As the use of low-power wireless devices for remote sensing is increasing day by day, radio frequency (RF) energy harvesters (RFEHs) provide a viable source of energy for microelectronic devices including wireless sensor networks and internet of things. The electromagnetic waves of RF energy sources, radiating in different frequency bands, are ubiquitous and available even in inaccessible places. However, the efficiency of an RFEH has been a major concern for years due to the low level of ambient RF power-density that varies between 0.2 nW per square cm and 1 µW per square cm. Among the building blocks of a typical RFEH system, the rectenna (integrated rectifier and antenna) plays the most important role in determining the efficiency of the entire system. Studies on the rectenna efficiency at low ambient power levels show that the theoretical maximum power conversion efficiency (PCE) of a rectenna ranges from 12% at 25 dBm (0.003 mW) input to 80% at 0 dBm (1 mW) input at 2.45 GHz. The rectenna becomes significantly inefficient below 25 dBm and the PCE goes to almost zero around 30 dBm (0.001 mW) at 2.45 GHz. Therefore, state-of-the-art technology demands for developing a broadband and efficient RFEH system with high rectenna PCE to overcome the current limitations of energy harvesting in low RF incident power regions. This paper presents an RF energy harvesting system with a multiband antenna configuration that can harvest energy at the frequency range of GSM-900 band to sub-6 GHz band. The performance of the RFEH system is studied from 25 dBm to 0 dBm input power levels underlying the maximization of the overall efficiency and possible optimization strategies. The maximum achievable PCE is formulated as a mathematical programming problem and solved by optimizing the design factors including antenna geometry, operational frequencies, rectifier topologies, and rectifier parameters. An array of broadband high gain patch antennas with reconfigurable rectifiers, an impedance matching network, and a voltage-doubler circuit are employed in the system to maximize the PCE. The voltage standing wave ratio (VSWR) and reflection coefficient (S11) of the antenna are estimated and optimized by numerical method. Simulations are conducted to evaluate the performances of the rectenna and the voltage-doubler circuit. Results for radiation pattern, wave absorption, input impedance, voltage, and power across the load resistance as a function of frequency are obtained for the optimized configuration. The overall efficiency of the RFEH is measured at various power inputs and load resistances. Finally, the validation of the numerical model is performed by comparing the numerical power output with the experimental results.


A Multiband RF Energy Harvesting System for Efficient Power Conversion

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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