Design and development of novel bio-based functionally graded foams for enhanced acoustic capabilities

Development of a super sound absorbing fixture to damp acoustic energy of sound wave over a wide range of frequencies, while occupying the least amount of space is of great interest to various industries. A broadband absorption effect can be achieved by appropriately grading the cell structure of a porous layer to enhance acoustic properties based on the specific application. Such porous structures with microstructural gradation are called functionally graded materials. A novel graded bio-based foam structure is presented with enhanced sound absorption capability compared to uniform foams of the same porosity with 20 % increase of maximum acoustic absorption coefficient and 9 % increase in average absorption. In addition, foams with different cell sizes and cell distributions were fabricated and characterized for acoustic and mechanical performance to investigate the effect of microstructure of open-cell foams on the macroscopic properties. Among the uniformly distributed cells, cell size of 380 μm illustrates the highest average absorption. The correspondence between sound absorption of open-cell foams under study to cell size indicates the importance of understanding the effect of microstructure on acoustic behavior of porous-condensed matter to determine the ideal cell size/arrangement and reach the engineering design with optimum performance for any specific application.