Characterizing the acoustic impedance and attenuation of biocompatible elastomers: An optimal design of experiments approach

Polymers have a range of densities and stiffnesses that can be further tuned with the addition of dopants to control their acoustic impedance and attenuation, important properties that impact acoustic transduction in underwater, medical, and other non-airborne applications. Previous research on impedance-matched polymers is limited in scope, focusing on a specific application and varying a limited number of variables independently. Here, we perform a more generalized study to model the relationship between multiple fabrication and characterization conditions on the acoustic impedance and attenuation of biocompatible elastomers with ceramic nanoparticle dopants. Following an I-optimal design of experiments approach, fifty samples were characterized with factors of polymer type (PDMS, Ecoflex, and Polyurethane), sample thickness, dopant density, concentration, and size, and characterization frequency and temperature. Statistical analysis revealed the main variables, as well as interactions between variables, that have a significant affect on the acoustic properties of the elastomers. The resulting statistical model specifies the conditions necessary to match the polymers to any acoustic impedance in the range of 1 to 2.5 MRayls. We demonstrate how the model is used to fabricate an elastomer with an acoustic impedance matched to skin and minimum attenuation.