Mar 8


When it’s time to reduce energy consumption in the bitter winter, the North American wood frog must take the award for the most dramatic and effective survival method. At the first touch of ice its body quickly transforms to enter a state of cryogenic suspension – allowing two-thirds of its body water to freeze solid with heart stopping results!

This amazing amphibian then survives the winter in this frozen state, cutting its demand for energy to practically zero. Then when the big freeze is over, it thaws out and happily returns to its active life with all its faculties intact!

In the world of IoT (Internet of Things) some types of remote device also need to be smart about conserving energy, because they need to be extremely compact, wireless, and often powered by small ‘button’ cells. These devices are typically sensors used to monitor and report on the state of a physical object such as a door or window in a home security system or the inside temperature of a remote industrial storage tank. Although the sensor doesn’t need to send much data, and only on rare occasions such as in an emergency or alarm condition when a door is opened by an intruder, the device needs to conserve as much energy as possible so that its batteries can last years [up to 5 years in some cases] without replacement.

Dormant Devices

There are two areas which can help to reduce power consumption. The first is in the device hardware itself, which is designed to go into a very low power ‘sleep’ mode when the device is not sending information. In this mode the device turns off all the power hungry parts of its electronics (which is most of it). While in this dormant mode, the device still needs to periodically send a minimum amount of information to its management system just to say ‘its ok I’m still here!’, so a watchdog timer wakes it up enough to send a short burst of data like a heartbeat. The period of this heartbeat can be as long as several hours or even days depending on the type of application and its security level. This is in case the device completely fails to wake up due to a fault or battery failure, then the management system would raise a maintenance alert for the device to be checked and its batteries replaced.

Low power communications standards

Secondly, sending data consumes power, especially on the radio side of the device, so there is a need to make data communications as efficient as possible. This is where the device firmware and its communications methods and protocols can be optimized to make best use of the power while keeping overall consumption to a minimum. Protocol standards like ZigBee, 6LowPAN and NB-IoT are all designed to help do this. In my next blog we will take a look at these low power communications standards and how they help to build power sensitive wireless device networks, both for Personal Area and Wide Area applications.

So next time you see a small white innocuous looking wireless device attached to a window or door, give a thought for the amazing North American wood frog and how it survives winter in a frozen state!


The Journal of Experimental Biology 216, 3461-3473 © 2013. Published by The Company of Biologists Ltd

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