Diapositive 1

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Recent Development of Multi-Sensors Eddy Current
Probes
JM. Decitre, B. Marchand, O. CasulaCEA
LISTemail olivier.casula_at_cea.frweb
http//www-civa.cea.fr
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Introduction
Limits of winding coils array
F1mm

• Non flexible probes
• Sensitive to lift-off variations
• Inspection of planar components only
• Limited spatial resolution
• Detection of few hundred micrometers defects only

• Development of other multisensors probe
  technologies

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Outline
Flexible Micro-coils Probes Magnetic Sensors
Probes Conclusions
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Flexible Micro-coils Probes (8 elements)
Application in aeronautics industry
Inspection of a dovetail

• Objectives
• Detection of surface flaws
• Defect length 400µm
• Complex surfaces

Mock-up
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Flexible Micro-coils Probes (8 elements)
Design of the probe

• the16 coils are etched on kapton film
• arrangement in staggered raw

Design optimized using CIVA software
scan
3 mm
2.5 mm

• Optimized scheme
• 2 coils, separate functions
• Best sensitivity and
• minimization of lift-off signal

gap of 350µm between 2 lines
Number of elements 8 (16 coils)
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Flexible Micro-coils Probes (8 elements)
Comparison with a classical winding coil
(experimental data)
Winding coil Ø 1mm
Element on Kapton film
R
E

• Better sensitivity
• Better resolution
• Better SNR
• - lesser sensitivity to lift-off variations
  (element design mechanical support)
• - preamplifier 20 dB

Notch 0.4x0.2x0.1mm
Notch 0.2x0.2x0.1mm
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Flexible Micro-coils Probes (8 elements)
Design of a prototype probe with 8 elements
electronics near sensors
flexible silicone roll (to fit complex
surfaces)
Kapton film with etched coils
Examples of mock-up with notches (200 to 800 µm
length)
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Flexible Micro-coils Probes (32 elements)

• Characteristics of the probe
• same technology
• 32 elements (4 lines with 8 elements)
• 64 micro-coils
• pitch 350 µm
• scan width 11 mm

direction of the scan
scan width 11 mm
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The MultiX-EC device (M2M)
Necessity of a multi-channels device in order to
speed up the acquisitions for the multi sensors
applications

• Design of an EC device with M2M company
• Frequencies range 10Hz to 10MHz
• 32 independent and multi-frequencies emitting
• channels
• 64 independent digital demodulators
• (extension to 128 in process)
• Time slots
• - Digital I/O (external multiplexers,)

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Flexible Micro-coils Probes (32 elements)

• Objective characterization of the length of the
  defect
• defect surface breaking flaw. length 4 mm
• f 2 MHz

EC signals in the impedance plane
11 mm 32 lines pitch 350µm
4mm (10 lines)
multiX-EC
probe
mock-up
detection of the defect with 350µm spatial
resolution
? The length of the defect is well estimated with
a 350µm spatial resolution
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Flexible Micro-coils Probes (32 elements)

• Objective detection of a small surface breaking
  flaw
• size of the defect 200 x 100 x 200 µm3
• f 2 MHz

11 mm 32 lines (32
elements) pitch 350µm
200 x 100 x 200 µm3 flaw
? The defect is well detected
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Aplication to austenitic pipe
Austenitic Mock up inspection of the inner
surface, 1MHz
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Evolution of flexible Micro-coils Probes 128
elements
128 elements (256 coils) probe

• micro-coils etched on kapton film well adapted
• to detect the surface breaking flaws (few
  hundred µm length)
• Inspection of complex surfaces
• scan width 70 mm
• driven by the MultiX-EC device

connector to MuliX-EC device
probe
70 mm
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Outline
Flexible Micro-coils Probes Magnetic Sensors
Probes Conclusions
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Basic Principle of GMR
e-
free layer magnetization depends on applied
magnetic field
thin conductor layer
pinned layer fixed orientation of the
magnetization
pinning layer
multilayers

• e-
• goes relatively freely through a layer which
  magnetization is
• - is blocked from a layer which magnetization is

