Principal Investigator: Fred K. Forster (Mechanical Engineering) and Martin A. Afromowitz
Sponsor: Washington Technology Center and MEMStek Products, LLC
Abstract: We have been pursuing the analysis, design, fabrication and testing of micro-fluidic pumping systems. Whereas the most effective pumping mechanism in low-Reynolds number flow relies on positive displacement, such as a moving membrane, without valves the fluid will be forced equally in both the input and output directions. Valves for such micro-pumps have already been demonstrated by others which utilize techniques ranging from passive flapping membranes to complex thermally-controlled active devices. Our research is directed specifically at the development of valves that have no moving parts. These valves rely upon an intrinsic fluidic diodicity created by their non-reciprocal forward vs. backward flow geometry. That is, a larger flow resistance is encountered in the backward flow direction than in the forward flow direction.
Figure 1. A scanning electron microscope photograph of one of our designs, which curiously is an adaptation of a design patented by Nicholas Tesla, the famous electrical engineer and inventor, in 1920.
The advantages of such a valve are obvious. First, no-moving-parts valves are simple and do not require special control electronics. Secondly, since all the former valve designs include valve seats, where two mating surfaces meet to close off a channel, they suffer from variable leakage and outright failure as the valve seat becomes fouled or dirty. No-moving-parts valves do not have a valve seat. And thirdly, any valve with a valve seat cannot be used successfully in fluids that contain particulates (such as inks), or especially cells (such as blood). These fluids represent a large fraction of the applications proposed for these devices.
The areas of emphasis of our work on these devices includes improved methods of fabrication, characterization of the valves, and design of integrated sensors to permit the measurement and control of pressures and flow rates
http://lettuce.me.washington.edu/~micropump
Principal Investigator: Martin A. Afromowitz
Sponsor: Center for Process Analytical Chemistry
Abstract: Optical fibers have been developed for many interesting sensor applications. The most sensitive detection methods involve interferometric devices, such as the Mach-Zehnder Interferometer (MZI), in which slight changes in the effective pathlength of light propagating in one fiber can cause enormous changes in the amplitude of two such beams interfering with each other. The main difficulty, in fact, is that these methods are so sensitive that slight changes in the temperature in the laboratory can produce enormous "noise" signals.
We are attempting to fabricate an integrated optic MZI chemical sensor device, incorporating waveguide channels created on a glass-covered silicon substrate, that will have the required sensitivity, but not be susceptible to environmental temperature effects. This integrated optical device is expected to outperform fiber-based MZI designs for several compelling reasons. In general, the entire length of each optical arm, from the first beam splitter to the detector, is sensitive to environmental effects. In fiber-optic MZIs, only a short length of one arm is treated to be sensitive to the chemistry of interest. The rest of the MZI arm picks up environmental noise. In the proposed integrated optical device, almost the entire length of the detector arm will be made chemically sensitive. Since the overall MZI length is reduced from typically a meter down to a centimeter, environmental noise will constitute a much smaller fraction of the output signal. The arms of the MZI cannot move with respect to one another in the integrated optical device. Thus, differential strains from fiber movement, microbending, stretching, etc., that plague fiber-based MZI structures will be eliminated. The waveguides of the integrated optic MZI are embedded below the surface of a glass-covered silicon chip. Therefore, they are rendered immune to humidity effects that can swell the buffer layer of optical fiber MZI arms, causing phase shifts from the induced strain. The chip also will tend to reduce rapid environmentally-induced temperature fluctuations between the arms.
A unique three-arm configuration is proposed for this design, and will force environmentally-induced thermal gradients to produce a different output pattern than the chemically-induced calorimetric or refractive-index response of the sensor. To our knowledge, this feature has never been investigated before. Finally, the potential for developing this device into an integrated array of chemical detectors is very attractive. As a generic micro-chemical sensor, any chemically-sensitive patch that either produces heat or changes the index of refraction can be incorporated onto the MZI. The exquisite sensitivity of the MZI to thermal or refractive index imbalance between the arms of the interferometer suggests that once we control the effects of environmental noise, as proposed herein, a wide variety of chemistries can be sensed with excellent quantitative results.
