Abstract: A method and apparatus for determining fatigue/surface crack features on metal surfaces is disclosed wherein the cracks may be empty, filled, or covered with a dielectric (e.g., paint). The present invention includes a microwave waveguide having an aperture for scanning over a surface and thereby characterizing changes in a standing wave within the waveguide when a crack is scanned. In particular, crack related data resulting from standing wave perturbations can be analyzed for determining crack geometric features such as crack width, crack depth, crack length and crack tips. These features are determinable with high precision in comparison to the size of the aperture. When locating and/or sizing the geometric features of a crack, voltage changes induced by higher order modes generated by various orientations of the crack in relation to the aperture are utilized for generating the crack related data.

Abstract: The present invention relates to a method and related apparatus for the nondestructive determination of n layers of coating of a target having n layers of dielectric coating applied to an electrically conductive base material, comprising; a generator of electromagnetic waves in the microwave frequency range, including a microwave oscillator, a waveguide attached to the oscillator output and having an output aperture, a voltage detecting diode disposed within the waveguide, a flat layer of material adapted to be placed in a position abutting the target and disposed over the aperture of the waveguide and having a thickness t which, together with the waveguide, will provide a fixed distance between the diode and the target, and a display responsive to the output of the detecting diode for indicating the layer characteristics of the dielectric coating on the electrically conductive base material.