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- Title
- INFRARED ANTENNA-COUPLED PHASED-ARRAY.
- Creator
-
Middlebrook, Christopher, Boreman, Glenn, University of Central Florida
- Abstract / Description
-
Phased-array antennas are commonplace in the radiofrequency portion of the electromagnetic spectrum. Exploitation of phasing effects between multiple antennas facilitates a wide range of applications, including synthetic-aperture radar, beam forming, and beam scanning. For the first time, the phased addition of multiple dipole antennas is demonstrated in the infrared, at a wavelength of 10.6 micrometers. Coplanar strip lines are used to interconnect the antennas, preserving the phase of the...
Show morePhased-array antennas are commonplace in the radiofrequency portion of the electromagnetic spectrum. Exploitation of phasing effects between multiple antennas facilitates a wide range of applications, including synthetic-aperture radar, beam forming, and beam scanning. For the first time, the phased addition of multiple dipole antennas is demonstrated in the infrared, at a wavelength of 10.6 micrometers. Coplanar strip lines are used to interconnect the antennas, preserving the phase of the individual contributions. Several different proof-of-concept experiments are performed, using planar antennas fabricated with direct-write electron-beam lithography. Infrared-frequency currents from two dipole antennas are summed together at a common feedpoint and dissipated in a bolometric load. Angular pattern measurements show that the direction of maximum gain depends on the phase difference between the antennas. As more antennas are added together in phase, beam narrowing is observed in the angular response. Another experiment uses a two-dipole array to directly measure the magnitude of the mutual coherence function, at the plane of the antennas, of a spatially incoherent narrowband source. Measurements are also made of the broadside antenna response comparing air-side and substrate-side situations for a dipole antenna fabricated on a hemispherical immersion lens. In all cases, the measured behavior is confirmed by electromagnetic analysis.
Show less - Date Issued
- 2007
- Identifier
- CFE0001709, ucf:47327
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001709
- Title
- DEMONSTRATING REFLECTARRAY BEHAVIOR AT INFRARED.
- Creator
-
Ginn, James, Lail, Brian, University of Central Florida
- Abstract / Description
-
Reflectarrays are traditionally passive, planar microstrip antenna devices designed for reflected phase manipulation at each individual antenna element making up the array. By varying the phase response across the surface with the antenna elements, reflectarrays allows a planar surface to exhibit electromagnetically an arbitrary geometry, such as a spherical surface. Initially proposed as a low-cost replacement for bulky parabolic reflectors, reflectarrays have been successfully developed and...
Show moreReflectarrays are traditionally passive, planar microstrip antenna devices designed for reflected phase manipulation at each individual antenna element making up the array. By varying the phase response across the surface with the antenna elements, reflectarrays allows a planar surface to exhibit electromagnetically an arbitrary geometry, such as a spherical surface. Initially proposed as a low-cost replacement for bulky parabolic reflectors, reflectarrays have been successfully developed and utilized at both RF and millimeter-wave frequencies. From the standpoint of an optical systems designer, adapting low-frequency reflectarray technology to develop a sub-millimeter and infrared reflectarray (SMIR) would provide a highly desirable alternative to similarly behaved polished or diffractive optical devices. Compared to traditional optical reflectors, SMIRs should be cheaper to fabricate, have a smaller physical footprint, allow for utility stacking, and encourage direct integration of aberration correction. To demonstrate the feasibility of utilizing reflectarray technology at infrared (IR), a simple SMIR proof of concept has been successfully designed, fabricated, and tested. The SMIR is comprised of three independent arrays or "stripes" of a single size element on a coated optical flat. Actual reflectarray elements consist of variable size patches that exhibit higher operating bandwidths than reflectarrays utilizing other types of elements and are easier to fabricate at small dimensions. For testing, each stripe element has been chosen to exhibit a unique phase shift for measurement using an IR interferometer. Preliminary investigation of future reflectarray development is also discussed. Emphasis is placed on improving operating bandwidth, development of a planar focusing element, and aberration correction. With further development, SMIR technology should present a powerful tool for low cost, flexible optical system design.
Show less - Date Issued
- 2006
- Identifier
- CFE0001037, ucf:46814
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001037
- Title
- Microstrip Patch Electrically Steerable Parasitic Array Radiators.
- Creator
-
Luther, Justin, Gong, Xun, Wahid, Parveen, Jones, W, Wu, Xinzhang, Flitsiyan, Elena, University of Central Florida
- Abstract / Description
-
This dissertation explores the expansion of the Electrically Steerable Parasitic Array Radiator (ESPAR) technology to arrays using microstrip patch elements. Scanning arrays of two and three closely-coupled rectangular patch elements are presented, which incorporate no phase shifters. These arrays achieve directive radiation patterns and scanning of up to 26(&)deg; with maintained impedance match. The scanning is effected by tunable reactive loads which are used to control the mutual coupling...
