139 research outputs found
Tri-band CMOS Circuit Dedicated for Ambient RF Energy Harvesting
RĂSUMĂ L'utilisation de systĂšmes sans fil connait une croissance rapide dans divers domaines tels que les rĂ©seaux de tĂ©lĂ©phonie cellulaire, Wi-Fi, Wi-Max, la radiodiffusion et les communications par satellite. Cette croissance mĂšnera Ă une quantitĂ© considĂ©rable d'Ă©nergie Ă©lectromagnĂ©tique gĂ©nĂ©rĂ©e dans l'air ambiant, mais toujours en dessous des limites de sĂ©curitĂ© internationales. Ainsi,
la recherche au niveau des systÚmes de récupération d'énergie RF pour alimenter des appareils
Ă©lectroniques miniaturisĂ©s Ă faible consommation de puissance devient attrayante et prometteuse. Le bloc principal dans un systĂšme de rĂ©cupĂ©ration d'Ă©nergie RF est le redresseur qui dĂ©termine l'efficacitĂ© et la sensibilitĂ© de l'ensemble du systĂšme. Ătant donnĂ© que la puissance RF
ambiante est trĂšs faible, la quantitĂ© d'Ă©nergie captĂ©e par l'antenne lâest Ă©galement. En outre, il y a des pertes au niveau du rĂ©seau d'adaptation dâimpĂ©dance qui rĂ©duisent encore plus la puissance transmise au bloc redresseur. Par consĂ©quent, la puissance disponible est trop faible pour faire fonctionner des redresseurs classiques.
Dans ce mĂ©moire, nous proposons trois redresseurs Ă trois-Ă©tages et Ă grilles totalement croisĂ©es-couplĂ©es en utilisant des transistors Ă faible tension de seuil afin dâopĂ©rer Ă de faibles puissances d'entrĂ©e. Les trois redresseurs ont Ă©tĂ© conçus et intĂ©grĂ©s au sein dâune mĂȘme puce fabriquĂ©e en utilisant une technologie CMOS 130nm dâIBM. Ils ont Ă©tĂ© optimisĂ©s Ă des frĂ©quences
de 880MHz, 1960MHz et 2.45GHz respectivement. Les rĂ©sultats expĂ©rimentaux dĂ©montrent quâils atteignent une efficacitĂ© de conversion de puissance maximale de 62%, 62% et 56.2%
respectivement. Les mesures montrent Ă©galement une grande amĂ©lioration de l'efficacitĂ© Ă de faibles niveaux de puissance d'entrĂ©e. Afin de rĂ©cupĂ©rer l'Ă©nergie ambiante de trois principales sources RF au Canada â GSM-850, GSM-1900 et Wi-Fi, un systĂšme de redresseur utilisĂ© pour la
combinaison de la puissance de ces trois canaux est simulĂ© et analysĂ©. Le systĂšme utilise une topologie consistant simplement Ă connecter les sorties des redresseurs ensemble pour charger le condensateur de charge. En dĂ©pit de la grande amĂ©lioration de l'efficacitĂ© et de la sensibilitĂ© dans la plage de 0-5ÎŒW, une baisse d'efficacitĂ© indĂ©sirable se produit aux puissances plus Ă©levĂ©es. Ainsi,
un nouveau bloc de gestion de l'alimentation est proposé. De plus, une antenne tri-bande est conçue et simulée pour diminuer le volume de l'ensemble du systÚme de récupération d'énergie RF. En particulier, les pertes par réflexion obtenues sont de -25.43dB, -13.92dB et -12.73dB aux
fréquences citées plus haut respectivement.---------- ABSTRACT Nowadays, the use of wireless systems has grown rapidly in various domains such as cellular phone networks, Wi-Fi, Wi-Max, radio broadcasting and satellite communications. The growing use of these wireless systems leads to considerable amount of electromagnetic energy
generated in ambient air (of course, still below international safety limits). Thus the research in
ambient RF energy harvesting system dedicated for powering up low-power-consumption miniaturized electronic devices becomes attractive and promising. The main block in a RF harvesting system is the rectifier which determines the efficiency and sensitivity of the whole system. Since ambient RF power is very low, the amount of power
captured by the antenna is extremely low. Besides, there is loss on matching networks, thus the available power given to the rectifier block is too low for traditional rectifiers to operate. Therefore, in this master thesis, three three-stage fully gate cross-coupled rectifiers using low-thresholdvoltage transistors are proposed to overcome the dead zone in low input power range. The three
rectifiers optimized at 880MHz, 1960MHz and 2.45GHz frequencies respectively are designed on one chip layout. Their experimental results are retrieved from this custom fabricated integrated circuit using IBM 130nm CMOS technology. They achieve peak efficiencies of 62%, 62% and
56.2% respectively and show great improvements on power conversion efficiency at low input power level.
