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Publications of Jordan M. Berg

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Refereed Journal Articles

  1. D. Aurongzeb, M. Holtz, J. M. Berg, A. Chandolu, and H. Temkin, “The influence of interface roughness on electrical transport in nanoscale metallic multilayers,” Journal of Applied Physics, Vol. 98, No. 6, Article No. 063708, Sep 2005.
  2. D. H. S. Maithripala, B. D. Kawade, J. M. Berg, and W. P. Dayawansa, “A General Modelling and Control Framework for Electrostatically Actuated Mechanical Systems,” International Journal of Robust and Nonlinear Control, Special Issue on Control at the Nanoscale, Vol. 15, pp. 839–857, 2005 (Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/rnc.1027).
  3. S. Bhattacharya, A. Datta, J. M. Berg, and S. Gangopadhyay, “Studies on Surface Wettability of Poly (Dimethyl) Siloxane (PDMS) and Glass Under Oxygen-Plasma Treatment and Correlation with Bond Strength, Journal of Microelectromechanical Systems, Vol. 14, No. 3, pp. 590–597, June 2005.
  4. D. H. S. Maithripala, W. P. Dayawansa, J. M. Berg, “Intrinsic Observer-Based Stabilization For Simple Mechanical Systems on Lie Groups,” SIAM Journal of Control and Optimization, Vol. 44, No. 5, pp. 1691–1711, 2005.
  5. D. H. S. Maithripala, J. M. Berg, W. P. Dayawansa, “Control of an Electrostatic MEMS Using Static and Dynamic Output Feedback,” ASME Journal of Dynamic Systems, Measurement, and Control, Vol. 127, No. 3, pp. 443–450, September 2005.
  6. J.F. Cárdenas-García, S. Ekwaro-Osire, J.M. Berg, and W.H. Wilson, “Nonlinear Least Squares Solution to the Moiré Hole Method Problem in Orthotropic Materials, Part I: Residual Stresses,” Experimental Mechanics, Vol. 45, No. 4, pp. 301–313, August 2005.
  7. J.F. Cárdenas-García, S. Ekwaro-Osire, J.M. Berg, and W.H. Wilson, “Nonlinear Least Squares Solution to the Moiré Hole Method Problem in Orthotropic Materials, Part II: Material Elastic Constants,” Experimental Mechanics, Vol. 45, No. 4, pp. 314–324, August 2005.
  8. I. Ahmad, V. Kasisomayajula, M. Holtz, J. M. Berg, S. R. Kurtz, C. P. Tigges, A. A. Allerman, and A. G. Baca, "Self-heating study of an AlGaN/GaN-based heterostructure field effect transistor using ultraviolet micro-Raman scattering," Applied Physics Letters, to appear.

    ABSTRACT: We report micro-Raman studies of self-heating in an AlGaN/GaN heterostructure field effect transistor using below (visible 488.0 nm) and near (UV 363.8 nm) GaN bandgap excitation. The shallow penetration depth of the UV light allows us to measure temperature rise (ΔT) in the two-dimensional electron gas (2DEG) region of the device between drain and source. Visible light gives the average ΔT in the GaN layer, and that of the SiC substrate, at the same lateral position. Combined, we depth profile the self-heating. Measured ΔT in the 2DEG is consistently over twice the average GaN-layer value. Electrical and thermal transport properties are simulated. We identify a hotspot, located at the gate edge in the 2DEG, as the prevailing factor in the self-heating.

  9. L. Grave de Peralta, A. A. Bernoussi, V. Gorbounov, J. M. Berg, and H. Temkin, "Control of center wavelength in reflective arrayed waveguide grating multiplexers," IEEE Journal of Quantum Devices, Vol. 40, No. 12, pp. 1725-1732, December, 2004.

    ABSTRACT: A new approach to compensate for the channel-wavelength shift due to fabrication errors and thermal effects in arrayed waveguide-grating multiplexers is described. The method combines a silica-based reflective multiplexer with a composite mirror made of materials with different coefficients of thermal expansion. Differential thermal expansion of the mirror assembly rotates its reflecting surface at constant rate with temperature, compensating for the temperature-induced changes in the efective index of refraction of the waveguide material. The use of an external mirror also allows for wavelength trimming that centers the channel wavelength at the standard grid. The channel wavelength can be tuned by up to 2 nm without increased insertion loss or changes in the channel-to-channel separation. The channel wavelength shifts linearly with the external mirror angle at a rate of ~66 nm/deg in excellent agreement with simulation. A finite element analysis of the composite mirror shows negligible deformation of the reflecting surface over a wide range of temperatures, in good agreement with experimental results.

  10. D. H. S. Maithripala, J. M. Berg, W. P. Dayawansa, "Control of an Electrostatic MEMS Using Static and Dynamic Output Feedback," ASME Journal of Dynamic Systems, Measurement, and Control, to appear.

    ABSTRACT: This paper examines control strategies for electrostatically-actuated MEMS, with the goals of using feasible measurements to eliminate the pull-in bifurcation, robustly stabilize any desired operating point in the capacitive gap, decrease settling time, and reduce overshoot. We show that input-output linearization, passivity-based design, and the theory of port-controlled Hamiltonian systems lead naturally to static output feedback of device charge. This formalizes and extends previously reported results from the MEMS literature. Further analysis suggests that significantly improving transient behavior in lightly damped MEMS requires dynamic estimation of electrode velocity. We implement output-feedback control using a reduced-order nonlinear observer. Simulations predict greatly improved transient behavior, and large reductions in control voltage.

  11. L. Menon, S. Patibandla, K. Bhargava Ram, S.I. Shkuratov, D. Aurongzeb, J. Yun, M. Holtz, J. Berg and H. Temkin, "Ignition Studies of Al/Fe2O3 Novel Energetic Nanocomposites," Applied Physics Letters, Vol. 84, No. 23, pp. 4735-4737, June 2004.

    ABSTRACT: We demonstrate a novel approach for preparing energetic nanocomposites which undergo an exothermic reaction when ignited at moderate temperature. The nanocomposites are a mixture of fuel and oxidizer materials where the oxidizer component (Fe2O3) is in the form of an array of nanowires embedded in the fuel component (Al), which is in the form of a thin film. Our approach allows for a very high packing density of the nanocomposites, precise control of oxidizer-fuel sizes at the nanoscale level, and direct contact between oxidizer and fuel. Ignition is demonstrated using an electrical heating wire. We find that the flame temperature does not depend on the ignition temperature.

