Integrated Vivaldi antenna for UWB/diversity applications in vehicular environment

This article presents the design of a three‐port diversity antenna capable of producing three‐directional radiation pattern for vehicular communications. The proposed antenna consists of three uncorrelated Vivaldi antennas that are interconnected and developed on a single printed circuit board. Unlike many other antennas reported for the vehicular environment, the proposed antenna offers ultra‐wideband characteristics with end‐fire radiation pattern leading to high realized antenna gain. The integrated antenna has a footprint of 65 × 40 × 1.6 mm³ and offers 6 GHz impedance bandwidth extending from 5 to 11 GHz. The port‐to‐port isolation is greater than 20 dB within the operating bandwidth. Furthermore, the diversity performance of the proposed three‐port antenna system is evaluated and presented. The calculated envelope correlation coefficient, diversity gain, and mean effective gain are well above the minimum requirement. The prototype antenna is fabricated and the experimental results are presented.     

Gain enhanced multipattern reconfigurable antenna for vehicular communications

This article presents the design and implementation of a high‐gain tunable dual‐band pattern reconfigurable antenna for vehicular communications. The proposed antenna consists of a slotted patch loaded with a double‐side FSS acting as superstrate. The proposed slotted antenna operates at 2.45 and 3.5 GHz and the frequency tuning over the dual‐band is accomplished by employing a varactor diode for tuning the center frequency from 2.41 to 2.62 GHz and from 3.38 to 3.65 GHz at lower and upper frequency bands, respectively. To obtain pattern reconfiguration, the slotted patch is divided into four regions by using two diagonal lines of vias. By properly choosing the excitation port combinations, 14 different radiation patterns are realized with a maximum realized gain of 8.4 and 7.9 dB. Further enhancement of gain is achieved using frequency‐selective surface (FSS) screens which act as a partially reflecting surface. The unique feature of this design is to provide reflection coefficient with high reflectivity in two predetermined frequency ranges. The prototype antenna is fabricated and the measurement results are reported. The experimental results show that the prototype antenna with FSS offers tunable dual‐band with beam reconfigurable properties.     

Capturing the participation and social dimensions of computer-supported collaborative learning through social network analysis: which method and measures matter?

International Journal of Computer-Supported Collaborative Learning - The increasing use of digital learning tools and platforms in formal and informal learning settings has provided broad access to...     

A comprehensive analysis on the state‐of‐the‐art developments in reflectarray,transmitarray, and transmit‐reflectarray antennas

Contemplating the advancements in communication technology, the analysis of the features of reflectarray, transmitarray, and transmit‐reflectarray becomes essential for future adaptability. This article presents a thorough review of such high‐gain antennas, presenting some of the most relevant solutions published by the scientific society in the field of antennas and wave propagation. Several examples of unit cells for array implementation and complete array designs discussed in various literatures are analyzed. The analysis is focused in identifying the unit cell layouts, such as those developed using microstrip patches, frequency selective surfaces, or metamaterials. The analysis is extended to the ways of improving bandwidth, for example, true time delay elements, phase delay lines, meander lines, and so on, and the various methods used to enable reconfiguration, for example, p‐i‐n diodes, varactor diodes, or microelectromechanical systems. In addition, some antennas, which produce bidirectional beams simultaneously, are also discussed. Finally, all the models are compared against each other in order to highlight their benefits and limitations, summarizing their main characteristics, such as the frequency of operation, bandwidth, phase range, gain, aperture efficiency, sidelobe levels, cross polarization levels, and maximum beam‐steering range.     

Volunteer nodes of ant colony optimization routing for minimizing delay in peer to peer MANETs

A Mobile ad hoc Network (MANET) is an infrastructure less network that permits nodes to make a wireless network with mobility. In MANETs, the node linkages breaks are frequent due to all nodes are in movement. When neighbor nodes travel out of other node communication range connection among both mobile nodes breaks. Thus it makes delay and packet loss in the network. In the present Traffic Control method, several times, since the highest traffic, heavy rain, accidents, or other reasons, there may be probabilities of jam on roads. Thus, people could get delay owing to the highest traffic. Therefore, it is highly preferred to have an effective way to track the traffic on roads and thus select the suitable road that is traffic free. To resolve these problems, the volunteer Nodes of Ant Colony Optimization Routing (VNACO) is proposed. The primary objective of VNACO is to reduce both the delay and routing overhead in Peer to Peer (P2P) MANETs. Here, peer node act as a volunteer node and mobile node for transmitting data from source to destination. During data transmission, the relay node moving out of communication range when the volunteer node overheard the dropped data packet then deliver the data to the corresponding relay node. As a result, minimizes both the delay and packet losses. In VNACO, the volunteer’s nodes are elected based on node aptitude. Node aptitude is calculated by iterating node connectivity, transmission processing time, node energy and available bandwidth. In addition, an ant colony optimization algorithm to finds the optimal route and reduce the routing overhead in P2P MANETs. The significant application of this mechanism is utilized for the traffic management system. Network simulation results indicate that the VNACO mechanism is minimizing 22% delay and reducing 14% packet losses compared to the baseline protocol.

