Dr. Ahmed G. Abo-Khalil

Electrical Engineering Department


The name inductrack comes from the word inductance or inductor; an electrical device made from loops of wire. As a Halbach magnet array passes over the loops of wire, the sinusoidal variations in the field induce a voltage in the track coils. At low speeds the loops are largely resistive impedance, and hence the induced currents are highest where the field is changing most quickly, which is around the least intense parts of the field, thus little lift produced.

However, at speed, the impedance of the coils increases, proportionate to speed, and dominates the composite impedance of the coil assemblies. This delays the phase of the current peak so that induced current in the track tends more closely to coincide with the field peaks of the magnet array. The track thus creates its own magnetic field which lines up with and repels the permanent magnets, creating the levitation effect. The track is well modeled as an array of series L-R, parallel LR-C circuits. A drawing of such a circuit is available in RLC circuit at. The intrawinding capacitance in an Inductrack combines with the low inductance of the large, air-core loops of wire, and is not neglible, increasing the phase shift which obtains with increasing speed, reducing the transition speed.

When neodymium–iron–boron permanent magnets are used, levitation is achieved at low speeds. The test model levitated at speeds above 22 mph, but Richard Post believes that, on real tracks, levitation could be achieved at "as little as 1 to 2 mph". Below the transition speed the magnetic drag increases with vehicle speed; above the transition speed, the magnetic drag decreases with speed. For example, at 500 km/h the lift to drag ratio is 200:1, far higher than any aircraft. This occurs because the inductive impedance increases proportionately with speed which compensates for the faster rate of change of the field seen by the coils, thus giving a constant current flow and power consumption for the levitation.

The Inductrack II variation uses two Halbach arrays, one above and one below the track, to double the magnetic field without substantially increasing the weight or area of the arrays, while also reducing drag at low speeds.

Several maglev railroad proposals are based upon Inductrack technology. The U.S. National Aeronautics and Space Administration (NASA) is also considering Inductrack technology for launching space planes.

General Atomics is developing Inductrak technology in cooperation with multiple research partners.

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