  12. P. Kuban, J. M. Berg, P. Dasgupta, "Fast Durable Microfabricated Humidity Sensors," Analytical Chemistry, Vol. 76, No. 9, pp. 2561-2567, May, 2004.

    ABSTRACT: We describe a durable microfabricated humidity sensor made of interdigitated Rhodium electrodes on a silicon substrate covered with a sensing film of Nafion® perfluorosulfonate ionomer. Rhodium electrodes are much less prone to oxidative degradation compared to gold electrodes and thus exhibit excellent long term response stability. When interrogated with a low amplitude (± 1V) square wave, even gold sensors exhibit stable response over several months; however, this mode of interrogation cannot provide fast response. Rhodium deposition on the microsensors is much more difficult than that of gold but crack-free Rh deposits were successfully attained by adaptation of pulsed electroplating techniques. At excitation voltages >2 V DC, the Rh sensors respond to moisture with a 10-90% rise and fall times of 30-50 ms. These are the fastest microfabricated water vapor sensors reported to date. We demonstrate applications as a breath monitor. Such sensors should also be of utility in atmospheric eddy measurements. Short-term repeatability is better than 0.59% RSD (n=7).

  13. D. Aurongzeb, M. Holtz, M. Daugherty, J. M. Berg, A. Chandolu, J. Yun, and H. Temkin, "Influence of nanocrystal growth kinetics on interface roughness in nickel-aluminum multilayers," Applied Physics Letters, Vol. 83, No. 26, pp. 5437-5439, December, 2003.

    ABSTRACT: We report a study of the layer morphology of Ni/Al multilayer structures, with 50 nm bilayer period, as-deposited and following 10 min anneals up through the melting temperature of Al. X-ray reflectivity measurement of the as-deposited film shows interference fringes, characteristic of a well-defined multilayer stack, with ~ 1nm interface roughness. Over a narrow anneal temperature range between 360 and 500 C these fringes diminish in amplitude and disappear, indicating elevated interface roughening. However, fringes are observed for anneal temperatures both below and above this range, indicating the presence of well-defined layers with smooth interfaces. A model, in which nanocrystal domains of intermetallic nickel aluminides form at the interfaces, is developed to quantify the annealing induced interface roughness. This model is found to be in excellent agreement with the experimental results.

  14. P. Kuban, J. M. Berg, and P. Dasgupta, "Vertically Stratified Flows in Microchannels. Computational Simulations and Applications to Solvent Extraction and Ion Exchange," Analytical Chemistry, Vol. 75 No. 14, pp. 3549-3556, July, 2003.

    ABSTRACT: In this paper we describe the conditions under which two immiscible fluids flow atop one another (viewed perpendicular to the plane on which the channel is inscribed) in a shallow microfluidic channel. First, we predict the behavior of a two-phase system using fluid dynamic simulations with water-butanol and water-chloroform as model systems. We numerically model effect of various physical parameters, such as interfacial surface tension, density, viscosity, wall contact angle and flow velocity on the type of flow observed and find that interfacial surface tension and viscosity are the parameters responsible for formation of vertically stratified, side-by-side or segmented flows. As predicted by numerical simulations, water-chloroform system never assumes a vertically stratified configuration, while water-butanol system does when the two liquids flow at sufficiently high flow velocities. In actual experiments, we test conditions under which potentially useful two-phase systems form stable vertically stratified flows. We also demonstrate that compared to side-by-side flow schemes, shorter diffusion paths are achievable and thus the system can be used at higher flow rates to obtain the same performance. We then apply such findings to practical analytical problems such as solvent extraction and ion exchange.

  15. J. M. Berg, R. Anderson, M. Anaya, B. Lahlouh, T. Dallas and M. Holtz, "A Two-Stage Discrete Peristaltic Micropump," Sensors and Actuators A, Vol. 104, No. 1, pp. 6-10, 2003.

    ABSTRACT: We demonstrate a discrete, two-stage peristaltic micropump for applications in microfluidics. Prototypes are fabricated in polydimethylsiloxane (PDMS) with water as the working fluid. Off-wafer compressed nitrogen gas provides the actuation energy. The device may be operated in three- or two-stage modes for direct comparison. We show that two-stage pumps have comparable flow rates to the three-stage counterparts, and produce ~ 2/3 the static head. Our results suggest that two-stage pumps may be a viable choice under low backpressure conditions where available on-chip area or the number of external connections is limited.

  16. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "Loss of Structurally Stable Regulation Implies Loss of Stability," IEEE Transactions on Automatic Control, Vol. 48, No. 3, pp. 483-486, 2003.

    ABSTRACT: We refer to systems violating the conditions for structurally stable regulation as critical. At least one of the following must fail at a critical system: asymptotic rejection of the exogenous system, stabilization of the closed-loop system, or structural stability. Exactly which, has not been explicitly addressed. We show that any structurally stable regulator is necessarily destabilizing when applied to a critical system, that destabilization is linked to structural stability, and we characterize the resulting unstable poles.

  17. P. K. Dasgupta, K. Surowiec and J. Berg, "Flow of Multiple Fluids in a Small Dimension," Analytical Chemistry, Vol. 74, No. 7, pp. 208A-213A, 2002. (Cover Article)

    ABSTRACT: Planar multi-fluid flows with a very small depth can be used to generate a variety of interesting patterns. This paper looks at some examples, and considers potential applications and devices based on these principles.

  18. J. M. Berg and N. Zhou, "Shape-Based Parameter Estimation and Design of Curve Evolution Processes with Application to Plasma Etching," IEEE Transactions on Automatic Control, Vol. 46, No. 12, pp. 1862-1873, December, 2001.

