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Why Batteries Are Ripe for Disruption
Energy-harvesting techniques are maturing and could provide a more sustainable approach to deploying IoT networks.
Dec 18, 2016—
As Internet of Things applications become more widely deployed, there is an increasing demand for edge devices that communicate wirelessly and are powered by batteries. But as the advance of technology has allowed for the ever-decreasing size of our computing devices and provided us with mobile devices that we may have never expected, there is increasing talk about how battery technology has just not kept up. There is, after all, no Moore's Law for batteries, and so the progress that we have seen has been slow in comparison, with battery sizes and capacities that are not much better than they were a decade ago. But rather than long for a dime-sized battery that will keep your cell phone operating for a week or more, there is another way to look at batteries: eliminating them entirely.
Many IoT devices, communicating via Wi-Fi, Bluetooth or Bluetooth-LE—or via one of the emerging low-power wide-area networking protocols—will need to operate in environments where battery refreshes are not possible. A common design target is for the edge device to operate in the field for 10 years without a battery replacement. But when operating lifetime estimates are simply based on power consumption—calculated from the discharge rate of the battery—we tend to see an unacceptable number of battery failures in the field.
But powering IoT devices through energy-harvesting techniques is an alternative to deployments being dependent on battery reliability. To harvest energy, a circuit scavenges power from energy sources that are already present for reasons other than powering the circuit. A solar-powered module is an example of energy harvesting, as is a self-winding watch that uses the kinetic energy of the wearer's arm movement to keep the watch running. For IoT applications, there are many more interesting power sources to consider.
Perhaps the best-known example of energy harvesting in edge devices is in passive radio frequency identification (RFID) tags, which are powered from the RF energy delivered over the air from nearby readers. As the distance from the reader increases, the power available to the tag is reduced to microwatts, but advanced circuit techniques and semiconductor processes keep the circuit power consumption to usable levels. Equally important, the most commonly used signaling protocol for passive RFID tags, EPC Gen 2, has been designed from the start to facilitate low-power operation.
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