A battery-less Internet of Things (IoT) offers a sustainable alternative to battery-powered IoT devices, which produce billions of dead batteries every year. Devices are instead powered by a small supercapacitor, which is recharged by a renewable energy source. However, since IoT devices are often characterized by intermittent periods of high energy consumption followed by periods of reduced activity, conventional average energy consumption models can not be used to assess if an IoT devices can be powered by energy harvesters. Therefore, this paper presents an alternative feasibility evaluation approach that focuses on modeling the worst-case periods with peak energy consumption and short idle times, which pose the highest constraints on the capacitor's behavior. This approach simplifies the characterization of the wireless technology energy consumption as these worst-case periods can be determined by a few parameters. The methodology is then applied to combinations of popular IoT technologies (LoRaWAN, BLE Mesh, and 6TiSCH) and energy sources (solar, kinetic, and radio frequency energy) for two common IoT use cases. We show that the proposed parameters can be successfully extracted with power measurements for different network configurations and that the Power Management Unit configuration has a non-negligible impact on the communication requirements. Finally, we discuss how to apply the model to other technologies and other use cases.
This paper presents novel insights and a new method for improving indoor light energy harvesting for Internet of Things (IoT) applications using a photovoltaic (PV) panel. The concept is based on enhancing the rectifying performance of the intrinsic diode of the PV panel using a high peak-to-average power ratio (PAPR) light waveform. Improving techniques for rectifying systems are well established in the radiofrequency (RF) community but are applied to a light-based system in this paper. A system model is presented to justify the used method. We prove that only a pulse-width modulation (PWM) signal can enhance the energy harvesting at the PV panel. We designed a light-emitting diode (LED) driver and measured the received power to evaluate our concept. For a constant power of the light source, the PWM waveform achieved a 28.8% improvement of the received power compared to a continuous direct current (DC) light source.
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