Diapositive 1

1
Flexible eddy current probes for the inspection
of complex parts
JM. Decitre, B. Marchand, O. Casula, C. Reboud
2
Introduction
Limits of winding coils
F1mm

• Non flexible probes
• ? Sensitivity to lift-off variations
• ? Only planar surfaces
• Bad adaptation to small flaws (a few hundred
  micrometers)

? Implementation of others multisensors probe
technologies
3
Outline
Flexible Micro-coils Probes Magnetic Sensors
Probes Conclusions
4
Flexible Micro-coils Probes (8 elements)
Application in aeronautics industry
Inspection of a dovetail
Detection of surface flaws Defect length
400µm Complex surfaces
Mock-up
5
Flexible Micro-coils Probes (8 elements)
The 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

Number of elements 8
gap of 350µm between 2 lines
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Flexible Micro-coils Probes (8 elements)
Design of a prototype probe with 8 elements
Amplifiers 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)
7
Flexible Micro-coils Probes (8 elements)
Comparison with a classical winding coil
(experimental data)
Winding coil Ø 1mm
Element on Kapton film
R
E

• Comparable 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)
Experimental results obtained with a mock-up (4
notches)
SNR gt 30dB
4
3
2
R2.5mm
1
2
3
4
1
Titanium
With the same probe, it is possible to inspect
? Planar, concave or convex surfaces, ?
Workpieces with a variable radius, ? 3D
geometries
Very good results obtained with ? notches not
longer than 200µm ? SNR gt 20dB
9
Flexible Micro-coils Probes (32 elements)
Same technology 32 elements (4 lines with 8
elements)
10
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 under process)
• Time slots
• - Digital I/O (external multiplexers,)

11
Flexible Micro-coils Probes (32 elements)
Experimental acquisition at 2 MHz with the
MultiX-EC device
Time encoder
4 mm length notch
EC signals in the impedance plane
Moving encoder
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Flexible Micro-coils Probes (32 elements)
Flexible 32 elements probe
2 MHz
200 x 100 x 200 µm3 flaw
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Evolution of flexible Micro-coils Probes 128
elements

• - Micro-coils etched on kapton film well adapted
• to detect the surface breaking flaws (few
  hundred µm length)
• Inspection of complex surfaces (Rcurvature
  2.5mm)
• Design of probes in order to cover wider areas.

128 elements (256 coils) Inspection of 70 mm wide
area
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Outline
Flexible Micro-coils Probes Magnetic Sensors
Probes Conclusions
15
Giant Magneto-Resistance Probes in NDT
Advantages

• Very small size of the sensor (lt 100?m) Useful
  for detection in which high
• spatial resolution is required
• Better sensibility than coils at low frequencies

Development of GMR high spatial resolution arrays
with
2.2 mm
1 GMR sensor
22 GMRs linear array pitch 100µm
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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

17
Giant Magneto-Resistance Probes
Packaging test of the 22 GMRs array
? Special packaging for lift-off reduction
f 2 MHz
PCB
beveled glass
? Mock-up used for tests
18
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
100x100x100 µm3
50x50x50µm3

• f 2 MHz
• Aluminum mock-up

? The 50x50x50 µm3 breaking flaw is detected
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Flexible Magnetic Sensors Probes
Development of flexible probes based on magnetic
sensors

• 3 flexible probes GMI, µFluxgate and GMR
  sensors

Magnetic sensor GMI, µFluxgate or GMR
Bending up to 5 mm
emitter coils

• Experimental results embedded defect (length
  10 mm / ligament 1mm)

f 10kHz 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 sensor

Output voltage
Off-set
Off-set

• Characteristics of the sensor

?
?
?
Bandwidth DC à 2MHz Sensibility 200 V/T.A
(20V/T _at_ I 100 mA)
?
1.2 mm
?
?
?
?
2.1 mm
sensor area 20 - 100µm
feeding
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Magnetic Transverse Effect Probes
Development of a probe to test the mono sensor
Sensor in DIL package
Design of the probe
PCB
coil
sensor
Development of the 96 linear array probe for
surface breaking flaws detection
100 µm
High spatial resolution probe
1 sensor
Output voltage
10mm
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Conclusion

• Flexible micro-coils probes
• High performances of the special element
• ? sensitivity
• ? lift-off noise reduction
• ? high spatial resolution
• kapton/silicone arrangement fits to complex
  parts inspection
• Industrial process
• Reliable
• Few 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 ? few disparity between
  sensors
• - Flexible probes ? inspection of complex parts
• - Under development ? use of the MultiX EC
  electronic device by M2M