Show moreThis dissertation explores the expansion of the Electrically Steerable Parasitic Array Radiator (ESPAR) technology to arrays using microstrip patch elements. Scanning arrays of two and three closely-coupled rectangular patch elements are presented, which incorporate no phase shifters. These arrays achieve directive radiation patterns and scanning of up to 26(&)deg; with maintained impedance match. The scanning is effected by tunable reactive loads which are used to control the mutual coupling between the elements, as well as additional loads which compensate to maintain the appropriate resonant frequency. The design incorporates theoretical analysis of the system of coupled antennas with full-wave simulation. A prototype of the three-element array at 1 GHz is fabricated and measured to exhibit a maximum gain of 7.4 dBi with an efficiency of 79.1%. Further, the microstrip ESPAR is thoroughly compared to uniformly-illuminated arrays of similar size. To satisfy the need for higher directivity antennas with inexpensive electronic scanning, the microstrip ESPAR is then integrated as a subarray. The three-element subcell fabrication is simplified to a single layer with an inverted-Y groove in the ground plane, allowing for DC biasing without the need for the radial biasing stubs or tuning stubs found in the two-layer design. The 1 GHz ESPAR array employs a corporate feed network consisting of a Wilkinson power divider with switchable delay line phase shifts, ring hybrid couplers, and achieves a gain of 12.1 dBi at boresight with (&)#177;20(&)deg; scanning and low side lobes. This array successfully illustrates the cost savings associated with ESPAR subarray scanning and the associated reduction in required number of phase shifters in the RF front end.
Show less - Date Issued
- 2013
- Identifier
- CFE0005107, ucf:50754
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005107
- Title
- Fundamental Properties of Metallic Nanolasers.
- Creator
-
Hayenga, William, Khajavikhan, Mercedeh, Christodoulides, Demetrios, Likamwa, Patrick, Abdolvand, Reza, University of Central Florida
- Abstract / Description
-
The last two decades have witnessed tremendous advancements in the area of nanophotonics and plasmonics, which has helped propel the development of integrated photonic sources. Of central importance to such circuits is compact, scalable, low threshold, and efficient coherent sources that can be driven at high modulation frequencies. In this regard, metallic nanolasers offer a unique platform. Their introduction has enabled confinement of light at a subwavelength scale and the ultra-small size...
Show moreThe last two decades have witnessed tremendous advancements in the area of nanophotonics and plasmonics, which has helped propel the development of integrated photonic sources. Of central importance to such circuits is compact, scalable, low threshold, and efficient coherent sources that can be driven at high modulation frequencies. In this regard, metallic nanolasers offer a unique platform. Their introduction has enabled confinement of light at a subwavelength scale and the ultra-small size of the modes afforded by these structures allows for cavity enhancing effects that can help facilitate thresholdless lasing and large direct modulation bandwidths. In this report, I present my work on the study of the fundamental properties of metallic nanolasers. I start with a rate equation model to predict threshold behavior and the modulation response of metallic nanolasers. Next, I explain the second-order coherence measurement setup that was built, based on a modified Hanbury-Brown and Twiss experiment, to assess the intensity autocorrelation of various optically pumped metallic nanolasers. These studies concluded that metallic coaxial and disk-shaped nanolasers are capable of generating truly coherent radiation. Subsequently, design considerations are taken into account for electrically pumped coaxial nanolasers. This has led to the demonstration of electrically injected coaxial and disk-shaped nanolasers at cryogenic temperatures. Lastly, the appearance of collective behaviors in metallic nanolasers lattices is explored. Individually supporting modes that are highly vectorial by nature, when such cavities are fabricated in close proximity to one another, coupling through their overlapping fields results in the formation of a set of supermodes. The tendency of the system to minimize the overall loss leads to each element of the lattice having a geometric dependent field distribution and helps promotes single-mode lasing. We show both through simulations and experimentally that this effect can lead to the direct generation of vector vortices.
Show less - Date Issued
- 2018
- Identifier
- CFE0007752, ucf:52391
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007752
- Title
- Enhancement of Antenna Array Performance Using Reconfigurable Slot-Ring Antennas and Integrated Filter/Antennas.
- Creator
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Li, Tianjiao, Gong, Xun, Wahid, Parveen, Yuan, Jiann-Shiun, Abdolvand, Reza, Kuebler, Stephen, University of Central Florida
- Abstract / Description
-
As modern communication system technology develops, the demand for devices with smaller size, higher efficiency, and more functionality has increased dramatically. In addition, highly integrated RF-front-end modules with a reduced footprint and less transition loss between cascaded devices are desirable in most advanced wireless communication systems. Antenna arrays are widely used in wireless communication systems due to their high directivity and beam steering capability. Moreover, antenna...
Show moreAs modern communication system technology develops, the demand for devices with smaller size, higher efficiency, and more functionality has increased dramatically. In addition, highly integrated RF-front-end modules with a reduced footprint and less transition loss between cascaded devices are desirable in most advanced wireless communication systems. Antenna arrays are widely used in wireless communication systems due to their high directivity and beam steering capability. Moreover, antenna arrays are preferred in mobile communication systems for diversity reception to reduce signal fading effects. In order to meet the various requirements of rapidly developing wireless communication systems, low cost, compact, multifunctional integrated antenna arrays are in high demand.Reconfigurable antennas that can flexibly adapt to different applications by dynamically changing their frequency and radiation properties have attracted a lot of attention. Frequency, radiation pattern, polarization, or a combination of two or more of these parameters in the reconfiguration of antennas was studied and presented in recent years. A single reconfigurable antenna is able to replace multiple traditional antennas and accomplish different tasks. Thus, the complexity of wireless communication systems can be greatly reduced with a smaller device size. On the other hand, the integration of antennas with other devices in wireless communication systems that can improve the efficiency and shrink the device size is a growing trend in antenna technology. Compact and highly efficient integrated filters and antennas were studied previously; the studies show that by seamlessly co-designing filters with patch antennas, the fractional bandwidth (FBW) of the antennas can be enhanced as compared to stand-alone antennas.However, the advantages of both the reconfigurable antenna and integrated filter/antenna technology have not been fully applied to antenna array applications. Therefore, this dissertation explores how to maximize the antenna array performance using reconfigurable antennas and integrated filter/antennas. A continuously frequency reconfigurable slot-ring antenna/array with switches and varactors is presented first. By changing the state of the loaded switches, the reconfigurable slot-ring antenna/array is able to operate as an L-band slot-ring antenna or a 2(&)#215;2 S-band slot-ring antenna array. In each frequency band, the operation frequency of the antenna/array can be continuously tuned with the loaded varactors. To further enhance the functionality of the reconfigurable slot-ring antenna array, a dual-polarized fractal-shaped reconfigurable slot-ring antenna/array is developed with a reduced number of switches and an increased FBW. Additionally, ground plane solutions are explored to achieve single-sided radiation. The benefits of filter/antenna integration are also investigated in both linearly polarized patch phased arrays and circularly polarized patch antenna arrays. Finally, a preliminary study of a tunable integrated evanescent mode filter/antenna is conducted to validate the concept of combining reconfigurable antennas and integrated filter/antennas.
