Scientists extend the battery life of forest climate monitors

Scientists in Germany have boosted the life of wireless sensors designed to protect forests by monitoring their climate conditions.

The devices allow researchers to observe trees’ health and study the effects of climate change, and could also help timber companies ensure that their plantations have the best conditions for growth.

Using wireless transmitters to relay the data on temperature, humidity and pollution makes the sensors more flexible, robust and easy to install, while specially designed software helps increase their battery life.

A team at the Fraunhofer Institute for Microelectronic Circuits and Systems, led by group manager Hans-Christian Müller, designed the sensors and has been trialling them as part of a ’Smart Forest’ project in Göttingen.

‘A problem for any group working on wireless networks is how to get the energy to the sensor nodes,’ Müller told The Engineer.

‘If you imagine you have hundreds of thousands of sensors in a forest and they are battery powered, then you have a logistical problem.

‘There is no very attractive alternative to batteries currently. You can’t use solar energy due to the fact that the forest can be very dark.’

The need for batteries affects the sensors’ size — they are around 10 by 10cm — but they are still small enough to attach to tree branches.

To address the power issue, the Fraunhofer team created management software that increased the battery life to 12 months.

The radio nodes are kept in an energy-saving sleep mode for the majority of the time and the measurement intervals are varied according to the data they are collecting.

For example, soil moisture doesn’t need to be measured as often as air temperature, which experiences bigger changes.

The sensor calculates the measurement values to reduce the size and power usage of the data transmissions, which can be made via the mobile phone network so that the forest can be monitored from any location.

Müller’s team is now planning to use the technology to develop agricultural sensors that measure the pH value inside cows’ stomachs.