Energy harvesting may one day power aircraft sensor networks
10 April 2013
Energy harvester modules that are suitable for aerospace applications are likely to have a future role powering the sensor nodes of structural monitoring networks.
Sensor networks distributed across an aircraft fuselage record and transmit essential data concerning its structural health. Traditionally, wired sensors are used, and while these are reliable, they introduce weight and increase the design complexity of this essential maintenance tool.
To solve the problem, EADS Innovation Works andthe Vienna University of Technology are collaborating to develop a thermoelectric energy harvesting module of just a few centimetres in diameter, which will supply enough energy to power wireless sensor nodes.
The artificial temperature difference created when the aircraft takes off and lands is sufficient to generate the required electrical energy (Seebeck effect). A flight test campaign on an Airbus aircraft with these modules has been successfully performed for the first time.
Autonomous wireless sensor nodes continuously monitor the health status of an aircraft and wirelessly transmit the data to a data acquisition system.
“Such a system obviously has major advantages, however, the main problem lies in the energy supply", says Professor Ulrich Schmid from the Institute of Sensor and Actuator Systems at Vienna University of Technology.
"Conventional batteries are not designed for such large temperature difference to which an aircraft is continuously exposed during operation. In addition, nobody wants to regularly replace all the sensor batteries in the aircraft. Using conventional cabling, on the other hand, would significantly increase the weight of the aircraft."
The outer shell of an aircraft undergoes a significant temperature change during take-off and landing. "We can make optimal use of these temperature gradients by attaching a small thermal mass to one side of the thermoelectric generator“, explains Alexandros Elefsiniotis, one of Professor Schmid's doctoral students.
"A water reservoir of about ten cubic centimetres freezes during take-off. It cools down at a slower rate than the fuselage, thus a thermoelectric generator located between these components creates electricity from that temperature difference."
Inversely, during landing, the fuselage temperature of the aircraft is warmer than that of the water reservoir and so energy is once again generated. A special low-power management system ensures that this variable voltage supply is maintained at a stable voltage appropriate to the sensor node supply requirements.
The research team was able to obtain around 23 joules of energy per flight, which is sufficient to power a wireless sensor node. It is possible that alternative materials, other than water, may be more suitable – research is currently ongoing into appropriate strategies for extreme situations, for example for flight routes in very cold regions.