Electromagnetic acoustic wave transducers /EMATS/ - Their operation and mode patterns

The term electromagnetic acoustic wave transducers (EMATS) is used when describing specific coil arrangements that are used for both generation and detection of acoustic waves in conducting media. The paper outlines EMATS operation with their advantages and disadvantages, along with the initial stages of a series of calculations and measurements aimed at providing the necessary engineering information to permit successful application of EMATS. Any application of electromagnetic acoustic wave generation to quantitative flaw determination in metals necessitates calculation of the spatial distribution of currents induced by the generator coil in the conducting surface with allowance for the separation between coil and surface. Acoustic mode patterns for spiral coils allowing for diffraction effects are calculated and found to be in good agreement with experimentally measured mode patterns.