Magnetorheological fluid clutch apparatus with low permeability drums

A magnetorheological fluid clutch apparatus comprising:

• at least one input adapted to be coupled to a torque input, the input having at least one input shear surface;
• an output rotatably mounted about the input for rotating about a common axis with the input, the output having at least one output shear surface, the input shear surface and the output shear surface separated by at least one annular space;
• magnetorheological fluid in the at least one annular space, the magnetorheological fluid configured to generate a variable amount of torque transmission between the input rotor and output rotor when subjected to a magnetic field;
• and
• at least one electromagnet configured to deliver a magnetic field through the magnetorheological fluid, the electromagnet configured to vary the strength of the magnetic field;
• whereby actuation of the electromagnet results in torque transmission from the input to the output,
• wherein at least one member defining the at least one of the shear surfaces is made of a low-permeability material.