Electromagnetic levitation

Previous work on levitation by induction has involved either iron-cored structures operated at power frequencies or simple coils operating at much higher frequencies. Previous theoretical treatment of the former is oversimplified, whilst analysis of the latter has hitherto been based on the complete solution of the field equations, which results in formulas so complex that problems such as those concerning dynamic stability cannot be attempted. The paper seeks to find a middle course, whereby the techniques of power-frequency systems can be extended to produce improved physical arrangements of primary coils. With regard to analysis, the paper suggests a new technique based on lines of constant phase, which, together with such analogies as the travelling magnetic field and equivalent circuit, can be used to predict qualitatively the behaviour of a variety of systems, including conditions of dynamic stability. The new technique is also applied to a study of the reluctance-start, single-phase induction motor and a homopolar machine. Levitation of spheres, cylinders, circular and rectangular plates is discussed with reference to recent experimental work. The relationship between levitation systems and metal-particle attractors, such as have been developed for optical surgical operations, is discussed. Fundamental limitations relating to the size of object attracted or suspended are discussed. The paper concludes with a brief summary on the suspension of liquid metal.