Metamaterials

Bringing the Era of Supernatural Properties Closer

Lately, the industry of materials has been experiencing the expansion of gigantic proportion, and we owe it largely to metamaterials. Metamaterials are substances that fundamentally alter physical properties of conventional materials or exhibit super-properties not found in nature. One of many examples is the invisibility cloak creating invisibility effect - the subject of many science fiction books, but today is simply the matter of technological feasibility. Invisibility cloak is able to bend light around an object, instead of reflecting of that object. Buildings could become invisible to earthquakes; boats have very little drag and the soldiers of tomorrow invisible to the enemy.

 

     

Plasmonic Metamaterials Producing Invisibility Effect

The group of researchers at the University of Texas (Austin, TX) have finally produced invisibility cloak that deals with visible light instead of microwaves. Previous experiments have proved that three-dimensional objects can be hidden from microwaves with the help of metamaterials, but now it became possible to cloak an object to visible light using plasmonic metamaterials. During the previous experiments 'carpet cloak' had to be placed right next to the object, the new technology allows an object to be placed at a distance, in open space - totally different opportunities! Normally, we see things around us when light is reflected back towards our eyes - the angle of incidence conventionally is equal the angle of reflection - not so with plasmonic metamaterials, they produce the opposite effect. Professor Andrea Alù says: "When the scattered fields from the cloak and the object interfere, they cancel each other out and the overall effect is transparency and invisibility at all angles of observation".

Metamaterials Reduce Hydrodynamic Drag by Producing Still Water Effect

This year, the group of scientists led by Professor Yaroslav Urzhumov at Duke University, NC has announced that metamaterials could be used to substantially reduce the drag on a ship by making the surrounding water to stick and move with the hull. The drag does not disappear completely but the friction is reduced, because water effectively becomes the outside surface of the hull. We are familiar with the fishing lure effect when small and light-weight object behaves like much heavier piece; the resistance is caused by the friction between the surface of moving lure and still water. The friction between any solid surface and liquid is always going to be higher than the friction between liquids; therefore the objective of the project was to simulate the water-surface standing as still as outside water is. This became possible by creating a porous, sponge-like metamaterial coating for the ship's hull that releases water through mini jets towards the back of the ship with the speed of the ship, this way outside environments perceives the ship as a standing still body, causing minimum drag. The water required for those jets is taken in up front and accelerated by electric pumps.

 

Changing Between Solid and Liquid States without Application of Heat

German and Chinese scientists Dr. Jörg Weißmüller and Hai-Jun Jin have developed a metallic metamaterial that changes its state from solid to liquid and back under the influence of electric current. The choice of metals used for the experiment is unfortunately expensive: gold or platinum. Acid is used to eat away part of the sample forming caves and cavities forming a sort of sponge. 

 

Next, cavities are filled with the conductive liquid. When electric current is passed through the sample its physical properties change making it soft or hard depending on a charge. The strength of the metallic material varies up to 200% upon the flip of a switch. Also, reverse effect takes place when the mechanical stress is applied on a metallic sample; it produces electric signals. The sample remains strong and hard, while selective parts can become soft in order to avoid physical damage.

 

References: OSA, Gizmag, Nanotechnology, Duke University, NC, University of Texas.

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