Show less - Date Issued
- 2017
- Identifier
- CFE0006950, ucf:51661
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006950
- Title
- Fabrication of Metallic Antenna Arrays using Nanoimprint Lithography.
- Creator
-
Lin, Yu-wei, Kik, Pieter, Schoenfeld, Winston, Fathpour, Sasan, University of Central Florida
- Abstract / Description
-
This Thesis describes the development of a cost-effective process for patterning nanoscale metal antenna arrays. Soft ultraviolet (UV) Nanoimprint Lithography (NIL) into bilayer resist was chosen since it enables repeatable large-scale replication of nanoscale patterns with good lift-off properties using a simple low-cost process. Nanofabrication often involves the use of Electron Beam Lithography (EBL) which enables the definition of nanoscale patterns on small sample regions, typically (
Show moreThis Thesis describes the development of a cost-effective process for patterning nanoscale metal antenna arrays. Soft ultraviolet (UV) Nanoimprint Lithography (NIL) into bilayer resist was chosen since it enables repeatable large-scale replication of nanoscale patterns with good lift-off properties using a simple low-cost process. Nanofabrication often involves the use of Electron Beam Lithography (EBL) which enables the definition of nanoscale patterns on small sample regions, typically (<) 1 mm2. However its sequential nature makes the large scale production of nanostructured substrates using EBL cost-prohibitive. NIL is a pattern replication method that can reproduce nanoscale patterns in a parallel fashion, allowing the low-cost and rapid production of a large number of nano-patterned samples based on a single nanostructured master mold.Standard NIL replicates patterns by pressing a nanostructured hard mold into a soft resist layer on a substrate resulting in exposed substrate regions, followed by an optional Reactive Ion Etching (RIE) step and the subsequent deposition of e.g. metal onto the exposed substrate area. However, non-vertical sidewalls of the features in the resist layer resulting from an imperfect hard mold, from reflow of the resist layer, or from isotropic etching in the RIE step may cause imperfect lift-off. To overcome this problem, a bilayer resist method can be used. Using stacked resist layers with different etch rates, undercut structures can be obtained after the RIE step, allowing for easy lift-off even when using a mold with non-vertical sidewalls. Experiments were carried out using a nanostructured negative SiO2 master mold. Various material combinations and processing methods were explored. The negative master mold was transferred to a positive soft mold, leaving the original master mold unaltered. The soft mold consisted of a 5 ?m thick top Poly(methyl methacrylate) (PMMA), or Polyvinyl alcohol (PVA) layer, a 1.5 mm thick Polydimethylsiloxane (PDMS) buffer layer, and a glass supporting substrate. The soft mold was pressed into a bilayer of 300 nm PMMA and 350 nm of silicon based UV-curable resist that was spin-coated onto a glass slide, and cured using UV radiation. The imprinted patterns were etched using RIE, exposing the substrate, followed by metal deposition and lift-off. The experiments show that the use of soft molds enables successful pattern transfer even in the presence of small dust particles between the mold and the resist layer. Feature sizes down to 280 nm were replicated successfully.
Show less - Date Issued
- 2013
- Identifier
- CFE0005026, ucf:49990
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005026
- Title
- GRAPH THEORETIC MODELING: CASE STUDIES IN REDUNDANT ARRAYS OF INDEPENDENT DISKS AND NETWORK DEFENSE.
- Creator
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Nanda, Sanjeeb, Deo, Narsingh, University of Central Florida
- Abstract / Description
-
Graph theoretic modeling has served as an invaluable tool for solving a variety of problems since its introduction in Euler's paper on the Bridges of Königsberg in 1736 . Two amongst them of contemporary interest are the modeling of Redundant Arrays of Inexpensive Disks (RAID), and the identification of network attacks. While the former is vital to the protection and uninterrupted availability of data, the latter is crucial to the integrity of systems comprising networks. Both are of...
