Mridula, S; Jacob,George; Mohanan, P(Microwave and Optical Technology Letters, December 20, 1999)
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Abstract:
A novel antenna configuration comprised of two circular
micro strip antennas (CMAs) resonating in the TMtt and TM2, modes,
producing radiation characteristics suitable for a mobile telephone handset,
is presented. The antennas operating at the same frequency are
placed back to back with a separation comparable to the thickness of a
typical handset. The radiation pattern consists of a region of reduced
radiation intensity, which minimizes the radiation hazards to the user
Jitha, B; Bybi, P C; Aanandan,C K; Mohanan, P(John Wiley & Sons, June , 2008)
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Abstract:
Design of a compact microstrip band reject filter is proposed. The device consists of an Open Loop Rectangular Resonator (OLRR) coupled to a microstrip line. The transmission line has a U-bend which enhances the coupling with the OLRR element and reduces the size of the filter. The filter can be made tunable by mounting variable capacitance to the system. Simulated and experimental results are presented.
Zhongyou,Yan(Microwave Engineering Group,Department of Electronics, January 5, 2002)
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Abstract:
patch resonator with a via connecting ground plane is
proposed and studied experimentally. The resonant frequency of this
patch resonator is tunable up to about 34 % by adjusting the via position
in the center line. The lowest resonant frequency of this patch resonator
has been reduced by more than 64% of the same size patch resonator
Anantharaman, M R; Senoy, Thomas; Al-Harthi, S H; Sakthi Kumar, D; Al-Omari, I A; Ramanujan, R V; Yasuhiko, Yoshida(IOP Publishing LTD, July 17, 2008)
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Abstract:
Nanocrystalline Fe–Ni thin films were prepared by partial crystallization of vapour deposited
amorphous precursors. The microstructure was controlled by annealing the films at different
temperatures. X-ray diffraction, transmission electron microscopy and energy dispersive x-ray
spectroscopy investigations showed that the nanocrystalline phase was that of Fe–Ni. Grain
growth was observed with an increase in the annealing temperature. X-ray photoelectron
spectroscopy observations showed the presence of a native oxide layer on the surface of the
films. Scanning tunnelling microscopy investigations support the biphasic nature of the
nanocrystalline microstructure that consists of a crystalline phase along with an amorphous
phase. Magnetic studies using a vibrating sample magnetometer show that coercivity has a
strong dependence on grain size. This is attributed to the random magnetic anisotropy
characteristic of the system. The observed coercivity dependence on the grain size is explained
using a modified random anisotropy model
Anantharaman, M R; Vinayasree, S; Soloman, M A; Vijutha, Sunny; Mohanan, P; Philip, Kurian(Elsevier, April 21, 2013)
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Abstract:
Flexible and thin single layer microwave absorbers based on strontium ferrite–carbon black–nitrile rubber
composites have been fabricated employing a specific recipe and their reflection loss characteristics
were studied in the S (2–4 GHz) and X-bands (8–12 GHz). The incorporation of carbon black not only
reinforces the rubber by improving the mechanical properties of the composite but also modifies the
dielectric permittivity of the composite. Strontium ferrite when impregnated into a rubber matrix
imparts the required magnetic permeability to the composite. The combination of strontium ferrite
and carbon black can then be employed to tune the microwave absorption characteristics of the resulting
composite. The complex dielectric permittivity and permeability were measured by employing a cavity
perturbation technique. The microwave absorption characteristics of composites were modelled in that
an electromagnetic wave incident normally on the metal terminated single layer absorber. The influence
of filler volume fraction, frequency, absorber thickness on the bandwidth of absorption are discussed and
correlated
Anantharaman, M R; Vamsi Krishna, G; Philip, Kurian(2013)
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Abstract:
Ferrite composites are magnetic composites consisting of fine particles of metal
ferrites dispersed in the polymer matrix. These composites have a variety of applications as
flexible magnets, pressure/photo sensors and microwave absorbers. Polymers and
magnetic materials play a very important role in our day to day life. Both natural and
synthetic polymers are today indispensable to mankind. The polymers, which include
rubber, plastics and fibers, make life easier and more comfortable.
