Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/22—Details, e.g. general constructional or apparatus details
  • G01N29/26—Arrangements for orientation or scanning by relative movement of the head and the sensor
  • G01N29/262—Arrangements for orientation or scanning by relative movement of the head and the sensor by electronic orientation or focusing, e.g. with phased arrays
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/04—Analysing solids
  • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
  • G01N29/0654—Imaging
  • G01N29/069—Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/04—Analysing solids
  • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
  • G01N29/0654—Imaging
• • 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
  • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
  • G01N29/4463—Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering
• • 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
  • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
  • G01N29/46—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by spectral analysis, e.g. Fourier analysis or wavelet analysis
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
  • G01S15/88—Sonar systems specially adapted for specific applications
  • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
  • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
  • G01S15/8909—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration
  • G01S15/8915—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration using a transducer array
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
  • G01S15/88—Sonar systems specially adapted for specific applications
  • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
  • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
  • G01S15/8977—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52046—Techniques for image enhancement involving transmitter or receiver
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/02—Indexing codes associated with the analysed material
  • G01N2291/028—Material parameters
  • G01N2291/0289—Internal structure, e.g. defects, grain size, texture
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/10—Number of transducers
  • G01N2291/106—Number of transducers one or more transducer arrays

Definitions

• the present invention relates to a transform imaging method of
• Two-dimensional fourier of an acquisition by ultrasonic probing of an object It also relates to a computer program and a corresponding ultrasonic sounding device.
• the invention applies more particularly to a two-dimensional Fourier transform imaging method of an acquisition by ultrasonic probing of an object, comprising the following steps:
• N reception transducers so as to receive simultaneously and for a predetermined period, for each transmission, N time measurement signals, measuring in particular echoes due to backscattering of the transmission considered in the object,
• This method is advantageous by its algorithmic speed and the quality of the result obtained.
• it operates in a simple context of medical imaging or non-destructive testing when the defects to be visualized are easily identifiable in direct mode, that is to say by direct backscattering without internal reflection in the object 102 and without changing the mode of propagation.
• the quality of the resulting image deteriorates rapidly.
• N reception transducers so as to receive simultaneously and for a predetermined duration, for each transmission, N time measurement signals, measuring in particular echoes due to backscattering of the emission considered in the object , [0017] time sampling of each time measurement signal in Nt successive samples,
• the L emission transducers are controlled for M successive emissions of plane ultrasonic waves of successive emission angles 0 m different in M emission zones.
• ku and kt are the wave numbers, respectively spatial and temporal, representative of the rows and columns of each spectral matrix FTMR m , kx and kz are the spatial frequencies representative of the rows and columns of each spectral image FTL, ⁇ represents an addition or a subtraction, g is the parameter characterizing the change in propagation mode during a backscattering in the object probed and 0 ' m is an incident angle during the backscattering determinable from 0 m using Snell-Descartes' law.
• the parameter g is defined as the ratio between the speed of propagation of any wave emitted according to its mode of propagation after its backscattering in the object probed and the speed of propagation of this same wave according to its mode of propagation before its back-diffusion in the object probed.
• the matrix transformation relation takes the following form:
• the imaging method does not take into account any reflection against a wall of the object and:
• the imaging method takes into account a reflection against a background of the object located at a distance H from a front face of the object receiving the waves emitted by the emission transducers, and:
• Y r is a parameter characterizing a possible change in propagation mode during the reflection against the background of the object probed, in particular defined as a ratio between the propagation speed of any wave emitted according to its propagation mode after its reflection and the speed of propagation of this same wave according to its mode of propagation before its reflection.
