Comparison of the effect of processing parameters and degradation on the DC and microwave properties of thin films and polycrystalline bulk high-Tc superconducting materials

The sharp increase in microwave power loss (the reverse of what has previously been reported) at the transition temperature in high-Tc superconducting systems such as YBaCu oxide (polycrystalline bulk and thin films obtained by the laser ablation technique) and BiPbSrCaCu oxide is reported. The differences between DC resistivity ( rho ) and the microwave power loss (related to microwave surface resistance) are analysed from the data obtained by a simultaneous measurement set-up. The influence of various parameters, such as preparation conditions, thickness and aging of the sample and the probing frequency (6-18 GHz), on the variation of microwave power loss with temperature is outlined.

Minimum weight design of fiber-reinforced laminated composite structures with maximum stress and Tsai-Wu failure criteria

In this article, a minimum weight design of carbon/epoxy laminates is carried out using genetic algorithms. New failure envelopes have been developed by the combination of two commonly used phenomenological failure criteria, namely Maximum Stress (MS) and Tsai-Wu (TW) are used to obtain the minimum weight of the laminate. These failure envelopes are the most conservative failure envelope (MCFE) and the least conservative failure envelope (LCFE). Uniaxial and biaxial loading conditions are considered for the study and the differences in the optimal weight of the laminate are compared for the MCFE and LCFE. The MCFE can be used for design of critical load-carrying composites, while the LCFE could be used for the design of composite structures where weight reduction is much more important than safety such as unmanned air vehicles.

A Feature-Based Solution to Forward Problem in Electrical Capacitance Tomography of Conductive Materials

A new feature-based technique is introduced to solve the nonlinear forward problem (FP) of the electrical capacitance tomography with the target application of monitoring the metal fill profile in the lost foam casting process. The new technique is based on combining a linear solution to the FP and a correction factor (CF). The CF is estimated using an artificial neural network (ANN) trained using key features extracted from the metal distribution. The CF adjusts the linear solution of the FP to account for the nonlinear effects caused by the shielding effects of the metal. This approach shows promising results and avoids the curse of dimensionality through the use of features and not the actual metal distribution to train the ANN. The ANN is trained using nine features extracted from the metal distributions as input. The expected sensors readings are generated using ANSYS software. The performance of the ANN for the training and testing data was satisfactory, with an average root-mean-square error equal to 2.2%.

Novel approach for simultaneous measurement of strain and temperature using a single tapered fiber Bragg grating

A novel approach for simultaneous measurement of strain and temperature with a single tapered fiber Bragg grating is proposed. This method is based on the fact that the reflectivity at central wavelength of FBG reflection changes with chirp (strain gradient). A diode laser is locked to the central wavelength of FBG reflection. Central wavelength of the FBG shifts with temperature. Change in reflectivity & wavelength of the diode laser were used to measure strain and temperature on the FBG respectively.

Simultaneous measurement of strain and temperature with a pair of matched fiber Bragg gratings

A novel approach for simultaneous measurement of static/dynamic strain and temperature with a pair of matched fiber Bragg grating(FBG)s is proposed. When a diode laser locked to the mid reflection frequency of reference FBG is used to illuminate the sensor FBG, reflected intensity changes with strain on sensor FBG. Reference FBG responds with temperature on sensor FBG and is immune to strain, hence, wavelength of the diode laser acts as a signature for temperature measurement. Theoretical sensitivity limit for static strain and temperature are 1.2n epsilon / root Hz and 0.0011 degrees C respectively. Proposed sensor shows a great potential in high sensitive strain measurements with a simplified experimental setup.

Non-linearity in piezo-fiber reinforced composites: an asymptotic approach

An asymptotically correct analysis is developed for Macro Fiber Composite unit cell using Variational Asymptotic Method (VAM). VAM splits the 3D nonlinear problem into two parts: A 1D nonlinear problem along the length of the fiber and a linear 2D cross-sectional problem. Closed form solutions are obtained for the 2D problem which are in terms of 1D parameters.

Simultaneous measurement of multiple parameters using a single fiber Bragg grating

A novel approach for simultaneous measurement of chirp (any parameter that can induce strain gradient on FBG) and temperature using a single FBG is proposed. Change in reflectivity at central wavelength of FBG reflection & Bragg wavelength shifts induced due to temperature were used for chirp & temperature measurements respectively. Theoretical resolution limit for chirp and temperature using an Optical Spectrum Analyzer (OSA) with 1pm wavelength resolution and >58dB dynamic range are 12.8fm and 1/13 degrees C respectively.

