CN104898123B - Water immersion ultrasonic synthetic aperture focusing imaging method based on angular domain virtual source - Google Patents

Water immersion ultrasonic synthetic aperture focusing imaging method based on angular domain virtual source Download PDF

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CN104898123B
CN104898123B CN201510332737.8A CN201510332737A CN104898123B CN 104898123 B CN104898123 B CN 104898123B CN 201510332737 A CN201510332737 A CN 201510332737A CN 104898123 B CN104898123 B CN 104898123B
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virtual source
scanning
angular domain
workpiece
imaging
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CN104898123A (en
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胡宏伟
王泽湘
杜剑
彭刚
王向红
李雄兵
倪培君
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Changsha Peng Xiang Electronic Technology Co., Ltd.
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Changsha University of Science and Technology
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88Sonar systems specially adapted for specific applications
    • G01S15/89Sonar systems specially adapted for specific applications for mapping or imaging
    • G01S15/8906Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
    • G01S15/8997Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using synthetic aperture techniques
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating 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
    • G01N29/04Analysing solids
    • G01N29/06Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0654Imaging
    • G01N29/0681Imaging by acoustic microscopy, e.g. scanning acoustic microscopy
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00Investigating 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
    • G01N29/04Analysing solids
    • G01N29/06Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0654Imaging
    • G01N29/069Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88Sonar systems specially adapted for specific applications
    • G01S15/89Sonar systems specially adapted for specific applications for mapping or imaging
    • G01S15/8902Side-looking sonar
    • G01S15/8904Side-looking sonar using synthetic aperture techniques
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52077Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging with means for elimination of unwanted signals, e.g. noise or interference
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/30Assessment of water resources

Abstract

The invention discloses a water immersion ultrasonic synthetic aperture focusing imaging method based on an angular domain virtual source. The method is used for ultrasonic imaging of water-immersed workpieces and comprises four steps including water-immersed workpiece acoustic beam propagation modeling, echo signal acquisition in the angular domain, echo signal reconstruction in the virtual source, and synthetic aperture focusing imaging. The method has technical effects that it is no need to consider influences of an acoustic beam propagation path and a sound velocity change on delayed superposition computation to perform ultrasonic synthetic aperture focusing imaging on the water-immersed workpieces by using virtual source technology, thereby reducing imaging computation complexity; and a delayed superposition algorithm based on an angular domain virtual source model is provided which effectively combines synthetic aperture focusing imaging technology and spatial composite imaging technology such that an angular domain ultrasonic synthetic aperture focusing image can be acquired just by one-time delayed superposition computation, thereby improving synthetic aperture focusing imaging efficiency and precision and reducing influence of spot noise on imaging.

Description

Water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source
Technical field
The present invention relates to a kind of water logging ultrasonic imaging method, including angular domain scanning technology, virtual source technology, synthetic aperture are poly- Burnt imaging technique, spatial compound imaging technology, realize efficient to water logging workpiece and high-precision ultrasonic synthetic aperture focusing imaging.
Background technology
Ultrasound examination is widely used to industrial products detection as a kind of important means of Non-Destructive Testing, and it can be Its defect is detected on the premise of not destroying Workpiece structure performance.Conventional ultrasound detection method using during single probe detection into As resolution βB=0.84 λ/D, D represents transducer aperture in formula, and λ represents the wavelength of transducer excitation acoustic beam, therefore to carry High ultra sonic imaging resolution is accomplished by increasing transducer aperture or reducing ultrasonic wavelength improving ultrasonic transducer work frequency Rate, but increase transducer aperture limits probe detection range, is not suitable for the detection of complex profile structural member, improves transducing Device operating frequency can increase ultrasound wave decay within the workpiece, be unfavorable for the detection of inside workpiece defect.Synthetic aperture focusing skill Art (Synthetic Aperture Focusing Technique, SAFT) as ultrasound examination field it is a kind of it is important into Image space method, its imaging is not affected by Fresnel region Underwater Acoustic Propagation characteristic, imaging resolution βsaft=D/2, only with transducer aperture It is relevant, the imaging of high-resolution can be obtained by small-bore and low operating frequency transducer.
