CN104198581A - Lorentz force-based electromagnetic acoustic surface wave sensor with high signal to noise ratio - Google Patents
Lorentz force-based electromagnetic acoustic surface wave sensor with high signal to noise ratio Download PDFInfo
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- CN104198581A CN104198581A CN201410441780.3A CN201410441780A CN104198581A CN 104198581 A CN104198581 A CN 104198581A CN 201410441780 A CN201410441780 A CN 201410441780A CN 104198581 A CN104198581 A CN 104198581A
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Abstract
The invention discloses a Lorentz force-based electromagnetic acoustic surface wave sensor with high signal to noise ratio. The sensor comprises a BNC interface, a plastic protection shell, an impedance matching circuit, a brass protection shell, a neodymium-iron-boron permanent magnet, a polyimide gasket, two layers of meandered line coils and a lead; in specific, the neodymium-iron-boron permanent magnet is arranged in a large cavity of the brass protection shell; the impedance matching circuit is arranged in a small cavity of the brass protection shell; the two layers of meandered line coils are arranged at the bottoms of the polyimide gasket and the impedance matching circuit; the plastic protection shell is arranged around the brass protection shell and enclose all the elements; and the BNC interface is arranged at one side of the small cavity of the brass protection shell. Compared with the traditional electromagnetic acoustic surface wave sensors, the Lorentz force-based electromagnetic acoustic surface wave sensor is capable of obtaining high signal to noise ratio under a self-excitation self-reception working mode, so that the detection sensitivity of the sensor is improved to a great extent.
Description
Technical field
The invention belongs to Electromagnetic Acoustic Transducer field, be specifically related to a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force.
Technical background
Surface wave (R wave) be only Semi-infinite Medium surface or with the interface of other media and near propagation and be not deep into the ultrasonic type of a kind of uniqueness of medium inside.Compare with other supersonic guide-wave mode with bulk wave, surface wave is in communication process, and energy mainly concentrates in the scope of the next wavelength in test specimen surface, and therefore its effects on surface crackle has very high detection sensitivity.
Electromagnetic Acoustic Transducer is a kind of hyperacoustic transducing head that encouraged in conductor and detected by electromagnetic coupled.Compared with piezoelectric transducer, the advantage of Electromagnetic Acoustic Transducer maximum is to realize non-contact detecting, without couplant, less demanding to test specimen surface appearance in testing process.Electromagnetic Acoustic Transducer can adopt different coil shapes and magnetic field configuration form to inspire easily different ultrasound in nature, and can produce the supersonic guide-wave mode that piezoelectric sensor can not encourage.
Electromagnetic sound surface wave sensor, as a kind of conventional nondestructiving detecting means, is widely used in the surface defects detection of train wheel hub, rail, steel plate and aluminium sheet.Transportation by railroad is a kind of means of transportation of high-speed overload, and in the middle of train travelling process, directly fatigue damage very easily occurs for train wheel hub and the rail of contact, cracks and weares and teares at wheel hub and rail surface, causes losing efficacy.Steel plate and aluminium alloy plate are widely used in fields such as industry, military affairs, infrastructure constructions, and the quality of its quality has determined the quality of product and engineering.
The signal to noise ratio (S/N ratio) of the Electromagnetic Acoustic Transducer of traditional form and detection sensitivity are very low.Electromagnetic Acoustic Transducer is operated in autoexcitation from receiving mode lower time, and hyperacoustic excitation and receiving course share same coil and magnet.Electromagnetic sound surface wave sensor in the course of the work, not only can produce surface wave in conduction test specimen to be measured, in the ndfeb magnet of conduction, also can inspire ultrasound wave.Same, sensor not only can detect the surface wave in test specimen, the ultrasound wave in magnet also can be detected.Because the size of magnet is less, ultrasound wave reflects very strong in magnet, decays also less, and this causes the useful signal in test specimen to be measured in testing process to be buried in the noise signal in magnet, greatly reduces signal to noise ratio (S/N ratio) and the detection sensitivity of detection signal.
