-layer wiring mode;
3. the performance of the sensor is improved by adopting a mode of connecting a plurality of clusters of the inflection coils 2 in parallel in the flexible circuit board;
4. the flexible circuit board is provided with a plurality of clusters of the inflection coils 2, each cluster of the inflection coils has five coils, the current direction of each coil is the same, and the current directions of the coils of adjacent clusters are opposite. The distance between two adjacent and opposite clusters of wires is L1Equal to the half wavelength lambda/2 corresponding to the theoretical center frequency of the designed directional magnetic concentrator lamb wave electromagnetic acoustic transducer and the theoretical center frequency fc＝Vp/2L1。
5. The magnetic concentrator 3 in the flexible circuit board has four dentate rectangular areas in total, and the dentate rectangular areas correspond to each cluster of areas of the multi-cluster inflection coil one by one. The distance between adjacent teeth is equal to the distance L between two clusters of wires1. The magnetic concentrator is matched with the size of the multi-cluster inflection coil, so that the performance of the sensor is improved.
Drawings
FIG. 1 is an exploded schematic view of a directional magnetic concentrator lamb wave electromagnetic acoustic transducer;
FIG. 2 is a schematic view of a rubidium-iron-boron magnet;
FIG. 3 is a schematic diagram of a multi-cluster turn-back coil in a flexible circuit board;
FIG. 4 is a schematic view of a magnetic concentrator;
FIG. 51 is a graph of ultrasonic guided wave group velocity and phase velocity dispersion of an aluminum plate with a thickness of 51 mm;
FIG. 6 Experimental System;
FIG. 7 shows a received signal at a conventional magnet excitation frequency of 272 kHz;
FIG. 8 shows the received signal at an excitation frequency of 272kHz with the addition of a magnetic concentrator;
FIG. 9 frequency characteristics of a directional magnetic concentrator lamb wave electromagnetic acoustic transducer;
FIG. 10 is a schematic diagram of a sensor arrangement for an omnidirectional test experiment;
FIG. 11 Directional magnetic concentrator type lamb wave electromagnetic Acoustic transducer to detect SH at different angles0The modal normalized amplitude.
In the figure: 1. the device comprises a rubidium iron boron magnet, 2 a multi-cluster inflection coil in a flexible circuit board, 3 a magnetic concentrator, 4 high-energy pulse excitation receiving devices RPR4000 and 5, a digital oscilloscope, 6 an excitation end impedance matching module, 7 a receiving end impedance matching module, 8 an excitation sensor, 9 a receiving sensor, 10 an aluminum plate.
Detailed Description
The invention is further illustrated by the following figures and examples.
Based on Lorentz force effect, a pointing type magnetic concentrator lamb wave electromagnetic acoustic transducer is designed, a magnetic concentrator is added on the basis of a traditional electromagnetic acoustic transducer to guide and concentrate a magnetic field generated by a magnet, so that the modal unity of the transducer is improved, and the sensor is utilized to excite the S with the single mode and the consistent circumference on an aluminum plate0Modal guided waves.
The schematic structural diagram of a pointing magnetic concentrator lamb wave electromagnetic acoustic transducer is shown in fig. 1, and the pointing magnetic concentrator lamb wave electromagnetic acoustic transducer comprises a rubidium-iron-boron magnet 1, a multi-cluster inflection coil 2 in a flexible circuit board, and a magnetic concentrator 3. The test object was an aluminum plate and the specification was 1000X 1 (unit: mm). FIG. 5 is the ultrasonic guided wave group velocity and phase velocity dispersion curves of the aluminum plate. When the wavelength λ is determined, the frequency of the generated ultrasonic wave can be uniquely determined. The rubidium iron boron magnet 1 is arranged at the upper end of the magnetic concentrator 3 to generate a static magnetic field which is vertically distributed. Clusters of meander coils 2 in a flexible circuit board are placed under the magnetic concentrator 3.
The rubidium iron boron magnet 1 has a rectangular cross section and is polarized along the vertical direction, and the width l of the rectangular magnet is shown in FIG. 22The width of the magnetic concentrator is 25mm and the length is l1Is 35mm and has a thickness h1Is 20 mm. The position distribution of the rubidium iron boron magnet 1 is shown in figure 1 and is arranged at the uppermost end of the whole sensor structure. A vertically distributed static magnetic field is generated near the specimen surface by the magnetic concentrator 3.
