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ELF/VLF radio signals, from approximately 300Hz to 30KHz, are commonly used for submarine communications, ionospheric remote sensing, geophysical prospecting, and studies of the near-Earth space environment. Naturally occurring ELF/VLF emissions caused by nearly every lightning strike can be detected for thousands of miles and provide an abundance of wave-particle interaction possibilities in the radiation belts. Any applied studies of these events, however, require electromagnetic waves in the ELF/VLF band to be amplified, captured, analyzed, and stored. Specific studies often require the placement of receivers in extremely remote locations such as Antarctica or the middle of an ocean, and are almost always located far away from power sources to decrease noise. These scientific requirements drive the creation of new ELF/VLF receiver systems. Two new receiver systems were designed for use in terrestrial, typically Antarctic, locations. Both new systems utilize 10-100 times less power than the lowest-power comparable existing ELF/VLF receivers and were designed for remote unmanned operation in extreme environments without external power. The so called Penguin system, comprised of a hybrid microcontroller and FPGA architecture, removes the overhead of a general purpose CPU to provide the most streamlined processing for data acquisition possible while still maintaining a relatively traditional sampling architecture. The drastically reduced architecture of the Penguin system, compared to traditional receiver systems, on average consumes less power than a typical LED indicator lamp while capturing high fidelity ELF/VLF magnetic field snapshots every fifteen minutes. The low power and thermal requirements of the Penguin system enables low-cost remote studies of medium to large timescale phenomena such as Chorus and Auroral Hiss without the need for local power. The system has been deployed and operated at the United States Amundsen Scott South Pole Station in Antarctica. A second ELF/VLF receiver architecture, the VLF Advanced Technology platform, or "VAT", removes the typical CPU from the sampling and recording loop further reducing power requirements and physical system size while gaining the ability to record continuously. This radically new architecture enables future scientific studies of the fine structure in time and frequency of long-term events, such as the onset mechanisms of natural Chorus emissions, due to the extremely low power requirements. The system architecture is also greatly applicable to any continuous time recording system, including but not limited to acoustic and electromagnetic arrays for subsurface imaging systems, ionospheric remote sensing, and optical sensors.
This book describes a new, extremely low frequency (ELF)/ very low frequency (VLF) miniaturized transmitter concept, based on the mechanical motion of permanent magnets or electrets. The authors explain how utilizing the very high energy density of modern ferromagnetic and ferroelectric materials, such “electromechanical transmitters’’ can provide much higher field generation efficiency than conventional antennas, thus enabling practical ELF/VLF wireless communications links. The text begins with the fundamental challenges of such links and provides an historical overview of the attempts that have been made to address these challenges. It then focuses on the design and implementation of practical electromechanical ELF/VLF transmitters, which is an interdisciplinary subject that spans multiple research areas including electromagnetics, power electronics, control systems, and mechanical design. The authors also describe how such transmitters can be combined with receivers and signal processing algorithms to realize complete ELF/VLF links in challenging environments.
Electromagnetic waves in the VLF frequency band from 300 Hz to 30 kHz are used to study the atmosphere, geolocate lightning, map subterranean features and provide navigation and timing signals. These waves can be generated by man-made sources, such as the VLF transmitters operated by the US Navy to communicate with submarines while they are submerged. They can also be generated by natural phenomena. For example, a lightning strike generates an impulsive signal known as a radio atmospheric. The interaction of these natural and man-made signals with the ionosphere, the magnetosphere, and the earth's electrical environment provides valuable data for scientific research. To facilitate this research, the VLF signals must be received and stored for further analysis. Due to the unique nature of these signals, specialized receiver hardware is required to receive them. Currently the most widely deployed VLF receiver is the AWESOME receiver developed at Stanford University. This receiver offers excellent data quality, but it has a power dissipation of around 60 Watts. The high power dissipation can be a problem because some of the most desirable locations to deploy receivers are remote locations, which are far away from power-lines and other sources of electromagnetic interference. In these cases, the receiver must have a very low power dissipation as it must operate on battery power for long periods of time. Low-power VLF receivers for remote deployments have been developed, but their lower power dissipation comes at the expense of data quality. The goal and challenge of this research is to design a low-power receiver without sacrificing data quality. To accomplish this goal, the first single-chip broadband VLF magnetic field receiver has been developed. The receiver consists of a low-noise amplifier (LNA) and an analog-to-digital converter (ADC) integrated on a single-chip. The LNA is implemented using a low-impedance bipolar input stage followed by a variable gain differential instrumentation amplifier. The ADC is implemented with a third-order continuous-time delta-sigma modulator, which was selected for its implicit anti-alias filtering capability and its robustness to mismatch and other non-ideal effects. The receiver also includes an automatic biasing system that compensates for the large temperature variations that are often encountered at remote deployment sites. The receiver was fabricated in a 0.13 um BiCMOS process. The LNA achieves a sensitivity of better than 1 fT/sqrt(Hz) using a standard six-turn 4.9 meter square loop antenna. It also has a peak spurious-free dynamic range of up to 104.02 dB and a 3 dB bandwidth that extends from 170 Hz to over 100 kHz. The power dissipation of the LNA is approximately 908 uW. The on-chip delta-sigma ADC has an effective resolution of 12.40 bits and a spurious-free dynamic range of over 93 dB. The power dissipation of the ADC is roughly 640 uW. The full receiver consists of the combination of the LNA and the ADC and has a total power dissipation of approximately 1.55 mW. A side-by-side comparison of field data from the single-chip receiver and the AWESOME receiver reveals that the data quality of the single-chip receiver is at least as good. Further, the single-chip receiver has a power dissipation that is over 30 times less than the current low-power receiver. The high data quality, low power dissipation and small size make the single-chip VLF magnetic field receiver especially well suited for remote VLF data collection.
