In 1953 F. F鰎ster [1] presented a method to separate the influence of two parameterson the impedance of a coil. He put the coil, applied as a sensor in nondestructivetesting, on the specimen磗 surface and was able to eliminate theinfluence of the distance a on the impedance. By that the various distance a betweenthe sensor and the surface did not influence the measurement of the electricalconductivity σ of the specimen for example. In 1995 Y. Wang and W.-J. Becker [2]represented a "function S_a ". They used this function to measure the distance aindependently of the specimen material. This "function S" connects the real and theimaginary part of the impedance . That way you eliminate the influence of twomaterials on the impedance and reduce the influence of other materials at anydistance.They were not forced to put the sensor on the surface of the specimen. Fromthat Flaschke and Tr鋘kler [3] developed a procedure for determination of the soilwater content. They defined a "function SΨ ". This function connects the both partsof the admittance and minimizes the influence of three or more materials on thedetermination of the soil water content. The coefficients of the "function S Ψ "were determined using a least square algorithm. In this paper the method of Wang andBecker is enlarged. A new "function T" connects two functions S at differentfrequencies. That way you can separate the influence of two and more parameters onthe impedance of the sensor. You can generalize this procedure and connect theimpedances at three and more frequencies for separation of four and more parameters.The conditions result out of the context between the "function S_a" and a method fordetermining of the concrete cover thickness and the bar diameter [4], [5].
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