A novel planar mesh-type microelectromagnetic sensor - Part II: Estimation of system properties

The use of planar-type sensors for the estimation of system properties has gained considerable importance in recent times because of its noncontact and nondestructive nature. The impedance of a coil in proximity of any conducting/nonconducting, magnetic/nonmagnetic surface is a complex function of many parameters, such as conductivity, permeability, and permittivity of near-surface materials, liftoff and coil pitch of the coil, etc. The transfer impedance (i.e., the ratio between the sensing voltage and the exciting current) of the planar-type microelectromagnetic sensors consisting of exciting and sensing coils is used for the estimation of the near-surface system properties. Two methods have been discussed for the postprocssing of output parameters from the measured impedance data. Based on the estimation of near-surface properties, it is possible to detect the existence of defects,to predict the degradation of material, fatigue, etc.