Performance of a flux locked series SQUID array

The operation of a SQUID array with 100 DC SQUIDs has been demonstrated using a single flux-locked loop. The SQUID array had a maximum dynamic range of ±1.3×10⁸/√(Hz) in the low frequency region, a high slewing rate over a wide frequency range, and an extrinsic white noise energy sensitivity of 6×10^-31J/Hz. These data were obtained with a very simple feedback circuit made from three inexpensive operational amplifiers that operated in the DC-feedback mode. The feedback loop did not have any impedance matching circuit between the SQUID array and the room temperature electronics. Our results show that a SQUID array can have a significant impact on those applications that demand good noise performance and a very high dynamic range