Browse by Year:

Jason Kyle Anderson (Senior Thesis, April 2014, Advisor: David Allred )

Abstract

Traditional microfabrication processes are confined to a small set of materials due to limitations on etching and confined to low-aspect-ratio fabrication due to limits in both etching and stability of thicker film deposition processes. Carbon Nanotube Templated Microfabrication (CNT-M) technology has introduced a dramatically different approach to microfabrication that fabricates without significant etch processes. This is achieved by forming the desired structure in carbon nanotubes (CNT) and then filling or infiltrating that structure with the material of choice. This technology has been developed at BYU using materials like silicon and carbon. Microfabrication with metals is needed because of their higher density and improved electrical and mechanical properties compared to traditional microfabrication materials. A suitable metals process has not yet been found. We endeavored to develop atomic layer deposition (ALD) of W using atomic H as the agent for abstracting the nonmetal atoms such as C, O or F that act as ligands for the gaseous form of W used to bring the W into the deposition. We used tungsten hexafluoride (WF6) and molecular hydrogen as our reactants, flowing them in alternating cycles onto carbon nanotube samples in a vacuum chamber. We did not achieve significant W deposition in the initial process, so we incorporated a microwave generator to replace the H2 with hydrogen plasma. This somewhat improved deposition, but an even bigger improvement in deposition came when the samples were ozone treated before deposition. This process achieved a final product composed of 60% W as measured using and EDAX system in an SEM. This deposition was still too limited to allow for mechanical and electrical tests of the samples, which were too fragile for liftoff from the substrate.

Zachary Anderson (Senior Thesis, April 2014, Advisor: Traci Neilsen Kent Gee )

Abstract

Correlation analysis is useful in extracting spatiotemporal relationships between signals and can be used to examine features of jet noise for source properties. When applied to F-22 jet noise, maximum correlation coefficients show noticeable distinctions between near-field and downstream microphones; these distinctions become increasingly apparent in the spatial variation between short and long correlation lengths. Waveform width analysis complements the meaningfulness of our results. Finally, the calculation of phase speed clearly defines the relevant regions: a fine-scale upstream region, a large-scale downstream region, and a midway region that shares properties of fine-scale and large-scale noise. [Work supported by the Office of Naval Research.]

Rachael Bakaitis (Senior Thesis, August 2014, Advisor: Kent Gee Derek Thomas )

Abstract

This thesis is a direct continuation of work done by Kuhn et al. [J. Acoust. Soc. Am. 63, S1, S84 (1978)] and Bodon et al. [J. Acoust. Soc. Am. 133, 5, 3507 (2013)] concerning propagation of finite-amplitude, or nonlinear, waves from a baffled pipe. Band-limited Gaussian noise and 1 kHz, 1.5 kHz, and 2 kHz sinusoidal acoustic waves were driven with initial peak pressure amplitudes ranging from 98 dB to 163 dB through a 6.1 m long circular cylindrical PVC pipe with a 5.1 cm inner diameter and baffled end. The pipe end was open, allowing the driven sound to propagate from the pipe. The waveform was measured along its propagation path, including near the driver, inside the pipe, at the pipe’s face, and at radial distances outside the pipe as far as 1.3 m from the pipe opening. This thesis examines characteristics of the waveform and its changes along its propagating path through and outside the pipe. Characteristics discussed include shock wave formation inside the pipe, reflection near the pipe opening, amplitude at the pipe face, amplitude of its positive impulse and nonlinear asymmetry at distances outside the pipe, and the rate of amplitude decay of the propagated wave as it travels away from the pipe.

James Brady (Capstone, April 2014, Advisor: )

Abstract

Designed and tested a robust stabilization platform for the Naval Research Laboratory. Motivation for this project was to create a means to stabilize a data sensor package. Development led to a neck structure consisting of a four-bar linkage and gimbal mechanism. Testing of the system indicated that it had stabilization qualities through specific frequency ranges. It also demonstrated a majority of the qualities necessary to deem the project a success by the Naval Research Laboratory

Collin Brown (Senior Thesis, April 2014, Advisor: David Allred )

Abstract

Abstract Text: The fabrication of microelectromechanical systems (MEMS) is generally limited by the same processes and materials used in the semiconductor industry. We have been investigating the infiltration of patterned carbon nanotube (CNT) forests to find more materials and potentially easier methods to make MEMS. Our goal is to fill in the void between the nanotubes in the CNT forest with deposited metal, creating a solid metal-carbon hybrid in the same shape as the CNT forest. Previous students here at BYU investigated the infiltration of molybdenum and tungsten metal using molybdenum carbonyl and tungsten carbonyl, respectively, as precursors in chemical vapor deposition (CVD). The current topic of research is infiltration by atomic layer deposition (ALD) using tungsten hexafluoride and hydrogen (including atomic hydrogen via microwave plasma) as precursors. In the course of this research, we have seen the tungsten deposited as a crust over the top of the CNT forest, penetrating only microns into the forest.

