|The output disk/shaft does not touch the rotor. The gap in between is filled with a fine, dry stainless steel powder.
The powder is free flowing, until a magnetic field is applied from the stationary coil. The powder particles form chains along the magnetic field lines, linking the disk to the rotor.
The torque transmitted from input shaft to the output shaft is proportional to the magnetic field strength, and therefore to the applied D.C. input current.