Analysis and Design of Coil-Based Electromagnetic-Induced Thermoacoustic for Rail Internal-Flaw Inspection

A novel coil-based electromagnetic-induced thermoacoustic system is presented for detecting the flaws inside a rail. The fundamental is derived and the overall energy density distribution is simulated using finite element method. This paper gives an overview of the system architecture and describes the design process in detail. A mixed numerical experimental methodology is employed to extract the lumped parameters of a planar coil with the ferrite plate for designing the matching network, and then the coil and rail are co-simulated to observe the current density distributions and directions. Through the relationship of energy density and depth in the rail, it is found that the thermal energy mainly concentrates at the surface local area. From the interaction between the coil and rail, the inductive power transfer topology is illustrated and the simplified equivalent circuit model is further obtained. By analyzing the simulated and measured data, the changes in the resistance and inductance are shown with the frequency increasing. The induced ultrasonic wave propagation is simulated inside the rail with flaws, where the wavefronts and reflected signals are observed. Finally, the experimental results demonstrate that the proposed design is feasible and a crack with a diameter of 8 mm can be detected in the rail.