«by Sangjo Choi A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Electrical Engineering) in ...»
for Terahertz and Optical Frequencies
A dissertation submitted in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
in the University of Michigan
Professor Kamal Sarabandi, Chair
Professor Anthony Grbic
Professor Amir Mortazawi
Assistant Professor Thomas Schwarz
© Sangjo Choi 2014
All Rights Reserved
To my father Siyoung Choi, and my mother Jaenam Jeon To my fiancé Saebom Jung ii
ACKNOWLEDGEMENTSFirst and foremost, I would like to deeply thank and dedicate all my success to God, my parents, sister, and fiancé. Without their love and care, I would not be able to accomplish my ph.D work.
I want to express my sincere gratitude and appreciation to my advisors Prof.
Kamal Sarabandi for his continuous support, encouragement and guidance throughout my studies. I would like to extend my sincere gratitude to my other committee members, Prof.
Amir Mortazawi, Prof. Anthony Grbic and Prof. Thomas Schwarz for devoting their time to review this thesis and advising me with valuable suggestions.
I would like to thank my colleagues and friends at the Radiation Laboratory and EECS for constructive and insightful discussions. I thank Dr. Adib Nashashibi, Dr.
Leland Pierce, Dr. Juseop Lee, Dr. Jungsuek Oh, Dr. Young Jun Song, Dr. Victor Lee, Dr.
Adel Elsherbini, Dr. DaHan Liao, Dr. Fikadu Dagefu, Dr. Meysam Moallem, Gurkan Gok, Jihun Choi, Michael Benson, Jiangfeng Wu, Abdulkadir Yucel, Hamid Nejatie, Kyunghoon Lee, Kyusang Lee, Seungku Lee, Taehee Jang, and Hyeongseok Kim.
Finally, I would like to thank Pastor. Sun Myung Lyu and my friends at Korean Presbyterian Church of Ann Arbor.
Sangjo Winter, 2014, Ann Arbor.
TABLE OF CONTENTSDEDICATION
LIST OF FIGURES
Chapter 1 Introduction
1.2 Thesis Outline
Chapter 2 Efficient Dipole Antenna using a Nanomaterial, Bundled Carbon Nanotubes
2.2 Carbon Nanotubes
2.3 Resistive Sheet Model of Bundled Carbon Nanotube
2.4 Resistivity of Bundled Carbon Nanotubes
2.5 Method of Moment (MoM) Formulation
2.6 Conductivity of Thin Gold Film
2.6.1 Drude-Smith Model
2.6.2 Surface Resistivity of Thin Gold Film
2.7 Antenna Simulation
2.7.1 Strip Antenna
2.7.2 Radiation Efficiency
Chapter 3 Gold Bowtie Antenna Topology for High-Efficiency Thermophotovoltaics
3.2 Bowtie Nanoantenna Design
3.2.1 Maximum Power Transfer
3.2.2 Open-ended Transmission Line Stub
3.2.3 Field Enhancement at the terminals of the bowtie antenna
3.2.4 Absorption Efficiency
iv 3.2.5 Radiation Efficiency
3.3 Array Design
Chapter 4 Gold Bowtie Antenna Topology
4.2 Bowtie Antenna Integrated with InGaAsSb Block
4.3 Sensitivity Comparison between Antenna-Loaded and Conven-tional IR Detectors
4.3.1 Johnson noise-limited case
4.3.2 Photon noise-limited case
4.4 Focal Plane Array Design
Chapter 5 Cross Dipole Antenna Topology for an IR Polarimetric Detector....... 76
5.1 Cross Dipole Antenna Topology and its usage for Direction Finding in the GHz range
5.1.2 Cross Dipole Antenna Structure
5.1.3 Antenna Measurement
5.2 Antenna-Loaded IR Polarimetry System
5.2.2 IR Cross Dipole Antenna Structure
Chapter 6 Conclusions and Future Work
6.1 Summary of Achievements
6.2 Future work
6.3 List of Publications
v LIST OF FIGURES
Figure 1.1: (a) 160 nm-length gold dipole antenna with diameter of 10 nm and the gap size of 3 nm filled by vacuum, (b) and (c) field magnitude (complex electric field) along a cut plane across the center of the antenna of the antenna consists of PEC (at f = 1,150 THz) and Drude model gold (at f = 278 THz).
