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Researchers at Aalto University and Duke University have succeeded in producing a thin material that can control the movement of sound waves with high efficiency. The material can easily be produced using a 3D printer. This is the first time that researchers have succeeded in producing a material that carries sound waves almost perfectly in a desired direction. Earlier attempts produced materials in which the simultaneous control of transmission and reflection of sound was not possible and consequently sound would also move in unwanted directions. 

Metamaterials are artificial materials in which waves, such as light and sound waves, interact with the structures and produce exotic effects not found in natural materials. For instance, in a plastic 3D printed metamaterials it is not only important the composition of the plastic, but the characteristics of the structure of the material. A metamaterial is composed of meta-atoms in which the desired effect is achieved by adjusting the size, shape, and the interaction with the neighbours. By altering pressure and the velocity of sound waves, it is possible to get sound to move in a certain direction.

'This is the first study of acoustic metamaterial at Aalto and I believe that this article will open new possibilities for expanding research. Research on electromagnetic metamaterials has been going on at Aalto for a long time and now those skills and knowledge can be applied in a new area', says Ana Díaz Rubio, who has been working as a postdoctoral researcher at Aalto for two years. She studied acoustic metamaterials for her doctoral dissertation in Spain.

'My supervisor, Professor Tretyakov, encouraged me to learn more about the topic and to develop myself as a researcher. I was advised to seek out a collaboration with top figures in the field, so Professor Steve Cummer was a natural choice when looking for a partner for cooperation. My initial contact got a very positive reception and the cooperation continues.'

'It felt wonderful to have the study published in Nature Communications. We have reached an important milestone and it is good to continue the research from here', Ana adds.

The article was published in the online version of the journal on 9 April 2018. The study has received funding from the Academy of Finland.