CN112986398B - Electromagnetic ultrasonic Lamb wave transducer and online detection system and method - Google Patents
Electromagnetic ultrasonic Lamb wave transducer and online detection system and method Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2412—Probes using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01N29/04—Analysing solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
Abstract
The invention discloses an electromagnetic ultrasonic Lamb wave transducer and an online detection system and method, wherein the transducer comprises a shell, N permanent magnets and N zigzag coils, wherein the N permanent magnets and the N zigzag coils are arranged in the shell; the N permanent magnets are arranged above the N zigzag coils in a one-to-one correspondence manner, and are arranged in a single row, and the N zigzag coils are connected in a parallel connection manner; the current flow directions of the N zigzag coils and the placement directions of the N permanent magnets are set based on a Barker code sequence, and when the same sinusoidal pulse string current signals are introduced into the N zigzag coils, ultrasonic waves generated in a piece to be tested correspond to ultrasonic waves generated when Barker code excitation signals are introduced; wherein the value of N is taken as the value of the Barker code sequence length. Through the special design, the Barker code pulse compression technology can be realized on the premise that the excitation signal is a traditional sine pulse train. The parameter limitation of the Barker code excitation signal duration on the power amplifier can be reduced, and the duration and the detection blind area of the initial wave and the electromagnetic crosstalk signal of the initial wave can be reduced.
Description
Technical Field
The invention relates to the field of ultrasonic detection, in particular to an electromagnetic ultrasonic Lamb wave transducer and an online detection system and method.
Background
The large-size plate metal member is widely applied to multiple fields such as buildings, ships and the like, defects such as metal damage cracks, corrosion and the like are the most common failure modes in the service process of the member, and the corrosion defects can seriously influence the safety and reliability of the service of the metal member. The steam pipeline is in a high-temperature and high-pressure environment for a long time, the pipe wall is thinned under the corrosion action, and even cracks occur to cause explosion accidents; the steel sheet pile under the ocean is easy to corrode and break; the structural steel plate of the bridge generates corrosion defects under the action of factors such as rain wash and the like, and the service life is ended in advance.
The electromagnetic ultrasonic transducer (EMAT) excites and receives ultrasonic waves in a sample in an electromagnetic coupling mode, and the EMAT is suitable for detection occasions such as high temperature, high speed, on-line, rough surface or coating due to the non-contact characteristic of the EMAT, and the like, but the technology is greatly limited from being widely applied in engineering due to the defects of low transduction efficiency, easy environmental electromagnetic interference and the like. The pulse compression technology is applied to EMAT detection, and has great significance for improving the signal-to-noise ratio (SNR) and the spatial resolution of the EMAT.
The ultrasonic detection range is related to the emitted ultrasonic energy, and the larger the ultrasonic energy is, the larger the detection range is. In practical detection, when short pulse excitation is adopted, due to the limitations of the limit output voltage of a power amplification circuit, the withstand voltage heating of a sensor and the like, the purpose of enhancing the transmitted ultrasonic energy is difficult to achieve by increasing the excitation voltage. The pulse compression technology takes a pulse signal with large time width and low amplitude as an excitation signal to excite ultrasonic waves, so that the ultrasonic waves have enough energy to ensure the detection distance; and the received ultrasonic signals are subjected to matched filtering and side suppression, and are compressed into ultrasonic signals with small time width and high amplitude, so that wave packet overlapping is avoided, and the EMAT transduction efficiency and the spatial resolution are improved.
Barker code is a single-emission binary phase coding compression technology, adopts a matched filtering mode to carry out pulse compression, and has lower distance side lobe. The compression ratio of the Barker code pulse compression algorithm is proportional to the sequence length, and the length of the Barker code sequence which is commonly used at present is 2, 3, 4, 5, 7, 11 and 13 bits.
As shown in fig. 7, a sinusoidal pulse train is used as a symbol of the Barker code sequence as an excitation signal of the EMAT. The excitation signal u [ m ] and the symbol sequence v [ s ] can be expressed as:
Wherein N represents the code length of Barker code, M represents the time width of sub-pulse, and TcRepresenting the duration of the symbol, Ck± 1 represents the Barker code coding sequence.
The Barker code signal u [ m ] is loaded to an EMAT exciting end, the ultrasonic signal received by the EMAT is s [ m ], and the relationship between the Barker code signal u [ m ] and the ultrasonic signal s [ m ] is as follows:
in the formula, yi[m]Is a pulse compressed signal.
