RF harvesting circuits have been demonstrated for more than 50 years, but only a few have been able to harvest energy from freely available ambient (i.e., non-dedicated) RF sources. In this paper, our objectives were to realize harvester operation at typical ambient RF power levels found within urban and semi-urban environments. To explore the potential for ambient RF energy harvesting, a city-wide RF spectral survey was undertaken from outside all of the 270 London Underground stations at street level. Using the results from this survey, four harvesters (comprising antenna, impedance-matching network, rectifier, maximum power point tracking interface, and storage element) were designed to cover four frequency bands from the largest RF contributors (DTV, GSM900, GSM1800, and 3G) within the ultrahigh frequency (0.3-3 GHz) part of the frequency spectrum. Prototypes were designed and fabricated for each band. The overall end-to-end efficiency of the prototypes using realistic input RF power sources is measured; with our first GSM900 prototype giving an efficiency of 40%. Approximately half of the London Underground stations were found to be suitable locations for harvesting ambient RF energy using our four prototypes. Furthermore, multiband array architectures were designed and fabricated to provide a broader freedom of operation. Finally, an output dc power density comparison was made between all the ambient RF energy harvesters, as well as alternative energy harvesting technologies, and for the first time, it is shown that ambient RF harvesting can be competitive with the other technologies.

Ambient RF Energy Harvesting in Urban and Semi-Urban Environments

More than a decade of research in the field of thermal, motion, vibration and electromagnetic radiation energy harvesting has yielded increasing power output and smaller embodiments. Power management circuits for rectification and DC-DC conversion are becoming able to efficiently convert the power from these energy harvesters. This paper summarizes recent energy harvesting results and their power management circuits.

Micropower energy harvesting

Li-ion batteries are the powerhouse for the digital electronic revolution in this modern mobile society, exclusively used in mobile phones and laptop computers. The success of commercial Li-ion batteries in the 1990s was not an overnight achievement, but a result of intensive research and contribution by many great scientists and engineers. Then much efforts have been put to further improve the performance of Li-ion batteries, achieved certain significant progress. To meet the increasing demand for energy storage, particularly from increasingly popular electric vehicles, intensified research is required to develop next-generation Li-ion batteries with dramatically improved performances, including improved specific energy and volumetric energy density, cyclability, charging rate, stability, and safety. There are still notable challenges in the development of next-generation Li-ion batteries. New battery concepts have to be further developed to go beyond Li-ion batteries in the future. In this tutorial review, the focus is to introduce the basic concepts, highlight the recent progress, and discuss the challenges regarding Li-ion batteries. Brief discussion on popularly studied “beyond Li-ion” batteries is also provided.

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Li‐ion batteries: basics, progress, and challenges

Recent emphasis on green communications has generated great interest in the investigations of energy harvesting communications and networking. Energy harvesting from ambient energy sources can potentially reduce the dependence on the supply of grid or battery energy, providing many attractive benefits to the environment and deployment. However, unlike the conventional stable energy, the intermittent and random nature of the renewable energy makes it challenging in the realization of energy harvesting transmission schemes. Extensive research studies have been carried out in recent years to address this inherent challenge from several aspects: energy sources and models, energy harvesting and usage protocols, energy scheduling and optimization, implementation of energy harvesting in cooperative, cognitive radio, multiuser and cellular networks, etc. However, there has not been a comprehensive survey to lay out the complete picture of recent advances and future directions. To fill such a gap, in this paper, we present an overview of the past and recent developments in these areas and highlight a number of possible future research avenues.

/pdf/advances-in-energy-harvesting-communications-past-present-3oubbkeycy.pdf

Advances in Energy Harvesting Communications: Past, Present, and Future Challenges

The last decade has witnessed significant advances in energy harvesting technologies as a possible alternative to provide a continuous power supply for small, low-power devices in applications, such as wireless sensing, data transmission, actuation, and medical implants. Piezoelectric energy harvesting (PEH) has been a salient topic in the literature and has attracted widespread attention from researchers due to its advantages of simple architecture, high power density, and good scalability. This paper presents a comprehensive review on the state-of-the-art of piezoelectric energy harvesting. Various key aspects to improve the overall performance of a PEH device are discussed, including basic fundamentals and configurations, materials and fabrication, performance enhancement mechanisms, applications, and future outlooks.

