Geophones

Seismic geophone is a type of sensor that converts ground movement or a kind of vibration into voltage, which could be acquired by the acquisition system. The deviation of this measured voltage from the base line is called the geophone response and is analyzed for structure of the earth, reflected inner structure of earth crust or monitoring vibration generated by nature, human or industrial engineering.

Geophones are typically comprise a spring-mounted wire coil moving within the field of a case-mounted permanent magnet to generate an electrical signal. The response of the geophone coil is proportional to ground velocity. The frequency response of a geophone is a kind of harmonic oscillator, which is determined by corner frequency (typically around 10 Hz) and damping (typically 0.707) but it is possible to lower the corner frequency electronically, at the price of higher noise and cost.

Although waves passing through the earth have a three-dimensional nature, geophones are normally constrained to respond to single dimension – usually the vertical. However, some applications require the full wave to be used and three-component or 3-C geophones are used. In analog seismic devices, three moving geophone elements are embedded in an orthogonal structure within a 3C geophone case.

The majority of geophones are used in reflection seismology to record the energy waves reflected by the subsurface geology, while nowadays more and more geophones have been applied in industrial vibration, safety monitoring, internet of things engineering, etc.