Show moreGraph theoretic modeling has served as an invaluable tool for solving a variety of problems since its introduction in Euler's paper on the Bridges of Königsberg in 1736 . Two amongst them of contemporary interest are the modeling of Redundant Arrays of Inexpensive Disks (RAID), and the identification of network attacks. While the former is vital to the protection and uninterrupted availability of data, the latter is crucial to the integrity of systems comprising networks. Both are of practical importance due to the continuing growth of data and its demand at increasing numbers of geographically distributed locations through the use of networks such as the Internet. The popularity of RAID has soared because of the enhanced I/O bandwidths and large capacities they offer at low cost. However, the demand for bigger capacities has led to the use of larger arrays with increased probability of random disk failures. This has motivated the need for RAID systems to tolerate two or more disk failures, without sacrificing performance or storage space. To this end, we shall first perform a comparative study of the existing techniques that achieve this objective. Next, we shall devise novel graph-theoretic algorithms for placing data and parity in arrays of n disks (n ≥ 3) that can recover from two random disk failures, for n = p – 1, n = p and n = 2p – 2, where p is a prime number. Each shall be shown to utilize an optimal ratio of space for storing parity. We shall also show how to extend the algorithms to arrays with an arbitrary number of disks, albeit with non-optimal values for the aforementioned ratio. The growth of the Internet has led to the increased proliferation of malignant applications seeking to breach the security of networked systems. Hence, considerable effort has been focused on detecting and predicting the attacks they perpetrate. However, the enormity of the Internet poses a challenge to representing and analyzing them by using scalable models. Furthermore, forecasting the systems that they are likely to exploit in the future is difficult due to the unavailability of complete information on network vulnerabilities. We shall present a technique that identifies attacks on large networks using a scalable model, while filtering for false positives and negatives. Furthermore, it also forecasts the propagation of security failures proliferated by attacks over time and their likely targets in the future.
Show less - Date Issued
- 2007
- Identifier
- CFE0001919, ucf:47475
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001919
- Title
- ANALYSIS AND MODELING OF THE EDS MAGLEV SYSTEM BASED ON THE HALBACH PERMANENT MAGNET ARRAY.
- Creator
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Han, Qinghua, Phillips, Ronald, University of Central Florida
- Abstract / Description
-
Electro-dynamic suspension (EDS) Magnetic levitation (Maglev) with its advantage in maintenance, safety, efficiency, speed, and noise is regarded as a leading candidate for the next generation transportation / space launch assist system. The Halbach array due to its unique magnetic field feature has been widely used in various applications. The EDS system using Halbach arrays leads to the potential EDS system without super-conductor (SC) technology. In this thesis, the Halbach array magnetic...
Show moreElectro-dynamic suspension (EDS) Magnetic levitation (Maglev) with its advantage in maintenance, safety, efficiency, speed, and noise is regarded as a leading candidate for the next generation transportation / space launch assist system. The Halbach array due to its unique magnetic field feature has been widely used in various applications. The EDS system using Halbach arrays leads to the potential EDS system without super-conductor (SC) technology. In this thesis, the Halbach array magnetic field and the dynamics of a novel Halbach array EDS Maglev system were considered. The practical Halbach array magnetic field was analyzed using both a Fourier series approach and the finite element method (FEM). In addition, the optimal Halbach array geometry was derived and analyzed. A novel active magnetic array was introduced and used in the Halbach array EDS Maglev configuration. Further more, since the system is self-regulated in lateral, roll, pitch, and yaw directions, the control was simplified and can be implemented electronically. The dynamic stability analysis and simulation results showed that the system is marginally stable and a control mechanism is needed for stability and ride comfort control. The six degree of freedom (DOF) dynamics, and the vehicle's mass center offset effects on those dynamics were investigated with multiple passive and active magnetic forces. The results indicated that the vehicle's mass center offset has a strong effect on the dynamics of the Maglev system due to the uniqueness of the magnetic force and also that the mass center offset can cause Maglev oscillations at the take off stage. In order to guarantee the dynamic stability and ride comfort of the Maglev system, an optimized active damping and a linear quadratic regulator (LQR) control were developed. Finally, the simulation confirmed the effectiveness of the proposed multi-input and multi-output (MIMO) control designs.
Show less - Date Issued
- 2004
- Identifier
- CFE0000072, ucf:46145
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000072
- Title
- INFRARED PHASED-ARRAY ANTENNA-COUPLED TUNNEL DIODES.
- Creator
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Slovick, Brian, Boreman, Glenn, University of Central Florida
- Abstract / Description
-
Infrared (IR) dipole antenna-coupled metal-oxide-metal (MOM) tunnel diodes provide a unique detection mechanism that allows for determination of the polarization and wavelength of an optical field. By integrating the MOM diode into a phased-array antenna, the angle of arrival and degree of coherence of received IR radiation can be determined. The angular response characteristics of IR dipole antennas are determined by boundary conditions imposed by the surrounding dielectric or conductive...
Show moreInfrared (IR) dipole antenna-coupled metal-oxide-metal (MOM) tunnel diodes provide a unique detection mechanism that allows for determination of the polarization and wavelength of an optical field. By integrating the MOM diode into a phased-array antenna, the angle of arrival and degree of coherence of received IR radiation can be determined. The angular response characteristics of IR dipole antennas are determined by boundary conditions imposed by the surrounding dielectric or conductive environment on the radiated fields. To explore the influence of the substrate configuration, single dipole antennas are fabricated on both planar and hemispherical lens substrates. Measurements demonstrate that the angular response can be tailored by the thickness of the electrical isolation stand-off layer on which the detector is fabricated and/or the inclusion of a ground plane. Directional detection of IR radiation is achieved with a pair of dipole antennas coupled to a MOM diode through a coplanar strip transmission line. The direction of maximum angular response is altered by varying the position of the diode along the transmission line connecting the antenna elements. By fabricating the devices on a quarter wave layer above a ground plane, narrow beam widths of 35° full width at half maximum and reception angles of ± 50° are achievable with minimal side-lobe contributions. Phased-array antennas can also be used to assess the degree of coherence of a partially coherent field. For a two-element array, the degree of coherence is a measure of the correlation of electric fields received by the antennas as a function of the element separation.