In order to harvest ambient RF energy from the three main RF contributors in Canada â GSM-850, GSM-1900 and Wi-Fi 2.4GHz, a rectifier system used for power combination from
these three channels is simulated and analyzed. The system employs a simple topology by connecting the outputs together to charge the load capacitor. In spite of its high improvements on efficiency and sensitivity in 0-5ÎŒW range, an undesirable efficiency drop happens at higher input
power levels. Thus an idea of power management block is proposed. In addition, a tri-band antenna is designed and simulated so as to decrease the volume of the overall RF energy harvesting system. It achieves return loss of -25.43dB, -13.92dB and - 12.73dB at each desired band respectively
Accretion-modified stellar-mass black hole distribution and milli-Hz gravitational wave backgrounds from galaxy centre
Gas accretion of embedded stellar-mass black holes\,(sBHs) or stars in the
accretion disk of active galactic nuclei\,(AGNs) will modify the mass
distribution of these sBHs and stars, which will also affect the migration of
the sBHs/stars. With the introduction of the mass accretion effect, we simulate
the evolution of the sBH/star distribution function in a consistent way by
extending the Fokker-Planck equation of sBH/star distributions to the
mass-varying scenario, and explore the mass distribution of sBHs in the nuclear
region of the galaxy centre. We find that the sBHs can grow up to several tens
solar mass and form heavier sBH binaries, which will be helpful for us to
understand the black-hole mass distribution as observed by the current and
future ground-based gravitational wave detectors\,(e.g., LIGO/VIRGO, ET and
Cosmic Explorer). We further estimate the event rate of extreme mass-ratio
inspirals\,(EMRI) for sBH surrounding the massive black hole and calculate the
stochastic gravitational wave\,(GW) background of the EMRIs. We find that the
background can be detected in future space-borne GW detectors after considering
the sBHs embedded in the AGN disk, while the mass accretion has a slight effect
on the GW background.Comment: 15 pages, 8 figures, Accepted by MNRA
Motion of Cesium Atoms in the One-Dimensional Magneto-Optical Trap
The force to which Cs atoms are subjected in the one-dimensional magneto-optical trap (lD-MOT) is calculated, and properties of this force are discussed. Several methods to increase the number of Cs atoms in the lD-MOT are presented on the basis of the analysis of the capture and escape of Cs atoms in the ID-MOT
ON THE SPECTRAL INSTABILITY AND BIFURCATION OF 2D-QUASI-GEOSTROPHIC POTENTIAL VORTICITY EQUATION
The analysis on hydrodynamic stability of shear flows is an active research direction in fluid dynamics. In this article, the spectral instability and bifurcation of forced shear flows governed by the 2D quasi-geostrophic equation with a generalized Kolmogorov forcing are investigated. We prove that the corresponding eigenvalue problem can be transferred into a family of algebraic equations with infinity number of variables, and the nontrivial solutions to the algebraic equations are expressed in form of continuous fractions. After obtaining the asymptotic estimate for the ratio of the imaginary parts of eigenvalues to a control parameter R as it approaches to infinity, we show that there exists a critical value Rc above which, the forced shear flows become unstable, where the control parameter R is the product of Reynolds number Re and the intensity of the curl of the forcing. To shed light on the bifurcation involved in the losing stability of the forced shear flows, a natural method used to reduce the quasi-geostrophic equation to ODEs is introduced. Based on numerical experiments on the coefficients in the ODEs, we show that both supercritical and subcritical Hopf bifurcations occur in the forced shear flows, which only depend on the type of generalized Kolmogorov forcing
A Parallel Batch-Dynamic Data Structure for the Closest Pair Problem
We propose a theoretically-efficient and practical parallel batch-dynamic
data structure for the closest pair problem. Our solution is based on a serial
dynamic closest pair data structure by Golin et al., and supports batches of
insertions and deletions in parallel. For a data set of size , our data
structure supports a batch of insertions or deletions of size in
expected work and depth
with high probability, and takes linear space. The key techniques for achieving
these bounds are a new work-efficient parallel batch-dynamic binary heap, and
careful management of the computation across sets of points to minimize work
and depth.
