Studies on underwater propagation development of programmable arrays

The thesis presented here includes the designing of underwater transducer arrays, taking into account the ‘interaction effects’ [30] among the closely packed radiators. Methods of minimizing the ‘interaction effects‘ by modifying the radiating aperture, are investigated. The need for this study arises as it is one of the important peculiar limitations that stands in the way of achieving maximum range of transmission of acoustic signals. Application of the modified array format for the generation of narrow beam low frequency sound waves, through nonlinear interactions, is discussed. Other techniques that can be advantageously exploited in array synthesis are also investigated

Beam shaping of sectoral electromagnetic horn antennas using corner reflector technique

In the present thesis, possibility of beam shaping of sectoral horns and corner reflector systems'has been studied in detail. The experimental results obtained in the above two cases are compared. As far as the flanged sectoral horns are concerned, the special advantage is that the gain is increased without impairing impedance conditions. An intense study on corner reflector antennas shows that the been broadening or focussing will be possible by adjusting parameters involved. Beam tilting by imposing asymmetries is another interesting property of the systems. A comprehensive study of these fields has been presented in Chapter II. Chapter III is exclusively for describing the experimental techniques used in the present investigation. In Chapter IV, experimental results on flanged sectoral horns and corner reflector eyetses are presented. A comparative analysis of the experimental results obtained with flanged sectoral horns and corner reflector systems is presented in the Chapter V. The similarity and close resemblance in each aspects are shown by presenting typical results from these two eysteee. Theoretical aspects of both types of antennas are considered in Chapter VI. Attempts are made for co-ordinating the theoretical aspects and drawing a final conclusion. In Chapter VII. the final conclusion that the flanged sectoral horn may be considered as a corner reflector system has been drawn. The importance of the conclusions and usefulness are pointed out. The scope for further work in these lines has been indicated.

Studies on optical attenuation in sea water using dye laser and laser propagation in a turbulent medium

The central theme of the work presented in this thesis is a careful investigation of the factors influencing the attenuation of laser beam through sea water. The thesis presents a detailed report of the work done by the author on the attenuation studies in sea water and on laser propagation through a turbulent medium. The thesis contains six chapters which are more or less self-contained with separate abstracts and references. The first chapter is divided into two parts. The first part introduces the subject of laser propagation through sea water. It includes a brief description of optical properties of sea water followed by a review of the earlier works on attenuation studies in water. The second part gives the theoretical background of the problem of laser propagation through a turbulent medium.

Corrugated flange technique for beam shaping of sectoral electromagnetic horn antennas

The need for improved feed systems for large reflector antennas employed in Radio Astronomy and Satellite tracking spurred the interest in horn antenna research in the 1960's. The major requirements were to reduce spill over, cross-polarisation losses,and to enhance the aperture efficiency to the order of about 75-8O%L The search for such a feed culminated in the corrugated horn. The corrugat1e 1 horn triggered widespread interest and enthusiasm, and a large amount of work(32’34’49’5O’52’53’58’65’75’79)has already been done on this type of antennas. The properties of corrugated surfaces has been investigated in detail. It was strongly felt that the flange technique and the use of corrugated surfaces could be merged together to obtain the advantages of both. This is the idea behind the present work. Corrugations are made on the surface of flange elements. The effect of various corrugation parameters are studied. By varying the flange parameters, a good amount of data is collected and analysed to ascertain the effects of corrugated flanges. The measurements are repeated at various frequencies, in the X— and S-bands. The following parameters of the system were studied: (a) beam shaping (b) gain (c) variation of V.S.U.R. (d) possibility of obtaining circularly polarised radiation from the flanged horn. A theoretical explanation to the effects of corrugated flanges is attempted on the basis of the line-source theory. Even though this theory utilises a simplified model for the calculation of radiation patterns, fairly good agreement between the computed pattern and experimental results are observed.

