Inductrack is a passive, fail-safe
A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....

 electrodynamic magnetic levitation
Electrodynamic suspension
Electrodynamic suspension is a form of magnetic levitation in which there are conductors which are exposed to time-varying magnetic fields. This induces currents in the conductors that creates a repulsive magnetic field which holds the two objects apart....

 system, using only unpowered loops of wire in the track and permanent magnets (arranged into Halbach array
Halbach array
A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side...

s) on the vehicle to achieve magnetic levitation
Magnetic levitation
Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields...

. The track can be in one of two configurations, a "ladder track" and a "laminated track". The ladder track is made of unpowered Litz wire
Litz wire
Litz wire is a type of cable used in electronics to carry alternating current. The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz...

 cables, and the laminated track is made out of stacked copper or aluminium sheets.

There are two designs: the Inductrack I, which is optimized for high speed operation, and the Inductrack II, which is more efficient at lower speeds.

Inductrack (or Inductrak) was invented by a team of scientists at Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

 in California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, headed by physicist Richard F. Post
Richard F. Post
Dr. Richard F. Post is an American physicist who has done work in nuclear fusion, magnetic levitation and magnetic bearing design and plasma physics, and winner of the James Clerk Maxwell Prize in Plasma Physics and who holds patents in the fields of nuclear fusion, particle accelerators, and...

, for use in maglev train
Maglev train
Maglev , is a system of transportation that uses magnetic levitation to suspend, guide and propel vehicles from magnets rather than using mechanical methods, such as friction-reliant wheels, axles and bearings...

s, based on technology used to levitate flywheels. At constant velocity, power is only required to push the train forward against air and electromagnetic drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

. Above a minimum speed, as the velocity of the train increases, the levitation gap, lift force and power used are largely constant. The system can lift 50 times the magnet weight.


The name inductrack comes from the word inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...

or inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...

; an electrical device made from loops of wire. As the Halbach magnet array
Halbach array
A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side...

 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 inductance of the coils increases, proportionate to speed, and dominates the impedance of the coils, and this delays the phase of the current peak so that induced current in the track coincides 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.

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
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...

 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
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 (NASA) is also considering Inductrack technology for launching rockets.

General Atomics
General Atomics
General Atomics is a nuclear physics and defense contractor headquartered in San Diego, California. General Atomics’ research into fission and fusion matured into competencies in related technologies, allowing the company to expand into other fields of research...

is developing Inductrak technology in cooperation with multiple research partners.

External links

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