Mode conversion and the path of acoustic energy in a partially water-filled aluminum tube

Mode conversion is observed in a water-loaded thin-walled Al tube with a horizontal central axis. A 1 MHz pulse is applied to the tube by a transducer coupled to the tube's external wall in a pulse-echo configuration. The tube is filled to 36 different levels, and a waveform is acquired at each level. Analysis shows that the acoustic energy must propagate both in the tube wall as an A(o)-mode Lamb wave and as a bulk wave in the water. Mode conversion between these two waves is shown to take place both in the air-water interface and as energy leakage in the water-loaded portion of the tube. A unique echo train is observed at each fill level, suggesting that a liquid level sensor can be developed based on this mode conversion. (C) 1999 Elsevier Science B.V. All rights reserved.