William T. Smith

Error bound for reduced system model by Pade approximation via the Lanczos process

Recently, there has been a great deal of interest in using the Pade Via Lanczos (PVL) technique to analyze the transfer functions and impulse responses of large-scale linear circuits. In this paper, a matrix-based derivation of the error between the original circuit transfer function and the reduced-order transfer function generated using the PVL technique is presented. This error measure may be used for the development of an automated termination of the Lanczos process in the PVL technique and achieve the desired accuracy of the approximate transfer function. PVL coupled with such an error bound will be referred to as the PVL-WEB algorithm.

An approximation of the radiation integral for distorted reflector antennas using surface-error decomposition

The physical optics/aperture integration (PO/AI) formulation is often used to analyze the radiation patterns of reflector antennas. In this study, the PO/AI radiation integrals for distorted reflector antennas are addressed. The surface error of the antennas is approximated by a series of surface expansion functions. The radiation integral is decomposed into a series of radiation-type integrals, each of which corresponds to one of the surface expansion functions. Each of these radiation-type integrals is then weighted by amplitude coefficients. The advantage of performing the decomposition is that each of the radiation-type integrals can be computed and the pattern data stored. The computation of the pattern for a distorted reflector antenna with a changing error profile is performed by recalling the pattern data for each perturbation term and weighting it with the amplitude coefficient. This facilitates rapid evaluation of the radiation integral in cases where the error profile is changing (for example, time-varying errors). The superposition of integrals presented in this paper was shown to be valid for surface-error profiles up to 0.1 /spl lambda/ rms amplitude.

BIG BLUE: high-altitude UAV demonstrator of Mars airplane technology

BIG BLUE (baseline inflatable-wing glider, balloon-launched unmanned experiment) is a flight experiment envisioned, designed, built, and flown primarily by undergraduate students in the College of Engineering at the University of Kentucky. BIG BLUE was conceived as a demonstration of unique inflatable wing technologies with potential for application for Mars airplanes. On May 3, 2003, BIG BLUE achieved the first-ever deployment and curing of UV hardening inflatable wings and reached an altitude of 27.1km (89,000ft). BIG BLUE II was launched successfully on May 1, 2004 with a second-generation optimized wing design. The wings were deployed and cured to an excellent symmetric flying shape from a flight ready fuselage with an autonomous autopilot, sensor and communication systems. To date, over 100 students have participated directly in the design, fabrication and testing of BIG BLUE, exposing them to the challenge and excitement of aerospace careers. BIG BLUE is supported by the NASA Workforce Development Program which has objectives to attract, motivate, and prepare students for technological careers in support of NASA, its missions, and its research efforts. BIG BLUE provides multidisciplinary experiential learning directed specifically toward entering the aerospace workforce

A pattern synthesis technique for array feeds to improve radiation performance of large distorted reflector antennas

Technologies exist for construction of antennas with adaptive surfaces that can compensate for many of the larger distortions caused by thermal and gravitational forces. However, as the frequency and size of the reflectors increase, the subtle surface errors become significant and degrade the overall electromagnetic performance. Electronic compensation through an adaptive feed array offers a means for mitigation of surface distortion effects. A pattern synthesis approach for electromagnetic compensation of surface error is presented. The pattern synthesis approach uses a localized algorithm in which pattern corrections are directed toward specific portions of the pattern requiring improvement. The pattern synthesis techniques uses radiation pattern data to perform the compensation. >

BIG BLUE II: Mars Aircraft Prototype with Inflatable-Rigidizable Wings

The present paper presents work on developing and flight testing a Mars prototype aircraft using inflatable-rigidizable wings under the NASA Workforce Development program. Undergraduate student teams have developed a test vehicle to determine the feasibility of using inflatable-rigidizable wings in extra-terrestrial missions. The wings are constructed of an outer composite layer impregnated with a UV curable resin and an inner inflatable bladder. The wings are stowed in the fuselage, deploy when inflated, and rigidize with exposure to UV radiation; pressurization is not required after rigidization. Vehicle, wing and avionics designs are discussed and results from low and high altitude test flights are presented. The project culminated in a successful high altitude flight test with deployment and rigidization of the wing under Mars like conditions.

