Regulating 3D Magnetic Flux Density for Stable Wireless Power Transfer in a Compact Planar Charger for Capsule Endoscopy

Wireless charging for small electronic devices remains a significant challenge, especially for applications that demand high-performance operation, such as wearable electronics and medical devices. Many compact devices, including smartwatches and capsule endoscopes, often suffer from limited battery life and frequent recharging requirements. To address these issues, this paper proposes a compact, planar, omnidirectional wireless power transmitter implemented on a multilayer printed circuit board. The proposed design achieves stable wireless charging across varying positions and orientations while maintaining a portable form factor that enables convenient use in diverse settings. To mitigate control challenges arising from overlapping transmitter coils in the planar configuration, a current source inverter is integrated with an LCCL compensation network. Comprehensive mathematical modeling is developed to provide design insights, and the system performance is further validated through computer simulations. In addition, we propose a robust wireless charging algorithm that maintains stable performance under arbitrary spatial positions and orientations, as evidenced by experimental tests demonstrating a mean receiving current fluctuation of only 2.16 mA. Moreover, in capsule endoscopy scenarios, the system achieved an effective charging performance with a maximum transmission power of 1904.4 mW, underscoring its competitiveness with current state-of-the-art designs.