3-D Printed Active Metamaterials for Sound and Vibration Control

The magnetoactive acoustic metamaterial (center front) affixed to a petri dish. (source: USC Viterbi, Ashleen Knutsen)

The magnetoactive acoustic metamaterial (center front) affixed to a petri dish. (source: USC Viterbi, Ashleen Knutsen)

July 16, 2018 | Source: USC University of Southern California, viterbischool.usc.edu, 11 Apr 2018, Ashleen Knutsen

Researchers have been pushing the capabilities of materials by carefully designing precise structures that exhibit abnormal properties that can control acoustic or optical waves. However, these metamaterials are constructed in fixed geometries, meaning their unique abilities are always fixed. Now, new 3-D printed metamaterial developed by a team led by USC Viterbi researchers can be remotely switched between active control and passive states.

USC Viterbi Assistant Professor Qiming Wang and Ph.D. student Kun-Hao Yu, along with MIT Professor Nicholas Fang and University of Missouri Professor Guoliang Huang, have developed 3-D printed metamaterials capable of blocking sound waves and mechanical vibrations. Unlike current metamaterials, these can be turned on or off remotely using a magnetic field. Their materials can be used for noise cancellation, vibration control and sonic cloaking, which can be used to hide objects from acoustic waves.

“When you fabricate a structure, the geometry cannot be changed, which means the property is fixed. The idea here is, we can design something very flexible so that you can change it using external controls,” said Wang, an assistant professor of civil and environmental engineering.

Metamaterials can be used to manipulate wave phenomena such as radar, sound and light and have been used to develop technology such as cloaking devices and improved communication systems. The team’s metamaterials are able to control environmental sounds and structural vibrations, which have similar waveforms. By 3-D printing a deformable material containing iron particles in a lattice structure, their metamaterials can be compressed using a magnetic field.

“You can apply an external magnetic force to deform the structure and change the architecture and the geometry inside it. Once you change the architecture, you change the property,” Wang said. “We wanted to achieve this kind of freedom to switch between states. Using magnetic fields, the switch is reversible and very rapid.”

The magnetic field compresses the material, but unlike a physical contact force like a metal plate, the material is not constrained. Therefore, when an acoustic or mechanical wave contacts the material, it perturbs it, generating the unique properties that block sound waves and mechanical vibrations of certain frequencies from passing through.

Wang believes they may be able to demonstrate another unique property called negative refraction, in which a wave goes through the material and comes back in at an unnatural angle, which according to Wang is, “anti-physics.” They plan to study this phenomenon further once they are able to fabricate larger structures.