Short-Distance Wireless Power Transfer Based on Microwave Radiation via an Electromagnetic Rectifying Surface

Microwave power transmission has traditionally been used for long-distance applications so far. For the first time, we experimentally demonstrate efficient short-distance wireless power transfer based on microwave radiation. To overcome the directivity deterioration of an antenna as the transfer distance decreases in the near field, an electromagnetic rectifying surface is proposed for reflection-less microwave reception and rectification. The rectifying surface is an array of metamaterial particles integrated with rectifiers, as a whole its impedance engineered to match with free space. Therefore, it keeps fully receiving the radiated power in the near field of a transmitting antenna without reflection; and maximally converts it into direct current. A rectifying surface of 14 × 14 unit cells is fabricated, and a short-distance wireless power transfer system is developed. Under an input power up to 45 dBm at 2.45 GHz, the measured transmission efficiency (from the microwave input to the direct current output) reaches 52.3%, 52.5%, 47.9%, and 41.7% over a distance of 5, 10, 15, and 20 cm, respectively. Even when the incident angle severely deviates to ±52.5° on E- and H-plane, the transmission efficiency over distance 15 cm merely declines 12% and 22.2% at most, respectively. The presented wireless power transfer based on microwave radiation via an electromagnetic rectifying surface provides a highly efficient and distance/angle-alignment insensitive alternative to the common coupling-based coil solution for short-distance applications.