The left hand of electromagnetism : metamaterials
Author
Alıcı, Kamil Boratay
Advisor
Özbay, Ekmel
Date
2010Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
90
views
views
25
downloads
downloads
Abstract
Metamaterials are artificial periodic structures whose electromagnetic
response is solely dependent on the constituting unit cells. In the present thesis,
we studied unit cell characteristics of metamaterials that has negative
permeability and permittivity. We investigated negative permeability medium
elements, especially in terms of their electrical size and resonance strength.
Experimental and numerical study of µ-negative (MNG) materials: multi split
ring resonators (MSRRs), spiral resonators (SRs) and multi-spiral resonators are
presented. The resonance frequency of the structures is determined by the
transmission measurements and minimum electrical size of λ0/17 for the MSRRs
and of λ0/82 for the SRs observed. We explain a method for tuning the
resonance frequency of the multi-split structures. We investigated scalability of
MNG materials and designed a low loss double negative composite
metamaterial that operates at the millimeter wave regime. A negative pass-band
with a peak transmission value of -2.7 dB was obtained experimentally at 100
GHz. We performed transmission based qualitative effective medium theory
analysis numerically and experimentally, in order to prove the double negative
nature of the metamaterial. These results were supported by the standard
retrieval analysis method. We confirmed that the effective index of the
metamaterial was indeed negative by performing far field angular scanning
measurements for a metamaterial prism. Moreover, we illuminated the split-ring
resonator based metamaterial flat lens with oblique incidence and observed from
the scanning experiments, the shifting of the beam to the negative side. The first
device was a horn antenna and metamaterial lens composite whose behavior was
similar to Yagi-Uda antenna.
We numerically and experimentally investigated planar fishnet metamaterials
operating at around 20 GHz and 100 GHz and demonstrated that their effective
index is negative. The study is extended to include the response of the
metamaterial layer when the metamaterial plane normal and the propagation
vector are not parallel. We also experimentally studied the transmission
response of a one dimensional rectangle prism shaped metamaterial slab for
oblique incidence angles and confirmed the insensitivity of split-ring resonator
based metamaterials to the angle of incidence. After the demonstration of
complete transmission enhancement by using deep subwavelength resonators
into periodically arranged subwavelength apertures, we designed and
implemented a metamaterial with controllable bandwidth.
The metamaterial based devices can be listed under the categories of antennas
absorbers and transmission enhancement. We studied electrically small resonant
antennas composed of split ring resonators (SRR) and monopoles. The electrical
size, gain and efficiency of the antenna were λ0/10, 2.38 and 43.6%,
respectively. When we increased the number of SRRs in one dimension, we
observed beam steerability property. These achievements provide a way to
create rather small steerable resonant antennas. We also demonstrated an
electrically small antenna that operates at two modes for two perpendicular
polarizations. The antenna was single fed and composed of perpendicularly
placed metamaterial elements and a monopole. One of the metamaterial
elements was a multi split ring resonator and the other one was a split ring
resonator. When the antenna operates for the MSRR mode at 4.72 GHz for one
polarization, it simultaneously operates for the SRR mode at 5.76 GHz, but for
the perpendicular polarization. The efficiencies of the modes were 15% and 40%
with electrical sizes of λ/11.2 and λ/9.5. Finally, we experimentally verified a
miniaturization method of circular patch antennas. By loading the space between
the patch and ground plane with metamaterial media composed of multi-split
ring resonators and spiral resonators, we manufactured two electrically small
patch antennas of electrical sizes λ/3.69 and λ/8.26. The antenna efficiency was
40% for the first mode of the multi-split ring resonator antenna with broad far
field radiation patterns similar to regular patch antennas.
We designed, implemented, and experimentally characterized electrically thin
microwave absorbers by using the metamaterial concept. The absorbers consist
of i) a metal back plate and an artificial magnetic material layer; ii) metamaterial
back plate and a resistive sheet layer. We investigated absorber performance in
terms of absorbance, fractional bandwidth and electrical thickness, all of which
depend on the dimensions of the metamaterial unit cell and the distance between
the back plate and metamaterial layer. As a proof of concept, we demonstrated a
λ/4.7 thick absorber of type i), with a 99.8% absorption peak along with a 8%
fractional bandwidth. We have also demonstrated experimentally a λ/4.7 and a
λ/4.2 thick absorbers of type ii), based on SRR and MSRR magnetic
metamaterial back plates, respectively. The absorption peak of the SRR layout is
97.4%, while for the MSRR one the absorption peak is 98.4%. We conveyed
these concepts to optical frequencies and demonstrated a metamaterial inspired
absorber for solar cell applications.
We finalized the study by a detailed study of split ring resonators at the
infrared and visible band. We studied i) frequency tuning, ii) effect of resonator
density, iii) shifting magnetic resonance frequency by changing the resonator
shape, iv) effect of metal loss and plasma frequency and designed a
configuration for transmission enhancement at the optical regime. By using
subwavelength optical split ring resonator antennas and couplers we achieved a
400-fold enhanced transmission from a subwavelength aperture area of the
electrical size λ2
/25. The power was transmitted to the far field with 3.9 dBi
directivity at 300 THz.
Keywords
MetamaterialAntenna
Absorber
Solar Cell
Miniaturization
Multiple Split Ring Resonator
Spiral Resonator
Multiple Spiral Resonator
Negative Permittivity
Negative Permeability
Negative Refraction
Planar Metamaterial
Oblique Response
Split Ring Resonator Antenna
Dual Band Antenna
Electrically Thin Absorber
Photonic Metamaterial