Iranian Journal of Electrical and Electronic Engineering
Volume:8 Issue: 1, Mar 2012

In recent years chaotic secure communication and chaos synchronization have received ever increasing attention. Unfortunately, despite the advantages of chaotic systems, Such as, noise-like correlation, easy hardware implementation, multitude of chaotic modes, flexible control of their dynamics, chaotic self-synchronization phenomena and potential communication confidence due to the very dynamic properties of chaotic nonlinear systems, the performance of most of such designs is not studied and so is not still suitable for wireless channels. To overcome this problem, in this paper a novel wide-band chaos-based communication scheme in multipath fading channels is presented, where the chaotic synchronization is implemented by particle filter observer. To illustrate the effectiveness of the proposed scheme, numerical simulations based on particle filter are presented in different channel conditions and the results are compared with two other EKF and UKF based communication scheme. Simulation results show the Remarkable BER performance of the proposed particle filter-based system in both AWGN and multipath fading channels condition, causes this idea act as a good candidate for asynchronous wide band communication.

The characteristics of dielectric backed planar conducting layers of arbitrarily shaped in a rectangular waveguide are calculated by means of coupled integral equation technique (CIET) which accurately takes higher order mode interactions. Equivalent structures for the accurate analysis whole structure are introduced in which magnetic surface currents are identified as the unknowns at the aperture parts of interfaces in all regions. Spectral dyadic green’s functions are derived for these equivalent structures. A coupled magnetic filed integral equation formulation is proposed which is solved using method of moment (MoM). Then one matrix equation that involves the all magnetic currents of non metallic parts (aperture parts) of discontinuities is derived. This single matrix formulation replaces the procedure of cascading individual GSM’s of each block. By dividing the area of cross section in discontinuities into a given number of subsections, it is possible to model any shape of metallic parts. In this method when the shape of metallic parts (in a given structure) changes, the related coupled integral equations can be extracted from the pre-computed general matrices in a given frequency and there is not need to repeat the all of process. The proposed technique permits modeling of a variety of structures such as cavity-backed micro strip antenna, frequency selective surfaces (FSS’s), waveguide filters with printed irises and generally multilayered media with printed circuits embedded between dielectric layers in a waveguide. The usefulness of the proposed method and its performance are verified by calculating and simulating of a given structure.

Differential Power Analysis (DPA) implies measuring the supply current of a cipher-circuit in an attempt to uncover part of a cipher key. Cryptographic security gets compromised if the current waveforms obtained correlate with those from a hypothetical power model of the circuit. As FPGAs are becoming integral parts of embedded systems and increasingly popular for cryptographic applications and rapid prototyping, it is imperative to consider security on FPGAs as a whole. During last years, there has been a large amount of work done dealing with the algorithmic and architectural aspects of cryptographic schemes implemented on FPGAs, however, there are only a few articles that assess their vulnerability to such attacks which, in practice, pose far a greater danger than algorithmic attacks. This paper first demonstrates the vulnerability of the Advanced Encryption Standard Algorithm (AES) implemented on a FPGA and then presents a novel approach for implementation of the AES algorithm which provides a significantly improved strength against differential power analysis with a minimal additional hardware overhead. The efficiency of the proposed technique was verified by practical results obtained from real implementation on a Xilinx Spartan-II FPGA

When the process is highly uncertain, even linear minimum phase systems must sacrifice desirable feedback control benefits to avoid an excessive ‘cost of feedback’, while preserving the robust stability. In this paper, the problem of supervisory based switching Quantitative Feedback Theory (QFT) control is proposed for the control of highly uncertain plants. According to this strategy, the uncertainty region is suitably divided into smaller regions. It is assumed that a QFT controller-prefilter exits for robust stability and performance of the individual uncertain sets. The proposed control architecture is made up by these local controllers, which commute among themselves in accordance with the decision of a high level decision maker called the supervisor. The supervisor makes the decision by comparing the candidate local model behavior with the one of the plant and selects the controller corresponding to the best fitted model. A hysteresis switching logic is used to slow down switching for stability reasons. Besides, each controller is designed to be stable in the whole uncertainty domain, and as accurate in command tracking as desired in its uncertainty subset to preserve the robust stability from any failure in the switching.