    ABSTRACT: This paper considers the problem of determining a finite number of discrete parameters appearing in a nonlinear partial differential equation describing a curve evolution process. The method is applied to the plasma etching of thin films for semiconductor manufacturing. Results are obtained within the mathematical framework of level set methods. Here, the evolution of the curve under study is captured through the evolution of a level set function. The underlying physics of the process are completely contained in a scalar function called the speed function. The degree of difficulty of treating the evolution equation depends on the functional dependencies of the speed function. This paper presents optimal estimation and design techniques based on analytical gradient computations for a class of position and orientation dependent speed functions. The technique is demonstrated on a plasma etching model taken from the literature. Only simulation results are presented here, but the model under study has been shown to reproduce experimental data with reasonable accuracy. In the estimation problem, parameters in the model are fit to best match the feature shape measured in experiments. In the optimal design problem, parameter values are selected to most closely attain a desired feature shape.

  19. J. F. Cardenas-Garcia, S. Ekwaro-Osire, and J. M. Berg, "Solution to the Moire Hole Method Problem," Mechanics Research Communications, Vol. 28, No. 1, pp. 13-32, 2001.

    ABSTRACT: This paper examines the use of the moire hole method to find material properties such as modulus of elasticity and Poisson's ration, as well as to solve for residual stresses. Emphasis is on the situation when the moire grating is misaligned with respect to the principal strain axes. Nonlinear least-squares methods are shown in simulation to be effective when used with comprehensive model equations.

  20. S. Ekwaro-Osire, D. H. S. Maithripala, and J. M. Berg, "A Series Expansion Approach to Interpreting the Spectrum of the Timeshenko Beam," Journal of Sound and Vibration, Vol. 240, No. 4, pp. 667-678, 2001.

    ABSTRACT: The Timoshenko beam model results in two fourth order partial differential equations in time and space. Consequently, solving the boundary value problem yields two independent sequences of natural frequencies and two corresponding sequences of mode shapes. A particular natural frequency and its corresponding mode shape describe one particular solution to the boundary value problem of the Timoshenko beam. From an eigenfunction expansion sense, all these possible solutions have to be considered in the complete series expansion of the solution. However, the question of whether these two independent sequences of natural frequencies implies the existence of two distinct spectra of frequencies has been a long-standing topic of debate, and hitherto has not been resolved completely. The object of this paper is to provide answers to some of the issues raised by this debate. In this context the complete solution in a series form to the Timoshenko beam is investigated, and it is shown for the first time that a particular mode shape of the solution is naturally expressed by an ordered pair of characteristic values, rather than a single characteristic value. This representation facilitates the progressive ordering of all the natural frequencies of the system and their respective mode shapes in a single set, and eliminates the remaining argument for the two spectra interpretation.

  21. J. Berg and K. Holmstrom, "On Parameter Estimation Using Level Sets," SIAM Journal on Control and Optimization, Vol. 37, No. 5, pp. 1372-1393, 1999.

    ABSTRACT: Consider the problem of selecting the member of a parameterized family of curves that best matches a given curve. This is a key step in determining proper values for adjustable parameters in low-order plasma etching and deposition models. Level set methods offer several attractive features for treating such problems. This paper presents a parameter estimation scheme that exploits the level set formulation. The method is completely geometric; there is no need to introduce an arbitrary coordinate system for the curves. Analytic results necessary for the application of gradient descent algorithms are derived, and some preliminary numerical results are presented.

  22. J. Berg, A. Yezzi, and A. Tannenbaum, "Curve Evolution Models for Real-Time Identification with Application to Plasma Etching," IEEE Transactions on Automatic Control, Vol. 44, No. 1, pp. 99-101, 1999.

    ABSTRACT: It is desirable, in constructing an algorithm for real-time control or identification of free surfaces, to avoid representations of the surface requiring mesh refinement at corners, or special logic for topological transitions. Level set algorithms provide a promising framework for such algorithms. In this paper we present: 1) A mathematical representation of free surface motion that is particularly well-suited to real-time implementation; 2) a technique for estimating an isotropic and homogeneous normal velocity based on a simple measurement; and 3) an application to a semiconductor etching problem.

  23. C. A. Schwartz and J. Berg, "Neural Network Control of an Extrusion," IEEE Transactions on Control System Technology, Vol. 6, No. 2, pp. 180-187, 1998.

    ABSTRACT: This work is concerned with the feedback control of microstructure during one of the simplest metal forming operations: round-to-round extrusion. Physically based semiempirical models of the microstructural dynamics are available, but they require flow variables such as strain strain rate, and temperature as inputs. Direct measurement of these quantities inside the deforming material is not feasible, so such models alone do not define a feedback controller. In the study presented here, the mapping from the temperature of the material flowing through the die to the ram load is estimated via finite-element simulation. The ram load can be measured, and so this mapping, composed with the microstructural model, does close the loop, but the simulation is far too slow for real-time implementation. This problem is addressed by training an artificial neural network to represent the simulation output. This approach is demonstrated on the simulated extrusion of a carbon steel rod.

  24. J. M. Berg, and V. R. Voller, "An Identification and Control Strategy for a Liquid Composite Molding Process," Applied Mathematical Modelling, Vol. 22, pp. 207-218, 1998.

    ABSTRACT: Liquid composite molding (LCM) is a manufacturing process that involves the injection of resin into a mold containing fiber preform and the subsequent curing. Control of the resin injection is an obvious way to increase process performance. Variability in the properties of the fibers makes open-loop approaches problematic. This paper presents a controller for a 1-D analog of the LCM process. The purpose is to demonstrate that a straightforward estimation and control scheme can adapt to unmodelled variations in the properties of the mold, and enforce a prescribed filling behavior. The scheme is applied to a simulation of an LCM process.

  25. J. Berg, W. G. Frazier, A. Chaudhary, and S. S. Banda, "Optimal Design of Open-Loop Ram Velocity Profiles for Isothermal Forging: A Variational Approach," ASME Journal of Manufacturing Science and Engineering, Vol. 120, No. 4, pp. 774-780, 1998.

    ABSTRACT: This paper considers the problem of selecting the ram velocity in an isothermal forging, to best obtain a desired material microstructure. This is to be accomplished by tracking a desired strain rate profile. A weighting function reflecting the rate at which the microstructure is transforming, describes the relative importance of different parts of the billet. Finding the optimal solution generally requires a search over an infinite-dimensional function space. However, for a certain class of forgings the task reduces to solving a single ordinary differential equation. The result is a globally optimal and unique ram velocity profile. The method is demonstrated for the simulated forging of a TiAl turbine disk.

