William W. Milroy

Detection and ranging of material flaws using microwave transmission-line reflectometry

Two methods for monitoring stmctural integrity with microwave transmission-line reflectometry are described. The first approach uses a meandering RF transmission line, while the second consists of a bounded dielectric region such as a parallel-plate waveguide. Either of these devices can be embedded in or adhered to a composite or metal panel of the stmcture. A microwave signal is introduced on the transmission line and produces a reflection at any discontinuity as the wave propagates. This creates a signature reflection wave whose salient features can be stored for future reference. If the substrate subsequently becomes flawed, an extraneous reflection is created in the vicinity of the flaw. By comparing this reflection with the signature, the presence and location ofboth new and progressive flaws can be determined. Experimental verification ofthe second technique for the detection of flaws is presented.