Sin Ming Loo

Three‐dimensional structure of electron holes driven by an electron beam

Using 3-D particle-in-cell (PIC) simulations we studied the structure and temporal behavior of electron holes (e-holes) in a magnetized plasma driven by an electron beam. When e-holes are fully evolved from high-frequency waves in a time of about a few tens of electron plasma periods, most of the wave energy in the plasma resides in them. Parallel to the ambient magnetic field Bo, the potential distribution of an e-hole is approximately a Gaussian, and the scalelength lz is only a few Debye lengths when determined by the effective temperature of the beam-modified electron distribution function. Transverse to Bo, the potential distribution tends to have a flat top, which makes it difficult to fit a Gaussian distribution, but the scalelengths at which the potential decays in the transverse directions (lx and lz) are found to be only slightly longer than lz. The passages of electron holes monitored at several points in the simulation volume has the signature of bipolar parallel electric field and unipolar perpendicular electric-field pulses as measured from FAST and POLAR. The eventual decay of e-holes is accompanied by the generation of lower hybrid (lh) waves.

Handel-C for rapid prototyping of VLSI coprocessors for real time systems

The current maturity of modern reconfigurable hardware elements such as field programable gate arrays now makes it possible to utilize application-specific reconfigurable coprocessor logic as part of real time system design. Such logic has great potential to improve both the level of performance and run time determinism of the system. It also gives the real time system designer the capability of performing nonintrusive high-speed monitoring operations such as the missed deadline detection and external bus I/O activity analysis that can be directly utilized by the system scheduler to dynamically adapt to changing process load conditions. In most cases, though, designers of real time systems are software development practitioners, not hardware developers. They know much more about traditional software high-level programming languages such as C and C++ than hardware description languages such as VHDL and Verilog. New hardware description languages such as Handel-C are now becoming available to make the hardware design process more accessible to these software developers. In this paper, we investigate the effectiveness of using Handel-C, in an academic setting, to develop real time embedded systems in environments that incorporates the reconfigurable FPGA based co-processor logic.

Electron hole as an antenna radiating plasma waves

Recent observations of electron holes (e-holes) in space plasma have led to theoretical and numerical studies which show that e-holes in a magnetized plasma are unstable nonlinear structures. Their decay generates plasma waves in the frequency bands of lower hybrid (LH) and electrostatic whistler (EW) waves. An analysis is presented demonstrating that the e-holes are an effective radiator of plasma waves in the above frequency bands critically depending on their scalelength (l⊥) transverse to the ambient magnetic field. In this sense, an e-hole acts like a radiating antenna. The results from 3-D numerical simulations are presented to examine the nonlinear consequences of the radiation from e-holes. When e-holes have long l⊥ during the initial stage of their existence, they undergo a beading process. This involves radiation of spatial Fourier components corresponding to long scalelength in the structure of e-holes, leaving behind smaller structures. This divides the initially large e-hole structure into several fragments. The resulting smaller structures with l⊥∼ l∥ eventually dissipate by radiating transversely structured lower hybrid waves.

Modular, Portable, Reconfigurable, and Wireless Sensing System for the Aircraft Cabin

This paper describes the design and prototyping of a modular, portable, reconfigurable, and wireless multipurpose sensor system for monitoring and recording environmental conditions in aircraft cabins. The objective of this small, portable embedded sensing system is to record aircraft cabin conditions on flights of convenience to generate a large database for determination of normal conditions. By designing a sensor system that can be easily reconfigured for different needs (with the ability and flexibility to accommodate different/extra sensors), the system can be used to measure parameters that meet multiple research requirements. Through design considerations such as generalized signal interface and hierarchical code structure that can be easily reworked for new sensors, this sensor system has been developed for optimum usefulness in aircraft environment research. In the current setup, the system is configured with temperature, humidity, sound level, carbon dioxide, and pressure sensors. The system has been calibrated in the laboratory without the use of a pressure chamber. Data from six flights are presented in this report.

Task Scheduling in a Finite-Resource, Reconfigurable Hardware/Software Codesign Environment

This paper describes how static task-scheduling methods using stochastic search techniques can be applied to digital systems that are composed entirely of reconfigurable hardware. Such reconfigurable hardware is characterized by the property that its low-level logical functionality is not determined at the time of manufacture, but rather that this functionality becomes set only shortly before or during the invocation of the targeted application. The purpose of this paper is to introduce the basic framework for applying static scheduling theory to arbitrarily-structured task systems targeted to be implemented in prefabricated resource-constrained reconfigurable hardware. The paper also describes initial solutions to this heterogeneous task-scheduling problem that combine a distributed list-based scheduling technique with three probabilistic search strategies. The techniques introduced produce detailed task scheduling and high-level hardware configuration information that can serve as inputs to the software and reconfigurable hardware design automation tools used in the hardware/software codesign process.

