Small Diameter Waveguide for Wideband Acoustic Emission
Marvin A. Hamstad
The signals obtained from two wideband conical sensors were compared in the time, frequency and the 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 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 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 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 inch diameter aluminum waveguide provided a signal that closely duplicated the signal from the plate-mounted sensor.