Hybrid Dual Band Radio Frequency and Solar Energy Harvesting System for Making Battery-less Sensing Nodes

Abstract

In this paper, a highly efficient dual band Radio Frequency (RF) energy harvester is coupled with a solar cell to make a hybrid RF/Solar Energy Scavenging system. The energy harvesting system utilizes a circularly polarized dual band omni directional antenna to receive GSM1800 and Wi-Fi 2400 signals from both sides. A low threshold and concurrent dual band rectifier is designed for RF to DC conversion. Schottky Diode SMS-7630 is used as rectifying element and microstrip lines and stubs based dual band input impedance matching network is used to match the non-linear input impedance of rectifier to the antenna. The antenna has a gain of 3.84dBi at 1.8GHz and 5.45dBi at 2.4GHz. The RF to DC conversion efficiency for a typical input power of -10dBm is 52.1% and 42.1% at 1.85GHz and 2.45GHz respectively. Monocrystalline solar cell SLMD121H10L is used for harvesting solar energy due to its wide spectral sensitivity range and compact size. The cell exhibits open circuit voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> = 6.30V, short circuit current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> = 50 mA and can provide up to 292mW of power under irradiance of 100mWcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The hybrid RF/solar energy harvester produces 192.9μW of DC power which can be utilized in making various battery-less sensing applications.