July 15, 2016

Nanoparticles create invisibility at a greater range of frequencies which will allow antennas in more shapes, sizes and materials

Scientists at Queen Mary University of London (QMUL) have made an object disappear by using a composite material with nano-size particles that can enhance specific properties on the object's surface.

Researchers from QMUL's School of Electronic Engineering and Computer Science, worked with UK industry to demonstrate for the first time a practical cloaking device that allows curved surfaces to appear flat to electromagnetic waves.

While the research might not lead to the invisibility cloak made famous in J.K Rowling's Harry Potter novels quite yet, this practical demonstration could result in a step-change in how antennas are tethered to their platform. It could allow for antennas in different shapes and sizes to be attached in awkward places and a wide variety of materials.

Co-author, Professor Yang Hao from QMUL's School of Electronic Engineering and Computer Science, said: "The design is based upon transformation optics, a concept behind the idea of the invisibility cloak.





Journal of Optics - Isotropic and anisotropic surface wave cloaking techniques

Optics Express - Metamaterial-based wideband electromagnetic wave absorber



"Previous research has shown this technique working at one frequency. However, we can demonstrate that it works at a greater range of frequencies making it more useful for other engineering applications, such as nano-antennas and the aerospace industry."

The researchers coated a curved surface with a nanocomposite medium, which has seven distinct layers (called graded index nanocomposite) where the electric property of each layer varies depending on the position. The effect is to 'cloak' the object: such a structure can hide an object that would ordinarily have caused the wave to be scattered.

The underlying design approach has much wider applications, ranging from microwave to optics for the control of any kind of electromagnetic surface waves.

First author Dr Luigi La Spada also from QMUL's School of Electronic Engineering and Computer Science, said: "The study and manipulation of surface waves is the key to develop technological and industrial solutions in the design of real-life platforms, for different application fields.

"We demonstrated a practical possibility to use nanocomposites to control surface wave propagation through advanced additive manufacturing. Perhaps most importantly, the approach used can be applied to other physical phenomena that are described by wave equations, such as acoustics. For this reason, we believe that this work has a great industrial impact."

Abstract - Journal of Optics - Isotropic and anisotropic surface wave cloaking techniques

In this paper we compare two different approaches for surface waves cloaking. The first technique is a unique application of Fermat's principle and requires isotropic material properties, but owing to its derivation is limited in its applicability. The second technique utilises a geometrical optics approximation for dealing with rays bound to a two dimensional surface and requires anisotropic material properties, though it can be used to cloak any smooth surface. We analytically derive the surface wave scattering behaviour for both cloak techniques when applied to a rotationally symmetric surface deformation. Furthermore, we simulate both using a commercially available full-wave electromagnetic solver and demonstrate a good level of agreement with their analytically derived solutions. Our analytical solutions and simulations provide a complete and concise overview of two different surface wave cloaking techniques.

Abstract - Metamaterial-based wideband electromagnetic wave absorber

In this paper, an analytical and numerical study of a new type of electromagnetic absorber, operating in the infrared and optical regime, is proposed. Absorption is obtained by exploiting Epsilon-Near-Zero materials. The structure electromagnetic properties are analytically described by using a new closed-form formula. In this way, it is possible to correlate the electromagnetic absorption properties of the structure with its geometrical characteristics. Good agreement between analytical and numerical results was achieved. Moreover, an absorption in a wide angle range (0°-80°), for different resonant frequencies (multi-band) with a large frequency bandwidth (wideband) for small structure thicknesses (d = λp/4) is obtained.

SOURCES - Journal of Optics, Optics Express, Eurekalert, Queen Mary University of London

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