Adam George (Senior Thesis, June 2014, Advisor: Joseph Moody )

Abstract

Non-invasive methods of measuring the composition of blood is of interest in the medical field. One such method is the spectroscopic study of how near-infrared light interacts with a human finger. Modeling theoretically the propagation of photon packets through a simulated multi-layer human finger provides useful information concerning the scattering and back scattering of light. This knowledge will increase the understanding of such medical devices as pulse oximeters and make strides in the possibility of measuring other compositions in blood.

Trevor Jex (Senior Thesis, April 2014, Advisor: Lawrence Rees )

Abstract

Neutron detection is an important component to Homeland Security. Portal monitors are put at points of entry into the country to detect illegal nuclear material entering the United States. In the past and currently, 3He-based detectors have and are being used in these portals. However, because of the current shortage of 3He, the BYU Nuclear Group is looking for alternative methods for neutron detection. In particular, I have been doing preliminary work on a two-photomultiplier tube hybrid neutron detector that utilizes lithium and cadmium components. This work focuses on how each component of the hybrid (lithium and cadmium) performs on its own. It then outlines what results are seen when both sides are simultaneously "watching" the same radiation source. Both the cadmium and lithium components work as expected when operating alone. When combined– i.e. both components are on and looking at the same radiation source–we see that the cadmium component is the dominating detection component in the hybrid detector. Relatively few events are seen from the lithium side. Further work should be done to confirm the results herein, to consider other setups that may yield more balanced results as well as to confirm the hope that a hybrid detector, such as the one here, can detect neutrons over a broader energy range than either component by itself. If this can be accomplished, the hybrid detector will become a more viable candidate for potential use in homeland security.

Enoch Lambert (Senior Thesis, April 2014, Advisor: Dallin Durfee )

Abstract

Extended-cavity diode lasers (ECDL's) are an important tool in atomic, molecular, and optical physics. Preventing ECDL's from mode-hopping can enable further advances in these fields. The research described in this paper seeks improvements in the frequency stability of a diode laser by using feedback techniques. The diode laser is locked to a frequency reference, in this case a simple optical cavity. Radio-frequency (RF) noise is measured at various points in the combined laser-cavity system and used to generate an additional feedback signal to help control the laser. The added feedback system improved the laser's stability range by a factor of three when the laser was scanned.

Joshua Marx (Senior Thesis, April 2014, Advisor: Steve Turley )

Abstract

I used extreme ultraviolet light to find the surface roughness of three Uranium Oxide thin films of approximate thicknesses 140 nm, 114 nm, and 40-45 nm. The wafers were first scanned to measure the non-specular reflectance of each sample. I combined the scans with the same angle of incidence, and then normalized the combined data to calculate the reflectance per unit angle using diffuse reflection. Next, I compared the data to Huygens' and geometrical optics calculations to estimate surface RMS height and the spatial frequency distribution. I have also compared the roughness height and frequency distribution to measurements taken on the SEM. By comparing our non-specular curves to geometrical optics, Huygens' calculations and physical measurements we are able to create a model accurate enough to describe the non-specular scattering from surfaces with roughness having spatial frequencies much less than one over the wavelength. Our research group hopes to be able to use this data make smoother samples in the future and find new and better ways to model thin film surfaces.

Jazmin Myres (Senior Thesis, April 2014, Advisor: Kent Gee Traci Neilsen )

Abstract

In scan-based array measurements, stationary reference sensors are needed to temporally correlate the different measurement scans and produce coherent complex pressure fields that can be used to perform near-field acoustical holography (NAH). Because the number of references required increases with the number of subsources contributing to the sound field, an extended, partially correlated source (e.g., a turbulent jet) comprising many ill-defined sources can result in significantly increased measurement complexity and expense. Demonstrated here a is a new approach to creating spatiotemporally coherent pressures using self-referencing between overlapping measurement positions instead of separate reference channels. A laboratory experiment was designed and the data have been used to explore "stitching" together a complex pressure field. This experiment is described and the “stitching” method is detailed. To successfully execute the technique, unwrapping of intrascan phases is first accomplished with a two-dimensional phase unwrapping algorithm. Individual scan positions are then stitched together using median phase differences between multiple adjacent scans to create coherent planes of data. Amplitude-stitching is done by averaging across scans and preserving the integrated squared pressure across the overall aperture. The validity of this method is shown by showing that a consistent local coherence maintained through the stitching process. The technique is applied to jet noise, and the possibility of applying it to NAH is discussed. This technique provides direction for efficient experimental design for scan-based array measurements of extended sources.