  26. J. Berg and H. G. Kwatny, "Unfolding the Zero Structure of a Linear Control System," Linear Algebra and its Applications, Vol. 258, pp. 19-39, 1997.

    ABSTRACT: This paper is motivated by the problem of controller design for a parameter-dependent linear system. Many compensation techniques depend critically on aspects of the zero structure of the system, such as relative degree, or the nonminimum-phase property. However, the zero structure is structurally unstable, meaning it may change discontinuously with small changes in the parameters. Thus it is crucial that the designer know what structures and structural transitions are possible. This paper uses a miniversal deformation, or unfolding, of the Kronecker form previously reported by the authors, and applies it directly to pencils in a canonical form of the system matrix. The unfolding is used to explore all zero structures in a neighborhood of a nominal system. Several examples are presented. When possible, the results are presented in the form of a bifurcation diagram.

  27. J. Berg and H. G. Kwatny, "Linear SISO Systems with Extremely Sensitive Zero Structure," IEEE Transactions on Automatic Control, Vol. 41, No. 7, pp. 1037-1040, July, 1996.

    ABSTRACT: If a system with regular system pencil and relative degree greater than one is perturbed, the relative degree will typically decrease, and new finite zeros will appear. These new zeros are singularly perturbed. This paper applies a new canonical parameterization to systems with singular system pencils. Such systems have undefined relative degree. In singular systems, new zeros also appear under small perturbations, but they are not necessarily singularly perturbed. Rather, these zeros may appear at any frequency.

  28. J. Berg, K. D. Hammett, C.A. Schwartz, and S.S. Banda, "An Analysis of the Destabilizing Effect of Daisy Chained Rate-Limited Actuators," IEEE Transactions on Control Systems Technology, Vol. 4, No. 2, pp. 171-176, March, 1996.

    ABSTRACT: The response of a rate-limited actuator will lag behind a rapidly changing command. This lag may destabilize the closed-loop system. When multiple actuators are arranged in a daisy chain this effect can be significantly worse. The cost of daisy-chaining, in terms of lost stability margin, is estimated analytically and numerically. A comparison of a simple daisy chain with a simple "cooperative" control selector shows that the daisy chain may cause as much as 30 degrees of additional phase lag.

  29. J. Berg, R. J. Adams, J. C. Malas, and S.S. Banda, "Nonlinear Optimization-Based Design of Ram Velocity Profiles for Isothermal Forging," IEEE Transactions on Control Systems Technology, Vol. 3, No. 3, pp. 269-278, September 1995.

    ABSTRACT: The development of good material models, accurate nonlinear finite element codes, and computer-controlled presses make practical the application of control techniques to metal forging. This paper considers the open-loop problem of selecting a nominal ram velocity profile to produce a desired microstructure, given a specified die and preform geometry and forging temperature. Two approaches for doing so are applied ot a simple, but representative problem. The first is based on classical numerical optimization techniques. The second is based on inverse neural networks and offers potential savings in critical computations. Simulation studies for the two methods show good results.

  30. J. Berg and H. G. Kwatny, "A Canonical Parameterization of the Kronecker Form of a Matrix Pencil," Automatica, Vol. 31, No. 5, pp. 669-680, May, 1995.

    ABSTRACT: The Kronecker form is the classical canonical form for matrix pencils under strict equivalence transformation. Consider a matrix pencil whose entries are smooth functions of a parameter vector. The Kronecker form of the parameterized pencil will, in general, be a discontinuous function of the parameters. For a linear time-invariant control system these discontinuities correspond to a change in the finite and infinite invariant zero structure. Since many control strategies require knowledge of, or place restrictions on, the zero structure, these points of discontinuity are of considerable interest. In this paper a general approach to the study of such points is developed in the framework of singularity theory. We derive a 'miniversal' parameterization of a given pencil. That is, a parameterized family of pencils that: (i) includes the given pencil, (ii) is locally equivalent to any other family up to a change of parameters, and (iii) uses the fewest number of parameters to achieve this property. All 'nearby' zero structures can be obtained by varying parameter values in the miniversal parameterization. From all miniversal parameterizations, one having a particularly uncluttered representation is selected as canonical. However, some restrictions on the finite elementary divisors are then required.

  31. J. Berg and H. G. Kwatny, "An Upper Bound on Structurally Stable Linear Regulation of a Parameter-Dependent Family of Control Systems," Systems & Control Letters, Vol. 23, pp. 85-95, August, 1994.

    ABSTRACT: We investigate the use of a linear compensator to regulate a parameter-dependent control system. This system may be linear or nonlinear. Our goal is to design a compensator that will ensure stable regulation over a wide range of parameter values. This paper reports a fundamental limitation on achieving this aim. In particular, we we show that systems with a special, unregulatable, structure form hypersurfaces on the open-loop equilibrium manifold. Such systems include, but are not restricted to, those with transmission zeros at the origin. These surfaces partition the open-loop equilibrium manifold into disjoint open sets. We show that a linear compensator designed to regulate a system in some such partion must fail to regulate almost all systems in an adjacent partition. Therefore, by consideration of the open-loop system only, we derive upper bounds on the robustness of any linear regulator. We discuss some other qualitative aspects of the closed-loop dynamics.

  32. H. G. Kwatny, W. H. Bennett, and J. Berg, "Regulation of Relaxed Static Stability Aircraft," IEEE Transactions on Automatic Control, Vol. AC-36, No. 11, pp. 1315-1323, November, 1991.

    ABSTRACT: We formulate and solve a regulator problem for nonlinear parameter-dependent dynamics. It is shown that the problem is solvable except at parameter values associated with bifurcation of the equilibrium equations and that such bifurcations are inherently linked to the system zero dynamics. These results are applied to the study of the regulation of the longitudinal dynamics of aircraft.

