DESIGN AND CHARACTERIZATION OF ACOUSTIC POROUS METASURFACE

In this work, a two-dimensional metasurface with attractive acoustic absorbing performance is designed according to generalized Snell's law for potential engineering applications in transport industry. The proposed design is a period structure consisting of eight cubic porous units aligned in a straight row. Each unit is defined by five specific parameters of rigid frame model for simulating sound wave propagation. A periodic length and uniform phase difference between each adjacent pair decide a specific phase gradient that determines propagation of refracted and reflected waves. The acoustic characteristics of the designed metasurfaces are studied by numerical solutions of the Helmholtz equation. There exists a critical incidence angle at which total internal reflection occurs. Above this angle, the acoustic wave carrying the most energy propagates along the metasurface, resulting in an enhanced acoustic absorption at target frequency (800 Hz in the current work). To extend the range of incidence angles with effective sound absorption capability, the period length of metasurface can be reduced to half wavelength so that the critical angle is below -90 degrees. This implies that the propagation of refracted and reflected waves and sound absorption performance can be tailored in achieving customized applications by adjusting period length of metasurface. In addition to the effective acoustic absorption property, the design also possesses potential thermal or vibration insulation property.