Study of a wireless power transmission system for an active capsule endoscope

Background An active capsule endoscope (ACE) will consume much more energy than can be power by batteries. Its orientation and position are always undetermined when it continues the natural way down the gastrointestinal track. Methods In order to deliver stable and sufficient energy to ACE safely, a wireless power transmission system based on inductive coupling is presented. The system consists of a Helmholtz primary coil outside and a multiple secondary coils inside the body. The Helmholtz primary coil is driven to generate a uniform alternating magnetic field covering the whole of the alimentary tract, and the multiple secondary coils receive energy regardless of the ACE's position and orientation relative to the generated magnetic field. The human tissue safety of the electromagnetic field generated by transmitting coil was evaluated, based on a high-resolution realistic human model. Results At least 310 mW usable power can be transmitted under the worst geometrical conditions. Outer dimensions of the power receiver, 10 mm diameter x 12 mm; transmitting power, 25 W; resonant frequency, 400 kHz. The maximum specific absorption rate (SAR) and current density of human tissues are 0.329 W/kg and 3.82 A/m(2), respectively, under the basic restrictions of the international Commission on Non-ionizing Radiation Protection (ICNIRP). Conclusions The designed wireless power transmission is shown to be feasible and potentially safe in a future application. Copyright (C) 2010 John Wiley & Sons, Ltd.