Fig. 7(b) and 7(c) show ultrasonic signals before and after pulse compression. The side lobe suppression is performed on the signal after the pulse compression (see fig. 7(c)), and the obtained signal is shown in fig. 7 (d). After the side suppression, the peak side lobe level (PSL) increased from 20.6dB to 43.0 dB.
The SNR of the ultrasonic echo is increased along with the increase of the duration time of a Barker code signal, but the Barker code signal cannot be separated from an initial wave and an electromagnetic crosstalk signal of the initial wave due to the overlong duration time of the Barker code signal, so that a defect wave packet is partially submerged in the initial electromagnetic crosstalk, and the short-distance detection capability of the defect wave packet is influenced. The duration of the Barker code excitation signal is limited by the device performance (such as duty ratio, single maximum pulse width and the like) of a pulse power amplifier and the like, and the device performance is unstable and even the functionality is damaged due to the overlong Barker code excitation current.
Disclosure of Invention
The invention provides an electromagnetic ultrasonic Lamb wave transducer, an online detection system and an online detection method, and aims to solve the problem that the performance of equipment such as a pulse power amplifier limits the duration of a Barker code excitation signal.
In a first aspect, an electromagnetic ultrasonic Lamb wave transducer is provided, which comprises a shell, and N permanent magnets and N zigzag coils which are arranged in the shell;
the N permanent magnets are arranged above the N zigzag coils in a one-to-one correspondence manner, and are arranged in a single row, and the N zigzag coils are connected in a parallel connection manner;
the current flow directions of the N zigzag coils and the placement directions of the N permanent magnets are set based on a Barker code sequence, and when the same sinusoidal pulse train current signals are introduced into the N zigzag coils, ultrasonic waves generated in a piece to be tested correspond to ultrasonic waves generated when Barker code excitation signals are introduced; wherein the value of N is taken as the value of the Barker code sequence length.
After the same sinusoidal pulse string current signals are introduced into the N zigzag coils, high-frequency eddy currents with the same frequency and opposite directions are generated in the piece to be detected, and surface particles of the piece to be detected periodically vibrate under the action of a bias magnetic field, so that ultrasonic waves are excited and propagate along the length direction of the piece to be detected. Because the current flow directions of the N zigzag coils and the placement directions of the N permanent magnets are set based on the Barker code sequence, ultrasonic waves can be generated in the piece to be tested, and the wave packet form of the ultrasonic waves is the same as the ultrasonic waves generated when the Barker code excitation signal is introduced. Through the special design, the Barker code pulse compression technology can be realized on the premise that the excitation signal is a traditional sine pulse train. The Lamb wave transducer designed according to the Barker code pulse compression technology can reduce the limitation of the duration time of a Barker code excitation signal on parameters (such as duty ratio, single maximum pulse width and the like) of a power amplifier, can reduce the duration time of a starting wave signal, particularly reduce the quick recovery time caused by electromagnetic crosstalk, and can effectively reduce the influence of a detection blind area on short-distance defect detection.
Further, the value range of N is {2,3,4,5,7,11,13 };
when N takes 2, the Barker code sequence is { +1, +1} or { +1, -1 };
when N takes 3, the Barker code sequence is { +1, +1, -1 };
when N takes 4, the Barker code sequence is { +1, +1, +1, -1} or { +1, +1, -1, +1 };
when N takes 5, the Barker code sequence is { +1, +1, +1, -1, +1 };
when N takes 7, the Barker code sequence is { +1, +1, +1, -1, -1, +1, -1 };
when N is 11, the Barker code sequence is { +1, +1, +1, -1, -1, +1, -1, -1, +1, -1 };
when N is 13, the Barker code sequence is { +1, +1, +1, +1, +1, -1, -1, +1, +1, -1, +1 }.
Furthermore, each zigzag coil and the corresponding permanent magnet above the zigzag coil form an EMAT;
among the N EMATs, the EMAT corresponding to the position of +1 in the Barker code sequence and the EMAT corresponding to the position of-1 in the Barker code sequence generate Lorentz forces in opposite directions in the piece to be detected when the same sinusoidal pulse string current signal is introduced.
