Sharif Digital Repository

Blindness is one of the destructive results of retinal diseases. Artificial retina is a device which can help blind people with AMD and RP diseases to restore their vision. Prevalent approaches to artificial retina use an external power supply and processor which the data and energy is transmitted to eye through an inductive link. Taking advantages of solar power, in this project we proposed a design which the required stimulation data and energy is produced internally so the patients don’t have to carry the processor and external power supply that is of major concern for them. This is the most important advantage of this device which doesn’t need any maintenance or battery either. In this... 

Trahertz gap science and technology is becoming more and more attractive due to the wide range of applications in medical science, communications and security. In addition, this band connect the optical and microwave devices. In this thesis, special optical structures composed of superconducting nanostructure based on the elemental type-II and layered high-Tc superconductors are proposed. The photonic band structure and the optical S-matrix are calculated for these proposed structures for different geometrical values. Such structures produce terahertz (THz) photonic band gap, which is controlled by the temperature and geometrical parameters. In addition, the proposed structures show... 

Fabrication of bulk superconductors with high critical current density widely has been studied because they have many applications, for example, Fault Current Limiter (SFCL), Superconducting Magnetic Energy Storage (SMES), and magnetic levitation. Providing pinning center by addings impurity into superconductor is usual and simple solution for increasing the superconductor critical current density. In this project we have fabricated superconductor YBCO bulk and optimized its critical current density. There are two major stream in this thesis, first design of Vibrating System Magnetization (VSM) for critical current measurements and then fabrication of YBCO bulk and optimization of its... 

The aim of this project is design and implementation of the “gradiometer RF SQUID base Vibrating Sample Magnetometer (VSM)”. Different sections of the system have been designed such as pick up coils, vibration system and electronic circuits. The piezoelectric crystal has been concerned for vibration system. At the first step, we have implemented the basic VSM system. In the basic system, voltage induces in two series opposite pick up coils and its output is recognizable via electronic circuits. At the second phase of the project, the electronic circuits of basic VSM system have been replaced with the RF SQUID gradiometer and its electronic circuits. Afterwards, the sensitivity and the gain... 

Superconducting Rapid Single Flux Quantum (RSFQ) Logic, is very fast (up to about THz) and ultra low power circuit technology and is the most recent and fastest superconducting logic family. So far one of the difficulties in RSFQ logic is associated to reading the circuit states in particular flip flops. In prevalent RSFQ logic using T1 Flip Flop gate instead of the T Flip Flop, the non-destructive reading of the registered bit is possible. Through this approach, it also has some limits in particular circuits. Another idea of resolving this issue, is considering the very new bi-directional RSFQ logic, which is based on alternative changing the bias current through the Josephson junctions.... 

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... 

Design of superconducting material based wide band radiation detectors has recently been attractive. Interesting features of detectors, which are based on Josephson Junctions such as high sensitivity in a wide range of frequencies and low power consumption, potentially have many advantages over other semiconductor-based photo-detectors. According to variety of applications of high-Tc superconductors, particularly YBCO, and significant progress in manufacturing of thin films and Josephson junctions, this thesis mainly focuses on investigation of radiation effects on I-V characteristics of high-Tc step-edge Josephson junctions experimentally. The current-voltage characteristics of fabricated... 

Analog SQUIDs have limited slew rate and dynamic range and these problems make it hard to operate SQUID systems in unshielded applications like Bio-magnetic imaging and NDE. Recently by combining analog SQUIDs and RSFQ Logic, new class of magnetic sensors are introduced. These sensors have an acceptable sensitivity and very high dynamic range. On the other hand these sensors, Which are called Digital SQUIDs, can be directly connected to digital signal processing stages. In This work, for first time, a digital SQUID completely based on i-directional RSFQ was designed and optimized. using Bi-directional RSFQ, one can significantly simplify the digital SQUID circuit design and therefore... 

The need for further improving the operation of the electronic and optoelectronic devices to raise the speed of the circuits, and to decrease their power dissipation, has led many researchers to investigate the structure of 2D material, such as graphene, transition metal dichalcogenides (TMDs) as MoS2, and other 2D compounds such as BN, due to their prominent electronic properties. TMDs have the highest significant potential for the next generation transistors due to their salient semiconductor characteristics such as electron mobility, band gap, and conductivity. For instance, Graphene is a favorable candidate for analog devices due to zero bandgap. Regarding the importance of bandgap in... 

