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Radio frequency (RF) energy harvesting system scavenges energy from electromagnetic waves and supplies power wirelessly enabling the usage of zero-energy sensors or devices. Frequency band of the electromagnetic wave is an important parameter for energy harvesting systems. In this study, simultaneous multiband RF energy harvesting systems are analyzed both theoretically and experimentally for zero-energy devices. An advanced measurement system, which consists of an RF energy harvesting circuit, universal software radio peripherals (USRPs), and other equipment, is established to obtain received power and charging time samples for Industrial, scientific, and medical (ISM) and Global system for mobile communications (GSM) radio bands. The effects of each band and their different combinations on the charging time as well as the conversion parameter are thoroughly investigated for RF energy harvesting. According to a real-life communication scenario, the outage probabilities of wireless zero-energy sensors are presented. It is demonstrated in this study that the use of multiband frequencies in energy harvesting, in addition to the low-power requirement, increases the feasibility of zero-energy devices. [ABSTRACT FROM AUTHOR]

In this study, charging time in RF energy harvesting systems is measured and statistically analyzed. The measurement system is carried out using an RF energy harvesting circuit, transmitters as RF sources, a patch antenna and other auxiliary devices. The RF power signals generated by single, double and triple RF sources are collected wirelessly by the RF energy harvesting circuit at distances from 1 to 5 m at the interval of 0.5 m. Measurement samples for the charging time are recorded and then evaluated. Test of normality using Kolmogorov–Smirnov shows that the measurement samples of the single, double and triple RF sources are not in a normal distribution. Based on Spearman's rho correlation coefficient, it is detected that there is no strong correlation among the measurement samples at different distances for each RF source. Additionally, it is observed that received power distributions of the RF sources match the charging time values. Based on the experimental results, charging time models are proposed for the single, double and triple RF sources. As a result, it is determined that there is a good match between the proposed models and the charging time values. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) energy harvesting as an alternative energy source is an emerging technology that supplies energy for low power wireless devices. In this study, the impacts of RF sources, antenna gains, output power levels and path losses on charging times of an RF energy harvesting system were measured and analyzed in detail. An advanced measurement system that consisted of RF sources used as signal generators, dipole and patch antennas, an RF energy harvesting circuit and the other auxiliary devices were installed for acquiring measurement samples. The generated RF power signals in continuous wave mode at 915 MHz carrier frequency were collected wirelessly by the RF energy harvesting circuit for different antenna gains and output power levels at distances from 20 to 50 cm at the interval of 5 cm. The measurement samples were analyzed statistically. According to the measurement results, it was determined that double RF sources, 6.1 dBi antenna gain and 17 dBm output power level reduced the charging times by 63.09%, 59.24% and 46.41% on average, respectively. [ABSTRACT FROM AUTHOR]