The FGS-03e is a low noise 3-axis fluxgate sensor. It extends the frequency range for MT measurements down to DC. The sensor core unit is a Bartington Mag-03
For lower frequencies all transfer functions are linear. This sensor is designed for crustal studies where periods of 10,000 seconds and more are needed. Recording time for those periods are three to eight weeks depending on the data quality (magnetic activity and external interferences by man made noise).
The fluxgate is measuring the total magnetic field (B). A induction coil is measuring dB/dt.
A good coincidence can be seen for periods greater than 30s. For higher frequencies (smaller periods) a fluxgate can not be used for MT.