Simulation and measurement of hts josephson heterodyne oscillator

We report continuing investigations into practical applications of the ac Josephson effect as the basis for a voltage-tunable radio-frequency oscillator. We have previously demonstrated experimentally that useful power levels (10 s of nW) and linewidths of a few kHz can be achieved in the heterodyne output from a High-Temperature-Superconducting Resistive SQUID (HTS-RSQUID) operating in the frequency range 1-50 MHz. Those results were achieved with 2-junction R-SQUIDs incorporating current-biased shunt resistors of a few micro-ohms. We have now modified the fabrication procedures, and adjusted the shunt resistors and bias current values so that higher frequencies can be achieved. The Josephson junctions are of step-edge type, rather than the bi-crystal type used in our earlier work. The step-edge technique permits much more flexibility in the geometrical lay-out and utilizes the more cost-effective single-crystal MgO substrates. In the present paper, we report numerical simulations and experimental measurements on these devices in the frequency range up to 2 GHz

The dynamics of high-frequency DC RSQUID oscillators

Josephson circuit simulation software has been used to study the properties of a range of two-junction DC RSQUIDs configured as current-controlled heterodyne oscillators. We find that, if the loop inductance is small, their current-voltage curves are modified substantially due to self-induced Shapiro steps. When the heterodyne frequency is comparable with the Josephson frequency of the junctions the step amplitude becomes very large and additional features are seen, including sub-harmonic steps and step tails. We point out that conventional DC RSQUIDs generally have too large a loop inductance for some of these effects to be seen in the I-V curves, and we suggest that nanofabrication techniques could be used to make novel low-inductance RSQUIDs. We have also demonstrated that by applying a sinusoidally varying RF flux to a DC RSQUID it is possible to phase-modulate the heterodyne oscillation, which could have useful practical applications

High Tc SQUIDs on Stepped and Grooved Substrates

No abstract available

High Tc SQUIDs on Stepped and Grooved Substrates

No abstract available

MgO Step Edge Thin Film RF SQUIDs with Potential Applications in NDE

No abstract available

Spatial response of symmetric and asymmetric planar SQUID gradiometers

First and second order symmetric gradiometers, and first order singly and doubly asymmetric gradiometers have been designed and fabricated using a standard niobium thin-film process. Here we present the results of our simulations of the effect of varying the gradiometer geometry, order and symmetry. In particular, we are interested in the spatial response of the gradiometer. We compare the simulations with experimental data

Assessment of HTS step-edge thin-film RF SQUIDs for NDT

The authors describe the fabrication of straightforward YBa2Cu3O7- delta thin-film step-edge Josephson junctions and RF SQUIDS on (100) MgO by pulsed laser deposition. At 77 K, a typical SQUID has a transfer function of 8 mu V/ Phi O. The SQUID has been operated in the open loop and flux-locked modes to assess the potential of HTS devices in NDT applications. Some attractive characteristics are apparent: the SQUIDS already have adequate field sensitivity and excellent spatial resolution, while the use of liquid nitrogen is convenient and has fundamental advantages over liquid helium in terms of cryostat design. However, experimental results also highlight the problems faced by HTS SQUID NDT including the need for reasonably low 1/f noise and gradiometric operation. Further work is necessary, particularly in the areas of device configuration and system design

Experimental Characterisation of Planar SQUID Gradiometers in Niobium Technology

No abstract available

Simulation and Experimental Characterisation of Planar Asymmetric SQUID Gradiometers

No abstract available

Single sensor high-temperature superconducting axial gradiometer with thick film pick-up loops

A high-temperature superconducting first-order axial gradiometer with thick film YBa2Cu3O7-delta pick-up loops inductively coupled to a thin film YBa2Cu3O7-delta superconducting quantum interference device magnetometer has been designed, fabricated and characterized. The gradiometer has a baseline of 79 mm, an estimated intrinsic system balance of 1:480 for uniform axial magnetic fields and an estimated axial magnetic field gradient sensitivity of 70 fT/(cm root Hz) at 1 kHz, in magnetic shielding