Sharif Digital Repository

Endoscopy is a medical operation in which a camera is sent into the patient's body and the physician starts taking pictures at specified times. In the traditional endoscopic procedure, a camera is sent into the body by a guiding wire. This can cause severe pain to the patient. In the newer method, a camera is mounted on a small capsule and the patient swallows the capsule. Then the camera inside the capsule starts taking photos and sends them out. This procedure, in addition to being painless, allows the physician to access the innermost parts of the body or the digestive tract.In capsule endoscopy, unlike the older method, one has to find the position and orientation of the capsule at any... 

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... 

Vibration based energy harvesting is the process of trapping and collecting vibrational energy from ambient sources which seem unusable at first sight. The smart materials with the capability of coupling two different fields can be used in converting vibrational energy to electrical one. One of this smart material which has been taken into account recently is the Magnetic Shape Memory Alloy (MSMA) and it can couple the magnetic and mechanical fields. In MSMAs the total magnetization vector changes with the application of stress and make it possible to harvest energy from Faraday law’s of induction. An important phenomena that exist in MSMA is the dependency of magnetization-strain behavior... 

Prediction and calculation of shielding tensors of H, C, F and P nuclei of different molecules has been the subject of much research, because these nuclei have the greatest importance in NMR experiments. The optimum wave functions and calculation method were obtained using empirical models and factorial design. Based on preliminary experiences, the following four factors at two levels were selected: electron correlation, triple-ξ valence shell, diffuse function and polarization function. The wave functions for calculating gas phase 1H and 13C chemical shifts of various types of alcohols, amines and simple hydrocarbons were optimized using empirical model. The B3LYP/6-311+G wave function is... 

Quantum spin liquids are characterized by the lack of long range magnetic order at zero temperature due to strong quantum fluctuations in frustrated magnets, emergent fractionalized excitations coupled to gauge fields, pattern of long-range entanglements, and topological orders. Since the theoretical predictions dated back to the seventies, a huge amount of both theoretical and experimental efforts put forward to explore these emerging phenomena in real materials. Besides the organic compounds with spin liquid ground states, recent years have witnessed the dawn of new oxide materials such as α - RuCl3 and Na2IrO3 which may host spin liquid at low temperatures. The ground states of the latter... 

In this research the relaxation processes of spin nuclei was quantitatively described using computer programs. According to our data, both longitudinal and transverse relaxations consist of five exponentials of the forms of and . The parameters and were represented as a functions of . Analytical expressions were extracted for dynamic frequency shift's components in addition to representing them as a function of . In solving of transverse and longitudinal relaxation's equations, the transverse and longitudinal relaxation matrices were extracted which are useful in the investigation of exchange effect in these nuclei. The accuracy of our computer program was confirmed using it for... 

Brain states analysis during consciousness is emerging research in brain-computer interface(BCI). Emotion recognition can be applied to learn brain states and stages of neural activities. Therefore, emotion recognition is crucial to the analysis of brain functioning. Electrical signals such as electroencephalogram (EEG), electrocardiogram (ECG) and functional magnetic resonance imaging(fMRI) are frequently used in emotion recognition researches. Convenience in recording, non-invasive nature and high temporal resolution are the factors that have made EEG popular in brain researches. EEG can be used to identify brain region activity solely or the connectivity of various regions in time in the... 

The design and implementation of the hybrid control method for a three-pole active magnetic bearing (AMB) is proposed in this paper. The system is inherently nonlinear and conventional nonlinear controllers are a little complicated while the proposed hybrid controller has a piecewise linear form, i.e., linear in each sub-region. A state-feedback hybrid controller is designed in this study and the unmeasurable states are estimated by an observer. The gains of the hybrid controller are obtained by the LQR method in each sub-region. To evaluate the performance, the designed controller is implemented on an experimental setup. The experimental results show that the proposed method can efficiently... 

In recent years, energy harvesting from ambient sources in order to use for low-powered electronics has been considered by many researchers. Wind energy, solar energy, water energy, mechanical energy from vibrations, etc are common sources of ambient energy. In this thesis, optimization of energy harvesting from ambient vibration using magnetic shape memory alloy is presented. To this end, a clamped-clamped beam coupled with MSMA units is considered. A shock load is applied to a proof mass which is attached to the middle of the beam. As a result of beam vibration a longitudinal strain is produced in the MSMA. This strain changes magnetic flux inside the coil connected to MSMA and as a... 

The flexible magnetic robot is used for minimally invasive surgeries where there is a complex environment. Precise control of the position of the end of the robot and quick adaptation of the robot to uncertainties are among the most important challenges in this field, where the controller is responsible for compensating the error and controlling the position of the end of the robot. Now, is it possible to create a kind of memory in the system that when faced with the same or similar errors in the same situations or close to previous errors, the system uses its past and compensates the error? The importance of this work is that the response speed of the system is increased and the system can... 

