Large torsional rotation and rotational inversion coupling with linear deformation of electromechanical actuators based on conductive micro-/nano-helices

A great variety of electrically conductive micro-/nano-helices provide the unique interconversion of torsional rotation and linear deformation, which makes them the excellent elements as electromechanical actuators in artificial muscle. In this paper, a comprehensive theory has been constructed for quantitatively analyzing the electromechanical properties involving coupled torsional rotation and linear deformation of the close packed and non-close packed electrically conductive helices with the aid of the concept of Cosserat curve. The distributed force in our model can be used to describe the resultant electromagnetic force and the internal pressure on the current carrying helices, which agree well with the experimental results. It is revealed that if the designers intend to realize the mechanical actuation of coupled rotational inversion and large axial contraction, they can choose the close packed conductive micro-/nano-helices; while if they want the much larger torsional stroke of unwinding during the contraction process, the non-close packed ones will be a good choice. The currents make both kinds of helices stronger, and decreasing helix angle is an additional option for the non-close packed ones. The present study supplies a reliable theoretical reference for further experimental research on the applications of conductive helices in micro-/nanoelectromechanical systems.