Metamaterial Sheets Make Invisibility Cloaks

Researchers at the University of Illinois at Urbana-Champaign have formulated a new method that can be used for large scale manufacturing of metamaterials. The metamaterials are alloys with slightly unusual properties. This class of materials can interact with light in a different manner. Some of these materials can be used for producing futuristic optical devices like invisibility cloaks, superlenses and other devices.


The prototypes for such state of the art gadgets have been already developed but the main problem is that these materials are hard to fabricate in large quantities. The new printing methodology is said to be able to manufacture sheets of metamaterials with dimensions large enough to create practical devices. Small sheets measuring hardly a few hundred nanometers were developed till now which were hardly sufficient for anything except laboratory demonstrations.


The team of scientists is led by John Rogers, professor of material engineering at the University of Illinois. Metamaterials have an intricate and complex molecular lattice. It has a layered structure with overlapping metal layers. The main constraint while designing these alloys is that the dimensions should be comparable to the wavelength of the light spectrum in which the material has to operate. Till now, complex techniques like electron beam lithography. Rogers and his group have developed a simpler alternative that is economically feasible. It is basically a stamp based printing technique that can be used for bigger pieces of metamaterials. Some of the substances belonging to this category of materials have a negative refractive index with respect to infrared light and hence do not reflect the incident light. This property makes it suitable for making super lenses, hi tech optical communication devices, night vision invisibility cloak, etc.


The fabrication process is pretty simple. Initially, the desires hard plastic stamp is shaped on which a fishnet like pattern of layer is embossed. This stamp is then placed in an evaporation chamber where it gets coated with alternative layers of sacrificial layer and metamaterials. The main metamaterial ingredients are oxides of magnesium and silver. In this way a mesh gets deposited on the stamp. Later, this stamp is placed on a plastic or glass plate. Then the sacrificial layer is etched away and the pattern is deposited on the glass layer. The size of the material can be increased by improving the stamp surface area and these stamp fabricated patterns have better optical characteristics.


Now, the most time consuming thing in this method is making the moulds for the stamps precisely. Once the mould is ready, any number of reusable stamps can be manufactured for the printing of metamaterial sheets. It might take a few more years for making this technology commercial. Let’s hope that this technology can make Harry Potter-like invisibility cloaks.