Magnetic bearings have been used in industry to achieve an acceptable performance, high precision and vibration suppression of rotating machinery in recent decades.The absence of physical contact between the bearing and rotating components provides access to high rotational speeds which is a problem in conventional bearings.In addition, capabilities such as stiffness and damping adjustment can be used to reduce the harmonic vibrations caused by mass unbalance. The unbalance compensation is one of the main topicswhich has attracted the attention of many researchers in the field of rotordynamics. The aim of this thesis is to design and fabricatea three-pole active magnetic bearing test rig and... 

High speed and high accuracy are two of the major trends for many systems in the 21st century, such as machine tools and semiconductor equipment. For the purpose of high speed, it is well known that active magnetic bearing (AMB) is an inevitable substitute for conventional bearings. The noncontact nature of AMB brings up many advantages over the conventional bearing, including energy efficiency, low wearing, long life span, and absence of lubrication. Hence, AMBs are especially essential for high-speed rotating devices nowadays.
While the 3-pole AMB has been proposed for many years, it received little attention due to the magnetic coupling between poles that makes the 3-pole AMB system... 

This paper presents a scalable and ultrasensitive magnetic biosensing scheme based on on-chip LC resonance frequency-shifting. The sensor transducer gain is demonstrated as being location-dependent on the sensing surface and proportional to the local polarization magnetic field strength |B|2 generated by the sensing inductor. To improve the gain uniformity, a periodic coil is proposed as a substitution for the standard process coil. As an implementation example, the circuit is designed in a 65nm CMOS process. The spatially uniform sensor gain of the array is verified by COMSOL simulations. Overall, the presented sensor demonstrates an improvement in the uniformity of the inductor’s magnetic... 

In this thesis, heterogenous catalysts based on magnetic nanoparticles coated with organosilanes and poly(ionic liquids) were synthesized. These catalysts were synthesized by hydrolysis of tetraethyl organosilanes and other organosilicons such as 3-aminopropyl triethoxy silane and polymerization of some monomers in the presence of ionic cross-link agents. The synthesized matrixes were used to stabilize precious metals such as Pd and Au. The magnetic properties of the catalysts aid to easy separation from the reaction medium by an external magnetic field. High thermal stability low toxicity and high-level loading of metals are some beneficiaries of the magnetic catalysts. At the end,... 

Hyperthermia (also called thermal therapy or thermotherapy) is defined as a type of cancer treatment in which body tissue is exposed to high temperatures, to damage and kill cancer cells, or to make cancer cells more sensitive to the effects of radiation and certain anticancer drugs. The temperature increase required by hyperthermia can be achieved via different heat sources, such as electromagnetic radiation waves (radiofrequency or microwave, ultrasound waves and electrical current. These techniques have shown good results, however, the major problem with present conventional methods is reaching homogenous heat distribution and therapeutic temperatures in the deep region of the tumor to be... 

In this thesis, it reports the fabrication of novel magnetic nanocomposites combining the unique properties of magnetic nanoparticles and cross-linked basic polymers that their surface functionalized by suitable groups such as carboxylate groups, pentaethylenehexamine and so on to achieve the maximum adsorption capacity of dyes and heavy metal ions. The performance of the magnetic nanocomposites for removal of anionic and cationic dyes and heavy metal ions were evaluated in different conditions of pH, contact time and initial concentrations. Moreover, the adsorption mechanism was investigated by kinetic models and isotherm studies. The results showed that the abovementioned adsorbents can... 

This thesis presents the prototype design and fabrication of magnetically actuated miniature pumps which utilize self-sealing capability of ferrofluid-covered permanent magnets in both pumping and valving mechanisms. The contactless external actuation feature of the design enables integration of the pump with other PMMA-based microfluidic systems with low cost and disposability. The body of the 1st fabricated prototype pump consists of three nozzle/diffuser elements and two pumping chambers connected to the ends of a flat-wall pumping cylinder. A cylindrical permanent magnet placed inside the pumping cylinder acts as a piston which reciprocates by using an external magnetic actuator driven... 

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.... 

Characterization of local magnetic activity of the heart muscles is named magnetocardiography (MCG), which measures magnetic field generated by electrical activity around heart. RF SQUID sensors are appropriate choice for measuring magnetic activity of the heart muscles. Because squid detects weak signals as low as fTesla, while heart magnetic field is near 50 pt which is one millionth of earth magnetic field and thousands of time weaker than the environment noise. One of the problems of mcg system is its urgency to shielding of unwanted magnetic field. In this project design of holders and resonators for well coupled input coil with RF SQUID is improved. As a result, at the first stage... 

The continuous rise in electricity demand and the ever growing power generation in different power networks over the world have caused the short circuit level in the power systems to exceed the operational rating of the installed power devices (including cables, circuit breakers and buses). Replacing these devices with new higher rating devices is an expensive solution. From this point of view, utilizing fault current limiters is an economical solution. Superconducting fault current limiters form an efficient category of current limiters. This type is expected to be studied and used widely in future due to their advantages. In this thesis, the first chapter reviews the superconductivity...