Some science behind the scenes
The earth itself produces a natural background magnetic field. It derives from convection in the outer iron rich core, combined with stirring caused by the rotation of the earth, together with the fact that the inner more solid core rotates faster than the outer core. Earth’s magnetic field is of very low frequency. It was Tesla who discovered that the resonant frequency of the Earth was approximately 8 hertz (Hz).
But the magnetic field is not constant, it fluctuates over time. In effect we have a changing magnetic field that varies over time.
We know that the magnetic field varies and fluctuates because there are instruments that have been specifically devised to measure the fluctuations. A magnetometer is one of the scientific instruments used to measure the strength and/or direction of the magnetic field. The earth's magnetic field, because it is so weak, is usually measured in nano Tesla (nT). 1nT = 1 Amp / meter. The terrestrial field varies from around 20,000nT (equator) to 80,000nT (poles).
The causes of fluctuations
The causes of the fluctuations in the earth’s magnetic field are as follows:
- Geomagnetic storms and space weather – Geomagnetic storms caused by the sun can result in large variations. As the solar wind has an effect upon the magnetic field, the field will vary between day and night. There is a daily variation of around 30nT at mid latitudes and hundreds at the poles. The magnetic field forms the magnetosphere, which deflects particles in the solar wind. The sunward edge of the bow shock is located at about 13 times the radius of the Earth. The collision between the magnetic field and the solar wind forms the Van Allen radiation belts, a pair of concentric, torus-shaped regions of energetic charged particles. When the plasma enters the Earth's atmosphere at the magnetic poles, it forms the aurora.
- Fault lines – it is the moving of fault lines that cause the change. Earthquakes, volcanoes, fractural splits, seismic swarms, and other earth movement can all create changes. There are millions if not trillions of both large and smaller fault lines over all the world, a great network of criss-crossed lines that generate a change in magnetic field when the faults slip. There is thus the potential, at any time, in numerous places on earth, to experience a change in magnetic field caused by slippage in the fault or movement in the earth’s surface. The movement does not have to be ‘felt’, it can be very minor.
- Man-made rock fracturing - rocks under explosive impact and man-made blasting of the earth can cause changes to the magnetic field of the earth.
- Geomagnetic 'hot spots' – which are either sources of magnetic fluctuations in their own right or become so when exposed to abnormal geomagnetic storms. These hot spots are usually places where metals are found close to the earth’s surface and can be caused by meteorite impact
In effect, there is a fluctuating magnetic field at various points on the earth that can be natural and permanently fluctuating or that can fluctuate under the influence of solar activity during geomagnetic storms.
All we need is suitably conductive material and an electric current will be generated. To repeat, a changing magnetic field will induce an electric current in anything that will conduct it. Since the fluctuations are low in frequency, the current so produced is also very low frequency.
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