We provide an optimized multicore implementation of our data structure using
dynamic hash tables, parallel heaps, and dynamic -d trees. Our experiments
on a variety of synthetic and real-world data sets show that it achieves a
parallel speedup of up to 38.57x (15.10x on average) on 48 cores with
hyper-threading. In addition, we also implement and compare four parallel
algorithms for static closest pair problem, for which we are not aware of any
existing practical implementations. On 48 cores with hyper-threading, the
static algorithms achieve up to 51.45x (29.42x on average) speedup, and Rabin's
algorithm performs the best on average. Comparing our dynamic algorithm to the
fastest static algorithm, we find that it is advantageous to use the dynamic
algorithm for batch sizes of up to 20\% of the data set. As far as we know, our
work is the first to experimentally evaluate parallel closest pair algorithms,
in both the static and the dynamic settings
On the noise effect of test mass surface roughness in spaceborne gravitational wave detectors
Spaceborne gravitational wave detection mission has a demanding requirement
for the precision of displacement sensing, which is conducted by the
interaction between the laser field and test mass. However, due to the
roughness of the reflecting surface of the test mass, the displacement
measurement along the sensitive axis suffers a coupling error caused by the
residue motion of other degrees of freedom. In this article, we model the
coupling of the test mass residue random motion to the displacement sensing
along the sensitive axis and derived an analytical formula of the required
precision of the surface error for the spaceborne gravitational wave detectors.
Our result shows that this coupling error will not contaminate the picometer
displacement sensing for the test masses in the LISA pathfinder.Comment: 8 page
Terahertz Artificial Dielectric Lens
We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100âÎŒm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2âcm diameter beam to a spot size of 4âmm, at the design frequency of 0.17âTHz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices
Probing phase transition in neutron stars via the crust-core interfacial mode
Gravitational waves emitted from the binary neutron star (BNS) systems can
carry information about the dense matter phase in these compact stars. The
crust-core interfacial mode is an oscillation mode in a neutron star and it
depends mostly on the equation of the state of the matter in the crust-core
transition region. This mode can be resonantly excited by the tidal field of an
inspiraling-in BNS system, thereby affecting the emitted gravitational waves,
and hence could be used to probe the equation of state in the crust-core
transition region. In this work, we investigate in detail how the first-order
phase transition inside the neutron star affects the properties of the
crust-core interfacial mode, using a Newtonian fluid perturbation theory on a
general relativistic background solution of the stellar structure. Two possible
types of phase transitions are considered: (1) the phase transitions happen in
the fluid core but near the crust-core interface, which results in density
discontinuities; and (2) the strong interaction phase transitions in the dense
core (as in the conventional hybrid star case). These phase transitions'
impacts on interfacial mode properties are discussed. In particular, the former
phase transition has a minor effect on the M-R relation and the adiabatic tidal
deformability, but can significantly affect the interfacial mode frequency and
thereby could be probed using gravitational waves. For the BNS systems, we
discuss the possible observational signatures of these phase transitions in the
gravitational waveforms and their detectability. Our work enriches the
exploration of the physical properties of the crust-core interfacial mode and
provides a promising method for probing the phase transition using the
seismology of a compact star.Comment: 18 pages, 14 figure
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