A comprehensive review on piezoelectric energy harvesting technology: Materials, mechanisms, and applications

Wireless sensor nodes (WSNs) are employed today in many different application areas, ranging from health and lifestyle to automotive, smart building, predictive maintenance (e.g., of machines and infrastructure), and active RFID tags. Currently these devices have limited lifetimes, however, since they require significant operating power. The typical power requirements of some current portable devices, including a body sensor network, are shown in Figure 1.

Energy Harvesting for Autonomous Wireless Sensor Networks

Vibration energy harvesters can replace batteries and serve as clean and renewable energy sources in low-consumption wireless applications. Harvesters delivering sufficient power for sensors operating in an industrial environment have been developed, but difficulties are encountered when the devices to be powered are located on the human body. In this case, classical harvester designs (resonant systems) are not adapted to the low-frequency and high-amplitude characteristics of the motion. For this reason, we propose in this paper an alternative design based on the impact of a moving mass on piezoelectric bending structures. A model of the system is presented and analysed in order to determine the parameters influencing the device performances in terms of energy harvesting. A prototype of the impact harvester is experimentally characterized: for a generator occupying approximately 25 cm3 and weighing 60 g, an output power of 47 µW was measured across a resistive load when the device was rotated by 180° each second. 600 µW were obtained for a 10 Hz frequency and 10 cm amplitude linear motion. Further optimization of the piezoelectric transducer is possible, allowing a large increase in these values, bringing the power density for the two cases respectively to 10 and 120 µW cm−3.

https://iopscience.iop.org/article/10.1088/0964-1726/18/3/035001/pdf

Harvesting energy from the motion of human limbs: the design and analysis of an impact-based piezoelectric generator

SUMMARY

Wireless sensor nodes (WSNs) are expected to play an increasing role in multiple application areas. These application areas vary from networks around the human body, sensors in smart tires, sensor networks that can control the safety and comfort levels throughout smart buildings, sensors that monitor the necessity for maintenance and sensors that track the conditions of food throughout the distribution chain. These wireless sensors need energy, which can be supplied by a battery or an energy harvester. However, even when an energy harvester is applied, energy storage is required to serve as energy buffer. In this review, the requirements that different types of wireless sensor networks impose on these batteries are explored, and several suitable types of batteries are reviewed. Moreover, the trends in battery development are described, and the future improvements are predicted. Finally, the possibilities are discussed to select a battery with properties that are matched to the requirements of the sensor nodes. Copyright © 2012 John Wiley & Sons, Ltd.

A review of the present situation and future developments of micro-batteries for wireless autonomous sensor systems

This paper presents a high voltage and low power inductive DC-DC buck converter for interfacing electrostatic energy harvesters. The system, implemented in TSMC 0.25 μm BCD, can convert input voltages from 5 to 60 V to recharge the energy storage system connected to the output. The system includes also a Maximum Power Point Tracking algorithm for matching the equivalent source resistance of harvester and AC-DC converter. Due to power consumption constrains, a conventional implementation of this algorithm, based on ADC, DAC and complex digital processing is replaced by a much simpler fully analog design. Measurements have shown a peak end-to-end efficiency of 88% with 99.8% MPPT peak efficiency.

A High Voltage Self-Biased Integrated DC-DC Buck Converter With Fully Analog MPPT Algorithm for Electrostatic Energy Harvesters

Disclosed is a highly reliable inductive vibration power generator wherein mechanical damping caused by the phenomenon of electrostatic pulling-in (stiction) and the like is suppressed even if the potential of an electret is increased and/or the gap between an electrode and the electret is reduced in order to increase the amount of power generation. The two surfaces of a movable substrate are respectively provided with first electrets and second electrets. By means of providing first electrodes and second electrodes to a lower substrate and an upper substrate and facing the respective electrets with a predetermined gap therebetween, electrostatic force is caused to arise on both sides of the movable substrate, and the pulling of the movable substrate in only one direction is prevented.

Rob van Schaijk

Papers

Energy Harvesting for Autonomous Wireless Sensor Networks

Harvesting energy from the motion of human limbs: the design and analysis of an impact-based piezoelectric generator

A review of the present situation and future developments of micro-batteries for wireless autonomous sensor systems

A High Voltage Self-Biased Integrated DC-DC Buck Converter With Fully Analog MPPT Algorithm for Electrostatic Energy Harvesters

Micro-electromechanical generator and electric apparatus using same