A geophone is a transducer that converts ground movement (velocity) into voltage, which may be recorded at a recording station. The deviation of this measured voltage from the baseline is called the seismic response and is analysed for the earth's structure.
A geophone sensor works using a coil of wire wrapped around a mass, suspended by spring over a magnet. As the mass moves, the interest moves the electrons through the coil, inducing an electrical voltage. Seismographs record this voltage signal at various points. A seismograph is a different type of voltage data that accurately measures tiny and substantial electrical signals. Thus, geoscientists obtain a high-resolution view of the ground movement.
The term "geophone" typically describes a purely mechanical type of high-frequency vibration sensor. Modern seismometers use electronic circuitry to improve sensitivity at specific frequencies. They do not need electricity to operate and, as such, are also referred to as "passive" sensors.
The lower frequency limit defines a geophone. If you turn a geophone at a speed of 10mm per second, it should produce the same voltage whether you are shaking it five times per second (5Hz) or at 100Hz. This is called the "linear response." of the geophone. A frequency band of a sensor is where the amplitude is within 50% of the linear response.
For instance, if you turn a sensor at 10mm/s, the output reads less than 5mm/s, the frequency you are testing is outside of the sensor's performance envelope. For example, a 4.5Hz geophone will output less than 50% of the correct voltage when shaken slower than 4.5Hz. Note that a difference of ±50% in amplitude equates to an earthquake magnitude difference of ±0.3 units.
To analyze the earth's structure
Estimate the composition of the ground and its chemical makeup
To Predict and simulate the possible earthquakes and seismic activity that is likely to occur
Discover and catalog sites of seismic activity
A geophone is made up of a mass suspended using mechanical springs. The geophone housing and the suspended mass begins moving with a velocity at frequencies lesser than the resonance frequency.
The mass will remain stationary for frequencies more significant than the resonance frequency. The movement of the mass depends on either magnets or coils of the geophone. The result of a coil/magnet geophone is directly proportional to the ground velocity.
Geophones help several industrial applications for vibration isolation purposes and exact speed sensing to get a high level of accuracy and precision. Geophone technology is used to measure accurate velocity for lithographic and high-level inspection applications to measure the payload disturbances by moving parts and other external disturbances.
They are also helpful in positioning and controlling a complex lens system. Leakage in oil and gas fields detection and earthquake prediction are also other significant applications of geophones.
Products in the market
The geophones available in the market today are highly sophisticated and sensible. They operate depending on the magnetic field generated by a coil suspended in a magnetic field. The current seismic industry market requires tight specifications to meet the standards of seismic surveys.
The SM-24 Rotating Coil borehole Geophone meets industrial standards with ION's Sensor. It provides high performance in seismic exploration with bandwidth from 10 Hz up to 240 Hz and gives two-dimensional and three-dimensional high-fidelity data. It also has a unique element design and exceptional quality, and low distortion with good specifications.
The geophone is versatile equipment that is just starting to see the wide range of uses that it is capable of. As prices for the device fall with its increasing popularity, there are sure to be many new uses of this device previously not even thought of, so get your hands on one and be the first!