A Compact High-Tc RF-SQUID System with Reduced Tank Circuit Damping
One requirement for good rf-SQUID operation is a coupling between SQUID-ring and tank circuit with k2Q≈1. For typical bulk SQUID structures of high-Tc materials, however k2Q<1 usually is found experimentally, when using a copper coil at 77 K for the tank circuit and a resonance frequency near 20 MHz. We therefore investigated the operation of high-Tc rf-SQUIDs where the damping of the tank circuit was reduced by a positive feedback circuit in order to achieve k2Q≥1. The reduction of damping leads to noise reduction. The SQUID can be operated without external rf-oscillator solely driven by the tank circuit noise. This elimination of the oscillator leads to a simplified compact “SQUID-STICK”.
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