Collaboratively Harvesting Ambient Radiofrequency and Thermal Energy

In this paper, an ambient power harvester with a single-diode device is proposed for simultaneously scavenging both radiofrequency (RF) and thermal energy in a mixed and cooperative manner. This cooperative harvesting process is theoretically examined through a proposed model of the diode and then validated by simulation and measurement. In the proposed cooperative power harvester, the harvested dc voltage from a thermal source is used to bias the diode for improving the diode's RF-to-dc power conversion efficiency (PCE). An accurate analytical model of the Schottky diode is developed for specifying the constraining parameters of RF-to-dc PCE and accurately predicting diode's performances in a low RF power range (≤ -25 dBm), respectively. The calculated results are found to be in a good agreement with the simulated ones obtained by the harmonic balance simulator in the advanced design system. For demonstration and validation, the proposed mixed cooperative power harvester is designed and prototyped on the basis of diode SMS7630. A total measured output dc power around 0.8 μW is obtained with an RF-to-dc PCE around 33.4%, when the two injecting power sources at the diode are both -30 dBm. In addition, rectennas with and without a matching network are both fabricated and tested. By eliminating the L matching network, the rectenna is found to offer a higher dc output power. The proposed mixed cooperative power harvester is hoped to find potential real-world applications in an ambient atmosphere with RF coverage and temperature gradient. It not only helps to produce a higher power but also provides a reliable way of improving the resilience of dc power production.