Edited Book Chapters

  1. D. H. S. Maithripala, J. M. Berg, and W. P. Dayawansa, “A Coordinate-Free Approach to Tracking for Simple Mechanical Systems On Lie Groups,” New Directions and Applications in Control Theory, Vol. 321, Lecture Notes in Control and Information Sciences, W. P. Dayawansa, A. Lindquist, Y. Zhou, Eds. Springer-Verlag, NY, pp. 223–238, 2005.
  2. T. Dallas, J. M. Berg, and P. K. Dasgupta, “Microfabricated Coulometric Humidity Sensors,” to appear in the Encyclopedia of Sensors, in press.
  3. J. M. Berg, M. Holtz, Y. Su, R. Bunuan, J. Wilhelm, T. Dallas, R. Gale, L. Gollahon, S. Gangopadhyay, H. Temkin, “Towards Integrating Graduate Research and Education with ‘Internal Research Internships’: Experiences and Assessment,” in Innovations 2004: World Innovations in Engineering Education and Research, W. Aung, R. Altenkirk, T. Cermak, R. W. King, and L. M. S. Ruiz, editors, iNEER. Arlington VA, pp. 291–301, 2004.
  4. T. Dallas, J. M. Berg, M. Holtz S. Gangopadhyay and H. Temkin, "Developing 'Internal Internships' for a Microsystems Engineering Curriculum," in Engineering Education and Research - 2002: A Chronicle of Worldwide Innovations, iNEER Special Volume, 2003.
  5. L. Smith, J. Berg, and J. Malas, "Optimal Die Shape and Ram Velocity Design for Metal Forging," in Large Scale Optimization with Applications. Part I: Optimization in Inverse Problems and Design, L. T. Biegler, T. F. Coleman, A. R. Conn, and F. N. Santosa, editors, IMA Volumes in Mathematics and its Applications, Vol. 92, Springer-Verlag, NY, pp. 119-133, 1997.
  6. J. Berg, R.J. Adams, J. C. Malas, and S.S. Banda, "Optimal Control of Metal Forging," in Optimal Design and Control, J. Borggaard, J. Burkhardt, M. Gunzberger, and J. Peterson, editors, Birkhauser, Boston, pp. 55-80, 1995.
  7. H. G. Kwatny and J. M. Berg, "Variable Structure Regulation of Power Plant Drum Level," in Systems and Control Theory for Power Systems, J.C. Chow, R. J. Thomas and P. V. Kokotovic, editors, IMA Volumes in Mathematics and its Applications, Vol. 64, Springer-Verlag, NY, pp. 205-234, 1994.

Book Reviews

  1. J. M. Berg, "Book review: Optimal control of singularly perturbed linear systems and applications by Z. Gajic and M-T Lim," Automatica, Vol 39, No. 2, pp. 369-372, February 2003.

Refereed Conference Proceedings

  1. J. M. Berg, D. H. S. Maithripala, B. D. Kawade, and W. P. Dayawansa, “Integrated Modeling and Control of Electrostatic MEMS, Part I: Modeling,” Proceedings of the 2005 IEEE International Conference on Industrial Automation.
  2. D. H. S. Maithripala, B. D. Kawade, J. M. Berg, and W. P. Dayawansa, “Integrated Modeling and Control of Electrostatic MEMS, Part II: Control,” Proceedings of the 2005 IEEE IEEE International Conference on Industrial Automation.
  3. B. D. Kawade, D. H. S. Maithripala, and J. M. Berg “Efficient Multi-Physics Transient Analysis Incorporating Feedback-Dependent Boundary Conditions,” Proceedings of the 2006 ANSYS Users Conference, to appear.
  4. J. M. Berg, D. H. S. Maithripala, B. D. Kawade, M. Goyal, K. Ragulan, L. Tian, W. P. Dayawansa, R. Gale, M. Holtz, “Passivity-Based Geometric Control with Application to Electrostatically-Actuated Microsystems,” Proceedings of ICMEM2005, The International Conference on Mechanical Engineering and Mechanics, Oct 26-28, 2005, Nanjing, CHINA, pp. 50–56.
  5. B. D. Kawade, J. M. Berg, D. H. S. Maithripala, and W. P. Dayawansa, “Advanced Finite Element Simulation Of Control Laws For Electrostatic MEMS Using ANSYS,” Proceedings of TEX-MEMS 2005, El Paso, TX, September 21–22, 2005.
  6. D. H. S. Maithripala, B. D. Kawade, J. M. Berg, W. P. Dayawansa, “A General Geometric Framework For Control of Electrostatically-Actuated MEMS And NEMS,” Proceedings of IMECE 2005, Orlando, FL, Nov. 5–11, 2005.
  7. M. Goyal, R. C. Anderson, J. M. Berg, R. O. Gale, M. Holtz, and H. Temkin, “A Microelectronics- Compatible Process For Surface Micromachining Of MEMS And MOEMS,” Proceedings of IMECE 2005, Orlando, FL, Nov. 5–11, 2005.
  8. E. Washington, D. Aurongzeb, D. T. Osborne, J. M. Berg, M. Holtz, and H. Temkin. “Spatial Oscillation In SHS Of Ni / Al Multilayer Foils: Measurements And Models,” Proceedings of IMECE 2005, Orlando, FL, Nov. 5–11, 2005.
  9. D. H. S. Maithripala, J. M. Berg, and W. P. Dayawansa, “State and Configuration Feedback for Almost Global Tracking of Simple Mechanical Systems on a General Class of Lie Groups,” Proceedings of the 2005 American Control Conference.

  10. R. C. Anderson, B. Kawade, D. H. S. Maithripala, K. Ragulan, J. M. Berg, R. O. Gale, “Integrated charge sensors for feedback control of electrostatic MEMS,” Proceedings of the SPIE conference on Smart Structures and Materials 2005: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, San Diego, 6-10 March 2005.

  11. P. Kuban, J. M. Berg, P. K. Dasgupta, and T. Dallas, “Highly Durable Microfabricated Humidity Sensors for Humidity Monitoring,” Proceedings of the Third International Conference on Earthquake Engineering: New Frontiers and Research Transformation, 19–20 October, 2004, Nanjing, PRC, pp. 909–913.

  12. D. H. S. Maithripala, J. M. Berg, W. P. Dayawansa, “An Intrinsic Observer for a Class of Simple Mechanical Systems on a Lie Group,” Proceedings of the 2004 American Control Conference. Best Student Paper finalist (one of five).

