Stephen M. Phillips

Decentralized and dynamic bandwidth allocation in networked control systems

In this paper, we propose a bandwidth allocation scheme for networked control systems that have their control loops closed over a geographically distributed network. We first formulate the bandwidth allocation as a convex optimization problem. We then present an allocation scheme that solves this optimization problem in a fully distributed manner. In addition to being fully distributed, the proposed scheme is asynchronous, scalable, dynamic and flexible. We further discuss mechanisms to enhance the performance of the allocation scheme. We present analytical and simulation results

Static and electrically actuated shaped MEMS mirrors

A novel digitally-actuated shaped micromirror for on-off optical switch applications is described. Reflective static spherical mirrors were designed and fabricated using conventional surface micromachining and the MultiPoly process, a technique for depositing multilayers of LPCVD polysilicon in order to control the overall stress and stress gradient. The resulting mirrors were measured to have radii of curvature of approximately 9 mm in agreement with design predictions. Based upon these static mirrors, an actuatable micromirror (diameter=500 /spl mu/m, static radius curvature=6.4 mm) was designed for snap action. This mirror was simulated using an electromechanical coupled-field model and fabricated using the MultiPoly process. Its performance was measured dynamically using an interferometer. A curved-to-flat digital actuation of the mirror was successfully achieved with a pull-in voltage of 38 V.

Complete stability region characterization for PI-AQM

This paper describes a method for finding the stability regions of the PI and PIP controllers for TCP AQM with delays. The method is applied on several representative examples, showing that stable controllers can exhibit widely different performance. Thus, the results highlight the importance of optimizing the design of PI AQM. Furthermore, the paper shows that the previously proposed PIP controller can be unstable in the presence of delays even for the control parameters given in the literature.

Velocity estimation using quantized measurements

This paper compares algorithms for velocity estimation for feedback control using position encoder measurements. Simulations and experiments for position-velocity control of motors using both fixed-time and fixed-displacement algorithms are compared for various operating conditions. While no single approach is optimal for all situations, least-squares fit algorithms are promising in general. Mathematical models are developed to predict the performances of the algorithms. Specifically, upper bounds on absolute and relative errors for each of the algorithms under different constant velocity and constant acceleration conditions are derived. The algorithms are extensively tested in simulation and also on data obtained from an experimental setup consisting of a motor, two encoders with different resolutions, and a real-time feedback control system. The theory and simulations are confirmed by experimental results.

Transform domain features for ion-channel signal classification

The study of the behavior of ion-channels can provide significant information to detect metal ions and small organic molecules in solution. Discrimination of different analytes can be performed by extracting appropriate features from the ion-channel signals and using them for classification. In this paper, we consider features extracted from the Fourier, Wavelet and Walsh-Hadamard domain representations of the ion-channel signals. The proposed approach uses the power distribution information in the transform domains as features for discrimination. We compare the performance of all the three sets of features using support vector machines for classification of analytes and present the results. Results obtained show that the transform domain features achieve high classification rates in addition to high sensitivity and specificity rates.

MEMS shock sensor fabricated on flexible substrate

Incorporating sensors onto a flexible substrate will add functionality to flexible displays. Though several attempts have been made to mount MEMS sensors[1, 2] on flexible substrates[1], none of the sensors have been integrally fabricated on the substrate[3]. Fabricating MEMS sensors on flexible substrates [4] along with display elements will provide new sensing capabilities and enhance functionality. We propose a MEMS capacitive sensor fabricated in a low temperature, flexible amorphous silicon process. This sensor will enable acoustic detection and have potential applications for blast dosimetry [5], a research topic currently of great interest.

Transform domain features for ion-channel signal classification using support vector machines

The study of the behavior of ion-channels can provide significant information to detect metal ions and small organic molecules in solution. Discrimination of different analytes can be performed by extracting appropriate features from the ion-channel signals and using them for classification. In this paper, we consider features extracted from the Fourier, Wavelet and Walsh-Hadamard domain representations of the ion-channel signals. The proposed approach uses the power distribution information in the transform domains as features for discrimination. We compare the performance of all the three sets of features using support vector machines for classification of analytes and present the results. Results obtained show that the transform domain features achieve high classification rates in addition to high sensitivity and specificity rates.

Nano-Resonators for RF-Enabled Networked-Control

Several types of microfabricated mechanical filters are analyzed for RF communica- tions applications and their advantages over the traditional SAW or FBAR filters are described. GHz frequency operation requires sub-micron dimensions. This work focuses on the modeling of a filter with torsional mode vibration. Ansys finite element simulation has been performed to make comparison with the analytical modelling. These devices enable a networked approach to control along with a specific application to velocity estimation in servocontrol.

CMOS-compatible RF MEMS switch

Mobile technologies have relied on RF switches for a long time. Though the basic function of the switch has remained the same, the way they have been made has changed in the recent past. In the past few years work has been done to use MEMS technologies in designing and fabricating an RF switch that would in many ways replace the electronic and mechanical switches that have been used for so long. The work that is described here is an attempt to design and fabricate an RF MEMS switch that can handle higher RF power and have CMOS compatible operating voltages.

Signal processing for biologically inspired sensors

Pores or channels with diameters in the range of nanometers up to micrometers can be used as Coulter counting apertures to detect particles and organic molecules such as proteins. Coulter counting is performed by applying a constant potential across a nano- or micropore while recording the drop in ionic current upon passage of a molecule. Looking at the shape and duration of these current pulses enables us to estimate the size as well as the concentration of these molecules. Discrimination between different analytes can be performed by extracting appropriate features from the Coulter signals (events) and using them for classification. The challenge in being able to identify particular analytes is that a drop in current can also be caused by a molecule bouncing off the pore wall rather than moving through the micropore. Such drops are called non-events and can be discriminated from the events using Support Vector Machines. In this paper, we consider the amplitude of the current drop and the duration of the current pulse as features to determine if an event occurred. The proposed approach uses the Dirichlet process mixture model to cluster the data in the feature domain as the type of the events in the signal record is unknown. Results obtained show that the Dirichlet process mixture model accurately finds the types of events and their count for each signal record.