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Zhou, T. Koschny, and C.M. Soukoulis, Magnetic response of metamaterials at 100 terahertz, Sci- ence 306 (2004), 1351–1353. 32. H.-T. Chen, J. F. O’Hara, A. K. Azad, and A. J. Taylor, R.D. Averitt, D. Shrekenhamer, and W. J. Padilla, Experimental demonstration of frequen- cy-agile terahertz metamaterials, Nat Photon 2 (2008), 295–298. © 2009 Wiley Periodicals, Inc. TRANSFORMATION OPTICS-INSPIRED METAMATERIAL COATINGS FOR CONTROLLING THE SCATTERING RESPONSE OF WEDGE/CORNER-TYPE STRUCTURES Ilaria Gallina, 1,2 Giuseppe Castaldi, 1 and Vincenzo Galdi 1 1 Waves Group, Department of Engineering, University of Sannio, Benevento, Italy; Corresponding author: vgaldi@unisannio.it 2 Department of Environmental Engineering and Physics, University of Basilicata, Potenza, Italy Received 20 May 2009 ABSTRACT: Transformation optics has recently emerged as a power- ful and systematic approach to design application-oriented metamateri- als. In this letter, following up on our previous studies on thin planar retroreflectors, we show how it is possible, in principle, to design “transformation medium” coatings capable of controlling the scattering response of metallic corner- and wedge-type structures so as, e.g., to strongly enhance the specularly reflected component. We validate our results via a full-wave study of the near- and far-field responses, and envisage possible applications. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2709 –2712, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 24720 Key words: transformation optics; metamaterials; scattering 1. INTRODUCTION The rapid advances in the engineering of metamaterials with controllable anisotropy and spatial inhomogeneity have recently led to the development of a novel framework, typically referred to as “transformation optics” [1, 2], for the design of metamaterial- based devices that allow unprecedented control in the electromag- netic (EM) response. Besides the celebrated “invisibility cloaking” (experimentally verified at microwave frequencies [3] and within the visible range [4]), many other exciting developments are fore- seen in a wide range of applications (see, e.g., [5–13] for a sparse sampling). In a series of ongoing investigations, we have been concerned with the application of transformation optics to the design of coatings for controlling the scattering response of flat metallic structures. For instance, in [14], we addressed the design of thin planar retroreflectors inspired by the dihedral corner-reflector ge- ometry. In this framework, we showed that it was possible to design a metamaterial layer (with anisotropic and inhomogeneous distribution, and with constitutive parameters values that were positive, everywhere limited, and not particularly high), which laid on a metallic plate, would lead to a strong enhancement of the monostatic radar cross-section (RCS) response. Following up on the earlier study, in this letter, we deal with more complicate geometries featuring wedge- or corner-type me- tallic scatterers. To illustrate the potentials of the transformation- optics approach in controlling the scattering response, we focus on a rather challenging example, namely, the design of metamaterial coatings capable of inducing an overall behavior similar to that exhibited by a planar metallic sheet (i.e., with a predominant specular response). Such response may be very useful in radar countermeasure applications, where dealing with wedge/corner- type structures represents a critical issue for the reduction of the overall visibility. Following the standard transformation-optics approach, we first design the desired field behavior, for both the wedge- and corner- DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 11, November 2009 2709