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Non-Contact EMAT Transduction. A current, I, in a wire near a metal surface induces an equal and opposite eddy current, I e 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

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non contact emat transduction
Non-Contact EMAT Transduction

A current, I, in a wire near a metal surface induces an equal and opposite eddy current, Iein 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

Sonic Sensors of EMAT Ultrasonics Inc. SLO CA USA

emats are versatile

S

L

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

Sonic Sensors of EMAT Ultrasonics Inc. SLO CA USA

emat are exceptional for guided waves
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

Sonic Sensors of EMAT Ultrasonics Inc. SLO CA USA

emats offer superior control of guided waves
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

Sonic Sensors of EMAT Ultrasonics Inc. SLO CA USA

automated analysis
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

Sonic Sensors of EMAT Ultrasonics Inc. SLO CA USA