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 d32 transverse extension mode. Modelling was done by adapting an existing lumped element mathematical model to include the d32 transducer orientation, from which an analytical transfer function was developed. The temperature dependence of the piezoelectric charge constant, d32, 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 k -10 M , and shown to be valid for predicting voltage and power levels for loads under 1 M . 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.