... (such as:rubber, paint, plastic, anodic oxide film,etc) on non-magnetic metal matrix iron. (Such as: copper, aluminum, zinc, tin, ... vortex thickness measurement methods,can detect the thickness of non-magnetic coating (such as: zinc, aluminum, chromium, copper, rubber, paint ... as:rubber, paint, plastic, anodic oxide film,etc) on non-magnetic metal matrix iron.(Such as: copper, aluminum, zinc, tin,etc ...