Impact of Layout Sequence of the Natural and Synthetic Adsorbents in Double-Layered Composites on Improving the Natural Fiber Acoustic Performance Using the Numerical Finite Element Method

The acoustic performance of natural fiber adsorbents has been investigated in numerous studies. A part of these materials show a poor adsorption within the frequency range of less than 1000 Hz. In the present study, attempts were made to investigate the effect of layout sequence of double-layered composites consisting of natural and synthetic fibers on improving the acoustic adsorption coefficient of natural fiber in the low-frequency range (63 to 1000 Hz) using the numerical finite element method.

In this study, the finite element method and the Johnson-Champoux-Allard model in COMSOL software version 5.3a were used to investigate the acoustic performance of the double-layered composites consisting of natural and synthetic adsorbents. The acoustic absorbers under study included date palm fiber, polyurethane foam and cellular rubber. Each double-layered composite included a date palm fiber with 10mm in thickness and a synthetic adsorbent (polyurethane foam or cellular rubber) with 10mm in thickness. In sum, four double-layered composite structures with different layouts of adsorbents in each structure were studied.

The location of natural fiber can play a critical role in the acoustic performance of the double-layered composite structures such that comparing the studied double-layered composites revealed that when the natural fiber was the first layer exposed to the normal sound in the double-layered composites with 20mm in thickness, the trend of acoustic performance was approximately the same as the single-layered composite of natural fiber with 20mm in thickness; but in the composite structures, when the synthetic adsorbent was the first layer exposed to the sound, the trend of acoustic absorption was improved.

On the basis of the results, the double-layered composite structure with a higher-density and lower-porosity upper layer showed a better acoustic absorption trend than the single-layered composite including the natural adsorbent.