Acoustic metamaterial silences sound without blocking airflow

Researchers at Boston University (BU) discovered that they can harness their mathematical skills and use 3D printing to produce a design that can essentially mute noise without limiting air passage. Reza Ghaffarivardavagh, a graduate student and research assistant in the Department of Mechanical Engineering at BU, said they wanted to create something that can help resolve today’s problems. He said living in a busy city like Boston makes it quite difficult to find quiet moments. Ghaffarivardavagh and Xin Zhang, a professor at the College of Engineering and Photonics Center, created a sound barrier that blocks noise up to 94 per cent. Details of their study, including the specific mathematical measurements, are published in the journal Physical Review B. “This ultra-open metamaterial design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among other,” wrote the authors. Ghaffarivardavagh and Zhang both share a passion for metamaterials and found a way to acoustic metamaterials to current structural designs. Though relatively young, Zhang believes acoustic metamaterial is the future in the field. The pair hypothesized that by shaping metamaterials in a way that will prevent sound, not air, from reverberating in an open space, they can greatly reduce noise levels. The researchers modelled a plastic structure created through 3D printing. They attached the end of the pipe into a loudspeaker. The other end was sealed with the sound barrier they created using their mathematical and physical dimensions. The metamaterial acted like a mute button ringing inside the pipe. What remained of the speaker is a screeching sound that echoed inside the lab. “We can design the outer shape as a cube or hexagon, anything really,” Zhang said. “When we want to create a wall, we will go to a hexagonal shape” that can fit together like an open-air honeycomb structure.” Zhang added that the design can be used to a variety of real-world applications such as reducing the vibrations of an MRI machine.