The University of Massachusetts Amherst
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Kwon Obtains Army Research Office Grant to Develop Invisibility and Cloaking Approaches

Do-Hoon Kwon

Do-Hoon Kwon

Associate Professor Do-Hoon Kwon of the University of Massachusetts Amherst Electrical and Computer Engineering (ECE) Department has received a research award of $367,004 over three years from the Army Research Office. Kwon’s project, "Single and dual polarized metasurface cloaks for microwave invisibility and low observability,” introduces and demonstrates a new electromagnetic cloaking physics applicable to large free-standing scatterers.

“The potential impact of the proposed effort reaches beyond demonstration of a new cloaking physics,” said Dr. Joe Qiu, program manager for Solid-State Electronics and Electromagnets at Army Research Office. “The design technique can be applied directly to electromagnetic computation for antenna design, radar cross-section calculation and optimization, and signature control and manipulation for electromagnetic illusion devices, all of which are needed for Army field operations.”

The Army Research Office is an element of the U.S. Army Combat Capability Development Command’s Army Research Laboratory.

As an article in Science News once explained the uses of potential “cloaking” technologies, “Beyond obvious applications, such as hiding military vehicles or conducting surveillance operations, cloaking technology could eliminate obstacles – for example, structures interrupting signals from cellular base stations could be cloaked to allow signals to pass by freely.”

The research allows the wave propagation behavior to be controlled using thin surfaces of arbitrary shape, free from the traditional limitation tied to the geometrical forms. Eliminating scattering results in invisibility cloaking; synthesizing the scattering signatures of another object gives camouflaging. These scattering signature control can now be realized using thin passive materials.

As Kwon explained the background of his research: “Currently, a few different cloaking approaches are available based on transformation optics, scattering cancellation, and gain-loss compensation. Each of them faces unique challenges and drawbacks in practical application scenarios in terms of relative dimensions of cloaks, losses, scatterer size limitations, and a necessity for active constituents.”

Kwon noted that his “proposed surface cloaking technique overcomes the major obstacle of each cloaking technique and shows promising realization prospects as printed metasurfaces in the microwave regime. The proposed surface cloaking is effective for electrically large scatterers in free space, and the cloaking surface can be realized using only passive and reciprocal materials by design.”

Kwon went on to say that cloaking is achieved by tightly guiding an incident wave around a scatterer using metasurfaces of subwavelength thickness. The bounding surface of a scatterer is the cloaking surface as an electromagnetically impenetrable surface represented by a gradient surface impedance. The surface impedance is designed such that an incident wave is converted in a reflectionless manner into a growing surface wave propagating along the object surface.

“Once power is guided around the object by the surface wave into the shadow side, a wave with planar wavefronts is continuously leaked in the forward scattering direction to restore the incident field in the shadow region,” said Kwon. “The required gradient scalar or tensor impedance can be discretized at a subwavelength interval for metasurface realization, such as an array of printed metallic resonators on a grounded dielectric substrate.”

Kwon observed that the significance of his project can be summarized by the following list of principal expected outcomes: establishing and understanding of a new cloaking physics based on surface wave-assisted guidance of the incident wave around a scatterer; establishment of a new design philosophy for power-preserving functional electromagnetic surfaces that can be realized using passive, reciprocal constituents; demonstration of a new wave control mechanism that is applicable to other wave phenomena such as acoustics.

Kwon is affiliated with the Antennas and Propagation Lab in the ECE Department and his research expertise is in wideband antennas, small antennas, frequency selective surfaces, metamaterials, as well as cloaking and transformation electromagnetics. (August 2019)