• Y ri is a parameter characterizing a possible change in propagation mode during the first reflection against the background of the object probed, in particular defined as a ratio between the speed of propagation of any wave emitted according to its mode of propagation after its first reflection and the propagation speed of this same wave according to its propagation mode before its first reflection
• y r 2 is a parameter characterizing a possible change in propagation mode during the second reflection against the front face of the probed object, notably defined as the ratio between the speed of propagation of any wave emitted according to its mode of propagation after its second reflection and the speed of propagation of this same wave according to its mode of propagation before its second reflection
• g G4 is a parameter characterizing a possible change in propagation mode during the third reflection against the background of the object probed, notably defined as a ratio between the propagation speed of any wave emitted according to its propagation mode after its third reflection and the propagation speed of this same wave according to its propagation mode before its third reflection
• 0 ” m
• the conversion of each FTMR m spectral matrix for obtaining the M FTI m spectral images includes a limitation of support of a spectral space of each FTMR m spectral matrix in order to conserve only the waves which propagate and to remove any ambiguity of correspondence between the spectral space of each spectral matrix FTMR m and that of the corresponding spectral image FTL when the system of equations of change of reference frame is not bijective.
• an ultrasonic probing device for the ultrasonic probing of an object, comprising:
• Control means of the N reception transducers so as to receive simultaneously and for a predetermined duration, for each transmission, N time measurement signals, measuring in particular echoes due to backscattering of the transmission considered , and
• a processor for reconstituting an ultrasound image for viewing the object configured to perform the following treatments:
• the processor being further configured for:
• Figure 1 schematically shows the general structure of an ultrasonic probing device according to an embodiment of the invention
• FIG. 2 illustrates a principle of successive transmissions of plane ultrasonic waves which can be implemented by the device of FIG. 1,
• FIG. 3 illustrates a first case of taking into account reflection (s) and / or change (s) of mode (s) possible for the device of FIG. 1,
• FIG. 4 illustrates a second case of taking into account reflection (s) and / or change (s) of mode (s) possible for the device of FIG. 1,
• FIG. 5 illustrates a third case of taking into account reflection (s) and / or change (s) of mode (s) possible for the device of FIG. 1,
• Figure 6 illustrates the result of a first example of matrix conversion that can be performed by the device of Figure 1, in the case of Figure 4,
• Figure 7 illustrates the result of a second example of matrix conversion that can be performed by the device of Figure 1, in the case of Figure 4,
• Figure 8 illustrates the result of a third example of matrix conversion that can be performed by the device of Figure 1, in the case of Figure 4, and
• Figure 9 illustrates the successive steps of a method of acquisition and processing of ultrasonic signals implemented by the device of Figure 1, according to one embodiment of the invention.
• the object 102 is for example a mechanical part which one wishes to examine by non-destructive testing or else, in a medical context, a part of the human or animal body which one wishes to control in a non-invasive manner.
• the object 102 is immersed in a liquid, such as water 1 10, and the probe 104 is kept away from the object 102 so that the water 1 10 separate.
• the probe 104 could be in direct contact with the object 102. It is even this other embodiment which will be discussed more below.
• the transducers 108 1 , ..., 108 N are designed to individually emit ultrasonic waves towards the object 102 in response to control signals identified under the general reference C, along main directions parallel to each other to the others, indicated by dotted arrows in FIG. 1, and in a main plane which is that of the figure.
• the transducers 108 1 , ..., 108 N are also designed to detect echoes of ultrasonic waves reflecting or backscattering on and in the object 102 and to provide measurement signals identified under the reference general S and corresponding to these echoes.
• the transducers 108i, ..., 1 08 N fulfill both the transmission and reception functions, but receivers different from the transmitters could also be provided in housings different and independent while remaining consistent with the principles of the invention.
• the number L of transmitters could quite be different from the number N of receivers.
• the sounding device 100 further comprises an electronic circuit 1 12 for controlling the transducers 108i, ..., 108 N of the probe 104 and for processing the measurement signals S.
• This electronic circuit 1 12 is connected to the probe 104 in order to transmit the control signals C to it and in order to receive the measurement signals S.
• the electronic circuit 1 12 is for example that of a computer. It has a central processing unit 1 14, such as a microprocessor designed to transmit to the probe 104 the control signals C and to receive the measurement signals S from the probe 104, and a memory 1 16 in which is notably recorded a computer program 1 18.
