Magnetic-field transducer based on closed-loop operation of magnetic sensors

A high-sensitivity magnetic transducer able to sense magnetic fields from dc up to tens of kilohertz is analyzed in this paper. The system is based on a nulling field coil fed by a current on the basis of the residual field, sensed by a magnetic sensor (Hall or magnetoresistive) placed in the coil center. In this way, the coil current proportionally represents the external field component along the coil axis, and it can be easily converted in a voltage signal by a series resistor. Then, a one-axis Gauss meter can be readily obtained. The sensitivity and the bandwidth of the overall system are discussed by a transfer function analysis. A hardware prototype has been realized, and significant test results are shown by means of a reference magnetic-field-generation setup. Useful guidelines for the overall system design are given.