Development of a Near-Field Wireless Power Transfer System for Controlling Electronic Motors within Capsule Endoscopes

Tethered endoscopic procedures have traditionally been used to study and perform minimally invasive surgeries in the gastro-intestinal (GI) tract but have drawbacks relating to patient discomfort and their inability to explore much of the small intestine. The advent of ingestible capsule endoscopes (CE) has allowed many of these drawbacks to be addressed. However, CE are still unable to reliably perform actions such as tis- sue/microbiota sample collection or microsurgery within the gut [1]. Such applications will require CE to be equipped with small, safe, and wirelessly controllable actuation mechanisms. Miniature electronic motors have previously been used to achieve actuation within CE [2-4]. While the high torque and repeatable motion of electronic actuators are advantageous, complex logic and communication circuitry are often required to control them. Furthermore, the internal batteries which power the motors raise concerns relating to their size, safety, and lifetime [4]. This work presents a near-field wireless power transfer (WPT) system and circuit for controlling electronic DC motors in CE without the need for batteries or complex circuitry. The WPT system works on the principle of magnetic inductive coupling under resonant conditions between a transmitter (Tx) coil external to the pa- tient’s body and a receiver (Rx) coil internal to the capsule (Fig. 1). A means of reversing the motor was developed using an H-bridge of reed switches which can be actuated by the application of a DC magnetic field. The maximum operating distance between Rx and Tx coils which allowed successful actuation of a motor was characterised. Fig. 1(a-d) show an example of how the system could be employed in a multi-capsule assembly for collecting and storing a site-specific sample of microbiota to aid in the early diagnosis of disease [5].