• the computer program 1 18 comprises first of all instructions 120 for generating the signals C for controlling the transducers 108i, ..., 108 N and receiving their echoes. These instructions are more precisely programmed so as to:
• transducers 108i, ..., 1 08 N Activate the transducers 108i, ..., 1 08 N as receivers for, following each transmission, receive simultaneously, by these N receivers and for a predetermined period of the desired inspection depth, N time signals measurement, in particular measuring echoes due to backscattering of each program considered in object 102.
• planar ultrasonic waves having M different successive emission angles in M emission zones of the object 102 can be obtained on emission by applying to the transducers 108i, ..., 108 N of the laws delays recorded in memory 11 16 in a base 122 of delay laws.
• Each delay law defines delays to be applied to transducers 108i, ..., 108 N in emission, so as to generate a planar ultrasonic wave at a desired emission angle among the M different successive emission angles. There are therefore as many delay laws as desired successive transmissions.
• the first plane wave emission is associated with a delay law Ti relating to signals emitted by the transducers 108i, ..., 108 N , allowing the emission of a plane wave with an emission angle 0i with respect to the direction z in a first emission zone ZEi partially located outside the opening of the probe 104.
• the (M + 1) / 2nd wave emission plane is associated with a uniform delay law T ( M + I) / 2 for the emission of a plane wave of zero emission angle with respect to the direction z in a (M + 1) / 2nd emission zone ZE ⁇ M + I ) / 2 covering the opening of the probe 104.
• the area to be imaged must be contained in the union of the M successive broadcast areas. As a result, this zone can extend beyond the opening of the probe 104, as can be seen in FIG. 2.
• the imaged zone can take the form of a sectoral zone delimited by the ends maximum and minimum angle emission zones. We can thus obtain an S-scan type image.
• the M successive different emission angles 0i to 0 M can be defined around an average direction 0 ⁇ M + I) / 2 not perpendicular to the network of transducers 108i, ..., 108N.
• this crack also being perpendicular to the network of transducers, it is preferable to offset the side area to be inspected in relation to probe 104 and to emit around an average of 45 ° for example. The area to be inspected can even be offset to the point of completely emerging from the opening of probe 104.
• apodization of the ultrasonic signals emitted by the transducers 108i, ..., 108 N is also possible to apply apodization of the ultrasonic signals emitted by the transducers 108i, ..., 108 N to form an ultrasonic wave better quality plane, without distortion due to side effects.
• Such apodization is carried out on the occasion of each emission spatially on all of the transducers using an apodization window such as a law of trapezoidal amplitude, of Hanning or of Blackman-Harris. The result is to provide a better definition of the successive emission zones.
• waves other than plane waves can be emitted, for example cylindrical waves as in the article by Hunter et al cited above. It suffices to adapt the number of transducers to be requested (between 1 and L) and the delay laws accordingly, depending on the acquisitions and applications targeted. However, in the following description and for the sake of simplifying the calculations which will be presented, it is plane emissions such as those illustrated in FIG. 2 which are used.
• the set S of the NxM time measurement signals received by the N transducers 108i, ..., 108 N is returned by the probe 104 to the central processing unit 1 14.
• these time signals are sampled and digitized in N t successive samples before being submitted for processing by the computer program 1 18.
• the computer program 1 18 then further comprises instructions 124 for constructing M matrices MR m , 1 £ m £ M, of ultrasonic time signals of size NxN t , qualified as plane wave matrices.
• the computer program 1 18 further comprises instructions 126 for performing a temporal filtering of each matrix MR m , this filtering aiming at removing any information found at flight times excluded from the area d interest in object 102.
