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

Introduction: 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. Material and Methods: 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. Results: 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. Conclusion: 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.