Experimental study on stabilizing range extension of diamagnetic levitation under modulated magnetic field

Abstract

The real energy-free levitation can be achieved with the help of diamagnetic materials. The floater for diamagnetic levitation can be a magnet or made of diamagnetic material. The stabilized levitation range of this floater is defined by two parameters: Levitation Stabilizing Range, RS, and Local Range, RL. RS signifies the range (both vertical and horizontal) that floaters of different masses can be stably levitated under a given magnetic field while RL is the maximum range that a floater of a given mass can be deviated from its stabilized levitation position. Regarding to engineering applications, the two levitation parameters, RS and RL, are significant and crucial to the loading and self-rotating performance of a diamagnetic levitation system. For example, the larger the RL, the less the energy dissipated of a self-rotating levitated floater due to the eddy current effect and the larger the RS, the greater the load range of the system can be, i.e. higher application potential. A recently published paper of Cazacu and Stanciulescu carried out a theoretical study of the stabilizing range, RS and RL. It found that both of the ranges could be increased by manipulating the magnetic field gradient, B' and the magnetic field curvature, B" using a stepped shape coil as a field source. The numerical simulation proved that a stepped coil shape with a larger outer diameter at the bottom and a smaller outer diameter at the top could extend the stabilized levitation range. This project furthered the work of Cazacu and Stanciulescu to carry out an experimental study of the shape and geometric effects of the coil or ring magnet stacking arrays on the Local Range, RL. Furthermore, the effects of using electromagnetic coils and permanent magnets were verified by comparing the results to the corresponding standard cylindrical shaped coil or ring magnet. The aim of the project was to find out how the stacked coils or permanent ring magnets of different shapes, layers and forming angles would affect the maximum performance of the RL. Coil stacking arrays of different shapes were constructed with four types of element coils of constant length, constant inner diameter, different numbers of turns and outer diameters. Experiments were carried out with three different overall shapes, namely 'Ascending', 'Descending' and 'Centre-Diverging'. The shape effects on RL were studied with different numbers of coil layers and applied currents. An additional shape 'Centre-Converging' was evaluated when permanent ring magnets were used as the source. A list of ring magnets of different outer diameters with constant thickness, inner diameter and magnetization were chosen as the elements for the magnet stacking array experiment. The experiments from this project produced original data for validating the theory. Besides, it was found that the local stabilizing range, RL, of a given diamagnetic levitation system can only be extended if the coil of uniform shape is replaced by stacked coils of 'Ascending' shape stacked coils with the same total number of coil turns N and overall length L. Other shape types of stacked coil arrays were found reducing the RL comparing to their corresponding standard coils. Similarly, the comparison of the effect of different shapes of permanent ring magnets was made based on a constant volume of the magnets. The results of permanent magnet experiments were depicted that no positive effect on RL could be made by using different forming shapes, use of layers and forming angles.