But for the ultrasound detection of water logging workpiece, traditional SAFT enter line delay be superimposed when need consider acoustic beam in water and The change of propagation path, acoustic speed of propagation in workpiece, causes time delay superposition calculation efficiency low.To improve time delay superposition calculation efficiency, Application publication number CN103018333A, date of publication is that the patent documentation on April 3rd, 2013 discloses a kind of synthesis of layering object Aperture focuses on ultrasonic imaging method, and using line scan conversion technology iterative calculation number of times when time delay is superimposed, the method are reduced The time delay superposition calculation time can to a certain extent be reduced, but remain a need for consider acoustic beam in water with the change of acoustic speed of propagation in workpiece Change.
Additionally, ultrasound examination is affected by the random noise of system and structure, speckle noise, notification number can be produced during imaging For CN101199430B, the patent documentation in authorized announcement date on December 28th, 2011 discloses a kind of spatial compound imaging method, The ultra sonic imaging at each scanning angle is obtained after by inclining different scanning angles, the image at adjacent scanning angle is carried out after difference processing Compound, the image speckle noise after being combined is effectively suppressed.But when the method is carried out into space compound to SFAT images, need Line delay superposition calculation is entered respectively to the echo-signal at each scanning angle, be obtained after the SAFT images at each scanning angle again Spatial compound imaging is carried out, imaging time is such a process increases, imaging efficiency is low.
To improve time delay superposition calculation efficiency of the SAFT in immersed ultrasonic test, present invention introduces virtual source technology, empty Intend source model schematic diagram as shown in figure 3, virtual source refers to the focus point after multiple array element delay emissions, be with immersed ultrasonic test Example, when being detected to workpiece using focusing probe, when focusing probe focuses on surface of the work Q1When, focus point can be considered as energy The virtual transducer of certain angle spherical wave is produced, if focusing probe aperture is D, the unit energy that transducer is produced is p0, it is right The arbitrfary point P in workpiece, its depth is zs, during using conventional ultrasound detection method, its imaging signal to noise ratio And when adopting virtual source technology, its imaging signal to noise ratio isIt can thus be appreciated that conventional ultrasound detection method imaging letter Make an uproar than reducing with the increase of detection depth, and when adopting virtual source technology to be imaged, if do not considered ultrasound wave in inside workpiece Decay, its imaging signal to noise ratio not with detection depth change change.Additionally, when carrying out SAFT imagings using virtual source, Transmitting and during receiving, it is believed that sound beam focusing in the virtual source of surface of the work, therefore without the concern for acoustic beam in water With the change of propagation path, acoustic speed of propagation in workpiece.
For reduce ultra sonic imaging in speckle noise, and improve spatial compound imaging method process SAFT images when imaging Efficiency, by angular domain virtual source model, model schematic as shown in figure 5, set up based on the model time delay superposition algorithm, can be real The combination of existing SAFT and spatial compound imaging method, can obtain angular domain ultrasound synthetic aperture and gather by a time delay superposition calculation Burnt image.
The content of the invention
It is an object of the invention to propose a kind of imaging efficiency and high precision and affected little water logging ultrasound by speckle noise Synthetic Aperture Focussing Imaging.
It is a feature of the present invention that pass through virtual source technology, it is not necessary to consider acoustic beam in water and workpiece in propagation path, The change of acoustic speed of propagation, so as to improve time delay superposition calculation efficiency.
It is a feature of the present invention that realizing synthetic aperture focusing imaging technique and space compound by angular domain virtual source model The combination of imaging technique, by a time delay superposition calculation angular domain ultrasound synthetic aperture focusing image can be obtained.
