Jacob, George; Dr. Mohanan, P(Cochin University of Science & Technology, June , 1998)
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Abstract:
The thesis is the outcome of the experimental and theoretical investigations on a new compact drum-shaped microstrip antenna. A new compact antenna suitable for personal communication system(PCS), Global position System(GPS) and array applications is developed and analysed. The generalised cavity model and spatial fourier transform technique are suitably modified for the analysis of the antenna. The predicted results are compared with experimental results and excellent agreement is observed. The experimental work done by the author in related fields are incorporated as three appendices in this thesis. A single feed dual frequency microstrip antenne is presented in appendix A.Appendix B describes a new broadband dual frequeny microstrip antenna. The bandwidth enhancement effect of microstrip antennas through dielectric resonator loading is demonstarted in Appendix C.
Description:
Department of Electronics,
Cochin University of Science and Technology
Bindhu, C V; Harilal, S S; Nampoori, V P N; Vallabhan, C P G(Society of Photo-Optical Instrumentation Engineers, 1998)
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Abstract:
Thermal diffusivity measurements are carried out in certain organic liquids using the pulsed dual beam thermal lens technique. The 532 nm pulses from a frequency doubled Q-switched Nd:YAG laser are used as the heating source and an intensity stabilized He-Ne laser serves as the probe beam. Experimental determination of the characteristic time constant of the transient thermal lens signal is verified theoretically. Measured thermal diffusivity values are in excellent agreement with literature values.
Riju C, Issac; Vasudevan Pillai, K; Harilal, S S; Geetha, K Varier; Bindhu, C V; Pramod, Gopinath,; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier Science, 1998)
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Abstract:
Laser produced plasma from silver is generated using a Q-switched Nd:YAG laser. Optical emission spectroscopy is used
to carry out time of flight (TOF) analysis of atomic particles. An anomalous double peak profile in the TOF distribution is
observed at low pressure. A collection of slower species emerge at reduced pressure below 4 X lO-3 mbar and this species
has a greater velocity spread. At high pressure the plasma expansion follows the shockwave model with cylindrical
symmetry whereas at reduced pressure it shows unsteady adiabatic expansion (UAE). During UAE the species show a
parabolic increases in the expansion time with radial distance whereas during shock wave expansion the exponent is less
than one. The angular distribution of the ablated species in the plume is obtained from the measurement of optical density of
thin films deposited on to glass substrates kept perpendicular to the plume. There is a sharp variation in the film thickness
away from the film centre due to asymmetries in the plume.
Issac, R C; Varier, G K; Harilal, S S; Nampoori, V P N; Vallabhan, C P G(Springer, 1998)
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Abstract:
The dynamics of diffusion of electrons and ions from the laser-produced plasma from a multielement superconducting material, namely YBa2Cu3O7, using a Q-switched Nd:YAG laser is investigated by time-resolved emission-spectroscopic techniques at various laser irradiances. It is observed that beyond a laser irradiance of 2.6 \xC3\x97 1011 W cm-2, the ejected plume collectively drifts away from the target with a sharp increase in velocity to 1.25 \xC3\x97 106 cm s-1, which is twice its velocity observed at lower laser irradiances. This sudden drift apparently occurs as a result of the formation of a charged double layer at the external plume boundary. This diffusion is collective, that is, the electrons and ions inside the plume diffuse together simultaneously and hence it is similar to the ambipolar diffusion of charged particles in a discharge plasma
Deepa, Jose; Shelly John, M; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier, July 18, 1998)
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Abstract:
A novel fibre optic sensor for the in situ measurement of the rate of deposition of thin films has been developed. Evanescent wave in the uncladded portion of a multimode fibre is utilised for this sensor development. In the present paper we demonstrate how this sensor is useful for the monitoring of the deposition rate of polypyrrole thin films, deposited by an AC plasma polymerisation method. This technique is simple, accurate and highly sensitive compared with existing techniques.
Nampoori, V P N; Vallabhan, C P G; George, A K; Radhakrishnan, P; Rajasree, K; Vidyalal, V(Elsevier, July , 1998)
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Abstract:
he phenomenon of single beam mirage effect, otherwise known as photothermal deflection (PTD) effect using a He–Ne laser beam has been employed to detect phase transitions in some liquid crystals. It has been observed that anomalous changes in amplitude occur in the PTD signal level near the transition temperature. The experimental details and the results of measurements made in liquid crystals E8, M21 and M24 are given in this paper.
Harilal, S S; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, 1998)
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Abstract:
The effect of ambient gas on the dynamics of the plasma generated by laser ablation of a carbon target using 1.06 μm radiation from a Q-switched Nd:YAG laser has been investigated using a spectroscopic technique. The emission characteristics of the carbon plasma produced in argon, helium and air atmospheres are found to depend strongly on the nature and pressure of the surrounding gas. It has been observed that hotter and denser plasmas are formed in an argon atmosphere rather than in helium or air as an ambient.
Bindhu, C V; Harilal, S S; Achamma, Kurian; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1998)
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Abstract:
Dual beam transient thermal lens studies were carried out in rhodamine 6G methanol solutions using 532 nm pulses from a frequency doubled Nd:YAG laser. Analysis of thermal lens signal shows the existence of different nonlinear processes like two photon absorption and three photon absorption phenomena along with one photon absorption. Concentration of the dye in the solution has been found to influence the occurrence of the different processes in a significant way.
Harilal, S S; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(Springer Berlin / Heidelberg, 1998)
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Abstract:
Laser radiation at 1.06 µm from a pulsed Nd:YAG
laser was focused onto a multielement YBa2Cu3O7 target in
vacuum and the plasma thus generated was studied using
time-resolved spectroscopic techniques. Line broadening of
the Ba I emission line at 553.5 nm was monitored as a function
of time elapsed after the incidence of a laser pulse on the
target. Measured line profiles of barium species were used to
infer the electron density and temperature, and the time evolution
of these important plasma parameters has been worked out.
Krishnan Nair, P R; Nandakumaran, V M(Springer, October , 1998)
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Abstract:
We present the analytical investigations on a logistic map with a discontinuity at the
centre. An explanation for the bifurcation phenomenon in discontinuous systems is presented. We
establish that whenever the elements of an n-cycle (n > 1) approach the discontinuities of the nth
iterate of the map, a bifurcation other than the usual period-doubling one takes place. The periods of
the cycles decrease in an arithmetic progression, as the control parameter is varied. The system also
shows the presence of multiple attractors. Our results are verified by numerical experiments as well.