Showing papers by "Mohamed Essaaidi published in 2011"

Compact Disc Monopole Antennas for Current and Future Ultrawideband (UWB) Applications

Abstract: Circular disc monopole antennas are investigated for current and future ultrawideband (UWB) applications. The studied antennas are compact and of small size (25 mm × 35 mm × 0.83 mm) with a 50-Ω feed line and offer a very simple geometry suitable for low cost fabrication and straightforward printed circuit board integration. More specifically, the impedance matching of the classic printed circular disc UWB monopole is improved by introducing transitions between the microstrip feed line and the printed disc. Two particular designs are examined using a dual and single microstrip transition. By using this simple antenna matching technique, respective impedance bandwidths (|Sn | <; -10 dB) from 2.5 to 11.7 GHz and 3.5 to 31.9 GHz are obtained. Results are also compared to a classic UWB monopole with no such matching network transitions. Measured and simulated reflection coefficient curves are provided along with beam patterns, gain and group delay values as a function of frequency. The transient behavior of the studied antennas is also examined in the time domain.

Tolerating malicious resources to ensure safe computations in grid systems

Abstract: Grid computing has recently seen a great importance in diverse applications domains of scientific, industrial, and commercial activities, which demand huge computational power. Unlike traditional cluster computing, large scale grids permit the sharing of grid resources spread through different administrative sites autonomy. The distributed and dynamic features of grid resources, their architectures heterogeneity, and unreliable interconnection network increases the probability of attacks and malicious behavior of grid resources. In Grid applications, reliability and security assurance of execution are two basic requirements. Thus, it is necessary to guarantee that, among the shared grid resources, there are no malicious behaviors interested in invalidating or corrupting the job results. In order to ensure reliable and safe jobs computation in grid systems, we have proposed a new approach for tolerating malicious grid resources by using reputation to improve the efficiency of majority voting mechanisms. The grid broker service investigates the trustworthy of the grid resources that are used in the voting procedure; this investigation is based on reputation management system which maintains a reputation value for each grid resource based on its historical behavior. The validation of the result is then decided based on the reputation level of the grid resources.

Simultaneous gain and bandwidth enhancement of a circularly polarized microstrip patch antenna using a coupled square-shape split ring resonators metamaterial superstrate

Abstract: We propose a coupled square-shape split ring resonators metamaterial structure as a superstrate for a circularly polarized microstrip patch antenna to achieve simultaneous enhancement on its gain and bandwidth‥ The coupled square-shape split ring resonators metamaterial superstrate is shown to enhance the bandwidth by a factor of 2 and to increase the gain of the antenna by 8.17 dB compared to the conventional circularly polarized microstrip patch antenna.

A novel compact dual-band antenna for IEEE 802.11 a/b/g/n WLAN

Abstract: This article presents a novel compact T shaped microstrip dual-band antenna for 2.4 GHz WLAN (2.4–2.484 GHz), and the 5-GHz WLAN (5.15–5.35/5.725–5.825 GHz) bands.The proposed antenna has a simple geometry, a small size of 15 mm × 15 mm, and the excitation is launched through a 50-Ω microstrip feed line. Several properties of the proposed compact antenna as impedance bandwidth, radiation pattern, and measured gain have been simulated and measured. This antenna is attractive by its simple configuration, low profile, compactness, low fabrication cost, and operation at all the frequencies defined by IEEE 802.11 a/b/g/n standards for WLAN. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:315–317, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25737

Transmission properties of stacked srr metasurfaces in free space

Abstract: In this paper, transmission properties of stacked split ring resonators metasurfaces in free space and under normal incidence are investigated experimentally and numerically. Emphasis is put on studying the interaction between adjacent SRRs metasurfaces. The thorough analysis of the electromagnetic flelds shows that both magnetic and electric coupling can occur between adjacents metasurfaces for vertical and horizontal polarization. In addition, we found that all propagating bands within our spectral window (up to 20GHz) support right-handed behaviour. Both simulation and experiment results in the microwave regime are in good agreement.

A fuzzy MADM approach for grid services composition

Abstract: In service oriented computing applications, different resources in grid systems are encapsulated abstractly as services. Sometime, single service software can provide valuable service functions for service consumers, but most of the time, single atomic service can not satisfy them. In this case, the system builds a new composite service, which selects all available qualified grid service for composition. Services with similar and compatible functionality may be offered at different QoS levels. Thus, to build a service process, decisions must be made to select component services at appropriate QoS levels. Therefore, quality of service (QoS) aspects is crucial for selecting the grid services to take part in the composition of the new service. In this paper, we address to the problem of Grid services composition based on QoS parameters with end-to-end constraints, we suggest a new model, which transform any model of composition to a sequential model, and we propose a new approach based on the application of a Fuzzy Multiple Attribute Decision Making technique in order to guide the composition process to selected an optimal composite service.