Composite Locally Resonating Stop Band Acoustic Metamaterials

This study presents a composite acoustic barrier metamaterial panel designed with internal resonant structures. To evaluate the effectiveness of the structure, cubes consisting of the designed acoustic metamaterial panels were fabricated by 3D printing to verify their operating frequency range and demonstrate their superior sound attenuation performance compared with conventional sound-barrier materials. Moreover, numerical models of the cubes were also constructed and were experimentally validated. Results indicate that the composite metamaterial structure acted extremely well in all frequencies, with a maximum transmission loss (TL) of 17.5 dB, while the Plexiglas and MDF cubes achieved a maximum TL of 11.1 dB and 4 dB, respectively. Another key achievement of the present research was the design of perforated metamaterial panels which can help achieve both noise reduction and a significant weight reduction compared to conventional panels. The metamaterials were modeled in a waveguide to study their stop-band behavior and a stop-band in the frequency range of 1060-1200 Hz, with a TL of over 40 dB was identified. This research is intended to pave the way for further studies using 3D-printed metamaterial samples of a variety of materials with complex designs with considerable noise reduction (up to 17.5 dB) and significant weight reduction (up to 64%), through a systematic comparison of various conventional materials (Plexiglas and MDF) and validation of numerical simulations with experimental measurements. A simulation model with experimental validation was presented, which can be further used in industrial and research applications, after being tuned to a target frequency band. A key novelty of the present research is to focus on perforated metamaterial panels which can help achieve noise reduction in applications such as ducts, mufflers and vents. The bare metamaterial structure was shown to be effective at certain frequencies and proved that the structure without cover can play a key role in cases where sound attenuation is to be obtained, without affecting the flow of the acoustic media or with significant weight reductions.