Department of Electrical Engineering

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IIT Jodhpur

World University root node

IEEE Control Systems

IEEE Fall School on Modern Sliding-Mode Control [Conference Reports]

Automatic diagnosis of the heart valve diseases generally requires the segmentation of heart sound signal. Henceforth, in this paper a novel algorithm for automatic segmentation of the heart sound signal is proposed. The heart sound signal is acquired using seismocardiography (SCG), which uses a sensor called accelerometer. The accelerometer is of small size and low weight and thus convenient to wear. The proposed algorithm performs in three steps. First, the signal is filtered using the developed denoising algorithm based on discrete wavelet transform. The computational complexity of this algorithm is reduced by processing only two levels, which are expected to have heart sound signal, and other levels are discarded. To improve the performance of denoising, an adaptive threshold is obtained for both the levels separately, and applied. Then, the denoised signal is obtained by reconstructing the thresholded coefficients. In the second step, peaks are detected in the denoised signal using an adaptive threshold, obtained using Otsu's method. Then, false detected peaks and noise contaminated parts of the signal are identified and discarded from further analyses. In the third step, the heart sound components are identified as S1, and S2 based on the energy of the particular component and segmentation is performed. The results of denoising, show that the developed algorithm outperforms the existing method. Further, the segmentation results show that the developed algorithm is able to identify the heart sound components, accurately, even in the presence of noise. © 2016 IEEE.

2016 International Conference on Systems in Medicine and Biology, ICSMB 2016

An algorithm for automatic segmentation of heart sound signal acquired using seismocardiography

The paper presents the robust finite-time tracking of Stewart platform using super-twisting sliding mode observer based forward kinematics solution. The forward kinematics problem-finding the states from the leg length measurements-in Stewart platform gives nonunique solution for any given leg lengths, and due to this it poses difficulties in the control design. The super-twisting observer is designed fromthe available leg length measurements which is the output of the system to obtain the position and orientation of movable platform and their respective derivatives. The finite-time convergence of this observer and the stability of the closed loop system are presented in detail. It is shown that using this leg length measurements, the states of the observer converge to actual state in finite-time and hence, it provides a solution to the forward kinematics problem. Using these estimated states, a robust finitetime tracking control is designed for the Stewart platform by considering all the uncertainties and parameter variations. However, the proposed method for forward kinematics solution can also be incorporated with any other control strategies. Simulation results are given to demonstrate the performance of the proposed observer for the Stewart platform. © 2017 IEEE.

IEEE Transactions on Industrial Electronics

Robust finite-time tracking of stewart platform: A super-twisting like observer-based forward kinematics solution

Effect of ultra-violet (UV) irradiation (λpeak = 365 nm) on the electrical characteristics of solution processed flexible TIPS-pentacene organic field-effect transistors (OFETs) has been investigated. Pristine TIPS-pentacene OFETs demonstrated average field-effect mobility of 0.1 cm2 V−1 s−1, with near zero threshold voltage and current on-off ratio of ∼104. On UV irradiation, OFETs displayed a joint photoconductive and photovoltaic effect due to photo-generated excitons. The maximum current modulation and photo-responsivity obtained from these OFETs were ∼500 and ∼43 mA/W respectively at an intensity of 1.8 mW/cm2 while operating at a low voltage of −5 V. On increasing the irradiation time, a positive shift in the threshold voltage was observed. At larger values of irradiation time, a roll-off in maximum drain current and mobility values were observed, which was attributed to slight deterioration in crystallinity due to prolonged UV exposure, as confirmed from X-ray diffraction studies. Similar trend was observed for mobility and threshold voltage values, when gate bias during UV irradiation was increased. In addition, transistors exhibited a repeatable dynamic response to periodic pulses of UV irradiation. © 2017 Elsevier Ltd

Superlattices and Microstructures

Effect of UV irradiation on solution processed low voltage flexible organic field-effect transistors

In recent years DC micro-grid has been widely accepted as one of the promising solutions to integrate renewableenergy sources and to supply power to critical loads such as data centres, remote villages and communication stations.However, DC micro-grid has a fundamental stability challenge due to constant power load (CPL) characteristics of point-ofloadconverters, which introduce destabilising effect in the system. This study presents a sliding mode control based nonlinearcontrol scheme for a solar photo-voltaic based DC micro-grid in the presence of CPLs. The objective of the proposedcontrol scheme is to tightly regulate the DC bus voltage and mitigate the destabilising effects of CPLs. The stability of thesystem is analytically established and a limit of CPL is obtained. Furthermore, a charging/discharging algorithm isimplemented for battery bank interfacing bidirectional converter which facilitates three modes charging namelyconstant current, constant voltage, and float mode, to enhance the battery life. The validation of the effectiveness ofthe proposed scheme is done through simulation and experimental results. It is found that the proposed controlscheme ensures desired operation of the DC micro-grid under various operating modes and maintains system stabilitywith CPL under variations in the primary resource and load demand. © The Institution of Engineering and Technology 2017.

