Miniaturized Printed Antennas for RF Energy Harvesting Application

Wireless sensors have been used in several daily life applications such as in medical applications, oil and gas exploration, control systems, among many more. One of the big obstacles in using wireless sensors is how to energize them because using batteries in most cases will not be the optimal way due to many factors like the large number of sensors, their high cost and also the inaccessibility of the sensors in some remote locations. One solution is to harvest ambient radio frequency (RF) energy that is being radiated from wireless systems which exist everywhere or to have dedicated wireless sources covering specific geographic location. An RF energy harvesting system consists of an antenna to capture RF waves and a rectifier to convert RF waves to DC power. In this work, two miniaturized dual-band printed antennas are designed to be integrated with small wireless sensors to energize them using RF harvested energy.;A dual band electrically small meander line antenna (MLA) is designed to cover the most known wireless cellular standards such as GSM 900, GSM 1800 and UMTS. The antenna resonates at 915 and 1900 MHz with wide bandwidth at the higher band. The dual band property is achieved by using two different radiators, each of them is responsible for covering one band and a lambda/4 transformer is used to match the antenna at 915 MHz. The MLA is tested for RF energy harvesting operation, then compared with a reference dipole antenna that comes with the Powercast P2110-EVAL-01 kit used to evaluate the amount of energy captured. The reference dipole antenna was able to receive the signal up to 5 meters away from the transmitter while the dual band MLA was able to receive the signal up to 3 meters, noting that the dipole antenna size is 4 times larger than the proposed MLA.;A highly miniaturized dual-band patch antenna is designed to cover two WLAN frequency bands at 2.45 and 5.2 GHz. A 74% miniaturization ratio is achieved by using a shorting post and a novel defected ground structure (DGS). The resultant miniaturization ratio is the highest reported thus far in literature for dual-band patch antennas. Two rectifiers are designed to test the patch antenna RF energy harvesting abilities. An Output DC voltage of 0.9 and 0.4 V is measured across 156 and 185 ? load at 12 and 5 dBm input power at 2.43 and 5.2 GHz, respectively. A 25% and 26.5% conversion efficiency is achieved when the rectifier input power is 12 and 5 dBm at 2.43 and 5.2 GHz, respectively.