Characteristics of integrated high- T_c superconducting quantum interference device magnetometer and gradiometer with serial array

We characterized the current-voltage, voltage-flux, and the field sensitivity of integrated high- Tc series superconducting quantum interference device (SQUID) magnetometers and gradiometers. The series two-SQUID magnetometers shows field sensitivities of ∼30-40 fT Hz12 at 1 kHz and ∼80-100 fT Hz12 at 1 Hz over that of a one-SQUID magnetometer in shielded environment. The field sensitivity of a series two-SQUID gradiometers is ∼60 fT Hz12 cm, while the one-SQUID gradiometer shows a gradient sensitivity of ∼80-150 fT Hz12 cm at 1 kHz in an unshielded laboratory environment. The series two-SQUID magnetometers or gradiometers show a significant improvement in flux noises over that of one-SQUID magnetometers or gradiometers.