Novel signal demodulation technique to estimate the amount of chirp in fiber Bragg gratings

A novel detection technique to estimate the amount of chirp in fiber Bragg gratings (FBGs) is proposed. This method is based on the fact that reflectivity at central wavelength of FBG reflection changes with strain/temperature gradient (linear chirp) applied to the same. Transfer matrix approach was used to vary different grating parameters (length, strength and apodization) to optimize variation of reflectivity with linear chirp. Analysis is done for different sets of `FBG length-refractive index strength' combinations for which reflectivity vary linearly with linear chirp over a decent measurement range. This article acts as a guideline to choose appropriate grating parameters in designing sensing apparatus based on change in reflectivity at central wavelength of FBG reflection.

High sensitive Static fiber Bragg grating strain sensing using lasers locked to relative frequency reference

A novel high sensitive fiber Bragg grating (FBG) strain sensing technique using lasers locked to relative frequency reference is proposed and analyzed theoretically. Static strain on FBG independent of temperature can be measured by locking frequency of diode laser to the mid reflection frequency of matched reference FBG, which responds to temperature similar to that of the sensor FBG, but is immune to strain applied to the same. Difference between light intensities reflected from the sensor and reference FBGs (proportional to the difference between respective pass band gains at the diode laser frequency) is not only proportional to the relative strain between the sensor and reference FBGs but also independent of servo residual frequency errors. Usage of relative frequency reference avoids all complexities involved in the usage of absolute frequency reference, hence, making the system simple and economical. Theoretical limit for dynamic and static strain sensitivities considering all major noise contributions are of the order of 25 (p epsilon) / root Hz and 1.2 n epsilon / root Hz respectively.

Self-assembled composite nano-materials exploiting a thermo reversible n-acene fibrillar scaffold and organic-capped ZnO nanoparticles

An organic-inorganic composite material is obtained by self-assembly of 2,3-didecyloxy-anthracene (DDOA), an organogelator of butanol, and organic-capped ZnO nanoparticles (NPs). The ligand 3, 2,3-di(6-oxy-n-hexanoic acid)-anthracene, designed to cap ZnO and interact with the DDOA nanofibers by structural similarity, improves the dispersion of the NPs into the organogel. The composite material displays mechanical properties similar to those of the pristine DDOA organogel, but gelates at a lower critical concentration and emits significantly less, even in the presence of very small amounts of ZnO NPs. The ligand 3 could also act as a relay to promote the photo-induced quenching process.

Fiber Bragg Grating Sensors for Real Time Monitoring of Evacuation Process

Fiber bragg grating (FBG) sensors have been widely used for number of sensing applications like temperature, pressure, acousto-ultrasonic, static and dynamic strain, refractive index change measurements and so on. Present work demonstrates the use of FBG sensors in in-situ measurement of vacuum process with simultaneous leak detection capability. Experiments were conducted in a bell jar vacuum chamber facilitated with conventional Pirani gauge for vacuum measurement. Three different experiments have been conducted to validate the performance of FBG sensor in monitoring vacuum creating process and air bleeding. The preliminary results of FBG sensors in vacuum monitoring have been compared with that of commercial Pirani gauge sensor. This novel technique offers a simple alternative to conventional method for real time monitoring of evacuation process. Proposed FBG based vacuum sensor has potential applications in vacuum systems involving hazardous environment such as chemical and gas plants, automobile industries, aeronautical establishments and leak monitoring in process industries, where the electrical or MEMS based sensors are prone to explosion and corrosion.

Chemical Approaches to the Design of Oxide Materials.

Chemical methods of synthesis play a crucial role in designing and discovering new and novel materials and in providing less cumbersome methods for preparing known materials. Chemical methods also enable the synthesis of metastable materials which are otherwise difficult to prepare. In this presentation, the various innovative chemical methods of synthesising oxide materials will be briefly reviewed with emphasis on soft-chemical routes. Electrochemical synthesis, ion-exchange method, alkali-flux method and some of the interaction reactions will be highlighted, besides topochemical aspects of solid state synthesis. Cuprate superconductors as well as intergrowth structures will also be examined.

Combustion synthesis of oxide materials for nuclear waste immobilization

Oxide materials like perovskite, zirconolite, hollandite, pyrochlore, NASICON and sphene which are used for nuclear waste immobilization have been prepared by a solution combustion process. The process involves the combustion of stoichiometric amount of corresponding metal nitrates and carbohydrazide/tetraformyl trisazine/diformyl hydrazide at 450 degrees C. The combustion products have been characterized using powder X-ray diffraction, infrared spectroscopy, and Si-29 MAS-NMR. The fine particle nature of the combustion derived powders has been studied using density, particle size, BET surface area measurements and scanning electron microscopy. Sintering of combustion derived powder yields 85-95% dense ceramics in the temperature range 1000 degrees-1300 degrees C.