A microwave dielectric ceramic resonator based on BaCe2Ti5O15 and Ba5Nb4O15 have been prepared by conventional solid state ceramic route. The dielectric resonators (DRs) have high dielectric constant 32 and 40 for BaCe2Ti5O15 and Ba5Nb4O15, respectively. The whispering gallery mode (WGM) technique was employed for the accurate determination of the dielectric properties in the microwave frequency range. The BaCe2Ti5O15 and Ba5Nb4O15 have quality factors (Q X F) of 30,600 and 53,000 respectively. The quality factor is found to depend on the azimuthal mode numbers. The temperature coefficient of resonant frequency (Tr) of BaCe2Ti5O15 and Ba5Nb4O15 have been measured accurately using different
resonant modes and are + 41 and + 78 ppm/K, respectively
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
microwave dielectric properties of ceramics based on Ba(Mgv3Ta(2-2x)t3W,t3Tixt3)O3 is investigated as a function of x. The
15 densification as well as dielectric properties deteriorate with increase in the substitution levels of (Ti 1,3W113)333 + at (Ta213)3.33+ site
16 in Ba(Mg113Ta213)03. The rt is approaching zero between x = 0.1 and 0.15 in Ba(Mg it3Ta(2-2,,.)t3W,it3Ti,Tt3)O3 where quality factor is
17 reasonably good (Qu x f = 80,000-90,000 GHz). The Ba(Mg1,3Ta(2_,013W,13Ti,,13)03 with x = 1.0 has e, = 15.4, rf= -25.1 ppm/
18 "C, Q„ x f = 35,400 GHz
The BaO-2CeO2-nTiO2 ceramics with n = 3, 4 and 5 have been prepared with CeO2 as starting material . The ceramics have been
characterized using scanning electron microscopy , X-ray diffraction , Raman and X-ray photoelectron spectroscopy techniques. The
microwave dielectric properties have been measured using standard dielectric resonator techniques . BaO-2CeO2-3TiO2 (123),
BaO-2CeO2-4TiO2 ( 124) and BaO-2CeO2-5TiO2 ( 125) ceramics showed dielectric constants of 38, 27 and 32, respectively . All the
ceramics showed fairly good unloaded Q - factors . 124 and 125 compounds exhibited low tf values, while 123 showed a high rf value
Isuhak, Naseembeevi Jawahar; Narayana Iyer, Santha; Mailadil, Thomas Sebastian(Materials Reserach Society, December , 2002)
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Abstract:
Single-phase polycrystalline ceramics in the MO-La2O3-Ti02 (M = Ca, Sr, Ba)
system, such as cation-deficient hexagonal perovskites CaLa4Ti4O15, SrLa4Ti4O15,
BaLa4Ti4O15, and Ca2La4Ti5O18 and the orthorhombic phases CaLa4Ti5O17 and
CaLa8Ti9O31, were prepared through the solid-state ceramic route. The phases
and structure of the ceramics were analyzed through x-ray diffraction and scanning
electron microscopy. The microwave dielectric properties of the ceramics were studied
using a network analyzer. The investigated ceramics show high Er in the range 42 to
54, high quality factors with Q x f in the range 16,222 to 50,215 GHz, and low Tf in
the range -25 to +6 ppm3/°C. These high dielectric constant materials with high Q x f
up to 50,215 GHz are suitable for applications where narrow bandwidth and extremely
low insertion loss is necessary, especially at frequencies around 1.9 GHz
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
Dielectric resonator ceramics with composition formula Ba[(D3+0.3 Bi0.2)Nb0.5]O3,where D3+=Y,Pr,Sm,Gd,Dy and Er,were prepared by the conventional ceramic preparation route
Eby Thomas, Thachil; Bindu, Sharmila T K; Ajalesh, Nair B; Beena, Abraham T; Sabura Begum, P M(Elsevier, May 22, 2014)
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Abstract:
Graphene has captured the attention of scientific community due to recently emerging high performance
applications. Hence, studying its reinforcing effects on epoxy resin is a significant step. In this study,
microwave exfoliated reduced graphene oxide (MERGO) was prepared from natural graphite for subsequent
fabrication of epoxy nanocomposites using triethylenetetramine (TETA) as a curing agent via insitu
polymerization. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy,
Fourier transform infrared spectroscopy (FTIR), C13 NMR spectroscopy, X-ray photoelectron spectroscopy
(XPS) and ultravioletevisible (UVevis) spectroscopy were employed to confirm the simultaneous
reduction and exfoliation of graphene oxide. The reinforcing effect of MERGO on epoxy resin was
explored by investigating its static mechanical properties and dynamic mechanical analysis (DMA) at
MERGO loadings of 0 to 0.5 phr. The micro-structure of epoxy/MERGO nanocomposites was investigated
using scanning electron microscope (SEM), transmission electron microscope (TEM) and XRD techniques.
The present work reports an enhancement of 32%, 103% and 85% in tensile, impact and flexural strength
respectively of epoxy by the addition of even 0.25 phr MERGO. At this loading elastic and flexural moduli
also increased by 10% and 65%, respectively. Single-edge-notch three-point-Bending (SEN-TPB) fracture
toughness (KIC) measurements were carried out where a 63% increase was observed by the introduction
of 0.25 phr MERGO. The interfacial interactions brought about by graphene also benefited the dynamic
mechanical properties to a large extent in the form of a significant enhancement in storage modulus and
slightly improved glass transition temperature. Considerable improvements were also detected in
dielectric properties. The epoxy nanocomposite also attained an ac conductivity of 10 5 S/m and a
remarkable increase in dielectric constant. The simple and cost effective way of graphene synthesis for
the fabrication of epoxy/MERGO nanocomposites may be extended to the preparation of other MERGO
based polymer nanocomposites. This remarkable class of materials has thrown open enormous opportunities
for developing conductive adhesives and in microelectronics