The technical scheme is that, a kind of water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source, Comprise the following steps:
Step one:Water logging workpiece acoustic beam propagation is modeled, and is set up water logging workpiece acoustic beam according to workpiece geometry and material parameter and is passed Model is broadcast, and angular domain scanning scope and scanning angular interval are determined according to acoustic beam propagation model, wherein angular domain refers to focusing probe to appoint Central axis and workpiece incidence point normal angle during meaning scanning angle scanning, scanning angular interval refers to focusing probe in angular domain during scanning Adjacent scanning angular spacing, if the velocity of sound of the acoustic beam in water and in workpiece is respectively cw、cs, the focal length size of focusing probe is d, Wafer diameter is φ, then angular aperture θ of popping one's head inw=2arctan (φ/2d), acoustic beam can be produced when reflecting at water logging workpiece interface Shape transformation, determines that angular domain scanning scope is according to first critical angle lawFurther to reduce ripple Impact of the shear wave to immersed ultrasonic test when type is changed, angular domain scanning scope is ultimately determined toFor Ensure acoustic beam in workpiece along the continuous scanning in angular domain direction, according to Snell's law | Δ the φ |≤θ that determine that scanning angular interval isw
Step 2:Echo wave signal acquisition in angular domain, the angular domain scanning scope determined according to step one and scanning angular interval, will Measured workpiece is placed in one and has X/Y/Z/A four-spindle automatic ultrasound detection platforms, and by motion control device focusing probe is adjusted Position makes it vertical and focuses on surface of the work, labelling starting point B (0,0) tailing edge X-direction swept with the step distance of Δ x (n, 0), synchronous storage echo-signal data (i, j, 0 °), wherein virtual source total number are n/ Δ x, and n is represented in formula to look into B to terminal Along X-direction coordinate, i represents the sampling number along X-axis scanning direction to beam index, and j represents the sampling that direction is detected along Z axis Points, define the clockwise direction of A axles just, by motion control device the rotation of A axles and Z axis movement to be controlled, and make focusing probe Rotation scanning angular interval Δ φ and focus on surface of the work starting point B (0,0), then along X-direction with the step distance of Δ x Carry out scanning to terminal B (n, 0), synchronous storage echo-signal data (i, j, Δ φ) is repeated to obtain angular domain after aforesaid operations and is swept Whole echo-signals data (i, j, ± N Δ φ) in the range of looking into, N is represented and inclined in half angular domain inner focusing probe scanning in formula Number of times;
Step 3:Echo-signal reconstruct in virtual source, sets up water logging workpiece angular domain virtual source model, obtains focusing probe at angle So that during any scanning angle scanning, the virtual source acoustic beam angle of flare size of reconstruct is in water logging workpiece in domain Accordingly echo-signal data (i, j, ± N Δ φ) that step 2 is obtained is reconstructed into into data (i, j, ± N in virtual source θt);
Step 4:Synthetic aperture focusing is imaged, and sets up based on the time delay superposition algorithm of angular domain virtual source model, to step 3 Echo-signal after being reconstructed enters line delay superposition calculation, the voltage magnitude after each imaging point superposition is obtained, to imaging region Interior whole point voltage amplitudes are normalized after calculating assignment again, realize the water logging ultrasound synthetic aperture based on angular domain virtual source Focal imaging.
