CN106694346B - Low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer and working method thereof - Google Patents
Low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer and working method thereof Download PDFInfo
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- CN106694346B CN106694346B CN201611237906.0A CN201611237906A CN106694346B CN 106694346 B CN106694346 B CN 106694346B CN 201611237906 A CN201611237906 A CN 201611237906A CN 106694346 B CN106694346 B CN 106694346B
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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
- B06B1/04—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with electromagnetism
- B06B1/045—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with electromagnetism using vibrating magnet, armature or coil system
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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
- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
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Abstract
The invention discloses a low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer and a working method thereof, wherein the transducer consists of a to-be-tested piece, a printed circuit board, a transmitting coil, a permanent magnet and a receiving coil, the transmitting coil and the receiving coil are arranged on different layers of the same printed circuit board and are alternately arranged, the permanent magnet is arranged on the transmitting coil and the receiving coil, the transmitting coil and the receiving coil share one permanent magnet to provide a bias magnetic field, the transmitting coil and the receiving coil are arranged on the to-be-tested piece, the transmitting coil is connected with a power amplifier, and the receiving coil is connected with a signal conditioning circuit. The invention increases the length of the coil wire by changing the structural form of the transducer coil, and changes the shape of the conducting wire inflection part of the adjacent half wavelength of the coil, so that the eddy current generated by the inflection part of the side surface of the coil is not influenced by the static bias magnetic field of the permanent magnet, thereby reducing the ultrasonic clutter interference generated by the side surface coil and improving the signal-to-noise ratio.
Description
Technical Field
The invention relates to an electromagnetic ultrasonic nondestructive testing technology, in particular to a low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer and a working method thereof.
Background
An Electromagnetic acoustic transducer (EMAT) is a device that excites and receives ultrasonic waves. The device does not need an acoustic coupling agent, has a simple structure, can conveniently excite ultrasonic waves in various modes, can realize non-contact measurement, and is widely concerned by researchers. The electromagnetic ultrasonic transducer mainly comprises 3 parts: transmitting and receiving coils, a magnet and a piece to be tested. Because the energy conversion efficiency of the electromagnetic ultrasonic transducer is low, the excited ultrasonic signal is extremely weak, the signal-to-noise ratio of the received signal is low, the signal is easily interfered, the erroneous judgment is easily generated during measurement, and the interference signal is taken as a defect signal. The inflection coil is used widely as ultrasonic transducer's excitation and receiving coil, in the manufacturing process, all adopts the right angle to walk the line between the coil wire of adjacent half-wave long distance, and the right angle is walked the line and is made the line width of transmission line change, causes the discontinuity of impedance, and the right angle is walked the influence that has three aspects to the signal: firstly, the corner can be equivalent to a capacitive load on a transmission line, and the rise time is slowed down; secondly, impedance discontinuity can cause signal reflection; and thirdly, the EMI generated by the right-angle tip enables eddy current generated on a piece to be tested to be unevenly distributed, so that the intensity distribution is uneven when the piece is ultrasonically excited, and the detection effect is influenced. On the other hand, in the existing electromagnetic ultrasonic transducer using the meander coil as the excitation coil, the length and width of the magnet are both greater than those of the coil, and since the length of the magnet is greater than those of the wires, the connection wires between the wires spaced by a half-wave long distance from the meander coil also cause the generation of ultrasonic waves in the test piece to be tested, when the transducer is used for both transmission and reception, the received signal will include the portion of ultrasonic signal, which becomes undesirable noise, and the influence of the noise is particularly obvious when the transducer is used for measuring a test piece with a small width.
Disclosure of Invention
The invention aims to provide an electromagnetic ultrasonic transducer which is provided with a single magnet, integrates receiving and transmitting, and is provided with a separate receiving coil and a separate transmitting coil and applied to narrow plate detection, and the influence of ultrasonic signal noise generated by a side coil on a measurement result is reduced.
The invention adopts the following technical scheme: a low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer comprises a to-be-tested piece, a printed circuit board, a transmitting coil, a permanent magnet and a receiving coil, wherein the transmitting coil and the receiving coil are arranged on different layers of the same printed circuit board and are alternately arranged on different layers, the permanent magnet is arranged on the transmitting coil and the receiving coil, the transmitting coil and the receiving coil share the permanent magnet to provide a bias magnetic field, the transmitting coil and the receiving coil are arranged on the to-be-tested piece, the transmitting coil is connected with an external power amplifier and used for generating ultrasonic waves inside the to-be-tested piece, and the receiving coil is connected with an external signal conditioning circuit and used for detecting ultrasonic vibration in the to-be-tested piece.
