Opening up new possibilities for sound waves

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We’ve all seen a booming loud speaker rattle a window. Imagine what those sound waves could do if you could effectively steer them.

Acoustics have already been used in medicine, pest control and speaker technology, and an international research team is looking at novel acoustic structures to see how they can control sound waves more effectively.

In a paper published today in the prestigious journal Nature Communications, the research team, including academics from UNSW Canberra and The University of Technology Sydney (UTS), describe how sound waves can be efficiently controlled by artificially engineered structures known as acoustic metamaterials.

Senior researcher, Dr David Powell of UNSW Canberra and Honorary Fellow at UTS, said the research is expected to lead to a new understanding of acoustic waves and how they can be effectively manipulated.

The research investigates the limits of an additional parameter known as Willis coupling. This parameter, which couples potential and kinetic energy, has been widely explored in optics, but it is relatively new to acoustics.

Dr Powell said the incorporation of Willis coupling into some metamaterial structures can improve the efficiency of soundwaves through more controlled steering.

Existing acoustic metamaterials are highly complex, with very fine features. This makes them ill-suited for mass production and can lead to a very high absorption of sound. The new structure is highly scalable to many different wavelengths, and readily manufacturable.

Co-author Dr Sebastian Oberst, a Senior Lecturer at the University of Technology and Visiting Fellow at UNSW Canberra, said one exciting possibility in the long term, is a new capability for the measurement of delicate mechanical structures, which avoids the cost, complexity and side-effects of existing systems.

“This should benefit many high-tech areas, including inflatable space structures, micro-mechanical sensors and precise optical components, as well as biological areas such as the study of insect locomotion,” Dr Oberst said.  

Background: The research Acoustic meta-atom with experimentally verified maximum Willis coupling was conducted by Anton Melnikov, Honorary Visiting Fellow at the University of Technology Sydney, Visiting Research Fellow at UNSW Canberra and PhD candidate of the Technical University Munich, and assisted by UNSW Canberra Research Associate Dr Yan Kei Chiang and PhD candidate Li Quan of the University of Texas at Austin. Senior researchers included Dr David Powell of UNSW Canberra, Dr Sebastian Oberst of University Technology Sydney and Visiting Fellow at UNSW Canberra, Prof Steffen Marburg of the University of Munich, and Prof Andrea Alu of the City University of New York.