RF losses due to matching circuits and

RF energy is more available among of all other ambient
energy like solar, water, wind, thermal etc. It is easy and continually
available to scavenge RF power from surrounds like cellular base stations,
Wi-Fi access points, television and radio broadcast stations. The power
transmits from these sources are very high in KW range, but just a little
amount of power is received by the antenna of the receiver. So the wasted
energy can be harvested to produce electricity which will energies the low
power devices. The typical block diagram of RF energy harvesting circuit is
shown in Fig. 1. It consists of a receiving antenna, impedance matching
circuit, rectifying circuit followed by energy storage. Moreover, losses due to
matching circuits and the nonlinearity properties of diode reduce the circuit
performance. Also the antenna distance, line of direction and the presents of
obstacles between the antennas is also a big challenge to scavenge the RF
power. So to reduce the losses of RF energy many approaches has been taken.
Many research works are now going on including antenna design, matching
circuits and optimization of several stages of rectifying circuit with different
types of voltage doubler like Cockcroft-Walton and Dickson voltage multiplier
etc. From the theory of transmission it is proved that if the RF power is
received in high amount and the power conversion efficiency is high then the
output voltage automatically became high. This paper focuses its design on impedance matching
circuit and rectifying diodes that receives RF power from cellular tower in the
range of frequency 900 band(Unlicensed ISM radio electric spectrum) as many
wireless sensor node like mica2mote operated on this frequency range 868/9161
MHz and 915 is the central frequency of this bandwidth. So the design and
simulation is done for this frequency and the defined input range -30dBm to
30dBm. At first section of this paper, ? type matching circuit is designed for
a single stage voltage doubler and then observed the result on the basis of
return loss and power conversion efficiency with respect to the variation of
components values of LC resonant circuit. Then the circuit is designed for five
stage voltage doubler with varying four types of HSMS-X series diode. Then
comparatively better resultant circuit is proposed to design a RF energy
harvesting circuit for low power devices.