a clutch for selective transmission of torque and power , utilizing pairs of coded arrays of permanent magnets affixed respectively to the driving member and the driven member . a shape memory alloy actuator brings to driving member and the driven member into proximity to engage the clutch via a higher - order mutual magnetic correspondence between the coded magnetic regions of the permanent magnet arrays . also provided is a clutch having a magnetorheological fluid between the driving member and the driven member , to increase the torque and power transfer through the fluid when its viscosity is increased by the magnetic field of the arrays in proximity . sets of corresponding teeth on the driving member and driven member mesh when the rotation of the members is synchronized , providing positive direct drive to prolong the service life of the fluid .