Acoustic metamaterial panel composed of funnel-shaped cell unit having multi-band negative material properties

This paper presents two dimensional sound-proof acoustic metamaterials having tunable multi-band negative effective mass density. The acoustic metamaterial panel was composed of many periodic funnel-shaped cell units into square lattice. Each unit cell operates as multi-band resonators. By tuning unit cell the local reflected acoustic wave was almost out of phase with the incident wave. It leads to the negative effective density and created band gap for absorbing incident sound energy without transmission. Measurement of the transmission loss and negative effective mass density was performed using four microphone methods for characterization of barrier performance.