Optimal Design and Experimental Assessment of a Wireless Power Transfer System for Home-Cage Monitoring

Techniques of long-term in vivo electrophysiological recording play important roles in brain research and neural rehabilitation. To avoid interruption of experiment and risk of infection, use of wireless power transfer (WPT) technique has been suggested to eliminate cumbersome wires and batteries attached to the animals in rodent electrophysiological applications. This paper presents a holistic assessment of the relationships among the physical sizes of the transmitting and receiving coils, power transfer characteristics, and specific absorption rate (SAR) in animals of a simple WPT system using two rectangular coaxial transmitting coils. With given space for the animal and size of the receiving coil, a procedure for designing the minimum driving current, and the transmitting coil dimensions and separation to deliver sufficient power to the receiver, and interactions between the transmitting and receiving coils is derived. A pi-capacitor network that can match the impedances of the receiving coil and the load to operate the receiver at the maximum power transfer condition is proposed. It is also optimized for the overall volume. A 100-mW prototype with an operating zone of 400 x 240 x 40 mm(3) and a receiving coil with a diameter of 11.45 mm is built and studied. The SAR in the animal is evaluated and compared with the recommended restriction level.