Furthermore, the N permanent magnets are arranged periodically, and the magnetizing directions of the two adjacent permanent magnets are opposite; when the zigzag coil corresponds to the position of +1 in the Barker code sequence, the current flow direction of the zigzag coil is a first direction, and when the zigzag coil corresponds to the position of-1 in the Barker code sequence, the current flow direction of the zigzag coil is a second direction, wherein the first direction is opposite to the second direction; when the zigzag coil corresponds to the position of +1 in the Barker code sequence, the current flow direction of the zigzag coil is the second direction, and when the zigzag coil corresponds to the position of-1 in the Barker code sequence, the current flow direction of the zigzag coil is the first direction, and the first magnetizing method and the second magnetizing method are opposite; or the like, or, alternatively,
One or more permanent magnets and corresponding zigzag coils in the structure are selected at will, and the magnetizing direction of the selected permanent magnets and the current flow direction of the corresponding zigzag coils are changed into opposite directions.
Furthermore, the zigzag coil is prepared by one preparation mode of manufacturing a PCB, manufacturing a flexible PCB and winding an enameled wire on a framework.
Further, each turn of the meander coil is comprised of a plurality of wires.
Further, the casing includes that shell, carbon steel support, BNC connect, the carbon steel support install in inside the shell, N permanent magnet install in on the carbon steel support, N meander line circle is set up in N permanent magnet below, BNC connect set up in on the shell, N meander line pass through connecting wire with BNC articulate.
Further, still include and set up in a plurality of antifriction bearing of shell below.
In a second aspect, an online detection system is provided, which comprises the electromagnetic ultrasonic Lamb wave transducer as described above, as well as an upper computer, a signal generator, a pulse power amplifier, an excitation end impedance matching circuit, an EMAT receiving probe, a receiving end impedance matching circuit, a pre-filter amplifier, an adjustable gain amplifier and an AD data acquisition card;
The signal generator, the pulse power amplifier, the excitation end impedance matching circuit and the electromagnetic ultrasonic Lamb wave transducer are sequentially connected; the EMAT receiving probe, the receiving end impedance matching circuit, the pre-filter amplifier, the adjustable gain amplifier, the AD data acquisition card and the upper computer are sequentially connected.
The signal generator generates a sinusoidal pulse string current signal, the pulse power amplifier amplifies the sinusoidal pulse string current signal, the sinusoidal pulse string current signal is subjected to impedance matching through the impedance matching circuit of the excitation end and then enters the electromagnetic ultrasonic Lamb wave transducer, ultrasonic waves are generated in the piece to be detected, and the wave packet form of the ultrasonic waves is the same as that of the ultrasonic waves generated when a Barker code signal is introduced; the EMAT receiving probe receives ultrasonic echo signals, after impedance matching is carried out through a receiving end impedance matching circuit, filtering and amplification are carried out through a pre-filter amplifier and an adjustable gain amplifier, analog-to-digital conversion is carried out through an AD data acquisition card and then the signals are input into an upper computer, the upper computer processes the received ultrasonic echo signals, ultrasonic signals after pulse compression are obtained, side lobe suppression is carried out, then defect echo signals are analyzed, and detection results can be obtained.
In a third aspect, an on-line detection method is provided, in which the electromagnetic ultrasonic Lamb wave transducer is used for detection, and the steps include:
Placing the electromagnetic ultrasonic Lamb wave transducer on the surface of a piece to be tested;
a sinusoidal pulse train current signal is led into the electromagnetic ultrasonic Lamb wave transducer;
adopting an EMAT probe to receive an ultrasonic signal;
filtering and amplifying the received ultrasonic signals, and sending the ultrasonic signals into an upper computer after analog-to-digital conversion;
the upper computer performs convolution operation on the received ultrasonic signal and a Barker code excitation standard reference signal to obtain a pulse-compressed ultrasonic signal and performs side lobe suppression;
analyzing and processing the amplitude and the arrival time of a defect ultrasonic echo signal in the signal after sidelobe suppression, calculating to obtain the position of a defect through d-v/f, and comparing the amplitude of the defect ultrasonic echo signal with an artificially preset defect ultrasonic echo signal to obtain the equivalent of the defect; wherein d represents the distance between the defect and the electromagnetic ultrasonic Lamb wave transducer, v represents the Lamb wave velocity, and f represents the Lamb wave frequency.
