Metamaterials are a new class of finely engineered surfaces that perform tasks that defy nature. The newly developed material pushes the boundaries of metamaterials, although they have already shown amazing results with light manipulation. This has for example allowed scientists to create a real version of Harry Potter’s invisibility cloak.
The research team from the Universities of Bristol and Sussex have now demonstrated that the materials can also work with sound waves. This new development could potentially transform personal audio and medical imaging.
Medical therapy and imaging uses finely shaped sound fields. These type of fields are also used in a wide range of products such as ultrasonic haptics and audio spotlights. In an article recently published in Nature Communications, a cheap and simple way of using acoustic metamaterials to create these shaped sound waves is shown.
The research team collaborated to assemble a metamaterial layer out of many small bricks that each coil up in space. The space coiling bricks slow down sound. This means that incoming sound waves can be changed into any sound field that may be required.
The new metamaterial layers could have many potential applications. Huge versions could be used to focus or direct sound to a specific location to create an audio hotspot. In a medical application, smaller versions could be used to destroy tumors deep within the body by focusing high intensity ultrasound on a specific spot. The layer could be fitted to existing loudspeaker technology in both cases, enabling cheap and rapid production.
The study was led by Dr Gianluca Memoli from the Interact Lab at the University of Sussex. He explained that the metamaterial bricks could be printed in 3D and then assembled to form any sound field imaginable. The team also demonstrated that this could be done with only a small amount of different bricks. Memoli thinks of a box of metamaterial bricks as a DIY acoustics kit.
The head of the Interact Lab at the University of Sussex, Professor Sriram Subramanian, added that their aim was to create acoustic devices that control sound with the same flexibility and ease with which projectors and LCDs manipulate light.
This research paves the way to new acoustic devices that can combine refraction, scattering and diffraction. This will in turn enable the future development of spatial sound modulators that are completely digital and can be controlled with minimal resources in real time.
A professor of Ultrasonics at the University of Bristol, Bruce Drinkwater, thinks there will be many exciting applications of this technology in the future. The team is now attempting to make the metamaterial layers reconfigurable dynamically. Once this is possible, cheap imaging systems, which could be used for crack detection or medical diagnostics, can be produced.