Suitably increase the distance between magnet and coil, can improve the signal to noise ratio (S/N ratio) of detection signal, thereby improve detection sensitivity.Lifting from apart from constant of holding coil and test specimen to be measured, suitably increase the distance 1mm-3mm between magnet and coil, the magnetic field intensity that acts on test specimen to be measured surface does not have too large change, and the surperficial wave intensity that inflection coil excites in test specimen to be measured only can decline a little.But because the distance of lifting from of coil and magnet increases, the size of the eddy current that inflection coil induces in magnet is on the one hand decreased significantly, hyperacoustic energy that coil excites in magnet reduces greatly, inflection coil is experienced the ability that particle displacement in magnet changes and also can be declined on the other hand, detects that the ultrasonic signal decay in magnet is very large.So, the energy as the surface wave in the test specimen to be measured of useful signal that sensor detects is substantially constant, and greatly reduces as the ultrasonic energy in the magnet of noise, and this has just effectively improved the signal to noise ratio (S/N ratio) of detection signal, thereby has improved detection sensitivity.
Summary of the invention
The object of the invention is to overcome the shortcoming of traditional electrical acoustic surface wave sensor, a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force is provided, can obtain higher signal to noise ratio (S/N ratio), improve detection sensitivity, realize quick, the efficient detection for the treatment of test block.
For achieving the above object, the technical solution used in the present invention is a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force, and this sensor comprises BNC connector, plastics protecting sheathing, impedance matching circuit, brass containment vessel, Nd-Fe-B permanent magnet, polyimide pad, double-layer back broken line circle, wire; Particularly, described brass containment vessel one end opening and be provided with size two chambers, the xsect of two chambers is rectangular groove structure; Nd-Fe-B permanent magnet is placed in the large chamber of brass containment vessel, and polyimide pad is placed in Nd-Fe-B permanent magnet bottom and Nd-Fe-B permanent magnet is fixed on to large chamber; Impedance matching circuit is placed in the capacitor of brass containment vessel; Double-layer back broken line circle is placed in polyimide pad and impedance matching circuit bottom, and double-layer back broken line circle is positioned at brass containment vessel inner bottom part by fastening the element of the large capacitor of brass containment vessel; Described plastics protecting sheathing is placed in brass containment vessel periphery, and by all element sealings; BNC connector is arranged on brass containment vessel capacitor one side; Double-layer back broken line circle is connected with impedance matching circuit by wire, and impedance matching circuit is connected with BNC connector by other two connecting lines.
The beneficial effect that the present invention has, compared with traditional form electromagnetic sound surface wave sensor, from receiving under mode of operation, can obtain very high signal to noise ratio (S/N ratio) in autoexcitation, has improved to a great extent the detection sensitivity of sensor.
Brief description of the drawings
Fig. 1 is the structural representation of electromagnetic sound surface wave sensor in the present invention.
Fig. 2 is the double-layer back broken line circle schematic diagram of electromagnetic sound surface wave sensor in the present invention.
Fig. 3 is the fundamental diagram of electromagnetic sound surface wave sensor in the present invention.
Fig. 4 is the sensor typical case detection system structural drawing in the present invention.
Fig. 5 is placement location and the defective locations schematic diagram of sensor in typical testing process.
The pumping signal figure of the typical detection system of Fig. 6.
Fig. 7 is the primary reception signal graph of typical detection system.
In figure: 1, BNC connector, 2, plastics protecting sheathing, 3, impedance matching circuit, 4, brass containment vessel, 5, Nd-Fe-B permanent magnet, 6, polyimide pad, 7, double-layer back broken line circle, 8, wire, 9, conduction test specimen.
Embodiment
Be described further for the present invention below in conjunction with the drawings and specific embodiments.