Further, the length L2 of the transmitting coil and the receiving coil is larger than the length L1 of the permanent magnet.
Further, the length L2 of the transmitting coil and the receiving coil is more than 1.2 times of the length L1 of the permanent magnet.
Further, the distance between the wires in the transmitting coil is a half wavelength of the ultrasonic wave to be excited.
Further, the areas of the respective cross sections of the wires in the transmitting coil are the same.
Further, the areas of the respective cross sections of the wires in the receiving coil are the same.
Further, the folding parts of the transmitting coil and the receiving coil between the adjacent half-wavelength wires are in a circular arc shape.
The invention also adopts the following technical scheme: the operation of the low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer comprises the following steps:
the method comprises the following steps: a signal generator connected with a power amplifier generates burst excitation signals, the excitation signals are applied to a transmitting coil after power amplification, the transmitting coil induces eddy currents on a to-be-tested piece, the eddy currents generate Lorentz force in the to-be-tested piece under the action of a static bias magnetic field generated by a permanent magnet, and the dynamic Lorentz force acts on the to-be-tested piece to generate ultrasonic waves;
step two: the ultrasonic wave is transmitted in the piece to be tested, the ultrasonic wave reflects an echo signal after encountering a defect or a boundary, when the echo passes below the receiving coil, particles inside the piece to be tested cut the permanent magnet to generate magnetic lines of force to generate current to form a dynamic electric field, the dynamic electric field generates a dynamic magnetic field, the receiving coil generates a dynamic current signal under the action of the dynamic magnetic field, and the dynamic current is conditioned by the signal conditioning circuit to be used for detecting the ultrasonic vibration in the piece to be tested.
The invention has the following beneficial effects: the low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer can achieve the following effects by changing the structural form of the coil of the transducer: the length of the exciting coil wire is increased, so that the eddy current generated by the folded part on the side surface of the coil reduces the influence of the static bias magnetic field of the permanent magnet, thereby reducing the ultrasonic clutter interference generated by the side coil and improving the signal-to-noise ratio; the transmitting coil and the receiving coil are designed on the same PCB, and leads of the transmitting coil and the receiving coil are overlapped and alternately arranged on different layers, so that the transmitting coil and the receiving coil can share the same permanent magnet to provide a bias magnetic field, when the transmitting coil transmits a signal, the receiving coil can sense an excitation signal and record the time of ultrasonic wave transmission, and the problems that the transmitting coil is firstly connected to an excitation power supply to transmit the signal, the coil is switched to a receiving circuit through a selector switch after the signal is transmitted, the original transmitting coil is used as the receiving coil, the transmitted signal has no transmission time point of a reference point on the time scale in the time domain, and the circuit switching brings delay errors are solved under the condition that one coil is used for transmitting and receiving the ultrasonic wave; the transmitting coil and the receiving coil adopt circular arc structures at the inflection positions between the leads spaced by half wavelength, so that the cross-sectional areas of the leads of the transmitting coil and the receiving coil are kept consistent, the impedance is continuous, and the noise caused by electromagnetic interference is reduced.
Drawings
Fig. 1 is a cross-sectional view of an electromagnetic ultrasonic transducer of the present invention.
Fig. 2(a) and 2(b) are graphs comparing the lengths of the transmitting coil and the receiving coil with the length of the permanent magnet.
Fig. 3(a) and 3(b) are diagrams comparing the structure of the conventional coil and the coil of the present invention.
Detailed description of the invention
The invention is further described below with reference to the accompanying drawings.
The invention relates to a low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer, which consists of a to-be-tested piece 1, a Printed Circuit Board (PCB) 2, a transmitting coil 3, a permanent magnet 4 and a receiving coil 5, wherein the transmitting coil 3 and the receiving coil 5 are arranged on different layers of the same multilayer PCB 2 and are alternately arranged on different layers, the permanent magnet 4 is arranged on the transmitting coil 3 and the receiving coil 5, the transmitting coil 3 and the receiving coil 5 share one permanent magnet 4 to provide a bias magnetic field, the transmitting coil 3 and the receiving coil 5 are arranged on the to-be-tested piece 1, the transmitting coil 3 is connected with an external power amplifier and used for generating ultrasonic waves inside the to-be-tested piece 1, and the receiving coil 5 is connected with an external signal conditioning circuit and used for detecting ultrasonic vibration in the to-be-tested piece 1.
