Browsing by Subject "instrumentation"
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Item Instrumentation for parallel magnetic resonance imaging(Texas A&M University, 2007-04-25) Brown, David GeraldParallel magnetic resonance (MR) imaging may be used to increase either the throughput or the speed of the MR imaging experiment. As such, parallel imaging may be accomplished either through a "parallelization" of the MR experiment, or by the use of arrays of sensors. In parallelization, multiple MR scanners (or multiple sensors) are used to collect images from different samples simultaneously. This allows for an increase in the throughput, not the inherent speed, of the MR experiment. Parallel imaging with arrays of sensor coils, on the other hand, makes use of the spatial localization properties of the sensors in an imaging array to allow a reduction in the number of phase encodes required in acquiring an image. This reduced phase-encoding requirement permits an increase in the overall imaging speed by a factor up to the number of sensors in the imaging array. The focus of this dissertation has been the development of cost-effective instrumentation that would enable advances in the state of the art of parallel MR imaging. First, a low-cost desktop MR scanner was developed (< $13,000) for imaging small samples (2.54 cm fields-of view) at low magnetic field strengths (< 0.25 T). The performance of the prototype was verified through bench-top measurements and phantom imaging. The prototype transceiver has demonstrated an SNR (signal-to-noise ratio) comparable to that of a commercial MR system. This scanner could make parallelization of the MR experiment a practical reality, at least in the areas of small animal research and education. A 64-channel receiver for parallel MR imaging with arrays of sensors was also developed. The receiver prototype was characterized through both bench-top tests and phantom imaging. The parallel receiver is capable of simultaneous reception of up to sixty-four, 1 MHz bandwidth MR signals, at imaging frequencies from 63 to 200 MHz, with an SNR performance (on each channel) comparable to that of a single-channel commercial MR receiver. The prototype should enable investigation into the speed increases obtainable from imaging with large arrays of sensors and has already been used to develop a new parallel imaging technique known as single echo acquisition (SEA) imaging.Item Novel instrumentation for a scattering independent measurement of the absorption coefficient of natural waters, and a new diffuse reflector for spectroscopic instrumentation and close cavity coupling(Texas A&M University, 2007-04-25) Musser, Joseph AlanWe report results for the development of a flow-through integrated cavity absorption meter (ICAM.) Absorption measurements have been made with 2% or less change in the signal in the presence of up to 10 m-1 of scattering in the medium. The operating range of the ICAM ranges from 0.004 m-1 to over 40 m-1 of absorption. This range allows one to use a single instrument to measure the absorption from sediment laden rivers out to the cleanest of ocean waters. Further, the ICAM signal has been shown to be independent of the flow rate and turbulence in the medium. In addition we report the development of a diffuse reflector which, to our best knowledge, has the highest measured diffuse reflectivity of 0.998 at 532 nm and 0.996 at 266 nm. We also show that the average distance a photon travels between successive reflections in an integrating cavity of arbitrary shape is four times the volume divided by the surface area, 4 V/S. Further, for a cavity which is formed by planes tangent to an inscribed sphere and which maintains a homogeneous and isotropic field, the average distance traveled by a photon between successive reflections is equal to 4 V/S of the inscribed sphere. Thus, each cavity has the same ratio of V/S as the inscribed sphere. These advances lead to an increase in the sensitivity of absorption spectroscopy. The sensitivity approaches that of cavity ring down spectroscopy (CARS), without the adverse scattering effects traditionally associated with CARS.Item Wireless, automated monitoring for potential landslide hazards(Texas A&M University, 2007-09-17) Garich, Evan AndrewThis thesis describes research efforts toward the development of a wireless sensor node, which can be employed in durable and expandable wireless sensor networks for remote monitoring of soil conditions in areas conducive to slope stability failures. Commercially available soil moisture probes and soil tilt sensors were combined with low-power, wireless data transmitters to form a self-configuring network of soil monitoring sensors. The remote locations of many slope stability hazard sites eliminates the possibility of real-time, remote monitoring instrumentation that relies on AC power or land-based communication methods for operation and data transfer. Therefore, various power supply solutions and data transfer methods were explored during this research and are described herein. Additionally, sensor modification and calibrations are discussed. Preliminary evaluations of field durability of the pilot instrumentation were undertaken during this research. Geotechnical engineering instrumentation must be able to withstand extreme weather related conditions. The wireless, solar-powered soil moisture and tilt sensor node was installed on the Texas A&M University campus, allowing evaluation of system reliability and instrument durability. Lastly, potential future research and conclusions arising from this research are presented. This research has shown that commercially available wireless instrumentation can be modified for use in geotechnical applications. The development of an active power management system allows for sensors to be placed in remote locations and operated indefinitely, thus creating another option for monitoring applications in geotechnical and environmental problems.