Pentamode metamaterials almost behave like fluids. Their manufacture opens new possibilities in transformation acoustics. (Source: CFN, KIT)
Here is what KIT says about its new class of metamaterial: A research team lead by Professor Martin Wegener at the Karlsruhe Institute of Technology (KIT) has succeeded in realizing a new material class through the manufacturing of a stable crystalline metafluid, a pentamode metamaterial. Using new nanostructuring methods, these materials can now be realized for the first time with any conceivable mechanical properties. The researchers will present their results in the cover story of the May issue of Applied Physics Letters.
The stable four-leg structure (shown in orange) is the basic element of the pentamode metamaterial. It is arranged in the form of a three-dimensional adamantine crystal such that the resulting material as a whole can be formed. (Source: CFN, KIT)
The Rubicon was crossed, so to speak, at the DFG Center for Functional Nanostructures (CFN) and at the Institute of Applied Physics (AP) in Karlsruhe during the past few months. Eventually, numerous three-dimensional transformation acoustics ideas, for example inaudibility cloaks, acoustic prisms or new loudspeaker concepts, could become reality in the near future.
The mechanical behavior of materials such as gold or water is expressed in terms of compression and shear parameters. Whereas the phenomenon that water, for example, can hardly be compressed in a cylinder is described through the compression parameter, the fact that it can be stirred in all directions using a spoon is expressed through the shear parameters.
The word penta is derived from ancient Greek and means “five”. In the case of water, the five shear parameters equal zero, and only one parameter, compression, differs from that value. In terms of parameters, the ideal state of a pentamode metamaterial corresponds to the state of water, which is why that material is referred to as a metafluid. Theoretically, any conceivable mechanical properties whatsoever can be obtained by varying the relevant parameters.
On the one hand, we must be capable of designing small sugar loaves in the nanometer range and connect them to one another at the right angle. On the other hand, the entire structure must eventually become as large as possible. Since the material itself contributes only little more than one percent to the respective volume, the composite obtained is extremely light.
The stable four-leg structure (shown in orange) is the basic element of the pentamode metamaterial. It is arranged in the form of a three-dimensional adamantine crystal such that the resulting material as a whole can be formed. (Source: CFN, KIT)
In recent years, a Professor at the Institute of Applied Physics and CFN coordinator, Martin Wegener and his collaborators, have developed direct laser writing and, based on that method, established optical lithography of three-dimensional nanostructures. Numerous achievements of Wegener’s group in transformation optics e.g., the first three-dimensional cloak of invisibility in the range of visible light have been due to that technique.
Further Reading