Show less - Date Issued
- 2011
- Identifier
- CFE0003589, ucf:48926
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003589
- Title
- Investigation of Breakdown Power During Electrical Breakdown of Aligned Array of Carbon Nanotubes.
- Creator
-
Bhanu, Udai, Khondaker, Saiful, Leuenberger, Michael, Zhai, Lei, University of Central Florida
- Abstract / Description
-
Massively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore,...
Show moreMassively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore, it is essential to selectively remove metallic nanotubes to obtain better transistor properties. It was recently found that although such a selective removal can be effective for a low density array, it does not work in a high density array and lead to a correlated breakdown of the entire array giving rise to a nanofissure pattern.In order to obtain a deeper understanding of such a correlated SWNT breakdown, we studied the breakdown power in the successive electrical breakdown of both low ( (<) 2 /um) and high density ((>)10 /um) SWNT arrays. We show that the breakdown voltage in successive electrical breakdown increases for low density array while it decreases for high density arrays. The estimated power required for the breakdown remains constant for low density arrays while it decreases for high density arrays in successive electrical breakdowns. We also show that, while a simple model of parallel resistor network can explain the breakdown of low density array, it cannot explain the behavior for the high density array implying that the correlation between the closely spaced parallel nanotubes plays a big role in the successive breakdowns of the high density SWNTs.
Show less - Date Issued
- 2012
- Identifier
- CFE0004518, ucf:49292
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004518
- Title
- Heat Transfer and Pressure Measurements from Jet Array Impingement onto a Large Radius Curved Surface.
- Creator
-
Harrington, John, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
This study investigates the heat transfer and pressure drop characteristics of jet array impingement in two distinct parts. In the first part, the performance of a uniform array of jets on both a flat and a large radius curved target surface are compared. This comparison was done at average jet Reynolds number ranging from 55,000 to 125,000. In the second part, the characteristics of a non-uniform array of jets, more typical of geometries used in actual gas turbine combustors, are...
Show moreThis study investigates the heat transfer and pressure drop characteristics of jet array impingement in two distinct parts. In the first part, the performance of a uniform array of jets on both a flat and a large radius curved target surface are compared. This comparison was done at average jet Reynolds number ranging from 55,000 to 125,000. In the second part, the characteristics of a non-uniform array of jets, more typical of geometries used in actual gas turbine combustors, are investigated, including the effects of the removal of downstream rows and the placement of rib features onto the target surface. The non-uniform configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behavior. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. A steady-state measurement technique utilizing temperature sensitive paint (TSP) was used on the target surface to obtain heat transfer coefficients, while pressure taps placed on the sidewall and jet plate were used to evaluate the pressure and flow distribution in the impingement channel. Alongside the experimental work, CFD simulations were performed utilizing the v^2-f eddy viscosity turbulence model. The results from the uniform array impingement onto a curved surface comparison show that the large radius curvature of the current geometry has little to no effect on the flow distribution and heat transfer of the array.The non-uniform array results illustrate the applicability of tuning a jet impingement array using varying jet diameters and spacing. However, there are some difficulties in obtaining streamwise pitch resolved heat transfer predictions for non-uniform arrays as current open literature correlations for uniform arrays are shown to be not applicable. The computational results from this study show that simulations can be used to obtain initial predictions, with streamwise pitch averaged Nu values found to be within 20% of experimental results. The use of ribs downstream in place of several jet rows was shown to yield similar heat transfer results at lower pressure drop levels.
Show less - Date Issued
- 2016
- Identifier
- CFE0006317, ucf:51547
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006317
- Title
- Customizable Antenna Array Using Reconfigurable Antenna Elements.
- Creator
-
Shirazi, Mahmoud, Gong, Xun, Wahid, Parveen, Jones, W Linwood, Abdolvand, Reza, Kuebler, Stephen, University of Central Florida
- Abstract / Description
-
A shared-aperture reconfigurable slot-ring antenna array switching between different frequency bands and polarizations is presented for phased array applications. PIN diode switches are incorporated into the slots of the antenna to change the state of the reconfigurable slot-ring antenna array. Each frequency band has its own feeding lines which allows for the use of high-performance narrow-band transmit/receive (T/R) modules instead of ultra wideband (UWB) T/R modules. Furthermore, the...
