Series SQUID Array for Biomagnetic Measurement

Abstract

We have demonstrated a gradiometer using a 20-dc SQUID array for biomagentic measurement. Because this SQUID array has a large voltage swing, it can be directly connected to room temperature amplifier without imped-ance matching circuit such as transformer, resonator or additional positive feedback. The voltage swing of the array has been 1.7 mV and the maximum voltage to flux transfer function has been 9.5 mV/Φo. The flux noise of the series SQUID array has been 0.56μ Φo/√ Hz in a flux locked mode, and the field sensitivity of the gradiometer which has an planner type pickup coil of 10 mm square has been 2.9 fT/√ Hz at 1kHz.