Abstract-In this article, a theoretical and computational analysis has been made to obtain the modal dispersion characteristics of an unconventional optical waveguide with a Piet Hein core cross section having a conducting sheath helix winding on its core-cladding boundary. A simple analytical method using the vector boundary conditions has been utilized to get the modal eigen value equation. From this equation dispersion curves are obtained and plotted for some particular values of the pitch angles of the winding. Next, these predicted results are compared with those of a new optical fiber having a conducting sheath helix winding on its core-cladding boundary. It is seen that the cutoff values are somewhat lower for the Piet Hein lightguide than those for the circular guide. This is not unexpected since the Piet Hein curve approaches the shape of a square. The introduction of a conducting helical winding leads to a modification of the modal characteristics of the lightguides and gives us an additional means to control them.
A simple analytical method using vector boundary conditions is proposed for the theoretical derivation of the modal characteristics equation for an unconventional optical waveguide having a hypocycloidal core cross-section with a conducting sheath helix winding on its core-cladding interface. Using this equation modal dispersion curves have been obtained for some particular values of pitch angles of the winding. Further, these obtained results are compared with those of a standard optical fiber loaded with a conducting sheath helix winding on its core-cladding interface. It is found that the cutoff values are somewhat lower for the hypocycloidal waveguide than those for the standard fiber. This is due to the fact that when a hypocycloid is distended from the inner side we get a circle and when a square is compressed from outside we get a hypocycloid. We also see that when a conducting sheath helical winding is added to the waveguides, Downloaded by [University of Connecticut] at 10:18 13 October 2014 1308 Maurya et al.their modal properties are modified. Among many new features, it is found that the hypocycloidal guide with a conducting helical winding supports fewer mode than the circular waveguide with a conducting helical winding, and this is relevant in the case of practical application.
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This review paper encompasses a study of metal-oxide and their composite based gas sensors used for the
detection of ammonia (NH3) gas. Metal-oxide has come into view as an encouraging choice in the gas sensor industry.
This review paper focuses on the ammonia sensing principle of the metal oxides. It also includes various approaches
adopted for increasing the gas sensitivity of metal-oxide sensors. Increasing the sensitivity of the ammonia gas sensor
includes size effects and doping by metal or other metal oxides which will change the microstructure and morphology of
the metal oxides. Different parameters that affect the performances like sensitivity, stability, and selectivity of gas sensors
are discussed in this paper. Performances of the most operated metal oxides with strengths and limitations in ammonia gas
sensing application are reviewed. The challenges for the development of high sensitive and selective ammonia gas sensor
are also discussed.
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