Department of Electrical Engineering

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In this paper, a novel technique to enhance the bandwidth of substrate integrated waveguide cavity backed slot antenna is demonstrated. The feeding technique to the cavity backed antenna has been modified by introducing offset feeding of microstrip line along with microstrip to grounded coplanar waveguide transition which helps to excite TE120 mode in the cavity and also to get improvement in impedance matching to the slot antenna simultaneously. The proposed antenna is designed to resonate in X band (8-12 GHz) and shows a resonance at 10.2 GHz with a bandwidth of 4.2% and a gain of 5.6 dBi, 15.6 dB front to back ratio and -30 dB maximum cross polarization level. © 2013 IEEE.

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2013 IEEE Applied Electromagnetics Conference, AEMC 2013

Bandwidth enhancement of substrate integrated waveguide cavity backed slot antenna by offset feeding technique

This paper presents a novel dynamic stochastic resonance (DSR)-based technique for robust extraction of a grayscale logo from a tampered watermarked image. The watermark embedding is done on the singular values (SV) of the discrete cosine transform (DCT) coefficients of the cover image. DSR is then strategically applied during the logo extraction process where the SV of DCT coefficients are tuned following a double-well potential model by utilizing the noise introduced during attacks. The resilience of this technique has been tested in the presence of various noises, geometrical distortions, enhancement, compression, filtering and watermarking attacks. The proposed DSR-based technique for logo extraction gives noteworthy robustness without any significant trade-off in perceptual transparency of the watermarked image. A maximization approach has been adopted for the selection of bistable double-well parameters to establish noise-enhanced resonance. When compared with existing watermark extraction techniques based in SVD, DCT, SVD-DCT domains, as well as with their combination with DSR, the results suggest that remarkable improvement of robustness is achieved by using DSR on singular values of DCT. © 2014 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.

Journal of the Franklin Institute

Dynamic stochastic resonance-based grayscale logo extraction in hybrid SVD-DCT domain

Rapidly increasing penetration of renewable energy sources into conventional power distribution systems has led to the rise in power electronic converter dominated power distribution systems. However, it has been a well established that the presence of tightly regulated point-of-load (POL) converters in the power distribution system, which act as Constant Power Loads (CPLs), cause serious stability challenge in spite of ensuring stability of individual converters. In this paper, we propose a sliding-mode controller with a non-linear sliding surface to mitigate negative impedance instabilities caused by the CPLs in dc distribution systems (dc Micro-grids). The stability of proposed surface and existence of sliding modes are proved. A simplified structure of a dc micro-grid system with dc/dc boost converter and CPL is used for the implementation of the proposed controller. Proposed controller is able to mitigate negative impedance instabilities and ensures stable operation of dc micro-grid system under various disturbances. The performance of the proposed controller, under steady state, line and load variations are validated through simulations in MATLAB Simulink environment. © 2014 IEEE.

IECON Proceedings (Industrial Electronics Conference)

Constant power loads: A solution using sliding mode control

DC micro-grids are getting increased attention around the world due to the paradigm shift in electricity generation and changing nature of the modern electrical loads. However, one of the major issues with dc micro-grids and other multi-converter systems is stabilization of the system against negative impedance instabilities caused by negative incremental resistance behavior of tightly regulated point-of-load converters. This paper presents a PWM based sliding mode controller for negative impedance stabilization of dc-dc converters in a dc micro-grid. The existence of sliding modes is proved. The proposed controller and simplified dc micro-grid are modeled in MATLAB SIMULINK and simulated response is studied to check the suitability of the proposed controller. Simulated response validates the effectiveness of the proposed controller with variations in the input voltage and the load. © 2014 IEEE.

Proceedings of 6th IEEE Power India International Conference, PIICON 2014

A PWM based sliding-mode control for negative impedance stabilization in DC Micro-girds

In this paper, a non-invasive, portable and inexpensive antenatal care system is developed using fetal phonocardiography. The fPCG technique has the potential to provide low-cost and long-term diagnostics to the under-served population. The fPCG signal contains valuable diagnostic information regarding fetal health during antenatal period. The fPCG signals are acquired from the maternal abdominal surface using a wireless data acquisition and recording system. The diagnostic parameters e.g., baseline, variability, acceleration and deceleration of the fetal heart rate are derived from the fPCG signal. A model based on adaptive neuro-fuzzy inference system is developed for the evaluation of fetal health status. To study the performance of the developed system, experiments were carried out with real fPCG signals under the supervision of medical experts. Its performance is found to be in close proximity with the widely accepted Doppler ultrasound based fetal monitor results. The overall performance shows that the developed system has a long-term monitoring capability with very high performance to cost ratio. The system can be used as first screening tool by the medical practitioners. © 2014 Elsevier Inc. All rights reserved.

