http://hdl.handle.net/2005/40 2013-04-30T23:13:47Z http://hdl.handle.net/2005/1963 Title: "Optical Diffraction By Micro Cylinder" - A Few Investigations Authors: Vyas, Khushi Abstract: Micro-cylinders with the diameters spanning the 1-20 μm range are growing in importance, for realizing devices with new functionalities. For custom functionalities, their device-designs impose, tolerance-related constraints on their critical dimension. To meet the challenges for the associated online micro-metrology, new methods for the micro-cylinder diameter measurement, are currently receiving considerable attention. „Optical diffraction under Fraunhofer Approximation‟ is one of the most viable experimental techniques for cylinder diameter measurement, in the laboratory as well as Industrial environment. In 1-20 μm diameter range, however, the cylinder-diffraction is not well understood. The reliability of the current models/formulations for this range is far from satisfactory in respect of speed, accuracy, resolution etc., and need a re-examination. The present thesis concerns with a few investigations on the „Optical Diffraction by Micro-Cylinder‟. It highlights both the theoretical and the experimental aspects of the investigations on micro-cylinders with diameters in the range of 1-50 μm. The results of the investigation are organized into two categories. The first of them details a pair of new analytical models obtained from the principles of „Geometrical Theory of Micro-Cylinder Diffraction‟ while the second category highlights another pair of new analytical models obtained from the principles of the „Customary Fraunhofer Theory of Micro-Cylinder Diffraction‟. The model from the „geometrical theory‟ is based on the hypothesis that the ‘ray-paths relevant to the location of ‘diffraction minima’, facilitate to construct, a geometrically-equivalent triangle’. The solution of such a triangle provides the new formulation for the micro-cylinder diffraction. The model from the „customary Fraunhofer theory‟, instead, relies on the on the fact that „the diffraction pattern for a micro-cylinder is essentially, a chirped-interference pattern modulated by a diffraction envelope’. The functional form of the formulation depends upon, the type of triangle constructed for geometrical theory and the type of illumination used in the customary Fraunhofer theory. The thesis highlights, four new formulations (two from each of the approaches) to describe the micro-cylinder diffraction. The principal conclusions of the investigations are as under. - All the new formulations for the micro-cylinder diffraction facilitate, enhanced diameter inversion accuracy, in the hitherto esoteric diameter range of 1-20 μm. For the reported experimental data on 3 μm diameter micro-cylinder, the models proposed in the present investigation improve the accuracy of diameter-estimation from 16.5% known from earlier models to less than 1%. - The investigation also brings out for the first time, the hitherto unnoticed difference between slit-diffraction and the micro-cylinder diffraction: When the micro-cylinder diameter approaches the wavelength of the illumination, the first order diffraction angle approaches nearly 200. It may be noted that for a slit of same width, the corresponding diffraction angle approaches 900. When the critical dimension of the cylinder and the slit decreases from λ to 5λ, the difference in the corresponding diffraction angles reduce from nearly 700 to nearly 1.50. - The investigation also highlights that in the micro-cylinder diffraction for the said range of interest, the absolute intensity at the zero-order interference- maximum provides a new signature for the distance of separation between the diffraction minima. The consequence of this new finding is a considerable simplification in the apparatus and algorithm for diameter inversion from a diffraction experiment. The function of an array detector can be replaced by a point detector at a fixed point for all the diameters in the range of interest. - The two formulations proposed from the geometrical theory are suited for diffraction- minima search based algorithm, while those from customary Fraunhofer theory are well suited for intensity minima search based method for diameter inversion. 2013-04-03T18:30:00Z http://hdl.handle.net/2005/1968 Title: Electrical Impedance Spectroscopic Studies On Bread Staling : Sensors And Instrumentation Authors: Bhatt, Chintan M Abstract: Quality control is essential in food industry and efficient quality assurance is becoming increasingly important. The assessment of food quality still centers on its sensory properties (appearance, aroma and texture). Bread is one of the most consumed food item all over the world. Bakery product manufacturers expect that the bread should retain all of its attributes during storage and consumers expect their bread to be ‘fresh’. Unfortunately, it remains truly ‘fresh’ for only a few hours after it leaves the oven because the ingredients of the bread undergo series of physical and chemical changes that eventually lead to deterioration, referred as “staling”, of bread quality. Bread staling is classified in two categories: crust (outer portion of bread) staling and crumb (center portion of bread) staling. Crust staling is associated to the moisture migration from crumb to crust during storage. This moisture migration leads to a phenomenon called glass transition at crust. This phenomenon changes the mechanical and dielectric properties of bread crust. Crumb staling is mainly associated to the physicochemical changes in starch. During storage, amorphous starch regains its crystallinity, which increases the firmnesss and dryness of bread crumb. Thus, the