Sharif Digital Repository

Gas Metal Arc Welding (GMAW) process is one of the most applicable component in the industry due to its high speed and capability of employing for wide ranges of materials. The quality of products in a welding process is relevant to the quality of welding which is determined by characteristics like shape and size of droplet during detachment. In order to improve the quality of welding, a precise model of the process is required. There are many various model presented for GMAW process based on its dynamic equations. Almost all of these models assume the process as a continuous state system. However the process includes sudden variants in droplet detachment that is known as hybrid behavior.... 

The parametric study of a new introduced metallic yielding damper called telescopic damper is addressed. The telescopic damper comprises of three concentric steel pipes connected together by lead shear keys. The inner and outer steel pipes are subjected to axial loading which results in the shear yielding of the embedded lead cylinders. The inner steel pipe has a lock which limits its movement to some certain extent and beyond this limit the outer tube activates. Employing ABAQUS software, the behavior of damper under cyclic loading is studied numerically. The finite element model is verified by available results in the literature. The effects of inner and outer steel pipes thickness,... 

This research examines the issues of design and fabrication of Phase Shifter circuits on Silicon substrates. The Phase Shifter circuits are designed to have wide operation band width. They also should have very low sensitivity to process and temperature variation. A six bit phase shifter is designed at this research. We use a new topology for implementing the small phase shift steps and some circuits have been designed which their phase shifts can be adjusted after fabrication. All circuits are implemented with the 0.18µm CMOS technology. The research also explains all the necessary steps for measurement of fabricated circuits. The result of measurements shows good agreement with the... 

Diabetes is one of the most catastrophic diseases in the world. There will be an end to patients’ problems if scientists can invent the artificial pancreas, but there is no implantable sensing core available. All of the sensors used for measuring blood glucose level were based on an electrochemical sensor which will generate a glucose level dependent electric current. The chemical structure of that sensor will deny its usability for in vivo applications. By exploring several biological and electrical literatures we introduced a fully electrical method for sensing the blood glucose level by impedance measurement. In this thesis we introduced a new method for sensing the blood glucose... 

Impedance spectroscopy is known as one of the important integrated sensing methods in micro scale Biosensors and electrochemical sensors. Recently, Impedance spectroscopy has been noticed in many micro scale applications. These micro scale applications is being developed specially in bioelectronics and biomedical. The goal of this thesis is designing an on-chip impedance spectroscope system for high frequency with 10 bits resolution via fully electrical blood glucose concentration measurement. This system extracts the blood glucose concentration data through measuring the permittivity coefficient of blood at 1 GHz frequency. In this thesis, new method for high frequency high resolution... 

In this project, issues related to designing and fabricating active phase shifter blocks on the silicon substrate have been examined. Phase shifter circuits are designed in a way that have the most bandwidth and the less sensitivity to process characteristics changes and environmental conditions. The purpose of this research, is designing an active 6 bits phase shifter. The active phase shifter synthesizes the required phase using a phase interpolation process by adding quadrature phased input signals. It uses a new quadrature all-pass filter for quadrature signaling with a wide bandwidth. Also substitute structure has been suggested to this filter which is the main block in determining... 

In line with developments in the technology of integrated circuits, transistors are implemented in silicon. Although the price is reduced; design is more complicated, which causes the efficiency and power consumption to face some difficulties in such design. The reason why modern GDI-based circuit is the focus of attention is that in designing a digital circuit, less power is required while more efficiency is obtained. Lowering the complexity of the logic circuit can bring about reduction of power consumption and propagation delay and decrease the circuit space. GDI-based integrated circuits resemble MOSFET transistors but have fewer transistors and higher performance capability. This study... 

Leachate migration from solid waste landfills into the subsurface environment is one of the significant problems of landfills. This can cause lots of problems for local soil and water to sources according to the contaminants appear in the leachate. Usually, landfill sites include at least one compact clay liner to prevent contamination of groundwater by produced leachate. Over the last decades investigators have been attracted to the structure and removal capacity of this liner. In this study, the effect of the addition of Zeolite to Kaolinite soil for the removal of heavy metal (manganese and zinc) from landfill leachate and the effect of decreasing the thickness of the soil layer has been... 

Adobe structures are considered as masonry structures which are out of scope of 2800 Iranian code. Due to this code, since these structures are made of weak materials, they do not have a considerable resistance to earthquakes. Since these structures can be found all around Iran; therefore, seismic study of walls as an important component of these structures, is, indeed, necessary. During this study, cyclic tests on three types of adobe walls, without opening, with window-opening, and with door-and-window-opening with a scale of 2:3 were done to study their in-plane behavior and also their failure modes. Based on our observations, in these walls, because of small ratio of height to length,... 

Metal and inter-metallic matrix composites offer high performance materials suitable for many low weight applications which are of growing interest in high tech industries. However, to submit their entire potential applications, their complex mechanical behavior has to be understood. Nevertheless, one of the major setbacks of designing with these materials has been the delamination phenomenon. So far, this phenomenon has been considered from macro-mechanical point of view regarding laminates to be semi-isotropic or orthotropic; which indicates the importance of micro-mechanical research to be done. Furthermore, the fact that macroscopic response and failure mechanisms of these composites are... 

