Relaxor ferroelectric transduction for high frequency vibration energy harvesting

This paper reports on the design, modelling and measured response of a high frequency vibration energy harvester that uses relaxor ferroelectric transduction. The ultimate goal is to build a harvester capable of extracting energy from the kilohertz frequency vibrations associated with the gear meshing-frequencies of a Bell 206B-1 Kiowa helicopter main rotor transmission. During operation the transmission oil temperature is 80°C–100°C. The harvester will be mounted externally to the transmission casing and is expected to operate at elevated temperatures. The prototype harvester reported in this paper uses a [011]c cut PIN-PMN-PT single crystal transducer configured for operation in d 32 transverse extension mode. Modelling was done by adapting an existing lumped element mathematical model to include the d 32 transducer orientation, from which an analytical transfer function was developed. The temperature dependence of the piezoelectric charge constant, d 32, the transducer capacitance, C, and the change in short circuit stiffness were measured from room temperature to 100°C for input into the model. The model predictions were compared to measured output of a prototype harvester over load resistances in the range 10 kΩ–10 MΩ, and shown to be valid for predicting voltage and power levels for loads under 1 MΩ. The model was used to optimise the design of the harvester, and predicts that the optimised design will generate a maximum average output power of 210 mW while operating at 100°C and driven by the measured Bell 206B-1 Kiowa main transmission vibrations near 1900 Hz.