• the computer program 1 18 further comprises instructions 128 for transforming each matrix MR m into a matrix FTMR m of frequency signals by two-dimensional Fourier transform in rows and columns, advantageously by discrete two-dimensional Fourier transform and, more advantageously still, by two-dimensional calculation of FFT (from the English “Fast Fourier Transform”) if the numbers N and N t of rows and columns of each matrix MR m allow it, that is to say if they correspond to powers of 2.
• the computer program 1 18 further comprises instructions 130 for converting each spectral matrix FTMR m into a spectral image FTI m in a space of spatial frequencies respectively relative to the abscissa and ordinate axes of the final image that one wishes to obtain.
• this conversion involves the application of a matrix transformation relation of the M matrices FTMR m into the M spectral images FTL and the application of a bilinear interpolation using '' a system of equations for changing the benchmark. More precisely, the matrix transformation gives values for the spectral images at points (kx'i, kz ' j ), 1 ⁇ i £ N and 1 £ j £ N t , which do not correspond to the discrete values (kxi, kz j ) chosen but depend on the system of equation of change of reference which links the values of the spatial frequencies kx and kz to the values of the wave numbers ku and kt.
• the desired FTI m (kXi, kZ j ) coefficients, with 1 ⁇ i £ N x and 1 £ j £ N z , can nevertheless be easily found by bilinear interpolation of the FTI m values (kx ', kz' j ) obtained by transformation matrix, using the system of equation of change of reference which allows to know the positioning of the points (kx'i, kz ' j ), 1 ⁇ i £ N and 1 ⁇ j £ N t .
• the computer program 1 18 further comprises instructions 132 for making a combination of the M spectral images FTL into a single resulting spectral image FTI of coefficients FTI (kX, kz j ), 1 ⁇ i £ N x and 1 ⁇ j £ N z .
• the spectral image FTI can result from a sum in each pixel (kxi, kz j ) of the M spectral images FTL.
• the computer program 1 18 includes instructions 134 for transforming the resulting spectral image FTI into an ultrasound image I for viewing the object 102 by two-dimensional inverse Fourier transform in rows and columns, advantageously by transform of discrete inverse Fourier, and, more advantageously still, by two-dimensional calculation of IFFT (from the English “Inverse Fast Fourier Transform”) if the numbers N x and N z of rows and columns of the resulting spectral image FTI allow it, that is to say if they correspond to powers of 2.
• the ultrasonic image I for viewing the object 102 is of size N x xN z and of pixel values l (Xi, Zj).
• FTI m (kx, kz) Vkt 2 - ku 2 FTMR m (ku, kt).
• the time wave number kt depends on the propagation mode, so that the number of waves corresponding to an incident transmitted wave may differ from the number of waves corresponding to this same wave when it has been reflected at least once as well as after back-scattering, due to the possible taking into account of changes in propagation modes.
• what remains constant for the same wave whatever the mode changes is the product of the wave number and the speed of propagation of the wave, i.e. its angular frequency .
• kt the number of waves corresponding to the wave in its propagation mode as it occurs just after its backscattering.
• the symbol! represents an addition or a subtraction according to the number of reflection (s) against one or more walls of the object 102.
• the angle 0 ' m is the incident angle during the backscattering. It can be obtained simply from the angle 0 m using the Snell-Descartes law and according to the number of reflection (s) preceding the backscatter considered. As 0 m , it is expressed as a function of the z axis illustrated in FIG. 2, that is to say an axis orthogonal to the plane or to the axis of the transducers.
• y is the parameter characterizing the change in propagation mode of a wave during a backscattering in the object 102.
• it is defined as the ratio between the speed of propagation of the wave emitted according to its mode of propagation after its backscattering in the object probed and the speed of propagation of this same wave according to its mode of propagation before its backscattering in the object probed. Consequently, if kt is the wave number corresponding to the wave after backscattering, y.kt is the wave number corresponding to the incident wave during the backscattering.
• FTI m (kx, kz) Vkt 2 - ku 2 FTMR m (ku, kt).
