Bipolar concentric-loop midfield transmitter for high-performance wireless power transfer to biomedical implants

In this paper, we propose a bipolar concentric-loop midfield transmitter (BCL-Tx) for wireless power transfer (WPT) to deep-tissue biomedical implants. A midfield plane using multiple semi-circular loops is investigated to generate a strong magnetic field inside human tissue. A simple feeding method is implemented to achieve field focusing characteristics without using multiple excitation ports. Furthermore, an impedance matching network (IMN) and a compensation plane are analyzed to match antenna impedance to source impedance and improve power transmission efficiency. In order to verify the BCL-Tx performance, an implantable receiver (Rx) is fabricated, whose operation principle is nearly the same as the BCL-Tx. Experimental results show that the transmission coefficient achieves a maximum transmission coefficient of -16dB at a distance of 20mm, which is relatively high compared to the previous midfield Tx source using the multiple-ports excitation method.