As a result of the limited available energy, RF- powered devices must be capable of efficiently utilizing scarce energy by planning task execution according to the current harvested energy. However, the energy utilization efficiency is challenging to be improved in RF-powered devices, since sensing the harvested energy consumes a significant amount of energy that should be used for task execution.
In this study, we propose Sentinel, a novel low power method to sense the harvested energy. Sentinel is fully delegated to detect the energy for the device, while the device does not participate in the energy sensing. By this means, the computing overhead of the device is reduced. Sentinel works with low energy consumption, and functions as a trigger to activate the device when, and only when, the energy reaches an expected energy threshold. We also present a lightweight scheme to set the desired thresholds so that Sentinel achieves detecting any expected thresholds. We implement Sentinel by off-the-shelf components and conduct experiments to show that Sentinel consumes only 5.2% of energy overhead of the general energy sensing technique. With Sentinel, we show that the energy utilization efficiency can be improved up to 94.9%, outperforming the best existing works at 64.7% in the WISP platform.

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