Magnetic Drag Force Research Articles

Magnetic levitation forces—finite conductor size

Magnetic levitation is attracting attention as a practical noncontact suspension system for high-speed guided ground transport. Detailed mathematical analysis of magnetic lift and drag forces for nonidealized practical configurations is, however, difficult. This analysis examines only the effects of finite cross-sectional area of electromagnetic windings. A simple model of the magnetic lift and drag forces acting on a long current-carrying wire moving above and parallel to a thin infinite conducting plane is used. Corrections derived for finite conductor size, in terms of width and height, are shown to be small. Consequently, in practice, coils with finite winding cross sections can justifiably be represented by thin wires at their geometric centers.

Levitation performance of magnetically suspended high speed trains

Analyses have been made of the design parameters which affect the magnetic lift and drag forces on the magnetically suspended very high speed train models of practical interest. In the suspension systems investigated here, the superconducting magnets are installed in the train and the roadbed is equipped with normal-conducting coils. As a result of this investigation, an improved suspension system is proposed, which consists of ladder-type conductor in the roadbed. This new system is investigated theoretically.

Magnetic suspension for levitated tracked vehicles

Magnetic suspension concepts are reviewed to discover their suitability for levitating high speed trains. In the two most promising proposed concepts, the conducting sheet and null flux suspensions, cryogenic d c magnets on the moving train induce currents in a metal track at ambient temperature. The magnetic interaction between the track and train currents can suspend trains weighing 100 000 lb per 100 ft (150 000 kg per 100 m) with track-train clearances of several inches. The two suspensions are critically evaluated with regard to lift capabilities, magnetic drag forces, stability, damping, and cryogenic requirements. The null flux suspension has much lower drag, greater stability, faster damping, but requires substantially more cryogenic equipment. The design, operation, and cost of the proposed train magnets (both super and cryoconducting) is considered. The required field strengths and refrigeration are easily met by current technology. Cryogenic costs are small compared with other system costs. Magnetic propulsion concepts using cryogenic train magnets are also discussed.

Forces on Moving Magnets due to Eddy Currents

A magnet or a current-carrying coil, moving with constant velocity above a conducting plate, will experience magnetic lift and drag forces from the eddy currents induced in the plate. The lift and drag forces are calculated for various coil geometries on the assumption that the conducting plate is thin. For this model, the lift at high speeds approaches the force between the coil and its ``image'' located directly below it, and the drag force falls off as (velocity)−1. The ratio of lift to drag is found to be independent of coil geometry, but the velocity dependence of the lift is greatly affected by the geometry. The ratio of lift to coil weight can be as high as 2000 for a superconducting coil moving at 300 mph at 0.1 m above a conducting plate. The relevance of the calculation to magnetically supported high-speed vehicles is discussed.