Inversion of Eddy Current Data and the Reconstruction of Flaws, Part 1: Acquisition of Data
Measuring the eddy currents in a material induced by an exciting field can provide useful information about the shape of the material. Several methods of nondestructive evaluation using eddy currents do not utilize a uniform exciting field over the area of interest . When a non-uniform exciting field is used, the presence or absence of a flaw in the material is detected. However, some applications require more specific information about the size and shape of the flaw. If reconstruction of the flaw is required, current mathematical algorithms [2,4] require that the magnetic field due to eddy currents induced by a uniform exciting field be accurately measured. The magnetic fields can be measured by placing small inductive pickup coils in the vicinity of the material. Several different frequencies can be used to take advantage of the skin depth effect in conductors. Low frequencies can be used to look for flaws relatively deep beneath the surface; high frequencies can be used to look for “shallow” flaws.