184 research outputs found
Planar monopole antennas with reflection plane for human body centric communication
Wireless Body Area Network (WBAN) is an emerging technology that requires an antenna to be placed on human body for a wide range of applications such as healthcare, entertainment, surveillance, emergency and military. The reflection coefficient magnitude of the antenna in closeness to the human body is degraded and shifted. Essentially, efficiency and gain reduction are the main disadvantages of the antenna performances due to the body effect. In this research, methods of improving efficiency, gain, Specific Absorption Rate (SAR) and stabilizing reflection coefficient magnitude have been proposed. In this work, the design, simulation and fabrication of two monopole antennas with P-shaped and circular-shaped are presented. The proposed P-shaped monopole antenna is designed to operate from 3.1 to 5.1 GHz while the proposed circular-shaped monopole antenna operates at 3.1-5.1 GHz and 6.5-8 GHz. The simulation of the proposed antennas in free space and close proximity of body surface has been carried out using Computer Simulation Technology (CST) Microwave Studio. It has been found that when the P-shaped and circular elements are introduced to the ground plane of the antennas, the reflection coefficient magnitudes with the presence of body for both antennas remain the same as in free space. Moreover, the efficiency and gain of the antennas have been improved by attaching the glass substrate to the ground plane. P-shaped antenna with the glass substrate has demonstrated about 34.6%, 35% and 39.2% improvement of the antenna efficiency at 3.3, 4.45 and 5 GHz, respectively, when placed directly on the human head. For the human chest placement, the antenna demonstrates 30.7%, 33.4% and 36%, and the gain of 3.4, 2.8 and 4 dBi of antenna efficiency and gain improvement at 3.3, 4.45 and 5 GHz, respectively. Similarly, for circular-shaped monopole antenna the improvement of the antenna efficiency obtained for human head are 39.8% and 37.23% at 3.3 and 7.5 GHz, respectively, and for the chest are 36.5% and 32.8% at 3.3 and 7.5 GHz, accordingly. The antenna demonstrates 2.9 and 2.54 dBi improvement of the gain at 3.3 and 7.5 GHz, respectively. These improvements are compared with the antenna without the glass substrate. This study concludes that the glass substrate has improved the gain, efficiency and SAR when placed near human body compared to other antennas and the S11 remains stable when some additional elements are introduced to the ground plane. It was observed that there is good agreement between the simulation and measurement results, thereby showing that the antennas have potential to be deployed for WBAN application
Non-gaussianity for a Two Component Hybrid Model of Inflation
We consider a two component hybrid inflation model, in which two fields drive
inflation. Our results show that this model generates an observable
non-gaussian contribution to the curvature spectrum, within the limits allowed
by the recent WMAP year 3 data. We show that if one field has a mass less than
zero, and an initial field value less than 0.06Mpl while the other field has a
mass greater than zero, and initial field value ranging between 0.5Mpl and Mpl
then the non-gaussianity is observable with 1<fnl<1.5, but that fnl becomes
much less than the observable limit should we take both masses to have the same
sign, or if we loosened the constraints on the initial field values.Comment: 10 pages and 5 figures. More extensive analysis of model, which shows
that observable fnl is possibl
Single-Field Inflation After WMAP5
Single-field models of inflation are analysed in light of the WMAP five-year
data. Assuming instantaneous reheating, we find that modular/new inflation
models with small powers in the effective inflaton self-interaction are more
strongly constrained than previously. The model with a cubic power lies outside
the 2 sigma regime when the number of e-folds is less than 60. We also find
that the predictions for the intermediate model of inflation do not overlap the
1 sigma region regardless of the power of the monomial potential. We analyse a
number of ultra-violet, DBI braneworld scenarios involving both wrapped and
multiple-brane configurations, where the inflaton kinetic energy is close to
the maximum allowed by the warped geometry. In all cases, we find that the
parameters of the warped throat are strongly constrained by observations.Comment: 10 pages, 5 figures, revtex4. Figures, table and text updated to
match the version that has been accepted to Phys Rev
On the dynamics of a quadratic scalar field potential
We review the attractor properties of the simplest chaotic model of
inflation, in which a minimally coupled scalar field is endowed with a
quadratic scalar potential. The equations of motion in a flat
Friedmann-Robertson-Walker universe are written as an autonomous system of
equations, and the solutions of physical interest appear as critical points.
This new formalism is then applied to the study of inflation dynamics, in which
we can go beyond the known slow-roll formalism of inflation.Comment: 14 pages, 6 eps figures, matches version to appear in IJMP
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