A tuneable piezoelectric vibration energy harvester for helicopter-gearbox sensing

Abstract. Piezoelectric vibration energy harvesters are critical for self-powered sensing on aircraft, however tuning a harvester to the desired source frequency is challenging. This is because aerospace ap-plications usually require energy harvesters to be small, lightweight and highly durable, making mechanical tuning methods impractical. Frequency tuning via shunting a piezoelectric transducer with variable electrical loads, as explored in this work, is practicable since the tuning mechanism is low mass and has no moving parts. This paper presents the modelling and experimental characterisation of a cantilevered bimorph configuration comprising a steel beam with two relaxor ferroelectric single crystal transducers for harvesting and tuning. A one-dimensional model for the tuneable harvester was developed and two finite element analyses (FEA) were conducted. The effect of temperature up to 90oC is discussed, being the upper gearbox temperature expected operationally. The first FEA model only couples the vibration to the direct production of charge in the transducers, while the second model includes both the direct and converse piezoelectric effects. A prototype harvester was tested on an electrodynamic shaker at 1g peak acceleration at frequencies around 1900 Hz which was the helicopter-gearbox meshing-frequency of interest. The predictions of the one-dimensional model and both finite element models are found to agree favourably with experimental measurements of the resonant frequency. The approach successfully tuned the resonant frequency of the prototype piezoelectric harvester by up to ±1.7%, matching the harvester’s resonant frequency to 1900 Hz gearbox frequency of interest.