A geophone converts seismic energy inputs (or vibrations) into electrical voltage which can be accurately measured. The term geophone derives from the Greek word “geo” meaning “earth” and “phōnē” meaning “sound”. A geophone is a passive device requiring no additional power which converts seismic energy (ground displacement) into an electrical signal producing an output voltage which is proportional to the geophone velocity.
The instrument is based on the principal of a spring mounted coil which moves within a magnetic field. The geophone’s coil remains stationary due to its inertia and the case moves in relation generating a voltage as the coil windings move through the magnetic field. Compared to active (powered) sensors a geophone offers the advantage of extreme low noise having only Brownian motion noise. The bandwidth of a geophone is generally defined from its natural frequency to the spurious frequencies which are unwanted parasitic resonances present in all geophones and caused by the sideward motion of the coil.