A kind of water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source, water logging in the step 3 The virtual source acoustic beam angle of flare θ of reconstruct in workpiecetComputational methods are:Water logging workpiece angular domain virtual source model is set up, by this alunite Tumour of external auditory meatus rule calculates virtual source acoustic beam angle of flareIf focusing probe scanning angular interval is Δ φ, when | Δ φ | < θwWhen, virtual source acoustic beam occurs overlap in workpiece along angular domain direction, to lap using averaging method process, Focusing probe is determined in angular domain so that during any scanning angle scanning, the virtual source acoustic beam angle of flare size of reconstruct is in water logging workpieceA kind of water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source, it is described Time delay superposition algorithm in step 4 based on angular domain virtual source model is comprised the following steps:
Step 1, for arbitrfary point P (i, j) in workpiece, it is effectively synthesized aperture lengthZs tables in formula Show depth of the point P apart from surface of the work,The probe for participating in time delay superposition calculation is moved along X-direction Dynamic number of timesK=round (n) is obtained after rounding to n;
Step 2, as the K > 2 in step 1, K is compensated to obtain to Kn, make KnFor even number, that is, participate in time delay superposition calculation Probe number be odd number;When K≤2, line delay superposition calculation, execution step 9 are not entered;
Echo signal data data (i, j, 0 °) when step 3, reading scanning angle are 0 °, is entered as initial value SUM0
Step 4, defined variable ii, represent the virtual source of i-th i participation time delay superposition calculation, and ii assigns initial value 1;
The tiltangleθ of virtual source to P (i, j) points in step 5, calculation procedure 4ii=atan (ii Δ x/zs), during time delay Between t=(zs/cosθii-zs)/c, along Z axis time delay sampling number T=round (t/dt) in direction is detected, dt is represented along detection side To sampling time interval, trace-changing coefficient ε=0.5 [1+cos (2 π η)], in formula, η=ii Δ x/L;
Step 6, the tiltangleθ for obtaining step 5iiWith single virtual source acoustic beam angle of flare θtIt is divided by, and result is carried out Round up N=ceil (θiit);
Step 7, the trace-changing coefficient ε in step 5 is added into time delay superposition calculation, computing formula is:
SUM=SUM0+ε(data(i-ii,j+T,-N·θt)+εdata(i+ii,j+T,N·θt));
Step 8, the result that step 7 is obtained is newly defined as into initial value SUM0, i-th i+1 virtual source is processed, continue executing with Step 3 is to 7, until ii=Kn/2-1;
Step 9, the SUM that obtain final to step 8 carry out average value processing, data (i, j)=SUM/ (Kn+ 1), and will process Afterwards the voltage magnitude of data gives P (i, j).
The method have technical effect that, for the ultrasonic synthetic aperture focusing of water logging workpiece is imaged, by using virtual Source technology, without the need for consider acoustic beam in water and workpiece in propagation path, acoustic speed of propagation change, so as to improve time delay superposition calculation Efficiency;By the time delay superposition algorithm based on angular domain virtual source model, realize that synthetic aperture technique is answered with space in ultra sonic imaging The combination of conjunction technology, can obtain angular domain ultrasound synthetic aperture focusing image, so as to improve into by a time delay superposition calculation As efficiency and precision, impact of the speckle noise to being imaged is reduced.
Below in conjunction with the accompanying drawings the invention will be further described.
Description of the drawings
Fig. 1 is the water logging ultrasound synthetic aperture focusing Irnaging procedures figure based on angular domain virtual source that the present invention is carried;
Fig. 2 is water logging workpiece acoustic beam propagation model schematic of the present invention;
Fig. 3 is virtual source model schematic diagram of the present invention;
Fig. 4 is echo wave signal acquisition schematic diagram in virtual source of the present invention;
Fig. 5 is angular domain virtual source model schematic diagram of the present invention;
Fig. 6 is time delay superposition calculation flow chart of the present invention based on angular domain virtual source model;
Fig. 7 is the pictorial diagram that test block is detected in the specific embodiment of the invention;
Fig. 8 sweeps image for focusing probe B of the present invention;
Fig. 9 adopts conventional synthesis aperture focus method image for the present invention;
Figure 10 is water logging ultrasound synthetic aperture focusing image of the present invention based on angular domain virtual source.
