Multiple property variations in coaxial cylindrical conductors determined with multiple-frequency eddy currents

To expedite and automate the taking of readings, computer programs were written that take simultaneous measurements of the magnitude and phase of the output voltage from an eddy current pickup at several different frequencies on standards with known properties. Empirical formulas are then constructed from powers of various possible functions of the magnitude and phase readings, and the formulas are fitted to the desired properties of the material by a least-squares process. Finally, the empirical formulas are used with readings on unknown samples to determine their properties. The computer programs, written in FORTRAN, are especially designed to be used with coils coaxial with multiple layers of cylindrical conductors, possibly containing defects. However, the instrument calibrating, data taking, and formula fitting parts of the programs are actually applicable to any configuration of coils and conductors.