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5.6.2 CNT Patch Antenna with Normal Metal Type in SONNET® . 43
5.6.3 CNT Patch Antenna with Thick Metal Type in SONNET® . 46
5.6.4 CNT Patch Antenna with Brick Material in SONNET® . 48
6 Conclusion . 52
7 Open Question and Further Work 53
7.1 Problem of Quality factor 53
7.2 Further Understanding of SONNET® . 53
7.3 Impedance Matrix Simulated in SONNET® . 53
8 Acknowledgements 55
9 Bibliography 56
1 Motivation & Introduction
Carbon Nano-Tube (CNT) networks is a promising material. It has conductive as
well as dielectric properties which can be controlled by the process of fabrication. The
ease of fabrication makes it cost effective and candidate for numerous applications;
specially replacing conductors in antennas which would be investigated in this thesis.
This thesis is a part of bigger project, in which CNTs are to be investigated
theoretically and experimentally. Accurate models would be developed on the basis of
analysis with numerical electromagnetic solvers (e.g. SONNET®). These investigations
would further be used in design and realizations of these antennas at Institute for
Nanoelectronics at Technische Universität München. Impedance and radiation
characteristics of the antennas will be measured and the measurements will be compared
with the results of the numerical modeling.
In the following chapters, CNTs would be discussed in some detail. This would be
followed by salient feature of SONNET® which is a numerical solver of electromagnetic
structures. These features are important to understand the results generated by this solver
as well as its limitations. A chapter is dedicated for properties and characteristics of
antennas, generally, followed by simulations of bow-tie antenna and patch antenna.
bow-tie antenna has relatively broad bandwidth and can be used in RFID type
applications. Patch antenna is mainly used to reproduce results in SONNET® already
generated by experimental as well as CST (electromagnetic simulation software). Lastly,
future directions of work and open questions still to be investigated are summarized.
2 Carbon Nano-Tubes
2.1 Introduction to Carbon Nano-Tubes
Carbon Nano-Tubes (CNT), as the name implies, are made-up of carbon atoms only.
In nature, carbon is found as three forms: diamond, graphite and coal. Diamond and coal
are non-conductive and have little interest in fields of electrical engineering. Graphite, on
the other hand, is conductive and has been used in the brushes of electric motors. The
conductivity of graphite is mainly due to its layered planar structure. In each layer, carbon
atoms are arranged in hexagonal shapes, as shown in Figure 2.
Graphite layers when rolled into a tube forms a CNT as shown in Figure 2. This
rolling is not done manually but fabrication process results in this type of structure. CNTs
are nanostructures, typically 1 to 100 nm in diameter. Unique properties of CNTs are due
to this structure at this miniature size [2]. Carbon nanotubes considered 1D nanomaterial
owing to their very small diameter that confines electrons to move along their length [2].
There’re two families of CNTs: single-wall CNTs (SWNT) and multi-wall CNTs
(MWNT), based on layers rolled concentrically. A single-wall CNT is a hollow
cylindrical structure of carbon atoms (diameter ~ 0.5 to 5nm and lengths of the order of
micrometers to centimeters). A MWNT is similar in structure to a SWNT but has multiple