NonContact EMAT Transduction

1
Non-Contact EMAT Transduction
A current, I, in a wire near a metal surface
induces an equal and opposite eddy current, Ie
in the surface of the metal.
N S
When the eddy current occurs in a magnetic field
a force is created in the metallic surface.
F I x B This force can generate elastic waves,
ie. ultrasonic Guided Waves
I
F
B
Ie
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EMATs are Versatile

• Surface Waves Rayleigh Wave
• Surface SH waves
• Angle Beam waves SH or SV
• Through Thickness Shear Waves
• Through Thickness L Waves

SH
SV
3
EMAT are Exceptional for Guided Waves
SHn Shear Horizontal

• Often called Plate Waves
• Sensitive to Plate Thickness
• There are many different kinds of Plate
  Waves
• These depend on the displacement through
  the plate thickness
• EMATs are great for SH waves

Propagation
Sn Symmetric
Propagation
An Anti-symmetric
Propagation
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EMATs offer Superior Control of Guided Waves

• There are MANY guided waves to possible
  in a single thickness plate
• Isolating a single mode can be very
  difficult with a piezo transducer
• EMATs isolate guided waves easily!
• EMAT defines the wavelength
• Choose the frequency at the defined EMAT
  wavelength, and only one mode generated and
  detected.

M120 EMAT only generates and receives these modes
in a 3/8 inch thick plate
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Automated Analysis
Example Sizing of defects in Pipe Girth Weld
Length
Depth
NDE Indication (sized between accept reject
curves)
Upstream Side of Weld
Downstream Side of Weld