Localization with acoustic wave guides

At extreme conditions of temperature and radiation signals of acoustic emission presently can best be detected with the aid of wave guides. Several types of wave guides were studied with respect to their suitability for the transmission of pulses and the localization of sources of acoustic emission. The rod- and were-type wave guides used up to now were compared with the stranded wire-type wave guide. Transmission of elastic pulses is affected by bends in the wave guide. Below certain radii of curvature there may be caused transmission losses by interferences as a function of frequency. The limiting radii for this were calculated from the dispersion curve for waves in a rod and the losses were measured for different curvatures. At a test piece of pipe (wall thickness 40 mm) pulse transmission in different receiving systems was compared with the results of directly coupled receiver transducers. The use of wave guides is associated with signal losses. The ascending flanks of the pulse signals proved to be suited for the determination of transit-time differences because of their steepness. For the calculation of travelling distances from transit-time differences there were performed sound velocity measurements at the test pipe. The coordinates of different transmitting points were determined by means of a computer from the transit-time differences measured with and without wave guide receiving systems. The average deviations for the geometrical localizations were nearly the same for both receiving systems: The accuracy of localization is not affected by wave guides. (orig./HP)