Sharif Digital Repository

By fabrication of several bolometric detectors on the YBCO film made of Metal-Organic Deposition (MOD) and the effect of pattering and film parameters on the optical responsivity of transition edge sensors is investigated. The low cost nonfluorine (MOD) method has been applied to fabricate YBCO thin films with different patterning parameters. The measurement results of the optical responsivity versus modulation frequency up to 100 KHz for these devices are reported  

Epitaxial cerium oxide (CeO2) buffer layer has been grown on lanthanum aluminate (LAO) single crystal substrates for fabrication of c-axis oriented YBa2Cu3O7-x (YBCO). Precursor solution of cerium acetylacetonates with viscosity of 0.6 centipoises was spin coated on the 1×1 cm area LAO substrates. The calcination was carried out by very slow ramp (1°C per minute) until the final temperature of 500°C in oxygen flow to remove most of the organic compounds. The final heat treatment has been done at 780°C by a ramp of 20° per minute in gas flow of mixed argon-oxygen with 5 Pa partial pressure of oxygen. The thickness of the deposited CeO2 buffer layer was 20 nm. Then, 100 nm thick YBCO film was... 

We theoretically demonstrate the tunabiltiy of terahertz random lasers composed of high temperature superconductor YBCO and ruby layers as active medium. The considered system is a one-dimensional disordered medium made of ruby grain and YBCO. Finite-difference time domain method is used to calculate the emission spectrum and spatial distribution of electric field at different temperatures. Our numerical results reveal that the superconductor based random lasers exhibit large temperature tunability in the terahertz domain. The emission spectrum is significantly temperature dependent, the number of lasing modes and their intensities increase with decreasing temperature. Also, we make some... 

Detectivity optimization of large-area freestanding-type YBCO superconducting bolometric detectors is theoretically and experimentally investigated. The effect of the device thermal parameters on the theoretical total noise-equivalent power based on background radiation, thermal fluctuation, and Johnson noise is considered. By analytical optimization of the total noise-equivalent power (NEP) of the device with respect to the thermal parameters and radiation modulation frequency, the maximum sensitivity and optimal thermal parameters of the bolometric detector are obtained. Relating device thermal parameters to the special case of the large substrate dimensions, the optimum device geometry is... 

The application of flat superconductor rings has been investigated in the structure of inductive shield-type high temperature superconducting fault current limiters, HT c-SFCL. A laboratory scale inductive shield-type HT c-SFCL has been designed and fabricated using flat superconductor rings. The fabrication process has been fully presented. YBCO powder has been used for the fabrication of superconductor rings. This fabrication process, being quite innovative, is introduced completely. The method of the trapped field measurement has been used for the critical current density measurement of the fabricated superconductor rings. The device with nominal current of 2 A was tested in a 30 V... 

We present the results of a bolometric transition-edge sensor made of a high-Tc superconductor YBCO thin film prepared by fluorine-free metal-organic deposition. The structure of the films was characterized by X-ray diffraction and scanning electron microscopy, and the superconducting properties were determined by R-T measurements. The applicability of the resulting film as an infrared sensor is reported here. The optical response in the range of near infrared and the noise characteristics of the patterned bolometer are measured and analyzed. The dependence of device sensitivity on the bias current and modulation frequency is also investigated. As it is presented in this paper, the results... 

A RF SQUID electronic system has been implemented which works at the frequency range of 650MHz to 1GHz. By incorporating particle swarm algorithm for the optimization of the system parameters, the readout system could automatically set its parameters for a desired RF SQUID. Using the implemented system, the noise characteristics of a RF SQUID gradiometer is being measured. The measured flux noise of the High-Tc YBCO magnetometer is below 100μ Φ0/ √ Hz at 100Hz in unshielded environment  

The noise level of the magnetometer and gradiometer RF SQUIDs were investigated using different shielding methods. The used methods include different active and passive shielding, such as Helmholtz configurations, locally compensation coils, superconducting bulks and μ-metal shields. For the passive shielding approach, using FEM simulation we have investigated the shielding effectiveness of superconducting bulks versus the use of μ-metal shielding. The superconducting shield is a YBCO circular bulk, which was made using melt-texture method and located in a distance in front of the SQUID. In this work the results of these shielding methods are presented and compared, while their effectiveness... 

Incorporating an efficient approach for the finite-element simulation of eddy current superconductive quantum interface device (SQUID) nondestructive evaluation (NDE) systems, an appropriate finite-element method (FEM) has been presented for simulating and analyzing such systems. We have introduced a new model for the planar double-D coils, which are used as the excitation source in eddy current SQUID NDE systems, and also another model for the description of the flaw effect on the induced current. We have also examined our simulation results with their associated measurements. Our system is based on a high-TC YBCO gradiometer RF-SQUID sensor with a flux noise level below 100 μΦ0 √Hz at 100... 

We report the results of the electronic structure calculation of a newly discovered member of the YBCO high-T c family, i.e., Y 3Ba 5Cu 8O 18 (Y358) with T c>100, based on the full-potential linearized augmented plane waves method (FP-LAPW) of density functional theory in the generalized gradient approximation (GGA). The evolution of the number of hole carriers in different sites of the CuO 2 planes and CuO chains has been investigated in comparison with the other YBCO family members, i.e., Y123, Pr123, Y124, and Y247. The results suggest that pumping hole carriers out of the chains toward the planes enhances the transition temperature. The band structure calculations have been performed for... 

