A magnetorheological fluid clutch apparatus comprising: a stator adapted to be connected to a structure, the stator having at least an annular wall; a first rotor rotatably mounted to the stator, the first rotor having at least one first shear surface; a second rotor rotatably mounted to the stator for rotating about a common axis with the first rotor, the second rotor having at least one second shear surface opposite the at least one first shear surface, the shear surfaces separated by at least one annular space; magnetorheological fluid in an MR fluid chamber including the at least one annular space, the MR fluid configured to generate a variable amount of torque transmission between the rotors (20, 40) when subjected to a magnetic field; at least one coil actuatable to deliver a magnetic field through the MR fluid, the magnetic field following a path comprising the at least one first shear surface and the at least one second shear surface; wherein one of the rotors (20, 40) is adapted to be coupled to a power input and the other of the rotors (20, 40) is adapted to be connected to an output whereby actuation of the at least one coil results in a variation of torque transmission between the rotors (20, 40) the apparatus being characterized in that: an inner magnetic core and an outer magnetic core with an annular cavity therebetween receive the annular wall of the stator, the inner magnetic core and the outer magnetic core being connected to at least one of the rotors (20, 40) to rotate therewith so as to be rotatably mounted to the stator; outer and inner fluid gaps (34A, 34B) are between the inner magnetic core and the annular wall, and between the outer magnetic core and the annular wall, the outer and inner fluid gaps (34A, 34B) being filled with at least one fluid; and the coil is supported by the annular wall and actuatable to further deliver the magnetic field through the MR fluid, the magnetic field following a path further comprising the annular wall, the outer fluid gap, the outer magnetic core, the inner magnetic core and the inner fluid gap. a stator adapted to be connected to a structure, the stator having at least an annular wall; a first rotor rotatably mounted to the stator, the first rotor having at least one first shear surface; a second rotor rotatably mounted to the stator for rotating about a common axis with the first rotor, the second rotor having at least one second shear surface opposite the at least one first shear surface, the shear surfaces separated by at least one annular space; magnetorheological fluid in an MR fluid chamber including the at least one annular space, the MR fluid configured to generate a variable amount of torque transmission between the rotors (20, 40) when subjected to a magnetic field; at least one coil actuatable to deliver a magnetic field through the MR fluid, the magnetic field following a path comprising the at least one first shear surface and the at least one second shear surface; wherein one of the rotors (20, 40) is adapted to be coupled to a power input and the other of the rotors (20, 40) is adapted to be connected to an output whereby actuation of the at least one coil results in a variation of torque transmission between the rotors (20, 40) the apparatus being characterized in that: an inner magnetic core and an outer magnetic core with an annular cavity therebetween receive the annular wall of the stator, the inner magnetic core and the outer magnetic core being connected to at least one of the rotors (20, 40) to rotate therewith so as to be rotatably mounted to the stator; outer and inner fluid gaps (34A, 34B) are between the inner magnetic core and the annular wall, and between the outer magnetic core and the annular wall, the outer and inner fluid gaps (34A, 34B) being filled with at least one fluid; and the coil is supported by the annular wall and actuatable to further deliver the magnetic field through the MR fluid, the magnetic field following a path further comprising the annular wall, the outer fluid gap, the outer magnetic core, the inner magnetic core and the inner fluid gap. an inner magnetic core and an outer magnetic core with an annular cavity therebetween receive the annular wall of the stator, the inner magnetic core and the outer magnetic core being connected to at least one of the rotors (20, 40) to rotate therewith so as to be rotatably mounted to the stator; outer and inner fluid gaps (34A, 34B) are between the inner magnetic core and the annular wall, and between the outer magnetic core and the annular wall, the outer and inner fluid gaps (34A, 34B) being filled with at least one fluid; and the coil is supported by the annular wall and actuatable to further deliver the magnetic field through the MR fluid, the magnetic field following a path further comprising the annular wall, the outer fluid gap, the outer magnetic core, the inner magnetic core and the inner fluid gap.