Peter D. Washabaugh

Modeling, identification, and feedback control of noise in an acoustic duct

Although active noise control has been a subject of interest for over 50 years, it has become feasible only with recent technological advances. This paper formulates the problem of noise control in a one-dimensional acoustic duct in a form that lends itself to the application of feedback control theory. In contrast to most of the literature on the subject which uses feedforward techniques, a feedback approach is used. Inconsistencies that appear in previous feedback control models are rectified, controllers are designed using precompensated linear quadratic Gaussian (LQG) synthesis, and experimental verification of the control designs is presented. The experimental results show a reduction of about 5-12 dB over a frequency range from 150-350 Hz.

A reconciliation of dynamic crack velocity and Rayleigh wave speed in isotropic brittle solids

Following earlier observations of multiple micro-crack formation accompanying crack propagation under dynamic conditions, the question regarding the discrepancy between the ‘theoretically anticipated’ maximal crack (Rayleigh wave) speed and those observed typically in amorphous, isotropic solids is examined experimentally. It is shown that if the production of these multiple micro-cracks ahead of the main fracture is suppressed by fabricating a material possessing a thin uniform region of vanishing intrinsic (molecular/atomic) material strength, the crack speed is materially increased to the point of approaching the Rayleigh wave speed. Moreover, it is also shown that the presence of small discreet flaws of sufficient spatial density similarly ‘weakens’ the material to produce fracture speeds comparable to the Rayleigh wave speed. One deduces, therefore, that for a single crack front the linearized theory of elastodynamics correctly predicts the dynamic crack propagation behavior of a solid with sufficiently low material strength.

Control of constrained nonlinear systems: a case study

Presents a Lyapunov function approach to the control of nonlinear systems that are subject to pointwise-in-time constraints on state and control. This approach is applied to an electromechanical system that serves as a prototype for the first mode of an electrostatically shaped membrane. Electrostatically shaped membranes have been proposed as mirrors and antennas since the early 1960s because they can be used as lightweight reflectors for radar, radio, and optics applications. Lightweight reflectors are in demand, for example, in spacecraft applications where launch weight is a significant constraint. A thin, electrically conducting membrane is formed into a desired shape by electrostatic forces that are controlled by varying the electrical potential between the membrane and an electrode mounted below it. Because the membrane is under lateral in-plane tension and a uniform normal stress due to the electrostatic potential, it assumes a paraboloidal shape for optics applications. Since the focal length can be varied by changing the gap distance, electrostatically controlled membranes are particularly suitable for adaptive optics applications. Small focal lengths needed for many applications can be achieved if the gap distance between the membrane and the fixed plate is made sufficiently small.

A fully integrated high-efficiency peristaltic 18-stage gas micropump with active microvalves

We report the design, fabrication, and test results of a fully integrated peristaltic 18-stage gas micropump consisting of 18 serially-connected pumping chambers and 19 microvalves. The peristaltic micropump achieves (1) high-pressure differentials by accumulating small pressure differentials that are evenly distributed across the individual stages using a low-compression multi-stage design, (2) high flow rate by operating pumping membranes at fluidic resonance and high frequency (>10 kHz), and (3) gas flow regulation by actively controlling the open/close timing of microvalves for either high flow or high pressure. The 18-stage micropump includes several new innovations, such as checkerboard microvalves, dual drive electrodes, and dual pumping chambers to achieve efficient electrostatic pumping. The fabricated 18-statge pump has produced an air flow rate of ~4.0 seem and maximum pressure differential of-17.5 kPa with a total power of only ~57 mW. It has a total package volume of 25.1 x 19.1 x 1 mm3 and each individual membrane is only 2x2 mm2.

Solus: an autonomous aircraft for flight control and trajectory planning research

The University of Michigan has developed a fixed-wing model aircraft (Solus) with an embedded control system to develop and demonstrate UAV technology. The analytical objective of this project is the development of intelligent flight control and trajectory planning techniques, focusing on automated fault detection and recovery. Our experimental objective is to implement and evaluate these techniques on Solus for a variety of mission and fault scenarios.