Advantageous effects
The invention provides an electromagnetic ultrasonic Lamb wave transducer and an online detection system and method, wherein the current flow directions of N zigzag coils and the placement directions of N permanent magnets are set based on a Barker code sequence, so that ultrasonic waves can be generated in a to-be-detected piece after the same sinusoidal pulse string current signals are introduced into the N zigzag coils, and the wave packet form of the ultrasonic waves is the same as the ultrasonic waves generated when Barker code excitation signals are introduced. Through the special design, the Barker code pulse compression technology can be realized on the premise that the excitation signal is a traditional sine pulse train. The Lamb wave transducer designed according to the Barker code pulse compression technology can reduce the limitation of the duration time of a Barker code excitation signal on parameters (such as duty ratio, single maximum pulse width and the like) of a power amplifier, can reduce the duration time of an initial wave signal at the same time, particularly reduce the quick recovery time caused by electromagnetic crosstalk, can effectively reduce the influence of a detection blind area on short-distance defect detection, improves the short-distance detection capability, the defect detection sensitivity and the resolution ratio, and is suitable for online quick scanning of the surface and internal defects of a large-sized plate metal component.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a schematic structural diagram of a Barker code electromagnetic ultrasonic Lamb transducer with a sequence length of 13 bits according to an embodiment of the present invention;
FIG. 2 is an EMAT transduction principle provided by an embodiment of the present invention;
FIG. 3 is a current flow (phase) control of 13 meander coils of the electromagnetic ultrasonic Lamb wave transducer provided in FIG. 1;
FIG. 4 is a schematic diagram of the configuration of the electromagnetic ultrasonic Lamb wave transducer provided in FIG. 1;
fig. 5 is a schematic diagram of an arrangement of an electromagnetic ultrasonic Lamb wave transducer and an EMAT receiving probe and a meander coil structure according to an embodiment of the invention;
FIG. 6 is a schematic diagram of the online detection system provided by the embodiment of the invention;
fig. 7 shows a 13-bit Barker code signal pulse compression and sidelobe suppression process provided by an embodiment of the present invention;
Fig. 8(a) is a 13-bit Barker code excitation signal provided by an embodiment of the invention; FIG. 8(b) is a sinusoidal pulse train current signal provided by an embodiment of the present invention;
fig. 9 is a processing procedure for exciting and receiving an ultrasonic echo signal by using a sinusoidal pulse train current signal according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It should be apparent that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", "center", "longitudinal", "lateral", "vertical", "horizontal", and the like indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience of description and simplicity of description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.
Example 1
As shown in fig. 1 to fig. 5, the present embodiment provides an electromagnetic ultrasonic Lamb wave transducer, which mainly combines a meander coil and a vertically magnetized permanent magnet based on a lorentz force mechanism, and is designed as a transducer designed according to a Barker code pulse compression technology, and includes a housing, and N permanent magnets 1 and N meander coils 2 disposed in the housing;
the N permanent magnets 1 are arranged above the N zigzag coils 2 in a one-to-one correspondence manner, the width of each permanent magnet 1 is the same as that of the corresponding zigzag coil 2, the N permanent magnets 1 are arranged in a single row, and the N zigzag coils 2 are connected in parallel;
the current flow directions of the N zigzag coils 2 and the placement directions of the N permanent magnets 1 are set based on a Barker code sequence, and when the same sinusoidal pulse train current signals are introduced into the N zigzag coils 2, ultrasonic waves generated in a piece to be tested correspond to ultrasonic waves generated when Barker code excitation signals are introduced; wherein the value of N is taken as the value of the Barker code sequence length.
After the same sinusoidal pulse string current signals are introduced into the N zigzag coils 2, high-frequency eddy currents with the same frequency and opposite directions are generated in the piece to be detected, and surface particles of the piece to be detected periodically vibrate under the action of a Lorentz force under the action of a bias magnetic field, so that ultrasonic waves are excited and propagate along the length direction of the piece to be detected. Because the current flow directions of the N zigzag coils 2 and the placing directions of the N permanent magnets 1 are set based on the Barker code sequence, ultrasonic waves can be generated in the piece to be tested, and the wave packet form of the ultrasonic waves is the same as that of the ultrasonic waves generated when the Barker code excitation signal is introduced. Through the special design, the Barker code pulse compression technology can be realized on the premise that the excitation signal is a traditional sine pulse train. The Lamb wave transducer designed according to the Barker code pulse compression technology can reduce the limitation of the duration time of a Barker code excitation signal on parameters (such as duty ratio, single maximum pulse width and the like) of a power amplifier, can reduce the duration time of an initial wave signal, particularly reduce the quick recovery time caused by electromagnetic crosstalk, and can effectively reduce the influence of a detection blind area on short-distance defect detection.
