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RTD Fluxgate

Research Activity

A RTD Fluxgate is based on the two-coils structure (a primary coil and a secondary coil) shown in Figure 1a. Coils are wound around a suitable ferromagnetic core showing a sharp hysteretic input-output characteristic which allows to infer that switching between the two stable states of the magnetization occurs instantaneously when the applied magnetic field exceeds the coercive field level Hc. A periodic driving current, I, is forced in the primary coil and generates a periodic magnetic field, He parallel to the geometry of the core (Figure 2a). This geometry is adopted to guarantee uniformity of magnetic field along the ferromagnetic core. A target field Hx is applied in the same direction of He; the secondary coil is used as pick-up coil and the output voltage Vout, shown in Figure 2b, carries information on the target magnetic field.

Figure 1. (a) The two-coils structure of RTD Fluxgate magnetometer (b) The dynamical behaviour of the device can be described with a bistable potential energy function

The principle of RTD Fluxgate is to exploit the information carried by the time position of spikes in the Vout signal. Time intervals, T+ and T-, defined by two successive peaks represent times spent by the core magnetization in the two steady states (Figure 1b). These time intervals are called Residence Times. In the case of a time-periodic excitation having amplitude large enough to cause switching between the steady states and in the absence of any target field, the hysteresis loop is symmetric and two identical Residence Times are obtained (Figure 2a). The presence of a target dc signal, Hx, leads to a skewing of the hysteretic loop with a direct effect on the Residence Times, which are no longer the same (Figure 2b). The difference between two Residence Times is directly correlated to the target field Hx.

Figure 2. (a) Interaction between excitation field H and coercitive fields H of the
Ferromagnetic core, with respect to the presence of an external target field H (b) Scope snapshots of the sensor response to an applied magnetic field


  • Biosensor (magnetic immunoassay)
  • Homeland Security
  • Volcanic Ash-fall monitoring
  • Geomegnetic Field measurements


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