How does the "Electromagnetic Position Tracking" work, exactly? I've been searching the web for the technology of the "Electromagnetic Position Tracking1," and have found the web to be surprisingly ineffectual!
I've just came up with some preliminary and basic concepts that follows. There is a "source" that emits an Electromagnetic Field using some coils. There are sensors2 that detect some characteristics of the Electromagnetic Field. The two parts are somehow connected to a central management unit (the System Electronics Unit, the SEU). The information detected by the sensors will be used to deduce the position of a sensor in the 3D-space.
The difficulties I'm facing with, are related to the physics and the logical parts behind the system, and not the software concerns.


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*How does the "source" work?

*What characteristics of the Electromagnetic Field do the sensors detect, and more
importantly, how do they do that?

*What is the fundamental methodology (e.g. time of flight) that the SEU implements for the positional recognition, and how does it work?
To summarize, suppose that I profoundly want to re-create a deadly simple Electromagnetic Position Tracking System. How may I put together a handmade craft of the technology using the essentials? How to do that?
I do have a deep eager to know, so please help me :)

1,2; Disclaimer: The links provided are only to better convey the idea I'm looking for, and that's because the web is really sufferring from the lack of information in this specific field.
 A: There are several categories of technology that can do this sort of thing (and note that there is considerable intellectual property involved):


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*Near-field detection: The sending unit is a simple transmitter. A receiver measures the phase of the magnetic field to the electric field. The closer they are in phase, the farther apart the radios. From this we can draw hollow spheres around a radio indicating possible positions of the other radio. The intersection of multiple spheres tells us the position of the radio in question.

*Absolute time of flight (time of arrival or TOA): Given the absolute time of transmission and of reception between multiple radios, we can draw hollow spheres around certain radios indicating the distance of the radio-in-question from that radio. The intersection of multiple spheres tells us the position of the radio in question.

*Relative time of flight (time difference of arrival, or TDOA): If we don't know the exact transmit time, but the receivers know an exact receive time (or vice versa), then if multiple receivers heard the same transmission, for each pair of receivers we can draw a hyperboloid sheet indicating the possible positions of the radio-in-question. The intersection of multiple hyperboloid sheets is the position of the radio. 
A: The technology was pioneered by Polhemus in the 1970's, and further advanced by Ascension Technology (founded by a pair of former Polhemus employees in the 1990's).
In the simplest form, the "source" is essentially a 3-axis (XYZ) electromagnet, each of which produces a dipole field.
The receiver is a 3-axis (XYZ) magnetic sensor.
In the original Polhemus system the sensor is another (smaller) 3-axis orthogonal coil set, and each source axis is energised at a different frequency - typically in the 5-50kHz range.
Ascension's system used what they called a "switched-DC" arrangement, where the X,Y,Z source-axes were energised time-sequentially (cycling through X,Y,Z  40-50 times/second), and used "DC-sensitive" magnetic field sensors based on flux-gates, rather than coils.
Either way, the receiver-system determines the magnitude and polarity of the signal from each of the XYZ source axes in each of the (call them) UVW receiver-axes. Knowing the physics equations for the magnitude and direction of a dipole magnetic field, in principle you can then do some math to determine the 6DoF position and orientation. For 2D the math isn't too bad, but for 3D it gets quite complicated!
Determining just the absolute distance (radial distance) between source and sensor turns out to be incredibly easy, using Pythagoras on all the received components.
The received magnetic field signal strength is proportional to 1/distance-cubed, so it is inherently a short-range technique.
There is no electric-field sensing. Just think "electromagnet".
The technology has been used for motion tracking for military pilot-head-tracking, immersive gaming, hand-controllers (Sixense / Razer Hydra), and medical needle/catheter tracking during surgery.
It's also now being used in high-end cars to track the location of a wireless keyfob dongle inside or immediately outside the car, keyless entry/start etc.
It's a brilliant application of some basic physics!
