Sharif Digital Repository

Microrobots have the potential to access small spaces for manipulation or for acting as a sensor. Magnetic microrobots are the most common types of microrobots. Magnetic microrobots have gained particular traction for medical applications due to safety of tissues. For instance, disease diagnosis, minimally invasive surgery and cell manipulation are potential applications of magnetic microrobots. The performance of a single microrobot could be improved by using multiple robots. For example each microrobot could carry a small payload to a goal inside a microfluidic channel, or could assemble fast and in parallel. In order to employ multiple robots, it is necessary to control each microrobot... 

Increasing and diversified use of micro electromechanical components necessitates further development of methods for their secure gripping and transfer. In this research, a piezoelectrically driven microgripper including two gripping sets with four arms has been designed. The system can hold and handle microparts from 100 to 150 microns by applying corresponding voltages between 80 to 20 volts. The design is such that after positioning the work piece between the two microgripper arms the piezoelectric comb-drive actuators are activated. Then the two gripping arms are moved toward each other and ultimately grasp the work piece. In order to determine the behavior of the... 

The present study deals with the analysis of Atomic Microscope with crack by making use of Strain Gradient Elasticity theory. Empirical observations represent that in micro dimensions, materials show behaviors, which the classic continuum mechanics theories are not able to explain. Thus, taking advantage of non-classic theories, which are capable of explaining such phenomena or behaviors in analyzing materials in micro dimensions seems necessary and of much significance. In this direction, by applying an Euler-Bernoulli beam assumption and neglecting the shear effects, governing equations and boundary conditions of the problem were obtained via taking advantage of variations in Hamilton... 

In this paper, a one-dimensional and two-dimensional numerical approach is used to study the effect of various parameters such as micro combustor height, mass flow rate and external convection heat transfer coefficient on the temperature and species mass fraction profiles. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used. The transient gas phase energy and species conservation equations result in an Advection-Diffusion-Reaction system (A-D-R) that leads to two stiff systems of PDEs, which can not be solved by conventional Computational Fluid Dynamics (CFD) methods. In the present work, Strang splitting method, which is suitable for nonlinear stiff... 

Because of the importance of purification units at the refineries, in this research the process of sulfur removing compounds from light naphtha product with 1 ppm concentration by adsorption method in a fixed bed tower was simulated by COMSOL Multiphysics software. In this work, simulation was done using two macro and micro perspectives. In the Macro-scale mass transfer takes place between the spherical particles of catalyst and in the micro-scale mass transfer takes place within the spherical particles and these two scales were coupled together by reaction rate variable. In Macro-scale one-dimensional and two-dimensional geometry were considered for model. Naturally, the result of the... 

In the current work, the two- and three-dimensional electro-elastic fields of periodically as well as arbitrarily distributed interacting quantum wires (QWRs) and interacting quantum dots (QDs) of arbitrary shapes within a piezoelectric matrix are studied analytically. The lattice mismatch between the QWR/QD and the barrier is accounted through prescribing an initial misfit strain field within the QWR/QD. The distinction between the electro-mechanical properties of the QWR/QD and those of the barrier is treated by introducing a novel electro-mechanical equivalent inclusion method in Fourier space (FEMEIM). Moreover, the theory can readily treat cases where the QWRs/QDs are multi-phase or... 

In the present study, we analyzed the mechanical behavior of micro rotating disk based on the most general form of strain gradient elasticity. According to the fact that micro rotating disks have an important role in MEMS, it is necessary to present an exact analysis of their mechanical behavior. It is noticed experimentally that materials behave stronger in deformation as they get smaller. The classical continuum theory is not capable to predict such behavior; therefore, it is essential to use one of the non-classical continuum theories to analyze the material in micro scales, which can capture this phenomenon. In this work, the strain gradient theory is utilized to derive the governing... 

Today air pollution has become one of the major urban management concerns. Air pollution could have dangerous effects on human health in short time or long time in many situations. Numerical modelling is one of the most applicable among different ways for predicting pollutant concentration like field measurement, physical model in wind tunnel, and simulation. Modelling of pollutant dispersion is a way for estimating concentration and aggregation of the pollutant near the surface and with different distances from pollution source. In different dispersion models, one of simplest is the Gaussian model. In this approach it is supposed that emission plume obeys from Gaussian distribution and is...