Electrical Engineering

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Shiv Nadar University

Power amplifier plays most important part of the electromagnetic suspension system. The recent advances in the technology of attraction type magnetic levitation are attributable almost entirely to the development of solid state electronic and power semiconductor devices. The amplifier should have properties like fast dynamics, wide bandwidth, ability to handle large payload, energy efficient, high reliability and should be cost-effective. Both linear and switching mode power amplifiers have been used in the field of DC electromagnetic suspension system. In this paper different possible switched mode power circuits for single magnet based electromagnetic levitation system have been discussed and a comparative study has been made of the different topologies of power amplifiers based on their structure and some experimental results. In the actual work design, fabrication and testing of an electromagnetic levitation scheme has been made as a complete project. But in this paper the emphasis is given on power amplifier portion due to limitation of space. A new single switch based switched mode power amplifier for electromagnetic levitation has been introduced. This circuit is simpler in topology and has some definite advantages over mostly reported asymmetrical H-bridge converter [10].

World University root node

(SoE) School of Engineering

Proceedings of the IEEE International Conference on Industrial Technology

Description and analysis of switched mode chopper amplifier for DC attraction type levitation system

A recently proposed novel technique for thermal non-destructive characterization based on digitized frequency modulated thermal waves is described. Defect detection in metallic, composite and semiconductor samples are presented as applications of digitized frequency modulated thermal wave imaging (DFMTWI). High peak power heat source requirement in pulsed thermography, and limited depth resolution of lock-in thermography due to fixed modulating frequency of sources, are over come by the proposed new technique by use of appropriately modulated excitation signal, limited both in time duration and frequency bandwidth.

Proceedings of SPIE - The International Society for Optical Engineering

Phase sensitive digitized frequency modulated thermal wave imaging and pulse compression for NDE applications

Thermography is a whole field, non-contact and non-destructive characterization technique that is widely used for the investigation of sub-surface features in various kinds of solid materials (conductors, semiconductors, insulators and polymers). In this work, a new method is proposed and demonstrated for the interface study of the bonded wafers that are frequently used in MEMS and VLSI. For the demonstration, two oxidized wafers are direct bonded: one plane and the other having anisotropically etched cavities. To observe the effect of annealing on bonding, the bonded pair was annealed at different temperatures for a fixed period, and also for different time periods at a fixed temperature. Compared to conventional passive wave and pulse thermography techniques, the proposed digitized linear frequency modulated thermal wave imaging (DFMTWI) method overcomes certain drawbacks associated with conventional thermal imaging techniques: in comparison to lock-in thermography it requires very less experimentation time whereas in comparison with pulse thermography less peak power heat sources are sufficient. It is further demonstrated that DFMTWI, in principle, is capable of differentiating depths of various cavities, and the thermal phase images can lead to actual depth estimation also. © 2006 Elsevier B.V. All rights reserved.

Sensors and Actuators, A: Physical

Interface study of bonded wafers by digitized linear frequency modulated thermal wave imaging

This paper presents a simple and inexpensive method for estimation of thermal diffusivity of solid materials. It is based on the time delay for applied temperature at one end of a material to reach onto the other side. A resistance-capacitance (RC) model of transient heat conduction has been used for obtaining the thermal delay time expression from the analogous voltage delay time in a distributed RC ladder. The derived expression of thermal delay time depends on the thickness and thermal diffusivity of material. By knowing the delay time and thickness of material, thermal diffusivity can be estimated by the proposed expression. Simulations and experiments have been performed on different materials for estimation of thermal diffusivity. For measurement of temperature, silicon spreading resistance temperature (SRT) sensor has been fabricated. It is ideally suited for present requirement of experiments because of its light weight, small size, moderate sensitivity and linear response in the temperature range of the interest. Copyright © 2005 American Scientific Publishers. All rights reserved.

Sensor Letters

Electro-thermal approach to thermal diffusivity measurement using silicon spreading resistance temperature sensor

A new, quantitative, whole field, non-contact and non-destructive technique for sub-surface defect detection is presented based on frequency modulated thermal wave imaging (FMTWI). Electro-thermal modeling and MATLAB-SIMULINK simulation has been carried out for the proposed technique. Experimental results of frequency modulated thermal wave imaging are reported, and defect detection by a correlation approach demonstrated. © 2005 2005 Taylor & Francis Group, LLC.

