Acoustic excitations and coherent oscillations in macroscopic solid-state structures

Abstract The propagation of acoustic waves in steel tendons is investigated within the framework of a research for non invasive localisation of defects in metal structures embedded in concrete. The possibility of determining the status and quality of the structures and eventually localising defects within them is demonstrated both in the frequency and time domain by using piezoelectric sensors activated by tiny mechanical excitations. A very interesting phenomenon is observed when defects are located at "nodal" points of one-dimensional bars/wires. In this case, the oscillations induced by the light mechanical excitations give rise to piezos output voltages whose spectral components amplitude exceeds up to six orders of magnitude the background noise level. This phenomenon is consistently observed when one, two, or three "nodal" defects are present in the bars and is generated by coherent oscillations of the sections of the bars separated by the defects. Finally, an application of 2 our technique to the post-tensioned structure of a highway viaduct is presented, confirming its potential for non-destructive testing and structural health monitoring.