Electrical Engineering

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Thermal non-destructive testing (TNDT) is a whole field and non-contact technique for defect detection The present work describes a variant of TNDT for subsurface defect detection based on frequency modulated thermal wave imaging (FMTWI) Use is made of the frequency dependence of thermal diffusion length, to achieve entire depth scanning of a sample in one run This novel technique overcomes some of the drawbacks associated with traditional pulse and lock-in thermography. Experimental results are presented in support.

World University root node

(SoE) School of Engineering

Insight: Non-Destructive Testing and Condition Monitoring

Implementation of frequency-modulated thermal wave imaging for non-destructive sub-surface defect detection

In this paper, we have shown that the fuzzy-rough set attribute reduction algorithm [Jenson, R., Shen, Q., 2002. Fuzzy-rough sets for descriptive dimensionality reduction. In: Proceedings of IEEE International Conference on Fuzzy Systems, FUZZ-IEEE'02, May 12-17, pp. 29-34] is not convergent on many real datasets due to its poorly designed termination criteria; and the computational complexity of the algorithm increases exponentially with increase in the number of input variables and in multiplication with the size of data patterns. Based on natural properties of fuzzy t-norm and t-conorm, we have put forward the concept of fuzzy-rough sets on compact computational domain, which is then utilized to improve the computational efficiency of FRSAR algorithm. Speed up factor as high as 622 have been achieved with this concept with improved accuracy. We also restructure the algorithm with efficient termination criteria to achieve the convergence on all the datasets and to improve the reliability of selected set of features. © 2004 Elsevier B.V. All rights reserved.

Pattern Recognition Letters

On fuzzy-rough sets approach to feature selection

Second breakdown phenomenon in advanced NMOS ESD protection devices has remained an enigma due to the complex electrical and thermal effects that are responsible for its triggering. For the first time, we present a critical study of the high current phenomenon in ultra short-time scale to understand the physics of instability in protection devices around the second breakdown region. It is demonstrated that for advanced protection devices, carrier heating in the high field drain region causes a fall in the saturation drift velocity, which increases the transit time of carriers through the depletion region. This in turn, causes greater impact ionization due to higher accumulation of avalanche-generated carriers; leading to the formation of a propagating ionizing wave front, which culminates in a regenerative avalanche injection induced second breakdown failure. © 2005 IEEE.

Technical Digest - International Electron Devices Meeting, IEDM

New physical insight and modeling of second breakdown (It2) phenomenon in advanced ESP protection devices

Aluminum nitride films (AlN) were grown on silicon and quartz substrates by DC reactive magnetron sputtering. They were annealed at 600 and 800 °C for 30 min in the presence of nitrogen gas. Ellipsometry, FTIR spectroscopy, optical transmission spectrum and C-V measurements were carried out to study the optical, structural and electrical properties of AlN films. It was found that annealing enhances the optical transmittance and bandgap. Annealing also results in an increase in Al-N bond density and band broadening of AlN absorption band. XRD studies revealed that the films are amorphous in nature. The refractive index of the films did not change significantly, whereas dielectric constant decreased with an increase in annealing temperature. Positive insulator charge density (Qin) increased, whereas interface electronic state density (Dit) decreased as a result of annealing. © 2004 Elsevier B.V. All rights reserved.

Surface and Coatings Technology

Effect of annealing on DC sputtered aluminum nitride films

Aluminum nitride films were deposited, at 200 °C, on silicon substrates by RF sputtering. Effects of rapid thermal annealing on these films, at temperatures ranging from 400 to 1000 °C, have been studied. Fourier transform infrared spectroscopy (FTIR) revealed that the characteristic absorption band of Al-N, around 684 cm-1, became prominent with increased annealing temperature. X-ray diffraction (XRD) patterns exhibited a better, c-axis, (0 0 2) oriented AlN films at 800 °C. Significant rise in surface roughness, from 2.1 to 3.68 nm, was observed as annealing temperatures increased. Apart from these observations, micro-cracks were observed at 1000 °C. Insulator charge density increased from 2×1011 to 7.7×1011 cm-2 at higher temperatures, whereas, the interface charge density was found minimum, 3.2×1011 eV-1cm-2, at 600 °C. © 2006 Elsevier Ltd. All rights reserved.

