Contact surface fraction evaluation between aluminium and polymer using acoustic reverberation

The propagation of acoustic waves in a finite medium with low attenuation produces long duration signals (reverberation). These complex signals contain useful quantitative and qualitative information about medium properties and are sensitive to structural changes. Available proper data extraction techniques could thus be convenient for structural characterization. The most common application of ensemble averaging of reverberated acoustic signals is in room acoustics, where reverberation time (RT) is directly related to walls absorption. Yet, this method is not frequently used in NDT of solid media. In this work, we aim to characterize contact surface fraction between aluminium-polymer interface. We adapted Sabine's concept (known in room acoustics) by establishing a relation between the RT and solid interfaces' absorption. Experiments were carried out on aluminium volume surrounded by air and aluminium-polymer interface with different surface fractions. Experimental setup consists of 9 piezoelectric patches placed on the aluminium-base surface. One PZT patch is used as an acoustic source while the others are used as receivers. Then, the RT of the linear-system is obtained from the Schroeder's integrals average over the received signals. Absorption is estimated and contact surface fraction is successfully deduced. This method offers a new way to distinguish different bonding conditions and provide a good alternative for NDT.