Advanced Techniques for Powering Wireless Sensor Nodes through Energy Harvesting and Wireless Power Transfer

This paper presents three different techniques for efficiently powering an energy-autonomous wireless sensor (EAWS) through both energy harvesting (EH) and RF wireless power transfer (WPT). The aim of the paper is to provide effective strategies and techniques to reduce, as far as possible, the cost of wiring of the automotive production process due to the continuous and constant increase in the use of sensors. The techniques employ a highly integrated state-of-the-art, ultra-low power 2.5 mu W system-on-chip (SoC) system, designed for multi-source RF wireless energy harvesting and power transfer and are designed with the goal of minimizing and, where possible, eliminating the costly maintenance required by conventional wireless sensors. Specific examples are reported that define both the aspects of convenience and the limits of use.

Ultra Low-Power Frequency Synthesizers for Duty Cycled IoT radios

Raghavasimhan Thirunarayanan

Internet of Things (IoT), which is one of the main talking points in the electronics industry today, consists of a number of highly miniaturized sensors and actuators which sense the physical environment around us and communicate that information to a central information hub for further processing. This agglomeration of miniaturized sensors helps the system to be deployed in previously impossible arenas such as healthcare (Body Area Networks - BAN), industrial automation, real-time monitoring environmental parameters and so on; thereby greatly improving the quality of life. Since the IoT devices are usually untethered, their energy sources are limited (typically battery powered or energy scavenging) and hence have to consume very low power. Today's IoT systems employ radios that use communication protocols like Bluetooth Smart; which means that they communicate at data rates of a few hundred kb/s to a few Mb/s while consuming around a few mW of power. Even though the power dissipation of these radios have been decreasing steadily over the years, they seem to have reached a lower limit in the recent times. Hence, there is a need to explore other avenues to further reduce this dissipation so as to further improve the energy autonomy of the IoT node. Duty cycling has emerged as a promising alternative in this sense since it involves radios transmitting very short bursts of data at high rates and being asleep the rest of the time. In addition, high data rates proffer the added advantage of reducing network congestion which has become a major problem in IoT owing to the increase in the number of sensor nodes as well as the volume of data they send. But, as the average power (energy) dissipated decreases due to duty cycling, the energy overhead associated with the start-up phase of the radio becomes comparable with the former. Therefore, in order to take full advantage of duty cycling, the radio should be capable of being turned ON/OFF almost instantaneously. Furthermore, the radio of the future should also be able to support easy frequency hopping to improve the system efficiency from an interference point of view. In other words, in addition to high data rate capability, the next generation radios must also be highly agile and have a low energy overhead. All these factors viz. data rate, agility and overhead are mainly dependent on the radio's frequency synthesizer and therefore emphasis needs to be laid on developing new synthesizer architectures which are also amenable to technology scaling. This thesis deals with the evolution of one such all-digital frequency synthesizer; with each step dealing with one of the aforementioned issues. In order to reduce the energy overhead of the synthesizer, FBAR resonators (which are a class of MEMS resonators) are used as the frequency reference instead of a traditional quartz crystal. The FBAR resonators aid the design of fast-startup oscillators as opposed to the long latency associated with the start-up of the crystal oscillator. In addition, the frequency stability of the FBAR lends itself to open-loop architecture which can support very high data rates. Another advantage of the open-loop architecture is the frequency agility which aids easy channel switching for multi-hop architectures, as demonstrated in this thesis.

EPFL2016

Speed detection of battery-free nodes based on RF Wireless Power Transfer

Catherine Dehollain, Roberto La Rosa

In the Internet of Things (IoT) era, Wireless Sensor Networks (WSNs) are rapidly increasing in terms of relevance and pervasiveness thanks to their notable real-time monitoring performance across several fields, including industrial, domestic, military, biomedical, commercial, environmental, and other sectors. A highly attractive implementation of WSNs is asset tracking with accurate data regarding the location and transportation conditions of goods, equipment, and the like. One highly promising application of WSNs along these lines is the remote speed monitoring of goods, ideally with battery-free sensor nodes that do not require any maintenance. This, however, represents a major challenge in power supply management. The goal of this paper is to investigate Radio Frequency (RF) Wireless Power Transfer (WPT) architecture to power a battery-free measurement system with time-domain readouts, for the speed detection of a moving sensor tag within a Wireless Sensor Network infrastructure. The performance characteristics and key features of a System-on-Chip (SoC) specifically designed to power a node through RF WPT will be discussed. The aim is to provide a strategy and a model to estimate the speed of a specific battery-free sensor that is powered by a transmitting hot-spot. Specific tests and experimental results are provided.

IEEE2020

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

Roberto La Rosa

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.