Electromagnetic tracking
Electromagnetic tracking is 3D tracking technology that generates magnetic fields and detects them from a sensor. It is a native technology for 6DOF tracking.
It is also called just "magnetic tracking". It was invented in about 1970 by Polhemus.
Another company that has made electromagnetic tracking devices is Ascension Technologies.
The Magic Leap 1 uses magnetic tracking for its handheld controller, but in a poor form.
Neuralink researched using magnetic tracking at up to 240hz for tracking monkeys' body movements in tests.
Examples of products include the Polhemus FASTRAK.
Sixense was a company that developed products.
Companies
AC magnetic tracking
AC magnetic tracking means "alternating current magnetic tracking". It uses an AC electric current to generate alternating magnetic fields, which are picked up by a tracking sensor.
The fastest electromagnetic tracking system in the world is the Polhemus Viper 16, which tracks up to 960hz. This is much faster than the kalman filtered 100hz or 150hz of all existing consumer VR systems like SteamVR. Magnetic tracking feels better and more natural because it has a higher update rate and preserves high frequency transients in the movement, like a flick of a finger.