CN104090034B - A kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography - Google Patents
A kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography Download PDFInfo
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- CN104090034B CN104090034B CN201410347751.0A CN201410347751A CN104090034B CN 104090034 B CN104090034 B CN 104090034B CN 201410347751 A CN201410347751 A CN 201410347751A CN 104090034 B CN104090034 B CN 104090034B
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Abstract
A kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography, belongs to the guided wave chromatography technical field of imaging of sheet metal, is specifically related to a kind of single-mode 180 degree and points to the electromagnetic acoustic Lamb wave transducer at angle.Solving existing electromagnetic acoustic Lamb wave transducer and point to the problem of the guided wave mode mixing that angle is little, excite, the permanent magnet of the present invention is the cuboid permanent magnet that length and width is all higher than coil diameter, and the magnetostatic field magnetic induction of permanent magnet is not less than 0.15T；The semi-circular tortuous coil of every circle comprises m root wire, and the centre distance that adjacent two circle wires are diametrically is d=λ/2, and the semi-circular tortuous coil of n circle is fabricated to two-sided PCB, and described PCB is arranged on the underface of permanent magnet.The present invention is applicable to the tomography of the uniform metal sheeting design of various material properties.
Description
Technical field
The invention belongs to the guided wave chromatography technical field of imaging of sheet metal, be specifically related to a kind of single-mode 180 degree and point to angle
Electromagnetic acoustic Lamb wave transducer.
Background technology
In the fields such as material, machinery and chemical industry, aluminium sheet easily cracks in producing, process, transport and using, corruption
The defects such as erosion.And product quality is required very strict by modern industry, environment and economy all may be caused serious prestige by little defect
The side of body.Therefore many countries all add Non-Destructive Testing the production system of oneself as the guardian technique link controlling product quality
In.Along with the lifting of detection technique, modern industry to the requirement of Non-Destructive Testing be the most no longer simply determine defect with or without, also
The information such as flaw size to be determined, the degree of depth, this is accomplished by using in combination the completing of new technique and detects.Electromagnetic acoustic orchid nurse
Electromagnetic acoustic Lamb wave is combined a kind of Novel lossless that developed by ripple chromatography imaging technique just with chromatography imaging technique
Detection technique.This technology can provide a large amount of visual information, can vividly describe defect profile, such that it is able to the most right
Workpiece quality, performance are evaluated.
It is currently used for the transducer at field of non destructive testing and mostly is piezoelectric ultrasonic transducer.When using this transducer, it is necessary to
The pure uniform couplant of test specimen surface smear (such as oil, water and ointment etc.).Introducing due to couplant so that pressure
Electricity ultrasonic technique application receive some limit, be not such as suitable for high temperature, at a high speed, the detection of rough surface test specimen；Again
As check frequency is relatively big, detection efficiency is relatively low.Electromagnet ultrasonic changer is not only without couplant, and detection efficiency is high, detection
Signal is strong, and can select excited Lamb Waves modes and optimal working point thereof neatly, and then is obviously improved ultrasound wave
Flaw sensitivity.Therefore, electromagnet ultrasonic changer is at large area, distance or the sheet material of buried underground, rail, pipeline
In quickly detecting Deng industry test specimen, there is unique advantage.
Lamb wave detection uses " line scanning " mode to detect test specimen, with " spot scan " mode phase specific efficiency of bulk wave detection
Higher.Meanwhile, Lamb wave is decayed little when propagating in test specimen, propagation distance is long.Use dual probe to carry out one one and receive detection
Time, the Lamb wave signal received carries the Global Information of test specimen between two probes, utilizes Joint iteration algorithm for reconstructing to orchid
Information when walking of nurse ripple signal carries out imaging, can obtain the information such as the position of defect, size.
The scan mode of test block is had multiple by guided wave tomography, including twin spans hole scan mode, parallel sweep mode, fan
Bundle scan mode, circular array scan mode etc., wherein sweep at twin spans hole scan mode, fan-delta sandbody mode, circular array
Retouch under mode, all transducer is had the requirement at bigger sensing angle.As a example by the scan mode of twin spans hole, in chromatography imaging technique
To the scan mode of test block as it is shown in figure 1, stain in Fig. 1 represents the position of transducer, the surrounding of plate construction is pressed
Arrange transmitting shown in Fig. 1, receive transducer.The upper end of plate and left side are equally spaced transmitting transducer, lower end and right side etc.
