Two mechanical engineers from Boston University are using 3D printing to pioneer what could very well be the noise-cancelling devices of the future. The researchers combined mathematics, metamaterials and 3D printing to create a structure that cancels out sound waves without preventing air flow.
The researchers, Reza Ghaffarivardavagh and Xin Zhang, set out to find a way to mute sound without having to resort to thick, air-blocking structures—something which could have important applications in muffling the sound of engines or other noisy mechanisms that require air flow.
The results of their research are nothing short of impressive, as the pair actually did find a way to achieve their goals using 3D printing. The device they created is a 3D printed ring-like structure that cancels out sound waves by capturing them in an intricate, mathematically precise structure.
“I’ve always been interested in acoustics,” said Ghaffarivardavagh, a PhD candidate at Boston University working in Zhang’s lab. “I like to work on something that I can hear or see the result. Something that I can have an impact on with issues we are facing nowadays.”
With Ghaffarivardavagh’s acoustic knowledge and Zhang’s expertise in metamaterials, the pair realized they could be onto something if they could create a sort of open conduit from a material with very specific acoustic properties.
“I’ve been working on metamaterials for more than a decade,” explained Zhang, a multidisciplinary professor at the College of Engineering and the Photonics Center. “But it was Reza that gradually got me more excited about the fundamental idea of a marriage between acoustics and metamaterials. If you ask me and my colleagues, acoustic metamaterials is a relatively young direction… It’s the future.”
3D printing and metamaterials are increasingly overlapping, as researchers from around the globe explore the technology’s potential to create objects with precise and complex structures that impart new mechanical properties. In this case, 3D printing enabled the two mechanical engineers to create a metamaterial structure that would deliberately interfere with sound waves without blocking air.
“Sound is made by very tiny disturbances in the air. So, our goal is to silence those tiny vibrations,” the researchers explained. “If we want the inside of a structure to be open air, then we have to keep in mind that this will be the pathway through which sound travels.”
In a demonstration of the 3D printed device, the researchers secured a PVC pipe to a loudspeaker and placed the 3D printed ring at the opposite end of the pipe. When the speaker was turned on, only a faint sound could be heard, despite the fact that the loudspeaker’s volume was high enough to see the subwoofers vibrating. As soon as the 3D printed ring was removed from the pipe, the sound became significantly louder, filling the room. Reportedly 94% of the speaker’s sound was silenced with the 3D printed device.
“The moment we first placed and removed the silencer…was literally night and day,” added Jacob Nikolajczyk, coauthor of the study and a former undergraduate researcher in Zhang’s lab. “We had been seeing these sorts of results in our computer modeling for months—but it is one thing to see modeled sound pressure levels on a computer, and another to hear its impact yourself.”
After seeing the success of the 3D printed prototype, the researchers believe their noise-cancelling device could have a range of silencing applications. Devices like drones, for instance, could benefit from the sound reduction, while fans, HVAC systems and even MRI machines could also integrate the metamaterials to emit less noise. On a larger scale, the metamaterial could even be assembled in a brick-like fashion to create noise-cancelling walls for highways and such.