Viscous and thermal dissipation during the sound propagation in the continuously graded phononic crystals

Abstract

The viscous and thermal effects contribute to the acoustic energy dissipation during sound propagation in complicated structures. In this study, the contributions of viscous and thermal effects, including either single viscous or thermal effects, to the entire acoustic energy dissipation during the sound propagation within graded structures have been investigated. The results show that the integral average of absorption capability coefficient of continuously graded phononic crystal (CGPC) increases by 40% than that of uniform phononic crystal (UPC), which demonstrates that the thermal and viscous effects in graded structures, compared with uniform structures, can improve the sound absorption performance. The thermal effects during the sound propagation in the CGPC account for about 12%-26% of the total thermoviscous dissipation in the studied frequency range (1–6 kHz). Therefore, the thermal effects should be considered an important factor during sound propagation. The viscous effects in CGPC account for about 74%-88% of the total thermoviscous dissipation in the studied frequency, which is slightly higher than that (72%–86%) in UPC due to graded structures. The understanding of the contribution of viscous and thermal effects in CGPC can serve for the next generation of gradient-index phononic crystals.