Advanced ultrasonic 2D Phased-array probes

Transcription

1 Advanced ultrasonic 2D Phased-array probes Frédéric REVERDY 1, G. ITHURRALDE 2, Nicolas DOMINGUEZ 1,2 1 CEA, LIST, F-91191, Gif-sur-Yvette cedex, France frederic.reverdy@cea.fr, nicolas.dominguez@cea.fr 2 EADS France. 18 rue Marius Terce, BP 13050, Toulouse Cedex, guillaume.ithurralde@eads.net, Nicolas.Dominguez@eads.net 18th WCNDT Durban

2 Why 2D array probes? While one-dimensional (1D) array have brought tremendous benefits to NDT inspections, their steering and focusing capabilities are limited to only one plane. Some applications may still require steering and focusing out of the inspection plane. 2D arrays such as matrix arrays and annular sectorial arrays are already available from probe vendors. 2 1 defects 3 Steering in three dimensions 2

3 Probe definition CIVA has a dedicated GUI that allows, through a set of parameters, a quick definition of various 2D array probes (matrix, annular, elliptical, bi-elliptical, flexible) Number of elements in each direction Element size Distance between the elements Flexible array Annular Elliptical array 5 1 3

4 Delay laws Calculation of delay laws CIVA allows to calculate complex delay laws (point focusing, beam steering, sectoral scanning ) to steer and focalize the energy in any directions. The delay laws algorithm takes into account irregular surfaces, anisotropic media and heterogeneous materials Simulation of the UT field radiated by a phased array transducer: Simulation of beam defect interaction : Calculate the interaction of the beam with defects using various models (side-drilled hole, flat-bottomed hole, cracks either planar or defined by CAD, inclusions ) Booth 111 4

5 2D probes limitations and need for new probes Limitations With a limited number of channels fixed by the electronic systems, often 128 or 256, respecting the pitch rule (λ/2) translates into a small total aperture thus decreasing the 2D probe focusing and electronic capabilities. Solutions Several authors have looked at increasing the size of the probe by adjusting the element pattern of the probe Hexagonal distribution with elements located on a triangular grid with a spacing λ/ 3 Random distributions have been investigated as a way to break periodicity Arrays with elements lying along spirals It is necessary to develop tools (probe and element definition, delay law calculation, spot size, grating lobes evaluation ) that allow definition of these probes to exploit their full potential 5

6 New probe definition in CIVA 2D array imports To allow more complex arrays, a GUI has been added to allow users to create or import designs from a spreadsheet file in which elements are defined by their size and positions in the array. 1. Define the crystal shape (rectangular, circular or oval) 2. Add and position elements (rectangular, triangular, circular and hexagonal 3. Rotate elements 6

7 New probe definition in CIVA 2D array imports hexagonal spiral Hexagonal element array Mix of elements 7

8 New probe definition in CIVA Poisson Disk Distribution Array We also added the possibility to create 2D arrays with random arrangements of elements using Poisson disk distribution The method, which satisfies a minimum distance between two elements but also provides maximal distribution. Maximal distribution is desirable to avoid large gaps in the array. 1. Define the crystal shape (rectangular, circular or oval) 2. Define the element shape and size 3. Define the minimum distance criterion 4. Define the number of elements CIVA positions as many elements as possible (up to the max) respecting the minimum criterion distance 8

9 New probes: comparison of performances Grating lobes evaluation To illustrate CIVA possibilities several 2D arrays designs have been generated: matrix, annular sectorial, hexagonal, spiral and Poisson-disk distribution with the idea to compare their performances. The maximum number of elements was fixed at 128, the central frequency set at 1.5 MHz and the total aperture at 52 mm. We tried to keep the aperture and the element size identical for all designs Matrix Annular sectorial hexagonal spiral Poisson 11x11 elements 2 mm wide 3 mm pitch 127 elements 8 rings 2 mm wide 127 elements 2mm wide λ/ 3 pitch 127 elements 9 branches of 14 elements 2 mm wide 128 elements 2 mm wide 1.1 mm minimum distance 9

10 New probes: comparison of performances Grating lobes evaluation We focus the energy at 45 (longitudinal wave) in the incident and transverse planes 100-mm deep in a plate made of ferritic steel We evaluate the grating lobes generated by each probe 45 along the incident plane 45 along the incident and transverse planes 10

11 New probes: comparison of performances 45 along the incident plane -9dB -8dB -12dB -19dB -17dB -8dB -4dB -7dB -14dB -13dB 45 along the incident and transverse planes We see that the amplitude of the grating lobes is relatively important for the designs that display a regular distribution of elements Because of the lack of periodicity of the spiral and sparse designs, the amplitude of the grating lobes is much smaller and more spread out 11

12 Hexagonal array for fast inspection in composite Fast inspection of composite structures The application is to evaluate new arrays and acquisition modes for an industrial facility in real manufacturing conditions with the aim to speed up scanning time, but also to make ultrasound inspections more tolerant regarding ramps and radii with one single array The new probe consists in two staggered rows of 31 hexagonal elements with a pitch of 2 mm; central frequency is 3.5 MHz To improve the acquisition speed, the probe is used in a paintbrush mode using one or three elements at reception depending on the water path 12

