New oligomer-bound antioxidants have been prepared by condensation reaction. The efficiency and permanence of these oligomer-
bound paraphenylene diamines as antioxidants has been compared with conventional amine type antioxidants in NR, SBR,
IIR and NBR and in elastomer blends like NR/BR and NR/SBR. The oligomer-bound antioxidants are found to impart improved
ozone, flex resistance and mechanical properties to the vulcanizates of NR, SBR, IIR and NBR and to blends of NR/BR and NR/
SBR in comparison with those containing conventional antioxidants.
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Sivsankara Pillai, V N; Suresh Kumar, P(Journal of Optics A : Pure and Applied Optics, March 8, 2002)
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Abstract:
A fibre optic technique for detecting trace amounts of nitrite compounds in
water is described. The off-line fibre optic sensor outlined here is based on
evanescent field absorption in a test solution formed by the reaction of nitrite
compounds in water with suitable chemical reagents. A short unclad portion
of a plastic clad silica fibre acts as the sensing region. The experimental
results clearly establish the usefulness of the present technique for detecting
very low concentrations of the order of 1 ppb (parts per billion) of nitrite
compounds with a large dynamic range of 1–1000 ppb. Such a high
sensitivity enables the present device to be used for measuring the nitrite
content in drinking water.
Manju,Paulson; Sona,Kundukulam O; Aanandan,C K; Mohanan,P; Vasudevan,K(Microwave and Optical Technology Letters, October 28, 2002)
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Abstract:
An arrow-shaped microstrip antenna with a pair of narrow
slots embedded near the non-radiating edges gives wide impedance bandwidth.
The experimental and simulated (!E3D) results show that antenna
bandwidth is -3.5 times that of a conventional patch with the added advantage
of reduced antenna size. The radiation characteristics are found to he uniform throughout the operating band
Binoy,G S; Aanandan,C K; Mohanan,P; Vasudevan,K(International Journal of Electronics, January 12, 2002)
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Abstract:
A new design of' a dual-frequency dual-polarized square microsh'ip antenna fed
along the diagonal, embedded with a square slot having three extended stubs for
frequency tuning, is introduced. The proposed antenna was fabricated using a
standard photolithographic method and the antenna was tested using the HP
3510(:; Vector Network Analyser. The antenna is capable of generating dual
resonant frequencies with mutually perpendicular polarizations and broad
radiation pattern characteristics. Such dual-frequency designs find wide
applications in personal mobile handsets combining GSM and CDS 1800 modes,
and applications in which different frequencies are used for emission and reception
such as personal satellite communications and cellular network systems.
Sreedevi,Menon K; Lethakumary,B; Vasudevan,K(Microwave and Optical Technology Letters, November 5, 2002)
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Abstract:
Bandwidth enhancement of a rectangular microstrip
antenna using a T-shaped microstrip feed is explored in this paper.
A 2:1 VSWR impedance bandwidth of 23% is achieved by employing
this technique. The far-field patterns are stable across the pass band.
The proposed antenna can be used conveniently in broadband communications
Choudhury, P K; Roger, Lessard S(Microwave and Optical Technology Letters, January 20, 2002)
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Abstract:
An attempt is made to determine the relative power
distribution in a step-index parabolic cylindrical waveguide (PCW) with
high deformation across the direction of propagation. The guide is
assumed to be made of silica. The scalar field approximation is employed
for the analysis under which a vanishing refractive-index (RI) difference
in the waveguide materials is considered. Further, no approximation for
folds- is used in the analytical treatment. Due to the geometry of such
waceguides, PCWs lose the well-defined modal discreteness, and a kind
of mode bunching is observed instead, which becomes much more
prominent in PCWs with high bends. However, with the increase in
cross-sectional size, the mode-bunching tendency is slightly reduced. The
general expressions for power in the guiding and nonguiding sections are
obtained, and the fractional power patterns in all of the sections are
presented for PCWs of various cross-sectional dimensions. It is observed
that the confinement of power in the core section is increased for PCWs
of larger cross-sectional size. Moreover, a fairly uniform distribution of
power is seen over the modes having intermediate values of propagation
constants
Choudhury, P K(Microwave and Optical Technology Letters, November 25, 2002)
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Abstract:
A fairly rigorous analytical treatment of the power characteristics
of dielectric optical waveguides with Piet Hein core-cross
sectional geometry is presented in this paper. This kind of wareguide
structure would be advantageous owing to the absence of corners,
which are found in rectangular guides, resulting in undesirable loss (hit
to the scattering of light. In order to simplify this theoretical approach.
em approximation of vanishing refractive index difference between the
guiding and the non-guiding sections is implemented. The variation eJ
logarithmic power is shown for different dimensions of the core, corresponding
to different azimuthal modal indices. It is found that the nutlet
with higher index values carry less logaritlunic power in the lower tail
of the propagation 's constant range, and this feature affects the higher
tail. A better kind of uniformity of the power distribution is observed
near the higher tail of the range of propagation Constants
Microwave dielectric ceramics based on RETiTaO6 (RE = La, Cc, Pr, Nd, Sm, Eu,
Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) were prepared using a conventional solid-state
ceramic route. The structure and microstructure of the samples were analyzed using
x-ray diffraction and scanning electron microscopy techniques. The sintered samples
were characterized in the microwave frequency region. The ceramics based on Ce, Pr,
Nd, Sm, Eu, Gd, Tb, and Dy, which crystallize in orthorhombic aeschynite structure,
had a relatively high dielectric constant and positive T f while those based on Ho, Er,
and Yb, with orthorhombic euxenite structure, had a low dielectric constant and
negative Tf. The RETiTaO6 ceramics had a high-quality factor. The dielectric constant
and unit cell volume of the ceramics increased with an increase in ionic radius of the
rare-earth ions, but density decreased with it. The value of Tf increased with an
increase in RE ionic radii, and a change in the sign of Tf occurred when the ionic
radius was between 0.90 and 0.92 A. The results indicated that the boundary of the
aeschynite to euxenite morphotropic phase change lay between DyTiTaO6 and
HoTiTaO6. Low-loss ceramics like ErTiTaO6 (Er = 20.6, Qxf = 85,500), EuTiTaO6
(Er = 41.3, Qxf = 59,500), and YTiTaO6 (Er = 22.1, Q„xf = 51,400) are potential
candidates for dielectric resonator applications
The microwave dielectric properties of (I -x)CaTiO3-xSm(Mg1/2Tit,2)O3(0.1 <-x< 1.0) have been investigated. The
system forms a solid solution throughout the entire compositional range. The dielectric constant decreases from 86 to 25 as x
varies from 0.1 to 1.0. The Qxf varies non-linearly and increases for composition with x> 0.6. The nonmonotonic variation
with composition x is more pronounced in Tt than in er. The microwave dielectric properties indicate the possibility of a phase
transformation for x between 0.4 and 0.5
Pazhoor Bijumon, Varghese; Mohanan, P; Mailadil, Thomas Sebastian(The Japan Society of Applied Physics, 2002)
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Abstract:
Microwave ceramic dielectric materials Ca5Nb2TiO12 and Ca5Ta2TiO12 have been prepared by a conventional solid-state
ceramic process. The structure was studied by X-ray diffraction and the dielectric properties were characterized at microwave
frequencies. The ceramics posses a relatively high dielectric constant, very low dielectric loss (Q5 x f > 30000GHz) and
small temperature variation of resonant frequency. These materials are potential candidates for dielectric resonator
applications in microwave integrated circuits. [DOI: 10. 1 143/JJAP.41.3834]