A Miniature Inductively Coupled Plasma Source for Ion Thrusters

A small inductively coupled plasma source has been developed for use in an ion thruster. A 10.1-mm-diameter thick film silver spiral antenna is fabricated on a low-temperature cofired ceramic with a 35-μm dielectric over the antenna. The antenna has been able to sustain an argon plasma over a frequency range from 448 to 1020 MHz with pressures ranging from 50 mtorr to 1.75 torr. Plasma start powers ranged from 3 to 50 W with minimum sustain powers down to 0.1 W. Antenna electric field measurements have been made in air and compared with simulation of the antenna field using COMSOL. These results show that the antenna pattern is dominated by the standing wave pattern of the spiral antenna. Simulations of the RF power density versus frequency compare well with the plasma start power variation except for a large start power peak between 600 and 700 MHz.

A Portable Wireless Particulate Sensor System for Continuous Real-Time Environmental Monitoring

Airborne particulate matter has been shown to be associated with morbidity and mortality, and may interfere with certain sensitive experiments. Understanding the levels and movements of particulate matter in an enclosed space can lead to a reduction in the impact of this material on health and experimental results. A system of environmental sensors including particulate matter, selected gases, humidity, temperature, and pressure can be used to assist in tracking air movement, providing real-time mapping of potential contaminants as they move through a space. In this paper we present a system that is capable of sensing these environmental factors, collecting data from multiple dispersed nodes and presenting the aggregated information in real-time. The highly modular system is based on a flexible and scalable framework developed for use in aircraft cabin environments. Use of this framework enables the deployment of a custom suite of sensors with minimal development effort. Individual nodes communicate using a self-organizing mesh network and can be powered from a variety of sources, bringing a high level of flexibility in the arrangement and distribution of the sensor array. Sensor data is transmitted to a coordinator node, which then passes the time-correlated information to a server-hosted database through a choice of wired or wireless networks. Presentation software is used to either monitor the real-time data stream, or to extract records of interest from the database. A reference implementation has been created for the National Institutes of Health consisting of a custom optical particle counter and off-the-shelf sensors for CO2, CO, temperature, humidity, pressure, and acoustic noise. The total environmental sensing system provides continuous, real-time data in a readable format that can be used to analyze ambient air for events of interest.

Case study of finite resource optimization in FPGA using genetic algorithm

Modern Field-Programmable Gate Arrays (FPGAs) are becoming very popular in embedded systems and high-performance applications. FPGA has benefited from the shrinking of transistor feature size, which allows more on-chip reconfigurable (e.g. memories and look-up tables) and routing resources. Unfortunately, the amount of reconfigurable resources in a FPGA is fixed and limited. This paper investigates an application-mapping scheme in FPGA by utilizing sequential processing units and task specific hardware. Genetic Algorithm is used in this study. We found that placing sequential processor cores into FPGA can improve the resource utilization efficiency and achieved acceptable system performance. In this paper, two cases were studied to determine the trade-off between resource optimization and system performance.

Monitoring of the Aircraft Cabin Environment via a Wireless Sensor Network

Wireless sensor networks consist of physically distributed autonomous sensor nodes that cooperatively monitor physical or environmental conditions. The key benefit of wireless sensor networks is that they are capable of generating a more complete view of the sensed environment by acquiring larger quantities of correlated data than independent sensor monitors. This makes them ideally suited for applications where a complex environment with many interdependent factors must be monitored. The aircraft cabin is one such example of a highly dynamic environment which necessitates the use of an advanced sensing system. Thus, in order to gain a better understanding of the aircraft cabin environment, a wireless sensor network was designed and prototyped. The network is comprised of a variable number of nodes, and each node is capable of adapting to monitor a wide variety of environmental parameters. The system, as described in previous publications, has now entered the testing phase. The current configuration includes twelve nodes sensing temperature, humidity, carbon dioxide, and barometric pressure. This paper discusses the results from a series of tests conducted with the prototype hardware/software in a mockup of the 767 cabin environment. Tests involved the use of humidifiers, heaters, and carbon dioxide to simulate changes in the cabin environment.

A wireless sensor data fusion framework for contaminant detection

In recent years, much research has been done on wireless sensor networks and sensor data fusion, however there has been limited work regarding implementation of real systems that are capable of providing a highly connected sensor network for data logging and data fusion applications. This paper describes the design and implementation of a wireless, portable, and reconfigurable sensor network framework. This sensor node design has proven to be effective for monitoring environmental conditions of aircraft cabins and is well suited to environmental monitoring and detection of contaminants in large areas when utilizing sensor data fusion features.