Interfacial effects in underwater acoustic panel measurements

Abstract

Underwater acoustic panel measurements were conducted on single layers of rubber or metal, and on rubber/metal bilayers that had been fabricated using various adhesives or attachment methods. Reflection and transmission measurements were carried out on submerged panels using a parametric array source. It was found that the condition of the various interfaces in the system (water/rubber, water/metal, or rubber/metal) had a dominant effect on the measured acoustic properties. Single layer (metal or rubber) panels with smooth surfaces behaved in accordance with theoretical predictions, but panels with even a small amount of surface roughness did not. This was attributed to a non-ideal water/sample interface, most likely due to the presence of air bubbles. The effect of various surface treatments on the acoustic behaviour of the panels was investigated. Different adhesion methods for fabricating aluminum/rubber bilayers were tested for their practicality and effects on underwater acoustic properties. Nitrile butadiene rubber and aluminum panels were adhered to one another using pressure sensitive adhesive, contact cement, banded duct tape, or epoxy, and tested in transmission and reflection. The results were strongly dependent on adhesion method, with only one method (epoxy cured under 15 psi pressure) giving results that matched theoretical predictions.