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18th WCNDT Durban - 2012
Advanced ultrasonic 2D Phased-array probes
Frédéric REVERDY1, G. ITHURRALDE2, Nicolas DOMINGUEZ 1,2
1CEA, LIST, F-91191, Gif-sur-Yvette cedex, France [email protected], [email protected]
2 EADS France. 18 rue Marius Terce, BP 13050, 31025 Toulouse Cedex,
■ 2 18th WCNDT Durban, South Africa 2012
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
3 defects
Steering in three dimensions
■ 3 18th WCNDT Durban, South Africa 2012
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)
5
1
Annular array
Number of elements in each direction
Element size
Distance between the elements
…
Elliptical
Flexible array
■ 4 18th WCNDT Durban, South Africa 2012
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
■ 5 18th WCNDT Durban, South Africa 2012
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
■ 6 18th WCNDT Durban, South Africa 2012
New probe definition in CIVA
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.
2D array imports
1. Define the crystal shape (rectangular, circular or oval)
2. Add and position elements (rectangular, triangular,
circular and hexagonal
3. Rotate elements
■ 7 18th WCNDT Durban, South Africa 2012
New probe definition in CIVA
hexagonal spiral
Mix of elements
Hexagonal element array
2D array imports
■ 8 18th WCNDT Durban, South Africa 2012
New probe definition in CIVA
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.
Poisson Disk Distribution Array
1. Define the crystal shape (rectangular, circular or oval)
CIVA positions as many elements as possible (up to the
max) respecting the minimum criterion distance
2. Define the element shape and size
4. Define the number of elements
3. Define the minimum distance criterion
■ 9 18th WCNDT Durban, South Africa 2012
New probes: comparison of performances
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
11x11 elements
2 mm wide
3 mm pitch
Matrix Annular sectorial
hexagonal spiral Poisson
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
Grating lobes evaluation
■ 10 18th WCNDT Durban, South Africa 2012
New probes: comparison of performances
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
Grating lobes evaluation
45° along the incident plane 45° along the incident and transverse planes
■ 11 18th WCNDT Durban, South Africa 2012
New probes: comparison of performances
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
-9dB -8dB -12dB -19dB -17dB
-8dB -4dB -7dB -14dB -13dB
45° along the
incident plane
45° along the incident
and transverse planes
■ 12 18th WCNDT Durban, South Africa 2012
Hexagonal array for fast inspection in composite
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
Fast inspection of composite structures
■ 13 18th WCNDT Durban, South Africa 2012
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
■ 14 18th WCNDT Durban, South Africa 2012
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
Beam field
Composite plate
Hexagonal element array
* *,ρC
■ 15 18th WCNDT Durban, South Africa 2012
Matrix Sparse array
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
Matrix Sparse Array definition
■ 16 18th WCNDT Durban, South Africa 2012
Matrix Sparse array: Total Focusing Method
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
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
repair
Application to the inspection of rails
■ 17 18th WCNDT Durban, South Africa 2012
Matrix Sparse array
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
11 12 13 14 15 16 17 18
21 22 23 24 25 26 27 28
31 32 33 34 35 36 37 38
41 42 43 44 45 46 47 48
51 52 53 54 55 56 57 58
61 62 63 64 65 66 67 68
71 72 73 74 75 76 77 78
81 82 83 84 85 86 87 88
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 kN
° re
ce
ive
rs
N° source
Sparse Matrix Capture acquisition
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
Full Matrix Capture Sparse Matrix Capture
■ 18 18th WCNDT Durban, South Africa 2012
Matrix Sparse array
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
k11(t)
kij(t)
kNN(t)
●
●
●
●
●
●
For each point in the ROI,
computation of the theoretical
time of flight using forward Civa
models
t11
tij
tNN
Amplitude Extraction
at these TOF
A11
Aij
ANN
S Observation point
Total Focusing Method reconstruction
■ 19 18th WCNDT Durban, South Africa 2012
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
■ 20 18th WCNDT Durban, South Africa 2012
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
TFM reconstruction
■ 21 18th WCNDT Durban, South Africa 2012
Matrix 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
Central 64 elements
of the sparse array
notches
L or T L or T
L or T
source receiver 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)
Application to the detection of random cracks
Observation point
■ 22 18th WCNDT Durban, South Africa 2012
Sparse array: Total Focusing Method using Corner echoes
The ROI is a 75x75x15 mm box with a resolution of 0.25 mm
notches
notches
ROI
64 element
sparse array
Specular echo at
the center of the
notch
Diffraction at the
edge
Specular echo at
the center of the
notch
Simultaneous detection of the three notches
without having to steer the energy in their
direction
Reconstruction with corner echo allowing full
imaging of the defects
■ 23 18th WCNDT Durban, South Africa 2012
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
■ 24 18th WCNDT Durban, South Africa 2012
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