Energy Harvesting and Energy Storage for Wireless and Less-Wired Sensors in Harsh Environments

Licentiate thesis, 2018

Engineering requires sensors to control and understand the environment. This is particularly important in harsh environments. The drawbacks, especially in gas turbines is the complexity of installing a wired sensor and the weight of the wires. This makes wireless sensors attractive.

A wireless sensor requires a power source for transmission of data. Batteries have previously taken the role of power source for most wireless sensors, but is unfortunately not suitable for all applications. Lately, with energy harvesting and supercapacitors in the picture, sensor applications in high temperature environments, with high power requirements or with long life requirements have the possibility of wireless interface.

A supercapacitor can handle higher temperatures, higher power output and can have a cycle life that exceeds batteries by a factor of 10000. The lower energy density and high self-discharge makes it unsuitable to power a wireless sensor without power source. However, connected to an energy harvester converting waste energy into electricity makes this a powerful combination.

Energy harvesters thrives in environments where waste energy is plentiful and low conversion efficiencies can be enough to power both the sensor and the transmitter. A thermoelectric harvester is designed and fabricated for the middle to rear part of a gas turbine. The temperature in this region can reach 1600 ◦ C and require extensive cooling. In the cooling channels the wall temperature reach 800-950 ◦ C when the cooling air is 450-600 ◦ C. In this location a thermoelectric harvester will have access to high thermal gradients and active cooling.

To harvest the vibrations a piezoelectric energy harvester was built. To harvest enough energy the resonance frequency of the energy harvester is frequency-matched with the high energy vibrations. In many applications these frequencies drift and thus require a broad bandwidth harvester. Simulation and assembly of a broadband coupled piezoelectric energy harvester is presented in the thesis.

A piezoelectric harvester require electronics and energy storage to gather enough energy to power up and run a wireless sensor. The thesis covers the fabrication of a high temperature supercapacitor capable of temperatures up to 181 ◦ C.