Characteristics of integrated high-Tc 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 ∼30–40fT∕Hz1∕2 at 1kHz and ∼80–100fT∕Hz1∕2 at 1Hz over that of a one-SQUID magnetometer in shielded environment. The field sensitivity of a series two-SQUID gradiometers is ∼60fT∕Hz1∕2cm, while the one-SQUID gradiometer shows a gradient sensitivity of ∼80–150fT∕Hz1∕2cm at 1kHz 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.