Sharif Digital Repository

In recent years due to the advances in semiconductor technology and the ability to implement small-scale manufacturing, communication at 60 GHz band receive more attention than ever has been. The use of this frequency band is not only about 7-9 GHz unlicensed broadband access provided, but getting smaller devices make it possible to use multiple antennas at the transmitter and receiver, and thus taking advantage of multiple input – multiple output systems. Antennas used in these systems should have features such as small size , low weight, high gain and bandwidth and also they should keep their high efficiency and gainat high frequency range (about a few GHz ). To achieve these features... 

Due to small size, flexibility, and low cost of manufacturing, micorobots are potentially suitable for implementation in a broad range of applications. Control and inspection, medical utilities, manufacturing and micromanipulation of small-sized devices with nano-metric precisions, and precise measurements are some of the most important applications of microrobots. Mobile microrobots are one of the significant divisions of microrobots that are capable of movement with small steps and possess a motion range of at least several times the robot’s body length. In this project, Modulated Friction Inertial Drive (MFID) is utilized as a mechanism for creating a mobile microrobot. The micorobot is... 

Computational complexity of graph problems is an important branch in the-oretical computer science. We introduce to some of ideas for computing the complexity of graph problems with some kind and beautiful examples. Next, we show hardness and inapproximability of some problems. Representation number of graphs has been introduce by Pavel Erdos by Number theory. We prove n1−ϵ inapproximability of that. Lucky number η has been studied by Grytczuk et.al . We show for planar and 3-colorable graphs, it is NP-Complete whether η = 2. Note that since a conjecture, for those graphs, 2 ≤ η ≤ 3. Also for each k ≥ 2, we show NP-completeness of η ≤ k for the graphs. Proper orientation number −→ is a... 

Nematic liquid crystal shells (droplets) containing cores have attracted considerable attention in recent years. Defect structures that form in such systems do not emerge in the bulk.These shells which could be created using double emulsion techniques in the laboratory have provided applications in microscale optical structures.In the past just boundary conditions and bulk parameters were noticed but recently the geometry of the core is considered likewise.In this work oblate ellipsoid cores are examined numerically using finite-element method. The boundary conditions in studied systems are perpendicular in outer surface of droplet and planar in the vicinity of the core. First by minimizing... 

The recent project can be considered as a subset of Telerehabilitation, in the field of Telerehabilitation can be defined as the need for long-term data recording in order to determine each individual's movement pattern and compare it to the individual's best model or best practice. With this perspective, it can be said that the recent project, in more detail, remotely targets the use of foot plantar pressure to determine locomotor parameters. With this description, the FSR or force sensitive resistor sensor was selected for a number of reasons, including low cost, low weight and low thickness, and the data acquisition circuit was used to convert the sensors' analog signal to digital output,... 

Nowadays, regarding the wide achievements in micro scale technology, it is possible to manufacture a micro robot. Micro swimmer have extensive applications in different fields especially in medical sciences. One of the most important problems of the micro robot is their propulsion system. The locomotion of microorganisms in fluids is ubiquitous and plays an important role in numerous biological processes. The physics of swimming governing life under the microscope is very different from the one we experience in the macroscopic world. This project is aimed at designing a propulsion system for a micro swimmer based on the swimming mechanism of the eukaryotic Spermatozoa. Simplicity to build is... 

Nowadays superconducting devices and especially high temperature superconductors (HTSs) have found very wide applications in microwave engineering. This technology is raised in the form of planar microwave structures and in the different shapes of superconducting microstrip transmission lines, strip lines and coplanar waveguide (CPW) lines and different kind of applications like resonators, couplers, filters, antennas, etc. Important advantage of these structures is very low loss, small size and high quality factor. However nonlinear behavior of superconducting microwave devices, due to the dependence of the surface impedance on the applied field, limits the power handling capability of... 

Nowadays high efficiency and power density are desired for designing a power electronic converter. Technology advances in power semiconductor devices, makes it possible to design converters for operation in higher frequencies to reduce size of the converters. As the frequency is increased, switching losses and temperature is also increased, so designing a converter for high frequency operation needs some tradeoffs. LLC resonant converter as a promising solution for battery chargers has ability to adjust its output voltage during Constant Current and Constant Voltage modes. However, its operation mode would change based on switching frequency change. Therefore, for efficiency-oriented...