Energy harvesting is promising to provide convenient and clean power for low-power sensors in the Internet of Things. Piezoelectric energy harvesters have proved particularly competitive because of their simple structure, flexible design and excellent power density.
This thesis first developed a miniature galloping piezoelectric energy harvester (GPEH) to scavenge wind energy. It worked within the wind speed band of 4.45-10 m/s in wind tunnel tests, and the maximum average power was 7.5 μW. Because of its flexible structure, the harvester could spontaneously return to the balanced position after mechanical overload, showing good robustness at high wind speeds.
Following this, the variation of galloping frequency with wind speed was systematically investigated. An analytical model considering axial aerodynamic force was established, successfully explained the dependence of frequency on wind velocity. A wind velocity sensor was developed based on this dependence. Further experiment showed the error of this sensor is below 4% compared to the standard Pitot tube.
Furthermore, a novel design combining nonlinear aeroelastic structure and synchronous mechanical switch-based P-SSHI (parallel synchronized switch harvesting on inductor) was introduced into the original GPEH. According to wind tunnel measurement, the cut-off speed increased to 13.5 m/s from 10 m/s with this design. Furthermore, the average power output has increased maximumly by 221% at 3.6 m/s than the GPEH only contained nonlinear aeroelastic structure.
Finally, to realise a soft piezoelectric tensile sensor, a second-order fractal structure was patterned using an ultraviolet laser on a PVDF film. In dynamic tensile testing, this sensor showed RMS voltages of 2.7 mV and 9.2 mV when the tensile velocities were 5 mm/s and 20 mm/s, respectively. The voltage-velocity curve increased monotonically.
In conclusion, this thesis investigated novel architectures for piezoelectric energy harvesting and ambient sensing, which are promising to be widely used in IoT applications.