Energy Harvesting Rectenna Using High-gain Triple-band Antenna for Powering Internet-of-Things (IoT) Devices in a Smart Office

A new rectenna that can be utilized for sending/receiving data and scavenging RF waves for linking and powering Internet-of-Things (IoT) devices is proposed. The rectenna has three operating frequency bands; the lower frequency band is used for energy harvesting, and the other two frequency bands are assigned for data communication. It comprises a stacked four-layer antenna integrated with a voltage doubler rectifier. The antenna consists of a driven element, a planar reflector, and a planar director composed of a periodic structure of a square patch with a hexagonal slot in its center. The measurement results show that the proposed antenna covers 1.86 – 2.65 GHz, 2.84 – 3.64 GHz, and 5.34 – 6 GHz with impedance bandwidth of 35%, 24.7%, and 11.64%, respectively. The antenna exhibits a high measured gain of 8.1, 8.9, and 9 dBi at 2.3, 3.5, and 5.7 GHz, respectively. The Industrial, Scientific and Medical (ISM) 2.45 GHz frequency band is selected for energy harvesting. Moreover, specific absorption rate (SAR) calculations are done for the antenna using the Hugo model to ensure lower absorption operation. The proposed antenna provides acceptable values of SAR; the values are under the safety standard limits for Radio frequency (RF) exposure. Then, a rectifier circuit is designed, fabricated, and tested separately. Finally, the rectifier is integrated with the proposed enhanced-gain antenna to produce a rectenna system. The rectenna presents a power conversion efficiency (PCE) of 69.7% and a DC output voltage of 1.9V at an input power of 2 dBm. PCE of the proposed rectenna is over 50% at a range of input power from –6.5 dBm to 4.7 dBm.