Sharif Digital Repository

Spatial-temporal duality is considered vastly as a powerful technic to process optical signal fast. Band-width and sampling rate are bottlenecks in real time capturing and processing of optical signals by analog to digital converters. There have been tremendous efforts in the field of optical processing in order to enhance the speed of processing or quality of optical beams. Another successful method in high speed processing of optical signals is the improvement of time-bandwidth product by applying group delay engineering. In this research I did my best to overcome the inherent restriction of band-width of imaging systems exploiting concepts of time lens and time prism in such a way that... 

A resolver is a position sensor that converts the angular position information of a mechanical shaft to electrical signals. Due to their machine-like structure, resolvers have been preferred to other position sensors like optical encoders for working in harsh environments with wide temperature variations, high vibrations, moisture, and dust. Besides, the resolution of a resolver is infinite, and it can provide absolute position information. A multi-turn resolver is a type of resolver that has been developed to provide absolute position information with very high precision. Conventional multi-turn resolver consists of two individual resolvers in a common frame. One of them determines... 

Photoacoustic imaging is one of the nascent imaging methods that has received a lot of attention in the last two decades. There are two major imaging challenges with this method, including the finite size of the transducer element and the limited view angles of the photoacoustic tomography arrangement. To compensate for the effects of finite transducer size, we have proposed a multi-angle detection method for circular photoacoustic imaging systems based on the synthetic aperture techniques, in the proposed method, each transducer, in addition to rotating around the scan center, also has a rotation in the around its center. This rotation depends on the cut-off frequency, the diameter of the... 

The fast-growing development of engineering and medical sciences leads to the diagnosis and treatment of diseases with higher accuracy and in the early stages of the disease. Medical imaging systems are considered as a crucial and effective tool in this field that based on the principle of technology used, are able to image various tissues with high quality. In recent years, photoacoustic imaging has attracted the attention of many researchers and engineers, because it able to image different tissues with good resolution and penetration depth non-invasively and without the use of ionizing radiation. The photoacoustic system response is a low-pass filter that passes only low-frequency... 

Nowadays, various policies are adopted by transportation managers and planners. These policies aim to improve system performance, reduce user costs, control and reduce air pollution, reduce noise pollution, and ultimately reduce congestion. A set of these policies in the form of transportation demand management is presented in the literature. A common way to find the effect of a policy on user behavior is to use questionnaires. Other causal inference models have been proposed in disciplines such as statistics, political science, marketing science, epidemiology, and psychology. The purpose of these models is to find the causal effect of an intervention (treatment) on a system. These studies... 

Position sensors are an integral part of electric machine control systems. There are different ways to determine the position. The most common methods are using resolvers or optical encoders. Resolver is the recommended in harsh environments where there is wide temperature variation, vibration, and dust. Despite their good features, resolvers face challenges such as eccentricity, short circuit fault, single-phase disconnection, and non-ideal signal voltage. The Resolver chosen in this research is the variable reluctance resolver with variable air gap length. Although this type of resolvers is cheaper than wound rotor resolvers, but its position error is high under electrical and mechanical... 

Measuring the speed and position of the rotating part and using the speed and position information in the closed loop control of electric machines is very important. Various sensors are available for this purpose, including resistive sensors, capacitive sensors, encoders, synchros, resolvers, Halleffect sensors, and etc. Common encoders include optical and magnetic types. There are two main problems in using an encoder as a sensor: determining/maintaining accuracy during change of rotational direction and determining the absolute position. Both of the mentioned challenges have been investigated in the case of optical encoders and some solutions have been provided to overcome them. Although... 

Position sensors are an inevitable part of motion control mechanisms with inverter-driven electric machines. Encoders and resolvers are two common types of position sensors. Resolvers are preferred over encoders due to their superior performance in polluted and noisy environments with wide temperature variation or high vibration. Conventional resolvers are synchronous generators whose excitation winding is fed by an AC instead of a DC voltage. There are different types of resolvers for determining position in linear or rotational motions. However, increasing usage of two-degree of freedom (2-DOF) motors for simultaneous rotational and linear motion leads to request for helical motion... 

With the recent developments in power electronics and electrical drives, there is a need for precise position sensors today more than ever. Having high precision and high reliability in harsh environments, resolvers are the most preferred position sensors among other types of prevalent position detectors. In order to control linear machines, which are widely used in different industries, linear resolvers are employed. This project aims to propose a structure for tubular variable reluctance resolvers, formulate an analytical model for and optimize the proposed structure. In addition to having an acceptable precision, the proposed model should be less time-consuming compared with finite... 

