Acoustics research centre
Sonic imaging with metamaterials
Research team: Dmitry Smirnov (PhD student), Olga Umnova (Supervisor)
Sonic imaging refers to the construction of an image of an object by sending sound waves towards or through it and processing the scattered waves. Two major examples of this are medical ultrasonography and underwater echolocation. This project investigates the development of improved sonic imaging techniques using metamaterials and digital data processing.
One of the often talked about ideas in metamaterials is negative refractive index – the ability of a metamaterial with specific properties to bend waves incident on it in the opposite direction to what is permitted by conventional refraction, with the waves inside the medium seemingly travelling backwards in relation to the direction of propagation. As a result of this, evanescent waves – wave components scattered by parts of an object too small in relation to the wavelength to generate a propagating scattered wave and instead exist only around the surface of the object – can be amplified by a lens made from this metamaterial and re-focused on the other side. This is the principle behind a superlens – a lens which can overcome the diffraction limit to resolve detail too small in relation to the wavelength for a conventional lens.
The aim of the project is to research sonic imaging techniques using metamaterial transducer lenses to guide the waves, with potential applications including the aforementioned medical and underwater imaging. One part of the project is developing new mathematical procedures to homogenise metamaterials and characterise their behaviour, with the objective of developing tools to predict the behaviour in such a way to design a metamaterial with a certain characteristic in mind. This stage of the project is kept as general as possible, so that the developed techniques are broadly applicable. Properties such as negative refractive index will be explored and considered more specifically in context with the imaging application, using a combination of the developed analytical models and numerical simulations. The other part of the project is specifying a proposed sonic imaging system using the investigated metamaterials, with a major component being developing digital data processing techniques to implement the processing of scattered waves to generate images.
The project started in October 2013.
Waves passing through a slab of metamaterial consisting of resonant split ring unit cells