Theoretical and Experimental Investigation on the Damping Phenomenon Occurring at the Movement of a Permanent Magnet inside of a Conductive Pipe

Abstract

In this work, an experimental and theoretical investigation on the damping phenomenon, occurring at movement of a permanent magnet inside a conductive pipe, is presented. Concretely, a neodymium magnet falling inside of a copper tube is experimentally investigated, and the falling time was measured for various dimensions (diameter and height) of the cylindrical magnet and various dimensions (inner and outer diameters) of the cylindrical pipe. A method to compute the electromagnetic damping coefficient, which does not require the value of the flux density of the magnet, is proposed. Influence of the dimensions of the magnet and pipe, and especially influence of the clearance between the magnet and pipe on the falling time and damping coefficient, is illustrated. During the performed tests, unexpectedly was observed that for certain combinations of the magnet and pipe, the magnet stopped inside the tube, being unable to continue its falling and finally exit the pipe. Such phenomenon, similar to the well-known sticky drawer effect is discussed, and a geometrical condition, to predict its occurrence is proposed.