A very small variation in pore size can dramatically change the flow behaviour. The flow is closely related to the pore size of the media. Porous medium such as a pile of sand contains many pores that allow fluids to pass through. Now, a collaborative team led by Professor Xu has found that the flow field of porous media can make the super device possible. However, the extreme requirements of material properties have meant that such a super device has never been realised before. As these can be made for one specific function only, scientists have been trying to design a super metamaterial device that can integrate all these functions in one system, and simply switch across them. They include concentrators, which can concentrate the field, and rotators, which can rotate the direction of field propagation. Over the years, scientists have extended the theory to other physical fields such as sound waves, mechanical waves, water waves, heat conduction and direct current electric fields, and developed various metamaterials that are both invisible and capable of manipulating the internal field. Artificial optical metamaterials can bend light rays to go around an object, leading to invisibility. The transformation mapping theory invented by the British physicist Professor John Pendry in 2006 provides a theoretical framework to realise optical cloaks. Similarly, in the ancient Chinese novel Investiture of the Gods, there are various magical items of clothing that can make people invisible. In the Harry Potter books and films, there is a magical cloak which can instantly make any object inside it disappear. The findings have been published in the prestigious scientific journal Proceedings of the National Academy of Sciences (PNAS).Ī metamaterial allowing simple switching of functions This has potential applications in cell and tissue culture, and creates new possibilities for the advancement of tissue engineering and drug delivery. A research team led by Professor Xu Lei in the Department of Physics at The Chinese University of Hong Kong (CUHK), in collaboration with scientists from mainland China, has invented a first-of-its-kind multifunctional metamaterial device that integrates the technology behind an invisibility cloak with a concentrator and rotator.
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