Apparatus and method for magnetizing a shaft circumferentially

An apparatus and method for magnetizing at least one region of a shaft 2 in a circumferential direction comprises applying electrical current to a shaft 2 such that it passes along the axis of the shaft. Conductive tubes 74, 76 and conductive contact assemblies 70, 72 may be used to apply the current via certain exterior circumference regions of a shaft such that a predetermined portion of the shaft is subject to a predetermined circumferential magnetic polarisation depending on the direction of the current flow. The shaft 2 may be a hollow or solid shaft. The apparatus may be arranged to provide a number of adjacent shaft portions with different circumferential magnetic polarisation directions. The conductive tubes 74, 76 and/or the contact assemblies 70, 72 may include diamagnetic or paramagnetic materials such as copper, bismuth, lead, mercury or aluminium, magnesium, titanium and tungsten. The current supplied may be from a single high-intensity capacitive or inductive pulse source. The apparatus and method may be used to magnetise magneto-elastic shafts used in torque detection and control arrangements.