IET Power Electronics

Mitigation of destabilising effect of CPLs in island DC micro-grid using non-linear control

This paper describes the framework for event triggered control of a plant possessing two time scales. The periodic sampling requirement is relaxed and states are sampled based on a triggering rule. The dynamic trigger function where event triggering threshold varies with time has been used. Triggering function parameters are different for slow and fast states and events are detected independently in the two subsystems. This also allows the sensors for slow and fast states to be geographically distributed in the network. Further singular perturbation technique is used to decouple the system into fast and slow subsystems and stability of the overall system is investigated. It is proved that the closed loop system asymptotically converges to an adjustable region around the equilibrium point and a minimum bound on inter-execution time is also guaranteed. Asymptotic stability may also be obtained if the parameters of trigger function are adequately selected. Simulation results manifest the efficacy of the proposed approach and verify the theoretical analysis. © 2017 IEEE.

Department of Chemistry

2017 Indian Control Conference, ICC 2017 - Proceedings

Event triggered control of two time scale system

Flexible resistive switching memory device is an excellent option for future high density memory and flexible electronics applications. Here, bipolar resistive switching behavior in Al/HfOx/Au resistive random access memory (RRAM) devices fabricated on ultra-flexible polyimide substrates is demonstrated. These devices can be programmed at read-write voltages as low as 0.18 V with on-off current ratios (Ion/Ioff) of 18, resistance ratio of ∼41 in high and low resistance states (HRS &amp; LRS) and stable set and reset voltages over 16 cycles of operation. The mechanism of resistive switching in these devices is explained with help of filament formation and rupture process due to oxygen vacancy and oxygen ions migration. Ohmic conduction prevails in HRS and LRS whereas conduction mechanism is dominated by space charge limited conduction (SCLC). These flexible RRAM devices could be an excellent option for future high density memory applications. © 2016 IEEE.

2016 3rd International Conference on Emerging Electronics, ICEE 2016

Low voltage resistive switching behavior of Al/HfOx/Au structure on ultra-flexible polyimide substrate

Transmission electron-microscopy examination revealed the appearance of a hexagonal silicon (9R polytype) inclusions in the subsrface silicon layer upon ion implantation and subsequent heat treatment of the SiO2/Si structure. The formation of this hexagonal phase is stimulated by mechanical stresses arising in the heterophase system in the course of ion implantation. © 2017, Pleiades Publishing, Ltd.

Technical Physics Letters

Formation of hexagonal 9R silicon polytype by ion implantation

We have studied surface chemical states of Ba0.5Sr0.5TiO3 (BST) thin films as a function of high energy photon doses. BST thin films were deposited on Si substrates by Sputtering technique and post irradiations were carried out with high energy 60Co gamma radiation. Core-level and Fermi-level spectra were measured by X-ray photoelectron spectroscopy. The gamma-ray irradiated BST films showed a higher binding energy shift of Ba, Sr, and Ti core level with increasing gamma doses due to shift in Fermi level. The Fermi level is shifted towards conduction band by ~ 1.1 eV for 200 kGy gamma irradiated BST with respect to pristine. An increase in full width at half maximum of X-ray diffraction peak and surface roughness were also observed with increasing gamma doses. Higher leakage current and decrease in capacitance with gamma doses are further evidence of higher carrier concentration which is consistent with the shift in Fermi level. © 2017 Elsevier B.V.

Thin Solid Films

High energy photon induced Fermi-level shift of Ba0.5Sr0.5TiO3 thin films

In this study, CdO thin films were grown by e-beam evaporation technique on glass, indium tin oxide (ITO), fluorine-doped tin oxide (FTO) and silicon (Si) wafer. The deposited films were analyzed by X-ray diffraction (XRD), UV–Vis spectrophotometer, scanning electron microscopy, energy dispersive spectroscopy (EDS) and source meter (current–voltage) for structural, optical, surface morphological, elemental and electrical analysis, respectively. The films have single phase of cubic structure (space group Fm3m) with (200) preferred orientation. The structural parameters viz. inter-planar spacing, grain size, lattice constant, internal strain and dislocation density are calculated and found to vary with the nature of the substrates. The optical band gap was found in the range 2.24–3.95 eV and strongly dependents on the substrates. The SEM analysis shows that the films are compact, homogeneous and have granular structure without any defects like pin holes and cracks. The EDS spectra confirmed the presence of cadmium (Cd) and oxygen (O) in the films deposited on different substrates. The current–voltage characteristics of the films show ohmic behavior. © 2017 Elsevier B.V.