In vivo validation of Wireless Power Transfer System for Magnetically Controlled Robotic Capsule Endoscopy

TL;DR

This work validates a battery-free, magnetically controlled robotic capsule endoscopy system by integrating a resonant inductive wireless power transfer link with a 3D receiving coil and adaptive load-shift keying control. The transmitter is mounted on the robotic arm’s end effector alongside an external permanent magnet for navigation, while the capsule carries axis-specific receivers and ASICs for rectification and LSK signaling. Laboratory characterization and in vivo porcine trials show reliable power delivery (≈100 mW received power at practical distances) despite coil misalignment and rotation, with SAR safety maintained through adaptive control. The results demonstrate the feasibility of autonomous, battery-free capsule endoscopy with precise magnetic control for realistic gastrointestinal conditions, opening avenues for extended diagnostic capability.

Abstract

This paper presents the in vivo validation of an inductive wireless power transfer (WPT) system integrated for the first time into a magnetically controlled robotic capsule endoscopy platform. The proposed system enables continuous power delivery to the capsule without the need for onboard batteries, thus extending operational time and reducing size constraints. The WPT system operates through a resonant inductive coupling mechanism, based on a transmitting coil mounted on the end effector of a robotic arm that also houses an external permanent magnet and a localization coil for precise capsule manipulation. To ensure robust and stable power transmission in the presence of coil misalignment and rotation, a 3D receiving coil is integrated within the capsule. Additionally, a closed-loop adaptive control system, based on load-shift keying (LSK) modulation, dynamically adjusts the transmitted power to optimize efficiency while maintaining compliance with specific absorption rate (SAR) safety limits. The system has been extensively characterized in laboratory settings and validated through in vivo experiments using a porcine model, demonstrating reliable power transfer and effective robotic navigation in realistic gastrointestinal conditions: the average received power was 110 mW at a distance of 9 cm between the coils, with variable capsule rotation angles. The results confirm the feasibility of the proposed WPT approach for autonomous, battery-free robotic capsule endoscopy, paving the way for enhanced diagnostic in gastrointestinal medicine.

Figures (9)

• Figure 1: Proposed capsule endoscopy with closed loop MCS and 3D inductive WPT system.
• Figure 2: (a) Block diagram of the Wireless Power Transfer System: Tx side with Power Driver and LSK Demodulator, Rx side with 3D coil and ASICs dedicated to AC-DC conversion and LSK modulation. (b) Block diagram of the custom ASIC, with detailed schematic view of the FWR, the programmable oscillator (OSC) and the bootstrap (BST) driver.
• Figure 3: Total and local SAR estimated from 3D electromagnetic simulations (performed with COMSOL Multiphysics software) on a human body model. The TX coil was placed above abdomen and underbelly (at 3 from the skin) and total and local SAR were measured for different amplitudes of the sinusoidal current on the Tx coil at 1.7 MHz.
• Figure 4: (a) Experimental setup of the proposed WPT transmitter. (b) Tx coil and 3D Rx coil connected to the 3 miniaturized PCBs, hosting the capacitive matching network, the modulation capacitance, and the ASIC integrating the rectifier and LSK modulator. (c) Optical micrograph of the ASIC.
• Figure 5: (a) Output power $P_{\rm{OUT-Rx}}$ with and without LSK modulation, at different input power levels $P_{\rm{IN-Tx}}$ and distances $d$ between Tx and Rx coils. (b) Transient behavior of $P_{\rm{IN-Tx}}$ and $P_{\rm{OUT-Rx}}$ resulting from the proposed adaptive control system, in response of continuous variation of $d$.