Metal-dielectric based metamaterial properties and applications at the millimeter wave regime Kamil Boratay Alici* and Ekmel Ozbay Nanotechnology Research Center, Department of Physics, Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, 06800 Ankara, Turkey *email: [email protected] Summary We present composite metamaterials in terms of their unusual properties and applications at 100 GHz. We studied both split-ring resonator based and fishnet metamaterials. Numerical and experimental qualitative effective medium theory analyses were supported by the standard retrieval results. Oblique incidence negative refraction experiments for the SRR-based case are also performed and the study is finalized by demonstrating the enhancement of radiated power passing through a subwavelength hole covered with a negative permeability medium, and characteristics of far field radiation passing through a negative index rectangular slab. Introduction In the presence of an applied electromagnetic field, materials’ linear response is described by (electric) permittivity (ε) and (magnetic) permeability (µ) parameters. By introducing an artificial periodic array wherein repeated elements of the so-called metamaterial (MTM) are arranged, we can obtain a medium with a controllable linear response at any desired narrow frequency band up to ultraviolet. Electrically small nonmagnetic metallic resonators are proposed as constituting elements of a µ-negative medium  and metallic wire mesh structures provide a low frequency plasma system with negative permittivity . We can demonstrate a µ-negative medium at different frequency bands of the electromagnetic spectrum. By scaling the physical size of the SRRs, a magnetic response at around 5 THz , 6 THz , 100 THz , and 370 THz  were demonstrated experimentally. In the present work, we analyzed a split ring resonator based and fishnet metamaterial medium operating at the millimeter wave regime and some of their applications [7, 8]. Discussions Our experiments were performed by using a millimeter-wave network analyzer with a 50 dB dynamic range from 75 GHz to 115 GHz. The transmission data in air was obtained by the aid of two standard gain horn antennae. The orientation of and distance between the antennae were kept fixed during the metamaterial characterization experiments. We inserted the MTM slab between the horn antennae and measured its transmission response, and then removed the slab and noted the calibration data. By measuring the transmission response of several single negative and double negative media, we characterized the composite metamaterial medium by using the qualitative effective medium theory . Results for the SRR-based case are shown in Fig.1. Fig. 1. Transmission spectrum for 3 layered metamaterials in the propagation direction. Left: the SRR and CRR. Right: the CMM and shorted CMM i.e. closed composite metamaterial (CCMM). As to demonstrate the enhancement of radiation passing through a subwavelength aperture we used a subwavelength slit and transmitter horn antenna. First we scanned the pattern at the far field for the case of subwavelength slit, then inserted the SRR-medium cover and measured the pattern. We observed a 10 dB enhancement of the gain without a decrease at the overall efficiency. Partial results are shown in Fig. 2. Fig. 2: Radiation patterns. Black-solid: horn antenna in air. Red-dash: subwavelength slit. Greendot: subwavelength slit covered with SRR-layer. Conclusions The characterization of split ring resonator-based and fishnet metamaterials operating at 100 GHz were demonstrated in terms of the qualitative effective medium theory and standard retrieval analysis. The structure layers were produced via printed circuit board technology and the transmission response for increasing the number of layers at the propagation direction was analyzed. We observed a stop-band for the SRR-only medium and pass-band for the CMM medium at around 100 GHz. The transmission peak value was ~ -2.5 dB. For the SRR-based case the experimental results were not very sensitive to the layer disorders or the angle of incidence, and they were in good agreement with the numerical calculations. On the other hand, fishnet metamaterials are sensitive to the angle of incidence and this is a major drawback for superlens applications. One of the major applications of the single negative metamaterials is to enhance the power passing through a subwavelength aperture. We demonstrated 10 dB enhancement at 100 GHz by covering the aperture with single layer of SRRs. References  J. B. Pendry, A. J. Holden, D. J. Robbins, W. J. Stewart, “Magnetism from conductors and enhanced nonlinear phenomena,” IEEE Trans. Microwave Theory Tech. 47, 2075 (1999).  J. B. Pendry, A. J. Holden, W. J. Stewart, I. Youngs, “Extremely low frequency plasmons in metallic mesostructures,” Phys. Rev. Lett. 76, 4773 (1996).  B. D. F. Casse, M. O. Moser, J. W. Lee, M. Bahou, S. Inglis, L. K. Jian, “Towards three-dimensional and multilayer rod-split-ring metamaterial structures by means of deep x-ray lithography,” Appl. Phys. Lett. 90, 254106 (2007).  N. Katsarakis, G. Konstantinidis, A. Kostopoulos, R. S. Penciu, T. F. Gundogdu, M. Kafesaki, E. N. Econoumou, Th. Koschny, C. M. Soukoulis, “Magnetic response of split-ring resonators in the far-infrared frequency regime,” Optics Lett. 30, 1348 (2005).  S. Linden, C. Enkrich, M. Wegener, J. Zhou, Th. Koschny, C. M. Soukoulis, “Magnetic response of matematerials at 100 Terahertz,” Science 306, 1351 (2004).  C. Enkrich, M. Wegener, S. Linden, S. Burger, L. Zschiedrich, F. Schmidt, J. F. Zhou, Th. Koschny, C. M. Soukoulis, “Magnetic metamaterials at telecommunication and visible frequencies,” Phys. Rev. Lett. 95, 203901 (2005).  K. B. Alici, E. Ozbay, “Characterization and tilted response of a fishnet metamaterial operating at 100 GHz”, J. Phys. D, (to be published).  K. B. Alici, E. Ozbay, “Effective medium theory characterization of split-ring resonator based millimeter-wave metamaterial” (submitted).  Th. Koschny, M. Kafesaki, E. N. Economou, C. M. Soukoulis, “Effective medium theory of lefthanded materials,” Phys. Rev. Lett. 93, 107402 (2004).