Boston, MA– Researchers at Boston University have designed an "acoustic metamaterial" that can cancel up to 94% of sound while maintaining airflow. Reza Ghaffarivardavagh, a PhD student at BU's Department of Mechanical Engineering, and Xin Zhang, a professor at BU's College of Engineering, set out to develop "a structure that can block noise but preserve air passage." This would be a game-changer, as current sound-proofing technologies require thick walls. They recently published a paper in Physical Review B showing how ring-like devices can silence noise while allowing air to pass through.
Ghaffarivardavagh and Zhang point out the potential uses of the device to decrease the amount of noise drone propellers, airplane turbines, and MRI machines. Though they know that sound baffles can help in certain instances, they also know that these devices are not the best when it comes to situations where airflow needs to be fluid.
In trying to create a sound baffle that could work for almost all airflow instances, Ghaffarivardavagh and Zhang decided to create a device that wasn’t a physical barrier, but an open conduit. The two engineers found that producing such a device would require them to use a metamaterial. In an interview, Zhang stated, “I’ve been working on metamaterials for more than a decade. But it was Reza that gradually got me more excited about the fundamental idea of a marriage between acoustics and metamaterials.”
The two engineers explained the basic principles behind their work:, “Sound is made by very tiny disturbances in the air. So, our goal is to silence those tiny vibrations.” Ghaffarivardavagh and Zhang calculated the mathematically precise dimensions and specifications that the device would need to interfere with sound waves.
Once the model was perfected, they brought the blueprints to the 3D printer to bring the device to life. The plastic structure was then tested in the lab. They sealed a loudspeaker onto one end of a PVC pipe and attached the acoustic metamaterial on the other end. The device performed as hoped, quieting the noises. The researchers then looked into the PVC pipe and found the subwoofers thrumming away; this proved that the experiment was a success.
Ghaffarivardavagh and Zhang found that the acoustic metamaterial worked like a mute button, silencing around 94% of noise produced. In the future, the device could be used to quiet things like fans, HVAC systems, and MRI machines.