Apr 12, 2018 | By David

A team of researchers based at USC Viterbi in Los Angeles has recently pioneered a new way to control sound. We’ve reported before on the development of 3D printed metamaterials, which have specifically engineered structures that enable them to harness light or sound waves, amongst other applications. This latest breakthrough is unique in that a magnetic field can be used remotely to switch the metamaterial’s acoustic properties on or off.

The project was led by 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. The team used 3D printing technology to create special metamaterials that are capable of blocking sound waves and mechanical vibrations, due to their unique lattice structure. Also, the presence of iron particles in the structure means that a magnetic field can be used to deform it, which will then change its properties. In this way, the 3D printed metamaterial can be remotely switched from active to passive states.

''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. ''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. We wanted to achieve this kind of freedom to switch between states. Using magnetic fields, the switch is reversible and very rapid.''

The acoustic properties of the metamaterial enable it to block sound waves of a certain frequency, as well as mechanical vibrations. This is useful for a number of purposes, including noise cancellation, vibration control, and sonic cloaking, which can be used to hide objects from acoustic waves.

The uniqueness of these 3D printed acoustic metamaterials’ structure gives them the properties of negative density and negative modulus. For everyday materials, these properties are both positive. If an object has a positive modulus, it will push back against you when you push it away. In contrast, objects with a negative modulus attract you, pulling you towards them as you push. The situation with objects exhibiting a negative density is similarly counter-intuitive. When you push these objects away from you, they will instead move toward you.

(All images, credit: USC Viterbi)

Sound waves and mechanical vibrations within a certain frequency can be controlled by objects whose structure gives them one negative property out of these two. When both properties are either negative or positive, the vibrations are able to pass through again. The USC Viterbi team were able to control their metamaterial remotely using a magnetic field, switching among double-positive (sound passing), single-negative (sound blocking), and double-negative (sound passing).

The ability to freely turn these functions on and off offers engineers an extra level of control over acoustics and vibrations when compared to other metamaterials, opening up a whole range of potential applications. The study was published in Advanced Materials. Funding for this project was provided by the National Science Foundation and the Air Force Office of Scientific Research Young Investigator Program.

 

 

Posted in 3D Printing Application

 

 

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