In specific implementation, the value range of N is {2,3,4,5,7,11,13 };
when N takes 2, the Barker code sequence is { +1, +1} or { +1, -1 };
when N takes 3, the Barker code sequence is { +1, +1, -1 };
when N takes 4, the Barker code sequence is { +1, +1, +1, -1} or { +1, +1, -1, +1 };
when N takes 5, the Barker code sequence is { +1, +1, +1, -1, +1 };
when N takes 7, the Barker code sequence is { +1, +1, +1, -1, -1, +1, -1 };
when N is 11, the Barker code sequence is { +1, +1, +1, -1, -1, +1, -1, -1, +1, -1 };
when N is 13, the Barker code sequence is { +1, +1, +1, +1, +1, -1, -1, +1, +1, -1, +1 }.
In this embodiment, this scheme will be described by taking N as 13 as an example.
Each zigzag coil 2 and the corresponding permanent magnet 1 above the zigzag coil form an EMAT; among the N EMATs, the EMAT corresponding to the position of +1 in the Barker code sequence and the EMAT corresponding to the position of-1 in the Barker code sequence generate Lorentz forces in opposite directions in the piece to be detected when the same sinusoidal pulse string current signal is introduced.
As shown in fig. 3 and 4, in order to achieve the above purpose, in this embodiment, the N permanent magnets 1 are arranged periodically, and the magnetizing directions of two adjacent permanent magnets 1 are opposite; the current flow of the zigzag coil 2 corresponding to the permanent magnet 1 arranged in the first magnetizing direction is in a first direction when the zigzag coil corresponds to the position of +1 in the Barker code sequence, and is in a second direction when the zigzag coil corresponds to the position of-1 in the Barker code sequence, wherein the first direction is opposite to the second direction; and the current flow of the zigzag coil 2 corresponding to the permanent magnet 1 arranged in the second magnetizing direction is in the second direction when the zigzag coil corresponds to the position of +1 in the Barker code sequence, and is in the first direction when the zigzag coil corresponds to the position of-1 in the Barker code sequence, and the first magnetizing method and the second magnetizing method are opposite. All the zigzag coils 2 are connected in parallel, so that the equivalent impedance of the excitation EMAT can be reduced.
Certainly, in other embodiments, one or more permanent magnets 1 and the corresponding meandering coils 2 in the above structure may be arbitrarily selected, and the magnetizing direction of the selected permanent magnet 1 and the current flow direction of the corresponding meandering coil 2 are changed to opposite directions, so that, in the N EMATs, an EMAT corresponding to a position of +1 in the Barker code sequence and an EMAT corresponding to a position of-1 in the Barker code sequence generate lorentz forces in opposite directions in the to-be-measured object when the same sinusoidal pulse string current signal is input.
When the method is implemented, the zigzag coil 2 is prepared through one preparation mode of manufacturing a PCB, manufacturing a flexible PCB and winding an enameled wire on a framework. In this embodiment, the meander coil 2 is selected as a PCB coil composed of four split conductors per turn, a single conductor is 0.15mm wide × 0.035mm high, a distance between adjacent single conductors is 0.3mm, four split conductors are 1 turn, a distance between 2 turns of the meander coil is related to an ultrasonic mode, a frequency and a sample thickness, if a size of a single permanent magnet 1 is 9mm high × 14mm wide × 24mm long, when a Lamb wave a0 mode is adopted, when an excitation frequency is 1MHz, an intersection point of a working line at a distance between 2 turns of the meander coil and a Lamb wave phase velocity dispersion curve with a thickness of 5.6mm can be obtained by calculating: the turn pitch of the zigzag coil is 1.5mm, and the number of 2 turns of the zigzag coil can be 6-14. Of course, the number of turns, the turn-to-turn distance, the specification of a single wire, the distance between adjacent wires and the like of the zigzag coil 2 can be selected according to actual detection requirements.
In this embodiment, the housing includes a shell 3, a carbon steel bracket 4, and a BNC connector 5, where the carbon steel bracket 4 is installed inside the shell 3 through screws 8, the N permanent magnets 1 are installed on the carbon steel bracket 4, the N meandering coils 2 are arranged below the N permanent magnets 1, the BNC connector 5 is arranged on the shell 3, and the N meandering coils 2 are connected to the BNC connector 5 through connecting wires 6; a plurality of rolling bearings 7 are provided below the housing 3.
