Sharif Digital Repository

This research is concerned with the study of the static, dynamic, vibration and instability of an electrostatically actuated microbeam gyroscope considering geometric nonlinearities and electrostatic fringing fields. A vibrating microbeam gyroscope consists of a beam with a rigid (proof) mass attached to it and undergoes coupled flexural-flexural vibrations coupled with base rotation. The primary oscillation is generated in drive direction of the microbeam gyroscope by a pair of DC and AC voltages on the mass. The secondary oscillation occurring in the sense direction is induced by the Coriolis coupling caused by the input angular rate of the beam along its axis. In this case gyroscope acts... 

Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices. Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this project instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user... 

Natural teeth are connected to alveolar bone by periodontal ligaments ( PDL). PDL in addition to supporting tooth have the damping effect on transferring load from tooth to the surrounding bone. The most common replacement for a complete tooth loss is the use of Osseointegrated dental implants. The healthy bone remodeling and full bonding between bone and titanium surface of the implant is subjected to a successful osseointegration. The lack of PDLs in the structure of implant-bone system could lead to the failure of implant’s components due to overloading or to the impact loads. The aim of this study is to use viscoelastic material in the structure of dental implants to compensate for the... 

New developments have led to the creation of functionally graded materials which their unique property is continous changing in material properties. The increasing use of these materials has caused a lot of research on various issues related to them. One of the applications is applying these materials in spherical structures and open and closed rings. In mechanical equipment spherical structures and rings are used in various ways. The spherical structures of small parts, such as bearings to large structures such as spherical tanks are used. Due to the rapid growth of technology in the construction of structures of functionally graded materials, analysis of these structures in different... 

In clinical applications of high intensity focused ultrasound, high amplitude acoustic waves are used to heat and ablate tumors and kidney stones. The high amplitude of ultrasonic waves leads to nonlinear effects within the acoustic filed. Heating stems from the acoustic power absorbed by tissues. The more the acoustic power is absorbed, the more the tissue temperature increases. On the other hand, more absorption means less penetration. Since the wave frequency is one of the important factors in power absorption, a compromise should be reached between the transferred energy and desired penetration depth. In this thesis, first, a problem with common HIFU-therapy conditions is simulated;... 

Cancer is one of the deadliest diseases of the modern era and accounts for 13% of all deaths in humans. Most cancers and lesions in the human body are related to soft tissue. Many soft-tissue cancers and lesions occur in sensitive areas of the body, such as the brain, pituitary, and intestine. The pituitary gland is located in the human head and near the optic nerves. Surgery in a typical way can result in risks such as heat loss of the optic nerve or injuries to healthy tissues due to the sharpness of the surgery tool. One of the alternatives to conventional surgery is water jet surgery. This method minimizes the risks of human error. In the present study, a water jet machine was designed... 

Cancer is one of the most critical diseases in the last century. Numerous efforts have been conducted to treat cancer. According to the report of World Health Organization, one death of every six deaths is due to this disease. More than 100 cancer types have been identified. Among these types, CNS tumor is one of the most critical cancer types with high mortality (65.9%). Various methods have been applied to treat this disease, but still, treatment efficiency is low. In this thesis, the effect of ultrasound waves on drug delivery into CNS tumors was evaluated using both experimental and simulation devices. A syringe pump was used to inject the drug solution into tissue-mimicking gels (CED).... 

The heart is a powerful muscle whose primary function is to pump blood into the body. many cardiac patients reach a stage that can no longer be kept function of their heart to a satisfactory level by using medication thus doctors undergo surgery. The common problem occurs to most patients undergoing cardiac surgery is that after the surgery, the patient's heart during a short period of time is unable to supply blood with the flow rate and pressure required for all organs, especially the end organs of the body. In this conditions, ventricular assist device help the patients. These devices are used parallel with patient’s heart and supply the large portion of blood that patient’s body needs.... 

Many heart attacks and strokes are caused by improper clot formation in the vascular system. Mathematical understanding of the clot formation process and the influence of various factors in the clot formation process is very important. In this study, the aim is to simulate and understand the clotting process mathematically by considering natural, external and general mechanisms in the clotting process. In this process, when damage occurs in the endothelial region of the vessel, tissue factor is released and 38 different substances react with each other inside the plasma, eventually forming fibrin. To simulate the movement of different chemical components and proteins in plasma, the... 

The introduction of Minimally Invasive Surgery (MIS) has deeply influenced modern surgery. Despite all the advantages for the patient, this method produces some limitations for the surgeon. Limitations such as reducing degrees of freedom resulting in the loss of dexterity, depriving surgeons of the depth perception and sense of touch lead to human errors due to fatigue and intense mental activity. Overcoming these limitations is the reason for robots entering the operating rooms. In this research a robot-assisted surgery system including two 5-DOF robots is utilized. The goal of this research is to model and simulate this system and also to design a bilateral controller to provide haptic... 