     

A compact tri‐band microwave resonator for ethanol gas detection

This article presents the design, simulation, fabrication, and testing of a compact two‐port microwave resonator coated with nanomaterials for ethanol gas sensing applications. The proposed gas sensor consists of a transmission line loaded with three triangular split ring resonators for ethanol detection at three frequency bands viz. 2.2, 4.6, and 6.3 GHz. The transmission line has all‐pass characteristics in which band gaps are introduced using three split ring resonators. The TiO₂ and ZnO nanorods are used as sensitive layers for the proposed sensing application. The nanorods, which are grown on a glass substrate of thickness 1 mm, are loaded on to the two‐port microwave resonator making the device sensitive to ethanol. The microwave behavior of the sensor is analyzed using the scattering parameters. The absorption of the ethanol gas causes frequency detuning which is used to analyze the presence of ethanol and its concentration. From the experiments, it is understood that there is an increase in the frequency shift with an increase in the concentration of ethanol gas. The sensing device with ZnO as a sensitive layer showed a higher average sensitivity of 2.35 compared to TiO₂ whose average sensitivity is 1.29.     

A GA-HP Model for the Optimal Design of Sewer Networks

This paper illustrates the application of a new model combined Genetic Algorithm with Heuristic Programming (GA-HP) technique in order to establish the optimal design for sewer networks. The objective is to minimise the construction cost function, which is represented by the depth of excavation and pipe diameter. The proposed GA-HP model has achieved the optimum design task in two stages. Firstly, the Genetic Algorithm (GA) was applied to obtain the diameters of the pipes needed for the preliminary design of the network. Secondly, Heuristic Programming (HP) preliminary designs were used to obtain the optimal slope for those pipes and to determine other characteristics such as the velocity, relative depth of water, excavation depths and total cost of the network. A MATLAB code was used to perform the GA-HP optimisation modelling. The performance of three different selection methods, four different crossover methods and different population sizes is examined with the proposed model, to determine their impact on convergence behaviour. The proposed GA-HP model is tested using some benchmark examples of sewer networks from the literature. The results show that the GA-HP model is superior to all previous methods and may be more efficient in the design of large networks.     

Observer‐based controller for constrained uncertain stochastic nonlinear discrete‐time systems

In this paper, an observer‐based control approach is proposed for uncertain stochastic nonlinear discrete‐time systems with input constraints. The widely used extended Kalman filter (EKF) is well known to be inadequate for estimating the states of uncertain nonlinear dynamical systems with strong nonlinearities especially if the time horizon of the estimation process is relatively long. Instead, a modified version of the EKF with improved stability and robustness is proposed for estimating the states of such systems. A constrained observer‐based controller is then developed using the state‐dependent Riccati equation approach. Rigorous analysis of the stability of the developed stochastically controlled system is presented. The developed approach is applied to control the performance of a synchronous generator connected to an infinite bus and chaos in permanent magnet synchronous motor. Simulation results of the synchronous generator show that the estimated states resulting from the proposed estimator are stable, whereas those resulting from the EKF diverge. Moreover, satisfactory performance is achieved by applying the developed observer‐based control strategy on the two practical problems. Copyright © 2015 John Wiley & Sons, Ltd.     

A first-order multigrid method for bound-constrained convex optimization

The aim of this paper is to design an efficient multigrid method for constrained convex optimization problems arising from discretization of some underlying infinite dimensional problems. Due to problem dependency of this approach, we only consider bound constraints with (possibly) a single equality constraint. As our aim is to target large-scale problems, we want to avoid computation of second derivatives of the objective function, thus excluding Newton-like methods. We propose a smoothing operator that only uses first-order information and study the computational efficiency of the resulting method.