As shown in fig. 3, the flexible circuit board has a plurality of clusters of zigzag coils 2, and adopts a multi-cluster zigzag wiring mode, wherein the wiring is double-layered, and each layer of four zigzag coils has eight fan-shaped zigzag coils. Each cluster has five coils, the current direction of each coil is the same, and the current directions of the coils of adjacent clusters are opposite. The distance between two adjacent and opposite clusters of wires is L110mm, which is equal to the half wavelength lambda/2 corresponding to the theoretical center frequency of the designed directional magnetic concentrator lamb wave electromagnetic acoustic transducer, and the theoretical center frequency fc＝Vp/2L1＝272kHz。
The experimental system is shown in fig. 6 and comprises a high-energy pulse excitation receiving device RPR40004, a digital oscilloscope 5, an excitation end impedance matching module 6, a receiving end impedance matching module 7, an excitation sensor 8, a receiving sensor 9 and an aluminum plate 10. The RPR40004 can generate a high-energy excitation signal, and the digital oscilloscope 5 is used for observing and storing the signal; the impedance matching modules 6 and 7 are used for enabling the sensor coil to obtain maximum energy and improving the energy conversion efficiency of the sensor.
1) Frequency characteristic test
Determining the structure of the pointing magnetic concentrator lamb wave electromagnetic acoustic transducer according to the selected parameter wavelength lambda, and designing the theoretical central frequency f of the pointing magnetic concentrator lamb wave electromagnetic acoustic transducercIs 272 kHz. The rubidium iron boron magnet 1, the magnetic concentrator 3 and the multi-cluster inflection coil 2 in the flexible circuit board are respectively arranged right above the test piece according to requirements, an experiment is carried out by adopting a one-excitation one-collection mode, and the sensor 8 is arranged on an aluminum plate of a detection objectThe position 10 away from the left end face by 350mm and the position 500mm from the lower end face are used as excitation sensors, the excitation signals are 5-period sine waves modulated by a Hanning window, and the sensor 9 is arranged at the position 10 away from the right end face by 450mm and the position 500mm from the lower end face of the aluminum plate to be detected and used as a receiving sensor. Fig. 7 shows waveforms of signals received by a conventional magnet (without a magnetic concentrator) when an excitation frequency is 272kHz, 4 echo wave packets can be distinguished, the wave packets 11, 12, 13, and 14 are predicted to be direct wave signals, left end surface reflection echoes, and right end surface reflection echoes, and actual propagation group velocities of the wave packets 11 and 12 are calculated to be 5494m/s and 2491m/s respectively by using a Time of Flight (ToF). Are respectively reacted with S0Sum of waves A0The theoretical group velocities of the waves in the aluminum plate 10 are basically identical to each other, namely 5421m/s and 2539m/s, and the errors are respectively 1.3 percent and 1.9 percent. Illustrating that a sensor without the addition of a magnetic concentrator is producing S0Sum of waves A0Two modes of waves cannot ensure the unity of the modes. Fig. 8 shows that the designed directional magnetic concentrator lamb wave electromagnetic acoustic transducer receives signal waveforms at 272kHz, and can distinguish 3 echo wave packets, the wave packets 15, 16, and 17 are predicted to be direct wave signals, left end surface reflection echoes, and right end surface reflection echoes, and the actual propagation group velocity of the wave packet 15 is calculated to be 5494m/s by using the Time of Flight (ToF). And S0The theoretical group velocity of the wave in the aluminum plate 10 is 5421m/s, the wave is basically consistent, and the error is 1.3%. The wave packets 16 and 17 are calculated by the time-of-flight method as left and right end-face reflected echoes, respectively. Therefore, the designed pointing type magnetic concentrator lamb wave electromagnetic acoustic transducer can generate S with single mode0Modal guided waves.
In order to test the frequency characteristics of the developed directional magnetic concentrator lamb wave electromagnetic acoustic transducer, the excitation frequency is increased from 172kHz to 372kHz by the step length of 10kHz, the direct wave envelope peak value in the received signal of each frequency point is extracted, the frequency characteristics of the directional magnetic concentrator lamb wave electromagnetic acoustic transducer are obtained as shown in FIG. 9, experimental data are respectively represented by circles, and through curve fitting, the central frequency of the directional magnetic concentrator lamb wave electromagnetic acoustic transducer is 275kHz and basically matched with the theoretical central frequency of 272kHz, and the relative error is only 1.1%.
