Stable Wireless Power Transfer Using a Novel Omnidirectional Receiver and a Flexible Transmitter for Capsule Robots

Non-invasive capsule robots offer significant advantages for painless gastrointestinal examination. However, with the advancement of capsule robot technology, its energy demand has significantly increased. Due to its compact size, integrating a high-capacity battery remains challenging, often leading to power insufficiency issues. In this paper, we propose a flexible transmitter independent of human body size and a 3-dimensional receiving coil (3DRC) based on flexible PCB. A mathematical model is developed to analyze the relationship between the transmitter and receiver, while a bending model is established to characterize the flexible transmitter coil. Furthermore, two control strategies, the dual-loop control strategy and the single-loop control strategy, are proposed to regulate the output voltage for stable wireless power transfer. Dynamic step response experiments are conducted to compare the performance of the two control algorithms. The stability of wireless charging is first evaluated under static conditions at various positions, followed by dynamic stability tests incorporating different translational velocities and angular rotation speeds. Experimental results demonstrate that at a target voltage of 3300 mV, the mean absolute error is limited to 20.2 mV, corresponding to less than 1% of the nominal voltage, thereby confirming the high regulation accuracy and stable performance of the proposed wireless charging system for capsule robots.