Time domain analysis of multilayer graphene nanoribbon (MLGNR) interconnects, based on ‎transmission line modeling (TLM) using a six-order linear parametric expression, has been ‎presented for the first time. We have studied the effects of interconnect geometry along with ‎its contact resistance on its step response and Nyquist stability. It is shown that by increasing ‎interconnects dimensions their propagation delays are increased and accordingly the system ‎becomes relatively more stable. In addition, we have compared time responses and Nyquist ‎stabilities of MLGNR and SWCNT bundle interconnects, with the same external dimensions. ‎The results show that under the same conditions, the propagation delays for MLGNR ‎interconnects are smaller than those of SWCNT bundle interconnects are. Hence, SWCNT ‎bundle interconnects are relatively more stable than their MLGNR rivals.‎

This paper presents a nonlinear analytical model for micromechanical silicon ring resonators with bulk-mode vibrations. A distributed element model has been developed to describe the dynamic behavior of the micromechanical ring resonator. This model shows the nonlinear effects in a silicon ring resonator focusing on the effect of large amplitudes around the resonance frequency, material and electrical nonlinearities. Through the combination of geometrical and material nonlinearities, closed-form expressions for third-order nonlinearity in mechanical stiffness of bulk-mode ring resonators are obtained. Using the perturbation method and the method of harmonic balance, the expressions for describing the effect of nonlinearities on the resonance frequency and stability are derived. The results, which show the effect of varying the AC drive voltage, initial gap, DC applied voltage and the quality factor on the frequency response and resonant frequencies, are discussed in detail. The nonlinear model introduces an appropriate method in the field of bulk-mode ring resonator design for achieving sufficient power handling and low motional resistance.

This paper presents an approach to calculate the equivalent stray capacitance (SC) of n-turn of the helical flux compression generator (HFCG) coil with multi layer conductor wire filaments (MLCWF) in the form of rectangular cross-section. This approach is based on vespiary regular hexagonal (VRH) model. In this method, wire filaments of the generator coil are separated into many very small similar elementary cells. By the expanded explosion in the liner and move explosion to the end of the liner, the coil turns number will be reduced. So, the equivalent SC of the HFCG will increase. The results show that by progress of explosion and decrease of the turns’ number in the generator coil; total capacitance of the generator increases until the explosion reaches to the second turn. When only one turn remains in the circuit, a decrease occurs in the total capacitance of the generator.

Torque ripple minimization of switched reluctance motor drives is a major subject based on these drives’ extensive use in the industry. In this paper, by using a well-known cascaded torque control structure and taking the machine physical structure characteristics into account, the proposed energy-based (passivity-based) adaptive sliding algorithm derived from the view point of energy dissipation, control stability and algorithm robustness. First, a nonlinear dynamic model is developed and decomposed into separate slow and fast passive subsystems which are interconnected by negative feedbacks. Then, an outer loop speed control is employed by adaptive sliding controller to determine the appropriate torque command. Finally, to reduce torque ripple in switched reluctance motor a high-performance passivity-based current controller is proposed. It can overcome the inherent nonlinear characteristics of the system and make the whole system robust to uncertainties and bounded disturbances. The performance of the proposed controller algorithm has been demonstrated in simulation, and experimental using a 4KW, four-phase, 8/6 pole SRM DSP-based drive system.

This paper presents a method to improve the accuracy of DC Optimal Power Flow problem, based on evaluating some nodal shares of transmission losses, and illustrates its efficiency through comparing with the conventional DCOPF solution, as well as the full AC one. This method provides three main advantages, confirming its efficiency: 1- It results in such generation levels, line flows, and nodal voltage angles that are more accurate than the conventional DCOPF solution. 2- Like the previous DCOPF problem, the new method is derived from a non-iterative DC power flow algorithm, and thus its solution requires no long run time. 3- Its formulation is simple and easy to understand. Moreover, it can simply be realized in the form of Lagrange representation, makes it possible to be considered as some constraints in the body of any bi-level optimization problem, with its internal level including the OPF problem satisfaction.

This paper presents a new design to reduce torque ripple in Switched Reluctance Motors (SRM). Although SRM possesses many advantages in terms of motor structure, it suffers from large torque ripple that causes problems such as vibration and acoustic noise. The paper describes new rotor and stator pole shapes with a non-uniform air gap profile to reduce torque ripple while retaining its average value. An optimization using fuzzy strategy is successfully performed after sensitivity analysis. The two dimensional (2-D) finite element method (FEM) results, have demonstrated validity of the proposed new design.