Quantitative InfraRed Thermography Journal

Defect detection by pulse compression in frequency modulated thermal wave imaging

The paper presents a novel algorithm based on game theory for optimizing controllers in presence of additive exogenous disturbances and parametric uncertainties of the controlled plant. The problem of controller design has been framed as a zero-sum Markov game between the controller and the disturber (disturbances). The proposed algorithm employs an 'annealed1 combination, of a variation of the 'cautious fictitious play' approach and the 'min-max5 solution methodology, for generating an optimal policy via a simple linear program. In Reinforcement Learning (RL) paradigm, controller optimization is done either in the Markov Decision Process (MDP) framework that assumes not only a stationary environment but is also inadequate for modeling noise and disturbances or the solution approach, which is computationally demanding and at times, even infeasible. The proposed approach generates a 'safe' and 'universally consistent' controller, by using a hybridization of the min-max strategy and a variation of cautious fictitious play. We empirically evaluate the approach on (i) Inverted Pendulum swing-up and, (ii) Non-holonomic Mobile Robot control tasks and compare its performance against standard O learning. Copyright © IICAI 2005.

Proceedings of the 2nd Indian International Conference on Artificial Intelligence, IICAI 2005

A safe and consistent game-theoretic controller for nonlinear systems

Standard valves typically have components in them, which are unsuitable for high temperature and corrosive environments. The usage of ceramic components in check and ball valves represents an effective solution for high temperature applications. Ceramic springs and seats were machined using a custom designed computer automated SD 300 Prazi lathe. This lathe was used to fabricate springs of 10, 12, 14 and 16 Turns per Inch (TPI) for check valves and a 17 TPI spring for the ball valve. All ceramic components were produced from Yttria stabilized zirconia. The ceramic seats were machined using a diamond round tool and installed into the valve body. The seats were lapped using a special Metadi diamond polish to mate the sealing surfaces. The valve components were specially altered by Parker Hannifin Corporation to accommodate the ceramic components. A spring pocket was provided in the check valve cap so that the poppet comes to a stop when it hits the spring pocket. This prevents the spring from getting compressed beyond reasonable limits. A spring pocket was also machined into the end flange for the ball valve to accommodate the inlet ceramic spring. Seat pockets were also provided in the valve cap and flange body to accommodate ceramic seats in both. Check valves was tested for leakage and cracking pressure both from ambient temperatures to temperatures of 898 K. Cracking pressures for the ceramic check valves were relatively constant and ranged from (26.455 +/- 0.186) to (8.44 +/- 0.182) psi for the 10 to 16 TPI springs installed in the valve. The ball valve was fabricated from a solid Alumina ceramic ball, core drilled and slotted to match Parker Hannifin's dimensions. Ball valves typically use bidirectional flow however the current design must be unidirectional. The exit seat was solidly mounted while the inlet seat was spring loaded. This arrangement enhances sealing pressure on the ball. The ball was lubricated using a high temperature graphite lubricant. The operating pressure of the ball valve with the 17 TPI spring exceeds our test pressure of 200 psig. The design withstood 200 psid over a two hour period without signs of leakage. These are preliminary experiments with this ball valve design, and represent the initial steps in the development of a high temperature variant.

2005 AIChE Spring National Meeting, Conference Proceedings

Dynamic performance of a high temperature check valve and initial testing of a ceramic ball valve

Although fuzzy decision trees (FDT) has been a very powerful methodology to extract human interpretable classification rules, it is often criticized to result in poor learning accuracy. In this paper, we propose a methodology to apply back propagation algorithm directly on the fuzzy decision tree structure for improving its learning accuracy without compromising the interpretability. By keeping the tree structure intact, this methodology efficiently tunes the tree parameters with significant increase in the learning accuracy. © 2005 IEEE.

IEEE International Conference on Fuzzy Systems

Improving the learning accuracy of fuzzy decision trees by direct back propagation

Based on some properties of fuzzy t-norm and t-conorm operators, the concept of fuzzy-rough sets on compact computational domain has been put forward. Various mathematical properties of this new definition of fuzzy-rough sets are discussed from pattern classification viewpoint. It is established that the proposed approach identifies various patterns in the sense of fuzzy-roughness, in addition to providing deeper insight into various concepts of fuzzy-rough sets. © 2005 Elsevier B.V. All rights reserved.

Pattern Recognition Letters

On the compact computational domain of fuzzy-rough sets

This paper discusses two different modes of breakdown in the reverse-biased I-V characteristics observed generically in bipolar junction transistors (BJTs) with the base emitter shorted, showing an erratic behavior, in the presence of large displacement currents. Experimental observations related to reverse-biased collector junctions of BJTs, that exhibit two different states of breakdown when a fast voltage ramp is applied are presented. Numerical simulations of the transient behavior of avalanche injection in p n- n+ structures show that two very close breakdown states coexist. The mechanisms leading to the erratic behavior of the second breakdown are discussed. The jittery nature of the breakdown is attributed to the delay associated with the buildup of the electric field across the n- n+ junction. © 2005 American Institute of Physics.