Analytical Modeling and Analysis of Electromagnetic Acoustic Transducers With Spiral Coils

In the current modeling process of electromagnetic acoustic transducers(EMATs),the finite element method and analytical calculation are widely applied.However,it takes long time for finite element calculation,and some previous analytical models are incomplete.By introducing a current loop instead of the permanent magnet and adopting the truncated region eigenfunction expansion(TREE) method,a complete analytical model of spiral coil EMAT with permanent magnet is established.The eddy-current,magnetic flux density,Lorenz force and impedance of coil can be obtained by this model.Based on this model,by analyzing the distribution of static magnetic field and the generated Lorenz forces,the design principle of magnet is put forward that the proper diameter is 1.5～2 times of the coil’s diameter and the proper thickness is equal to its diameter.Finally,the frequency,magnitude and distribution of static and dynamic magnetic Lorenz forces are compared.The validity of the model and the analysis results are verified by combining finite-element and experiment methods.