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DC SQUID As an Enhanced Magnetometer

IP.com Disclosure Number: IPCOM000061180D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Chi, CC: AUTHOR [+2]

Abstract

The DC SQUID Chain is an enhanced magnetometer consisting of a chain of SQUIDs (Superconducting Quantum Interference Devices) 11 connected in series. In a chain of N SQUIDs, each one is coupled inductively to an input circuit consisting of N coupling coils 12 which are connected in series with N matched superconducting input coils 13 for magnetometer applications, or to a voltage source with source resistance increased by a factor of N over the optimal value for a single inductively coupled SQUID magnetometer used as a linear voltage amplifier. The figure shows the basic structure for N=4. In order to avoid chaotic interference between the coupled non-linear SQUIDs, the devices must either have widely dissimilar Josephson oscillation frequencies, or must be coupled to the input circuit through a low-pass filter.

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DC SQUID As an Enhanced Magnetometer

The DC SQUID Chain is an enhanced magnetometer consisting of a chain of SQUIDs (Superconducting Quantum Interference Devices) 11 connected in series. In a chain of N SQUIDs, each one is coupled inductively to an input circuit consisting of N coupling coils 12 which are connected in series with N matched superconducting input coils 13 for magnetometer applications, or to a voltage source with source resistance increased by a factor of N over the optimal value for a single inductively coupled SQUID magnetometer used as a linear voltage amplifier. The figure shows the basic structure for N=4. In order to avoid chaotic interference between the coupled non-linear SQUIDs, the devices must either have widely dissimilar Josephson oscillation frequencies, or must be coupled to the input circuit through a low-pass filter. In this case the noise at the output of the chain is the incoherent sum of the noise in the individual devices. However, the signal has been increased by a factor of N. As a result, the overall signal-to-noise ratio for the chain has been improved by a factor of the square root of N, with no additional elaboration of the readout electronics. For the case of a magnetometer, the input coil inductance has been increased by a factor of N, which can be translated into an increase of a factor of N in the detector area. For linear amplifier applications, the optimal source resistance and dynamic range (for an unlocked device)...