In other embodiments, when N takes other values, the numbers of the permanent magnets 1 and the meandering coils 2 may be changed according to the above description, and the magnetizing direction of the permanent magnet 1 and the current flow direction of the meandering coil 2 at the corresponding position may be adjusted according to the corresponding Barker code sequence, which is not described herein again.
Example 2
As shown in fig. 5 and fig. 6, the present embodiment provides an online detection system, which includes the electromagnetic ultrasonic Lamb transducer 14, an upper computer 21, a signal generator 11, a pulse power amplifier 12, an excitation end impedance matching circuit 13, an EMAT receiving probe 16, a receiving end impedance matching circuit 17, a pre-filter amplifier 18, an adjustable gain amplifier 19, and an AD data acquisition card 20;
The signal generator 11, the pulse power amplifier 12, the excitation end impedance matching circuit 13 and the electromagnetic ultrasonic Lamb wave transducer 14 are sequentially connected; the EMAT receiving probe 16, the receiving end impedance matching circuit 17, the pre-filter amplifier 18, the adjustable gain amplifier 19, the AD data acquisition card 20 and the upper computer 21 are connected in sequence.
The EMAT transduction principle is shown in fig. 2. The permanent magnet 1 is arranged on the zigzag coil 2, and the zigzag coil 2 is electrified with high-frequency high-power excitation current IcGenerating induced eddy current J with opposite direction and same frequency on the surface of the object 15e. The induced eddy currents generated by the adjacent wires of the zigzag coil 2 are opposite in direction and bias in a static magnetic field BsAnd an alternating magnetic field BdUnder the action of the force, Lorentz force f in opposite direction is generatedL。fLThe particles are driven to vibrate, and ultrasonic waves are generated on the surface layer of the piece to be measured.
In this embodiment, the signal generator 11 inputs a sinusoidal pulse train (5 cycles-20 cycles) with a frequency of 1MHz to the pulse power amplifier 12, as shown in fig. 8(b), and after power amplification, the sinusoidal pulse train is impedance-matched by the excitation-end impedance matching circuit 13 and then enters the meander coil 2 of the electromagnetic ultrasonic Lamb transducer 14; as shown in fig. 2, after the sinusoidal pulse train current is introduced into the meandering coil 2, an induced eddy current is generated on the surface of the device under test 15, the induced eddy current generates a lorentz force under the action of the bias magnetic field provided by the permanent magnet 1, and after N EMATs (one permanent magnet 1 and the corresponding meandering coil 2) are combined, an ultrasonic wave similar to a Barker code signal (as shown in fig. 8 (a)) is generated. In this embodiment, the EMAT receiving probe 16 (which uses a single EMAT, that is, a permanent magnet 1 and a corresponding meander coil 2) receives an ultrasonic echo signal, and according to the inverse lorentz force effect, the surface of the device 15 to be measured vibrates to cause the change of its surrounding magnetic field, thereby generating an induced voltage signal in the meander coil 2, after the EMAT receiving probe 16 receives the ultrasonic echo signal, the ultrasonic echo signal is subjected to impedance matching by the receiving end impedance matching circuit 17, then filtered and amplified by the pre-filter amplifier 18 and the adjustable gain amplifier 19, and then subjected to analog-to-digital conversion by the AD data acquisition card 20, and then input into the upper computer 21, and the upper computer 21 processes the received ultrasonic echo signal by LabVIEW software, so as to obtain an ultrasonic signal after pulse compression, and perform side lobe suppression, and then analyzes the defect echo signal, thereby obtaining a detection result.
Example 3
The embodiment provides an online detection method, which performs detection by using the electromagnetic ultrasonic Lamb transducer, and comprises the following steps:
placing the electromagnetic ultrasonic Lamb wave transducer on the surface of a piece to be tested;
introducing a sinusoidal pulse train current signal into the electromagnetic ultrasonic Lamb wave transducer;
adopting an EMAT receiving probe to receive an ultrasonic signal;
filtering and amplifying the received ultrasonic signals, and sending the ultrasonic signals into an upper computer after analog-to-digital conversion;
the upper computer performs convolution operation on the received ultrasonic signal and a Barker code excitation standard reference signal to obtain a pulse-compressed ultrasonic signal and performs side lobe suppression;
analyzing and processing the amplitude and the arrival time of a defect ultrasonic echo signal in the signal after sidelobe suppression, calculating to obtain the position of a defect through d-v/f, and comparing the amplitude of the defect ultrasonic echo signal with an artificially preset defect ultrasonic echo signal to obtain the equivalent of the defect; wherein d represents the distance between the defect and the electromagnetic ultrasonic Lamb wave transducer, v represents the Lamb wave velocity, and f represents the Lamb frequency. .