  13. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "A Port-Controlled Hamiltonian Approach to Control of Electrostatically-Actuated MEMS," Proceedings of the 2003 International Mechanical Engineering Congress and Exposition, Washington, DC, November, 2003.

    ABSTRACT: While mechanical, electrical and electromechanical systems may exhibit complex nonlinear dynamics, their behavior is typically governed by relatively simple underlying principles of energy transfer. Modeling methodologies that seek to capture this underlying order give rise to a special form of the equations of motion, called a port controlled Hamiltonian structure with damping (PCHD). Often the natural behavior of a system is unacceptable for a desired application, and must be modified. A body of work on passivity-based control exists that shows how to use Casimir functions---certain invariant quantities of the open-loop PCHD---to reshape the natural dynamics in a desired way. We seek to apply this approach to an electrostatically-actuated MEMS device subject to the saddle-node bifurcation known as snap-through. We show that the equations describing this system do not have an appropriate Casimir function, but that they can be suitably modified through an implementable output feedback. We fully characterize the Casimirs of the modified system, and show how they may be used to eliminate snap-through. Unfortunately the transient behavior of the resulting closed-loop system is governed by the damping of the mechanical subsystem, which may or may not provide adequate performance.

  14. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "A Virtual Velocity Sensor for Improved Transient Performance of Electrostatically-Actuated MEMS," Proceedings of the 2003 International Mechanical Engineering Congress and Exposition, Washington, DC, November, 2003.

    ABSTRACT: Electrostatically-actuated MEMS devices suffer from a nonlinear bifurcation phenomenon called "snap-through" or "pull-in." This bifurcation severely limits the operating region of such devices. Control schemes have been proposed to eliminate snap-through. These stabilizing controllers can be implemented using relatively straight forward current and voltage measurements. However, in order to alter the transient behavior of the system, for example to reduce settling time, or to minimize the likelihood of contacting the bottom electrode, the controller should also include terms dependent on the velocity of the movable electrode. Direct sensing of this velocity during normal device operation is typically not feasible. In this paper we show how the electrode velocity may be indirectly sensed using only capacitance and voltage measurements. Our approach is based on well known techniques of nonlinear observer design, and provides arbitrarily fast linear error dynamics. Simulation results show excellent performance.

  15. D. H. S. Maithripala, R. O. Gale, M. W. Holtz, J. M. Berg and W. P. Dayawansa, "Nano-Precision Control of Micromirrors Using Output Feedback," Proceedings of the 2003 IEEE Conference on Decision and Control.

    ABSTRACT: Micromirror arrays may be used as spatial light modulators, to vary the amplitude and phase of an incident image. The difficulty of controlling analog micromirrors to within a fraction of a wavelength of the incident light---that is, to within a few nanometers---has led to the development and successful commercialization of digital devices, in which the components take one of only two possible configurations. In this paper we revisit true analog operation, in light of recent advances in nonlinear control. Our focus is electrostatically actuated mirrors, for which control objectives include extending the range of motion, improving transient performance, improving positioning accuracy and preventing electrode contact. We consider two models of individual micromirrors, suitable for controller design. The first treats each micromirror as a rigid body, and allows arbitrary rotation and translation. This model is developed in the context of dynamics on the Lie group SE(3). We simulate the performance of an observer-based controller for this system. The second model, based on work by Pelesko, is developed directly from a PDE representation of an electrostatically forced membrane. We show via simulation that an unstable equilibrium point of this model may be stabilized by proportional output feedback.

  16. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "Nonlinear Dynamic Output Feedback Stabilization of Electrostatically-Actuated MEMS," Proceedings of the 2003 IEEE Conference on Decision and Control.

    ABSTRACT: Operating regions of electrostatically-actuated microelectromechanical systems are limited by a bifurcation phenomenon called "snap-through" or "pull-in." It is known that charge feedback control can be employed to avoid this bifurcation. The performance of such controllers may be poor, especially if the natural damping of the system is very low or very high. This paper discusses two possible feedback control strategies that eliminate snap-through as well as improve performance. A serious drawback of these control laws is that they require the measurement of the device velocity. A reduced order observer is presented to overcome this. The observer is based on well known nonlinear observer design techniques, and can be assigned arbitrary linear error dynamics.

  17. J. M. Berg, M. Holtz, S. Gangopadhyay, J. Wilhelm, Y.-L. Su, R. Bunuan, L. Gollahon, R. Gale, T. Dallas and H. Temkin, "Towards Integrating Reasearch and Education Using 'Internal Internships,'" Proceedings of the 2003 International Conference on Engineering Education, ICEE-2003, Valencia, Spain.

    ABSTRACT: We describe our efforts towards integrating graduate-level research and education in a highly interdisciplinary laboratory environment. The educational innovation we wish to evaluate is the "Internal Research Internship," in which a graduate student with an established research project is placed in a host laboratory for a semester or more to work in a distinct, but complementary, area. The test bed for our study is the third course of a three-semester sequence in microsystem design and fabrication. Participants in this class lead teams of less experienced students, to accomplish a difficult design challenge. Each of five teams is responsible for a critical component of a sophisticated device; the five leaders are responsible for coordinating and integrating the separate efforts. Partial success should be attainable through interdisciplinary communication and teamwork. Complete success represents work at the level of the current state of the art. In this study we focus on interactions between the team leaders. In particular, a cell biology graduate student was brought into a microfabrication laboratory specifically to work with a physicist and an electrical engineer leading teams developing a DNA amplification chamber and a target DNA pre-filter. Initially awkward, inefficient and unproductive, the relationship between these students gradually became fluid, respectful and ultimately extremely fruitful. Unanticipated benefits also sprang from interactions between the biologist and other team leaders, and with the graduate education student assigned to assess the effectiveness of the project.

  18. S. Bhattacharya, J. M. Berg, D. James, and S. Gangopadhyay, "A Flow Visualization Experiment for a First Course in Microfluidics," Proceedings of the 2003 ASEE-GSW Conference, Arlington, TX, March 19-21, 2003.