Show moreA shared-aperture reconfigurable slot-ring antenna array switching between different frequency bands and polarizations is presented for phased array applications. PIN diode switches are incorporated into the slots of the antenna to change the state of the reconfigurable slot-ring antenna array. Each frequency band has its own feeding lines which allows for the use of high-performance narrow-band transmit/receive (T/R) modules instead of ultra wideband (UWB) T/R modules. Furthermore, the spacing between the elements in each frequency band is less than half free-space wavelength (?0) over the frequency band of operation which enables grating-lobe-free beam scanning. This is the first shared-aperture reconfigurable dual-polarized antenna with separate feeding for each band which is scalable to a larger array with element spacing of less than 0.5?0 in all frequency bands of operation.First, a switchable-band reconfigurable antenna array switching between L and C bands is presented. This antenna operates at 1.76/5.71 GHz with a fractional bandwidth (FBW) of 8.6%/11.5%, realized gain of 0.1/4.2 dBi and radiation efficiency of 66.6%/80.7% in the L-/C- band operating states, respectively. Second, a wideband version of the reconfigurable antenna element using fractal geometries is presented. This dual-polarized antenna element is switching between S and C bands with wide bandwidth in each operating state. In the S-/C-band operating state, this antenna shows 69.1%/58.3% FBW with a maximum realized gain of 2.4/3.1 dBi. Third, the wideband antenna element is extended to an antenna array. The reconfigurable dual-polarized antenna array with vertical coaxial feeding switches between S- and C-band states with full-band coverage. A 2(&)#215;2 S-band antenna array can be reconfigured to a 4(&)#215;4 C-band antenna array by activating/deactivating PIN diode switches. This antenna array shows 64.3%/66.7% FBW with 8.4/14.3 dBi maximum realized gain in the S-/C-band operating states, respectively. Finally, a reconfigurable antenna element covering three adjacent frequency bands is presented. The FBW of this tri-band antenna element is 75%/63%/26% in the S/C/X band state.
Show less - Date Issued
- 2018
- Identifier
- CFE0007373, ucf:52092
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007373
- Title
- SOLAR-BASED SINGLE-STAGE HIGH-EFFICIENCY GRID-CONNECTED INVERTER.
- Creator
-
Tian, Feng, BATARSEH, ISSA, University of Central Florida
- Abstract / Description
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Renewable energy source plays an important role in the energy cogeneration and distribution. Traditional solar-based inverter system is two stages in cascaded, which has a simpler controller but low efficiency. A new solar-based single-stage grid-connected inverter system can achieve higher efficiency by reducing the power semiconductor switching loss and output stable and synchronized sinusoid current into the utility grid. Controlled by the digital signal processor, the inverter can also...
Show moreRenewable energy source plays an important role in the energy cogeneration and distribution. Traditional solar-based inverter system is two stages in cascaded, which has a simpler controller but low efficiency. A new solar-based single-stage grid-connected inverter system can achieve higher efficiency by reducing the power semiconductor switching loss and output stable and synchronized sinusoid current into the utility grid. Controlled by the digital signal processor, the inverter can also draw maximum power from the solar array, thereby maximizing the utilization of the solar array. In Chapter 1, a comparison between the traditional two-stage inverter and the single-stage inverter is made. To increase the ability of power processing and enhance the efficiency further, a full-bridge topology is chosen, which applies the phase-shift technique to achieve zero-voltage transition. In Chapter 2, average-mode and switch-mode Pspice simulations are applied. All the features of the inverter system are verified, such as stability, zero voltage transition and feed-forward compensation, etc. All these simulation results provide useful design tips for prototyping. In Chapter 3, a phase-shift controller is designed based on UCC3895. Also, a detailed design procedure is given, including key components selection, transformer and inductor design and driver circuits design. In Chapter 4, experimental results of a prototype DC/DC converter are presented and analyzed. By optimization of the circuit, the problems of the prototype are solved and the prototype is working stably. The thesis' conclusion is given in Chapter 5.
Show less - Date Issued
- 2005
- Identifier
- CFE0000468, ucf:46414
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000468
- Title
- DISCRETE WAVE PROPAGATION IN QUADRATICALLY NONLINEAR MEDIA.
- Creator
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Iwanow, Robert, Stegeman, George, University of Central Florida
- Abstract / Description
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Discrete models are used in describing various microscopic phenomena in many branches of science, ranging from biology through chemistry to physics. Arrays of evanescently coupled, equally spaced, identical waveguides are prime examples of optical structures in which discrete dynamics can be easily observed and investigated. As a result of discretization, these structures exhibit unique diffraction properties with no analogy in continuous systems. Recently nonlinear discrete optics has...
Show moreDiscrete models are used in describing various microscopic phenomena in many branches of science, ranging from biology through chemistry to physics. Arrays of evanescently coupled, equally spaced, identical waveguides are prime examples of optical structures in which discrete dynamics can be easily observed and investigated. As a result of discretization, these structures exhibit unique diffraction properties with no analogy in continuous systems. Recently nonlinear discrete optics has attracted a growing interest, triggered by the observation of discrete solitons in AlGaAs waveguide arrays reported by Eisenberg et al. in 1998. So far, the following experiments involved systems with third order nonlinearities. In this work, an experimental investigation of discrete nonlinear wave propagation in a second order nonlinear medium is presented. This system deserves particular attention because the nonlinear process involves two or three components at different frequencies mutually locked by a quadratic nonlinearity, and new degrees of freedom enter the dynamical process. In the first part of dissertation, observation of the discrete Talbot effect is reported. In contrast to continuous systems, where Talbot self-imaging effect occurs irrespective of the pattern period, in discrete configurations this process is only possible for a specific set of periodicities. The major part of the dissertation is devoted to the investigation of soliton formation in lithium niobate waveguide arrays with a tunable cascaded quadratic nonlinearity. Soliton species with different topology (unstaggered – all channels in-phase, and staggered – neighboring channels with a pi relative phase difference) are identified in the same array. The stability of the discrete solitons and plane waves (modulational instability) are experimentally investigated. In the last part of the dissertation, a phase-insensitive, ultrafast, all-optical spatial switching and frequency conversion device based on quadratic waveguide array is demonstrated. Spatial routing and wavelength conversion of milliwatt signals is achieved without pulse distortions.
