3D printed acoustic metamaterials can be switched on and off to block out sound

researchers from the USC viterbi school of engineering have developed new 3D printed acoustic metamaterials that are able to be remotely switched on and off using a magnetic field. the materials consist of precisely designed, geometric structures that exhibit abnormal properties allowing them to control acoustic or optical waves.

the materials can be controlled using a magnetic field, switching them between active control and passive states. 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. however, due to their fixed geometry their unique abilities are also fixed.

all images courtesy of viterbischool

the USC viterbi school of engineering 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. unlike a physical contact force like a metal plate, the magnetic field compresses the material and so it is not constrained. therefore, when an acoustic or mechanical wave contacts the material, it perturbs it.

the abstract reads: ‘the mechanism relies on the abnormal properties of their metamaterials – negative modulus and negative density. in everyday materials, these are both positive…typically, when you push on an object, it pushes back against you. in contrast, objects with a negative modulus attract you, pulling you towards them as you push. objects exhibiting a negative density work in a similarly contradictory way. when you push these objects away from you, they instead move toward you. one negative property, either negative modulus or negative density, can work independently to block noise and stop vibrations within certain frequency regimes. however, when working together, the noise or vibration can pass through again. 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.’

‘there are indeed a number of possible applications for smartly controlling acoustics and vibrations,’ ph.d. student kun-hao yu and part of the research group said. ‘traditional engineering materials may only shield from acoustics and vibrations, but few of them can switch between on and off.’