Design and laboratory testing of pneumatic devices for the acoustic excitation of water filled plastic pipes

Tracing of buried plastic pipes by the means of acoustic methods has become a subject undergoing intense study, thanks to the encouraging results in comparison to other commercial techniques. The current acoustic technique for tracing underground plastic pipes involves the excitation of the pipe wall or the contained fluid at a fixed location. As wave attenuations are generally large for plastic water pipes, signals cannot be sensed at large distances away from the exciter's location, or at high frequencies. Although in-pipe sources allow tracking of the pipe at larger ranges, current acoustic exciters are not always appropriate, being cumbersome and too large to fit into smaller pipes. In this work, two types of pneumatic device were evaluated, with the aim of generating high amplitude signals at low frequencies and with the ability of accessing pipes with a wide range of diameters, down to 1 cm. The devices are experimentally characterised by a series of laboratory tests in a water-filled plastic pipe section. A comparison of the acoustic power transmission to a fluid filled pipe between a standard electro-acoustic device, an electromagnetic shaker, and the pneumatic ones is made. (paper)