Linear motors are mostly used in industrial applications and linear position sensors are one of the main components of their motion-control systems. The most common position sensors are optical encoders and resolvers. The optical encoders are not suitable for use in high temperature and high-vibration environments. In addition, their mechanical installation is difficult. In contrast, the resolvers are capable of generating absolute position signals with high precision, and low cost. Resolvers can be used in the polluted environments with the wide range of frequency, temperature and vibration. Among different linear sensors, linear resolvers are appropriate choice for harsh environments.... 

One of the main challenges of resolver as a position sensor is using at high speeds. Because in a situation where the speed of moving part is close to the frequency of the resolver excitation voltage, the speed-dependent part in the resolver output signals will be significant and cannot be ignored. In this project, the aim is to provide a method to solve the problem of using a variable reluctance linear resolver with a sinusoidal cross section in a wide speed range. This method is based on the hybrid use of AC and DC excitation in such a way that AC excitation is used at low speeds and DC excitation at high speeds. Considering that determining the threshold speed requires a large number of... 

In this thesis the goal is to use data Mining techniques for finding features of different Partial discharges happen in power transformer insulation defect models in order to monitor the insulation condition of in-service power transformers continuously and on-line and to identify any type of insulation defect in power transformers at the early stage of formation.For this purpose, power transformer Insulation defects are modeled physically and partial discharge current pulses are recorded as Partial discharge data.Tow format of data are investigated, in first one, recorded data in one power frequency cycle are explored and in second one, individual PD pulses are considered for study.In... 

In this investigation, hydroxyapatite-carbon nanotube nano composite coatings were applied on the 316L stainless steel implants. After polishing with 1200 sand paper, stainless steel implants were coated via dip coating method. The specimens were heat treated at 350˚C after being coated with HAP and HAP-CNTs composite. In vitro test was done in simulated body fluid (SBF) in 1 to 4 weeks periods. XRD evaluation of powder obtained from sol-gel process, showed the presence of HAP and CNTs in the powders. Comparison of XRD results of HAP and HAP-CNTs powders showed the better crystalinity of composite hydroxyapatite. After in vitro tests, specimens were studied with atomic force microscope (AFM)... 

The aim of this project is investigation on synthesis and characterization of the TiO2-CNT nanocomposite films on aluminum substrate by sol-gel dip coating method. The pure TiO2 and TiO2-CNT nanocomposite layers were coated on aluminum substrate and heat treated in 400 C. In this work Ti-tetra isopropxide and different amounts of CNTs (5,10,15 %wt), were used for obtain the composites. The coatings were characterized by X-Ray diffraction (XRD) and the crystallite size of TiO2 was calculated by Scherrer formula. The corrosion properties of coating were examined by polarization test, and corrosion resistance of pure TiO2 was compared with TiO2-CNT coatings, and It showed that the composite... 

Aerodynamic shape optimization has been always of great importance in aerospace design. Recent advancements in computational algorithms and hardware, has made it feasible to have advanced optimization as a standard part of desing procedure. Here we have promoted aerodynamic optimization of air propeller.
Propeller optimization process requires a propeller performance analysis program and an efficient optimization algorithm. A vortex lattice model is used for the propeller performance analysis and a computer program is developed based on it. Experiment and litritures are used for validation of VLM code. In order to optimize the propeller peformance, propeller efficiency is applied as cost... 

In this thesis, an X band vector modulator chip in CMOS .18 um technology is designed, implemented and measured. The receiver with two RF signal path includes differential amplifier, hybrid, attenuaters, variable gain amplifiers (VGA) and power combiner blocks respectively. Capability of gain and phase control is provided by 14 digital bit. 6 bits are used to control gain of each RF path, so that changing the phase and gain of the output signal in a trigonometric quarter shall be possible. The trigonometric quarter is selected by two single pole double throw switch. Cascode structure is utilized in amplifiers stages for its stability and isolation feature. Furthermore, in order to to enhance... 

A novel low noise quadrature voltage-controlled oscillator (QVCO) with differential N-path filter is proposed in 0.18-μm CMOS technology. The said QVCO benefits from a cross-coupled structure and a current-reuse technology to produce the quadrature signal and to save power consumption and area, respectively. The new architecture reduces the phase noise by 8dBc/Hz at a 1MHz offset frequency for 2.4GHz oscillation frequency. QVCO consumes 9.8mW from 1.8V power supply when operating at 2.4GHz. QVCO has a frequency tuning range from 2.4GHz to 3GHz and achieves a FOM of 191dB at 1MHz offset. Switches of N-path filter are controlled by outputs of QVCO, so the center frequency of N-path filter is...