September 06, 2015

Full invisibility for UAVs and other vehicles might be possible in near future with cloaking progress

University of California, San Diego have created a new design for their cloaking device, using a Teflon substrate, studded with cylinders of ceramic, that is thinner than any prior development and does not alter the brightness of light around concealed objects. The Teflon has a low refractive index, while the ceramic’s refractive index is higher, which allows light to be dispersed through the sheet without any absorption. Compared to an invisibility cloak, this technology has not only the ability to conceal, but the ability to increase optical communication signal speed and to collect solar energy.

Cloaking device would be valuable to many technologies, including unmanned air vehicles (UAVs) due to the capability to disappear from view and leaving no visual, electronic or infrared signature for an enemy to detect.

Creating the effect of an invisibility cloak offers a real-world solution to concealment, which can provide the military with air superiority. While this cloak has numerous applications for the military, this technology will create a ripple effect beyond the battlefield that will improve the performance of other diverse applications.

Nextbigfuture has covered the UCSD cloaking work in July.

Extremely Thin Dielectric Metasurface for Carpet Cloaking

Researchers demonstrate a novel and simple geometrical approach to cloaking a scatterer on a ground plane. We use an extremely thin dielectric metasurface to reshape the wavefronts distorted by a scatterer in order to mimic the reflection pattern of a flat ground plane. To achieve such carpet cloaking, the reflection angle has to be equal to the incident angle everywhere on the scatterer. We use a graded metasurface and calculate the required phase gradient to achieve cloaking. Our metasurface locally provides additional phase to the wavefronts to compensate for the phase difference amongst light paths induced by the geometrical distortion. We design our metasurface in the microwave range using highly sub-wavelength dielectric resonators. We verify our design by full-wave time-domain simulations using micro-structured resonators and show that results match theory very well. This approach can be applied to hide any scatterer under a metasurface of class C1 (first derivative continuous) on a ground plane not only in the microwave regime, but also at higher frequencies up to the visible.

Researchers propose in this paper a dielectric metasurface with a tailored phase gradient for carpet cloaking. We show that a single extremely thin (λ/12) all-dielectric metasurface is sufficient to accomplish invisibility. Once the scatterer is covered with the designed metasurface, no observer can distinguish it from a flat surface

The geometrical scheme presented is general and can be used for any surface of class C1 and for frequencies up to the visible. The proposed design flow chart gives a powerful and easy to use recipe to design metasurface cloaks for a given geometry. A specific design has been presented and cloaking performance has been shown to be robust with respect to surface discretization. The observed wavefronts reflected from the proposed metasurface have been shown to be quasi-planar, with little to no distortion. With this design, any observer will just see a flat ground plane and the scatterer will be invisible and thus effectively cloaked. We have also shown that despite being designed for 45 degrees, accepting a phase advance/delay of 3% of the period, results in an angular bandwidth of ±6 degrees. Moreover, this approach of bending electromagnetic waves with metasurfaces can be used not only for carpet cloaks but also for light focusing to make flat optics devices such as thin solar concentrators, quarter-wave plates, and spatial light modulators. Making these surfaces reconfigurable, we expect ideas proposed here to find applications in flexible devices.

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