Spacing is arranged and is received transducer.The transmitting transducer of upper end is launched successively, and is received by lower end transducer each point simultaneously；Left end
Transmitting transducer launch successively, right-hand member transducer each point receive simultaneously.Conventional tortuous coil has stronger directivity,
Transmitting reception is required for adjusting direction makes the axis of coil point-blank, and otherwise received signal strength will weaken,
It could even be possible to artificial introducing error, it is unfavorable for detection.In order to meet the scanning requirement of guided wave chromatography imaging technique, need
The transducer that sound field overlay area is big, it is possible to launch on bigger sensing angle, receive ultrasonic guided wave signals.
The transducer being currently used in guided wave tomography mostly is spiral winding transducer based on electromagnetic acoustic technology, this transducing
Although device can reach all referring to the requirement to angle transmitting and receiving signal, but the waveform excited is often for the mixed recharge of various modes guided wave
Shape, guided wave tomography to be used for also needs to carry out signal processing and isolates the guided wave of single-mode, and processing method is complex,
And in processing procedure, easily produce new error.The present invention is the semicircle tortuous coil that spacing is certain, is selecting suitable work
Make in the case of point can the single guided wave of excitation mode, and the big requirement pointing to angle can be met, it is adaptable to guided wave chromatographs
Imaging.
What patent of invention " a kind of omnidirectional SH guided wave electromagnet ultrasonic changer " (application number: 201210125086.1) was mentioned is suitable for
In including conduction and non-conducting material various uniformly, the defects detection of isotropic elasticity plate structure and health monitoring
Omnidirectional SH guided wave electromagnet ultrasonic changer.Its limitation is in ducting layer analysis imaging process, is 360 degree when transducer points to angle
Time area occupied relatively big, the transducer volume being finally made is big, the most portable with use.Needs when this invention excites SH guided wave
Premagnetization circular iron-nickel alloy band, then uses adhesive tape to be fixed on the iron-nickel alloy band having pasted inflection coil to be detected flat
On plate structure, structure is complex, and operation more bothers.And the transducer that this patent is 180 degree of sensing angles, it is possible to completely
Meet tomography scanning to require and small volume, and excite Lamb wave only need to be placed in above coil by Magnet, excite simplicity,
Technique is simple.
What patent of invention " Electromagneltic sonic flaw detector " (application number: 99250252.7) was mentioned to is focused back into accordion coil, launches line
Circle and receiving coil are arc line shaped, and arc centers is sound focusing point, owing to acoustic interference effect sound focusing point becomes post type,
The reflex amplitude of the defect in burnt column length is higher.Although this patent designs for arc line shaped, but its function is focused sound waves
Increase resolution, do not play big angle of pointing to and launch the effect receiving guided wave, be not suitable for the tomography of guided wave.
" Chinese journal of scientific instrument " (2010.6, v31n6) are published an article, and " the consistent Lamb wave electromagnet ultrasonic changer of circumference designs
With realization " and patent of invention " the consistent single S0 mode Lamb wave Electromagnetic Acoustic Transducer of a kind of circumference " (application number:
201110280961.9) a kind of transducer architecture for the circumferential consistent Lamb wave of excitation in nonferromagnetic aluminium sheet is related to,
This transducer can only produce the Lamb wave of single S0 pattern, and its coil is utilize that pcb board makes close around discoid helix
Circle, reaches the function of model selection by the boss ratio and Lamb wave wavelength parameter changing coil.And this patent is selecting
It is that plan excites Lamb wave wavelength by the radial distance between two circle wire centers adjacent in coil in the case of proper operation point
The principle of half is designed so that the particle vibration sound source caused below each circle wire forms strong constructive interference, thus
More effectively excite single-mode Lamb wave.
Summary of the invention
The present invention is to point to the problem of the guided wave mode mixing that angle is little, excite to solve existing electromagnetic acoustic Lamb wave transducer,
Propose a kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography.
A kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography of the present invention, it includes the permanent magnetism longitudinally magnetized
Ferrum and the semi-circular tortuous coil of n circle；Wherein, 2≤n≤14；
Described permanent magnet is the cuboid permanent magnet that length and width is all higher than coil diameter, and the magnetostatic field magnetic induction of permanent magnet
It is not less than 0.15T；
The tortuous coil that often circle is semi-circular comprises m root wire, and the centre distance that adjacent two circle wires are diametrically is d=λ/2,
Wherein λ is selected Lamb Waves modes wavelength under frequency f；Wherein, 3≤m≤23；
The semi-circular tortuous coil of n circle is fabricated to two-sided PCB, described PCB be arranged on permanent magnet just under
Side；This permanent magnet produces magnetic direction and is perpendicular to the magnetostatic field of PCB；
Described Lamb Waves modes is divided into: antisymmetric mode and symmetric pattern；
Antisymmetric mode: be divided into zeroth order antisymmetric mode, single order antisymmetric mode, second order antisymmetric mode ... K rank are opposed
Title pattern, K is positive integer；
Described antisymmetric mode is that in plate, particle makees antisymmetry motion relative to plate intermediate layer；
Symmetric pattern: be divided into zeroth order symmetric pattern, single order symmetric pattern, Second-order Symmetric pattern ... K rank symmetric pattern；
Described symmetric pattern is that in plate, particle makees symmetric motion relative to plate intermediate layer.
The present invention is by electromagnetic coupled mode excitation ultrasound ripple, it is not necessary to couplant, can be used for non-contact detection；
Semicircular transducer has 180 degree of directivitys, small volume compared with omnidirectional ultrasonic transducer, and disclosure satisfy that
The demand at guided wave chromatography imaging technique sensing bigger to ultrasonic transducer angle.
It is plan that the present invention passes through the radial distance in coil between adjacent two circle wire centers in the case of selecting proper operation point
The principle exciting Lamb wave wavelength half is designed so that the particle vibration sound source caused below each circle wire is formed strong
Constructive interference excites single-mode Lamb wave, eliminates multimodal impact, the convenient characteristic parameter extracting echo, is suitable for
Tomography in the uniform metal sheeting design of various material properties.
Accompanying drawing explanation
Fig. 1 is that schematic diagram is scanned in guided wave tomography twin spans hole；In figure, P side is for launching tortuous coil position, and Q side is for connecing
Receipts penetrate tortuous coil position, indicate the defect point that circle is test specimen to be measured of a in figure；
Fig. 2 is transducer schematic diagram；
Fig. 3 is A0 pattern and PCB coil figure that operating point is 0.5MHz mm on 2mm aluminium sheet；
Fig. 4 is S0 pattern and PCB coil figure that operating point is 1.5MHz mm on 2mm aluminium sheet；
Fig. 5 is the A0 mode echoes signal graph that transducer receives.
Detailed description of the invention
Detailed description of the invention one, combining Fig. 1 and Fig. 2 present embodiment is described, the one described in present embodiment is used for guided wave
The electromagnetic acoustic Lamb wave transducer of tomography, it includes the tortuous coil that longitudinal permanent magnet 1 and n circle magnetized is semi-circular
2；Wherein, 2≤n≤14；
Described permanent magnet is the cuboid permanent magnet 1 that length and width is all higher than coil diameter, and the magnetostatic field magnetic induction of permanent magnet 1
Intensity is not less than 0.15T；
The tortuous coil 2 that often circle is semi-circular comprises m root wire, and the centre distance that adjacent two circle wires are diametrically is d=λ/2,
Wherein λ is selected Lamb Waves modes wavelength under frequency f；Wherein, 3≤m≤23；
The semi-circular tortuous coil 2 of n circle is fabricated to two-sided PCB, and described PCB is arranged on permanent magnet 1
Underface；This permanent magnet 1 produces magnetic direction and is perpendicular to the magnetostatic field of PCB；
Described Lamb Waves modes is divided into: antisymmetric mode and symmetric pattern；
Antisymmetric mode: be divided into zeroth order antisymmetric mode, single order antisymmetric mode, second order antisymmetric mode ... K rank are opposed
Title pattern, K is positive integer；
Described antisymmetric mode is that in plate, particle makees antisymmetry motion relative to plate intermediate layer；
Symmetric pattern: be divided into zeroth order symmetric pattern, single order symmetric pattern, Second-order Symmetric pattern ... K rank symmetric pattern；
Described symmetric pattern is that in plate, particle makees symmetric motion relative to plate intermediate layer.
