| Electromagnetic acoustic transducers (EMATs) are non-contact, non-destructive testing devices for conducting specimens. The efficiency of EMATs is inherently low and methods for increasing it have been the subject of intense research.; In publications, the finite element (FE) technique has been applied to the diffusion equation in order to model EMATs. However, electromagnetic theory indicates that the diffusion equation must be solved for the magnetic vector potential (MVP) in conjunction with an equation for the total current. An existing FE formulation considering the two equations becomes unstable when modeling transient inputs in EMAT transmitters. The limitation posed by the instability prompted the development of an improved FE formulation, which solves the two equations and is suitable for the modeling of EMATs.; The objective of the research work described in this thesis is to properly and accurately model EMATs, so that their efficiency could be improved at the design stage. The thesis describes the governing equations of EMATs, improved techniques for their solution, and the application of these techniques to the analysis of such devices. The improved techniques are used for modeling EMATs for both non-ferromagnetic and ferromagnetic specimens. The following aspects are developed: (a) Derivation of various types of forces and current densities in EMATs. (b) Computation of the MVP in EMAT transmitters by an improved FE formulation. (c) Accurate computation of the induced voltage in EMAT receivers by an improved method. (d) Derivation of analytical solutions to validate the FE solutions. |
