2 September 2020
by Idha Valeur

Fighting the fires - a device that can detect flaming forests

A batteryless device that detects forest fires and monitors the environment might be the saving grace for forests in the future. Idha Valeur finds out more.

© Getty / ico_k-pax

Only powered by tree movement in the wind, a new device aims to be both a detection and alarm system to prevent the spread of roaring forest fires. The MC-TENG is the creation of a research team from Michigan State University (MSU). 

Changyong Cao, Director of the University’s Laboratory of Soft Machines and Electronics, explains that the kit is a multi-layered cylindrical triboelectric nanogenerator that can produce electrical power by harvesting kinetic energy. It detects fires as it has sensors sensitive to temperature and carbon monoxide, and signals can be wirelessly transmitted to fire stations and other stakeholders. 

He notes that traditional methods in the fight against forest fires include watching towers, ground patrolling, satellite monitoring and other assistant tools, but that none of these options are optimal as they are labour-intensive, offer low efficiency and are capital-intensive. Although advanced fire sensors offer an alternative, low-cost, accurate and rapid approach in both response and stability, they are powered by batteries and so need replacing. ‘A self-powered alarm system using sustainable energy is thus much needed,’ insists Cao. 

‘The MC-TENG consists of two major functional components, a top fixed sleeve hanging on the branches and a bottom sliding sleeve connected by a highly stretchable rubber band with the top sleeve, forming a spring-mass vibration structure,’ Cao says. 

‘A mass block is bonded with the bottom sliding sleeve to tune the natural frequency of the device, aiming to change the intrinsic frequency of the MC-TENG for a resonant response based on the shaking of tree branches in different regions or situations. The sliding and contract-separation between the two sleeves under tree branches swings will make it generate electricity.’ 


Cao adds that the two types of sensors will achieve a multimodal mechanism to accurately detect an event, and remove the possible false alarms.

The cylindrical shell is made from a 3D-printed thermoplastic polymer and is 1.5mm-thick. This shell is then bonded to a thin layer of copper (Cu) film, both the inside and outside surface. This Cu film acts as the triboelectric material and the electrode. ‘A polytetrafluoroethylene (PTFE) film of 50µm is used as the electrification contact material and bonded onto the surface of the Cu film electrodes of the bottom sliding sleeve because of its strong ability of electrons attraction and low friction coefficient,’ Cao explains. 

A micro-supercapacitor will store the energy that the device harvests to drive the detection sensors, as this is more durable than coin batteries. 
The researchers foresee that it will be able to remain in the trees for several years before any maintenance is required, and if biodegradable and/or sustainable materials are used, there will be no need to retrieve them at all. 

In laboratory tests, the device has performed ‘pretty good’, Cao says, but they are currently working on advanced versions that will yield a device that is more resilient. The following steps include field tests. He adds that the team has filed invention discourse to MSU Technologies and is currently preparing to file a patent. 
 

Authors

Idha Valeur