As shown in Figure 1-2, a high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force, this sensor comprises BNC connector 1, plastics protecting sheathing 2, impedance matching circuit 3, brass containment vessel 4, Nd-Fe-B permanent magnet 5, polyimide pad 6, double-layer back broken line circle 7, wire 8; Particularly, described brass containment vessel 4 one end openings and be provided with size two chambers, the xsect of two chambers is rectangular groove structure; Nd-Fe-B permanent magnet 5 is placed in the large chamber of brass containment vessel 4, and polyimide pad 6 is placed in Nd-Fe-B permanent magnet 5 bottoms and Nd-Fe-B permanent magnet 5 is fixed on to large chamber; Impedance matching circuit 3 is placed in the capacitor of brass containment vessel 4; Double-layer back broken line circle 7 is placed in polyimide pad 6 and impedance matching circuit 3 bottoms, and double-layer back broken line circle 7 is positioned at brass containment vessel 4 inner bottom parts by fastening the element of brass containment vessel 4 large capacitors; Described plastics protecting sheathing 2 is placed in brass containment vessel 4 peripheries, and by all element sealings; BNC connector 1 is arranged on brass containment vessel 4 capacitor one sides; Double-layer back broken line circle 7 is connected with impedance matching circuit 3 by wire 8, and impedance matching circuit 3 is connected with BNC connector 1 by other two connecting lines.
Described brass containment vessel 4 provides protection for whole sensor, and BNC connector 1 is placed in brass containment vessel 4 one sides, for the input and output of signal; Brass containment vessel 4 has two chambers of size, and the dividing wall between two chambers, lower than other wall, is convenient to double-layer back broken line circle 7 and is placed; On the two side of described large cavity bottom, be processed with respectively a rectangular channel running through, polyimide pad 6 can be inserted into opposite side from a side of brass containment vessel 4 by these two rectangular channels.
Described double-layer back broken line circle 7 is placed in brass containment vessel 4 bottoms and is encased by plastic protection casing 2; Described plastic protection casing 2 is in order to protect brass containment vessel 4 and double-layer back broken line circle 7 not frayed; Plastics protecting sheathing 2 by duroplasts paper cut out, folding forming, one end has circular hole so that bnc interface 1 to be installed, and fixes with adhesive tape, cheap, make simple, easy accessibility.
Described Nd-Fe-B permanent magnet 3 is solid rectangular parallelepiped magnet, requires magnetic direction in the bottom even of magnet and direction vertically downward or upwards.
Described polyimide pad 6 adopts the identical polyimide of flexible PCB (FPC) base material with double-layer back broken line circle 7, to eliminate the impact of gasket material on sensor performance.The effect of polyimide pad 6, the one, Nd-Fe-B permanent magnet 5 is fixed in large chamber, even in the time that steel plate is detected, Nd-Fe-B permanent magnet 5 is subject to very large power and also can not comes off, the 2nd, increase the distance of lifting from of double-layer back broken line circle 7 and Nd-Fe-B permanent magnet 3, improve the signal to noise ratio (S/N ratio) of sensor.
Described impedance matching circuit 3 is 50 Ω by the output impedance coupling of double-layer back broken line circle 7.
The thickness of the sheet metal that described electromagnetic sound surface wave sensor detects should be greater than this sensor and produce 4 times of surface wave wavelength.
Apply the detection system of the above-mentioned high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force, this system is launched receiving instrument, oscillograph and sensor by high energy pulse and is formed; Adopt autoexcitation from receiving mode, high energy pulse transmitting receiving instrument is connected with sensor, produces the signal that narrow frequency modulation signal receiving sensor detect, sensor encourages and receiving surface ripple in plate, and oscillograph is connected with high energy pulse transmitting receiving instrument.Sensor is placed on steel plate to be measured or aluminium sheet.
Double-layer back broken line circle 7 is placed on conduction test specimen 9 to be measured, and Nd-Fe-B permanent magnet 5 is placed on double-layer back broken line circle 7, when passing to exchange current in double-layer back broken line circle 7, under conduction test specimen in produce same frequency the alternation eddy current of inducting, the direction of eddy current is contrary with sense of current in double-layer back broken line circle 7, because the direction of current of adjacent wires in double-layer back broken line circle 7 is contrary, the direction of the inductive loop producing under adjacent wires is also contrary, the direction of the eddy current under so whole inflection coil alternately changes, if the direction of fixed magnetic field as shown in Figure 3 vertically downward, the direction of the Lorentz force that in conduction test specimen 9 so to be measured, in eddy current effect region, charged corpuscle is subject to is also alternately to change, under the effect of the Lorentz force alternately changing, charged corpuscle in eddy current produces the vibration that direction replaces, thereby produce the surface wave perpendicular to winding wire direction to coil both sides.The reception of surface wave is the inverse process of excitation.
