Department of Electrical Engineering

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Lecture Notes in Control and Information Sciences

Sliding mode control using novel sliding surfaces

Semiconducting nanowires have the potential to function as highly sensitive and selective sensors for label-free detection of biological and chemical species. In this paper, we describe the preparation and applications of oligopeptide-modified single crystal silicon nanowire (SiNW) arrays as multichannel metal ion sensors. Because these SiNW arrays were fabricated by using a "top-down" process, a very high density of individually addressable SiNW (180 SiNWs grouped into 36 clusters) can be manufactured on a single chip. Furthermore, after two different SiNW clusters are modified with Pb2+-selective and Cu2+-selective oligopeptide, respectively, concentrations of Pb2+ and Cu2+ in aqueous solutions can be detected simultaneously and selectively in two different channels. By using the SiNW arrays, we successfully achieved a detection limit of 1 nM for Pb2+ and 10 nM for Cu2+, respectively. These results demonstrate the potential utility of oligopeptide-modified SiNW arrays for highly sensitive and selective chemical and biological sensing applications. © 2009 Elsevier B.V. All rights reserved.

Biosensors and Bioelectronics

Oligopeptide-modified silicon nanowire arrays as multichannel metal ion sensors

The recent reports on giant piezoresistance effect in highly resistive silicon nanowires (SiNWs) have offer greater sensitivity in stress measurements. Despite enhanced sensitivity, the piezoresistance of highly conductive silicon are preferred as they are less prone to thermal noise and hence better accuracy. Here we report a thermal induced buckled micro-bridge technique to accurately characterize the temperature dependent piezoresistivity effect in SiNWs. Phosphorus doped (110) SiNWs with 50 nm wide, 60 nm thick and 100 μm in length were encapsulated within SiO2 micro-bridges. The electrical measurement of both reference SiNWs and SiNWs at micro-bridges was carried out, followed by the optical profiling of the micro-bridges with embedded SiNWs. N-type SiNWs with doping of 1×1020 ion/cm3 exhibit a strong dependence on temperature with a piezoresistive coefficient that decreased by 22.5% between 25°C to 60°C; whereas its bulk counterpart is independent of temperature across this range. The results demonstrated that thermal noise may be more detrimental to nano-scale electromechanical sensors than its bulk counterparts. © 2009 Materials Research Society.

Materials Research Society Symposium Proceedings

Extracting piezoresistance in SiNWs using thermal induced buckling of micro-bridges

Temporal changes in signal intensity of Surface Enhanced Raman Scattering (SERS) upon laser excitation is an interesting phenomenon in plasmonics. In-depth understanding of the phenomena is highly important especially when developing a SERS sensor based on the intensity variation of particular Raman peak/band. One of the main challenges in such a technique is the intensity reduction at a given location upon consecutive measurements. Previously, signal loss in SERS measurement was attributed to the electric-field induced roughness relaxations in the SERS active surface. In such cases, as the surface is smoothened out, signals are completely lost. In our observation, the reduction in the spectral intensity is irreversible but never completely lost and a major part of it can be attributed to the plasmon induced heating effect. Here, we experimentally demonstrate this effect by studying the SERS signal from four different Raman active molecules adsorbed onto substrates that contain uniform nano-roughened bi-metallic silver/gold coating. Possible mechanism that leads to irreversible signal loss is explained. Moreover, solutions for minimising such plasmonic heating when developing a biosensor are also discussed. © 2009 SPIE.

Proceedings of SPIE - The International Society for Optical Engineering

Fluctuation in surface enhanced Raman scattering intensity due to plasmon related heating effect

A study was conducted to demonstrate the fabrication of significantly aligned arrays of silicon nanowires (SiNW), using top-down complementary metal oxide semiconductor (CMOS)-compatible technology. The study focused on demonstrating the ability of these arrays for real-time extracellular recording of cellular bioelectricity. It was demonstrated that the CMOS-compatible technology enables noninvasive, highly sensitive, and long-term electrophysiological measurements at the single-cell level, or from tissues. The study employed a reproducible, scalable, and CMOS-compatible top-down method, to produce uniform and aligned long SiNWs, involving deep ultraviolet (UV) lithography and self-limiting oxidation. The reproducible, scalable, and CMOS-compatible top-down method was employed in the investigations, to avoid the limitations of bottom-up processes that are restricted to research laboratories.

