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This is a sample of the 3-D printed acoustic metamaterial. CREDIT Qiming Wang

A new class of 3D printed metamaterials which can be controlled using a magnetic field are opening the door to a number of new applications.

A team from the University of Southern California has created metamaterials that can be remotely switched between active control and passive states, and block sound waves and mechanical vibrations. The researchers believe that the material could ultimately be used for noise cancellation applications, vibration control and sonic cloaking to hide objects from acoustic waves.

“When you fabricate a structure, the geometry cannot be changed, which means the property is fixed,” USC Viterbi School of Engineering Assistant Professor Qiming Wang, said in a statement. “The idea here is, we can design something very flexible so that you can change it using external controls.”

Metamaterials can manipulate wave phenomena like radar, sound and light and have been used to develop technologies including cloaking devices and improved communication systems.

However, the new metamaterials can control environmental sounds and structural vibrations, opening the door to a number of new applications. By 3D printing a deformable material with iron particles in a lattice structure, the 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 metamaterial, but does not constrain it, enabling an acoustic or mechanical wave to perturb the material and generate unique properties, including negative modulus and negative density that blocks sound waves and mechanical vibrations of certain frequencies from passing through.

“Material with a negative modulus or negative density can trap sounds or vibrations within the structure through local resonances so that they cannot transfer through it,” PhD student Kun-Hao Yu said in a statement.

Objects with negative modulus pull towards you as you push them and objects that exhibit a negative density work in a similarly contradictory way.

Both negative properties allow noise or vibration to pass through. The team is able to maintain versatile control over the metamaterial, switching among double-positive (sound passing), single-negative (sound blocking), and double-negative (sound passing) just by switching the magnetic field.

“This is the first time researchers have demonstrated reversible switching among these three phases using remote stimuli,” Wang said.

The researchers now plan to scale down or scale up the fabrication system that would give the team an opportunity to work with a larger range of wavelengths.

The study was published in Advanced Materials.

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