Extending the Range of Geophones by Negative Impedance Converter

This paper shows a method to increase the vibrational amplitude range of commercial geophones. One major limitation of geophones is the maximum stroke of the seismic mass at its resonance frequency, which also limits the vibrational amplitude range. Reduction of the stroke is achieved by electrical damping. Via an applied shunt resistor a back electromotive force is introduced, which acts as damping. The maximum electrical damping is limited by the value of the passive resistor. This paper proposes the negative resistance of a negative impedance converter, allowing to overcome this limitation and further increasing the effective damping. It is theoretically derived and experimentally demonstrated that the increased damping reduces the required stroke of the geophones seismic mass. This allows to measure higher vibrational amplitudes or choosing a smaller geophone for the same vibrational amplitude.