Show less - Date Issued
- 2005
- Identifier
- CFE0000420, ucf:46382
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000420
- Title
- USER-DEFINED PATTERNING OF NEURAL PROGENITOR CELLS ON 3D MICROPILLAR ARRAYS USING ROUND CROSS-SECTIONAL GEOMETRY, SPECIFIC DIMENSIONS AND THIOL-BASED CHEMICAL ADHESION.
- Creator
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Wesser, Andrea, Cho, Hyoung Jin, University of Central Florida
- Abstract / Description
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The ability to control stem cell functions, particularly neuronal progenitors, has long since been believed to be the key to successful treatment of neurodegenerative disorders such as Alzheimer's, Parkinson's and accidents involving head trauma. The neurology field calls for many new solutions to address the controlled neural stem cell seeding and placement of cells for neural tissue regeneration. Self-assembled monolayers (SAM) from the alkanethiol group provide a straightforward...
Show moreThe ability to control stem cell functions, particularly neuronal progenitors, has long since been believed to be the key to successful treatment of neurodegenerative disorders such as Alzheimer's, Parkinson's and accidents involving head trauma. The neurology field calls for many new solutions to address the controlled neural stem cell seeding and placement of cells for neural tissue regeneration. Self-assembled monolayers (SAM) from the alkanethiol group provide a straightforward applicable, reliable treatment for cell adhesion. An ODT/gold treatment was used to adhere the cells to patterned areas, due mainly to a high confluence of cells attracted to it, as well as the viable environment it produced for the cells. Arrays of micropillars, made of SU-8 photoresist, then covered with a thin film of gold and treated with the ODT, created scaffolding allowing manipulation of neural stem cells. Based on multiple trials of observing varying cross-sectional geometric parameters, metal layer thicknesses and the ODT/Gold treatment, this study explores seeding density control, base and circumferential cell population dependence on those parameters.
Show less - Date Issued
- 2008
- Identifier
- CFE0002054, ucf:47563
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002054
- Title
- MODELING AND ANALYSIS OF THE EDS MAGLEV SYSTEM WITH THE HALBACH MAGNET ARRAY.
- Creator
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Ko, Wonsuk, Ham, Chan, University of Central Florida
- Abstract / Description
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The magnetic field analysis based on the wavelet transform is performed. The Halbach array magnetic field analysis has been studied using many methods such as magnetic scalar potential, magnetic vector potential, Fourier analysis and Finite Element Methods. But these analyses cannot identify a transient oscillation at the beginning stage of levitation. The wavelet transform is used for analyzing the transient oscillatory response of an EDS Maglev system. The proposed scheme explains the under...
Show moreThe magnetic field analysis based on the wavelet transform is performed. The Halbach array magnetic field analysis has been studied using many methods such as magnetic scalar potential, magnetic vector potential, Fourier analysis and Finite Element Methods. But these analyses cannot identify a transient oscillation at the beginning stage of levitation. The wavelet transform is used for analyzing the transient oscillatory response of an EDS Maglev system. The proposed scheme explains the under-damped dynamics that results from the cradle's dynamic response to the irregular distribution of the magnetic field. It suggests this EDS Maglev system that responds to a vertical repulsive force could be subject to such instability at the beginning stage of a low levitation height. The proposed method is useful in analyzing instabilities at the beginning stage of levitation height. A controller for the EDS maglev system with the Halbach array magnet is designed for the beginning stage of levitation and after reaching the defined levitation height. To design a controller for the EDS system, two different stages are suggested. Before the object reaches a stable position and after it has reached a stable position. A stable position can be referred to as a nominal height. The former is the stage I and the latter is the stage II. At the stage I, to achieve a nominal height the robust controller is investigated. At the stage II, both translational and rotational motions are considered for the control design. To maintain system stability, damping control as well as LQR control are performed. The proposed method is helpful to understand system dynamics and achieve system stability.
Show less - Date Issued
- 2007
- Identifier
- CFE0001697, ucf:47196
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001697
- Title
- OPTICAL WAVE PROPAGATION IN DISCRETE WAVEGUIDE ARRAYS.
- Creator
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Hudock, Jared, Christodoulides, Demetrios, University of Central Florida
- Abstract / Description
-
The propagation dynamics of light in optical waveguide arrays is characteristic of that encountered in discrete systems. As a result, it is possible to engineer the diffraction properties of such structures, which leads to the ability to control the flow of light in ways that are impossible in continuous media. In this work, a detailed theoretical investigation of both linear and nonlinear optical wave propagation in one- and two-dimensional waveguide lattices is presented. The ability to...
