Optimization of a dc SQUID magnetometer to minimize the field resolution

The circuit parameters of a dc SQUID magnetometer have been optimized by computer simulations. Our principle of optimization is to minimize the field resolution. We have optimized the circuit parameters of a dc SQUID magnetometer, such as a Ketchen type, Drung type, directly-coupled type, etc. The only noise source was thermal noise from the shunt resistors. For a Ketchen type SQUID, our results show that the inductance of the input coil should be larger than that reported previously. It is also the case for a Drung type SQUID that the inductance of the SQUID washer coil should be slightly increased. By this design method, the optimum field resolution of a Ketchen type SQUID magnetometer is improved by a factor of 2/3. Furthermore, we compared the resolution of 3 types of dc SQUIDs and concluded that the optimum type of SQUID depends on the value of the critical current and the radius of the pick-up coil. Finally, we have proposed a new design method that can optimize the field resolution of dc SQUIDs under constraints on the critical current and the spatial resolution.<
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