Make Surfaces Invisible to Microwave Beams

Make Surfaces Invisible to Microwave Beams

Out of the battlefield and into a peacetime role—achieving simple but effective microwave cloaking using a frequency-selective surface.

Automotive electronic safety systems are increasingly using radar technology to warn of obstacles and other vehicles in a driver’s path. It’s just one electronic technology that has made a transition from warfare to peacetime applications. Could it be just a matter of time when electronic cloaking systems also find their way over to peacetime applications?

Cloaking systems for warfare usually have a way of applying some layer of negative permittivity to a conducting or dielectric object to ensure that it does not appear on an adversary’s radar screen. A conceivable peacetime cloaking system could provide police officers with a means of avoiding detection by motorists ignoring posted speed limits and on the lookout for law enforcers.

Researchers at the CommSensLab of the Universitat Politecnica de Catalunya-BarcelonaTech (Barcelona, Spain) essentially took a “ground-floor” look at microwave cloaking and investigated a means for achieving simple but effective microwave cloaking using a frequency-selective surface (FSS). Their approach involves the use of an inhomogeneous layer to bend electromagnetic (EM) waves around the region occupied by the cloaked object without interacting with it. This “mantle coat” for EM scattering cancellation made it possible to build a microwave cloak for electrically thin cylinders using a thin, patterned, conducting surface that’s light in weight, broad in bandwidth, and with a low profile.

The researchers detailed the design approach for their microwave cloaking method, along with software simulation procedures for modeling the effects of the method and the prototypes used to demonstrate its effectiveness. Objects to be cloaked consisted of thin sheets of copper wrapped around a polyvinyl-chloride (PVC) cylinder. Bistatic scattering measurements were performed in a well-equipped test laboratory/anechoic chamber, with transmit and receive antennas and wideband commercial vector network analyzer (VNA).

Design equations are presented for achieving a surface reactance at a frequency of interest, such as 192.5 Ω at 3.77 GHz using a mesh grid of FSS cells on a target surface. Full-wave, three-dimensional (3D) computer simulations of the FSS microwave cloaking surface were performed to show the computed attenuation of a microwave cloak.

See “A Microwave Invisibility Cloak,” IEEE Antennas & Propagation Magazine, Vol. 60, No. 4, August 2018, p. 49.

 

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