Energy conversion through local piezoelectric effect in polymer foams for enhancing sound absorption

• Main Author: Ayman Mahmod Mohamed Khalil Shahin
• Other Authors: Wang Junling
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/137057
• Institution: Nanyang Technological University

Airborne sound absorption in porous materials is a complex process that involves multiple working mechanisms of converting mechanical acoustic energy into heat, including thermal effect due to the dynamic heat conduction forced by the rarefaction and the densification of the air, viscous effect caused by the adherence of the fluid at the interface with the solid, and structure’s damping effect with mechanical energy dissipation when the sound wave impacts on the solid. Electromechanically active coupling effect, particularly piezoelectric effect, has so far been studied mainly for structural vibration damping but not for airborne sound absorption. This thesis examines contributions of the electromechanical conversion mechanism to the airborne sound absorption effect, particularly local piezoelectric effect in porous polar materials. The study on the local piezoelectric effect on airborne sound absorption properties tested in a standard impedance acoustic tube was carried out in three sections. Firstly, open-cell poly(vinylidene fluoride) (PVDF) homopolymer foams were prepared and used in order to obtain porous samples with comparable morphology and structure, but with and without substantial piezoelectric property, for providing an example showing the local piezoelectric property effect on sound absorption. Secondly, composite foams comprising piezoelectric poly(vinylidene fluoride-co trifluoroethylene) (P(VDF-TrFE)) matrix and multi-walled carbon nanotubes (MWCNTs) were fabricated and tested, with the experimental results and theoretical analyses showing how an optimal conductivity of the piezoelectric composite foams improved sound absorption coefficient. Thirdly, composite foams comprising PVDF matrix and inorganic piezoelectric potassium sodium niobate (K0.5Na0.5) NbO3 (KNN) nanofibers were produced and tested, with the investigation results showed that introducing the piezoelectric KNN nanofibers in the foams improved sound absorption coefficient. The experimental results and theoretical analyses indicate that the introduction of piezoelectric property with mechanical-into-electrical energy conversion effect in porous polymer materials can substantially enhance the airborne sound absorption performance, which is valuable to be explored for noise mitigation applications.