ELECTROMECHANICALLY ACTIVE POROUS POLYMER MATERIALS FOR AIR-BORNE NOISE ABSORPTION

Abstract

Sound absorption in porous materials is a process that entails different mechanisms of converting acoustic mechanical energy into heat, including the viscous, thermal and material damping effects. Electromechanically active effect, particularly piezoelectric effect, has only been studied for structural damping but not for air-borne noise absorption. This thesis examines air-borne noise absorption effect attributed to electromechanical mechanism, particularly in porous polymer electret materials. Firstly, polyethylene ferroelectret foams were used in order to obtain porous samples with comparable morphology and structure, but with and without piezoelectric property, for providing a proof of concept of the piezoelectric property’s effect on sound absorption. Secondly, composite foams comprising polyurethane and polyvinylidene fluoride mixed with single-walled carbon nanotubes were made and tested, with the experimental results showed that increased conductivity improves to an extent sound absorption coefficient. Thirdly, finite element analysis was conducted on porous electromechanical active polymers, showed that the piezoelectric property can generate substantial contributions to sound absorption, with optimal outcome obtained with presence of a conductive phase that would allow the electric charges to be dissipated sufficiently. Both experimental testing results and theoretical analyses indicate that the introduction of electromechanical effect in porous polymer materials can enhance the air-borne sound absorption performance.