A sensor for very low-frequency magnetic fields

In this paper, we propose a technique for sensing very low frequency magnetic fields. The method is based on the modulation of the parametric oscillation voltage of a RLC circuit. Under appropriate conditions, if the capacitor of the RLC circuit is sinusoidally varied at 2/spl omega//sub 0/, where /spl omega//sub 0/ is the natural angular resonance frequency, oscillation will occur at the frequency /spl omega//sub 0/. If the inductance is appropriately biased, an external magnetic field can be made to modulate its permeability, thereby modulating the oscillation output voltage or current as the case maybe. Subsequent demodulation then yields a signal proportional to the modulating field. We shall explain the characteristics of parametric oscillation and its application in the measurement of low-frequency magnetic fields. Simulation and experimental results are included to verify the theoretical analysis.