Phased array systems which are used for sending and receiving electromagnetic signals in mandatory directions are widely used in today’s wireless communication, satellite communication, and radar systems. Phased array systems are composed of units called transmitter/ receiver (TR) modules. These units are connected to antennas in one end and to the combiner/divider at the other end and are playing a major role in determining the quality of phased arrays. Transmitter/Receiver units include a phase shifting circuit for controlling the phase and an attenuator circuit for amplitude control of the signal being sent or received, solid state switches and a number of amplifiers. The aim of this... 

Today, phased array antennas have important role in wireless communication systems. Utilizing optimum channel capacity, having better signal to noise ratio and, high data rate are the most important features of these systems. These systems are composed of several thousands of separated transceivers which provide possibility of directional electromagnetic radiation by changing the phase and the amplitude of the signal in each transceiver independently. So, the main components of such a system are amplifiers, phase shifters and, amplitude controllers. Also a high resolution phased array military radar system is another vital applications of these systems at frequency band of 9-10 GHz. The... 

Dynamic response of structures, against ground motion, is one of the most important issues in earthquake engineering. A variety of approaches and apparatus have been developed for this purpose. One of these equipments is metallic dampers. Such apparatuses provide damping, accompanied with reasonably strong lateral stiffness; hence, they are named as “Added Damping And Stiffness” (ADAS). The present study aims to evaluate the performance of a common metal damper consisted of triangular metal plates known as “Triangular Added Damping And Stiffness” (TADAS). In this investigation, the performance of TADAS, in an eight story irregular in plan steel structure, is extensively considered. A 3-D... 

The microstructure and wear performance of WC/Cu-Zn-Ni composite surface coating has been investigated using a combination of microscopy, hardness, and wear testing. The oxidation behavior of tungsten carbide hard metal in the temperature range between 600 and 900 ◦C was also researched. The oxidation mass gain of WC correlated almost directly with temperature as well as time. The particle of hard metal is surrounded by the α Cu+β Zn phase in the surface coating. The size of hard metal is almost unchanged from its original one. There exists an inter-diffusion zone at the interface of the hard metals and Cu-based matrix. The wear volume of the WC/Cu-Zn-Ni composite surface coatings increased... 

Nanocrystalline metals and alloys have some appealing characteristics with significance potential compared to their microcrystalline counterparts for engineering applications. These include ultra-high yield and fracture strengths, decreased elongation and toughness, superior wear resistance, and the promise of enhanced superplastic formability at lower temperatures and faster strain rates. This leads us to study the effects of different nanocrystalline parameters on crack propagation process in these materials. In the present study, the behavior of a crack in a columnar nanocrystalline structure is examined. One of the methods of modelling nanocrystals primary structures is the Voronoi... 

In this thesis, a Ku-band (16.3-17.3) Variable Gain Amplifier (VGA) for realizing a phase array T/R module is designed, implemented and measured in CMOS 0.18μm technology. In order to achieve a maximum gain of 15dB and NF of 4.3dB and with the idea of improving the 1-dB compression point, two gain-stages and a novel inter-stage is proposed according to pre-distortion method. Applying this linearizing technique, makes it possible to get output P-1dB higher than 18dBm. Current steering technique is used for gain control mechanism. Gain tunabality range of 31.5dB is needed and this forces 6-bit operation with 0.5dB gain-step for the VGA. Because of loading effect of higher bits on the lower... 

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... 

Phase shifters are commonly used in the implementation of phased-array antenna systems.The function of these systems is highly dependent on the performance of phase shifters. In addition, phase shifter circuits are used in some applications such as antenna test and regulation, power amplifier linearization, and QAM modulator implementation, to name but a handful. In this project, design of phase shifter blocks, as well as limitations of fabrication on silicon substrate, is studied and these blocks are designed for maximum bandwidth and minimum sensitivity based on fabrication characteristics and environmental conditions. Design of a 6-bit phase shifter based on vector-sum method is the... 

One of the passive control systems that are used widely in today’s buildings are metallic yielding dampers. Metallic yielding dampers by absorbing earthquake input energy, prevent inelastic defromations form in beams and columns. In this research, the behavior of an innovated metallic yielding damper, named pistonic damper is investigated. This damper consists of a number of circular parallel plates with constant or variable thickness that dissipate seismic input energy by flexure yielding in small displacements. at large displacements stress field in plates is changed and this caused the stiffness and strength of damper are increased and show shell behavior. this kind of behavior... 

In this thesis, a new wide band variable gain distributed amplifier (VGDA) is presented. A novel approach to implement uniform gain control in the wide band frequency range of 8 – 18 GHz is demonstrated. A different technique has been employed to provide necessary DC bias current, avoiding large DC-Feed inductors. A five-section wideband VGDA has been designed and fabricated in 0.18 μm CMOS technology. The VGDA have a flat gain of 11 dB, noise figure better than 5 dB, P1dB of 14 dBm at the output, input and output matching better than -12 dB and -14 dB, respectively, for maximum gain state over the 10 GHz UWB band. The gain control range is between 3 – 11 dB with gain steps of 0.5 dB and rms...