Studies on the propagation of errors in physical oceanographic computations

The results of an investigation on the limits of the random errors contained in the basic data of Physical Oceanography and their propagation through the computational procedures are presented in this thesis. It also suggest a method which increases the reliability of the derived results. The thesis is presented in eight chapters including the introductory chapter. Chapter 2 discusses the general theory of errors that are relevant in the context of the propagation of errors in Physical Oceanographic computations. The error components contained in the independent oceanographic variables namely, temperature, salinity and depth are deliniated and quantified in chapter 3. Chapter 4 discusses and derives the magnitude of errors in the computation of the dependent oceanographic variables, density in situ, gt, specific volume and specific volume anomaly, due to the propagation of errors contained in the independent oceanographic variables. The errors propagated into the computed values of the derived quantities namely, dynamic depth and relative currents, have been estimated and presented chapter 5. Chapter 6 reviews the existing methods for the identification of level of no motion and suggests a method for the identification of a reliable zero reference level. Chapter 7 discusses the available methods for the extension of the zero reference level into shallow regions of the oceans and suggests a new method which is more reliable. A procedure of graphical smoothening of dynamic topographies between the error limits to provide more reliable results is also suggested in this chapter. Chapter 8 deals with the computation of the geostrophic current from these smoothened values of dynamic heights, with reference to the selected zero reference level. The summary and conclusion are also presented in this chapter.

Studies on some nonlinear optical phenomena-optical phase conjugation and continuous wave second harmonic generation

Nonlinear optics has emerged as a new area of physics , following the development of various types of lasers. A number of advancements , both theoretical and experimental . have been made in the past two decades . by scientists al1 over the world. However , onl y few scientists have attempted to study the experimental aspects of nonlinear optical phenomena i n I ndian laboratories. This thesis is the report of an attempt made in this direction. The thesis contains the details of the several investigations which the author has carried out in the past few years, on optical phase conjugation (OPC) and continuous wave CCVD second harmonic generation CSHG). OPC is a new branch of nonlinear optics, developed only in the past decade. The author has done a few experiments on low power OPC in dye molecules held in solid matrices, by making use of a degenerate four wave mixing CDFWND scheme. These samples have been characterised by studies on their absorption-spectra. fluorescence spectra. triplet lifetimes and saturation intensities. Phase conjugation efficiencies with r espect to the various parameters have been i nvesti gated . DFWM scheme was also employed i n achievi ng phase conjugation of a br oadband laser C Nd: G1ass 3 using a dye solution as the nonlinear medium.

Studies on sporulation and propagation in selected agarophytes

Studies on sporulation of four commercially important red (sea-weeds) algae ^(agarophytes) namely Gelidiella acerosa, Gracilaria corticata, G edulis and Hypnea musciformis growing in the vicinity of’ Mandapam coast were carried out from October 1981 to September 1983. During the two years of study; fruiting behavior in the natural population of these species was also investigated. Laboratory experiments were carried out with the four algae sea weeds to collect information on seasonal aspects of spore production and diurnal variation of spore shedding. Detailed studies were made under laboratory conditions to know the effects of some selected environmental factors such as desiccation, salinity, temperature, light intensity and photoperiod on spore output in Gelidiella acerosa, Gracilaria edulis and kypnea musciformis hydrological data were also collected from the inter-tial region around mandapam area. The result obtained on all the above aspects are presented in this thesis

Wave Height Ano Speotral Transformation In The Shallow Waters Of Kerala Ooast And Their Preoiotion

There are basically two methods for prediction of shallow water waves, viz. the graphical method and the numerical method. The numerical methods are being widely used, now—a—days, because they are fast, accurate and are especially useful when the prediction over a large spatial frame is required. Practically little has been done on the development of numerical models for the prediction of height and spectral transformation of waves as applicable to our coasts. Synchronized deep and shallow water wave measurements which are essential for study of wave transformation are very much lacking for our coasts. Under these circumstances, a comprehensive study of the wave transformation in the shallow waters of our coast was felt very important and is undertaken in the present investigation.

Investigations on the radiation characteristics of flanged sectoral horn antennas and corner reflector systems

Antennas play an important role in determining the characteristics of any electronic system which depends on free space as the propagation medium. Basically, an antenna can be considered as the connecting link between free space and the transmitter or receiver. For radar and navigational purposes the directional properties of an antenna is its most basic requirement as it determines the distribution of radiated energy. Hence the study of directional properties of antennas has got special significance and several useful applications.