13 Hexagonal array for fast inspection in composite The component is a 21-mm thick plate made of multilayered CFRP material [0,45,90,-45] Beam field calculations were performed in CIVA using a multiple-scale homogenized model We see that the staggered rows and the way the sequences are selected allow to perform half-step scanning (1 mm) along the axis between the two rows Scanning speed was improved by a factor of 15 using the paintbrush method compared to the current linear phased-array probes used on site while maintaining detectability capabilities 13

14 Hexagonal array for fast inspection in composite The component is a 21-mm thick plate made of multilayered CFRP material [0,45,90,-45] Beam field calculations were performed in CIVA using a multiple-scale homogenized model Hexagonal element array Composite plate * *,ρ C Beam field We see that the staggered rows and the way the sequences are selected allow to perform half-step scanning (1 mm) along the axis between the two rows Scanning speed was improved by a factor of 15 using the paintbrush method compared to the current linear phased-array probes used on site while maintaining detectability capabilities 14

15 Matrix Sparse array Matrix Sparse Array definition A 256-element sparse array probe was designed using the Poisson-disk distribution algorithm The array shape is a hippodrome with the first 64 element contained within a central disk (red circle), the 128 first elements within two disks (blue circles) and the 128 elements left filling the rest of the array while respecting the minimum distance criterion The central frequency of the probe is 5 MHz, the elements are circular and 1.3 mm in diameter and the minimum distance criterion is 0.2 mm. The probe dimensions are 62.5 x 17.5 mm allowing the inspection of a large area. If we want to respect the λ/2 rule, we would need 3114 elements for the same size 15

16 Matrix Sparse array: Total Focusing Method Application to the inspection of rails The probe was used for the inspection of running band of a repaired rail. During reparation, small inclusions can appear within the first 15 mm to the surface repair The inclusions can be as small as 0.3 mm Several Hemispherical Bottom Holes (HBH) with diameters ranging from 0.3 to 0.9 mm were machined in a ferritic bloc with a curved front surface (210-mm radius) to represent porosities Inclusions > Ø 0.3 mm 16

17 N receivers Matrix Sparse array Sparse Matrix Capture acquisition The acquisition is a SMC for which we alternately excited 29 elements located on the edge of the array plus three central elements while receiving on all the elements SMC delay law We use a SMC instead of a Full Matrix Capture to speed use the acquisition since we need to electrically commute among less element The amount of data recorded is smaller (29x256 signals instead of 256x256) Post-processing is much faster k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k k N source Sparse Full Matrix Capture 17

18 Matrix Sparse array Total Focusing Method reconstruction The ROI is 60x35x13 mm with a resolution of 0.17 mm (~ 6 million points) The forward models take into account the curved surface and the sparse distribution of the elements Experimental or simulated signals from PA inspection A 11 k 11 (t) k ij (t) t 11 A ij S Observation point k NN (t) t ij Amplitude Extraction at these TOF For each point in the ROI, computation of the theoretical time of flight using forward Civa models A NN t NN 18

19 Matrix Sparse array We detect all the hemispherical bottom holes even those not located just underneath the probe By combining a Matrix Sparse Array probe, which covers a larger area with a SMC/TFM method we can inspect a large area while focalizing at all depths 19

20 Matrix Sparse array TFM reconstruction We detect all the hemispherical bottom holes even those not located just underneath the probe By combining a Matrix Sparse Array probe, which covers a larger area with a SMC/TFM method we can inspect a large area while focalizing at all depths 20

21 Matrix Sparse array Application to the detection of random cracks Central 64 elements of the sparse array The central 64 elements of the sparse array were used for the detection of cracks of random orientations The mockup is an aluminum plate with three 5-mm high, 25-mm long notches with three different orientations notches We use a SMC firing alternatively 12 elements and receiving on the 64 receivers We use a Total Focusing Method but we consider the waves that reflect off the backwall (LLL) source L or T receiver L or T L or T Observation point 21

22 Sparse array: Total Focusing Method using Corner echoes The ROI is a 75x75x15 mm box with a resolution of 0.25 mm Diffraction at the edge 64 element sparse array ROI notches Specular echo at the center of the notch Specular echo at the center of the notch Simultaneous detection of the three notches without having to steer the energy in their direction notches Reconstruction with corner echo allowing full imaging of the defects 22

23 Sparse array: Total Focusing Method using Corner echoes 128-element matrix array with FMC acquisition ~16000 signals 64-element matrix array with SMC acquisition 768 signals We obtain the same results using less elements allowing faster inspection 23

24 Conclusions Definitions of new array: Import of designs with rectangular, circular, triangular and hexagonal elements of any size Design of Matrix Sparse Array using Poisson disk distribution Connexion to CIVA models: Calculation of any delay laws already available in CIVA Beam field and beam defect interaction models usable with new probes Applications: An hexagonal probe was manufactured for fast inspection of composite structures A 256-element Matrix Sparse Array was manufactured and used for the inspection of rails and randomly oriented cracks Perspectives: Allow elements of random shapes 24