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Analog and Digital Signal Processing for a Fluxgate-Magnetometer

Martin S. Sommer

Martin S. Sommer

A fluxgate-magnetometer is a sensing device for the measurement of the direction and the amplitude of dc or low frequency ac magnetic fields in the range of 100 pT up to 100 mT. In this diploma-thesis the effect is analyzed theoretically and a sensor is constructed.

The main components of a fluxgate-magnetometer are the electrical excitation, a soft magnetic core and a sensing coil. Due to the equal orientation between the excitation field an the external field the configuration shown in Figure1 a) is called parallel-type fluxgate [1]. Because of the orthogonal orientation between the excitation fields an the external field the fluxgate displayed in Figure 1 b) is called orthogonal-type fluxgate [2].

The basic idea of a fluxgate-magnetometer is to take advantage of the nonlinearity of the soft magnetic core. The core material is alternately saturated by the excitation field as shown in Figure 2 a). Due to an external field the pulses of the voltage induced are shifted on the time axis for parallel-type sensors and on the other hand the shape of the pulses is varied by orthogonal-type sensors. Because the influence of an external field on a parallel-type fluxgate can easier be shown and the parallel-type sensor is more widespread, in Figure 2 b) only the influence of an external field on a parallel-type fluxgate is displayed.

Figure 1: Configuration of a fluxgate-magnetometer.  In a) the sensor is excited by an excitation coil; in b) the sensor's core is excited directly by the excitation current.

Figure 1: Configuration of a fluxgate-magnetometer.
In a) the sensor is excited by an excitation coil; in b) the sensor's core is excited directly by the excitation current.

Figure 2: Characteristics of a parallel-type fluxgate.   a) without superposition with an external field; b) with superposition with an external field.

Figure 2: Characteristics of a parallel-type fluxgate.
a) without superposition with an external field; b) with superposition with an external field.

References

  • [1] Pavel Ripka: magnetic sensors and magnetometers, Artech House, Norwood, 2001
  • [2] I. Sasada: Orthogonal fluxgate mechanism operated with dc biased excitation, Journal of Applied Physics, vol. 91, nr. 10, 2002.

April 2007