A thin, flexible receiving coil for wireless power transmission based on magnetic induction to an implantable device: Measuring the power efficiency of receiving coils with varying numbers of mounted magnetic sheets

Implanted medical devices require wireless power transmission. The wireless system proposed here uses a transmitting coil that could be worn around the waist to send power to a thin, flexible receiving coil located deep in a liquid NaCl solution of 0.25% mass concentration, simulating conditions in the human body. To determine optimal transmission efficiency, we examined receiving coils mounted with varying numbers of magnetic sheets. A maximum transmission efficiency of 19.2% was obtained at 1.8 MHz with no magnetic sheet. The maximum transmission efficiencies of receiving coils mounted with one sheet and two sheets were 12.5% at 1.3 MHz and 4.68% at 0.8 MHz, respectively. Our investigation confirmed that our wireless power transmission system is able to supply power to the microcontroller in the liquid solution.