Principle and Performance of a Dual-Band Search Coil Magnetometer: A New Instrument to Investigate Fluctuating Magnetic Fields in Space

Search-coil magnetometers are of common use in space physics thanks to their simplicity, robustness and ability to measure weak magnetic fields: their sensitivity can reach a few tens of fT/¿Hz in the range 10-100 kHz. The frequency band is grossly determined by the resonance of the coil. Simply adding a second coil does not efficiently extend the frequency band beyond the first resonance due to the mutual impedance of the two coils. We present a solution, called ¿mutual reducer,¿ which allows us to take full benefit of the second coil and efficiently extends the frequency band. The physical principle is described first, followed by a detailed presentation of this ¿dual-band search-coil¿ (DBSC) that will be part of the plasma wave instrument (PWI) onboard the Mercury magnetospheric orbiter (MMO) of the ESA-JAXA mission BepiColombo dedicated to the exploration of the plasma environment of planet Mercury.