The transmitting coil 3 and the receiving coil 5 are arranged on different layers of the same multilayer printed circuit board 2 and are alternately arranged on different layers, the transmitting coil 3 and the receiving coil 5 work independently, the same transducer can transmit ultrasonic waves and receive the ultrasonic waves, a complex switching control circuit is avoided when a single-coil transducer is used as both the transmitting coil and the receiving coil, and time difference caused by circuit switching is reduced. The length L2 of the transmitting coil 3 and the receiving coil 5 is larger than the length L1 of the permanent magnet 4, the length L2 of the transmitting coil 3 and the receiving coil 5 is more than 1.2 times of the length L1 of the permanent magnet 4, namely, the conducting wire is folded back outside the permanent magnet 4, the permanent magnet 4 is placed in the middle of the conducting wire, when the exciting current passes through the transmitting coil 3 and the receiving coil 5, the eddy current generated by the conducting wire folded back part between the transmitting coil 3 and the receiving coil 5 at the interval half-wavelength conducting wire is not influenced by the static bias magnetic field generated by the permanent magnet to generate ultrasonic noise.
The spacing distance between the wires of the transmitting coil 3 for generating ultrasonic waves is half wavelength of the ultrasonic waves, the inflection parts between the wires are connected by circular arcs with the same cross section as the width of the wires, the cross sections of the wires are the same, the cross sections of the wires are uniform, the impedance change of the wires caused by the change of the cross sections of the wires due to the right-angle inflection adopted for the connection between the wires apart from the half wavelength is avoided, meanwhile, the electromagnetic interference caused by the charge concentration at the inflection sharp corner is eliminated, and the noise is reduced.
During detection, a signal generator generates burst excitation signals, the excitation signals are applied to the transmitting coil 3 after power amplification, the transmitting coil 3 induces eddy currents on the to-be-tested piece 1, the eddy currents generate Lorentz forces in the to-be-tested piece 1 under the action of a static bias magnetic field generated by the permanent magnet 4, and dynamic Lorentz forces act on the to-be-tested piece 1 to generate ultrasonic waves; the ultrasonic wave propagates in the to-be-tested piece 1, an echo signal is reflected after encountering a defect or a boundary, when an echo passes below the transducer, particles in the to-be-tested piece 1 move to cut magnetic lines of force generated by the permanent magnet 4 to generate current to form a dynamic electric field, the dynamic electric field generates a dynamic magnetic field, the receiving coil 5 generates a dynamic current signal under the action of the dynamic magnetic field, and the dynamic current is conditioned by the signal conditioning circuit to serve as a basis for detection. As shown in fig. 2, the length L2 of the transmitting coil 3 and the receiving coil 5 of the electromagnetic ultrasonic transducer is more than 1.2 times of the length L1 of the permanent magnet 4, and the conducting wire is folded back outside the permanent magnet 4, so that useless interference noise generated by the folded back conducting wire under the action of a static bias magnetic field is avoided. Fig. 3(a) shows a conventional coil, in which a folded portion is a straight line, a sharp corner is formed at the folded portion, an interface area of a wire at the folded portion is increased, impedance of the wire is changed, and charge accumulation is generated at the sharp corner; and 3(b) is the coil designed by the invention, the lead at the return position is designed into a semicircular arc shape, the sectional area of the lead at the return position is unchanged, and the impedance of each cross section of the lead is consistent, so that the reflection of signals is reduced. Because the sharp corner at the inflection point is not provided, the electromagnetic interference caused by the accumulation of charges at the sharp corner due to the charge skin effect is avoided, and the signal-to-noise ratio of the electromagnetic ultrasonic transducer is improved.
The foregoing is only a preferred embodiment of this invention and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the invention and these modifications should also be considered as the protection scope of the invention.