Studies on pulp propogation in single mode optical fibres

Studies on pulse propagation in single mode optical fibers have attracted interest from a wide area of science and technology as they have laid down the foundation for an in-depth understanding of the underlying physical principles, especially in the field of optical telecommunications. The foremost among them is discovery of the optical soliton which is considered to be one of the most significant events of the twentieth century owing to its fantastic ability to propagate undistorted over long distances and to remain unaflected after collision with each other. To exploit the important propertia of optical solitons, innovative mathematical models which take into account proper physical properties of the single mode optical fibers demand special attention. This thesis contains a theoretical analysis of the studies on soliton pulse propagation in single mode optical fibers.

Reduction of radar cross section of targets using periodic strip grating technique

The- classic: experiment of Heinrich Hertz verified the theoretical predict him of Maxwell that kxnfli radio and light waves are physical phenomena governed by the same physical laws. This has started a.rnnJ era of interest in interaction of electromagnetic energy with matter. The scattering of electromagnetic waves from a target is cleverly utilized im1 RADAR. This electronic system used tx> detect and locate objects under unfavourable conditions or obscuration that would render the unaided eye useless. It also provides a means for measuring precisely the range, or distance of an object and the speed of a moving object. when an obstacle is illuminated by electromagnetic waves, energy is dispersed in all directions. The dispersed energy depends on the size, shape and composition of the obstacle and frequency and nature of the incident wave. This distribution of energy’ is known as ‘scattering’ and the obstacle as ‘scatterer’ or 'target'.

Effect of Concentration of DYE on the Storage Life of Plane Wave Gratings on Photopolymer Film

Holographic grating with good storage life in poly(vinyl alcohol) based photopolymer film, prepared by gravity settling method, with reduced concentration of the dye was found to give good diffraction efficiency without crosslinking. The material was found to show good diffraction efficiency and sensitivity (75% diffraction efficiency at exposure energy of 80 mJ/cm2). The shelf life of the photopolymer solution could be improved by storage at a temperature 4 C in refrigerator

Studies on the interaction of two level atoms with quantized electromagnetic field

The present study described about the interaction of a two level atom and squeezed field with time varying frequency. By applying a sinusoidal variation in the frequency of the field, the randomness in population inversion is reduced and the collapses and periodic revivals are regained. Quantum optics is an emerging field in physics which mainly deals with the interaction of atoms with quantised electromagnetic fields. Jaynes-Cummings Model (JCM) is a key model among them, which describes the interaction between a two level atom and a single mode radiation field. Here the study begins with a brief history of light, atom and their interactions. Also discussed the interaction between atoms and electromagnetic fields. The study suggest a method to manipulate the population inversion due to interaction and control the randomness in it, by applying a time dependence on the frequency of the interacting squeezed field.The change in behaviour of the population inversion due to the presence of a phase factor in the applied frequency variation is explained here.This study also describes the interaction between two level atom and electromagnetic field in nonlinear Kerr medium. It deals with atomic and field state evolution in a coupled cavity system. Our results suggest a new method to control and manipulate the population of states in two level atom radiation interaction,which is very essential for quantum information processing.We have also studied the variation of atomic population inversion with time, when a two level atom interacts with light field, where the light field has a sinusoidal frequency variation with a constant phase. In both coherent field and squeezed field cases, the population inversion variation is completely different from the phase zero frequency modulation case. It is observed that in the presence of a non zero phase φ, the population inversion oscillates sinusoidally.Also the collapses and revivals gradually disappears when φ increases from 0 to π/2. When φ = π/2 the evolution of population inversion is identical to the case when a two level atom interacts with a Fock state. Thus, by applying a phase shifted frequency modulation one can induce sinusoidal oscillations of atomic inversion in linear medium, those normally observed in Kerr medium. We noticed that the entanglement between the atom and field can be controlled by varying the period of the field frequency fluctuations. The system has been solved numerically and the behaviour of it for different initial conditions and different susceptibility values are analysed. It is observed that, for weak cavity coupling the effect of susceptibility is minimal. In cases of strong cavity coupling, susceptibility factor modifies the nature in which the probability oscillates with time. Effect of susceptibility on probability of states is closely related to the initial state of the system.

Square Wave Voltammetric Determination of Various Pharmaceuticals

Cochin University of Science & Technology