Study On The Circuit Technologies Of SQUID Sensor For Practical Applications

Superconducting Quantum Interference Device(SQUID)based magnetic field sensor is one of the most sensitive sensors in practical applications.It has been widely applied in extremely weak magnetic field measurement systems for biomagnetism or geophysics studies,such as Magnetocardiogram(MCG),Magnetoencephalography(MEG),and Full tensor gradiometer(FTG)system.SQUID system consists of SQUID cryogenic circuit,room-temperature readout electronics,cryostat,and peripherals.It involves circuit technologies of SQUID circuit design and optimization,room-temperature readout electronics design,and system integration.For the extension of the SQUID industrial applications,this dissertation carried out comprehensive studies of circuit technologies on the device,circuit,and system.First,we studied the circuit analysis method for superconducting quantum interference hybrid circuits.We presented the mesh-current method,which describes the working principles between circuit elements and mesh currents with the macroscopic wave-function of superconductivity.This method derives the general circuit equation and the dynamic system model for any superconducting interference hybrid circuits.The general equation and dynamic model reveal the internal microwave interference mechanism inside the superconducting quantum interference circuits and can be utilized for SQUID simulation and optimization.Second,we researched the SQUID linear readout electronics design technology.We introduced the readout design concept of the SQUID-based flux-feedback operational amplifier(FFOPA).It is more general and flexible than the conventional design model of integrator-based Flux-locked loop(FLL).Based on the FFOPA model,we proposed a high slew rate FLL circuit with only two operational amplifiers,which achieves the maximum slew rate of 106?0/s.We design a novel wide-range auto-reset SQUID readout scheme using only one proportional amplifier;the counting error less than±0.1 ?0 is realized.We developed a practical two-stage SQUID low noise readout circuit and solved the multiple working point problem encountered in conventional two-stage SQUID readout schemes;the noise level less than 1??0/?Hz is measured.Finally,we studied the design and integration scheme for the multichannel SQUID sensor system.The integration scheme utilized the miniature readout electronics with the photoelectric digital control interface and embedded the whole SQUID FFOPA in the liquid helium cryostat to achieve electromagnetic compatibility with the external equipment and improve the environmental adaptability for practical applications.The multichannel SQUID system integration concept has been successfully applied to the unshielded magnetocardiography(MCG)system and the airborne superconducting full tensor magnetic measurement system.This thesis presents the general circuit theories and design methodologies for superconducting electronic circuits analysis,readout electronics,and system design.Those are solutions for developing practical SQUID systems and have particular significance for the practical application of SQUID sensors.