Processing and the assembling process of the high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force of the present invention are as follows:
The support that brass containment vessel is whole sensor also provides protection for inner member, high 17mm, long 80mm, wide 40mm, brass processes, one side is processed with BNC connector hole, there are two chambers of size, the large high 13mm of chamber, long 52mm, wide 32mm, the high 13mm of capacitor, long 19mm, wide 32mm, the isolation wall thickness 2mm of two chambers, the side thickness that bnc interface is installed is 3mm, all the other wall thickness and top thickness are 4mm, dividing wall between two chambers is than the low 1mm of other walls, be processed with respectively one in large chamber two side lower middle position apart from 1mm place, edge and run through rectangular channel, long 30mm, high 2mm.
In large chamber, pack Nd-Fe-B permanent magnet into, its physical dimension is long 50mm, wide 30mm, and thick 10mm, Surface field intensity is 3800 Gausses.
Polyimide pad in load map 1, it is of a size of long 40mm, wide 30mm, thick 2mm, is inserted into the rectangular channel of opposite side from the rectangular channel of brass containment vessel one side.
BNC connector hole on alignment plastics protecting sheathing and brass containment vessel, packs BNC connector into, connects the signal wire between BNC connector and signal wire and impedance matching circuit and the double-layer back broken line circle of impedance matching circuit.
Pack impedance matching circuit into, this circuit is 50 Ω by the output impedance coupling of double-layer back broken line circle, impedance matching circuit by electric capacity and resistance with certain order after in parallel and series connection through being welded.
Double-layer back broken line circle is packed in brass containment vessel; double-layer back broken line circle as shown in Figure 2; have 6 circles; in coil, the spacing of adjacent two wires is 2mm; double-layer back broken line circle is printed on flexible PCB (FPC) two sides, upper and lower surface coil be connected by through hole, the direction of current in upper and lower two-layer coil corresponding lead is identical; the long 60mm of whole flexible PCB, wide 30mm.
Plastics protecting sheathing is packaged, fixes with adhesive tape, prevent that brass containment vessel and double-layer back broken line circle from wearing and tearing, plastics protecting sheathing by duroplasts paper cut out, folding forming, cheap, make simple, easy accessibility.
Using method:
Apply typical detection system of the present invention as shown in Figure 4, formed by high energy pulse transmitting receiving instrument, oscillograph and sensor, adopt autoexcitation from receiving mode, high energy pulse transmitting receiving instrument is connected with sensor, high energy pulse transmitting receiving instrument produces the signal that narrow frequency modulation signal receiving sensor detect, sensor encourages and receiving surface ripple in plate, and oscillograph is connected with high energy pulse transmitting receiving instrument.Sensor is placed on sheet metal to be measured.High energy pulse transmitting receiving instrument produces the ToneBurst signal in 6 cycles that frequency is 750kHz.Because the energy conversion efficiency of Electromagnetic Acoustic Transducer is lower, for obtaining larger signal amplitude, output signal crest voltage is amplified to 300V.The direct input pickup of output signal produces surface wave in sheet metal, and surface wave is propagated forward along the surface of sheet metal, runs into crackle or end face reflects.The pulse producer of high energy pulse transmitting receiving instrument can be decayed pumping signal 20dB to oscillographic passage 1, so that observe excitation signal waveforms.Sensor receives after reflection wave, be input in the receiving instrument of high energy pulse transmitting receiving instrument, signal is amplified 80dB by the incorporated amplifier of instrument again, and after the filtering of built-in 400kHz-2.5MHz hardware band-pass filter, output to channel oscilloscope 2, show detection signal waveform.Shown in one group of typical testing process Fig. 5, sensor is placed in one end of steel plate to be measured, the thick 25mm of steel plate, long 600mm, wide 450mm, along there being a long 30mm on steel plate length direction center line, wide 0.5mm, the simulating crack of dark 1.5mm, crackle and sensor are at a distance of 500mm.One group of typical testing result is as Fig. 6 and Fig. 7, and Fig. 6 is pumping signal figure, and Fig. 7 is the original signal figure that sensor receives, and first ripple bag is flaw echo.
