abstract - Faculty of Science at Bilkent University

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]
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.
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 [1] and metallic wire mesh
structures provide a low frequency plasma system with negative permittivity [2].
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 [3], 6 THz [4], 100 THz [5], and 370 THz [6] 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].
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
[9]. 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.
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.
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