Department of Electrical Engineering

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In this paper a new approach is presented for discrete time sliding mode control based on multi-rate output samples. It will be shown here if the outputs of the system are some of the states only or system is in a special form, multi-rate observer i.e the state of the system can be obtained by the matrix inverse of lower dimension than the existing multi-rate observer proposed earlier. This can be further used to obtain sliding mode control based on multi-rate output samples. © ICROS.

World University root node

ICCAS 2007 - International Conference on Control, Automation and Systems

A new formulation on discrete-time sliding mode control using multirate output feedback

The paper presents a new method for design of power system stabilizer (PSS) based on relay-free sliding mode control technique. The control objective is to enhance the stability and to improve the dynamic response of the single machine infinite bus (SMIB) system. We apply this relay-free sliding mode controller to design power system stabilizer for demonstrating the availability of the proposed approach. © 2007 IEEE.

Proceedings of the American Control Conference

Relay-free sliding mode control technique based power system stabilizer for single machine infinite bus system

In the present work, we report the deposition of high resistivity c-axis oriented ZnO films by RF magnetron sputtering. The deposition parameters such as RF power, target-to-substrate spacing, substrate temperature, and sputtering gas composition affect the crystallographic properties of ZnO films, which were evaluated using XRD analysis. The self-heating of the substrate in plasma during film deposition was investigated and we report that highly "c-axis oriented" ZnO thin films can be prepared on different substrates without any external heating under optimized deposition parameters. The post-deposition annealing of the film at 900 °C for 1 h in air ambient increases the intensity of (002) peak corresponding to c-axis orientation in addition with the decrease in full width at half maxima (FWHM). Bond formation of ZnO was confirmed by FTIR analysis. Grains distribution and surface roughness have been analyzed using SEM and AFM. The DC resistivity of the films prepared under different deposition conditions was measured using MIS/MIM structures and was found to be in the range of 1011-1012 Ω cm at low electric field of 104 V/cm. The ZnO film of 1 μm thickness has transmittance of over 85% in the visible region. Applications of these films in MEMS devices are discussed. © Springer Science+Business Media, LLC 2007.

Journal of Materials Science

Growth and characterization of high resistivity c-axis oriented ZnO films on different substrates by RF magnetron sputtering for MEMS applications

High-throughput screening of drug candidates for channelopathies can greatly benefit from an automated patch-clamping assay. Automation of the patch clamping through microfluidics ideally requires on-chip integration of glass capillaries with substantially round cross section. Such round capillaries, if they can only be integrated to connect isolated reservoirs on a substrate surface, will lead to a "lateral" configuration which is simple yet powerful for the patch clamping. We demonstrate here "lateral" patch clamping through microfluidic integration of substantially round glass capillaries in a novel process. The process adopts two well-known phenomena from microelectronics: keyhole-void formation and thermal-reflow of phosphosilicate glass in silicon trenches. The process relies on the same physical principle as the preparation of conventional micropipette electrodes by heat-pulling and fire-polishing glass tubes. The optimized process forms capillaries with a diameter ∼1.5 μm and variation <10%. Functionality of the integrated glass capillaries for the patch-clamp recording has been verified by statistical test results from a sample of one hundred capillaries on mammalian cells (RBL-1) in suspension: 61% formed gigaseals (>1 GΩ) and of those ∼48% (29% of all) achieved whole-cell recordings. Pharmacological blockade of ion channel activity and longevity of a whole-cell mode on these capillaries have also been presented. © The Royal Society of Chemistry.

Lab on a Chip

Microfluidic integration of substantially round glass capillaries for lateral patch clamping on chip

CMOS compatible silicon technologies are used to fabricate schematically arranged arrays of nanostructures for Surface Enhanced Raman Spectroscopy (SERS), incorporating processes like DUV photolithography, reactive ion etching and physical vapour deposition of silver and gold. The surface treatment of cuvette and tubes used to handle Rhodamine 6G (R6G) and the substrate pre-treatment procedures, being significant for concentration less than 10 -9 M, are elaborated. The Raman signal is also enhanced by the addition of sodium chloride to R6G and by optimizing the sample immersion time in the analytes. 10-10 and 10-12 M R6G with 1mM sodium chloride is detected on silver and gold terminated SERS substrates respectively. ©2007 IEEE.

