Dispenser Printed Flexible Rectenna for Dual-ISM Band High-Efficiency Supercapacitor Charging

This paper presents a dual-band sub-1 GHz rectenna for near and far-field powering of Internet of Things (IoT) nodes. The rectifier is based on a coplanar waveguide (CPW) voltage doubler with inductive matching, achieving over 80% power conversion efficiency (PCE) at 10 dBm and 915 MHz. The rectifier is designed to directly charge a 6.8 mF supercapacitor with no DC power management circuitry or load tracking, achieving the highest reported average charging efficiency of 47.2% and 33.3%, at 433 and 915 MHz respectively. From 6 dBm input power, a 1.5-2.8 mA dummy load can be RF-powered with over 30% duty-cycle at 915 MHz. A dual-band single-layer antenna is designed and fabricated using dispenser printing on a flexible polyimide substrate. The antenna maintains over 2.1 dBi gain at 915 MHz with omnidirectional patterns, while occupying under 10 × 10 cm. The integrated rectenna is evaluated in two real-world applications: energy harvesting from a 915 MHz transmitter showing a 49% wireless charging efficiency for a $7.4 μW/cm² incident power density; and ambient energy harvesting generating 47 mJ in 5 seconds at 3 to 5 cm from a handheld two-way radio.