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Non-Battery Power Supply for Aircraft Sensors Flight Tested

Alexandros Elefsiniotis, left, and Ulrich Schmid (Vienna University of Technology)

Alexandros Elefsiniotis, left, and Ulrich Schmid (Vienna University of Technology)

Engineers from Vienna University of Technology in Austria and the commercial aircraft manufacturer EADS are collaborating on a new type of power supply for sensors to monitor a fuselage’s structural integrity. The team reports the first successful flight tests of the devices on an Airbus aircraft.

These energy harvesting modules, as they’re called, are the work of the university’s Institute of Sensor and Actuator Systems and EADS Innovation Works, the company’s network of research labs. Energy harvesting modules are a few centimeters in diameter and generate thermoelectric power with the Seebeck effect, resulting from the temperature differential created when an aircraft takes off and lands.

Maintenance is a major expense for airlines and can amount to as much as 20 percent of the total lifetime cost of a commercial aircraft. Thus, sensors for monitoring a commercial aircraft’s structure are vitally important, not only for safety, but also for controlling costs.

The problem says institute director Ulrich Schmid is powering all of those sensors, particularly with the extreme temperatures routinely faced by commercial aircraft. “Conventional batteries are not designed for such large temperature difference to which an aircraft is continuously exposed during operation,” says Schmid. “In addition, nobody wants to regularly replace all the sensor batteries in the complete aircraft.” Batteries and cables would add weight to aircraft’s load as well.

Schmid and doctoral candidate Alexandros Elefsiniotis decided to use the large temperature differentials encountered by aircraft to solve the problem. The researchers take advantage of the Seebeck effect that creates an electric current when two different electrically conductive materials are joined and their contact points have different temperatures.

“We can make optimal use of these temperature gradients by attaching a small thermal mass to one side of the thermoelectric generator,” says Elefsiniotis. A small water reservoir — about ten cubic centimeters — freezes during take-off, and then cools down at a slower rate than the fuselage. Thus, adds Elefsiniotis, “a thermoelectric generator located between these components creates electricity from that temperature difference.”

Upon landing, a reverse phenomenon occurs, where the fuselage temperature of the aircraft is warmer than that of the water reservoir, but an electric current is still generated. A power management system, itself requiring little energy, normalizes the power flow, smoothing out the voltage fluctuations.

After lab tests, EADS Innovation Works carried out test flights with the energy harvesting modules on an Airbus aircraft. “We have been able to obtain around 23 joules of energy per flight, which is sufficient to power up a wireless sensor node,” reports Elefsiniotis. The researchers are testing alternatives to water in the thermal mass that would work better when flying in extremely cold temperatures.

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