Prototype of a Small Low Noise Absolute Displacement Sensor

Inertial seismic sensors typically have a velocity readout, to offer a large dynamic range in a large frequency range. However, in some precision engineering applications, it can be preferable to have access to the displacement. An example is the so-called sky-hook spring strategy used for active vibration isolation. In this paper, we present a prototype of small inertial sensor with a displacement readout. It is based on a commercial low cost geophone, which has been modified to measure the displacement with a capacitive sensor. It results in a compact sensor with a resolution which is a factor 10 better than the commercial geophone, but a limited range of amplitudes. This paper finished with an attempt to extend the bandwidth of the sensor at low frequency.