Closed-loop Frequency MET Geophone – Operating Principles and Parameters

A closed-loop, compact, wideband active geophone based on the MET sensing cell is designed. Experiments using an accurate shake table and noise analysis have been performed. The frequency response is flat within 3 dB in the 1 to 300 Hz range, the self-noise spectrum density 5*10-7 m/sec2/√Hz, and the THD at 18 mm/sec peak to peak input is 0.02%. The instrument tested has self-noise and linearity close to the best conventional geophones, but is more sensitive and has a wider operating frequency range.