Small

CMOS-compatible nanowire sensor arrays for detection of cellular bioelectricity

Recent advances in small, low cost satellite technology has generated a renewed interest in formation flying missions. One challenging aspect of satellite formation flying missions is collision free navigation and control. In this paper, novel robust control algorithm using Sliding Mode Control is presented for a three-dimensional, high Earth orbit satellite formation scenario. The paper presents the comparison of results of three types of Sliding Mode Controllers (SMC): the first one is a tan-hyperbolic SMC, the second one is a constant plus proportional rate SMC and the third one is a power rate SMC. Hybrid propulsion system minimises the use of on-board power for close formations. Artificial Potential Field method is used for collision-free path planning of the satellites in the formation. Simulation results show that for the formation flying scenario considered in this study, the constant plus proportional rate SMC and the power rate SMC gives better performance over the tan-hyperbolic SMC. Simulation results prove that for the tetrahedron formation considered in this study, the total control effort is less when the constant plus proportional rate controller and the power rate controller are used compared to the tan-hyperbolic sliding mode controller. Very little formation center movement is observed for the three SMCs.

60th International Astronautical Congress 2009, IAC 2009

Robust control and path planning algorithms for small satellite formation flying missions

A nonlinear sliding surface is proposed to improve the transient response for general discrete multiple-input-multiple-output linear systems with matched perturbations. The tracking case is analyzed, and it is shown that the scheme is able to achieve low overshoot and low settling time simultaneously; this is not possible with a linear sliding surface. The control law is based on the discrete-time sliding mode equivalent control and thus eliminates chattering. The control law is proposed based on two approaches: 1) reaching-law-based approach which needs only disturbance bounds and 2) disturbance-observer-based approach. Multirate output feedback is used to relax the need of the entire state vector for the implementation of the control law. A magnetic tape position control application is used to show the effectiveness of the proposed scheme. © 2009 IEEE.

IEEE Transactions on Industrial Electronics

High-performance tracking controller for discrete plant using nonlinear sliding surface

Prenatal monitoring enables early diagnosis of congenital anomalies and genetic disorders in the uterus. Several systems and techniques have been either developed or under development for this purpose. Every system under its developmental stage needs testing and validation of its performance. In this paper, a Signal Simulation Module (SSM) for simulation of maternal abdominal conditions has been developed. The developed module replicates the pregnant women's abdomen by generating various signals similar to actual signals using Matlab™. A comparison between signals from developed module and actual abdominal signals shows that presented system closely simulates acoustical conditions of the mother's abdomen. The developed module can be used for testing and calibration of prenatal monitoring systems during its different developing stages.

Proceedings of INDICON 2009 - An IEEE India Council Conference

Development of a signal simulation module for testing of phonocardiography based prenatal monitoring systems

Low-voltage pentacene organic field-effect transistors are demonstrated (operating voltage of -3 V) with high- κ hafnium dioxide gate dielectrics grown by atomic layer deposition at 200 °C. A high hole mobility of 0.39 cm2 /V s with low threshold voltage (&lt;-0.5 V) and low subthreshold slope of 120 mV/dec is achieved with a HfO2 dielectric layer modified with a phosphonic acid based treatment. A high value of 94.8 nF/V s is obtained for the product of mobility and capacitance density. The devices show excellent bias stress stability with or without the phosphonic acid at the HfO2 gate dielectric surface. © 2009 American Institute of Physics.

Fulltext

Applied Physics Letters

Low-voltage pentacene organic field-effect transistors with high- κ HfO2 gate dielectrics and high stability under bias stress

In this letter, the integration of a high-κ gate dielectric has been demonstrated for achieving low-operating-voltage organic field-effect transistors (OFETs) and circuits based on solution-processed poly(3-hexylthiophene) (P3HT). We have successfully demonstrated all-p-type organic circuits based on P3HT operating at below 4 V supply voltage. The switching behavior is improved by using the bootstrapping technique, with the bootstrapped inverter showing good results with a dc gain (Av) of -1.7 and VOH and VOL values of 3.3 and 0.35 V, respectively. The output swing of the bootstrapped inverter is improved by about 40% when compared to that of simple all-p-type inverters, as demonstrated by using experimental characterizations. © 2009 IEEE.