Contents I. Introduction
Magnetic manipulation has been widely investigated, since it enables remote and accurate robotic procedures [1], [2]. The utilization of a remote procedure incorporating magnetic manipulation has strong advantages. First, it limits the practitioners’ exposure to hazardous environments (such as X-ray radiation). Second, it enables a more precise procedure since the accuracy of the manipulator is not affected by the practitioners’ hand techniques or proficiency. Third, a battery (or additional power delivery system, including a cable inside the human body) is not necessary for the manipulation. Due to these advantages, manipulation of magnetic robots controlled by magnetic navigation systems (MNSs) is a preferred strategy for remote procedures [3], [4], [5]. Magnetic robots have the potential to perform various practical therapeutic functions in the gastrointestinal (GI) tract, the brain, the eye, and in vasculature [1]. Especially, as occlusive vascular diseases are becoming a major cause of human death in modern society [6], many researchers have developed MNSs and magnetic helical robots (MHRs) as a possible alternative to conventional endovascular intervention [7], [8], [9], [10], [11]. An MHR can be actuated by a rotating magnetic field (RMF) generated by current flowing in the MNS using the robot's helical structure. At times, a high-speed rotational motion of the MHR is required during the tunneling process of the clogged blood vessel. To provide rotational motion robust enough to overcome the friction generated by contact with blood or a clogged lesion, the magnitude of the magnetic torque acting on the MHR must be sufficiently large [12]. In addition, the magnitude of the RMF should be large enough to allow other magnetic robots to perform various therapeutic functions [13], [14].
