This paper proposes to recover the concept of spherical induction electrical machines to conceive a shell-like actuator with multi-DOF (Degrees-Of-Freedom). The actuator is formed by a shell stator and a spherical rotor. This work contains the feasibility study of that solution when applied as an active joint actuator in assistive devices. Its electromechanical characteristics are first analyzed using an analytic model that includes: the distribution of the magnetic potential vector and thus the components of the magnetic flux density in the airgap due to a sinusoidal current distribution imposed in the stator; the model also shows the induced electromotive forces and associated current density distribution in the rotor; and at last the radial and tangential components of the force density in the rotor. The shell-like actuator is concretized as an active joint for assisting movement of the lower leg of a typical 70kg person. Based on its requirements, the joint actuator electromechanical characteristics are analyzed according to its sensitivity to a set of electrical and mechanical variables.