We report on the results of a YBa2Cu3O7−x (YBCO) superconductive transition edge bolometer (TEB) fabricated on a Ce0.9La0.1O2−7 (CLO) buffered single crystalline yttria-stabilized zirconia (YSZ) substrate. Metal organic deposition was used for the fabrication of both the YBCO thin film as well as CLO buffer layer, while standard photolithography was applied for TEB preparation. YBCO thin film properties were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), AC susceptibility and resistance versus temperature measurements. Optical response of the TEB in terms of voltage amplitude and phase was analysed and measured through four-probe technique in a liquid nitrogen... 

In order to achieve stable operation for a developed high-Tc SQUID-based magnetocardiography system, a two-stage active magnetic shielding technique is implemented. This technique is based on a combination of fluxgate and high-Tc SQUID magnetometers feedback loops. While two YBCO rf SQUIDs in a gradiometric configuration are used at liquid Nitrogen temperature as the main sensors for the heart signal detection and low-amplitude noise signals cancellation in one stage, a fluxgate is used to cancel large far-field environmental noise in the other stage feedback loop. The fluxgate sensors working in the fundamental mode under the optimized bias conditions have white noise levels less than 10... 

The effect on the thermal parameters of superconducting transition-edge bolometers produced on a single crystalline SrTiO3 (STO) substrate with and without a CeO2 buffer layer was investigated. Metal-organic deposition was used to deposit the 20-nm CeO2 buffer layer, whereas RF magnetron sputtering was applied to fabricate 150-nm-thick superconducting YBa2Cu3O7-δ (YBCO) thin film. The critical transition temperature for both of the YBCO films was 90 K, and the transition width was ∼1.9 K. The bolometers fabricated from these samples were characterized with respect to the voltage phase and amplitude responses, and the results were compared with that of simulations conducted by applying a... 

An active noise cancellation method is proposed for superconducting quantum interference devices (SQUID)-based magnetocardiography systems working out of magnetically shielded rooms. Using YBCO high-Tc rf-SQUID magnetometers as magnetic field sensors, an active shielding system was implemented based on this method. This method incorporates two different shielding frequency regimes of operation simultaneously. This is because the unwanted background magnetic field signals range from very low frequencies up to high frequencies with a wide range of amplitudes at the upper and lower frequency spectra. Therefore, the shielding system is designed in a bistage configuration, and each stage covers... 

In order to achieve stable operation for a developed high-Tc SQUID-based magnetocardiography system, a two-stage active magnetic shielding technique is implemented. This technique is based on a combination of fluxgate and high-Tc SQUID magnetometers feedback loops. While two YBCO rf SQUIDs in a gradiometric configuration are used at liquid Nitrogen temperature as the main sensors for the heart signal detection and low-amplitude noise signals cancellation in one stage, a fluxgate is used to cancel large far-field environmental noise in the other stage feedback loop. The fluxgate sensors working in the fundamental mode under the optimized bias conditions have white noise levels less than 10... 

We report on the results of a YBa2Cu3O7−x (YBCO) superconductive transition edge bolometer (TEB) fabricated on a Ce0.9La0.1O2−7 (CLO) buffered single crystalline yttria-stabilized zirconia (YSZ) substrate. Metal organic deposition was used for the fabrication of both the YBCO thin film as well as CLO buffer layer, while standard photolithography was applied for TEB preparation. YBCO thin film properties were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), AC susceptibility and resistance versus temperature measurements. Optical response of the TEB in terms of voltage amplitude and phase was analysed and measured through four-probe technique in a liquid nitrogen... 

The authors propose a new design for monolayer superconducting planar flux transformer integrated with a coplanar resonator serving as a gigahertz range tank circuit for high-Tc rf-SQUID magnetometers. Based on the proposed design, which is optimized using the finite element method, the transformer-resonator configuration is made of 200-nm-thick monolayer YBCO film on a crystalline LaAlO3 substrate. In this optimized design, the SQUID magnetometer is coupled through flip-chip configuration with the configuration providing high coupling coefficient between the devices. The design permits coupling of the rf signals to the SQUID efficiently, whereas the transformer is designed to couple the dc... 

We have investigated various geometrical design dependencies for rapid single-flux-quantum (RSFQ) circuits in high- Tc superconductors (HTS) technology, including the characteristics of the intermediate inductances. Structural- and temporal-dependent combinations of Cn - Rn (capacitance and normal resistance of the Josephson junctions, JJs) in the HTS technology are also investigated. Relatively favorable combinations of normal resistance and low capacitance of the JJs needed in the HTS technology for RSFQ circuits have been made possible by recent fabrication methods of high-quality YBCO films. Obtaining these devices is made achievable by using the grain boundary structures and high... 

We present a new approach for depth detection of hidden defects based on the analysis of the frequency spectrum of the output waveform in a nondestructive testing (NDT) system. In our eddy current Superconducting quantum interference device (SQUID) based NDT system, we apply multiple frequencies to its single excitation coil in a magnetically unshielded environment. The excitation coil is a planar D-shaped printed circuit board coil, and a high-Tc gradiometer YBCO rf-SQUID is used as the electromagnetic sensor in this system. An automated two-dimensional nonmagnetic scanning robot is used to test samples with intentional defects at different depths. In this approach, a diagram labeled 'FFT... 

We developed a novel magnetic coupling module, formed of a monolayer superconducting flux concentrator that is integrated with a coplanar resonator, strongly coupled to high-temperature superconducting radio frequency superconducting quantum interference device (SQUID). Three types of resonators, including a long stripline resonator between the input loop and the pick-up loop of the flux concentrator, a complementary split ring resonator, and a spiral shape inside the input loop, are explored. The resonance quality factor of different patterns of these three types of the resonators, as well as their coupling to the SQUID, is evaluated using finite-element-method simulations. Several readout...