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Department Library

2021

Lucas Barnes (Senior Thesis, April 2021, Advisor: Brian Anderson )

Abstract

Time reversal (TR) is a method of focusing wave energy at a point in space. The optimization of a TR demonstration is described that is designed to knock over only one selected LEGO minifigure among other minifigures by focusing vibrations within an aluminum plate at the target minifigure. The goal is to achieve high repeatability of the demonstration along with reducing the cost of the demonstration. By comparing the motion of the minifigure and the plate directly beneath its feet, it is determined that a major factor inhibiting the repeatability of the demonstration is that smaller vibrations leading up to the focal event cause the minifigure to bounce repeatedly, losing contact with the plate and ending up in the air during the main focal event intended to knock over the minifigure. The effects of amplitude, frequency, TR technique, plate thickness, and vibration sensor type are explored to determine their impact on the repeatability of the demonstration. A description is given of the implementation of the demonstration for a museum exhibit. This demonstration illustrates the power of TR focusing and the principles learned by optimizing this demonstration can be applied to other real-world applications.

2020

Timothy Puente (Capstone, April 2020, Advisor: Brian Anderson )

Abstract

During production, Burr OAK Inc. ran into several problems with their die presses. The problem that they had is their current design of their cut-off. They identified the problems with the design and asked us to redesign the drive system of the cut-off mechanism. Alternative power sources were considered, the amount of force that is required to cut through aluminum and steel sheets was calculated, and the configurations of the actuators were compared. An alternative cut-off design was developed through product development, analyzed using computational analysis of the pressure and CFM, and then tested with aluminum and steel sheets, and then adjusted based on the results of the tests. The results of the tests and the readjustments resulted in the design of pneumatically powered cut-off that is able to cut through aluminum and steel sheets, which are the most common materials that Burr OAK Inc. uses.

Paige Simpson (Senior Thesis, June 2020, Advisor: Brian Anderson )

Abstract

Time reversal may be used as an energy-focusing technique. It is applied in many different ways including, for example, nondestructive evaluation (NDE) of cracks in structures, reconstructing a source event, and providing an optimal carrier signal for communication. In NDE applications, it is often of interest to study small samples or samples that do not lend themselves to the bonding of transducers to their surfaces. A reverberant cavity, called a chaotic cavity, attached to the sample of interest provides space for the attachment of transducers as well as a more reverberant environment, which is critical to the quality of time reversal focusing. Transducers are attached to the chaotic cavity which is attached to the sample under test. The goal of this research is to explore the dependence of the quality of the time reversal focusing on the size of the chaotic cavity used. An optimal chaotic cavity will produce the largest focusing amplitude, best spatial resolution, and most linear focusing of the time reversed signal. This thesis shows experimentally that as the size of an aluminum rectangular chaotic cavity increases, the peak amplitude of the time-reversed focus tends to increase as well.

Carla Wallace (Senior Thesis, August 2020, Advisor: Brian Anderson )

Abstract

Time reversal (TR) focusing of airborne ultrasound in a room is demonstrated. Various methods are employed to increase the amplitude of the focus. These methods include creating a small wooden box (or chamber) to act as a miniature reverberation chamber, using multiple sources, and using the clipping processing method. The use of a beam blocker to make the sources more omnidirectional is examined, and it is found that for most source/microphone orientations, the use of a beam blocker increases the amplitude of the focus. A high-amplitude focus of 134 dB peak re 20 µPa SPL is generated using TR. The waveform and spectrum of the focus are examined to determine if it the focus is loud enough to generate nonlinear effects in the air. Using 4 sources centered at 36.1 kHz and another 4 sources centered at 39.5 kHz, nonlinear difference frequency content near 3.4 kHz is observed in the focus signal. If the nonlinearities are generated in the air, the TR setup could perhaps be used to create a virtual sound source (spherically symmetric parametric array) within a room, from which audible sound may propagate.

2019

Josh Gregg (Senior Thesis, June 2019, Advisor: Brian Anderson )

Abstract

Nonlinear resonant ultrasound spectroscopy (NRUS) is a method that can be used for detecting the amount of microcracking in structures. NRUS detects global damage in a sample by measuring shifts in resonance frequencies that depend on excitation amplitude and correspond to nonlinear elastic properties of the material. NRUS measurements typically are excited with a piezoelectric transducer, but here the application of an electromagnetic transducer is explored as an alternative. The electromagnetic transducer, unlike a single piezoelectric, allows selective excitation of longitudinal, torsional, and bending vibrations in a rod-shaped sample. Measurement of the nonlinear properties of the sample for each type of vibration is therefore possible. This electromagnetic technique involves gluing a coil of wire onto the end of a rod sample and placing it in a magnetic field. By controlling which part of the coil is inside the strongest region of the magnetic field, the principle direction of the driven oscillations in the rod can be controlled. Both piezoelectric and electromagnetic excitation techniques are tested by measuring the nonlinear elastic parameter, alpha_E, of Berea sandstone. The electromagnetic technique was shown to measure a 30% higher mean value for alpha_E than the piezoelectric technique.

