A single probe spatial averaging technique for guided waves and its application to surface wave rail inspection

The nondestructive testing of structures using guided waves requires systems with high mode selectivity. Usually this is achieved with relatively complex probes comprising multiple transducer rings or arrays. For the rapid inspection of very long structures with only partial access to the waveguide, this may not be a viable solution. In this paper we present a very flexible alternative whereby a simple robust probe is scanned along the wave guide, and the acquired scan data is used for customizing the mode selectivity at the postprocessing stage. The characteristics of this spatial averaging method are discussed using a simple analytical model and compared to an existing linear array technique. The mode selectivity is found to be mainly limited by the uncertainty of the phase velocity assumed for the mode of interest. The method was successfully applied to surface wave rail inspection and was found to suppress unwanted modes very efficiently.