Sharif Digital Repository

The ability and how to use a microwave life-detection system to search for the humans buried under earthquake rubble or laid behind various barriers has been investigated. Based on the behavior of a human under multiple layers of barriers and the detection capability of the microwave tools a system has been proposed. This system operating at 1150 MHz can remotely detect the movement of the heart of the trapped alive people. The operation principle is based on detection of the Doppler frequency shift of the electromagnetic wave reflected from the periodic moving part of a living human body such as the heart. In this paper, various parts of a microwave life-detection system such as patch... 

An efficient method for the analysis fo the shielding effectiveness in high frequency communication circuits based on the Transmission Line Matrix (TLM) method is presented. Since the formulation is in the time domain, wide band effects are easily and accurately modeled. Through comparisons, results obtained from that proposed numerical method with those obtained from measurement show that the TLM method gives more accurate results than other methods reported  

This paper presents analytical soltions for the nonlinear problem of electrostatically actuated torsional micromirrors considering the bending of the torsional beams. First the energy method is used for finding the equilibrium equations. Then the explicit function theorem is utilized for finding the equations governing the instability mode of the mirror. These equations are then solved using Homotopy Perturbation Method (HPM) for the especial case of α = 0 where α is a small nondimensional geometrical parameter defining the starting point of the underneath electrodes. Then straight forward perturbation method is applied for finding the pull-in angle and pull-in displacement of the... 

A technique that expands dynamic range (DR) of frequency down-converters in the C band frequency is presented. Primary characteristics of down-converter are evaluated to confirm that it can be used in microwave receivers. The C band down-converter is carried out by the combination of RF mixers, band pass interdigital filter, and X band combline filter which are designed entirely for this project. Attainment of the perfect receiver is the final purpose of this paper, and a method that causes 72 dB dynamic range, high tangential signal sensitivity and fine gain flatness is used for achieving the mentioned purpose. These efforts improve the dynamic range about 19 dB and gain flatness about 3.07... 

This paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and Casimir force. At the First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained. The dependency of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of casimir force can considerably reduce the stability limits of nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the casimir force applied to the... 

In the current paper, analytical solutions are presented for the nonlinear problem of electrostatically actuated torsional micromirrors considering the bending of the torsional beams. Energy method is used for finding the equilibrium equations. Then the explicit function theorem is utilized for finding the equations governing the instability mode of the mirror. The presented results show that neglecting the bending effect in electrostatic torsion micro actuators can cause to several hundred percent of overestimation of the stability limits of the device. In order to study the voltage-angle and voltage-displacement behavior of the micromirror, equilibrium equations are solved using HPM.... 

The staggered quantum walk is a type of discrete-time quantum-walk model without a coin which can be generated on a graph using particular partitions of the graph nodes. We design Hamiltonians for potential realization of the staggered dynamics on a two-dimensional lattice composed of superconducting microwave resonators connected with tunable couplings. The naive generalization of the one-dimensional staggered dynamics generates two uncoupled one-dimensional quantum walks; thus more complex partitions need to be employed. However, by analyzing the coherence of the dynamics, we show that the quantumness of the evolution corresponding to two independent one-dimensional quantum walks can be... 

Dirential frequency hopping (DFH) was introduced as a new technology for reliable high data rate transmission. Since the system utilizes lower transmitting power relative to the other spread spectrum techniques and also principle part of the technique, frequency transition function (FTF), is designed privately and uniformly, the scheme is said to be safe and secure. In spite of previous researches, this paper shows that an intelligent eavesdropper may threat the security of the system by finding FTF and sending jamming signal toward authorized receivers. As a result, regular DFH can not provide consumers with security in wireless networks and hence we propose that FTF should be designed with... 

Tunable metasurfaces can shift their resonant frequency through different approaches, one of which is applying mechanical deformations. Here, we show the effects of two key factors on the tunability of deformable metasurfaces; the resonator geometry and substrate stiffness. To show the effects, we compared the tunability of unit cells with three resonator geometries and three common substrates at microwave frequencies from 1 GHz to 10 GHz under a given mechanical deformation. We showed that the resonator geometry affects the deformation field, as a consequence, causes different resonant frequency shifts. Moreover, it affects the stress field in the metasurface which in turn limits the... 

The current paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and van der Waals force. First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained using the newtons first law of motion. The dependence of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of vdW torque can considerably reduce the stability limits of the nano/micromirror. It is also found that rotation angle of the mirror due to capillary force... 

In this paper, the static behavior of micromirrors under the effect of capillary forces is studied. First the equation governing the static behavior of micromirrors is obtained using both Newton method and minimum potential energy principle. Then energy method is employed to investigate the static instability of micromirrors equilibrium points. It is proved that when there exist two equilibrium points, the smaller one is stable and the larger one is unstable. Furthermore a design equation is suggested for the successful fabrication process of micromirrors in the stable operatives range. Then the statical behavior of micromirrors is investigated numerically and analytically using the Homotopy... 

In this paper, a novel method for high-repetition-rate high-power radio frequency (RF) pulse generation, which involves only passive solid-state devices and is capable of being used for generating high power microwaves using a low-to-high power converting scheme based on nonlinear self-compression is proposed. The method is also expected to be of low jitter. In the proposed circuit, two high voltage diodes with proper reverse recovery characteristics are used. The simulation results show that the proposed circuit generates RF pulses, with central frequencies up to gigahertz range. By applying a sub-kilowatt power supply, the maximum output power was well over 10 kW. This power can be... 

Point matching technique is applied to a pyramidal horn antenna to expand its aperture field in a wide angular range in terms of Gaussian beams using the Jacobi iterative method. The obtained far field pattern is compared with the results of Gabor's Gaussian beam expansion. Convergence, speed, the impact of initial condition and the selection of sample points is discussed. The implemented point matching scheme is almost as fast and accurate as the Gabor's expansion. It can even be faster and more accurate in some cases especially when the Gaussian beams are neither wide-waisted nor narrow-waisted  

In this paper, extended composite right/left-handed (E-CRLH) structures are studied to design multiband microwave devices. As an example, a three-way series power divider (SPD) is designed. The overall effects of the E-CRLH structures, as the feeding networks of the antenna arrays, on the antenna arrays main-beam variations are investigated. We also design and implement two antenna arrays with N=3 elements and the same interelement distances each fed by a distinct three-way SPD. The radiation patterns of the antennas are examined. Simulation and measurement results demonstrate that the desired main-beam squinting of the antenna array could be obtained by engineering the parameters of the... 

This paper applies the homotopy perturbation method to the simulation of the static response of nano-switches to electrostatic actuation and intermolecular surface forces. The model accounts for the electric force nonlinearity of the excitation and for the fringing field effect. Using a mode approximation in the Galerkin projection method, the nonlinear boundary value differential equation describing the statical behavior of nano-switch is reduced to a nonlinear algebraic equation which is solved using the homotopy perturbation method. The number of included terms in the perturbation expansion for achieving a reasonable response has been investigated. Three cases have been specifically... 

The ceramic fracture in output RF window is one of the most important failure factors in high power microwave sources. Fast protection systems are used to protect the source. The methods for determining the required protection response time are conservative and rough. In this paper, an investigation is presented about the twin growth in the ceramic of RF window in faulty condition. It is shown that the twin growth in ceramic can be a reliable figure of merit for the response time calculation of the microwave source protection system  

The contour integral (CI) method is developed to analyze H-plane waveguide circuits filled with inhomogeneous dielectric such as circuits including full height dielectric posts. In order to reduce the computational costs, the multimode CI method, which considers the effect of higher order TEnO modes, is introduced and we present a hybrid method based on multimode CI and mode matching (MM) techniques. The accuracy of method is validated by comparison of results with those reported in literatures  

In this paper, we consider the network coding in networks with broadcast channels (called hypernetworks) as the first step for applying network coding to wireless networks. We first prove a Max-Flow Min-Cut theorem for such networks. While we propose an algorithm to achieve this bound, we will introduce new definitions and provide sufficient tools to extend many of the theorems stated for flows in wireline networks to the case of hypernetworks. As an example, we will extend the Max-Flow Min-Cut condition for feasibility of the point-to-point connection in wireline networks to the case of hypernetworks. Then, we will extend the algebraic approach of Koetter and Medard in [3] to the... 

Co2+ and Cr3+-substituted SrBaCu2-xCoxCryFe28-yO46 X-type hexaferrite with x = y = 0, 0.1 to 0.5 (step = 0.1) were prepared through auto-combustion sol–gel method and sintered at 1250 °C for 5 h which was found from thermal analysis. The thermal investigation, phase detection, spectral, magnetic, and dielectric characteristics of the prepared composition were investigated by TGA, XRD, FTIR, VSM, and dielectric measurement. XRD patterns of the entire composition confirmed the development of a single phase of X-type structure. The enhancement in the lattice parameters and cell volume was observed by varying the Co–Cr concentration, attributed to the larger ionic radii substitution. FTIRspectra...