Michelle Nuttall (Capstone, December 2019, Advisor: Brian Anderson )

Abstract

Unlike many ions, the organic molecule tetraphenylphosphonium (TPP) has the ability to pass through a lipid bilayer without the help of ion channels. Many lipid compositions show this behavior, but at room temperature, TPP is unable to pass through a bilayer made out of a mixture of the lipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and cholesterol. When TPP is heated to higher temperatures, however, the ion is able to pass through the bilayer. It has been realized that the transition temperature of DMPC is very close to room temperature, and as such, it should be possible to determine the transition temperature of this mixture by determining when the ion is able to pass through the bilayer.

2018

Trent Furlong (Senior Thesis, June 2018, Advisor: Brian Anderson )

Abstract

Time reversal (TR) acoustics is capable of remotely focusing sound energy to a point in space. This thesis explores the remote delivery of a noise-canceling signal to a desired location (e.g. a patient’s ears) using TR. A parameterization study testing frequency dependence, and signal length is conducted in a reverberation chamber to determine the effectiveness of using TR with active noise control (ANC). The reduction of Magnetic Resonance Imaging (MRI) noise using ANC delivered by TR (ANC+TR) is demonstrated using recordings of MRI noise. For both the parameterization study and the MRI noise experiments, the simulated noise and ANC+TR signals are broadcast from two separate sources, recorded by a microphone, and their responses are linearly superposed in post-processing to determine the noise attenuation. The parameterization study results show that TR is better at reducing noise at frequencies below 1 kHz and for narrowband signals with reductions as great as 20 dB. MRI noise is reduced by up to 18 dB in overall sound pressure level. Both the parameterization study and the MRI noise reduction study utilized a single control loudspeaker; further reductions should be possible with the use of more control sources.

Stephen Hogg (Senior Thesis, June 2018, Advisor: Brian Anderson )

Abstract

Spent nuclear fuel rods are stored in stainless steel containers and may be stored for decades. In order prevent radiation leakage, the stainless steel structure must not be compromised. These containers are susceptible to stress corrosion cracking (SCC). Traditional nondestructive evaluation methods have been developed to detect open cracks but these cannot detect the closed portion of the crack that may extend further. Nonlinear Resonant Ultrasound Spectroscopy (NRUS) is used here to determine if it can be used to quantify a cumulative amount of SCC in a structure. To induce SCC in a timely manner, cylindrical, 304L stainless steel rods are immersed in a heated 42% magnesium chloride solution. A set of rods are removed one by one after different lengths of exposure to the hot magnesium chloride solution. NRUS measurements are then conducted on longitudinal modes in the rods. Rods exposed longer did indeed result in a larger resonance frequency shift, and therefore a larger nonlinear parameter, α, in NRUS measurements. It is observed that α can be used to detect SCC before visible cracks appear on the rods.

2017

Matthew Willardson (Capstone, August 2017, Advisor: Brian Anderson )

Abstract

Time reversal (TR) is a signal processing technique that can be used for intentional sound focusing. While it has been studied in room acoustics, the application of TR to produce a high amplitude focus of sound in a room has not yet been explored. The purpose of this study is to create a virtual source of spherical waves with TR that are of sufficient intensity to study nonlinear acoustic propagation. A parameterization study of deconvolution, one-bit, clipping, and decay compensation TR methods is performed to optimize high amplitude focusing and temporal signal focus quality. Decay compensation is introduced in this paper. Of all TR methods studied, clipping is shown to produce the highest amplitude focal signal. An experiment utilizing eight horn loudspeakers in a reverberation chamber is done with the clipping TR method. A peak focal amplitude of 9840 Pa (174 dB peak re 20 μPa) is achieved. Results from this experiment indicate that this high amplitude focusing is a nonlinear process.

2016

Christopher Heaton (Capstone, August 2016, Advisor: Brian Anderson )

Abstract

The purpose of this research is to develop a visual demonstration of time reversal focusing of vibrations in a thin plate. Various plate materials are tested to provide optimal conditions for time reversal focusing. Specifically, the reverberation time in each plate and the vibration coupling efficiency from a shaker to the plate are quantified to illustrate why a given plate provides the best spatially confined focus as well as the highest focal amplitude possible. A single vibration speaker and a scanning laser Doppler vibrometer (SLDV) are used to provide the time reversal focusing. Salt is sprinkled onto the plate surface to allow visualization of the high amplitude, spatially localized time reversal focus; the salt is thrown upward only at the focal position. Spatial mapping of the vibration focusing on the plate using the SLDV is correlated to the visual salt jumping demonstration. The time reversal focusing is also used to knock over an object when the object is placed at the focal position; some discussion of optimal objects to use for this demonstration are given.

