Reconfigurable Magnetic Field Shaping via Current-Controlled Relay Coils for Wirelessly Powering Capsule Endoscopy

Wireless power transfer (WPT) for wireless capsule endoscopy (WCE) extends the operation time by replacing the capacity-limited on-board batteries with a receiver for a continuous power supply. However, the magnetic field pattern is usually fixed once the transmitting (Tx) coil is determined. Due to the uneven dwelling time of the capsule along the gastrointestinal tract, the desired charging region may vary in different practical scenarios. Under existing Tx configurations, such variation is mainly accommodated by adjusting the overall field intensity rather than the spatial field distribution, which may cause unnecessary magnetic exposure outside the target region. To address this limitation, a relay-based reconfigurable magnetic-field-shaping method is proposed to enable switching between the axial-dominant mode and the radial-dominant mode without rewinding the coil. Specifically, an analytical relay-based current-control method is formulated by parametrizing the Tx coil array, and the desired field pattern is realized through joint optimization of the array variables. In addition, field uniformity and electromagnetic exposure are compared with representative existing designs under unified conditions. Experimental results show that the proposed design achieves measured current ratios of 0.705 and 0.509 for the axial-dominant and radial-dominant modes, corresponding to measured field uniformities of 88% and 75.3%, respectively.