what is a "GEOPHONE" ?? might be the question tumbling in your mind!
Geophone is a device which gives electrical output corresponding to the ground movement i.e.,converts seismic energy inputs into electrical voltage a easy to measure and record quantity.
Its derived from Greek word, 'Geo' means 'Earth' and 'phone' means 'sound'.
It is classified to be a passive device responding to ground displacement which is proportional to the Geophone velocity.
Similar to this we ground based equipment we have similar for water called as 'HYDROPHONE' !!
Know how it functions ?? and know its importance??
Above diagram might have given you bit clue as how it works and how its build up!!
nonconducting, whirled by a copper or any good conducting wire.
Active element is suspended using a spring in region enclosed by magnet.This magnet is fixed to the earth using a long spine fixed to it to attach firmly to ground. We all know that any object at rest continues to be at rest until a sufficient force is applied to move it. similarly here when the ground moves the entire configuration moves except the mass which is freely suspended due to inertia and hence we get relative motion between the magnet and the coil and hence output voltage is generated which is proportional to the ground velocity since the magnetic flux changes at a rate equal to the ground velocity. The output can be further amplified to and the setup can be made more precise since even small variations can be recorded. Due to electrical output it is easy to store the data or to process it to any other form.
Nowadays this setup has been modified to give highly accurate measurement. MEMS (microelectromechanical system) technology that uses a feedback circuit to maintain the position of the small piece of silicon and are basically used to respond to acceleration. They have much higher noise level and hence are only used for strong motion and active seismic application.
Geophone has frequency response similar to the harmonic oscillator. Geophone's are normally constrained to respond to only single dimension variation.
Reflection seismology makes majority use of Geophone to record energy waves reflected by subsurface geology i.e., vertical motion is monitored. Many a times these vertical waves are destroyed by strong horizontally transmitted wave (known as ground roll) which generate vertical motion. This is avoide using them in arrays and tuned to wavelength of ground roll due to which these dominant noise signals are attenuated and weaker data signals are recorded.
Passive Geophones are typically very sensitive and thus used in measuring distant tremors.
Interested to know more abt the recent geophone's manufactured visit www.geophone.com
CONTRIBUTION:
Jaseem Ahamed
NMAMIT NITTE
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