Claims (6)
1. A low-noise transmitting-receiving integrated electromagnetic ultrasonic transducer is characterized in that: the device comprises a to-be-tested piece (1), a printed circuit board (2), a transmitting coil (3), a permanent magnet (4) and a receiving coil (5), wherein the transmitting coil (3) and the receiving coil (5) are arranged on different layers of the same printed circuit board (2) and are alternately arranged on different layers, the permanent magnet (4) is arranged on the transmitting coil (3) and the receiving coil (5), the transmitting coil (3) and the receiving coil (5) share the permanent magnet (4) to provide a bias magnetic field, and the receiving coil (5) induces an excitation signal while the transmitting coil (3) transmits the signal;
the test device comprises a transmitting coil (3) and a receiving coil (5), wherein the transmitting coil (3) and the receiving coil (5) are placed on a piece to be tested (1), the transmitting coil (3) is connected with an external power amplifier and used for generating ultrasonic waves inside the piece to be tested (1), and the receiving coil (5) is connected with an external signal conditioning circuit and used for detecting ultrasonic vibration in the piece to be tested (1); the length L2 of the transmitting coil (3) and the receiving coil (5) is more than 1.2 times of the length L1 of the permanent magnet (4).
2. The low noise, transmit-receive, integral electromagnetic ultrasonic transducer of claim 1, wherein: the distance between the wires in the transmitting coil (3) is half the wavelength of the ultrasonic wave to be excited.
3. The low noise, transmit-receive, integral electromagnetic ultrasonic transducer of claim 2, wherein: the areas of the cross sections of the wires in the transmitting coil (3) are the same.
4. The low noise, transmit-receive, integral electromagnetic ultrasonic transducer of claim 3, wherein: the areas of the cross sections of the wires in the receiving coil (5) are the same.
5. The low noise, transceiver-integrated electromagnetic ultrasound transducer of claim 3 or 4, wherein: the transmission coil (3) and the receiving coil (5) are in circular arc shapes at the inflection parts between the adjacent half-wavelength wires.
6. A method for operating a low noise transmit-receive integrated electromagnetic ultrasonic transducer according to any one of claims 1 to 5, comprising the steps of:
the method comprises the following steps: a signal generator connected with a power amplifier generates burst excitation signals, the excitation signals are applied to a transmitting coil (3) after being amplified by power, the transmitting coil (3) induces eddy currents on a piece to be tested (1), the eddy currents generate Lorentz force in the piece to be tested (1) under the action of a static bias magnetic field generated by a permanent magnet (4), and the dynamic Lorentz force acts on the piece to be tested (1) to generate ultrasonic waves;
step two: the ultrasonic wave is transmitted in the piece to be tested (1), an echo signal is reflected after encountering a defect or a boundary, when an echo passes below the receiving coil (5), particles inside the piece to be tested (1) move to cut the permanent magnet (4) to generate magnetic lines of force to generate current to form a dynamic electric field, the dynamic electric field generates a dynamic magnetic field, the receiving coil (5) generates a dynamic current signal under the action of the dynamic magnetic field, and the dynamic current is conditioned by the signal conditioning circuit to be used for detecting the ultrasonic vibration in the piece to be tested (1).
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| CN107084692A (en) * | 2017-06-30 | 2017-08-22 | 沈阳工业大学 | Electromagnetic acoustic shear wave thickness measuring transducer |
| CN107727742B (en) * | 2017-10-11 | 2020-07-31 | 哈尔滨工业大学 | Electromagnetic ultrasonic phased array system |
| CN110043810A (en) * | 2019-05-23 | 2019-07-23 | 山东省科学院激光研究所 | Detection method, the packaging method of sensor and sensor of defect of pipeline |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6038925A (en) * | 1997-03-21 | 2000-03-21 | Ebara Corporation | Focal type electromagnetic acoustic transducer and flaw detection system and method |
| CN206373042U (en) * | 2016-12-28 | 2017-08-04 | 南京航空航天大学 | A kind of transceiver electromagnet ultrasonic changer of low noise |
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| GB0314357D0 (en) * | 2003-06-19 | 2003-07-23 | Pii Ltd | Electromagnetic acoustic transducer |
| KR101052800B1 (en) * | 2009-03-30 | 2011-07-29 | 한국표준과학연구원 | Method for wall thinning monitoring of a pipe using magnetostrictive transducers and the variation of the dispersion characteristics of the broadband multimode SH waves |
| DE102010027250A1 (en) * | 2010-07-15 | 2012-01-19 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Electromagnetic ultrasonic receiver |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6038925A (en) * | 1997-03-21 | 2000-03-21 | Ebara Corporation | Focal type electromagnetic acoustic transducer and flaw detection system and method |
| CN206373042U (en) * | 2016-12-28 | 2017-08-04 | 南京航空航天大学 | A kind of transceiver electromagnet ultrasonic changer of low noise |
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