TRANSDUCERS and EUROSENSORS '07 - 4th International Conference on Solid-State Sensors, Actuators and Microsystems

Highly ordered nanostructures for ultra-sensitive sers

Lecture Notes in Control and Information Sciences

Modeling, control and implementation of smart structures

In γ - δ Routh approximation of interval systems, interval Routh approximant may not be robustly stable even if the original interval system is robustly stable. Thus, in this paper an improvement is proposed to the γ - δ Routh approximation for interval systems using Kharitonov polynomials such that the resulting interval Routh approximant is always robustly stable. A numerical example illustrates the procedure. © 2007 IFAC.

IFAC Proceedings Volumes (IFAC-PapersOnline)

Improved γ-δ routh approximation of interval systems using interval arithmetic

This paper presents the modeling, design and simulation of a Robust Decentralized Fast Output Sampling (RDFOS) feedback controller for the vibration control of a smart structure (flexible cantilever beam) when there is actuator failure. The beam is divided into 8 finite elements and the sensors/actuators are placed at finite element positions 2, 4, 6, and 8 as collocated pairs. The smart structure is modeled using the concepts of piezoelectric theory, Euler-Bernoulli beam theory, Finite Element Method (FEM) techniques and the state space techniques. Four multi-variable state-space models of the smart structure plant are obtained when there is a failure of one of the four actuators to function. The effect of failure of one of the piezo actuators to function during the vibration of the beam is observed. The tip displacements, open and closed loop responses with and without the controller are observed. For all of these models, a common stabilizing state feedback gain F is obtained. A robust decentralized fast output sampling feedback gain L which realizes this state feedback gain is obtained using the LMI approach. In this designed control law, the control inputs to each actuator of the multi-model representation of the smart structure is a function of the output of that corresponding sensor only and the gain matrix has got all off-diagonal terms zero and this makes the control design a robust decentralized one. Then, the performance of the designed smart system is evaluated for Active Vibration Control (AVC). The robust decentralized FOS controller obtained by the designed method requires only constant gains and hence may be easier to implement in real time.

Asian Journal of Control

Fault tolerant control of flexible smart structures using robust decentralized fast output sampling feedback technique

A new single wafer process with a unique integration of bulk and surface micromachining process steps has been designed, developed, and demonstrated for MOEMS/MEMS devices, which require large free space for structural movements. 3D free space electrostatic micromirror device was used as the test vehicle for this development. Bottom electrode, flexure springs, and micromirror plate were fabricated in single crystal silicon substrate layer, while the top electrode plate and bending springs were realized in polycrystalline silicon layers. The realized test chip 3D micromirror devices were tested and an angular deflection of up to 2° was measured. © 2005 Elsevier B.V. All rights reserved.

Thin Solid Films

A novel electrostatic microactuator for large deflections in MEMS applications

The effects of thermal annealing on amorphous silicon deposited using low-pressure chemical vapour deposition (LPCVD) are presented in this paper. The amorphous silicon film is being subjected to different annealing conditions ranging from 600 to 900 °C for a varying period of 30 to 90 min holding time in nitrogen ambient. X-Ray diffraction (XRD) shows that crystallization of amorphous silicon to poly-silicon starts to occur after 30 min of thermal cycle at 600 °C. Atomic force microscope (AFM) has been used to study the surface roughness and grain size of the films after different annealing times and temperatures. The nanocrystalline grains result in photoluminescence behavior. Stress measurement, using curvature analysis, shows that the stress magnitude reduces with decreasing annealing temperature and time. This is likely due to stress relief during grain growth and crystallization at higher temperatures. The detailed study of the structural, morphology and property changes in amorphous silicon upon annealing will be presented.