Detailed description of the invention two, present embodiment are to a kind of electricity for guided wave tomography described in detailed description of the invention one
Further illustrating of magnetic ultrasonic Lamb waves transducer, the semi-circular tortuous coil 2 of n circle uses enamel-covered wire coiling to form.
Detailed description of the invention three, present embodiment are to a kind of electricity for guided wave tomography described in detailed description of the invention one
Further illustrating of magnetic ultrasonic Lamb waves transducer, permanent magnet 1 uses N52 type Nd-Fe-B permanent magnet.
Specific embodiment:
The selected material properties of test block, thickness, is substituted into the characteristic equation of Lamb wave, obtain Lamb wave excite equation with
Excitation curve.After the pattern of selected Lamb wave, the excitation curve of Lamb wave can find the phase velocity of anticipated operating point
CpWith the information of frequency f, substitute into formula λ=CpIn/f, obtain the wavelength information of Lamb wave；In coil in adjacent two circle wires
Radial distance between the heart is d=λ/2, calculates the adjacent wires spacing of tortuous coil.
As a example by printed circuit board (PCB) technique, the electromagnetic acoustic Lamb wave transducer for guided wave tomography is used to exist
When exciting the Lamb wave of single A0 pattern (zeroth order antisymmetric mode) on the aluminium sheet of 2mm, select 0.5MHz mm work
Point determines that operating frequency is 0.25MHz.Obtain when frequency is 0.25MHz according to the excitation curve of Lamb wave in aluminium sheet,
Phase velocity is 1891.34m/s, substitutes into formula λ=Cp/ f, can obtain the wavelength X=7.562mm of Lamb wave, tortuous coil
Adjacent two circle wire pitch L are 3.784mm, and 180 degree of final sensing angle Lamb wave coils are as shown in Figure 3；
When the aluminium sheet of 2mm excites the Lamb wave of single S0 pattern (zeroth order symmetric pattern), select 1.5MHz mm
Operating point determines that operating frequency is 0.75MHz；Obtain in frequency being 0.75MHz according to the excitation curve of Lamb wave in aluminium sheet
Time, phase velocity is 5212.5m/s, substitutes into formula λ=Cp/ f, can obtain the wavelength X=6.95mm of Lamb wave, tortuous coil
Adjacent wires spacing L be 3.475mm, 180 degree of final design sensing angle Lamb wave coils are as shown in Figure 4.
When test block is steel plate, the shear wave in the material properties parameter i.e. steel plate of steel plate and the velocity of wave of compressional wave and steel need to be substituted into
Plate thickness is to the characteristic equation of Lamb wave, and obtain Lamb wave excites equation and excitation curve.Can obtain according to same procedure
Lamb wave wavelength, so that it is determined that radial distance between adjacent two circle wire centers in coil.
Comprising 3～23 wires in coil one circle wire, the distance at the most adjacent two circle wire centers is d.
Semicircular transducer has 180 degree of directivitys, small volume compared with omnidirectional ultrasonic transducer, and can expire
The demand at foot guided wave chromatography imaging technique sensing bigger to ultrasonic transducer angle.
By tortuous coil is passed through the tone burst signal that frequency is 0.1～2MHz in 3～10 cycles, by impedance matching,
High-frequency high-power emission current can be produced in electromagnet ultrasonic changer.
One group of typical case's application is two transducers 320mm apart, and transducer utilizes one one detection mode received, at 2mm
Testing on thick aluminium sheet, centered by pumping signal, frequency is the sine wave signal in 5 cycles of 250kHz, and Fig. 5 is for connecing
Receiving signal graph, first echo-signal is A0 pattern (zeroth order antisymmetric mode) ripple bag signal.