As shown in fig. 9, fig. 9(a) shows the input sinusoidal burst current signal, fig. 9(b) shows the ultrasonic echo signal received by the EMAT receiving probe, fig. 9(c) shows the ultrasonic signal after pulse compression, and fig. 9(d) shows the ultrasonic signal after side lobe suppression, and the peak side lobe level (PSL) is increased from 20.0dB to 42.7dB after side-lobe suppression by .
It is understood that the same or similar parts in the above embodiments may be mutually referred to, and the same or similar contents in other embodiments may be referred to for the contents which are not described in detail in some embodiments.
In the existing scheme, a Barker code coding compression technology is rarely combined with an electromagnetic ultrasonic technology, and a pulse compression technology is introduced into an electromagnetic ultrasonic surface wave transducer, so that the signal-to-noise ratio and the resolution of a detected echo can be greatly improved, but the Barker code excitation signal has overlong duration, so that the requirements on the performances (such as duty ratio, single maximum pulse width and the like) of equipment such as a pulse power amplifier and the like are high, even a power amplifier circuit can be damaged to a certain extent, and the duration of an initial wave and the electromagnetic crosstalk time caused by the initial wave are longer, so that the short-distance defect detection capability is influenced.
Barker codes are binary coding sequences transmitted once, pulse compression is generally carried out in a matched filtering mode, because the matched filtering can obtain lower distance side lobes, the transduction efficiency of the EMAT is 20dB-40dB lower than that of a conventional piezoelectric transducer, the signal-to-noise ratio and the resolution of a received signal can be effectively improved by applying a pulse compression technology to the EMAT, and the detection capability and the application range of the EMAT can be widened.
The invention adopts N single EMATs to combine a novel EMAT configuration form by the Barker code sequence principle, the excitation signal adopts a single frequency pulse train, namely, the ultrasonic signal which can implement the Barker code pulse compression technology can be excited, the duration of the initial wave and the electromagnetic crosstalk signal thereof can be reduced through the ultrasonic signal received by the single EMAT, the detection blind area is reduced, the requirements on performance parameters such as the duty ratio of a pulse power amplifier, the maximum pulse width of single excitation and the like are reduced, the ultrasonic signal with longer duration and the Barker code sequence characteristic can be excited, and the signal to noise ratio and the spatial resolution of the detected echo signal can be effectively improved.
The invention designs an electromagnetic ultrasonic guided wave transducer which is designed based on a Barker code phase coding pulse compression principle and on the basis of a Barker code pulse compression technology, and an online detection system and method, wherein an excitation signal is a single-frequency sinusoidal pulse train, surface waves or Lamb waves which can implement the pulse compression technology can be excited, and the system and the method are suitable for online rapid scanning of defects on the surface and the inside of a large-size plate metal component.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (9)
1. An electromagnetic ultrasonic Lamb wave transducer is characterized by comprising a shell, N permanent magnets and N zigzag coils, wherein the N permanent magnets and the N zigzag coils are arranged in the shell;
the N permanent magnets are arranged above the N zigzag coils in a one-to-one correspondence manner, the N permanent magnets are arranged in a single row, and the N zigzag coils are connected in parallel;
the current flow directions of the N zigzag coils and the placement directions of the N permanent magnets are set based on a Barker code sequence, and the current flow directions and the placement directions of the N zigzag coils are used for enabling ultrasonic waves generated in a piece to be tested to correspond to ultrasonic waves generated when a Barker code excitation signal is introduced into the piece to be tested when the same sinusoidal pulse string current signal is introduced into the N zigzag coils; wherein the value of N is the length value of the Barker code sequence;
the N permanent magnets are arranged periodically, and the magnetizing directions of the two adjacent permanent magnets are opposite; when the zigzag coil corresponds to the position of +1 in the Barker code sequence, the current flow direction of the zigzag coil is a first direction, and when the zigzag coil corresponds to the position of-1 in the Barker code sequence, the current flow direction of the zigzag coil is a second direction, wherein the first direction is opposite to the second direction; when the zigzag coil corresponds to the position of +1 in the Barker code sequence, the current flow direction of the zigzag coil is the second direction, and when the zigzag coil corresponds to the position of-1 in the Barker code sequence, the current flow direction of the zigzag coil is the first direction, and the first magnetizing method and the second magnetizing method are opposite; or the like, or a combination thereof,
One or more permanent magnets and the corresponding zigzag coils are selected at will, and the magnetizing directions of the selected permanent magnets and the current flow directions of the corresponding zigzag coils are changed into opposite directions.
