Strategies, Techniques and Systems for powering low-maintenance and battery-free devices through Energy Harvesting and Wireless Power Transfer

The purpose of this research has a background in the market for Internet of Things (IoT)devices and wireless sensor networks. The Market Forecast predicts the connection of a trillion"things" by 2025. The global smart sensor market size trend grows from USD 36.6 billion in2020 to USD 87.6 billion by 2025, at a CAGR of 19.0 %. The energy harvesting systems market is worth USD 440.39 million in 2019 with a forecast to reach USD 817.2 million by 2025, at a CAGR of 10.91 %, over the forecast period(2020-2025). In this scenario, to power a trillion node IoT infrastructure would require trillions of batteries which poses maintenance problems and related non-negligible management costs. Indeed, for every trillion nodes installed, 274million batteries would need to be replaced every day, even in the best-case scenario where it is possible to assume that batteries reach their 10-year life expectancy. In this context, this thesis aims to show innovative systems, strategies, techniques, and circuits for powering low-maintenance,energy-autonomous, and battery-free devices. The principal intention is to contribute to the research effort of Wireless Sensor Node (WSN) that is sustainable and needs minimal or no maintenance. More, in particular, it shows how RF wireless power transfer (WPT) with its pervasiveness is, in some practical use cases, a very convenient way to remotely supply wireless nodes, especially when installed in locations difficult to reach. In terms of systems and circuits, this work presents a state-of-the-art, ultra-low-power 2.5µW highly integrated mixed-signal system on chip (SoC), for multi-source energy harvesting(EH) and RF wireless power transfer. The SoC implements an architecture that integrates a high-performance nano-power management, a wide-bandwidth (350 MHz - 2.4 GHz)RF to DCconverter, with low power sensitivity (-22 dBm at 868 MHz) and maximum Power Conversion Efficiency (PCE) (55% at the minimum input power). For the PCE optimization over several operating conditions, the system integrates an innovative ultra-low-power Maximum Power Point Tracking (MMPT) system. The IC integrates an accurate Amplitude-Shift-Keyingand Frequency-Shift-Keying (ASK/FSK) demodulator and digital circuitry to allow over the air configuration of the SoC while powered by an RF power source. The integration of an ultra-low-power asynchronous finite state machine and a programmable logic allow the implementation of several features that render the system versatile and able to deal with different energy sources and use cases with minimal external components. The SoC is fabricated in a0.13µmCMOS technology in a core area of 2.7mm2.vAs for the strategies and techniques, this thesis discusses several innovative methods that aim both to postpone the maintenance interventions of battery-powered nodes over time, and when possible, to cancel the maintenance of the nodes by eliminating the battery. Therefore, it is shown how to power a WSN through energy harvesting and RF wireless power transfer by discussing system architectures and experimental results in detail. One of the presented strategies highlights that the main issue to solve in battery-suppliedWSN is how to reduce or better null standby power consumption. Indeed, while on standby, power management circuits are permanently active and consume unnecessary energy. This work presents an innovative technique based on RF wireless power transfer to null standby power consumption.