Numerical study on sound absorption of vegetation enhancement by means of embedded sonic crystal.

It has been known that sound absorptions of vegetation are poor, particularly at a low and medium frequency. In contrast, vegetation is widely used as part of a building or urban city design and development. It is instructive to seek technical ways to enhance sound absorption of vegetation. Thereby, the use of vegetation is more beneficial to noise reduction due to traffic noise. In this study, sonic crystal is introduced near the vegetation to enhance its absorption coefficient. The Finite Element Method (FEM) is employed to model the combined system of vegetation and sonic crystal. At the same time, the resulting calculation in terms of absorption, reflection, and transmission coefficients are discussed. The effect of variation in vegetation length, number of the sonic crystal lattices, and lattice length to the mentioned parameters are also investigated in this study. The result shows enhancement in both sound absorption and reflection of vegetation while the transmission decreased due to reabsorption of reflected sound from sonic crystal. Increasing the vegetation layer length leads to an overall increase in sound absorption, while increasing the number of sound sonic crystal layers leads to a higher gradient of change on absorption coefficient between the bandgap frequency and the non-bandgap frequency. Variation in lattice length leads to variation in the bandgap frequency, where enhancement of sound absorption occurs. Although further investigation is needed, the simulation result shows that the combination of vegetation and sonic crystal is favorable to reduce traffic noise significantly. [ABSTRACT FROM AUTHOR]