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Non-Contact EMAT Transduction

Non-Contact EMAT Transduction

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Non-Contact EMAT Transduction

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  1. 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

  2. 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

  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 Sonic Sensors of EMAT Ultrasonics Inc. SLO CA USA

  4. 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

  5. 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