knowledge of moisture content, starch recrystallization and the glass transition helps in understanding the bread staling mechanism. There are some volatiles produced from the bread during storage, which forms the characteristic flavor or aroma of the bread. The loss of this characteristic flavor during storage also gives the information about the loss of freshness and staling. Thus, there is a need for detection and monitoring the loss of these volatiles to determine the characteristic flavor during storage. Hence, the present investigations are focused on these issues and developed a measurement facility to monitor the above physicochemical changes in bread during storage. As a part of experimental investigations, two separate test facilities have been developed. A multichannel ring electrodes with suitable instrumentation based on impedance spectroscopy technique is developed for simultaneous measurement of electrical properties of bread at crust and crumb during storage in the frequency range from 50 Hz to 100 kHz. The detailed investigations have been conducted on wheat bread. The variation in capacitance showed that the glass transition phenomenon, at room temperature, in bread crust occurs after 96 h of storage with 18% of moisture in it. The resistance changes at bread crumb showed the starch recrystallization during staling. The electrical property results are justified with the results obtained from the conventional differential scanning calorimmetery (DSC) studies. The impedance measurement at crust and crumb estimates the moisture content at the respective zones of bread. Thus the test facility is used for the simultaneous measurement of moisture content, starch recrystallization and glass transition at crumb and crust respectively without destructing the bread loaf. A few experiments are conducted on maida bread and the obtained results are compared with the wheat bread results. Another test facility has been developed for the detection of volatiles produced from the wheat bread during storage. The gas chromatography and mass spectroscopy (GC-MS) experimentations are conducted to identify the volatiles produced from the bread during storage. The major volatiles produced from wheat bread are found to be 1-Heptanol, 1-Pentanol, 1-Octanol, Furan and Hydroperoxyde. A conducting polymer based gas sensor is designed and developed to sense these volatiles and the changes in its electrical property is monitored with a suitable instrumentation based on impedance spectroscopy technique in the frequency range from 10 Hz to 2MHz. Experimental investigations are carried out in an in-house air tight closed test chamber. The bread sample and the designed sensor are kept inside the test chamber and closed tightly so that only bread volatile can interact with the sensor. The sensor response is monitored by measuring the changes in its capacitance upon exposure to organic volatiles produced from bread during storage. It is observed that the capacitance of the sensor changes with the quantitative changes of the above volatiles. Thus, the test facility is found quite suitable for the detection and monitoring the bread volatiles produced during storage, which finally affects the aroma property. Thus, the developed experimental test facilities with suitable sensors and instrumentation based on impedance spectroscopy technique are found quite suitable to monitor the changes in physicochemical properties and aroma of bread during storage. The correlation between the measured electrical properties and the changes in the textural and flavor properties of bread during storage has been established. The results obtained with the developed test facilities are in good agreement with the results obtained from the standard traditional techniques like DSC and GC-MS. 2013-04-14T18:30:00Z http://hdl.handle.net/2005/1926 Title: Novel Methods To Interrogate Fiber Bragg Grating Sensors Authors: Mahesh, Kondiparthi Abstract: 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 work acts as a guideline to choose appropriate grating parameters in designing sensing apparatus based on change in reflectivity at central wavelength of FBG reflection. A novel high sensitive 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 respectively of the order of 25 pε/ Hz and 1.2nε / 2013-02-13T18:30:00Z http://hdl.handle.net/2005/1922 Title: Numerical Study of Directionality of Ion Ejection In Axially Symmetric Ion Traps Authors: Naveen Reddy, D S Srinivas Abstract: In the normal operation of quadrupole ion trap mass spectrometers, the trapped ions are ejected symmetrically through both the upper (detector) and lower(source) endcap electrodes during mass selective boundary ejection experiment. This reduces the sensitivity of the instrument by almost 50%. In this preliminary study, we altered the geometry parameters of the quadrupole ion traps to introduce asymmetry. The asymmetry displaced the ion cloud towards the detector endcap which resulted in a preferential ejection through this endcap, thus imparting directionality to the ejected ions and hence to the sensitivity enhancement. Two symmetrical mass analyzers have been taken up for numerical study. They include the Paul trap(QIT) and the cylindricaliontrap(CIT). Asymmetry to these geometries is introduced in two ways, one by varying the upper endcap hole radius alone and in other by stretching the trap along the upper endcap only. The escape velocity plots and mass selective boundary ejection simulations are used to demonstrate the directionality of ion ejection for these geometries. The simulations revealed a significant increase in the number of ions getting ejected in the direction of asymmetry. 2013-02-12T18:30:00Z