Nowadays, Microelectromechanical accelerometers are of the main parts of inertial navigation systems, and so it is essential to characterize and understand the parameters affecting their performance in order to design them in a way that enables them to survive different practical applications. Mechanical shock is one of the factors existing in almost every industrial environment and cause damages or even permanent failures in MEMS devices. Identifying these damages and protecting the microstructure against them seems inevitable for the designer and engineer of this field.
In general, approaches of protecting microstructures against mechanical shock are categorized into two major... 

In this research, based on the strain gradient theory, mechanical behavior of functionally graded microbeams is analyzed and the results are used to investigate the static and dynamic responses of electrostatically actuated microswitches and microresonators.
The nonlinear governing equations of motion of functionally graded microbeams are derived using Hamilton’s principle. Afterward, the nonlinear model is implemented to analyze the mechanical response of electrostatically actuated microswitches and microresonators. Pull-in instability and nonlinear vibration of these components are investigated considering the effects of squeeze film damping, mid-plane stretching and initial curvature... 

With the expansion of global trade and economy and, in parallel, with the development of maritime transport, noise pollution caused by the sounds emitted by ships, vessels, submarines and offshore turbines threatens the environment of marine life. In addition, with the development of maritime weaponry, the need to cover the submarines with materials that reduce the reflection of sonar waves and absorbs them to provide acoustic stealth is felt more. Considering the focus of the most of the researches on the second topic and its practical importance, the present research is also in the same direction. The main goal of this project is to study the acoustic behavior of a polymer-based porous... 

The purpose of this work, is to design a cantilever arm made of functionally graded materials so that the arm has maximum natural frequency and minimum mass. In this work the arm is modeled by Euler-Bernoulli beam theory and properties are assumed to be varying through the thickness. The beam is considered to be made of Aluminum and Alumina as metal and ceramic respectively and Genetic Algorithm method is used for optimization step. Finally using FGMs in atomic force microscopes is proposed as a new application of these materials  

Grasping and manipulation of biological cells have an extensive applications in genetics ,cell proliferation ,cell injection and etc. In robotic manipulation ,it is often assumed that the objects being handled are rigid and only small deformations occurred during manipulation. this does not apply for the case of biological cells. biological cells are highly deformable structures, and their material properties are not well quantified. Therefore strategies for characterizing and manipulating of such deformable objects needs to develop. Different experimental techniques have recently been used and devised to study biological cells. On the one hand, although this experimental techniques have... 

In this research a microrobot constructed from three series connected microcantilever has been introduced and its behavior has been evaluated. Length of each microcantilever is about several hundred microns. Due to actuation of microrobot, piezoelectric has been employed. Considering one DOF of each microcantilever, this microrobot has three DOF. Manipulation and microscopy in nano and micron scale can be mentioned as main duties for this microrobot. In devices which are used for these purposes commonly parallel mechanisms are employed. Also in some devices such as AFM, samples are needed to be placed on platform. However in this study a serial mechanism has been employed which make this... 

In recent year carbon nanostructures (CNS) has been the pinnacle of academic and industrial research. After development and refinement of better methods of controlled fabrication of high-quality CNS, these structures started substituting nanotubes in their renowned applications including nanochannels and nanocarriers. Due to the tunable core size of CNS using electric fields, they can be used as controlled ion channels and nanocarriers with controlled drug release as well as more dynamics oriented applications including nano-oscillators, nano-actuators and artificial muscle tissue. However lack of vibrational studies on CNS has hindered researchers in this path. In this thesis vibrational... 

Carbon nanoscroll (CNS) is a graphene sheet rolled into a spiral structure. The Equilibrium structure of a CNS depends on the elastic bending energy and van der Waals interactions between layers. In recent decade, research on CNSs received high attention after discovering new techniques to produce high purity CNSs. Modal analysis of the CNS is essential in various applications like sensors and actuators. Therefore, in this research, a shell model for free vibration analysis of the CNS is proposed. After considering CNS as an equivalent shell, the assumed mode technique is used to extract natural frequencies and mode shapes of CNSs in different boundary conditions. The effect of geometric... 

Recently, micro-electromechanical systems have absorbed much attention due to their many applications in various industries, such as actuators, sensors, microswitches, and so on. These systems usually consist of a cantilever beam or a fixed-fixed beam in micro scale which can change shape under electrical force. In sensors and electrical actuators, Microbeams are under so much vibration that they undergo distortion and fracture in a short period of time. One way to prevent such phenomena is to use materials that have high flexibility during use and have a longer life span. In order to achieve this, the selection of nanocomposite microbeams which incorporate light materials as the matrix... 

Since its successful synthesis as single layer during the past decades, Graphene and its derivatives have been extensively employed by many researchers in various science and engineering fields. The studies to characterize and define graphene behaviour are still in demand to answer the questions around these structures. The unique feathures of graphene such as high strength, good conductivity, large available surface, intoxicity and biocompatibility, has made it a suitable candidate to used in novel structures and materials. In this work, hybrid structures made from graphene and carbon nanotubes are investigated which can be utilized as scaffolds in tissue engineering.After an introduction...