Claims (8)
1. the high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force, is characterized in that: this sensor comprises BNC connector (1), plastics protecting sheathing (2), impedance matching circuit (3), brass containment vessel (4), Nd-Fe-B permanent magnet (5), polyimide pad (6), double-layer back broken line circle (7), wire (8); Particularly, described brass containment vessel (4) one end openings and be provided with size two chambers, the xsect of two chambers is rectangular groove structure; Nd-Fe-B permanent magnet (5) is placed in the large chamber of brass containment vessel (4), and polyimide pad (6) is placed in Nd-Fe-B permanent magnet (5) bottom and Nd-Fe-B permanent magnet (5) is fixed on to large chamber; Impedance matching circuit (3) is placed in the capacitor of brass containment vessel (4); Double-layer back broken line circle (7) is placed in polyimide pad (6) and impedance matching circuit (3) bottom, and double-layer back broken line circle (7) is positioned at brass containment vessel (4) inner bottom part by fastening the element of the large capacitor of brass containment vessel (4); Described plastics protecting sheathing (2) is placed in brass containment vessel (4) periphery, and by all element sealings; BNC connector (1) is arranged on brass containment vessel (4) capacitor one side; Double-layer back broken line circle (7) is connected with impedance matching circuit (3) by wire (8), and impedance matching circuit (3) is connected with BNC connector (1) by other two connecting lines.
2. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, it is characterized in that: described brass containment vessel (4) provides protection for whole sensor, BNC connector (1) is placed in brass containment vessel (4) one sides, for the input and output of signal; Brass containment vessel (4) has two chambers of size, and the dividing wall between two chambers, lower than other wall, is convenient to double-layer back broken line circle (7) and is placed; On the two side of described large cavity bottom, be processed with respectively a rectangular channel running through, polyimide pad (6) can be inserted into opposite side from a side of brass containment vessel (4) by these two rectangular channels.
3. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, is characterized in that: described double-layer back broken line circle (7) is placed in brass containment vessel (4) bottom and is encased by plastic protection casing (2); Described plastic protection casing (2) is in order to protect brass containment vessel (4) and double-layer back broken line circle (7) not frayed; Plastics protecting sheathing (2) by duroplasts paper cut out, folding forming, one end has circular hole so that bnc interface (1) to be installed, and fixes with adhesive tape.
4. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, it is characterized in that: described Nd-Fe-B permanent magnet (3) is solid rectangular parallelepiped magnet, require magnetic direction in the bottom even of magnet and direction vertically downward or upwards.
5. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, it is characterized in that: described polyimide pad (6) adopts the identical polyimide of flexible PCB base material with double-layer back broken line circle (7), to eliminate the impact of gasket material on sensor performance.
6. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, is characterized in that: described impedance matching circuit (3) is 50 Ω by the output impedance coupling of double-layer back broken line circle (7).
7. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, is characterized in that: the thickness of the sheet metal that described electromagnetic sound surface wave sensor detects should be greater than this sensor and produce 4 times of surface wave wavelength.
8. a kind of high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force according to claim 1, it is characterized in that: apply the detection system of the above-mentioned high s/n ratio electromagnetic sound surface wave sensor based on Lorentz force, this system is launched receiving instrument, oscillograph and sensor by high energy pulse and formed; Adopt autoexcitation from receiving mode, high energy pulse transmitting receiving instrument is connected with sensor, produces the signal that narrow frequency modulation signal receiving sensor detect, sensor encourages and receiving surface ripple in plate, and oscillograph is connected with high energy pulse transmitting receiving instrument; Sensor is placed on steel plate to be measured or aluminium sheet.
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| CN107271572A (en) * | 2017-07-31 | 2017-10-20 | 沈阳工业大学 | Electromagnetic acoustic sheet metal flaw detection transducer |
| CN107774552A (en) * | 2016-08-24 | 2018-03-09 | 哈尔滨零声科技有限公司 | A kind of electromagnet ultrasonic changer of more magnet arrangements |
| CN114216600A (en) * | 2021-12-15 | 2022-03-22 | 北京工业大学 | L based on double-folding coil electromagnetic acoustic sensorCRWave sound beam deflection regulating and controlling method |
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| CN202330358U (en) * | 2011-11-23 | 2012-07-11 | 北京工业大学 | SH0 electromagnetic acoustic transducer for detecting defects of plate structure |
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