A Micropump-Driven High-Speed MEMS Gas Chromatography System

We report (1) the integration of the first functioning MEMS gas chromatography system ( muGC) featuring a micropump, a micro-column, and a micro-chemiresistor sensor array; and (2) experimental demonstration of the state-of-the-art multi-vapor gas separation and detection. In particular, we report the best GC analysis data from the first micropump-driven muGC system to date: the separation and detection of 11 volatile organic compounds (VOC)s within only 78 seconds while consuming only 15.1 mW of power within a small volume of 0.5 cc. We also report the use of temperature programming (TP) of the separation column for fast analysis, which shortened the analysis time from 78 seconds to 24 seconds while maintaining gas analysis resolution.

An Integrated Combustor-Thermoelectric Micro Power Generator

This paper reports a micromachined thermoelectric (TE) power generator based on catalytic combustion in a micromachined combustion chamber. The 2mm×8mm×0.5mm combustion chamber is covered by a dielectric diaphragm supported on a silicon substrate that is bonded to a glass substrate. The generator integrates polysilicon-Pt thermopiles on the diaphragm to take advantage of high combustion temperature as well as excellent thermal isolation of the diaphragm. Combustion of hydrogen and air mixture is self-sustained inside the combustor after ignition and output power level of ∼1µW/thermocouple has been obtained. Temperature measurements indicate that power level of 10µW/thermocouple could be achieved by slight geometric modification to fully exploit the high temperature gradient of combustion on diaphragm.

Flow structure and performance of axisymmetric synthetic jets

ABSTRACT Experimental analysis is presented of the flow structure and performance of axisymmetric synthetic jets. We report direct thrust and Particle Image Velocimetry (PIV) measurements at varying amplitude and frequency for Reynolds numbers in the range 200-2200. It is shown that the jet performance is determined by the flow length, L, defined as the length of fluid ejected during the output stroke of the synthetic jet. Two flow regimes are identified. At small flow lengths L/D ~3, the thrust equals the momentum flux ejected during the output stroke, and is proportional to L 2 . The entrainment rate of the synthetic jet was measured and found comparable to that of conventional axisymmetric turbulent jets. The mean and time-resolved flow structure in the near field of the synthetic jet varies with flow length. At small flow lengths, vortex rings form close to the orifice and loose some of the vorticity during the input stroke. At large flow lengths, vortex rings with some trailing vorticity form and move away from the orifice thus avoiding re-ingestion of vorticity during the input stroke. The amount of trailing vorticity does not affect the thrust produced by the synthetic jet.

Bi-directional electrostatic microspeaker with two large-deflection flexible membranes actuated by single/dual electrodes

This paper reports a bi-directional electrostatic microspeaker that has three main features: (1) a thin and flexible Parylene membrane for large deflection (>7.5 mum), thus, large acoustic pressure generation, (2) dual electrodes on both sides of the membrane to pull it in two opposite directions and overcome the weak restoration force of the polymer membrane, thus allowing the use of flexible membranes as a high-speed vibration element, and (3) bi-directional (forward/backward) packaged structures for symmetric and loud acoustic sounds of 113.4 dB (SPL: sound pressure level) at 7.68 kHz when actuated using a single electrode, and 98.8 dB (SPL) at 13.81 kHz when actuated using two electrodes at a distance of 1 cm from the microspeaker. By actuating two membranes, the microspeaker also produced symmetric sound pressures at both the front and back sides of the device. The generated sound frequency range is from 1 kHz (measurement cut-off frequency) to 25 kHz, and the sound level was reasonably uniform over a wide frequency range. The fabricated microspeaker has an active area footprint of 3 times 5 mm2, while the total packaged device (including electrical pads area of 3.5 times3.5 mm2) has a volume of 13 times 16 times 1 mm3. The micropump is built on two bonded silicon wafers and incorporates a flexible polymer, Parylene, membrane as the actuation membrane

Micro combustion-thermionic power generation: feasibility, design and initial results

This paper reports for the first time the design, development and initial results from a micro power generator based on thermionic (TI) emission using combustion. Several major results are achieved. Thin-films of BaO are integrated with Si to form the emitter and collector of a TI converter. Field emission and TI emission currents are successfully measured from this converter. Thick SiO/sub 2/ rings are formed to achieve excellent thermal isolation. An integrated process to fabricate micromachined TI power generators is developed. Combustion has been achieved in the micromachined combustor. And power generation of /spl sim/1 /spl mu/W has been measured in emitter-collector subsystem testing. Improvement of the device and testing is needed for achieving system-level power generation from combustion.