Simulation of the Flux-to-voltage Characteristics of DC SQUID with Small Screening Parameter and a Large Stewart-McCumber Parameter

There are three important parameters in the RCSJ Model of direct current superconducting quantum interference devices (DC SQUIDs), namely screening parameter βL, Stewart- McCumber parameter βC, and thermal noise parameter Γ. The three parameters will dominate the SQUID sensor intrinsic noise, but not the application system noise, because the electric noise of readout in room temperature always cannot be neglected. In order to suppress the readout electric noise, a large flux to voltage (∂V/∂Φ) character of SQUID sensor is essential in direct readout scheme. In the real application system, SQUID sensor temperature fluctuation noise is negligible, so we simulated influence of the parameter βL and βC to SQUID's ∂V/∂Φ. In the simulation we used three combinations based on βL and βC under the condition of biased current i=1.65 μA and noise parameter Γ = 0.05. We found that the weakly damped SQUID with small βL have a high flux response ∂V/∂Φ. At last some experiment have been done, and the results fit well to our simulation.