Electrical Engineering

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Shiv Nadar University

Energy detection in frequency domain is a preferred technique for the spectrum sensing and the accuracy of frequency estimation depends on the DFT size. A new technique for energy detection is proposed here. Instead of computing full length (N-point) DFT of the whole data, this paper proposes a two level (coarse-fine) approach. In the first (coarse) level, time averaging of smaller size (L≪N) data blocks of the whole data and its DFT are computed and Neymen Pearson based detection is performed to determine the presence of energy in the subbands. In the second level (fine), Goertzel algorithm is applied to determine the fine estimates in those subbands. Matlab based experiments were performed to verify the proposed method. Simulation result also shows that this method can be applied for non-uniformly occupied spectrum also. The complexity of this approach is evaluated and it is about 51% computationally more efficient at -5 dB signal to noise ratio of received signal. © 2012 IEEE.

World University root node

(SoE) School of Engineering

Proceedings of the 2012 3rd International Conference on Computer and Communication Technology, ICCCT 2012

Non-uniform spectrum sensing using computationally efficient 2-level (FFT-Goertzel) based energy detection

Purpose - The purpose of this paper is to give a comprehensive description of various safety factors that need to be determined while assessing the short-circuit strength of transformers. Design/methodology/approach - Factors of safety are divided into two categories: radial and axial. Some of the latest approaches in assessing the strength are elaborated. Findings - Six major sets of calculations are identified: three each for radial and axial electromagnetic forces. Corresponding factors of safety are defined and calculated for practical transformers. These factors are related to the strength and stability aspects of windings. Research limitations/implications - The work gives pointers for further research at appropriate places while highlighting the challenges involved in the assessment of the short-circuit strength. Practical implications - The presented overview of the factors of safety can be a useful guide for the practicing transformer engineers. Originality/value - The main contribution of the reported work is in highlighting the intricacies associated with the subject of short-circuit strength of power transformers. It can serve as a reference document for future research works in the area since the procedures are outlined for calculating the factors of safety through six case studies. © 2012 Emerald Group Publishing Limited. All rights reserved.

COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

Towards short-circuit proof design of power transformers

The pseudospark (PS) discharge is, however, more recently recognized as a different type of discharge which is capable of generating electron beams with the highest combined current density and brightness of any known type of electron source. PS discharge is a specific type of gas discharge, which operates on the left-hand side of the hollow cathode analogy to the Paschen curve with axially symmetric parallel electrodes and central holes on the electrodes. The PS discharge generated electron beam has tremendous applications in plasma filled microwave sources where normal material cathode cannot be used. Analysis of the electron beam profile has been carried out experimentally for different applied voltages. The investigation has been done at different axial and radial location inside the drift tube in argon atmosphere. This paper represents experimentally derived axial and radial variation of the beam current inside the plasma filled drift tube of PS discharge based plasma cathode electron (PCE) gun. With the help of current density estimation the focusing and defocusing point of electron beam in axial direction can be analyzed. It has been further confirmed the successful propagation of electron beam in confined manner without any assistance of external magnetic field.

Fulltext

Journal of Physics: Conference Series

Experimental investigation of pseudospark generated electron beam

We propose a new way to estimate the sparse multipath channel of an Amplify and Forward Two Way Relay Network (AF-TWRN) based on Compressive Sensing (CS), using Compressive Sampling Matching Pursuit (CoSaMP). MSE based performance of CoSaMP and OMP methods and corresponding BPSK based BER performance of the system using the estimated channels are plotted. CoSaMP based channel estimation is performing similar to OMP based channel estimation, with lesser time complexity, in both MSE and BER measures of the system, when the sparsity/worst case sparsity of the channel is known. © 2012 IEEE.

Performance comparison of OMP and CoSaMP based channel estimation in AF-TWRN scenario

We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar-N 2 (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV-vis spectroscopy. Photo-luminescence broad band was observed in the range of 420-600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects. © 2011 Elsevier B.V. All rights reserved.

Applied Surface Science

Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating

The possibility of detecting very small defects in concrete was presented, representing disbands, voids and inhomogeneities, using the thermal imaging technique. Results are compared with pulse travel times measured using the ultrasonic pulse velocity (USPV) technique. Two types of specimens were prepared, beams and slabs, using grade 43 cement, Zone II sand as per IS 383 and 10-mm crushed coarse aggregate. The USPV and the thermal imaging techniques were applied on the four specimens to study the variations introduced by the experimental defects. A thermal image of the slab which had wooden blocks embedded at different depths can easily identify the region of discontinuity at depths of 10, 20, 30 and 40 mm. It is found that as compared to the conventional techniques, the thermal imaging provides an easy to interpret visual picture, in a single scan of the specimen used.

Experimental Techniques

Defect detection in concrete structures using thermal imaging techniques

We present a novel word image based document indexing scheme by combination of string matching and hashing. The word image representation is defined by string codes obtained by unsupervised learning over graphical primitives. The indexing framework is defined by distance based hashing function which does the object projection to hash space by preserving their distances. We have used edit distance based string matching for defining the hashing function and for approximate nearest neighbor based retrieval. The application of the proposed indexing framework is presented for two document image collections belonging to Devanagari and Bengali script. © 2011 IEEE.

Proceedings of the International Conference on Document Analysis and Recognition, ICDAR

Document image indexing using edit distance based hashing

The pseudospark (PS) discharge has been shown to be a promising source of high brightness, high intensity electron beam pulses. The PS discharge sourced electron beam has potential applications in plasma filled microwave sources where normal material cathode cannot be used. Analysis of the electron beam profile has been done experimentally for different applied voltages. The investigation has been carried out at different axial and radial location inside the drift space in argon atmosphere. This paper represents experimentally found axial and radial variation of the beam current inside the drift tube of PS discharge based plasma cathode electron (PCE) gun. With the help of current density estimation the focusing and defocusing point of electron beam in axial direction can be analyzed. © 2011 Springer Science+Business Media, LLC.

Journal of Infrared, Millimeter, and Terahertz Waves

Experimental analysis of Pseudospark sourced electron beam

This paper presents a MIMO two-way relaying scheme where the transceiver filter at the Relay Station (RS) processes the data using Least Mean Square Algorithm (LMS) and Normalized Least Mean Square (NLMS) algorithm. The relaying technique used is Amplify and Forward scheme (AF). Channel State Information (CSI) is assumed to be available only at the RS. So the transmit and receive processing are both done at the RS. The data at the two nodes S1 and S2 is Quadrature Phase Shift Keying (QPSK) modulated. The metrics considered for performance comparison of the LMS/NLMS transceiver filter is Mean Square Error (MSE) and Bit Error Rate (BER). The computer simulations are performed using MATLAB. © 2011 IEEE.

ICCSP 2011 - 2011 International Conference on Communications and Signal Processing

Performance comparison of LMS/NLMS based transceiver filters for MIMO two-way relaying scheme

We propose a novel hierarchical framework for scene categorization. The scene representation is defined by latent topics extracted by Latent Dirichlet Allocation. The interaction of these topics across scene categories is learned by probabilistic graphical modelling. We use Conditional Random Fields in a hierarchical setting for discovering the global context of these topics. The learned random fields are further used for categorization of a new scene. The experimental results of the proposed framework is presented on standard datasets and on image collection obtained from the internet. © 2011 Springer-Verlag Berlin Heidelberg.