Energy Harvesting for Wireless Sensor Nodes Using Rectenna

Introduction

Wireless sensor nodes generally operate using energy from source line batteries which needs to be replaced or recharge from time to time. Connection of electromagnetic energy to DC energy which is called Radio frequency (RF) energy harvesting is one of the best techniques to act as energy source to these equipments. Ambient amount of RF energy is present in our environment radiated from numerous sources so it can act as much predictable source of energy as compared to other techniques of energy harvesting. This system eliminates the periodic replacement of energy batteries for these sensor nodes. Despite the enormous RF energy present in environment, the power per unit area is quite low. Hence, the major barrier is to increase the output of rectifier circuit even though the power density is low.

Different antenna designs are placed forward for higher efficiencies, line dipole, wide band and so on. Circular patch antenna provides higher gain for a given size of an antenna. Though wideband antennas provide higher efficiency by reception of larger amount of RF energy but impedance mismatching and lower output voltage may occur as compared to single band antenna. Diode in the rectifier circuit operates on the basis of frequency and input power levels, hence the rectifying effect of diode have impedance mismatch and lower output voltage in wide band antennas. Hence, to harvest more and more energy from environment, an array antenna is employed in this paper based on superposition of energy from each antenna in the form of exponentials.

The gain of antenna is ratio of intensity of given antenna in given direction to radiation intensity of isotropic antenna.G = ---(1) Where ψ (θ, φ) is intensity of given antenna and ω_r is the power radiated by isotropic antenna.