Resistance R
Applied magnetic field
Variation of the resistance as a function of the
applied field
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Advantages of GMR for NDE
2.2 mm
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Detection of deep defects

• Mock-up with deep notches
• Stainless Steel
• 6 deep notches

probe
ligament
20 mm

• Design of the specific probe
• distance between transmitter and sensor ?
• frequency ?

defect
coil
GMR sensor
d
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Experimental Results
AA

• Thanks to the linear frequency combination, all
  defects are detected
• SNR is 13 dB when ligament is 10 mm and 7 dB
  when it is 12 mm

A
C
B
BB
D
E
F
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Advantages of GMR for NDE

• Very small size lt 100?m

22 GMRs linear array

• Detection of small surface breaking flaws
• Array Probe

2.2 mm
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Giant Magneto-Resistance Probes
Characteristics of the elements composing the
linear array resistance variation versus
magnetic field amplitude

• Disparity between sensors less than 5
• Sensibility 18 V/T (i 3 mA)
• linearity zone -0.5 mT B 0.5 mT
• ?R/R0 4.5

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Giant Magneto-Resistance Probes
Packaging test of the 22 GMRs array
Special packaging for lift-off reduction
f 2 MHz
PCB
beveled glass
the emitter is put just above the sensor
Mock-up used for tests
x direction of the scan
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Giant Magneto-Resistance Probes

• Experimental results
• f 2 MHz

Defect 1 200x100x200 µm3
Defect 2 100x100x200 µm3
Defect 3 100x100x100 µm3
? Good detection, even of the smallest defect
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Giant Magneto-Resistance Probes

• Further experimental results
• f 2 MHz
• aluminium mock-up

100x100x100 µm3
x
y
50x50x50µm3
x direction of the scan
? The 50x50x50 µm3 breaking flaw is detected
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Flexible Magnetic Sensors Probes
Development of flexible probes based on magnetic
sensors (GMI, µFluxgate and GMR)
Magnetic sensor GMI, µFluxgate or GMR
vertical travel up to 5 mm
emitter coils
Experimental result detection of an embedded
defect

• Parameters
• defect
• length 10mm
• ligament 1 mm
• f 10kHz
• mock-up Inconel 600
• Bz orientation

? The defect is detected with the 3 probes with
the same signature
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Magnetic Transverse Effect Probes
Development of a multisensor probe (96 in-line
elements) for surface breaking flaws detection
(IMAGINE Project)
Design of the AMR sensor
Output voltage
Characteristics of the AMR sensor
Off-set
Off-set

• Bandwidth DC to GHz
• Sensibility 20 V/T.A (2V/T _at_ i 100 mA)
• Sensibility axis perpendicular to the feeding
  axis

?
?
?
?
Sensitivity axis
1.2 mm
?
?
?
?
2.1 mm
sensor area 50 - 50µm
current supply
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Magnetic Transverse Effect Probes
Experimental validation of one sensor probe
Design of the probe
Parameters
emitter current foil

• f 1 MHz
• surface breaking flaw length 400µm
• mock-up aluminium

PCB
front layer
shield
sensor AMR
Bx measurement
experimental result
simulation
scan
400 µm
? good detection of the defect ? experimental
result close to the simulation
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Magnetic Transverse Effect Probes
Development of the 96 linear array probe for
surface breaking flaws detection
one AMR
High spatial resolution probe
sensor area
5 mm
sensitivity axis
electric contacts
10 mm

• number of AMRs 96
• sensor area 50µm
• pitch 100µm
• scan width 9.6 mm

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Advantages of GMR for NDE
2.2 mm
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Conclusion

• Flexible micro-coils probes
• High performances of the element
• ? sensitivity
• ? lift-off noise reduction
• ? high spatial resolution
• kapton/silicone arrangement fits to complex
  parts inspection
• Industrial process
• Reliable
• Low disparity between elements
• Magnetic Sensors Probes
• - Advantage for NDT application small size ?
  high spatial resolution probes
• - High sensitivity ? detection of small defects
  (50µm)
• - GMRs linear array ? low disparity between
  sensors
• - Development of a 96 high spatial resolution
  linear array probe
• - Electronic ? use of the MultiX EC electronic
  device by M2M