Browsing by Subject "Left-Handed Material"

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Open Access
Characterization and applications of negative-index metamaterials
(2008) Aydın, Koray
Metamaterials offer novel electromagnetic properties and promising applications including negative refraction, flat-lenses, superlenses, cloaking devices. In this thesis, we characterized the negative-index metamaterials that is composed of periodic arrangements of split-ring resonators (providing negative permeability) and thin wire (providing negative permittivity) arrays. The resonances of split-ring resonators (SRR) are investigated experimentally and theoretically. By combining SRR and wire arrays together, we observed a transmission band where both permittivity and permeability are simultaneously negative, indicating a left-handed behavior. Reflection measurements reveal that the impedance is matched to the free space at a certain frequency range. The lefthanded metamaterial is also shown to exhibit negative refractive index by using three different experimental methods namely, refraction from a wedge-shaped negative-index metamaterial (NIM), beam-shift from a slab-shaped NIM and phase shift from NIMs with different lengths. Flat-lens behavior is observed from a slabshaped negative-index metamaterial based microwave lenses. Furthermore, we demonstrated subwavelength imaging and subwavelength resolution by using thin superlenses constructed from SRR-wire arrays with an effective negative index. We have been able to image a point source with a record-level, λ/8 resolution. SRRand wire arrays exhibit negative index provided that the wave propagates parallel to the plane of SRR structure which makes it hard to fabricate at higher frequencies. An alternative structure called fishnet metamaterial however could yield negative index with wave propagation normal to the structure. We observed left-handed transmission and negative phase velocity in fishnet type metamaterials. Finally, we studied enhanced transmission from a single subwavelength aperture by coupling incident electromagnetic wave to a single SRR placed at the near-field of the aperture.
Open Access
Negative refraction using true left-handed metamaterials
(2004) Aydın, Koray
Left-handed materials and negative refraction attracted a great amount of attention in recent years due to their unique physical properties. It is possible to obtain a left-handed material by combining a novel artificial structure (split ring resonator) and a wire structure periodically. We investigated the transmission and reflection properties of split ring resonators (SRR), wires and composite metamaterials consisting of SRR and wire structures. We have successfully demonstrated true left-handed behavior in free space with a high transmission peak (-1.2 dB). This is the highest transmission peak reported for a left-handed material. The left-handed transmission band coincides exactly with the region where both dielectric permittivity and magnetic permeability have negative values. We proposed and demonstrated a new method to distinguish the magnetic resonance of the SRR structures. We experimentally confirmed that composite metamaterial has a negative refractive index, at the frequencies where left-handed transmission takes place. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments (-1.87) and the phase shift experiments (-1.78) are in good agreement.
Open Access
Sub-wavelength resolution in a photonic crystal superlens
(2003) Çubukçu, Ertuğrul
Materials that can bend light in the opposite direction to normal (’left-handed’ materials) reverse the way in which refraction usually works-this negative refractive index is due to simultaneously negative permeability and permittivity. Here we demonstrate negative refraction of electromagnetic waves in a two-dimensional dielectric photonic crystal that has a periodically modulated positive permeability and a permeability of unity. This experimental verification of negative refraction is a step towards the realization of a ’superlens’ that will be able to focus features smaller than the wavelength of light. Our structure consists of a square array of alumina rods in air. To obtain the frequency range within which the negative refraction and the other peculiar properties incorporated with it, we have calculated the the equal frequency contours of our photonic crystal with the photonic plane wave expansion method. We found out that 13.7 GHz is the optimum frequency for negative refraction. We took transmission measurements to confirm our structure’s predicted negative refraction: we used the the interfaces of the photonic crystal in the Γ − M direction. Our experiments were simulated with the finite-difference time-domain method (FDTD). The negative index of refraction was determined to be −1.94, which is close to the theoretical value of −2.06 calculated by the FDTD method. Since we know that we have a negative refractive material , we used our crystal to test the superlensing effect that was predicted for negative refractive materials. We have demonstrated that the image of two coherent point sources separated by a distance of λ/3 can be resolved. We have extended our approach to the case with two incoherent point sources, and we have achieved subwavelength resolution for this configuration as well. To our knowledge, this is the first demonstration of subwavelength resolution of electromagnetic waves in a negative index material.