Stephen Rupper (Senior Thesis, April 2014, Advisor: Scott Bergeson )

Abstract

We report the design and fabrication of a simple integral-gain feedback circuit. This circuit is used in our laboratory to control the frequency of single-frequency lasers. A short tutorial on feedback control is given. The \$80 control circuit will be used to replace more expensive commercial systems currently in use in our lab.

Emily Stoker (Senior Thesis, June 2014, Advisor: Denise Stephens )

Abstract

An unanticipated result of researching transiting planet candidates from the Kepler spacecraft mission was the discovery of several variable objects in the fields of some of the targets. One particular object, which it was determined had not been previously documented, had a light curve that indicated it was a contact eclipsing binary star system. We found that this object has a period of about 0.3462 days. We worked to find a model that best fit our observed data of this system. Our results indicate that the two stellar components have similar temperatures, one around 6240 Kelvin, and the other is about 110-130 K warmer. The mass ratio is about 4.5, and the system is nearly edge-on relative to the plane of the sky. We emphasize the inconclusive nature of our results as other models may also be valid and more data is needed to confirm the binary nature of this system.

Bradford Talbert (Senior Thesis, April 2014, Advisor: Lawrence Rees )

Abstract

The cadmium capture-gated neutron spectrometer utilizes a dual-pulse signal from incoming neutrons to differentiate between neutrons and gamma rays. We have built such a detector and performed a time-of-flight experiment at Ohio University to measure incident neutron energy. We determined the detector efficiency as a function of neutron energy for neutrons with energies 0.5 MeV - 9 MeV. The detector has a peak efficiency of 12% for 2 MeV neutrons. The cadmium capture of the neutrons provides a low energy neutron detection boost that keeps the efficiency above 9% for neutrons with energy less than 2 MeV. A properly calibrated cadmium-capture gated neutron detector can be used to measure low energy neutrons from fission sources.

Philip White (Capstone, March 2014, Advisor: )

Abstract

Because of the importance of Antarctic surface mass balance (SMB) in predicting sea level change, models are created to predict SMB on the Antarctic ice sheet. Using Favier et al.'s quality-controlled aggregate data set N=3529, a fully Bayesian spatial model has been utilized to predict Antarctic SMB (Favier et al. 2013). Utilizing Markov random fields constructed through Gaussian process models, SMB is predicted over the entire Antarctic ice sheet. An SMB surface over the Antarctic ice sheet is computed by this model and compared with previous maps. An SMB prediction error surface is created to identify regions of high prediction uncertainty. These results suggest lower Antarctic water accumulation than previously purported. The calculated SMB surface showed more negative SMB regions and higher spatial variation than is likely plausible. Lastly, Antarctic boundary regions and areas with little data show high prediction uncertainty by the generated SMB prediction uncertainty surface.

Jenny Whiting (Senior Thesis, April 2014, Advisor: Timothy Leishman )

Abstract

The purpose of this research was to create a real-time convolution system for use in auralizations and to study subject behavior. To do this, models of real acoustical spaces were first created using the EASE software package. Impulse responses with a single collocated speaker and listener designed to represent a human subject were then generated from those models. These impulse responses were convolved in real time with voice signal from a live subject in the anechoic chamber. The resultant auralization was sent to the subject’s ears via offear headphones in real time, so as to create the illusion of physically being in an acoustical space different from the anechoic chamber. The primary result of this research was the successful implementation of the convolution system with models from EASE in the anechoic chamber at BYU. Many future studies will involve this convolution system, including studies of human perception of their own speech, and musican/performer perception of their own sound in various acoustic environments.

Nathaly Young (Senior Thesis, April 2014, Advisor: Eric Hintz )

Abstract

The star BD+53 2262 is an emission line star that has been hypothesized to be a High Mass X-ray Binary system (HMXB). The only time this star has been looked at in the X-ray wavelength, it was below detection levels. The purpose of this thesis is to see if there is any variability in the visible wavelengths to suggest that this is indeed a HMXB system. After 4 years of observation, BD+53 2262 shows a 1/10th decrease in magnitude and some small variations within each observation year. This long-term variation is small but consistent with a super orbital period that the star may be exhibiting.