Patent ID: 6885190
Filing Date: 2005-04-26
Classification: G01N

Abstract:
1. A method for measuring conductance of a sample using an eddy current probe comprising a sensing coil, comprising: (a) with the eddy current probe at a first separation from the sample, and with an AC voltage in the sensing coil, measuring a first voltage pair comprising in-phase and quadrature components of an induced AC voltage in the sensing coil; (b) with the eddy current probe at the first separation from a reference material, and with the AC voltage in the sensing coil, measuring a second voltage pair comprising in-phase and quadrature components of an induced AC voltage in the sensing coil; (c) calibrating the first signal based on the measured second signal; (d) performing N repetitious of operations (a) and (b), where N is a positive integer, with the eddy current probe at a different separation from the sample and reference material during each of said repetitions; (e) determining a conductance function relating conductance with location along a selected curve; and (f) after operations (a) through (e), processing the calibrated first voltage pairs obtained in operations (a) through (c) to generate a lift-off curve, determining an intersection voltage pair representing intersection of the lift-off curve with the selected curve, and determining the conductance of the sample from the intersection voltage pair and the conductance function.