Jose Martin Davila

A Simple Technique to Extend the Bandwidth of Electromagnetic Sensors

Electromagnetic sensors are typically loaded with an external resistance value that provides an effective damping factor of 0.7. The velocity response of the sensor is given by a third-order equation but can be approximated by an equation of second order if the coil inductance is neglected. We propose to use a capacitor in series with the resistance (series RC load) instead of a resistance only. The transfer function is then given by a fourth-order equation that can be reduced to a third-order one, as a zeros-poles analysis shows. This is the simplest and cheapest way to extend the response of an electromagnetic sensor. If appropriated values of R and C are selected, then the flat band of the frequency response is increased by moving the corner frequency down by a factor of 1/4 without any effective gain reduction.