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Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

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Precision Velocity Measurements (using EMATs)<br />

Electromagnetic-acoustic transducers (EMAT) generate ultrasound in the<br />

material being investigated. When a wire or coil is placed near to the surface<br />

of an electrically conducting object and is driven by a current at the desired<br />

ultrasonic frequency, eddy currents will be induced in a near surface region. If<br />

a static magnetic field is also present, these currents will experience Lorentz<br />

<strong>for</strong>ces of the <strong>for</strong>m<br />

F = J x B<br />

where F is a body <strong>for</strong>ce per unit volume, J is the induced dynamic current<br />

density, and B is the static magnetic induction.

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