Principal Investigator: Martin A. Afromowitz
Sponsor: Senmed Medical Systems, Defense Advanced Research Projects Agency
Abstract: In collaboration with faculty in the Center for Bioengineering and the Departments of Mechanical Engineering and Laboratory Medicine, we are working on the design of a series of optic-based devices that will be used for the clinical analysis of microliter samples of blood. This project, known as "The Portable Stat Lab," seeks to miniaturize the apparatus used for chemical and physical analysis of blood by orders of magnitude, thus permitting critical analyses to be done in med-evac helicopters, in ambulances, and/or at accident sites if necessary, instead of requiring the patient to be brought to the hospital first.
Two paths are being pursued:
1) Designing devices that will permit the currently accepted methods to be used, but in miniature form, and
2) Inventing entirely new methods that are made possible because of the miniaturization.
Our part of this large interdisciplinary effort involves the design and development of micro-fluidic, micro-optical modules in which whole blood (possibly with a variety of added reagents) flows through micro-channels on a chip, and optical absorption, fluorescence or scattering measurements indicate the important clinical parameters, such as pH, oxygen saturation, ionic concentrations, hematocrit, white blood cell count, etc.
The advantages of working in micro-channels can be shown easily for the case of quantitative measurement of the concentrations of the various forms of hemoglobin (Hb) found in blood. In the clinical laboratory, this measurement is made using blood whose cells have been lysed, that is, broken up either by ultrasonic agitation or addition of strong detergents. The hemoglobin in the red blood cells then colors the plasma, and absorption spectra on this largely homogeneous sample reveal the concentrations of oxygenated and de-oxygenated Hb. The cells are lysed so that optical scattering from the cells will not interfere with the absorption measurement. We have shown that accurate measurements of Hb can be made in unlysed whole blood, as long as the transmission cell is on the order of 50 um in thickness. Such transmission cells can be easily fabricated using silicon micromachining techniques.
We are currently developing a technique for measuring the fluorescence of microscopic beads that are mixed with whole blood and forced to flow single-file through microchannels. These beads contain a pH-sensitive dye on their surface, whose fluorescent signal changes with the pH of the blood plasma. Thus, the pH of a whole blood sample of a few microliters can be ascertained, again without lysis or centrifugation of the blood sample. Other beads, containing dyes sensitive to other chemicals of interest in the blood, may also be added to the sample, and simultaneous measurements of an array of chemical constituents of the blood can be made by this technique.
Principal Investigator: Martin A. Afromowitz and Les Atlas
Sponsor: Washington Technology Center and Combustion Specialists, Inc.
Abstract: We have developed improved techniques for measuring the temperature of the gases inside large utility boilers (steam plants used to generate 600 MW of electrical power). The temperature of the boiler gases ranges upwards of 1700deg. C, and is an important parameter in the control of the entire system. The measurement technique relies upon the fact that the speed of sound in an ideal gas is proportional to the square root of the absolute temperature of the gas. Thus, whereas at room temperature and standard atmospheric pressure, sound travels at 346 m/sec in air, the velocity increases to 887 m/sec at 1700deg. C. By sending a sharp pulse of sound across the 40 foot expanse of the boiler and measuring the time of flight, one can infer the average temperature along the sound path.
A further enhancement that we are planning to investigate involves the use of many such acoustic paths, intersecting each other in a grid pattern. By analyzing the sound propagation along all the paths, one can infer the temperature distribution over the whole space probed by the different paths. This acoustic tomography approach is very useful for finding hot and cold spots in the boiler and for adjusting the fuel delivery for optimum efficiency of heat transfer to the steam.
Principal Investigator: Peter O. Lauritzen
Sponsor: National Science Foundation-Center for the Design of Analog Integrated Circuits (CDADIC) University/Industry Research Center
Abstract: Models for circuit simulation with high accuracy and fast simulation times are being developed for the family of semiconductor devices used in power electronics. Models already developed include: step-recovery, P-i-N, and P-nu-N diode models; MOS capacitor; power MOSFET; BJT, SCR and GTO models. Models have been developed with two levels of complexity: basic models which are relatively simple for general circuit simulation and more complex but highly accurate models which give precise waveform accuracy. With this project now in its eighth year, many of its models are now available on commercial circuit simulators.
The project's activities are now shifting to the power devices used in power ICs. Currently, a lateral DMOSFET model is being developed for the output drivers in power and RF IC designs.
High voltage and current laboratory test facilities provide device measurement, characterization and parameter extraction capability.
