Ambient radio frequency energy harvesting featuring antenna with multistage rectifier

The work presented in this thesis focuses on a radio frequency (RF) energy harvesting approach which scavenging energy from RF electromagnetic radiation to generate electrical signal in a real environments. Compared to other alternative energy sources, such as solar and wind, RF energy is the only one that can provide continuous supply of energy regardless days or nights and not affected by bad weather conditions. One of the challenging problems of RF energy harvesting is the low power densities yielded from ambient RF energy. Thus, it is very crucial to design a highly efficient harvester operating at widespread use of RF spectrums. One of the novelty of this thesis is contributes by the investigation of the feasibility of RF energy harvesting in Malaysia, in advance of the harvester design. Through this power density measurements, the scavengeable ambient frequency sources with their associated available RF power level were identified. It is demonstrated that wireless communication systems of GSM 900 (860 – 960 MHz), GSM 1800 (1730 – 1866 MHz) and UMTS (2100 – 2200 MHz) bands provide optimal sources for power harvesting at both measured urban and semi-urban location in Malaysia. The antenna and rectifier circuit are then designed separately prior to their combination and performance assessment. Operated from 1800 MHz up to 2.5 GHz, the proposed RF energy harvester features a broadband antenna and a multistage rectifier in one integrated circuit. Furthermore, the harvester sensitivities are optimized between -30 to -20 dBm, based on the measured available power in the surroundings. The performance of the harvester is investigated by six combination of two rectifiers and three different antennas, tested in both indoor and outdoor environment for dedicated and non-dedicated RF power sources. To further demonstrate the relation between the rectenna polarizations with the capability to harvest the RF energy, a polarization study is conducted. To realize this measurement, a novel simple and broadband circular polarized antenna is proposed. The obtained measurement results are consistent with the power densities measured in power density measurement, where more dc output are obtained in urban areas compared to semi-urban areas. In an urban area, the measurement results indicate the system is capable of harvesting up to 1.8 V dc output from non-dedicated ambient RF energy sources. The dc generated in RF energy harvesting may be less than generated by solar and wind techniques, however it can be significant in the absence of other energy sources.