Scalable electromagnetic instrumentation

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2004.Includes bibliographical references (leaves 171-178).This thesis explores spin manipulation, fabrication techniques and boundary conditions of electromagnetism to bridge the macroscopic and microscopic worlds of biology, chemistry and electronics. This work is centered around the design of a novel electromagnetic device scalable from centimeters to micrometers called a microslot. By creating a small slot in a planarized waveguide called a microstrip, the boundary conditions of the system force an electromagnetic wave to create a concentrated magnetic field around the slot that can be used to detect or produce magnetic fields. By constructing suitable boundary conditions, a detector of electric fields can be produced as well. One of the most important applications of this technology is for Nuclear Magnetic Resonance (NMR). As demonstrated experimentally in this thesis, microslots improves the mass-limited detectability of NMR by orders of magnitude over conventional technology and may move us closer to the dream of NMR on a chip.(cont.) Improving sensitivity in NMR may lead to a dramatic increase in the rate and accessibility of protein structural information accumulation and a host of other applications for fundamental understanding of biology and biomedical applications, and micro/macroscopic engineering. This microslot structure was constructed at both 6.9mm and 297 [mu]m in order to understand the properties as a function of scale. The 297 [mu]m structure has the best signal to noise ratio of any published planar detector and promises to have higher sensitivity with decreasing size. The detector has been used to analyze water and a relatively simple organic molecule with nanomole sensitivity. 940 picomoles of a small peptide was analyzed and a 2D correlation spectra was obtained which allowed identification of the amino acids in the peptide and could be further used to determine structure. This 297 [mu]m microslot probe was constructed using conventional printed circuit board fabrication and a laser micromachining center. A homebuilt probe was made to house the circuit board. Since this geometry is simpler than previously demonstrated techniques, fabrication can be automated for arrays and is inherently scalable to small sizes (less than 10 [mu]m).(cont.) The planar nature of the device makes it ideal for integration with microfluidics, transceivers and applications such as cell/neuron chemistry, protein arrays, and HPLC-NMR on pico to nanomoles of sample. Furthermore, this work suggests that a physically scalable, near-field device may have a variety of further uses in integrated circuit chip diagnosis, spintronic devices, nanomanipulation, and magnetic/electric field imaging of surfaces.by Yael Gregory Eli Maguire.Ph.D

Towards a table top quantum computer

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 1999.Includes bibliographical references (leaves 135-139).In the early 1990s, quantum computing proved to be an enticing theoretical possibility but a extremely difficult experimental challenge. Two advances have made experimental quantum computing demonstrable: Quantum error correction; and bulk, thermal quantum computing using nuclear magnetic resonance (NMR). Simple algorithms have been implemented on large, commercial NMR spectrometers that are expensive and cumbersome. The goal of this project is to construct a table-top quantum computer that can match and eventually exceed the performance of commercial machines. This computer should be an inexpensive, easy-to-use machine that can be considered more a computer than its "supercomputer" counterparts. For this thesis, the goal is to develop a low-cost, table-top quantum computer capable of implementing simple quantum algorithms demonstrated thus far in the community, but is also amenable to the many scaling issues of practical quantum computing. Understanding these scaling issues requires developing a theoretical understanding of the signal enhancement techniques and fundamental noise sources of this powerful but delicate system. Complementary to quantum computing, this high performance but low cost NMR machine will be useful for a number of medical, low cost sensing and tagging applications due the unique properties of NMR: the ability to sense and manipulate the information content of materials on macroscopic and microscopic scales.Yael G. Maguire.S.M

Physical principles for scalable neural recording

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical, magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. Based on this analysis, all existing approaches require orders of magnitude improvement in key parameters. Electrical recording is limited by the low multiplexing capacity of electrodes and their lack of intrinsic spatial resolution, optical methods are constrained by the scattering of visible light in brain tissue, magnetic resonance is hindered by the diffusion and relaxation timescales of water protons, and the implementation of molecular recording is complicated by the stochastic kinetics of enzymes. Understanding the physical limits of brain activity mapping may provide insight into opportunities for novel solutions. For example, unconventional methods for delivering electrodes may enable unprecedented numbers of recording sites, embedded optical devices could allow optical detectors to be placed within a few scattering lengths of the measured neurons, and new classes of molecularly engineered sensors might obviate cumbersome hardware architectures. We also study the physics of powering and communicating with microscale devices embedded in brain tissue and find that, while radio-frequency electromagnetic data transmission suffers from a severe power–bandwidth tradeoff, communication via infrared light or ultrasound may allow high data rates due to the possibility of spatial multiplexing. The use of embedded local recording and wireless data transmission would only be viable, however, given major improvements to the power efficiency of microelectronic devices

Physical principles for scalable neural recoding

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical, magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. Based on this analysis, all existing approaches require orders of magnitude improvement in key parameters. Electrical recording is limited by the low multiplexing capacity of electrodes and their lack of intrinsic spatial resolution, optical methods are constrained by the scattering of visible light in brain tissue, magnetic resonance is hindered by the diffusion and relaxation timescales of water protons, and the implementation of molecular recording is complicated by the stochastic kinetics of enzymes. Understanding the physical limits of brain activity mapping may provide insight into opportunities for novel solutions. For example, unconventional methods for delivering electrodes may enable unprecedented numbers of recording sites, embedded optical devices could allow optical detectors to be placed within a few scattering lengths of the measured neurons, and new classes of molecularly engineered sensors might obviate cumbersome hardware architectures. We also study the physics of powering and communicating with microscale devices embedded in brain tissue and find that, while radio-frequency electromagnetic data transmission suffers from a severe power–bandwidth tradeoff, communication via infrared light or ultrasound may allow high data rates due to the possibility of spatial multiplexing. The use of embedded local recording and wireless data transmission would only be viable, however, given major improvements to the power efficiency of microelectronic devices