Researchers Can Tune Acoustic Metamaterials on Demand
3D-printed acoustic metamaterials are being eyed for new applications in noise cancellation and sound cloaking.
April 28, 2018
Researchers have used 3D printing to develop acoustic metamaterials that can be tuned to different frequencies—something that is a rare quality in these types of structures and opens the door to new applications of them.
The metamaterials, which are capable of blocking sound waves and mechanical vibrations, were developed by a team at USC Viterbi led by Assistant Professor Qiming Wang. They also can be remotely switched between active control and passive states using a magnetic field.
Acoustic metamaterials are materials with negative stiffnesses and/or negative densities designed to control, direct, and manipulate acoustic waves, Wang explained. They are different from other acoustic-mitigating materials—such as a cotton pad—in that they can control acoustic waves within frequencies associated with the local resonances, but not their size scales, he said.
These types of materials are used for noise canceling, sonic cloaking for submarines, acoustic focusing for manipulating small objects, and abnormal acoustic refraction to guide acoustic wave directions. Typically, they have limitations in the flexibility of their applications, however, which Wang said he and his team have solved with their new materials.
A magnetoactive acoustic metamaterial developed by researchers at USC Viterbi is shown affixed to a petri dish. The material is different from other similar materials in that researchers can use remote magnetic fields to deform its structure, thereby altering the geometry on demand for new applications. (Image source: Ashleen Knutsen, USC Viterbi) |
“Most of the acoustic metamaterials have fixed geometries; therefore, their performance can only be turned on forever and for a certain frequency region,” he explained. “The key innovation of our materials is that we can use remote magnetic fields to deform the structures to alter the geometries on demand.”
This allows the acoustic-manipulating performance of the materials to be turned on and off reversibly and rapidly, Wang said. “The function frequency can also be tuned just by modulating the external magnetic field,” he said.
3D printing plays a key role in enabling this new material function, Wang explained. By 3D printing a deformable material that contains iron particles in a lattice structure, researchers can compress the metamaterials using a magnetic field.
“The 3D-printing technology can enable freeform-design of the structures and can rapidly fabricate the structures,” Wang explained.
READ RELATED ARTICLES HERE:
There are two methods for 3D printing the new materials: directly using magnetic-particle-filled photoelastomers through a micro-projection stereolithography system, or inversely printing by using a water-dissolvable 3D-printed scaffold, he said. In the latter process, the elastomers—filled with magnetic particles—are cured within.