EXPERIMENTAL INVESTIGATION OF AN ACOUSTIC METAMATERIAL BARRIER DESIGN COMPOSED OF A SQUARE PRISM WITHIN A HEXAGONAL RECESS

Abstract

This paper presents an experimental investigation of an acoustic barrier composed out of an acoustic
metamaterial unit cell. The design of the unit cell consists of a square prism, acting as a resonator,
within a hexagonal recess manufactured out of a single material. Two materials were used to
manufacture the unit cell: PolyMide Polycarbonate and Polylite Polylactic Acid. The acoustic
performance of the unit cell was quantified for both materials using the acoustic absorption
coefficient and acoustic transmission loss values for frequencies between 100 Hz and 5,000Hz. The
experimental results indicate that the design reduced the peak absorption coefficient for both
materials while also introducing two additional peaks at around 1,500 Hz and at 4,000 Hz. Changes
to the absorption coefficient values were observed for frequencies above 1,000 Hz while minimal
changes were observed for frequencies below 1,000 Hz. These results indicate that the proposed
design, is able to widen the effective frequency band, or stop band for acoustic absorption for
frequencies above 1,000 Hz compared to the absorption coefficient of the material. The experimental
results also indicate that the design increases the peak transmission loss by about 7 dB at 4,000 Hz.
For sounds below 3,000 Hz, the design will only change the transmission loss by about 3 dB for
frequencies between 100 Hz to 3,000 Hz. These results indicate that the acoustic metamaterial design,
consisting of resonator in a recess manufactured out of a single material, is able to broaden the
effective frequency range for sound absorption for frequencies between 1,000 Hz and 4,000 Hz and
at increasing the transmission loss values for frequencies between 3,000 Hz and 5,000 Hz. It can be
concluded that the resonator in recess metamaterial design, manufactured out of a single material,
can be used to increase the stop band for acoustic absorption for frequencies above 1,000 Hz and to
increase the transmission loss for frequencies above 3,000 Hz.