Energy Harvesting for Wireless and Less-Wired Sensors in Gas Turbines

Doctoral thesis, 2019

The development of low power electronics and more efficient wireless communication has led to an increase in the use of wireless sensors, both with new sensor applications but also by replacing existing wired sensors with wireless solutions. One of the key reasons for replacing a wired sensor with a wireless sensor is to reduce the amount of wires used, reducing both the cost of the wires and the time needed to install a sensor.

However, wireless sensors require a power source to function. A battery is often preferred with the combination of high energy content, low self-discharge and low cost. If for some reason the environment is not suitable for batteries (e.g. if the temperature is too high, if the sensor is inaccessible under long periods of time or the peak power is too high) the battery should be replaced or combined with other power source solutions. Also, even if the wireless sensor can be battery powered for many years it can be beneficial to combine it with an energy harvester to increase the life time further. To have, for example, a car or a truck to go into service only to change sensor batteries is impractical.

The unique gas turbine environment and the high demands associated with the aerospace industry has shaped the outcome of this thesis. Various gas turbines located in test facilities in Europe has contributed to the vibrational- and temperature data used in this project and has also been subject to harvester measurements for powering wireless sensors. The gas turbines in these test facilities can have thousands of sensors, with many of them requiring difficult wire placements. In these harsh environments the complexities of wireless sensors increase as well. However, one of the key reasons for replacing a wired sensor with a wireless or less-wired sensor is to reduce the amount of wires used, reducing both the cost of wires and the time needed to install/debug the sensor. Reduced weight can also be an additional reason for wireless sensors, e.g. in aircraft gas turbines.

Developing energy harvesters for gas turbines is a combination of energy conversion and survivability in harsh environments. It requires aerospace grade materials and cables and sometimes that electronics are placed far away from the harvester. This approach gives a different prerequisite of the harvester designs than if the harvesters are investigated without considering a specific application. Another consequence of this approach is the aim and presentation of the harvester results, with more focus on connectivity with a wireless sensor system than the more conventional power output/efficiency of the energy harvesters.