2012

Blaine Harker (Honors Thesis, August 2012, Advisor: Brian Anderson )

Abstract

Time reversal (TR) acoustics is a technique used to locate sources, using a set of transducers called a time reversal mirror (TRM) and is especially useful in reverberant environments. TR is commonly used to find acoustically small sources using a pulsed waveform. Here TR is applied to simple sources using steady-state waveforms using a straightforward, computational point source propagation theoretical model in a half-space environment. It is found that TR can effectively localize a simple source broadcasting a continuous wave, depending on the angular spacing. Furthermore, the aperture (angular coverage around the source) of the TRM is the most important parameter when creating a setup of receivers for imaging a source. This work quantifies how a TRM may be optimized when the source's location is known to be within a certain region of certainty.

2011

Trevor Jenny (Senior Thesis, April 2011, Advisor: Brian Anderson )

Abstract

Qualifying an anechoic chamber for frequencies that extend into the ultrasonic range is necessary for research work involving airborne ultrasonic sound. For example, an anechoic chamber allows for measurements of the direct sound radiated by an object without reflections from walls. The ANSI S12.55/ISO 3745 standard which covers anechoic chamber qualification does not extend into the ultrasonic frequency range, nor have issues pertinent to this frequency range been fully discussed in the literature. An increasing number of technologies are employing ultrasound; hence the need to develop facilities to conduct basic research studies on airborne ultrasound. This thesis will specifically discuss the need to account for atmospheric absorption and issues pertaining to source transducer directivity by presenting some results for qualification of a chamber at Brigham Young University. [This work has been funded by the Los Alamos National Laboratory]

2010

John Esplin (Capstone, April 2010, Advisor: Brian Anderson )

Abstract

Reduction of undesirable reflections in a room (by treating the offending reflecting surfaces) may only be accomplished if the locations of the offending surfaces are determined. Several measurement techniques exist to identify these surfaces, including the Polar Energy Time Curve (Polar ETC) method, which requires six cardioid impulse response measurements along each Cartesian axis. The purpose of the current study is to quantify the angular estimation error introduced into the Polar ETC due to non-ideal microphone directivities, faulty microphone positioning, and different signal processing techniques. It is shown that although errors in directivity minimally affect the Polar ETC method (as long as certain constraints are satisfied), errors due to positioning and signal processing variations have a relatively large effect on the overall performance of the Polar ETC. This implies that although microphone directivity is unimportant, microphone positioning and post-processing techniques are important.

2009

Jayrin Farley (Capstone, December 2009, Advisor: Brian Anderson )

Abstract

Transmission loss measurements of building materials at audible frequencies are commonly made using various techniques such as plane wave tubes or as a panel between reverberant rooms. These measurements provide vital information for noise isolation control in architectural acoustics. However, not much has been done to explore airborne ultrasonic sound transmission through common building materials. Technologies and products that utilize ultrasonic frequencies are becoming increasingly more common. This paper will present various measurements of the ultrasonic, normal-incidence insertion loss for various building materials over a frequency range of 28 kHz – 90 kHz. The materials tested include: medium density fiberboard, Styrofoam, galvanized steel, and polycarbonate plastic. Results show that the insertion loss is approximately 10 dB less than predicted by the theoretical mass-law transmission loss. This paper will also discuss the challenges involved in making such measurements.

David Ripplinger (Senior Thesis, August 2009, Advisor: Brian Anderson )

Abstract

Large displacement amplitudes in a freely vibrating string require that one consider the dynamic tension of the string to determine the normal frequencies instead of the commonly used equilibrium tension approximation. Large amplitudes can cause these frequencies to be significantly sharper. A theoretical model is presented to provide a more accurate approximation of the tension, which includes a correction term that is proportional to the total energy in the string. Experiments have been performed using a repeatable plucking mechanism on a monochord string apparatus. The motion of the plucked string was recorded for both vertical and horizontal displacements using a high speed camera. The instantaneous total energy in the string was then calculated as the string’s motion decayed, using the instantaneous frequency method and a narrow band-pass Bessel filter. A comparison is made between the model and the experimental results of the total energy in the string as a function of time. The data show that when a string is plucked at large displacement amplitudes the partial frequencies can be as much as 83 cents sharp relative to their stable frequency values.