Theoretical and Experimental Evaluation of System Energy Balance and Power Generation Efficiency for Piezocomposite Vibration Energy Harvester Under Low Intensity Excitation Condition

In the authors’ previous study, the vibration energy harvester of the piezoelectric bimorph cantilever type was proposed for vibration condition monitoring applications of industrial rotating machinery. According to an ISO standard, vibration level of newly commissioned class I rotating machinery is under 0.71mm/sec rms in all frequency range. Authors assumed that the typical casing or pedestal vibration amplitude of the rotating machinery was 0.71 mm/sec rms and this low intensity excitation condition was the input for experimental evaluation of the voltage generation performance of the piezocomposit vibration energy harvester. The vibration energy harvester consists of the surface bonded two Macro-Fiber Composites (MFCs). In this study, energy transfer efficiency was derived from the system energy balance during the natural period of the proposed vibration energy harvester. Energy balance equations were successfully obtained from the governing equations of the piezoelectrically coupled electromechanical system. The maximum AC power through 114.3 Kilo-Ohm resistor which includes instrument internal resistances experimentally obtained 242.07 microwatt when subjected to vibration source input magnitude of 0.71 mm/s rms at the resonant frequency of the harvester (29.42 Hz). The impedance matching between MFCs and the electrical resistive load was effective for maximizing AC power transfer of the vibration energy harvester. Estimated energy transfer from mechanical system to electrical system shows the agreement with the experimentally evaluated generating power during the natural period of the vibration energy harvester with about 3% difference. Estimated energy transfer efficiency was about 30% for different excitation magnitudes: 0.71, 0.568 and 0.355 mm/sec rms.