In the application of tomography, transducer works under one one mode received.Transducer can be required with tomography
Scan mode is arranged, and the Lamb wave signal received carries the Global Information of test specimen between two probes, utilizes and combines repeatedly
When walking Lamb wave signal for algorithm for reconstructing, information carries out processing computing, sheet metal is carried out imaging, completes accurately to detect.
Above content is to combine concrete preferred implementation further description made for the present invention, it is impossible to assert this
Bright being embodied as is confined to these explanations.For this person of an ordinary skill in the technical field, without departing from this
On the premise of inventive concept, it is also possible to make some simple deduction or replace, all should be considered as belonging to the power that the present invention is submitted to
The scope of patent protection that profit claim determines.
Claims (3)
1. the electromagnetic acoustic Lamb wave transducer for guided wave tomography, it is characterised in that it includes that longitudinal direction magnetizes
Permanent magnet (1) and the semi-circular tortuous coil (2) of n circle；Wherein, 2≤n≤14；
Described permanent magnet is the cuboid permanent magnet (1) that length and width is all higher than coil diameter, and the magnetostatic field magnetic of permanent magnet (1)
Induction is not less than 0.15T；
The tortuous coil (2) that often circle is semi-circular comprises m root wire, and the centre distance that adjacent two circle wires are diametrically is
D=λ/2, wherein λ is selected Lamb Waves modes wavelength under frequency f；Wherein, 3≤m≤23；
The semi-circular tortuous coil (2) of n circle is fabricated to two-sided PCB, and described PCB is arranged on permanent magnet (1)
Underface；This permanent magnet (1) produces magnetic direction and is perpendicular to the magnetostatic field of PCB；
Described Lamb Waves modes is divided into: antisymmetric mode and symmetric pattern；
Antisymmetric mode: be divided into zeroth order antisymmetric mode, single order antisymmetric mode, second order antisymmetric mode ... K rank are opposed
Title pattern, K is positive integer；
Described antisymmetric mode is that in plate, particle makees antisymmetry motion relative to plate intermediate layer；
Symmetric pattern: be divided into zeroth order symmetric pattern, single order symmetric pattern, Second-order Symmetric pattern ... K rank symmetric pattern；
Described symmetric pattern is that in plate, particle makees symmetric motion relative to plate intermediate layer.
A kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography the most according to claim 1, its feature exists
Enamel-covered wire coiling is used to form in the tortuous coil (2) that, n circle is semi-circular.
A kind of electromagnetic acoustic Lamb wave transducer for guided wave tomography the most according to claim 1, its feature exists
In, permanent magnet (1) uses N52 type Nd-Fe-B permanent magnet.
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| CN107064311B (en) * | 2017-06-05 | 2019-08-23 | 哈尔滨工业大学 | A kind of omni-directional A0 mode Lamb wave electromagnet ultrasonic changer |
| CN107817292B (en) * | 2017-10-30 | 2019-07-26 | 清华大学 | The whole directive property Corkscrews Lamb wave energy converter of double array adjustables of guided wave tomography |
| CN108680652B (en) * | 2018-05-14 | 2020-07-24 | 哈尔滨工业大学 | Full-directional S0 modal lamb wave electromagnetic ultrasonic transducer |
| CN109725058A (en) * | 2018-12-20 | 2019-05-07 | 电子科技大学 | The twin spans pitch-row tomographic reconstruction imaging method of contactless Lamb wave |
| CN110193460B (en) * | 2019-05-29 | 2021-04-27 | 北京工业大学 | Omnidirectional magnetic concentrator type lamb wave electromagnetic acoustic transducer |
| CN110702799B (en) * | 2019-10-19 | 2022-09-23 | 北京工业大学 | Omnidirectional high-order Lamb wave modal electromagnetic acoustic sensor based on variable-angle magnetic concentrator |
| CN115235390B (en) * | 2022-05-26 | 2023-07-25 | 国网安徽省电力有限公司亳州供电公司 | Method and system for detecting thickness of weathering resistant steel rust layer |
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