    ABSTRACT: Physical intuition developed for fluid flows at the macro-scale can be very misleading when applied to flows in microchannels. The Reynolds number of these flows is typically low, and thus they remain totally laminar. Under microflow conditions, familiar phenomena such as fluid mixing behave counter to the intuition developed by students in a standard engineering curriculum. We present a laboratory project designed to stress this point to students taking a first-year graduate introduction to microsystems. The pilot group found the results surprising and counter-intuitive. It appears that the project was instrumental in clarifying key concepts in microfluidics.

  19. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "Capacitive stabilization of an electrostatic actuator: an output feedback viewpoint," Proceedings of the 2003 American Control Conference, Denver, CO.

    ABSTRACT: With constant voltage control, use of the entire capacitive gap in analog operation of electrostatically-actuated MEMS devices is restricted by a bifurcation phenomenon known as "pull in" or "snap through." It is well known that a properly-sized series capacitor will eliminate this bifurcation. We re-visit this result from the viewpoint of control theory, and show that the series capacitor implements static charge feedback, and can semi-globally stabilize any position in the gap. In fact, with charge as output, the system is relative degree one, and input-output linearizable with asymptotically stable zero dynamics, suggesting that more general compensation schemes may be fruitful. In fact, the system may be input-output linearized using only the voltage across the electrodes---an easily measured quantity. We show that any position in the gap may be globally asymptotically stabilized with output feedback of voltage and charge.

  20. S. Gangopadhyay, J. M. Berg, M. Holtz and T. Dallas, "A Three-Course Sequence in the Engineering of Micro Total Analytical Systems," Proceedings of the 2002 International Conference on Engineering Education, ICEE-2002, Manchester, UK.

    ABSTRACT: We describe a three-course introductory sequence in fluorescence-based microanalytical systems. The series is aimed at beginning graduate students and advanced undergraduates who have an interest in MEMS and microelectronics. The first course is introductory with the objective of educating students in the basics of silicon microfabrication. Devices are produced. This course is more project- and product-oriented, with a strong technology component building on the first course. The second course has been offered twice, with drastically different formats as described in the article. The third course has been offered once. The ultimate goal of this course is to produce students capable of leading a team to produce a product. The objectives, methods, and assessment of each course are described.

  21. R. Manor, A. Datta, A. Dhar, M. Holtz, J. Berg, S. Gangopadhyay, P. Dasgupta, H. Temkin, V. Veeraraghavan, R. Vijayaraghavan and T. Dallas, "Microfabricated Liquid Core Waveguides for Microanalysis Systems," Proceedings of IEEE Sensors 2002, First IEEE International Conference on Sensors, pp. 660-664, Orlando, FL, June 12-14, 2002.

    ABSTRACT: We report on the microfabrication of liquid core waveguides (LCW) using Teflon AF for integration in microfabricated micro total analysis systems. Teflon AF has an index of refraction less than that of water. Straight micro channels (<500 mm width, <100 mm depth) etched into a Pyrex wafer were coated with Teflon AF and sealed with a Teflon AF coated Pyrex capping wafer. This formed a low index of refraction channel in which a higher index, aqueous solution was flowed. Light generated in the lumen propagated by total internal reflection (TIR) to the end of the channel where the light was detected using either a photomultiplier or a miniature spectrometer. An optical microscope was used to transversely illuminate the channel at various distances from the end to measure the waveguide properties.

  22. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "Loss of Structurally Stable Regulation Implies Loss of Stability," Proceedings of the 2002 Automatic Control Conference, pp. 2738-2740, Anchorage, AK, June, 2002. An expanded version of this paper has been published in journal form.

    ABSTRACT: Consider the problem of selecting a single compensator capable of regulating any member of a family of linear systems in the presence of a specified exogenous system. Necessary and sufficient conditions for the existence of a structurally stable, regulating and stabilizing compensator at a particular plant are well known. We refer to systems for which these conditions fail as critical. Clearly any choice of compensator must fail in at least one respect at a critical point. Either it is not structurally stable, or it does not asymptotically reject the exogenous system, or it does not stabilize the closed-loop system. However, existing theory does not reveal which of these occurs. In fact, we show that a compensator designed to regulate, with structural stability, a specified exogenous system, is necessarily destabilizing at a critical point. As an application of this result we derive an upper bound on structurally stable regulation under unstructured perturbation for any choice of system metric.

  23. D. H. S. Maithripala, J. M. Berg and W. P. Dayawansa, "The Existence and Codimension of Submanifolds Limiting Simultaneous Regulation," Proceedings of the 2002 Automatic Control Conference, pp. 4415-4420, Anchorage, AK, June, 2002.

    ABSTRACT: For unstructured perturbation it has been shown that the robustness of any structurally stable regulating compensator is limited by the minimum distance to a class of “critical” systems. These critical systems also play a central role for parametrized families, but in this case it is not enough merely that such a system exists. Their structure in the parameter space must also be considered. We prove that if the parametrized family contains a critical point, then generically some closed-loop systems in a neighborhood of that point corresponding to any single structurally stable regulating compensator must be exponentially unstable. However we also show, with a numerical example, that if the family contains no critical points it may be possible to regulate every member—even if a nearby critical point severely limits robust regulation in the unstructured sense. Under these circumstances, the submanifold structure, and in particular the codimension, of the set of critical poin ts in the parameter space becomes a matter of critical interest. We show that in general the critical points form a codimension-two submanifold. However, in special cases of engineering interest, these submanifolds are codimension-one, and hence naturally partition the parameter space.

  24. J. Berg and N. Zhou, "Shape-Based Estimation and Design of a Plasma Etching Process," Proceedings of the 2000 IEEE CDC, pp. 2023-2028, Sydney, Australia, December 2000. An expanded version of this paper has been published in journal form.

  25. J. Malouf, J. Berg, and P. Johnson, "Optimal Peak Shaving Capacity and Control for a Known Load Curve: Application to Irrigated Agriculture," Proceedings of the 2000 American Control Conference, pp. 2897-2901, Chicago, IL, June 2000.

  26. J. Berg, "Estimation of Parameter Values Appearing in Space and Orientation Dependent Curve Evolution Process Models," Proceedings of the 1999 American Control Conference, pp. 3905-3909, San Diego, CA, June 1999.

  27. J. Berg, "Estimation of Parameters Appearing in the Level Set Evolution Equation," Proceedings of the 37th IEEE Conference on Decision and Control, pp. 2323-2328, Tampa, FL, December 1998.