Specific embodiment
By taking the immersed ultrasonic test of aluminum test block as an example, test block pictorial diagram is as shown in fig. 7, test block for the specific embodiment of the invention Size is 120mm × 100mm, and targeted imaging region size is 15mm × 30mm, a diameter of 2mm of defective hole, to target imaging area Domain carries out the water logging ultrasound synthetic aperture focusing imaging based on angular domain virtual source, and its step includes:
Step one, the modeling of water logging workpiece acoustic beam propagation, determine angular domain scanning scope and scanning angular interval.Compressional wave is in water Spread speed cwFor 1480m/s, spread speed c in aluminumsFor 5840m/s, this example ultrasonic probe is using GE company types of the U.S. Number for IS-5.0-1.0-5.0 water immersion focusing probe, center probe frequency be 5MHz, wafer diameter is 25mm, and focal length is 125mm.Water logging aluminum workpiece acoustic beam propagation is modeled, determines that angular domain scanning scope is -4.5 ° of < βw4.5 ° of <, scanning angular interval is Δ φ≤11.4 °, with reference to actually detected needs, determine that angular domain scanning scope is -4 °≤βw≤ 4 °, scanning angular interval Δ φ= , with -4 °, -3 °, -2 °, -1 °, 0 °, 1 °, 2 ° in angular domain, 3 °, 4 ° of scanning angles carry out scanning for 1 °, i.e. focusing probe;
Echo wave signal acquisition in step 2, angular domain, is positioned over test block one and has X/Y/Z/A four-spindle automatic ultrasound detection Platform, adjusting focusing probe position by motion control device makes its vertical workpiece surface, and ensures that the underwater sound, away from for 125mm, is marked Remember initial point B (0,0) tailing edge X-direction, step distance Δ x be 0.1mm, scanning to terminal B (120,0), along X-axis scanning direction Sampling number be 1200, detect that the sampling number in direction is 4096 along Z axis, virtual source total number is 1200, synchronous storage Echo-signal data (1200,4096,0 °);The rotation of control A axles and B axle movement make probe edge rotate clockwise 1 ° of scanning angle, and Focus on starting point B (0,0), then along X-direction with the step distance of 0.1mm carry out scanning to terminal B (120, it is 0), synchronous Storage echo-signal data (1200,4096,1 °), repeats aforesaid operations and can obtain in angular domain scanning angle to be respectively -4 °, -3 °, - 2 °, -1 °, 0 °, 1 °, 2 °, 3 °, whole echo-signals when 4 °;
Echo-signal reconstruct in step 3, virtual source, sets up water logging workpiece angular domain virtual source model, obtains focusing probe and exists With during any scanning angle scanning in angular domain, virtual source acoustic beam angle of flare size θ of reconstruct in water logging workpiecet=3.9 °, accordingly will The echo data that step 2 is obtained is reassembled as in angular domain:data(xi,4096,N·θt),(xi=1 ... 1000, N=-4 ... 0,…4);
Step 4, synthetic aperture focusing imaging, by the time delay superposition algorithm based on angular domain virtual source model, to step 3 Echo-signal after being reconstructed enters line delay superposition calculation, the voltage magnitude after each imaging point superposition is obtained, to imaging region Interior whole point voltage amplitudes are normalized after calculating assignment again, realize the water logging ultrasound synthetic aperture based on angular domain virtual source Focal imaging, wherein being comprised the following steps based on the time delay superposition algorithm of angular domain virtual source model:
Step 1, for arbitrfary point P (i, j) in workpiece, it is effectively synthesized aperture lengthZ in formulasTable Show depth of the point P apart from surface of the work,The probe for participating in time delay superposition calculation is moved along X-direction Dynamic number of timesK=round (n) is obtained after rounding to n;
Step 2, as the K > 2 in step 1, K is compensated to obtain to Kn, make KnFor even number, that is, participate in time delay superposition calculation Probe number be odd number;When K≤2, line delay superposition calculation, execution step 9 are not entered;
Echo signal data data (i, j, 0 °) when step 3, reading scanning angle are 0 °, is entered as initial value SUM0
Step 4, defined variable ii, represent the virtual source of i-th i participation time delay superposition calculation, and ii assigns initial value 1;
The tiltangleθ of virtual source to P (i, j) points in step 5, calculation procedure 4ii=atan (ii Δ x/zs), during time delay Between t=(zs/cosθii-zs)/c, along Z axis time delay sampling number T=round (t/dt) in direction is detected, dt is represented along detection side To sampling time interval, trace-changing coefficient ε=0.5 [1+cos (2 π η)], in formula, η=ii Δ x/L;
Step 6, the tiltangleθ for obtaining step 5iiWith single virtual source acoustic beam angle of flare θtIt is divided by, and result is carried out Round up N=ceil (θiit);
Step 7, the trace-changing coefficient ε in step 5 is added into time delay superposition calculation, computing formula is:SUM=SUM0+ε (data(i-ii,j+T,-N·θt)+εdata(i+ii,j+T,N·θt));
Step 8, the result that step 7 is obtained is newly defined as into initial value SUM0, i-th i+1 virtual source is processed, continue executing with Step 3 is to 7, until ii=Kn/2-1;
Step 9, the SUM that obtain final to step 8 carry out average value processing, data (i, j)=SUM/ (Kn+ 1), and will process Afterwards the voltage magnitude of data gives P (i, j).
