A new study by researchers out of The Ohio State University investigates a different kind of design for absorbing vibrations that could better soundproof materials. 

Ryan Harne, senior author of the paper and former associate professor of mechanical engineering at Ohio State, along with former Ohio State doctoral student Sih-Ling Yeh, tested how well built-in resonators handled vibrations under a variety of scenarios. Resonators are devices that use spring-like oscillation to control and change vibrations. Some absorb and neutralize them, and others amplify and direct them to specific places. They’re present in some vehicles, which use them to limit the sound emitted from a car’s muffler. Bridges and buildings also utilize them to limit noise and movement. 

Contrary to previous studies relating to resonators, which focused on adding one to an existing structure or vehicle part, Harne and Yeh considered embedding resonators directly into a material, rather than adding it later.

"We wanted to create and test a design that would reduce vibration," said Harne. "Vibration is integral to a lot of problems in engineering, both in how we construct buildings and in how we make better airplanes and other vehicles."

The team cut resonators into rectangular acrylic plates. The plates were held in place using different mechanisms, with some clamped tightly, some suspended in the air, and some held up by supports. They then used a mechanized hammer to strike the plates and measured the force of the vibrations created by each plate following the hammer’s impact. One plate was left unaltered as a control. They found that vibrations traveled farther on the unaltered plates than on those with built-in resonators. The resonators helped the plates flex and absorb the vibrations from the hammer. In addition, the resonators were able to absorb vibrations regardless of how the plates were held in place. 

The study was organized to test a design that could have multiple real-world applications, used to better soundproof walls and to build airplane frames that automatically lessen the sound that enters the cabin. 

"You can imagine a sandwich-like construction, where you put a lightweight panel with a built-in resonator between two panels of sheetrock, or layer it inside the walls of an airplane," Harne said. "And you could use this to reduce vibration of the whole system without reducing the aerodynamics or efficiency since mass is eliminated. It controls that vibration, and vibration affects what we hear, and it affects how streamlined an airplane or an automobile is."

Harne and Yeh’s study has been published in the October 2021 volume of the journal Thin-Walled Structures.