Closed loop applied to magnetic measurements in the range of 0.1-50 MHz

After a brief historical review of inductive sensors used for measuring terrestrial magnetic field variations, this article explains the difficulty in extending the working range of the well known search coil toward high frequencies. The theory of the closed loop magnetometer is exposed and practical considerations leading to an optimized sensor are discussed. Two examples of prototypes are then shown, with the simulated and experimental curves of the transfer function and the noise spectral density. Finally, an experimental facility to measure the sensitivity of the sensor to the pure electric field is shown, and the results of one of the prototypes are presented