Fig. 8 show focusing probe B and sweeps imaging, and Fig. 9 is shown using conventional synthesis aperture focus method image, Figure 10 It show the water logging ultrasound synthetic aperture focusing imaging based on angular domain virtual source, a diameter of 2mm defective holes under three kinds of imaging methods Characteristic information and image quality as shown in table 1, as shown in Table 1 the water logging ultrasound synthetic aperture focusing based on angular domain virtual source into Picture resolution is higher, and eliminates the impact of system and construct noise to being imaged.
Table 1

Claims (3)

1. a kind of water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source, it is characterised in that including following step Suddenly:Step one:Water logging workpiece acoustic beam propagation is modeled, and according to workpiece geometry and material parameter water logging workpiece acoustic beam propagation mould is set up Type, and angular domain scanning scope and scanning angular interval are determined according to acoustic beam propagation model, wherein angular domain refers to focusing probe arbitrarily to sweep Central axis and workpiece incidence point normal angle when looking into angle scanning, scanning angular interval refers to that focusing probe is adjacent during scanning in angular domain Scanning angular spacing, if the velocity of sound of the acoustic beam in water and in workpiece is respectively cw、cs, the focal length size of focusing probe is d, chip A diameter of φ, then angular aperture θ of popping one's head inw=2arctan (φ/2d), acoustic beam can produce wave mode when reflecting at water logging workpiece interface Conversion, determines that angular domain scanning scope is according to first critical angle lawTurn further to reduce wave mode Impact of the shear wave to immersed ultrasonic test when changing, angular domain scanning scope is ultimately determined toTo ensure Acoustic beam in workpiece along the continuous scanning in angular domain direction, according to Snell's law | Δ the φ |≤θ that determine that scanning angular interval isw
Step 2:Echo wave signal acquisition in angular domain, the angular domain scanning scope determined according to step one and scanning angular interval, will be tested Workpiece is placed in one and has X/Y/Z/A four-spindle automatic ultrasound detection platforms, and by motion control device focusing probe position is adjusted Make it vertical and focus on surface of the work, labelling starting point B (0,0) tailing edge X-direction scanning is carried out extremely with the step distance of Δ x (n, 0), synchronous storage echo-signal data (i, j, 0 °), wherein virtual source total number are n/ Δ x to terminal B, and n represents acoustic beam in formula Along X-direction coordinate, i represents the sampling number along X-axis scanning direction to incidence point, and j represents the sampled point that direction is detected along Z axis Number;The clockwise direction of A axles is defined just, by motion control device the rotation of A axles and Z axis movement to be controlled, focusing probe is revolved Turn scanning angular interval Δ φ and focus on surface of the work starting point B (0,0), then entered with the step distance of Δ x along X-direction Row scanning B (n, 0), synchronous to store echo-signal data (i, j, Δ φ), acquisition angular domain scanning after repetition aforesaid operations to terminal In the range of whole echo-signals data (i, j, ± N Δ φ), N is represented and inclined time in half angular domain inner focusing probe scanning in formula Number;
Step 3:Echo-signal reconstruct in virtual source, sets up water logging workpiece angular domain virtual source model, and acquisition focusing probe is in angular domain So that during any scanning angle scanning, the virtual source acoustic beam angle of flare size of reconstruct is in water logging workpiece Accordingly echo-signal data (i, j, ± N Δ φ) that step 2 is obtained is reconstructed into into data (i, j, ± N in virtual source θt);
Step 4:Synthetic aperture focusing is imaged, and sets up based on the time delay superposition algorithm of angular domain virtual source model, and step 3 is obtained Echo-signal after reconstruct enters line delay superposition calculation, the voltage magnitude after each imaging point superposition is obtained, to complete in imaging region Portion's point voltage amplitude is normalized after calculating assignment again, realizes the water logging ultrasound synthetic aperture focusing based on angular domain virtual source Imaging.
