For low input radio frequency (RF) power from −35 to 5 dBm, a novel quad-band RF energy harvester (RFEH) with an improved impedance matching network (IMN) is proposed to overcome the poor conversion efficiency and limited RF power range of the ambient environment. In this research, an RF spectral survey was performed in the semi-urban region of Malaysia, and using these results, a multi-frequency highly sensitive RF energy harvester was designed to harvest energy from available frequency bands within the 0.8 GHz to 2.6 GHz frequency range. Firstly, a new IMN is implemented to improve the rectifying circuit’s efficiency in ambient conditions. Secondly, a self-complementary log-periodic higher bandwidth antenna is proposed. Finally, the design and manufacture of the proposed RF harvester’s prototype are carried out and tested to realize its output in the desired frequency bands. For an accumulative −15 dBm input RF power that is uniformly universal across the four radio frequency bands, the harvester’s calculated dc rectification efficiency is about 35 percent and reaches 52 percent at −20 dBm. Measurement in an ambient RF setting shows that the proposed harvester is able to harvest dc energy at −20 dBm up to 0.678 V.
This article proposes a quad-band multiport harvester that can scavenge ambient radio frequency (RF) energy of available frequency bands (i.e. GSM-900, GSM-1800, 3G and Wi-Fi) efficiently. This design's novelty is the use of frequency-dependent multiple antenna ports that enables the harvester to fully exploit all available frequency bands, spatial diversity, and polarization for maximizing the harvested RF energy at a lower power density level in an ambient environment. Indistinctly, the proposed antenna consists of 8-port which maintain 0.33λ × 0.33λ (i.e. wavelength λ calculated at 0.9 GHz in free space) average area per port and has achieved more than 35% relative bandwidth (BW) with a maximum gain of 6.5 dBi to cover the selected frequency bands. Besides, the proposed quad-band rectifier with a multi-stub impedance matching network is feasible for RF harvesting over the available ambient frequency bands. The proposed rectenna's measurement results show that the generated average dc output voltage is increased up to 0.750 V at a low RF input power density of -27 dBm for a load resistance of 2.11 kΩ. The overall dc rectification efficiency of the 8-port pixel harvester is also assessed and depicted to be 66.52% when the resultant RF input power density level is -27 dBm. Measurement in an ambient outdoor and controlled indoor environment is also conducted, demonstrating that the new 8-port pixel RF harvester can produce a dc output voltage of 0.797 V which is greater than some of the reference RF harvesters.
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