Graduate students working on semiconductor device modeling must be knowledgeable in three fields: semiconductor device physics, circuit applications, and principles of circuit simulation.
References:
C.L. Ma and P.O. Lauritzen, "A Simple Power Diode Model with Forward and Reverse Recovery,"IEEE Transactions on Power Electronics, Vol. 8, No. 4, October 1993.
I. Budihardjo, and P. O. Lauritzen, "The Lumped Charge Power MOSFET Model, Including Parameter Extraction," IEEE Transactions On Power Electronics, Vol. 10, No. 2, May 1995
Cliff L. Ma, and P. O. Lauritzen, "A Physics-Based GTO Model for Circuit Simulation," IEEE PESC Conf. Proceedings, Atlanta, GA, June 18-22, 1995
K.Y.Wong, P.O. Lauritzen, S.S. Venkata, A. Sundaram, and R. Adapa, "An SCR/GTO Model Designed for a Basic Level of Model Performance," IEEE IAS Annual Meeting, October 1996
C.L.Ma, P.O.Lauritzen, and J.Sigg, "Modeling of Power Diodes with the Lumped-Charge Modeling Technique," IEEE Transactions on Power Electronics, Vol. 12, No. 3, May 1997
I. Budihardjo, P. O. Lauritzen, and H.A. Mantooth, "Performance Requirements for Power MOSFET Models," IEEE Transactions on Power Electronics, Vol. 12, No. 1, January 1997
http://www.eecs.wsu.edu/~cdadic/index.html
Design, Test and Reliability Research Laboratory
Pricipal Investigator: Mani Soma
Sponsor: Semiconductor Research Corporation
Abstract: This project seeks to build a cohesive built-in self-test (BIST) system for analog and mixed-signal integrated circuits designed in CMOS, bipolar, or the combined BiCMOS technologies.
References:
M. Soma, "Challenges in analog and mixed-signal fault models," IEEE Circuits & Devices Magazine, Vol. 12, No. 1, pp. 16-20, Jan. 1996.
A. Charoenrook and M. Soma, "A fault diagnosis technique for flash ADCs," IEEE Trans. Circuits & Systems II, Vol. 43, No. 6, pp. 445-458, June 1996.
M. Soma, "Automatic test generation algorithms for analog circuits," IEE Proceedings Special Issue on Mixed Signal & Analogue IC Test Technology, Vol. 143, No. 6, pp. 366-373, December 1996.
G. Devarayanadurg and M. Soma, "Dynamic test signal design for analog Ics," in Proc. IEEE International Conf. on CAD, November 5-9, 1995, San Jose, CA.
G. Devarayanadurg, P. Goteti, and M. Soma, "Hierarchy-based statistical fault simulation of mixed-signal ICs," in Proc. IEEE International Test Conf., October 22-24, 1996, Washington, DC.
P. Goteti, G. Devarayanadurg, and M. Soma, "DFT for embedded charge-pump PLL systems incorporating IEEE 1149.1," in Proc. IEEE Custom Integrated Circuits Conf., May 1997, Santa Clara, CA.
Summer 1997: http://www.ee.washington.edu/mad/madtest.html
Design, Test and Reliability Research Laboratory
Principal Investigator: Mani Soma
Sponsor: Defense Advanced Research Projects Agency/Boeing
Abstract: This project is a part of the Mixed-signal Test Consortium involving the University of Washington, Boeing, Integrated Measurement Systems, Cadence, and Georgia Institute of Technology. The UW research program focuses on the design of a control/acquisition IC for current-based analog scan, the design of building blocks for stimulus and measurement on MCM, and the development of testability analysis tools for analog circuits.
References:
M. Soma, "Mixed-signal design-for-test techniques: a tutorial," IEEE Int. Mixed-signal Testing Workshop, May 15 - 18, 1996, Quebec City, Canada.
M. Soma, "Review of IEEE P1149.4 mixed-signal test bus standard," in Proc. IEEE Northcon., November 11-14, 1996, Seattle, WA.
M. Katoozi, H. Kutz, M. Soma, and S. Huynh, "Strategies and circuits for test access in mixed-signal MCMs," IEEE International MCM Conference, February 5-7, 1997, Santa Cruz, CA.
Summer 1997: http://www.ee.washington.edu/mad/madtest.html
Return to Index Page. Go forward to Mechatronics and Intelligent Control
Updated February 5, 1999