Figure 1.2: Dissertation Overview.
Figure 2.1: Densely aligned carbon nanotubes using repetitive CVD growths .
....... 19 Figure 2.2: Geometry of a strip antenna made up of bundled Carbon Nanotubes............ 21 Figure 2.3: Relative permittivity and conductivity (real) of thin gold film as a function of frequency
Figure 2.4: Strip dipole antenna geometry fed at center using a thin voltage gap.
........... 28 Figure 2.5: Input impedance of 150 µm strip antenna with BCNT density of (a) N:10 [CNTs/µm], (b) N:50 [CNTs/µm].
Figure 2.6: Reflection coefficient of 150 µm strip antenna with different BCNT densities [CNTs/µm].
Figure 2.7: Normalized antenna length (2L/λ) versus resonant frequencies.
Figure 2.8: Normalized antenna length (2L/λ) versus density of BCNT.
Figure 2.9: Radiation resistance of BCNT (N is higher than 5∙103[CNTs/µm]) and thin gold film at its resonant frequencies.
Figure 2.11: A magnified plot of antenna efficiencies for BCNT densities of 104 to 5∙104 [CNTs/µm] and a comparison to efficiencies of thin gold antenna.
Figure 2.12: Radiation efficiency (including impedance mismatch power loss to a 50 Ω transmission line) of strip dipole antenna of BCNTs (N: CNTs/µm) and thin gold film BCNT densities of 102 to 5∙104 [CNTs/µm].
Figure 2.13: A magnified plot of BCNT densities of 104 to 5∙104 [CNTs/µm] and a comparison to efficiencies of thin gold antenna.
Figure 3.1: Thermophotovoltaic structure.
Figure 3.2: Dielectric constant and conductivity of InGaAsSb.
Figure 3.3: Bowtie antenna structure in one plane.
Figure 3.4: Input impedance of bowtie antenna loaded with an air gap(dashed line) and bowtie antenna intrinsic input impedance(solid line) with L = 605 nm, W = 160 nm, α = 30°, H = 30 nm, and l = 30 nm.
Figure 3.5: Equivalent circuit of the bowtie antenna loaded with InGaAsSb load in receiving mode.
Figure 3.6: Input impedance of the bowtie antenna loaded with the InGaAsSb load (solid line with dots), and input impedance of the bowtie antenna loaded with the InGaAsSb load and a shunt ideal inductor having inductance of 0.
12 pH (dashed line), and bowtie antenna intrinsic input impedance (solid line).
Figure 3.7: Open-ended transmission line connected in shunt with the InGaAsSb load.
.. 52 Figure 3.8: Magnitude of complex electric field on a plane between the two strips of the transmission line for a plane wave illumination at 180 THz.
Figure 3.10: Unit cell (950 nm × 610 nm) of the bowtie antenna for infinite array.
........ 55 Figure 3.11: Absorption efficiency of InGaAsSb slab as a function of the slab thicknesses from 500 nm to 4000 nm.
Figure 3.12: Absorption efficiency of bowtie antenna loaded InGaAsSb block (30 nm × 30 nm × 30 nm) with and without a back metallic reflector.
Figure 3.13: The series and its parallel array configuration of the bowtie antennas and the field distribution calculated from the tangential H field on the gold surfaces.
................. 60 Figure 4.1: Unit cell (950 nm × 610 nm) of the bowtie antenna for infinite array of IR detector.
Figure 4.2: Optical area and detector area for a bulk InGaAsSb detector and an antenna loaded IR detector.
