Small Diameter Waveguide for Wideband Acoustic Emission | NIST

The signals obtained from two wideband conical sensors were compared in the time, frequency and time/frequency domains. The signals were generated by pencil-lead breaks on the surface (out-of-plane) or close to the midplane of the edge (in-plane) of a large (1220 mm by 1525 mm) aluminum alloy plate (thickness of 3.1 mm). One sensor was coupled to the plate surface by vacuum grease at a propagation distance of 254 mm, and the other sensor was coupled with vacuum grease to the end of a nominal 300 mm or 400 mm long small-diameter waveguide. The other end of the waveguide was coupled to the plate surface by vacuum grease at a 254-mm propagation distance. The waveguides were either aluminum alloy (1.59-mm or 3.18-mm diameter) or brass (1.59-mm diameter). The goal was to determine how closely the waveguide sensor signal duplicated the signal obtained from the plate-mounted sensor. Results were considered in the light of group velocity diagrams for the aluminum plate and the aluminum rods. The sensor mounted on the 1.59-mm diameter aluminum waveguide provided a signal that closely duplicated the signal from the plate-mounted sensor.