  28. Z. Lin and J. Berg, "Semi-Global Stabilization of Linear Systems with Position and Rate Limited Actuators in Daisy Chain," Proceedings of the 37th IEEE Conference on Decision and Control, pp. 1979-1980, Tampa, FL, December 1998.

    ABSTRACT: It is shown that, if a linear system is aysmptotically null controllable with bounded controls, then, when actuators are arranged in daisy chains and are subject to both position and rate saturation, it is semi-globally stabilizable by linear state feedback. If, in addition, the system is also detectable, then it is semi-globally stabilizable via linear output feedback.

  29. J. M. Berg, "On Parameter Estimation Using Level Sets," Proceedings of the 1998 American Control Conference, pp. 3758-3762, Philadelphia, PA, 1998. An expanded version of this paper has been published in journal form.

  30. J. Berg, A. Yezzi, and A. Tannenbaum, "Toward Real-Time Estimation of Surface Evolution in Plasma Etching: Isotropy, Anisotropy, and Self-Calibration," Proceedings of the 36th IEEE Conference on Decision and Control, pp. 860-865, San Diego, CA, 1997.

  31. J. Berg, T. Higman, and A. Tannenbaum, "Real-Time Control of Etching Processes: Experimental Results," Proceedings of the SPIE: Process, Equipment, and Materials Control in Integrated Circuits, Vol. 3213, A. Ghanbari and A. J. Toprac, Eds., SPIE Conference on Process, Equipment, and Materials Control in Integrated Circuits, pp. 249-260, Austin, TX, October 1-2, 1997.

  32. J. Berg, W. G. Frazier, A. Chaudhary, and S.S. Banda, "A Variational Approach to Optimal Design of Open-Loop Ram Velocity Profiles for Isothermal Forging," Proceedings of the American Control Conference, pp. 150-154, Albuquerque, NM, 1997.

  33. J. Berg, A. Yezzi, and A. Tannenbaum, "Phase Transitions, Curve Evolution, and the Control of Semiconductor Manufacturing Processes," Proceedings of the 35th IEEE Conference on Decision and Control, pp. 3376-3381, Kobe, Japan, 1996.

  34. L. Smith and J. Berg, "Shape and Velocity Optimization for Hot Metal Forming," Proceedings of the 13th IFAC World Congress B, San Francisco, CA, pp. 85-91, 1996.

  35. J. Berg, A. Chaudhary, and J. Malas, "Open-Loop Control of a Hot Forming Process," in Simulation of Materials Processing: Theory, Methods, and Applications: NumiForm '95, S-F Shen and P.R. Dawson, editors, pp. 539-544, A.A. Balkema, Rotterdam, 1995.

  36. K. D. Hammett, J. Berg, C. A. Schwartz, and S. S. Banda, "Stability Considerations in Daisy Chaining," Proceedings of the 1995 AIAA Guidance, Navigation and Controls Conference, Baltimore, MD, pp. 312-317, 1995.

  37. C. A. Schwartz, J. Berg, M. Mears, and R. Chang, "Neural Network Identification and Control in Metal Forging," Proceedings of the American Control Conference, Seattle, WA, pp. 1782-1786, 1995. An expanded version of this paper has been published in journal form.

  38. H.-H. Yeh, B.-C. Chang, J. Berg, and S. S. Banda, "Dynamic Inversion of Linear Multivariable Systems with Observers," Proceedings of the American Control Conference, Seattle, WA, pp. 4408-4412, 1995.

  39. J. Berg, R. J. Adams, J. C. Malas, and S. S. Banda, "Design of Ram Velocity Profiles for Isothermal Forging via Nonlinear Optimization," Proceedings of the American Control Conference, Baltimore, Md, pp. 323-327, 1994.

  40. J. Berg and H. G. Kwatny, "Unfolding of Singular System Pencils with Application to Regulation," Proceedings of the 12th IFAC World Congress, Sydney, Australia, Vol. 5, pp. 153-156, 1993.

  41. H. G. Kwatny and J. Berg, "Drum Level Regulation at All Load Levels," Proceedings of the 12th IFAC World Congress, Sydney, Australia, Vol. 3, pp. 405-408, 1993.

  42. H. G. Kwatny, W. H. Bennett, and J. Berg, "Local Regulation of Non-linear Dynamics," Proceedings of the American Controls Conference, San Diego, CA, pp. 1707-1712, 1990.

  43. C. H. Hubert, D. S. Shaw, and J. M. Berg, "Computer-aided Stability Analysis of Spinning Spacecraft with On-board Liquids," Proceedings of the AIAA Conference on Guidance, Navigation, and Control, 1988.

  44. J. M. Berg, A. J. Kelly, and R. G. Jahn, "Direct Measurement of MPD Thrust," Proceedings of the JSASS/AIAA/DGLR 17th International Electric Propulsion Conference, Tokyo, Japan, pp. 193-199, 1984.

Technical Reports

  1. J. M. Berg, T. T. Maxwell, M. Parten, System Integration and Field Test of a 1.2 MW Natural Gas Powered Gas Turbine Genset, Final Report for Gas Research. Institute contract #5027, December, 2001.

  2. J. Berg and N. Zhou, Shape-Based Parameter Estimation and Design of Curve Evolution Processes with Application to Plasma Etching, IMA Preprint Series #1693, April, 2000.

  3. J. Berg, On Parameter Estimation Using Level Sets, IMA Preprint Series #1547, February, 1998.

  4. J. Berg, A. Yezzi, and A. Tannenbaum, Phase Transitions, Curve Evolution, and the Control of Semiconductor Manufacturing Processes, IMA Preprint Series #1454, February, 1997.

  5. J. Berg, A Robust Optimal Material Trajectory for a Material with Rapidly Transforming Microstructure, IMA Preprint Series #1417, July, 1996.

  6. J. Berg and H. G. Kwatny, Unfolding the Zero Structure of a Linear Control System, IMA Preprint Series #1390, March 1996.

  7. J. Berg, W. G. Frazier, A. Chaudhary, and S.S. Banda, Optimal Design of Open-Loop Ram Velocity Profiles for Isothermal Forging: A Variational Approach, IMA Preprint Series #1389, March 1996.

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