Showing papers by "Sabah M. Ahmed published in 2020"

Small Frequency Ratio Multi-Band Dielectric Resonator Antenna Utilizing Vertical Metallic Strip Pairs Feeding Structure

Abstract: In this study a quintuple band rectangular dielectric resonator antenna (RDRA) with a small frequency ratio and small size of 30 mm × 30 mm × 9813 mm is introduced The proposed RDRA covers the frequency bands of WLAN (24/52 GHz), WiMAX (35 GHz) and 5G (41/48 GHz) exploiting TE 10 y , TE 211 x , TE 1δ1 y , TE 111 y , and TE 2δ1 y modes, respectively A rectangular slot aperture is optimized to serve as a resonator with resonance mode TE 10 y as well as to couple the electric field from microstrip line to the DRA to excite TE 211 x mode Furthermore, a new feeding approach employing three vertical metallic strip pairs (VMSPs) is proposed to excite further TE 1δ1 y , TE 111 y , and TE 2δ1 y modes in the RDRA The VMSPs are configured on both sides of the dielectric resonator (DR) along the y - direction to act as vertical electric current sources The lengths, width, and positions of the VMSPs are carefully determined in order to attain the desired modes The four RDRA modes have broadside patterns while the slot resonator mode has a pattern like a dipole Good agreement between both measured and simulated results of the reflection coefficient, radiation pattern, and the gain is achieved

Autonomous Flight Take-off in Flapping Wing Aerial Vehicles

Abstract: This paper presents the design and dynamic simulation of a jumping mechanism for flight initiation in flapping wing aerial vehicles to enhance their autonomous mobility. It is inspired by avian flyers that start flight by jumping using their hind limbs. A 4-bar linkage that performs the prescribed take-off maneuvers has been geometrically designed using dimensional synthesis by motion generation. The kinematic dimensions obtained thereof have been ascertained analytically. A magnetic latching solenoid actuator and its corresponding transmission mechanism has been proposed for jumping actuation due to its compact structure, and low power consumption with no heat nor electrical noise generation. After take-off, the necessity to sustain the aerial vehicle airborne by providing adequate supportive forces at low air speeds has been demonstrated by the prospect of unsteady aerodynamics. Fluid-structure interaction has been analyzed by co-simulation between ADAMSⓇ and MATLABⓇ/Simulink. The designed legs give an inclined take-off of about 64° and an initial speed of almost 2m/s with an angular deflection of 110° between the leg segments. Flight performance indicates an increase in lift/drag ratios with in both flapping rate and forward velocity up to some limit. The results also compared favorably with those from wind tunnel tests and previous analysis of related work. They all exhibited an increase in wing efficiency with decreasing mean angles of attack as the air vehicle approaches stable flight.

Model Predictive Control for an Active Magnetic Bearing System

Abstract: Active magnetic bearing (AMB) systems have attracted much attention in the high speed rotating machinery industry. This paper presents an application of discrete-time model predictive control (MPC) subject to input/states constraints to control an AMB system based on linear time-invariant (LTI) model. The main control objectives are to levitate the rotor shaft of the AMB system while tracking a reference trajectory and to reject possible disturbances without violating the input and state constraints. A nonlinear (NL) model of the AMB system is considered; at each sampling instant, a finite horizon MPC problem is solved to compute the optimal control input. The performance and the efficiency of the proposed MPC is validated via simulation and comparison with another classical PID controller.

Detection of Primary User in Wide-band Cognitive Radio Networks over Fading Channel using Compressed Sensing

Abstract: In wideband cognitive radio networks, Nyquist sampling rate is very challenging problem. It required expensive high speed analog to digital converter and large storage spaces. Lately, compressive sensing has been emerged as significant solution to crack the conventional sampling rate requirements. It proved the ability to sample below Shannan-Nyquist criteria and reconstructing back the signal after considerable dimensional reduction. Mostly in cognitive radio networks, energy detection is widely used due to its simple implementation and blind detection property. However, regardless that energy detection is subject to noise uncertainty as well as shadowing and fading which deteriorate its detection performance. Several articles have been published to improve energy detection performance using large number of measurements. In this paper, since, the detection performance using small number of measurements or compressed measurements achieved significant performance using energy detection under additive white Gaussian noise channel. This motivated us to investigate the performance of compressed measurements-based detection over fading channels which has not been studied yet. The proposed algorithm has been implemented using MATLAB. We also studied the tradeoff between the compression ratios and using fraction of transmitted signal and its impact on detection performance and threshold choice. In comparison with the ordinary compressed energy detection over the Rayleigh fading channel the results reveal that the proposed enhanced compressed measurements-based energy detection is better in performance of detection.