• the parameter y is different from 1. It is equal to the ratio C / C between the propagation speed C of the backscattered wave in mode M 2 and the propagation speed ci of the incident wave in mode M before its backscattering against the fault D. It is strictly less than 1 if the mode change is that of a longitudinal propagation mode noted L (before backscattering) into a transverse propagation mode noted T (after backscattering). On the contrary, it is strictly greater than 1 if the mode change is that of a propagation mode T (before backscattering) into a propagation mode L (after backscattering).
• a reflection against the background of the object 102 is taken into account, and a change in propagation mode can be taken into account during this reflection or any subsequent backscatter against a defect in the object 102.
• This second case is illustrated by FIG. 4.
• the x axis of the chosen abscissa is always parallel to the transducers, on the plane of the front face and on the plane of the bottom of the object 102.
• the z axis of the chosen ordinates is also always orthogonal to the transducers, to the plane of the front face and to the plane of the bottom of the object 102. It is also a question of an extended shear defect located at the bottom d object 102.
• the calculations exploiting the identity of Weyl to the M emissions of plane waves illustrated in FIG. 2 then give, for the relatio n of aforementioned general matrix transformation:
• y r is the parameter characterizing the possible change in propagation mode during the reflection against the background of the probed object. It is defined as a ratio C2 / C1 between the propagation speed C2 of the wave emitted according to its propagation mode M 2 after its reflection against the background of the object probed and the propagation speed ci of this same wave according to its propagation mode M1 before its reflection against the background of the object probed.
• the parameter y is then defined as a ratio C3 / C2 where C3 is the speed of propagation of the wave backscattered in mode M 3 .
• the parameter g can be equal to 1 if there is no taking into account of a change in propagation mode during the backscattering.
• g G is equal to 1 if there is no taking into account of a change in propagation mode during the reflection against the background of the object 102.
• This third case is illustrated by FIG. 5.
• the x-axis of the abscissa chosen is always parallel to the transducers, on the plane of the front face and on the plane of the bottom of the object 102.
• the z-axis of the ordinates chosen, from from which the angles 0 m and 0′m are defined, is also always orthogonal to the transducers, to the plane of the front face and to the plane of the bottom of the object 102.
• the angle 0 ′ m remains the incident angle during the backscatter, that is to say the one after the second reflection against the front face of the object.
• we introduce another angle 0 ” m also defined from the z axis, corresponding to the angle of the wave after its first reflection against the background of the object 102.
• kt is always the wave number just after backscattering by the default, corresponding here to the mode of propagation M.
• g G i is the parameter characterizing the possible change in propagation mode during the first reflection against the background of the probed object
• g G2 is the parameter characterizing the possible change in mode of propagation during the second reflection against the front face of the probed object
• g G4 is the parameter characterizing the possible change in propagation mode during the third reflection against the background of the probed object.
• the parameter g is then defined as the ratio c 4 / C 3 where c 4 is the speed of propagation of the backscattered wave in M mode and C 3 is the speed of propagation of the wave just before backscattering in M 3 mode.
• kt is always the wave number corresponding to the wave just after backscattering
• Y M .Y r2 .Y.kt is the wave number corresponding to the incident wave emitted before its first reflection against the background of the object 102 and Y r2 -Y-kt corresponds to the wave just after this first reflection.
• kt / Y r4 is the wave number corresponding to the wave received by the transducers.
• the parameter g can be equal to 1 if there is no consideration of a change in propagation mode during the backscattering.
• the supports of the respective spectral spaces of the matrices and spectral images FTMR m and FTI m it is advantageous to limit, by windowing, the supports of the respective spectral spaces of the matrices and spectral images FTMR m and FTI m .
• the system of equations of change of reference frame can be bijective or not .
• the support can be even more limited to avoid any ambiguity involving a risk of artefacts, which simplifies the calculations even more.
• the missing data resulting from these media limitations is anyway compensated by the combination of the M FTL spectral images which brings together all their media.
