Patent ID: 6392421
Filing Date: 2002-05-21
Classification: G01V

Abstract:
A method for creating a spectral EM frequency to calculate the thickness of a material of unknown permeability and conductivity comprising the steps of:(a) calculating the penetration depth &dgr; using Î´=1Ïƒ&it;â€ƒ&it;Î¼r&it;Î¼o&it;fwhere&dgr;=penetration depth, Æ’=frequency, &sgr;=conductivity, &mgr;r=relative permeability, and &mgr;o=absolute permeability. (b) impinging the material with at least one electromagnetic wave selected from a first set including constant and relatively low frequency waves and having constant amplitude, (c) impinging the material with at least one second electromagnetic wave of variable frequency and constant amplitude selected from a group having a minimum frequency higher than the first set and generating a sensing signal within the material, (d) varying the frequency of the second electromagnetic wave and monitoring the sensing signal, (e) determining the relationship of the frequencies such that Æ’6>Æ’5>Æ’4>Æ’3>Æ’2>Æ’1, where Æ’6 is a higher frequency, Æ’1 is a lower frequency and one of the intermediate frequencies Æ’5, Æ’4, Æ’3, Æ’2, is a frequency of the second wave impinging the material when the sensing signal does not change with an increase in frequency and changes with a decrease in frequency, (f) impinging the material with at least one electromagnetic wave of known and variable current selected from a third group including constant and relatively low frequency waves, (g) impinging the material with a fourth electromagnetic wave of constant frequency and amplitude and generating a sensing signal, (h) measuring the current of the third set of waves when the sensing signal does not change with an increase in the current of the third wave and does change with a decrease in the current, and (i) using the measured amplitude, current and frequency of the electromagnetic waves to calculate the permeability and conductivity of the material and the penetration depth of the measured frequency where the penetration depth is related to the thickness of the material.