Recent emphasis upon the importance of the physical environment has made science and the public even more cog nizant of the many components of the biosphere. While much attention has been given to ionizing electromagnetic stimuli which causes blatant and unalterable changes in biological systems, relatively little research has been concerned with those electromagnetic signals whose frequencies overlap with time-varying processes in living organisms. Extremely low frequency (ELF) electromagnetic fields can occur as waves between about I Hz to 100 Hz or as short pulses within this range of very low frequency (VLF) and higher frequency sources. The natural occurrence of ELF signals is associated with weather changes, solar disturbances and geophysical ionospheric perturbations. Man-made sources have also been reported. Certain physical properties of ELF signals make them excellent candidates for biologically important stimuli. Unlike many other weather components, ELF signals have the capacity to penetrate structures which house living organ isms. ELF wave configurations allow long distance propaga tional capacities without appreciable attenuation of inten sity, thus making them antecedent stimuli to approaching weather changes. Most importantly, ELF signals exhibit the frequencies and wave forms of bio-electrical events that occur within the brain and body. Thus resonance inter actions between animal and nature become attractive possi bilities.
Radiation-induced soft errors are a major concern for modern digital circuits, especially memory elements. Unlike large Random Access Memories that can be protected using error-correcting codes and bit interleaving, soft error protection of sequential elements, i.e. latches and flip-flops, is challenging. Traditional techniques for designing soft-error-resilient sequential elements generally address single node errors, or Single Event Upsets (SEUs). However, with technology scaling, the charge deposited by a single particle strike can be simultaneously collected and shared by multiple circuit nodes, resulting in Single Event Multiple Upsets (SEMUs). In this work, we target SEMUs by presenting a design framework for soft-error-resilient sequential cell design with an overview of existing circuit and layout techniques for soft error mitigation, and introducing a new soft error resilience layout design principle called LEAP, or Layout Design through Error-Aware Transistor Positioning. We then discuss our application of LEAP to the SEU-immune Dual Interlocked Storage Cell (DICE) by implementing a new sequential element layout called LEAP-DICE, retaining the original DICE circuit topology. We compare the soft error performance of SEU-immune flip-flops with the LEAP-DICE flip-flop using a test chip in 180nm CMOS under 200-MeV proton radiation and conclude that 1) our LEAP-DICE flip-flop encounters on average 2,000X and 5X fewer errors compared to a conventional D flip-flop and our reference DICE flip-flop, respectively; 2) our LEAP-DICE flip-flop has the best soft error performance among all existing SEU-immune flip-flops; 3) In the evaluation of our design framework, we also discovered new soft error effects related to operating conditions such as voltage scaling, clock frequency setting and radiation dose.
The distribution of relativistic electrons that form the Earth's radiation belts is extremely variable, with the trapped flux changing by several orders of magnitude on timescales of a few hours to days. These energetic particles pose a significant hazard to satellites and astronauts in the near-Earth space environment. The dynamic evolution of the radiation belts is believed to be controlled in large part by two separate but related classes of naturally occurring plasma waves: extremely low frequency/very low frequency (ELF/VLF) chorus and hiss. This dissertation explores characteristics of chorus and hiss observed at Palmer Station, Antarctica with the goal of improving our ability to differentiate between variations in emission generation and the effects of emissions' propagation to the ground. Results are presented from a two-part study, consisting of both observations and modeling, which explores the manner in which the plasmapause affects the propagation of chorus from its magnetospheric source to the ground. Results indicate that the observed chorus propagates in a non-ducted mode, which is contrary to a long-standing belief that guiding structures are necessary for chorus to propagate to the ground. This newly-explored mode of ground propagation indicates that ground stations may be able to observe a larger portion of waves than previously thought and provides for a more accurate interpretation of ground-observed waves and their influence on energetic particle distributions. Following this, an automated system of detecting chorus and hiss in broadband ELF/VLF data using neural networks is discussed. Results of running the automated detector on ten years of data are discussed including diurnal, seasonal and solar cyclical variations of emissions.
International Series of Monographs in Electromagnetic Waves, Volume 3: Electromagnetic Waves in Stratified Media provides information pertinent to the electromagnetic waves in media whose properties differ in one particular direction. This book discusses the important feature of the waves that enables communications at global distances. Organized into 13 chapters, this volume begins with an overview of the general analysis for the electromagnetic response of a plane stratified medium comprising of any number of parallel homogeneous layers. This text then explains the reflection of electromagnetic waves from planar stratified media. Other chapters consider the oblique reflection of plane electromagnetic waves from a continuously stratified medium. This book discusses as well the fundamental theory of wave propagation around a sphere. The final chapter deals with the theory of propagation in a spherically stratified medium. This book is a valuable resource for electrical engineers, scientists, and research workers.