2. The electromagnetic ultrasonic Lamb wave transducer according to claim 1, wherein the value range of N is {2,3,4,5,7,11,13 };
when N takes 2, the Barker code sequence is { +1, +1} or { +1, -1 };
when N takes 3, the Barker code sequence is { +1, +1, -1 };
when N takes 4, the Barker code sequence is { +1, +1, +1, -1} or { +1, +1, -1, +1 };
when N takes 5, the Barker code sequence is { +1, +1, +1, -1, +1 };
when N takes 7, the Barker code sequence is { +1, +1, +1, -1, -1, +1, -1 };
when N is 11, the Barker code sequence is { +1, +1, +1, -1, -1, +1, -1, -1, +1, -1 };
when N is 13, the Barker code sequence is { +1, +1, +1, +1, +1, -1, -1, +1, +1, -1, +1 }.
3. The electromagnetic ultrasonic Lamb wave transducer according to claim 2, wherein each meander coil and the corresponding permanent magnet above it form an EMAT;
among the N EMATs, the EMAT corresponding to the position of +1 in the Barker code sequence and the EMAT corresponding to the position of-1 in the Barker code sequence generate Lorentz forces in opposite directions in the piece to be detected when the same sinusoidal pulse string current signal is introduced.
4. An electromagnetic ultrasonic Lamb wave transducer according to any one of claims 1 to 3, wherein the meander coil is prepared by one of PCB (printed circuit board), flexible PCB and winding enameled wire on a skeleton.
5. The electromagnetic ultrasonic Lamb wave transducer according to claim 4, wherein each turn of the meander coil is comprised of a plurality of wires.
6. The electromagnetic ultrasonic Lamb wave transducer according to any one of claims 1 to 3, wherein the housing comprises a shell, a carbon steel bracket mounted inside the shell, N permanent magnets mounted on the carbon steel bracket, N meander coils disposed below the N permanent magnets, and a BNC connector disposed on the shell, wherein the N meander coils are connected to the BNC connector through connecting wires.
7. The electromagnetic ultrasonic Lamb wave transducer according to claim 6, further comprising a plurality of rolling bearings disposed below the housing.
8. An on-line detection system, which comprises the electromagnetic ultrasonic Lamb transducer according to any one of claims 1 to 7, and an upper computer, a signal generator, a pulse power amplifier, an excitation end impedance matching circuit, an EMAT receiving probe, a receiving end impedance matching circuit, a pre-filter amplifier, an adjustable gain amplifier and an AD data acquisition card;
The signal generator, the pulse power amplifier, the excitation end impedance matching circuit and the electromagnetic ultrasonic Lamb wave transducer are sequentially connected; the EMAT receiving probe, the receiving end impedance matching circuit, the pre-filter amplifier, the adjustable gain amplifier, the AD data acquisition card and the upper computer are sequentially connected.
9. An on-line inspection method, wherein the inspection is performed by using the electromagnetic ultrasonic Lamb transducer according to any one of claims 1 to 7, and the steps comprise:
placing the electromagnetic ultrasonic Lamb wave transducer on the surface of a piece to be tested;
introducing a sinusoidal pulse train current signal into the electromagnetic ultrasonic Lamb wave transducer;
adopting an EMAT receiving probe to receive an ultrasonic signal;
filtering and amplifying the received ultrasonic signals, and sending the ultrasonic signals into an upper computer after analog-to-digital conversion;
the upper computer performs convolution operation on the received ultrasonic signal and a Barker code excitation standard reference signal to obtain a pulse-compressed ultrasonic signal and performs side lobe suppression;
analyzing and processing the amplitude and the arrival time of a defect ultrasonic echo signal in the signal after sidelobe suppression, calculating to obtain the position of a defect through d-v/f, and comparing the amplitude of the defect ultrasonic echo signal with an artificially preset defect ultrasonic echo signal to obtain the equivalent of the defect; wherein d represents the distance between the defect and the electromagnetic ultrasonic Lamb wave transducer, v represents the Lamb wave velocity, and f represents the Lamb wave frequency.
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