Prediction of anechoic chamber radiated emissions measurements through use of empirically-derived transfer functions and laboratory common-mode current measurements

In this study common-mode current measurements made in a laboratory (without an anechoic chamber) were correlated with radiated emissions measurements (made in an anechoic chamber) over a broad frequency range. The goal was to evaluate the use of current measurements as an alternative to avoid repeated testing of an electronic device in an anechoic chamber while improvements are made to the device during the design phase. Empirical transfer functions based on current and field measurements made in an anechoic chamber are used with laboratory (nonanechoic chamber) measured common-mode current data for prediction of radiated emissions. Comparisons are made between the fields data measured in an anechoic chamber and the predicted fields data based on the laboratory common-mode current measurements.

Using partial element equivalent circuit full wave analysis and Pade Via Lanczos to numerically simulate EMC problems

In this study, an approach for numerical modeling of transmission line-type interconnects is proposed. In order to achieve the accuracy of a full wave technique, partial element equivalent circuit (PEEC) analysis is used to model the interconnects. PEEC models do not require transmission lines to be parallel and nonuniform geometrical details can be included. PEEC models for electrically large interconnects, however, generate very large system matrices. Circuit simulations can be overly time consuming if conventional solution algorithms are used. In this study, the solutions are developed using a computationally efficient Pade Via Lanczos (PVL) algorithm. The PVL algorithm is an approximate method for extracting the dominant poles and residues of the system response. Once the poles and residues have been determined, it is straightforward to evaluate the time or frequency domain responses. In this paper, the particular PEEC modeling approach used to form the system matrices is outlined. A PVL algorithm which incorporates a measure of the error between the actual system response and the approximate system response is used to evaluate the PEEC models. PEEC-PVL simulations of interconnect models are compared to other analysis techniques such as Spice and AWE.

Crosstalk modeling for automotive harnesses

Automotive wiring harnesses are used to transmit a wide variety of signals which range from low level control signals to high current signals for DC motors. Crosstalk on the cable harnesses is a potential problem for these typically tightly-packed cable bundles. Accurate computer modeling of the crosstalk allows for identification of potential crosstalk problems early in the design process. Decreased harness design time can be achieved by reducing the number of prototype harnesses constructed and the corresponding empirical testing. This translates into a direct cost savings for a given harness design. In this study, crosstalk modeling for an automotive wiring harness is evaluated. In general, harness data exist within a CAE/CAD vehicle layout tool. Information is usually not available, however, for the distribution of wires within a cross section of the harness. Assumptions then have to be made concerning the distribution of wires within a harness cross section. The assumptions made during this study are outlined and their impact on the predictions is evaluated. Computed results are presented and are compared to experimental data from prototype harnesses.<<ETX>>

A Low-Cost Control System for a High-Altitude UAV

The BIG BLUE project at the University of Kentucky is a test bed UAV for Mars airplane technology. A major focus of the BIG BLUE effort has been the development of a low-cost and light-weight avionics, control, and communication system to manage the aircraft and correspond with ground stations. BIG BLUE I, launched in May 2003, achieved the first successful deployment of inflatable/rigidizable wings at altitude. BIG BLUE II, launched in May 2004, had a flight-ready fuselage and control system. This paper describes the BIG BLUE project detailing the design and implementation of the avionics, control, and communication system

Evolution of an Avionics System for a High-Altitude UAV

The UAV Research Group at the University of Kentucky is developing a test-bed UAV platform for Mars airplane technology, dubbed BIG BLUE. A major focus of the BIG BLUE effort has been the development of a low-cost and light-weight avionics, control, and communication system to manage the aircraft and relay data between the UAV and the ground stations during long-range high-altitude missions. BIG BLUE I, launched in May 2003, achieved the first successful deployment of inflatable/rigidizable wings at altitude. BIG BLUE II, launched in May 2004, had a flight-ready fuselage and control system. BIG BLUE 3 employed a new wing design and an enhanced avionics suite. This paper discusses the history of the BIG BLUE avionics, control, and communication systems, as well as the continuing design changes for future phases of the project.