2) Test for omnidirectionality
In order to test the omni-directionality of the designed directional magnetic concentrator lamb wave electromagnetic acoustic transducer, an omni-directional test was performed. The experimental system is the same as the above experiment, the schematic sensor layout of the omnidirectional test experiment is shown in fig. 10, the excitation sensor 8 is a developed directional magnetic concentrator lamb wave electromagnetic acoustic transducer, and is placed at the center of the aluminum plate 10 as an excitation source, the receiving sensors 14 are placed on a half circle with the excitation source as a circle center and the radius of 300mm, the interval is 5 degrees, and the direction of the receiving sensors always points to the directional magnetic concentrator lamb wave electromagnetic acoustic transducer as the excitation source.
FIG. 11 is S detected at different angles by a directional magnetic concentrator lamb wave electromagnetic acoustic transducer0The normalized amplitude of the modal direct wave shows that the directional magnetic concentrator lamb wave electromagnetic acoustic transducer has a higher normalized amplitude in a range of 75-105 degrees, so that the directivity of the directional magnetic concentrator lamb wave electromagnetic acoustic transducer is better.
Claims (3)
1. A pointing magnetic concentrator type lamb wave electromagnetic acoustic transducer comprises a rubidium-iron-boron magnet (1), a multi-cluster inflection coil (2) in a flexible circuit board and a magnetic concentrator (3); the method is characterized in that: the rubidium iron boron magnet (1) is arranged at the uppermost end; the magnetic concentrator (3) is arranged at the lower end of the rubidium-iron-boron magnet (1); a plurality of clusters of inflection coils (2) in the flexible circuit board are arranged at the lower end of a magnetic concentrator (3), and each cluster region of the plurality of clusters of inflection coils corresponds to the tooth-shaped rectangular region of the magnetic concentrator structure one by one;
the cross section of the rubidium iron boron magnet (1) is rectangular and is polarized along the vertical direction; the length of the rectangular magnet isl 1Wide isl 2A thickness ofh 1Providing a bias static magnetic field vertical to the surface of the test piece through a magnetic concentrator (3);
a double-layer wiring mode is adopted by a plurality of clusters of inflection coils (2) in the flexible circuit board, so that the performance of the sensor is improved.
2. A directional magnetic concentrator lamb wave electromagnetic acoustic transducer as claimed in claim 1Can ware, its characterized in that: each cluster of the multi-cluster reverse-folded coils (2) in the flexible circuit board comprises five coils, the current direction of each coil is the same, and the current directions of the coils of adjacent clusters are opposite; the distance between two adjacent and reversed clusters of wires isL 1Equal to half wavelength corresponding to theoretical center frequency of designed directional magnetic concentrator type lamb wave electromagnetic acoustic transducerλ2, theoretical center frequencyf c=V p/2L 1，V pIs the actual propagation group velocity of the wave packet.
3. A directional magnetic concentrator lamb wave electromagnetic acoustic transducer according to claim 1 in which: the magnetic concentrator (3) in the flexible circuit board has four dentate rectangular areas, and the dentate rectangular areas correspond to the areas of each cluster of the multi-cluster inflection coils one by one; each of the toothed rectangular regions has a length ofl 3Wide isl 2High ish 2(ii) a Overall height of magnetic concentratorh 3Is long asl 1Wide isl 2(ii) a The distance between adjacent teeth is equal to the distance between two clusters of wiresL 1。
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| CN110702798A (en) * | 2019-10-19 | 2020-01-17 | 北京工业大学 | Oblique incidence type electromagnetic acoustic sensor based on variable-angle magnetic concentrator |
| CN113866264B (en) * | 2021-08-20 | 2024-04-19 | 北京工业大学 | Directional A0Modal electromagnet type electromagnetic acoustic sensor |
| CN114371217A (en) * | 2021-11-27 | 2022-04-19 | 北京工业大学 | Intelligent lamb wave defect positioning method based on dense array |
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