Joel E. Schindall

Electrochemical Double-Layer Capacitors Using Carbon Nanotube Electrode Structures

The structure and behavior of the electrical double-layer capacitor (EDLC) are described. The use of activated carbon electrodes is discussed and the limitations on voltage and accessible surface area are presented. Metrics for evaluating EDLC performance are defined and previously reported results of experimental carbon nanotube (CNT) electrodes are tabulated. New experimental results of electrodes constructed of vertically aligned CNTs grown on a conducting substrate are presented. By extrapolating prior and new experimental data the energy density of CNT-based EDLCs is shown to be potentially up to seven times that of commercial activated carbon-based EDLCs.

An integrated methodology for the dynamic performance and reliability evaluation of fault-tolerant systems

We propose an integrated methodology for the reliability and dynamic performance analysis of fault-tolerant systems. This methodology uses a behavioral model of the system dynamics, similar to the ones used by control engineers to design the control system, but also incorporates artifacts to model the failure behavior of each component. These artifacts include component failure modes (and associated failure rates) and how those failure modes affect the dynamic behavior of the component. The methodology bases the system evaluation on the analysis of the dynamics of the different configurations the system can reach after component failures occur. For each of the possible system configurations, a performance evaluation of its dynamic behavior is carried out to check whether its properties, e.g., accuracy, overshoot, or settling time, which are called performance metrics, meet system requirements. Markov chains are used to model the stochastic process associated with the different configurations that a system can adopt when failures occur. This methodology not only enables an integrated framework for evaluating dynamic performance and reliability of fault-tolerant systems, but also enables a method for guiding the system design process, and further optimization. To illustrate the methodology, we present a case-study of a lateral-directional flight control system for a fighter aircraft.

Reliability evaluation of the power supply of an electrical power net for safety-relevant applications

In this paper, we introduce a methodology for the dependability analysis of new automotive safety-relevant systems. With the introduction of safety-relevant electronic systems in cars, it is necessary to carry out a thorough dependability analysis of those systems to fully understand and quantify the failure mechanisms in order to improve the design. Several system level FMEAs are used to identify the different failure modes of the system and, a Markov model is constructed to quantify their probability of occurrence. A new power net architecture with application to new safety-relevant automotive systems, such as Steer-by-Wire or Brake-by-Wire, is used as a case study. For these safety-relevant loads, loss of electric power supply means loss of control of the vehicle. It is, therefore, necessary and critical to develop a highly dependable power net to ensure power to these loads under all circumstances.

A backup system for automotive steer-by-wire, actuated by selective braking

In this paper we propose an alternate approach to improve steer-by-wire (SbW) reliability in which we utilize brake-actuated steering (BAS) as an independent secondary backup steering system. In SbW systems, component and module redundancy is the common approach used to maintain the steering function when a failure occurs. Unfortunately this adds a significant amount of complexity and cost and, what is more important, it is not possible to overcome unanticipated and common mode failures of the SbW system. BAS utilizes the torque generated by selective wheel braking and/or acceleration to actuate the steering mechanism. With this approach, if the primary steering system (SbW) fails uncovered or there is a common mode failure, the steering rack is decoupled from the primary steering actuator and the wheels are instead steered by the torque generated by application of asymmetric braking (or acceleration). BAS, as well as SbW, will be a heavy user of power electronics, electrical actuators, sensors and sophisticated control systems, many of which are already available from electronic stability systems (e.g., ESP), which are becoming more common in passenger cars. In this paper we detail the characteristics of the BAS system and provide the models necessary for designing appropriate power electronics and control systems.

On the Use of Behavioral Models for the Integrated Performance and Reliability Evaluation of Fault-Tolerant Avionics Systems

In this paper, the authors propose an integrated methodology for the reliability and performance analysis of fault-tolerant systems. This methodology uses a behavioral model of the system dynamics, similar to the ones used by control engineers when designing the control system, but incorporates additional artifacts to model the failure behavior of the system components. These artifacts include component failure modes (and associated failure rates) and how those failure modes affect the dynamic behavior of the component. The methodology bases the system evaluation on the analysis of the dynamics of the different configurations the system can reach after component failures occur. For each of the possible system configurations, a performance evaluation of its dynamic behavior is carried out to check whether its properties, e.g., accuracy, overshoot, or settling time, which are called performance metrics, meet system requirements. After all system configurations have been evaluated, the values of the performance metrics for each configuration and the probabilities of going from the nominal configuration (no component failures) to any other configuration are merged into a set of probabilistic measures of performance. To illustrate the methodology, and to introduce a tool that the authors developed in MATLAB/SIMULINKreg that supports this methodology, the authors present a case-study of a lateral-directional flight control system for a fighter aircraft

Constant amplitude voltage controlled variable bandwidth crystal filters

A transistorized crystal I.F. stage featuring variable bandwidth with constant midband amplitude has been developed. No mechanical tracking devices or mechanical bandwidth controls are employed: the constant amplitude feature is electronic, while the bandwidth is proportional to a D.C. control voltage. At narrow bandwidth the response curve is Gaussian with relatively steep skirts; as the bandwidth nears its maximum value the top of the curve first flattens, then exhibits a double peak at either side of midband frequency. The bandwidth of the 100KC stage actually constructed varied from 8 to 1400 cycles at the 3 DB points as the control voltage varied from 0 to 3 volts. The circuit exhibited a midband amplitude variation of less than 3% over the entire bandwidth range. Circuit operation has been analyzed both qualitatively and theoretically, and empirical results are given.