Energy Harvesting Solution for Wireless Sensors in IoT Applications

Abstract

Internet of Things (IoT) is applied for connecting physical devices with the internet using wireless sensors. Consequently, the IoT sensors can be fixed or buried in hard-to-reach areas. Primary batteries (non- rechargeable batteries) are used to power sensors instead of the complex wire cables. However, non- rechargeable batteries only are not the ideal solution for powering the IoT sensors due to their essential replacement after a certain time. Therefore, energy harvesting in conjunction with rechargeable batteries or supercapacitors should be applied to store the harvested energy and deliver the power to the IoT sensors besides to the non- rechargeable batteries. Different opaque, transparent antennas single element and arrays are designed, fabricated, measured and applied for radio frequency energy harvesting (RF-EH). Moreover, an indoor, outdoor survey on the RF spectrum at different locations and time slots are presented for determining the frequencies of maximum ambient radio frequency power. A 2×2 opaque linearly polarized antenna array with high gain is introduced for increasing the amount of the harvested power at low level of energy density. However, the environment of indoor and outdoor causes multipath effects which makes a depolarization of the received ambient waves. This leads to decrease the efficiency of the energy harvesting system because the received EM waves have unknown angle of incidence. This problem is handled by designing opaque dual linearly polarized antenna array with simple and low-profile structure to be suitable for radio frequency energy harvesting. Furthermore, different rectifier circuits are implemented in order to convert the received ambient AC power to DC power for charging the IoT sensors batteries. Two different Schottky diodes of HSMS 2850 and SMS 7630 are used to design rectifier circuits. All the proposed antennas are integrated with rectifiers, matching circuits and tested.