Study on the magnetic self-levitation of the ring permanent magnet with inserted inner cores in ferrofluid

Abstract

The self-levitation of a magnetized object composed of ring permanent magnet, soft magnetic pure iron core (Fe-core), and nonmagnetic aluminum core (Al-core) in ferrofluid (FF) is studied, and the focus is the influence of Fe-core (Al-core) on the magnetic fluid levitation force (MFLF) received by the immersed magnetized object. The formula for calculating MFLF is derived focusing on the gas–liquid and solid–liquid boundary interface between FF and surroundings, and experiments have been done to study the dependence between MFLF and the levitation height of the magnetized object and mass of FF. Researches show that Fe-core has a significant influence on MFLF, and the influence is determined by the magnetization of Fe-core and the distance between Fe-core and the boundary interface. In a word, the use of Fe-core is beneficial to obtain a smaller MFLF, the greater the magnetization of the Fe-core is and the closer it is to the boundary interface of FF, the smaller the MFLF is. The Fe-core near the bottom surface of the ring magnet tends to reduce the maximum MFLF corresponds to an approximate horizontal gas–liquid boundary interface when the levitation height is constant, and the Fe-core near the top surface of the ring magnet is more likely to reduce the change of MFLF caused by the disappearance of surface instability of FF. Or, in other words, the Fe-core near the top surface of the ring magnet tends to reduce the MFLF when magnetized object moves upward, and vice versa.