Invisibility cloaks, Prepared by : Sameh Hamzawy Egypt
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Transcript of Invisibility cloaks, Prepared by : Sameh Hamzawy Egypt
Prepared by :Sameh HamzawyMESC9
Experimental demonstration of a broadband array of
invisibility cloaks in the visible frequency range
What are Metamaterials ?History of MetamaterialsPrinciple and FabricationApplications
Outline
the invisibility cap secret.flv
May 1959
What are Metamaterials ?
Metamaterials are artificial materials engineered to have properties that may not be found in natural materials.
They gain their properties not from their composition, but from their exactingly-designed structures.
HistoryTheoretical design by Victor Veselago in 1968.Predicted the possibility of opposite properties
for materials by getting negative refractive index.V.G.Veselago
Dr. John Pendry showed practical method of making metamaterials in 1999 .
Dr. John Pendry In 2009,Vera Smolyaninova and her colleagues
at Towson University and the University of Maryland have been built a 2-D invisibility-cloak array which was the first of its kind and operates in the visible frequency range.
V.Smolyaninova
Principle and Fabrication
Normally, waves propagate and interact with different media according to Snell’s law ()
Metamaterials can : create negative index of refraction guide wave in desired direction
Figure(b) shows the deal case scenario light would propagate through such an array without scattering.
As a first fabrication step, microlens array was coated on the microlens side with a 30 nm gold film.
The array was placed with the gold-coated side facing down on top of a flat glass slide coated with a 70 nm gold film.
Two gold-coated surfaces were pressed against each other using a mechanical arrangement.
Fabrication Process:
Results: When a 514nm light propagates
through the array, the cloaked areas appear as dark circles surrounded by concentric rings in the experimental images. However, the angular performance of this dense hexagonal cloak array clearly shows signs of decay/damage
This decay may be due to the light direction does not coincide with one of the three main symmetry axes of the array which leads to a reduction in the symmetry of the cloaking arrangement
Potential applications
This paper reported the first experimental realization of an array of 2-D broadband invisibility cloaks that operates in the visible frequency range.
The broadband performance appears to be similar to the performance of individual cloaks in the array.
Almost 20% of the surface area is cloaked in this experiment,
the angular performance of a dense array shows signs of decay/damage due to a reduction of the symmetry of the cloaking arrangement.
Conclusion
References
• V.N Smolyaninova, I I Smolyaninov, and H K Ermer1, New Journal of Physics 14 (2012) 053029,1367 2630/12/053029.
• Smolyaninov I I, Hung Y J and Davis C.C 2008 Opt.Lett.33 1342 44.
• Farhat M, Chen P-Y, Guenneau S, Enoch S, McPhedran R,Rockstuhl C and Lederer F 2011 Phys. Rev. B84 235105.
Although we have thorough knowledge of theoretical concept of invisibility but we have not enough practical implementation of these concepts.
Security concern is another serious issue.
The tiny structures embedded in the metamaterial would have to be smaller than the wavelength of the electromagnetic rays you wanted to bend.
Barriers in development of metamaterilas: