Sharif Digital Repository

First and second law analyses of the pulse tube refrigerator cycle are performed in the present thesis. In this respect, mass, momentum and energy balance equations are employed to derive the system of governing equations. Three models have been resulted depending on the employed theoretical model to analyze the pulse tube and thermal regenerator sections. In the first model, the tube section governing equations have been descritised and finite volume technique has been employed to solve the equations. In the regenerator a linear trend was assumed for the pressure and temperature to complete the solution procedure. To improve the regenerator model, harmonic approximation technique has been... 

Analysis and design of power systems are challenging due to ever increasing dimension of the system and also the nonlinearities involved in the system. The conventional approach is to use linear analysis tools and then investigate the nonlinear impacts by the means of computer simulations. This requires great deal of trial and error and it is not always a timely approach. In this project, we initiate a comprehensive nonlinear analysis for a single-machine infinite-bus system by studying a Hopf bifurcation in its dynamics. We use results of our nonlinear analysis to study how a capacitive compensation such as TCSC works. Subsequently, we design a nonlinear controller for a PSS to have... 

A new class of design has been introduced in the RF circuits and Frequency Synthesizers, which is based on the digital circuits. Implementation of the digital synthesizers suppresses the need to use loop filter and thus reduces the loop lock time. In this thesis different topologies of digitally controlled oscillators using inductor and capacitor tank and all digital architectures used in high frequency all digital synthesizers in 0.18um CMOS technology has been inspected and simulated. Novel techniques introduced to improve the ring oscillator-based design’s specifications which doesn’t need inductor. Using the introduced techniques, the phase noise has been lessened acceptably with respect... 

Integration of radio transceivers results in developing low power low cost wireless systems and allows delivery of multimedia contents to battery-powered mobile terminals. Portable reception of digital video for hand-held devices is one of the applications, for which, some telecommunications standards have been developed in the recent years. This research deals with the integrated implementation of the radio frequency parts of the digital video receiver, especially the frequency synthesizer. The key aspects of the digital video reception system are the required signal to noise ratio, which is relatively high, wide band input signals and strong interferers in the receiving band.
In... 

Periodic orbits are one of the basic objects of interest in Dynamical systems. And methods for detecting, counting and determining the periods of periodic orbits are of great interest. In spite of this interest, periodic orbits remain difficult to detect. The most celebrated existence result is the Poincare-Bendixson theorem. Unfortunately, this theorem is false in general for higher dimensional systems. The success of fixed point theory inspired the hope that similar topological techniques could be of use in proving the existence of periodic orbits. In this Thesis we have analyzed some topological and geometrical theories which could be of use in proving the existence of periodic orbits.... 

As the traditional MOSFET is reaching to its scaling limit, it is crucial to find an alternative. Single Electron Devices have shown promising features, such as nano-scale dimensions and extremely low power consumption that can lead to new generation of integrated circuits. In this thesis we have presented an analytical study of metallic single electron devices, particularly single electron transistors (SET). We have illustrated our study with some major logic applications of SET. The main goal of this thesis is to develop simulation software for single electron circuits, comparable with the well-known commercial software “SIMON”, which can provide steady-state and transient analysis of the... 

Recent growth in wireless communications leads to higher demand for smaller and cheaper wireless products. This increasing demand for high speed wireless products and therefore development of new modulation techniques, results in higher sensitivity to phase deviations. This means that the voltage controlled oscillator or VCO circuit must has lower phase noise. VCO is an important part in Phase Lock Loop or PLL that has been used in most of transceivers. This thesis focuses on design of a Programmable VCO for DVB-H Application in 0.18um TSMC process. A VCO is an oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the... 

Nowadays, general electronic devices such as computers, notebooks, cellular phones and etc. are supporting Bluetooth, RFID and Zigbee standards. By integrating all of RF sections of mentioned standards, total power consumption, occupied area and total cost and price will be decreased. RF devices communications with maximum bandwidth and data rate with minimum power consumption are the main purposes in designing RF and digital building blocks. Bluetooth and Zigbee standards are applied for networking the desired RF devices. RFID standard is providing automatic identifications, item tracking and tracing, item management and inventory. RFID standard makes the communication between Tags and... 

Vibration of a stationary structure excited by another structure moving on the surface of the stationary Structure is very common in engineering, such as vibration of bridges or railway track under travelling vehicles. In the simplest case, the moving structure maybe modeled as a constant load or a mass or an oscillator, in this case the moving mass is attached to the structure either by a spring or by a mass-spring assembly.The model of a moving mass brings some improvements to the model of the moving load where there is no inertia effect. However, the relative displacement between the moving structures and the beam cannot be considered in the moving mass model. A more appropriate model in... 

In this thesis, a modified method based on frequency discriminator technique is presented for measuring phase noise of microwave oscillators. In the proposed method, we use two oscillators with similar phase noise, but their free running frequencies are different in the range of 10MHz~50MHz. Mixing these two oscillators results in the IF frequency, for which the phase noise power at each offset has been doubled.The delay line is used in IF frequency and a phase shifter at microwave or millimeter wave range is used to provide quadrarure condition. Hence the cable loss at IF frequency is low and the sensitivity of system will be very good. Comparison of the measured data at X-band (the... 

Oscillators in microwave communication systems play very important role. Therefore, designing an oscillator with a good performance, influences the final performance of the system. One of the parameters that determine the performance of an oscillator is the phase noise. This parameter in systems that have a large number of adjacent frequency channels, is causing many problems. Therefore, designing an oscillator with low phase noise improves the entire system performance.
Microwave oscillator phase noise is influenced by various factors, which one of the most important is the resonator. In microwave applications cavities have small sizes, thus it is difficult to use of them. Thus, in... 

In this thesis, a laminated composite beam with single delamination under the action of moving force/oscillatory mass has been modeled and analyzed. The beam has been divided into four sub-beams and based on Bernoulli-Euler and also shear deformation theories and by applying the Hamilton’s principle, equations of motion along with boundary conditions and continuity and compatibility conditions are obtained. Primarily, based on the constrained mode model the delaminated layers have been analyzed then by implementing the Lagrange multipliers method, the nature of dynamic contact is incorporated. In the analysis of delaminated beam based on the constrained mode, by applying the mode summation... 

With the invention of the Chirped Pulse Amplification (CPA) technique in 1985, it became possible to amplify ultra-short laser pulses to high intensities with suitable pre-pulses contrast. By considering the importance of the short wavelengths radiation sources, the interaction of the intense laser with dense plasma is one of the most promising routs to reach this goal.
This thesis is devoted to theoretical studies of the interaction of intense laser pulses with solid-state targets. The Relativistically Oscillating Mirror (ROM) and the nanobunching regime models, which introduced in 2006 and 2010 respectively, are presented and discussed. The reflection of a laser pulse from an overdense... 

With the advancement of the technology, Design of low power devices such as biomedical systems, wireless sensor network, portable devices and … has received more attention. Digitally controlled oscillator (DCO) is one of the sub-blocks in systems such as all digital phase locked loop (ADPLL) which consumes the major power of the system. Therefore, Design of a low power DCO will decrease the power consumption of the system significantly.
In this thesis, a digital control oscillator which is ultra low power is design for system on chip applications. Coarse-Fine architecture is used with binary weighted cells in this design. For the Coarse tuning stage, a new delay cell is proposed which... 

In recent years, eLoran system has been introduced as backup to global navigation systems like GPS, because of their vulnerability. eLoran is a low frequency (100 kHz) system. Its long wavelength allows indoor positioning.
Main eLoran advantages rather than Loran-C are: better accuracy (near 10m), using 9th pulse positioning modulation (PPM) as loran data channel (LDC) and all-in-view receivers
In this thesis, eLoran pulses are simulated in GRI. Also, a new analoge-digital circuit for faster pulse detection is developed.
Also, it is proved that an oscillator with same frequency and phase as enterance signal, responses faster than a band pass filter and envelope detector. So, a... 

In this dissertation, a system consisting of two oscillating and amplifier lasers was designed and constructed. The aim was to use this combination to measure important parameters of CuBr vapor laser. Therefore, two separate Thyratrons switching by a two-pulse control circuit with an arbitrary time delay have been used. Due to the sensitivity of these lasers to tube pressure, two quartz tubes with specific designs was used. This enables us to get a proper vacuum as well as to prevent from impurities in the windows, in a short range of time. In this system, the output light from oscillator is led to the amplifier and after a proper delay time, amplifying was observed.
Based on... 

EEG Signal Processing has really important role in study of nerves system and nervous diseases. In most applications, signals occur in the frequency band ranging below 100 Hz are considered. In this study, the higher frequency components of the signal, especially in patients with epilepsy, reported which they are called high frequency oscillations (HFOs). Some sources considered that HFOs are up to 1000 Hz and some other considered up to 2500 Hz. In study of HFOs, the high frequencies between 100 and 200 Hz that are called ripple and seen in normal mode are separated from the faster frequencies from 200 to 500 Hz and these components can accurately help to detect epileptic foci generator (to... 

In this thesis, at first, we study the active inductors have been reported in the literature. Then by choosing one of them and investigating its advantages and disadvantages, we changed the structure in a way to solve its problems. On the way by using this active inductor and a negative capacitor, we designed an oscillator in 1.5 GHz frequency that has -106 dBc/Hz phase noise at 1MHz offset and its FOM value is 160 dBc. Also this oscillator is capable of frequency tunability of oscillation from 500 MHz to 2.2 GHz. In this spectrum the phase noise is changing between -100 dBc/Hz and -110 dBc/Hz. In the second part, in the aim of improvement of phase noise of oscillator structures based on... 

In the present investigation, graphene sheets are simulated as Nano resonators using Kirchhoff plate theory and nonlocal continuum theory. External force and interlayer forces are simulated as harmonic and Winkler-like elastic foundation, respectively. Equations are solved analytically and numerically and corresponding results are presented. Considering a two layer resonator, natural frequencies and oscillation amplitude are investigated by free vibration and forced vibration analysis. Also, the effects of parameters such as small scale, sheets dimensions and inciting frequency on the vibration of the resonator, are displayed  

Networks of neurons produce diverse patterns of oscillations, arising from the net-work’s global properties, the propensity of individual neurons to oscillate, or a mixture of the two. Here we describe noisy limit cycles and quasi-cycles, two related mech-anisms underlying emergent oscillations in neuronal networks whose individual com- ponents, stochastic spiking neurons, do not themselves oscillate. Both mechanisms are shown to produce gamma band oscillations atthepopulation level while individualneu-rons fire at a rate much lower than the population frequency. Spike trains in a network undergoing noisy limit cycles display a preferred period which is not found in the case...