Digital Signal Processing: A Review Journal

A novel approach for phonocardiographic signals processing to make possible fetal heart rate evaluations

This paper deals with the bandwidth sharing and dynamic rate control in a connection-oriented multi-source network from the multivariable control theory perspective. Multi-source networks are characterised by heterogenous delays associated with their flows. General methodology in such cases involves design of a single input control (based on the upper bound of the delay) which is shared among the participating sources with the help of fairness algorithms. However, most of these fairness algorithms are iterative procedures and do not take into account the impact of variable delays on bandwidth allocation. By approaching this task from the multivariable control theory base, proposed method gives the flexibility to design optimal rate control in correspondence to the delays and removes the requirement of an explicit fairness algorithm. A novel discrete multivariable model of network is derived by segregating the sources according to their delays which leads to the property that the rank of input matrix and the system dimension are determined by the number of distinct delays and the upper bound of the delay respectively. With suitable choice of weighing matrices in the optimal control design, required fairness and throughput are ensured in the network. © 2014 IFAC.

IFAC Proceedings Volumes (IFAC-PapersOnline)

Multivariable approach to bandwidth sharing in a multi-source connection-oriented network with heterogenous delays

Low cost actuators and linkages used in Micro Aerial Vehicles will lead to unmodeled nonlinearities like dead zone and backlash in the actuator. These actuator nonlinearities are often neglected in the design of feedback control system and can detoriate the system performance remarkably. This paper presents the design of robust control laws for Micro Aerial vehicles (MAV) using sliding mode control approach to deal with nonlinear uncertain plant models. The uncertainties can be in the form of parametric variations, external disturbances or uncertain actuator nonlinearities. The uncertainties are assumed to be bounded with known values. Simulation has been carried out using MAV 6 DoF nonlinear model and the results are provided to check the performance of the control laws.

International Journal of Micro Air Vehicles

Robust stabilization of micro aerial vehicles with uncertain actuator nonlinearities

In this paper, sliding mode control for discrete time systems with stochastic noise in their input channel has been discussed. The idea of process control using control charts has influenced this new approach towards dealing with systems with stochastic noise. The new approach approximates the stochastic noise as a bounded uncertainty, similar to having bounds in the control charts for stochastic process control data. For discrete time systems, this results in a bounded stability in probability of the quasi sliding mode, which is referred to as the N-sigma bounded stability. The probability associated with the stability notions is not fixed and the control engineer may desire lower or higher degrees of stability in terms of this probability. Thus one has design flexibility while implementing the theory in practice, where one might have to adjust the desired degree of stability due to hardware limitations. © 2013 The Franklin Institute.

N-sigma stability of stochastic systems with sliding mode control

Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 1010 cm-2, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120-300 K and it shows a rectifying behavior. Barrier height (φB) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A*) was evaluated using Richardson plot of ln(Io/T2) versus q/kT plot by linear fitting in two temperature range 120-180 K and 210-300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic equation gives mean barrier heights of 0.55 ± 0.01 eV and 0.86 ± 0.02 eV for two different temperature regions 120-180 K and 210-300 K, respectively. Modified Richardson plot provided two values of Richardson constant for two temperature regions. However, for higher temperature range (210-300 K), the calculated value of Richardson constant ∼123 A cm-2 K-2 was close to the ideal Richardson constant for n-Si. © 2014 AIP Publishing LLC.

Fulltext

Journal of Applied Physics

Temperature dependent electrical transport studies of self-aligned ZnO nanorods/Si heterostructures deposited by sputtering

Uniformly distributed and defect-free vertically aligned ZnO nanorods (NRs) with high aspect ratio are deposited on Si by sputtering technique. X-ray diffraction along with transmission electron microscopy studies confirmed the single crystalline wurtzite structure of ZnO. Absence of wide band emission in photoluminescence spectra showed defect-free growth of ZnO NRs which was further conformed by diamagnetic behavior of the NRs. H2 sensing mechanism based on the change in physical dimension of channel is proposed to explain the fast response (∼21.6 s) and recovery times (∼27 s) of ZnO NRs/Si/ZnO NRs sensors. Proposed H2 sensor operates at low temperature (∼70 °C) unlike the existing high temperature (&gt;150 °C) sensors. © 2014 AIP Publishing LLC.