Browsing by Subject "SNR"
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Item A 24-channel radio frequency receive array for magnetic resonance imaging of primates at 10.5 T(2023-08) Jungst, SteveMagnetic resonance imaging (MRI) is a unique modality which offers many advantages and challenges compared to other imaging technologies. The radio frequency (RF) coil is one of the key hardware sub-systems, which drives overall MRI system performance to enable higher resolution imaging and the collection of high fidelity information about organism structure and function. To optimize RF coil performance, notably the signal-to-noise ratio (SNR) of the received signal, it is imperative that each coil be custom made to the specific static field strength of the MRI system, the anatomical region of interest, and the desired experimental constraints. This thesis explores some of the technical underpinnings of MRI with a focus on RF coil construction for non-human primate (NHP) imaging. A 24-channel RF receive array coil with integrated transmitter is presented, followed by a discussion of its performance, imaging results, and future directions.Item System and Media Optimizations for improved HAMR Performance(2020-08) Natekar, NiranjanIt is said that data never sleeps. It has a ubiquitous presence and is being generated at an exceptional pace from different sources. The insurmountable demand for data must be met with an equally fast paced data supply which has led to the development of data servers by companies like Microsoft and Google. In spite of facing an existential crisis due to the development of SSD’s, the Compound Annual Growth Rate (CAGR) of ~ 40% maintained by the HDD industry has ensured that these devices are a necessity when it comes to large scale data storage. The growth of the HDD industry is helped by the fact that a huge amount of research is dedicated to developing new data recording technologies to improve the storage capacity of HDD’s. Significant investment has gone into developing a new data recording technology called Heat Assisted Magnetic Recording (HAMR) that is expected to improve the storage density up to at least 5Tb/in2. In conjunction with other improvements (like the development of Bit Patterned Media BPM), the expected density output for HAMR can be even higher. The optimization of the HAMR technology has focused on different aspects of the HAMR system, optical, magnetic, mechanical and electrical. In this thesis, different system and media optimizations that may help improve the HAMR performance are explored. The effect of doped L10 FePt media, which is an extremely popular HAMR media, is considered to understand how a change in its Curie temperature (Tc) can actually influence its intrinsic magnetic properties. This is followed by the implementation of micromagnetic simulations with the use of the stochastic Landau Lifshitz Gilbert (LLG) equation that is used to mimic the magnetization dynamics of grains. These simulations are used to vary the media properties and HAMR process parameters to optimize a thin 3nm (write layer)/6nm (storage layer) Thermal Exchange Coupled Composite (ECC) HAMR media. Introducing finite exchange coupling between the grains of the write layer and scaling the damping in the write layer are techniques that can help reduce the DC noise and improve the Signal to Noise Ratio (SNR). The Ensemble Waveform Analysis technique identifies Transition SNR as the main cause of SNR variation. This optimization process lends credence to the idea that a thinner composite media may be used to realize significant enhancements of SNR. Micromagnetic simulations are also used to address an important issue related to HAMR; the high temperature for writing data can cause heating issues with long term HAMR use. A low temperature Thermal ECC media is proposed that can significantly reduce the writing temperature (by about 34%) and that can reduce the peak temperature of the heat spot used to heat the media in the HAMR process by 200K. This is followed by an analytical formulation that is derived to calculate the transition jitter in the HAMR process. The jitter is known to depend on the grain size as well as the heat spot thermal gradient. It also depends on the Voronoi Grain Size Distribution, as well as exhibiting a surprising nonlinear dependence on the reader width. By combining the noise due to these dependencies the analytical formulation can be derived. This simple formulation provides both physical insight and conserves computational time relative to lengthy (and complex) recording simulations. A detailed analysis of the Adjacent Track Erasure (ATE) in the HAMR process is also explored. The numerical extent of ATE in different HAMR media is established and techniques are implemented using micromagnetic simulations in an attempt to reduce the ATE effect. A hypothesis is established to explain the presence of extent of ATE in different HAMR media. Research in the area of HAMR process and system optimization is of huge importance especially since the data storage industry has invested a lot in terms of research and manpower in this technology. Potential directions of research include techniques to reduce the ATE, improving the designs of different HAMR system components and developing better data post processing techniques like Neural Networks and 2D detectors.