SWS-Based Methods for Non-Destructive Monitoring of Absorbing Coatings

A novel method for monitoring parameters of absorbing coatings, which are widely used for stealth technology, is described in this paper. The offered method of measurements is based on the use of slow-wave structures (SWSs), which electrodynamic parameters strongly depend on the electromagnetic properties of the absorbing coatings. The main advantages of the SWS-based measurements are in the possibility to concentrate electromagnetic field in a volume with linear dimensions much smaller the wavelength in free space and to split electric and magnetic fields, providing practically independent monitoring of dielectric and magnetic properties of the coatings. Resonant frequencies and Q-factor of a SWS section placed in parallel to a monitored coating can be used as primary measuring parameters. Analysis of the dispersion equation derived for a SWS-based sensitive element in the presence of a coating allows creating algorithms for converting measured electrodynamic parameters into the reading of the coatings´ electromagnetic properties. It is shown also that the use of coupled SWSs leads to the increase in the informative parameters´ number and to the significant increase in sensitivity.