Lock-On Magnetometer Utilizing a Superconclucting Sensor

A magnetometer utilizing a superconducting quantum interference device (SQUID) as a magnetic flux sensor is described. Its unique capabilities include: sensitivity of about an order of magnitude better than that of heretofore published magnetometers of other types, measurement range extending to zero field, and appreciable frequency response at high sensitivity (12 c/s bandwidth at 10.7 μGs full scale). The SQUID is a null detector in a feedback circuit in which unknown field changes are measured in terms of bucking field changes. Some limitations and design considerations are discussed. A recording of micropulsations of the earth's magnetic field is shown.