This article describes a novel rectifying-antenna design with extended input power range operating at 2.4 GHz for both ambient wireless energy harvesting and wireless power transmission (WPT) systems. The rectenna consists of a 2 × 2 fractal antenna array and a rectifier circuit with a high-power conversion efficiency (PCE) in a wide input power range. This circuit contains two conversion stages based on two different Schottky diodes, and a third stage that dissipates the unconverted input power, which can disturb the harvesting process. These three stages are controlled by a power management block based on circulators, that direct the input power to the adequate stage according to its power range. A prototype of the proposed harvesting system is fabricated and experimentally validated. The measurement results confirm the wide input power range behavior of the designed rectenna with a relatively constant and high PCE (between 58% and 67%) for a power density ranging from 4 to 252 μW/cm 2. The proposed solution can be successfully used for both ambient energy harvesting and WPT systems.
This paper describes a wireless power transfer (WPT) system operating at 2.4 GHz, which is based on waveform optimization technique and a wide input power range rectifier. This latter consists of an RF-to-dc power conversion circuit based on circulators. The waveform optimization is then applied in order to enhance the power conversion efficiency at very low input power levels. The proposed WPT system was prototyped and tested in open and closed loop configurations with different types of obstacles placed between the transmitter and the receiver. The generation of power-optimized waveforms and the control process in the closed loop configuration were carried out using software-defined radio. The obtained experimental results validate the wide input power behavior of the two proposed WPT systems especially when dealing with very low input power levels and relatively dynamic environments. In fact, for the two WPT systems featured a distance of 1 m and a transmitted power of 50mw, dc power levels of about 38 and 11 μW are harvested in the cases of no obstacle and low attenuation obstacle respectively.
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