Tracking Optimal Efficiency of Magnetic Resonance Wireless Power Transfer System for Biomedical Capsule Endoscopy

This paper presents a new method to track the optimal efficiency of a magnetic resonance (MR)-wireless power transfer (WPT) system for biomedical capsule endoscopy. Recently, capsule endoscopy technology has been developed and emerged as an alternative to small bowel endoscopy, gastroscopy, and colonoscopy, all of which cause discomfort to patients because of their relatively large-diameter and flexible cables. However, commercialized capsule endoscopy still suffers from limited battery capacity. This paper presents a theory for tracking the optimal efficiency of an MR-WPT system, along with its experimental verification. An MR-WPT system with a 9-mm-diameter receiver is implemented, which is small enough to fit in the current capsule endoscope. The proposed system improves the efficiency despite variations in the distance, angle, and axial misalignment, with maximum increases of 2.45, 4.69, and 1.48 dB, respectively. Penetrative transfer through biological tissue is demonstrated with a low degradation in efficiency of 0.390 dB. The proposed system was found to have a very low specific absorption rate of 1.74 W/kg, which demonstrated that it is safe to use in the human body.