Show moreThe propagation dynamics of light in optical waveguide arrays is characteristic of that encountered in discrete systems. As a result, it is possible to engineer the diffraction properties of such structures, which leads to the ability to control the flow of light in ways that are impossible in continuous media. In this work, a detailed theoretical investigation of both linear and nonlinear optical wave propagation in one- and two-dimensional waveguide lattices is presented. The ability to completely overcome the effects of discrete diffraction through the mutual trapping of two orthogonally polarized coherent beams interacting in Kerr nonlinear arrays of birefringent waveguides is discussed. The existence and stability of such highly localized vector discrete solitons is analyzed and compared to similar scenarios in a single birefringent waveguide. This mutual trapping is also shown to occur within the first few waveguides of a semi-infinite array leading to the existence of vector discrete surface waves. Interfaces between two detuned semi-infinite waveguide arrays or waveguide array heterojunctions and their possible applications are also considered. It is shown that the detuning between the two arrays shifts the dispersion relation of one array with respect to the other. Consequently, these systems provide spatial filtering functions that may prove useful in future all-optical networks. In addition by exploiting the unique diffraction properties of discrete arrays, diffraction compensation can be achieved in a way analogous to dispersion compensation in dispersion managed optical fiber systems. Finally, it is demonstrated that both the linear (diffraction) and nonlinear dynamics of two-dimensional waveguide arrays are significantly more complex and considerably more versatile than their one-dimensional counterparts. As is the case in one-dimensional arrays, the discrete diffraction properties of these two-dimensional lattices can be effectively altered depending on the propagation Bloch k-vector within the first Brillouin zone. In general, this diffraction behavior is anisotropic and as a result, allows the existence of a new class of discrete elliptic solitons in the nonlinear regime. Moreover, such arrays support two-dimensional vector soliton states, and their existence and stability are also thoroughly explored in this work.
Show less - Date Issued
- 2005
- Identifier
- CFE0000833, ucf:46687
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000833
- Title
- Thermally annealled plasmonic nanostructures.
- Creator
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Wang, Chaoming, Su, Ming, Coffey, Kevin, Chai, Xinqing, Schelling, Patrick, University of Central Florida
- Abstract / Description
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Localized surface plasmon resonance (LSPR) is induced in metal nanoparticles by resonance between incident photons and conduction electrons in nanoparticles. For noble metal nanoparticles, LSPR can lead to strong absorbance of ultraviolet-violet light. Although it is well known that LSPR depends on the size and shape of nanoparticles, the inter-particle spacing, the dielectric properties of metal and the surrounding medium, the temperature dependence of LSPR is not well understood. By...
Show moreLocalized surface plasmon resonance (LSPR) is induced in metal nanoparticles by resonance between incident photons and conduction electrons in nanoparticles. For noble metal nanoparticles, LSPR can lead to strong absorbance of ultraviolet-violet light. Although it is well known that LSPR depends on the size and shape of nanoparticles, the inter-particle spacing, the dielectric properties of metal and the surrounding medium, the temperature dependence of LSPR is not well understood. By thermally annealing gold nanoparticle arrays formed by nanosphere lithography, a shift of LSPR peak upon heating has been shown. The thermal characteristics of the plasmonic nanoparticles have been further used to detect chemicals such as explosive and mercury vapors, which allow direct visual observation of the presence of mercury vapor, as well as thermal desorption measurements.
Show less - Date Issued
- 2012
- Identifier
- CFE0004454, ucf:49322
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004454
- Title
- Frequency Selective Detection of Infrared Radiation in Uncooled Optical Nano-Antenna Array.
- Creator
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Modak, Sushrut, Chanda, Debashis, Schoenfeld, Winston, Fathpour, Sasan, University of Central Florida
- Abstract / Description
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Mid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 ?m and 8-12 ?m bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we...
Show moreMid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 ?m and 8-12 ?m bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we designed an optical nano-antenna array based detector with narrow frequency band of operation. The structure consists of a two-element antenna array comprised of a perforated metallic hole array coupled with an underneath disk array which trap incident radiation as dipole currents. The energy is dissipated as electron plasma loss on the hole-disk system inducing close to ~100% absorption of the incident radiation. This near perfect absorption originates from simultaneous zero crossing of real component of permittivity and permeability due to the geometrical arrangement of the two antenna elements which nullifies overall charge and current distributions, prohibiting existence of any propagating electromagnetic modes at resonance. Moreover, the continuous perforated film allows probing of the induced (")micro-current(") plasma loss on each nano hole-disk pair via a weak bias current. Such optical antenna design enables flexible scaling of detector response over the entire mid-infrared regime by change in the antenna dimensions. Furthermore, the development of simple nanoimprint lithography based large area optical antenna array fabrication technique facilitates formation of low cost frequency selective infrared detectors.
Show less - Date Issued
- 2014
- Identifier
- CFE0005845, ucf:50932
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005845
- Title
- COMPARISON OF SINGLE STAGE AND TWO STAGE STAGE GRID-TIE INVERTERS.
- Creator
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Mansfield, Keith, Batarseh, Issa, University of Central Florida
- Abstract / Description
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This thesis compares two methods of designing grid-tie inverters. The first design topology is a traditional two stage approach consisting of an isolated DC-DC converter on the input followed by a high switching frequency SPWM (Sinusoidal Pulse Width Modulation) stage to produce the required low frequency sine wave output. The novel second design approach employs a similar DC-DC input stage capable of being modulated to provide a rectified sine wave output voltage/current waveform. This stage...
Show moreThis thesis compares two methods of designing grid-tie inverters. The first design topology is a traditional two stage approach consisting of an isolated DC-DC converter on the input followed by a high switching frequency SPWM (Sinusoidal Pulse Width Modulation) stage to produce the required low frequency sine wave output. The novel second design approach employs a similar DC-DC input stage capable of being modulated to provide a rectified sine wave output voltage/current waveform. This stage is followed by a simple low frequency switched Unfolding Stage to recreate the required sine wave output. Both of the above designs have advantages and disadvantages depending on operating parameters. The following work will compare the Unfolding Output Stage and the SPWM Output Stage at various power levels and power densities. Input stage topologies are similarly examined in order to determine the best design approach for each output stage under consideration.
Show less - Date Issued
- 2007
- Identifier
- CFE0001783, ucf:47258
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001783