2. a kind of water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source as claimed in claim 1, it is special Levy and be, the virtual source acoustic beam angle of flare θ reconstructed in water logging workpiece in the step 3tComputational methods are:Set up water logging workpiece Angular domain virtual source model, by snell law virtual source acoustic beam angle of flare is calculatedIf focusing on Probe scanning angular interval is Δ φ, as | Δ φ | < θwWhen, virtual source acoustic beam occurs overlap in workpiece along angular domain direction, right Lap determines focusing probe in angular domain during any scanning angle scanning, to reconstruct in water logging workpiece using averaging method process Virtual source acoustic beam angle of flare size be
3. a kind of water logging ultrasound Synthetic Aperture Focussing Imaging based on angular domain virtual source according to claim 1, its It is characterised by, the time delay superposition algorithm in the step 4 based on angular domain virtual source model is comprised the following steps:
Step 1, for arbitrfary point P (i, j) in workpiece, it is effectively synthesized aperture lengthZ in formulasRepresent point P apart from surface of the work depth,The probe of time delay superposition calculation is participated in along X-direction movement time NumberK=round (n) is obtained after rounding to n;
Step 2, as the K > 2 in step 1, K is compensated to obtain to Kn, make KnFor even number, that is, participate in the spy of time delay superposition calculation Head number is odd number;When K≤2, line delay superposition calculation, execution step 9 are not entered;
Echo signal data data (i, j, 0 °) when step 3, reading scanning angle are 0 °, is entered as initial value SUM0
Step 4, defined variable ii, represent the virtual source of i-th i participation time delay superposition calculation, and ii assigns initial value 1;
The tiltangleθ of virtual source to P (i, j) points in step 5, calculation procedure 4ii=atan (ii Δ x/zs), delay time t= (zs/cosθii-zs)/c, along Z axis time delay sampling number T=round (t/dt) in direction is detected, dt is represented along detection direction Sampling time interval, trace-changing coefficient ε=0.5 [1+cos (2 π η)], in formula, η=ii Δ x/L;
Step 6, the tiltangleθ for obtaining step 5iiWith single virtual source acoustic beam angle of flare θtIt is divided by, and result is carried out upwards Round N=ceil (θiit);
Step 7, the trace-changing coefficient ε in step 5 is added into time delay superposition calculation, computing formula is:
SUM=SUM0+ε(data(i-ii,j+T,-N·θt)+εdata(i+ii,j+T,N·θt));
Step 8, the result that step 7 is obtained is newly defined as into initial value SUM0, i-th i+1 virtual source is processed, continue executing with step 3 To 7, until ii=Kn/2-1;
Step 9, the SUM that obtain final to step 8 carry out average value processing, data (i, j)=SUM/ (Kn+ 1), and after processing count According to voltage magnitude give P (i, j).
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