Figure 4.3: 45°-titled array configuration of bowtie antennas illuminated with a vertical and 45°-titled polarizations and the resulting current distributions (calculated from the tangential H field on the gold surface).
Figure 5.1: CP cross dipole antenna.
Figure 5.2: Polarization map of CP cross dipole antenna.
Figure 5.3: Illustration of polarization status at (a) the y-z plane and (b) the x-z plane (red-colored and blue-colored shapes indicate LHCP and RHCP respectively).
............. 83 Figure 5.4: A comparison between radiation pattern (gain) for the cross dipole antenna and a half-wave dipole antenna at (a) x-y plane as a function of phi (ϕ) and (b) x-z plane as a function of theta (θ).
Figure 5.5: (a) The CP cross dipole antenna using a balun structure in simulation and (b) the fabricated antenna.
viii Figure 5.6: The CP cross dipole antenna structure using the balun structure in simulation.
Figure 5.7: S11 of the CP cross dipole antenna using the balun structure in simulation and fabricated antenna.
Figure 5.8: Axial ratio of the CP cross dipole antenna using the balun structure in simulation and fabricated antenna.
Figure 5.9: Radiation pattern (normalized gain) of the antenna of in measurement and simulation of (a) x-y plane as a function of phi(ϕ) and (b) x-z plane as a function of theta (θ) at 2.
Figure 5.10: Tapered-bowtie antenna geometry for vertical polarization.
Figure 5.11: Input impedance (Rin + jXin) of the tapered-bowtie antenna loaded with vacuum and the intrinsic input impedance (Rbowtie + jXbowtie) of the antenna (vacuum is de-embedded).
Figure 5.12: CP cross tapered bowtie antenna structure and its dimensions.
Figure 5.13: The magnitude ratio and the normalized phase difference between radiated electric field in ϕ and θ direction in the antenna's boresight.
Figure 5.14: Input impedance (Rin + jXin) of the cross bowtie antenna loaded with vacuum and the intrinsic input impedance (Rbowtie + jXbowtie) of the antenna (vacuum is de-embedded).
Figure 5.15: CP cross tapered bowtie antenna structure connected with open-ended transmission lines and its dimensions.
Figure 5.16: The magnitude ratio and the normalized phase difference between radiated electric field in ϕ and θ direction in the antenna's boresight.
Figure 5.17: The field enhancement at the gap of the cross tapered-bowtie antenna.
1.1 Background The crowded wireless communication bands in the gigahertz (GHz) frequency range and the ever-increasing demand for more bandwidth has motivated the exploitation of the unexplored spectrum of electromagnetic waves such as the terahertz (THz) band.
The higher bandwidth of the THz band has a potential to achieve an extremely high data rate, such as 1 terabit-per-second, for future wireless devices . The THz band corresponds to the segment of the electromagnetic spectrum from 0.3 THz to 3 THz (corresponding to wavelengths in the range of 0.1 mm ~ 1 mm) in between the millimeter and far-infra (IR) waves . Due to the lack of THz sources and detectors, the THz band has not been thoroughly explored for communications . Until now, low bandwidth upand down-converters as well as low gain amplifiers in the lower part of the THz band have limited the output power level and bandwidth of THz communication systems. THz sources are also hard to find. Current technology relies on mixing optical sources such as lasers to generate low to moderate power levels. Such sources suffer from large power consumption and are very bulky. Current receivers at THz frequencies rely on direct detection, using Schottky diodes, bolometers, thermopiles, pyroelectrics, etc, which is not band selective and has a low dynamic range and sensitivity . As mentioned earlier, THz radiation is absorbed by most materials, including the molecules in the atmosphere such as water vapor. For such systems, line of sight propagation is needed and even for such conditions, the range is rather limited due to the inherently high path loss. Since path-loss is relatively high and receivers are not sensitive, much effort has been placed on maximizing the available incident power to the detector. This is where nanoantennas can play a significant role.