Materials Science in Semiconductor Processing

Influence of rapid thermal annealing on morphological and electrical properties of RF sputtered AlN films

This paper exploits a resistance-capacitance (RC) model of transient heat conduction for estimation of defect depth, and more significantly of the defect area, from single point surface temperature evolutions over the defect and non-defect regions of material subjected to step heating. For the initial time behaviour of the surface temperature, a distributed RC model has been presented and analysed for estimation of defect depth and area. In contrast, a lumped RC model forms the basis for obtaining an analytical expression for defect area from the later part of the surface temperature evolution. The derived analytical expression estimates the defect area from the defect depth, the saturation value of the absolute thermal contrast and the slopes of the initial and final surface temperature evolution. The presented method does not require knowledge of material thermal properties or the value of the incident heat flux for estimation of defect parameters. The method has been validated by estimating the parameters of defects of various sizes and at different depths from experimental and simulated surface temperature evolutions. © 2004 Elsevier Ltd. All rights reserved.

NDT and E International

Electro-thermal modelling and analysis for estimation of defect parameters by stepped infrared thermography

This paper proposes novel techniques for thermal nondestructive testing based on frequency modulated thermal waves. A mild steel sample having discontinuities at different depths is taken as a test sample. The limited depth resolution of the lock in thermography due to the fixed driving frequency of the excited heat sources is overcome by the proposed new technique. A pulse compression approach is used to detect subsurface discontinuities using linear frequency modulated thermal wave imaging and digitized linear frequency modulated thermal wave imaging. In this way, the peak power for probing the specimen can be decreased markedly by increasing the average transmitted energy, which is proportional to the length of the modulated excitation signal. Comparison between the techniques based on the analog frequency modulated signal and its digital form are presented.

Materials Evaluation

Digitized frequency modulated thermal wave imaging for nondestructive testing

In this paper, increase in data rate is achieved by removing the cyclic prefix between the OFDM symbols. The intersymbol interference and intercarrier interference caused by the removal of cyclic prefix are removed by equalization. We propose two methods of equalization. In the first method, the zero frequency domain equalization (ZF-FEQ) is done by making use of spill over in the unused carriers. The pre-FFT time domain Equalizer minimizes the noise amplification caused by ZF-FEQ. In the second method, the Inter Symbol Interference and Inter Carrier Interference are removed at the transmitter itself by transmitting data in the unused carriers, which is the combination of data in the used carriers. The requirement of power in the unused carriers increases as the length of the channel increases. Using the TEQ, the effective length of the channel is reduced to minimum. The simulation results are presented in support of these two methods.

IEEE Region 10 Annual International Conference, Proceedings/TENCON

Enhancing data efficiency in IEEE- 802.11a using frequency and time domain equalization

The aim of this paper is to provide an efficient input feature selection algorithm for modeling of systems based on modified definition of fuzzy-rough sets. Some of the critical issues concerning the complexity and convergence of the feature selection algorithm are discussed in detail. Based on some natural properties of fuzzy t-norm and t-conorm operators, the concept of fuzzy-rough sets on compact computational domain is put forward, which is then utilized to construct improved Fuzzy-Rough Feature Selection algorithm. Various mathematical properties of this new definition of fuzzy-rough sets are discussed from pattern classification viewpoint. Speedup factor as high as 622 has been achieved with proposed algorithm compared to recently proposed FRSAR, with improved model performance on selected set of features. © 2005 Taylor & Francis.

International Journal of General Systems

Improved feature selection algorithm with fuzzy-rough sets on compact computational domain

The objective of this paper is to present an optimal design of Fuzzy Logic Controllers (FLCs) by Genetic Algorithms (GAs). As part of this objective, the design of input and output Membership Functions (mfs) of FLC is carried out simultaneously with input and output Scaling Factors (sfs). FLC since can be subjected to a range of set points, so the step size for mutation of alleles, and fitness function are adapted based upon Set Point Change (SPCs) commands, and besides, bounds of either input and output mfs or else of sfs are SPC-adapted; the latter two adaptations are demonstrated to be equivalent. Tuning is based upon maximization of a comprehensive fitness function constructed as inverse of a weighted-average of Integral Square Error (ISE), Peak Overshoot (Mp), Rise Time (tr) and Settling Time (ts), wherein weights for ISE and Mp are adapted. GA-evolved FLC (henceforth GAFLC) shows better closed-loop performance on linear and nonlinear stable and unstable systems as compared to a hand-designed FLC and a GA-designed PID (Proportional-Integral- Derivative Controller). This performance is almost fully preserved by GAFLC, under a wide range of SPCs, for linear systems (and the PID is demonstrated to share this property) and is better preserved by GAFLC than by PID for nonlinear systems. Some future directions are listed.