• FIGS. 6, 7 and 8 Three examples of which given purely by way of illustration in FIGS. 6, 7 and 8 in the aforementioned second case and illustrated by FIG. 4 with a single reflection against the background of the object 102 with or without changes in modes propagation of the waves emitted.
• FIG. 7 illustrates the effect of the system of reference change equations on the supports of a spectral matrix FTMR m and of its conversion into a spectral image FTL, when a change in propagation mode from L to T takes place during the backscattering of the waves (y ⁇ 1).
• FIG. 8 illustrates the effect of the system of reference change equations on the supports of a spectral matrix FTMR m and of its conversion into a spectral image FTL, when a change in propagation mode from T to L takes place during the backscattering of the waves (y> 1).
• the support Z can be split into two zones Z1 and Z2, Z1 projecting onto two zones Z1 'and Z2' of the support Z 'by changing the reference, while Z2 projects onto two zones Z2' and Z3 'of the support Z '.
• zone Z2 ' each pair (kx, kz) has two antecedents respectively in zones Z1 and Z2.
• FIG. 9 an example of a method 900 for acquiring and processing ultrasonic signals which the device 100 of FIG. 1 can use will now be described according to a preferred embodiment of the invention.
• the processing unit 1 14 executing the instructions 120 controls the emission and reception sequences of the transducers 108i, ..., 108 N for the acquisition of the measurement signals.
• Step 904 the processing unit 11 14 executing the instructions 124 records the measurement signals, these being sampled, digitized and distributed in the M matrices MR m , 1 ⁇ m £ M, to allow further processing.
• Steps 902 and 904 can be executed simultaneously, i.e. it is not necessary to wait until all the shots have been taken before starting to record the measurement signals and carry out a processing such as a image reconstruction.
• the processing unit 1 14 executing the instructions 126 performs a temporal filtering of each matrix MR m , this filtering aiming at removing any information found at flight times excluded from the area of interest.
• This step 906 makes it possible to limit the area to be imaged to a neighborhood close to the defects. in particular by excluding disturbing echogenic interfaces. It finds all its interest in the imagery of cracks forming from the bottom of the object.
• the processing unit 1 14 executing the instructions 128 performs a discrete two-dimensional Fourier transform in rows and columns of each matrix MR m to obtain the M spectral matrices FTMR m .
• the processing unit 1 14 executing the instructions 130 converts each matrix FTMR m to obtain the M spectral images FTI m using a REL of matrix transformation and a system SYS of reference change equations, chosen according to the consideration of reflection (s) and / or change (s) of desired mode (s).
• a step 912 the processing unit 1 14 executing the instructions 132 performs the combination of the M spectral images FTI m into a single resulting spectral image FTI.
• the processing unit 1 14 executing the instructions 134 performs a reverse discrete two-dimensional Fourier transform in rows and columns of the resulting spectral image FTI to obtain the ultrasound image I for viewing the object 102.
• an example (d) of an ultrasound image I in which a defect of 4.3 mm in length on the front face of the object is visible, is given for TTTTT imaging in transmission in T mode with taking account of two rebounds at the bottom and in front face of the object 102 without change of mode.
• faults which are of a type generally difficult to detect and visualize, are here very clearly visible, localized and measurable.
• an ultrasonic sounding device such as that described above makes it possible to visualize complex and usually not very visible defects by cleverly taking into account reflections and changes in possible propagation modes of waves emitted in ultrasound imaging. by two-dimensional Fourier transform. This clever consideration does not add complexity to the treatments performed. A limitation of spectral support can also be envisaged, further simplifying the calculations.
• the computer program instructions could be replaced by electronic circuits dedicated to the functions performed during the execution of these instructions.
• the probe 104 can be at a distance from object 102, for example immersed in a liquid for the good transmission of ultrasonic waves.
• the general principles of the present invention remain valid, only the equations having to be adapted by adding phase terms for taking account of wave transmissions, on emission and on reception, in the liquid medium considered between the probe and the front of the object. This adaptation is particularly simple and within the reach of the skilled person.

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