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An EMAT is an Electro-Magnetic Acoustic Transducer which couples to a metalic sample through electromagnetic forces. Thus the EMAT need not touch the metal sample. The EMAT is a non-contact device. The elecromagnetic coupling works on two different principals. Non-ferromagnetic materials use a Lorentz force mechanism where a curent in a magnetic field creates a force. In ferro magnetic materials the metal changes shape in the presence of a magnetic field. Placing a current carrying conductor in the magnetic field near the metal surface chnages the field as a function of the wire current and thuseffects the shape of the adjacent metal. This is know as magnetostrictive coupling and can be much larger than Lorentz orces as the material is displaced directly as oppossed to forces being applied.