Sharif Digital Repository

Ultra-sensitive magnetometers based on Radio Frequency Superconducting Quantum Interference Device (rf SQUID), have wide applications in Non-destructive Evaluation (NDE), geophysical measurements and biomagnetic measurements, especially in magnetocardiography (MCG) systems. A superconducting module coupled to rf SQUID is designed to provide a resonance frequency in GHz range (according to the electronic system frequency), as well as concentrating the magnetic flux in the effective area of SQUID. The signal can be measured through a port pumping AC power to the module. The resonator has been also implemented by lumped element tank circuits, but the quality factor of these circuits are usually... 

Proton precession magnetometers are one of the most sensitive scalar magnetic sensors. Their function is based on Zeeman effect and also nuclear magnetic resonance phenomena. In this project we have designed and implemented needed coils, swithching and signal detection circuits. Because of extremely high sensitivity of this sensor to induced noises and also gradient of earth’s magnetic fileld, detection of precession signal needs design of low noise electronic circuits with special EMC considerations. The implemented system in this project contains different blocks, such as switching circuit and its related control unit, amplifier, filter and frequency meter. Using this system, the obtained... 

Proton precession is used in measurement of scalar magnetic field intensity. In this sensor, the magnetic field intensity is calculated through Larmor frequency using the proton precession frequency around the magnetic field. The accuracy of this sensor is in the range of picoTesla which is used for magnetic field measurement as well as the calibration of vector magnetic sensors. The signal to noise ratio in this sensor is due to the dimension and resistances of the wires and is a kind of RMS random noise. Although, changing the dimension of the wires for noise reduction and increasing the signal amplitude requires the fabrication of a bulky sensor with low power consumption. Therefore, it... 

Superconducting SQUID sensors are one of the most sensitive magnetic sensors that have been ever produced. Due to their high sensitivity, these sensors have many applications in different fields. Magnetic Imaging and far away targets detections are of these applications. In this project, a magnetic imaging system based on Superconducting SQUID sensors have been designed and implemented. In SQUID applications one of the most important problems is the cancelation of the unwanted fields including background low frequency and high frequency fields. In residential and urban areas the interference of Electricity network is considered as one of the major noise sources. While the high frequency... 

In this thesis, we have investigated nonuniform normal and superconducting microstrip transmission lines in microwave regime. Photonic structures with subwavelength features can be homogenized and thus be accurately approximated by homogeneous structures. This idea is here applied to nonuniform transmission lines with subwavelength nonuniformities, i.e. subcentimeter features in the microwave regime. We present an analytical model based on telegraphers’ equations in order to obtain line propagation characteristics; characteristic impedance, propagation constant, and group velocity. The accuracy of analysis in normal and superconducting lines is evaluated by measurement and electromagnetic... 

Surface plasmons are the result of a resonant interaction between the waves and the mobile electrons at the interface between negative and positive permittivity materials stimulated by incident light. Due to their specific quantum mechanical nature and zero electrical resistance, superconductors are capable of supporting low-loss plasma waves with extremely large propagation length. In this study, palsmon confinement in some superconducting waveguide structures has been measured by computing the effective index parameter. Superconductors are classified in to high-Tc an low-Tc categories. It is not possible for plasma waves to propagate in low-Tc superconductors, because the plasma energy... 

A Focal Plane Array (FPA) consists of one or two dimensional array of sensor elements and is widely used in imaging systems. Generally an FPA can be divided into two main parts: Sensor array and read-out/test circuit. In this thesis we design and implement a test circuit for an FPA that works in 77K. The circuit will be attached to the sensor to detect and amplify its very low level current that is in the range of 10 pA to more than 10 nA. Reducing MOSFET temperature from room temperature (300K) down to liquid nitrogen (77K) will greatly changes its parameters and characteristics such as Threshold Voltage and carrier mobility. However MOSFET models in low temperature are either... 

The purpose of this thesis is the incorporation of RF SQUID ultra-sensitive magnetic sensors in an implemented SQUID NDE system and also the development of associated inverse solution algorithms for the detection of defects in metallic samples. The system is based on the induction of Eddy currents and the incorporation of SQUIDs for precise detection of the magnetic field anomalies related to the defects in the sample. One of the major parts of the system is the highly stable, multi-channel RF SQUID readout system which has been designed and implemented with novel features for this project. For the magnetic inverse analysis of our SQUID NDE measurements, new models have been presented for... 

Quantum bits, also known as Qubits are the smallest building blocks of quantum computers, their correct operation has a great impact on quantum computing fidelity. For this purpose, Qubits need to have the necessary properties. Many properties have been defined for Josephson junction-based Qubits in order to implement better qubits. In this master thesis, the main characteristics of superconducting quantum bits including resonant frequency, anharmonicity factor, output readability signal, and quantum decoherence time including relaxation time and dephasing time have been calculated for cooper pair box topology in different operational regimes from cooper pair box regime to quantronium and... 

Temperature reduction from room temperature to liquid nitrogen temperature has a significant effect in improvement of semiconductor devices operation such as field effect transistors. Nowadays cryoelectronics as a considerable branch of electronics is concerned by several groups. In order to optimize the procedure of low temperature IC design and fabrication we investigated the temperature effects on different parameters of MOSFET in this thesis. Several transistors in a variety of channel lengths were fabricated in different technology files. Wide measurement experiments were done on these transistors in order to find their drain current vs. drain to source voltage characteristics. From... 

DNA is big protein molecule consisting of two strands intertwining each others. Recently DNA molecule has drawn attention of researchers to be used in electronic circuits and molecule electronic field. Therefore, many experiments have been carried out to measure DNA conductivity in different temperature in single molecule or bundle mode with varying size and shape. In this thesis, metallic bundle DNA at normal room temperature is studied and their resistance characteristic is obtained and compared. In order to improve DNA conductivity Metal Ions like zinc are adulterated to each of its structure period. DNAs with these metallic impurities are called metallic DNAs.
Thus, golden electrodes... 

In this thesis, we are focusing on the heat transport mechanism in one of the most applicable kinds of superconducting detectors called, YBa2Cu3O7-x (YBCO) transition-edge bolometer. The Time Domain Thermoreflectance (TDTR) method is described as a tool for investigating the thermal boundary conductance and thermal conductivity of the materials, and the measured thermal conductivity of our YBCO films is reported here. Although some recent papers have shown a dependence of the thermal conductivity of the YBCO films to their thickness, our results on many samples with different substrates didn’t show the reported thickness dependency and we have obtained the thermal conductivity of the YBCO... 

In many neuroscience studies, the aim is to investigate the functional role of a population of neurons in response to a certain stimulus. Electrophysiology methods usually can only record from a small population of neurons and this is not sufficient for studying functional properties of the cortex. An alternative is to use functional neuroimaging methods. However, some of these methods are expensive and also they do not offer suitable spatial and temporal resolutions. Optical imaging systems can solve these problems because they are low-cost, easy to design, and also have good temporal and spatial resolutions. These systems can generate functional maps from the brain. In this study, a... 

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...