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.