Energy Harvesting and Power Delivery

Abstract

As we have seen in previous chapters, the increasing miniaturisation and cost reduction of sensors, circuits and wireless communication components is creating new possibilities for networks of wireless sensors, in wearable and other applications. However, in order for sensors to be wireless, or untethered, this requires not only wireless communication to and from the nodes, but also wireless powering. Batteries, of course, provide this capability in the great majority of portable electronic devices, and thus are the obvious solution also for the wireless sensor node application. However, their need for replacement or recharging introduces a cost and convenience penalty which is already undesirable in larger devices, and is becoming increasingly unacceptable for sensor nodes as the number of these (their ubiquity) grows. As an alternative, therefore, sources which harvest energy from the environment are very attractive. At the same time, the power demands of many electronic functions, wireless communication being a particularly important example in this context, are continuously falling. Although this lightens the demands for batteries, it also makes alternatives based on energy harvesting look more and more realistic.Where batteries can power a sensor node for its whole expected lifetime without maintenance, and without dominating the node cost or weight, this is likely to remain the favoured solution in most cases, although even there, energy harvesting methods have advantages to offer. The materials required in batteries are often toxic or environmentally unfriendly, adding to the burden of both bio-compatibility for implanted use and to the end-of-life disposal. Where a lifetime beyond what a battery can provide is needed, the "eternal" nature of the harvesting supply clearly becomes particularly favourable.

Energy Harvesting Combat Boot for Satellite Positioning

“…Certain human processes, such as the blood coursing through veins and arteries, run continuously in the background, while others, such as sprinting, occur as acutely executed functions of motion. Regardless of the nature of each activity, every physical motion of the human body presents an opportunity to harvest energy and power a portable device without relying on a battery in remote areas [ 1 ]. Of these activities, the impact of the human foot on the ground during walking and running presents the greatest occasion to harvest energy in terms of energy expenditure [ 2 ].…”

Footstep energy harvesting using heel strike-induced airflow for human activity sensing

“…Wearable and portable devices, including smart watches, activity trackers and wearable cameras, are increasingly popular to enhance the convenience and quality of our lives [1], but the batteries for these devices require frequent recharging or replacement, which creates other types of inconvenience. There are massive energy sources from human body, such as exhalation, arm motion, body heat and footfalls, which are readily to be harnessed; otherwise the energy would be wasted.…”

Alternative power sources for miniature and micro devices

“…Indeed, the flashlight was so called because these early models could only flash on a light for brief periods of time due to limitations of their zinc-carbon batteries. The modern equivalent device for which the user would like an inexhaustible and mobile source of power is the cell phone, but there are of course may more applications which demand high-capacity portable power outside of the consumer electronics market, including medical devices and the body sensor network [2], electric vehicles, portable instrumentation and infrastructure monitoring wireless sensor networks [3].…”