Ultra-Thin Unidirectional Carpet Cloak and Wavefront Reconstruction With Graded Metasurfaces

Metamaterials and artificial materials with effective properties that may be controlled to a large degree have been at the basis of exciting schemes for wave manipulation and are particularly well suited to hide an object from electromagnetic waves. To realize practical invisibility cloaks, transformation electromagnetics (TE) methods and scattering cancellation techniques are currently the most popular approaches. Simplified versions of these proposals have been implemented and examined in recent years. 

Here, WNCG Prof. Andrea Alù and student Nasim Mohammadi Estakhri propose a different approach to cloaking applied to an arbitrarily shaped object placed over a ground plane, based on point-by-point wave reconstruction on a surface. Using a suitably designed, ultra-thin graded metasurface, The WNCG team demonstrates the possibility of hiding an arbitrarily shaped and sized object from an impinging plane wave, where an observer would perceive the whole system as a flat reflector. The metasurface is tailored to provide an abrupt, inhomogeneous discontinuity to the electromagnetic field that compensates for the unwanted scattering created by the object. This technique offers several advantages compared to TE-based carpet cloaks in terms of ease of implementation, low profile, and conformability to the geometrical shape of the object. The researchers investigate the performance of their proposed method through numerical simulations and demonstrate successful concealment of electrically large 2D and 3D structures at optical wavelengths, along with high angular stability in the cloaking performance. The presented graded metasurface-based cloaks may find interesting applications as low-profile, tunable covers for low observability and noise reduction in wireless commutation systems.Their proposed technique may bring cloaking devices one step closer to practical implementation, especially at radio frequencies where there is the additional advantage of straightforward reconfigurability.

This research was originally published in IEEE Antennas and Wireless Propagation Letters. This work was supported by the AFOSR under Grant No. FA9550-13-1-0204 and the NSF under CAREER Award No. ECCS- 0953311.

Read full paper HERE.