Pulsed Eddy-Current Interaction with Subsurface Cracks
Calculations have been carried out to evaluate pulsed eddy-current interaction with a planar crack in a conductor. The field is excited by a coil carrying current pulses while crack signals are detected by measuring changes in the magnetic field above the conductor or by monitoring variations in the induced emf across the coil. An integral formulation of the problem has been used to determine the field at the surface of the crack as a function of time. A discrete matrix approximation of the integral equation is derived based on the moment method. Using a time-stepping procedure, the matrix equation is solved to obtain the field at a specific time using the solutions at all previous time steps starting at the initiation of the excitation pulse. The signal detected by a magnetic field sensor on the axis of the coil is then computed.