Design considerations for a PIN-PMN-PT relaxor ferroelectric based vibration energy harvester for use on a helicopter main-transmission

High frequency vibration energy harvesting is being investigated as a potential power source for the Prognostic Health Monitoring (PHM) of helicopter transmissions. Potentially, the use of vibration energy harvesting will reduce the requirement for power cabling or batteries for PHM applications. Gear meshing frequencies in the range of kilo-Hertz are found within helicopter main transmissions, and the meshing frequencies are often accompanied by large regular periodic vibrations present on the casing of the transmission. The prototype harvester described in this paper uses a relaxor ferroelectric single crystal ([011] cut PIN-PMN-PT) for mechanical to electrical transduction. This relaxor ferroelectric was chosen because of its giant piezoelectric charge constant of 1200 pC/N which is significantly greater than that of traditional sintered piezoceramics (e.g. PZT). The prototype harvester described in this paper was designed for harvesting from the vibrations present in a Bell206B Kiowa main-transmission. Kiowa main-transmission vibrations include periodic accelerations with amplitudes of up to 12 g (where g = 9.8 m/s2), and contain a major frequency component centred at around 1900 Hz corresponding to the input pinion meshing frequency. To ensure successful harvesting operation near 1900 Hz the mechanical energy transfer behaviour of the adhesive used to manufacture the prototype harvester (CB359) was investigated and found suitable for use at both room temperature and the elevated temperatures expected in the main-transmission environment. The mechanical quality factor (Qm) and natural frequency (fn) of the prototype harvester were measured under short circuit conditions and found to be around 20 and 1570 Hz respectively. The harvester response to (i) a 30-3000 Hz broadband excitation and (ii) an acceleration-magnitude scaled time-history derived from actual Kiowa main-transmission accelerations were measured over a range of resistive loads. The harvester response at the frequency of interest of 1900 Hz was 4.13 muW/g.