Advanced ultrasonic 2D Phased-array probes - CIVA · 18th WCNDT Durban - 2012 Advanced ultrasonic...

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,

[email protected], [email protected]

mailto:[email protected]




■ 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


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


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


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


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



hexagonal spiral

Mix of elements

Hexagonal element array

2D array imports



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


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



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



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


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



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



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


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


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


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


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


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


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


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


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


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


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

Advanced ultrasonic 2D Phased-array probes - CIVA · 18th WCNDT Durban - 2012 Advanced ultrasonic...

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