Wireless sensors can be used to monitor a building’s water usage and power consumption, they can be used to predict when a machine needs maintenance, when a pipe might burst, stop you getting sunburnt, and even alert parents’ if baby needs changing.
These sensors make up an Internet of Things that is growing by the day. By 2020, Gartner predicts there will be over 26 billion connected devices, a huge proportion of them small simple sensors.
But what happens when a sensor’s battery runs out?
"A major problem hindering the widespread deployment of wireless sensor networks is the need to periodically replace batteries," said Dr Salman Durrani from the Australian National University's Research School of Engineering. “Current wireless sensors for buildings, biomedical applications or wildlife monitoring use batteries which are often difficult to replace.”
Durrani’s team are exploring the possibility of such sensors using ‘energy harvesting’ to generate the power they need, instead of relying on battery power, and have proved it feasible in a recent study.
Energy harvesting involves the collection of renewable energy like solar, or ambient energy, such as from radio signals put out by communications towers and mobile phone base stations.
“Energy harvesting provides a means of greatly enhancing the lifetime of wireless sensor nodes,” explains Durrani in a paper, Energy Harvesting Wireless Sensor Networks: Delay Analysis Considering Energy Costs of Sensing and Transmission published in the scientific journal IEEE.
“However, the randomness inherent in the energy harvesting process may cause significant delay for performing sensing operations and transmitting sensed information.”
While previous studies had been limited to understanding the energy required for just transmitting the information a sensor collects, Durrani’s study explored the energy requirements for both transmitting and sensing.
Their modelling found that by including the energy requirements of the sensing it was possible to power a sensor with ‘harvested’ energy, although there was a trade-off with the timeliness of the information transmitted and a less frequent update cycle.
Dr Durrani said we were nevertheless a ‘step closer’ to energy harvesting sensors, although the technology was still some years away.
"If we can use energy harvesting to solve the battery replacement problem for wireless sensors, we can implement long-lasting monitoring devices for health, agriculture, mining, wildlife and critical national infrastructure, which will improve our quality of life."