A free-membrane superconducting transition edge detector was designed and fabricared for IR and THz detection. YBCO superconducting thin films was grown on SrTiO3 (STO) and Yttria Stabilized Zirconia (YSZ) crystalline substrates using RF magnetron sputtering technique and Metal Organic Deposition method. The electrical and optical characterization of the fabricated transition-edge detectors was carried out in a liquid nitrogen based cooling system. The voltage response of the detector was studied in relation to the thermal parameters and the biasing parameters of the device for optimal design of the transition edge detector. Analytical simulations conducted by applying a one-dimensional... 

Microelectrode array technology is a broad platform for studying and characterization of the electrophysiological properties of excitable tissues derived from both brain and heart in vitro. Microelectrode arrays can either record or stimulate cells by accessing multiple sites of neural networks and cell tissues and detect signals from all sources around each electrode simultaneously. By using recorded signals, one can detect cell potential changes and its minor fluctuations. Unlike intracellular recording techniques, the noninvasive interface of microelectrode arrays with cells provides durable studying of neural networks and cell tissues. Using related microelectronics fabrication... 

Microfluidics is a novel technology that brought a revolution in the field of chemistry and biology. This technology allows precise control and manipulation of fluids and particles in sub-millimeter bio-compatible channels. This makes microfluidics a powerful tool to study and examine bio-particles and bio-processes. One of the most prominent areas in microfluidics is the integration of developed measurement tools and devices of the electrical engineering field, with microfluidic chips. The purpose of this thesis is to measure the electrical impedance spectrum of bio-particles with high precision and in a wide bandwidth. These valuable spectrums are useful in many applications such as... 

A bolometer is a device for measuring electromagnetic waves, which uses the heating of a material with variable resistance to temperature. Due to the existing limitations and quality improvement, superconducting materials are used in the manufacture of these devices. In this dissertation, the construction and improvement of the components of a high temperature transient edge superconducting radiometer with terahertz detection capability is discussed. In the construction of these detectors, the superconducting material YBa2Cu3O7-x is used as a thermal sensor with a transition temperature of 93.5K. In order to characterize these detectors, an automatic system for measuring the voltage response... 

Today, microfluidics, representing the precise and controlled displacement of small amounts of fluid, is one of the most efficient tools available in various research fields, including medicine. Digital microfluidics is one of the newest microfluidic methods, which is based on the theory of electrowetting on dielectric. According to this theory, by applying a voltage difference to a droplet of fluid on a hydrophobic surface, the droplet can be moved on that surface. Therefore, by fabricating a plate containing a number of electrodes completely isolated from each other and controlling them, small droplets of fluid can be moved on a hydrophobic surface. In this thesis, the electrodes of this... 

Microfluidics, employing fluids in structures with micrometer dimensions, is an emerging technology that has brought great opportunities to develop various devices including lab-on-a-chip systems. Lab-on-a-chip systems have the advantages of integrating several stages of different analytical methods, application in diverse fields, consumption of small volumes of samples, and portability. One of the crucial applications of lab-on-a-chip devices is sorting cells and biological particles, done by different methods. In separator devices, high separation efficiency and repeatability are critical. When a neutral particle is polarized in a non-uniform electric field, the dielectrophoresis force... 

Neural probes, as brain-machine interface devices, are essential tools for recording electrophysiological signals or neural stimulation of a single neuron or a set of them. Nowadays, neural probes are widely used by cognitive and neuroscience researchers to understand brain functions in order to develop new treatments and therapies for neurological disorders. Making neural probes based on microelectrodes has the advantages of compatibility of their construction with the use of integrated circuit microfabrication technologies, as well as the ability to be made based on flexible materials. The purpose of this research is to design and manufacture a neural probe based on microelectrode to... 

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... 

Superconducting Quantum Interference Devices (SQUIDs) are one of the most sensitive magnetic flux detectors. According to their high sensitivity, these sensors have many applications such as magnetic imaging, magnetocardiography and magnetoencephalography. In this project we have designed and implemented a fluxgate based active shield that would be used in magnetocardiography. One of the main concerns in RF-SQUID applications is suppression of the low and high frequency noises. These noise sources includes earth magnetic force, humming noise and RF noise caused by cell phones. These sources could unlock RF-SQUID sensors and hence needs to be shielded. Low frequency noise suppression could be... 

Detectors play an important role in almost all scientific experiments and the results of the experiment highly depend on the performance of the applied detector (e.g. the detector detectivity, noise, detection threshold, time constant, …). In general a detector is defined as a device which transforms a quantity (e.g. pressure, energy, photon, …) to another one(e.g. mechanical displacement, electrical current, voltage, …). High temperature superconductor transition edge bolometers (TEB) are one of the most promising devices that due to the wavelength independent nature of their optical response can be used to detect the electromagnetic radiation over the whole spectrum from x-ray to the far...