Pressure induced by roll-down foam-earplugs on earcanal

Physical discomfort of earplug is a common complaint, so much so it jeopardizes the health and safety of workers, resulting in frequent noncompliance to proper wearing of earplugs. A pressing need thus arises to understand the underlying mechanics for the interaction of earplugs with earcanal walls. An idealized cylindrical geometry of earcanal is first treated with computational and analytical modeling to predict the pressure induced by roll-down cylindrical PVC foam earplugs. In order to predict representative pressure values and distribution, we estimated the hyperelastic properties of foam-based earplugs and characterized their behavior using a stent testing machine (J-Crimp^TM machine) that mimics the radial compression of earplugs inside earcanals. Similarly, we estimated the hyperelastic properties of skin based on a simplified model consisting of a single hyperelastic layer. As a crosscheck of those found properties and the calibrated models, we validated them with literature and against a set of three experiments: (i) earplug expansion in a cylindrical holder, (ii) quasi-static uniaxial and (iii) transverse compression. We finally used those validated properties of the foam and skin to compute the pressure magnitude and distribution in an axisymmetric representation of earcanal as well as in a 3D realistic earcanal reconstructed from MRI images of a human subject.