Acoustic Characterization and Optimization of Sound Transmission Loss in Polymer-Based Materials

摘要

Sound attenuating thermoplastic materials designed to be used as barrier systems in the automotive and consumer industries have certain acoustical characteristics that vary in function of the stiffness and density of the selected material. An important acoustic property for any barrier material is its sound transmission loss (STL). For a polymeric material, the STL determines its effectiveness in attenuating sound energy. The STL is the proportion of energy lost as sound waves travel through a medium. In general, a higher STL is indicative of increased barrier performance. To reduce noise, conventional methods revolve around increasing the surface density (density x thickness) of a finite plate for example, or adding stiffening ribs and mass in selective areas where the noise source has been identified. The current interest is to improve the barrier properties of thermoplastic materials especially those targeted for replacing the incumbent metal counterparts. In the context of this study, the increase in sound energy emission stems primarily from structural differences inherent of plastic materials when compared to metals. In this case, we present the use of an analytical technique for acoustic characterization of plastics, tailored around the STL properties of finite homogenous and heterogeneous panels. This technique facilitates the simulation of an infinite plate behavior in predicting trends for a finite size plate, and can be backward integrated into the formulation stage. This approach will permit STL gain without the added barrier weight, which has been a significant limitation to-date. The real life systems of interests are numerous and can be classified into open and closed systems. Here we focus on open systems and we use an experimental "mass law" approach, which applies to relatively thin, homogenous, single layer panels, but modified for multi-layered panel systems. This experimental approach can be used to validate analytical STL parameter estimation for various heterogeneous systems. At the present time we will not elaborate on the experimental approach, due to confidentiality and the commercial nature of the experimental validation performed using a novel acoustic material that is light in weight and high in structural capability, and which was developed with the predictive analytical techniques mentioned before. We rather emphasize that the development cycle of polymeric engineered materials with enhanced STL properties can be driven and optimized using similar predictive characterization techniques.