Coupling effect analysis for hybrid piezoelectric and electromagnetic energy harvesting from random vibrations

Through establishing the electroelastic model of hybrid piezoelectric(PE) and electromagnetic(EM) energy harvesting from random vibrations, normalized expressions of mean amplitude, voltage, current, power and their spectral density (SD) are derived, and effects of electromechanical coupling strength on harvester’s performances are studied by numerical calculation and experimental test. It is found that the stronger coupling effect, the smaller amplitude and working space required, and the bigger mean voltage, current and power output until up to their maximums. Furthermore, variation extent of mean voltage, current and power with the PE and EM load increasing varies with the coupling strength. Besides, coupling strength changes the SD distributing in frequency domain. In the weak coupling, maximal SD of voltage, current and power are at the natural frequency of harvester. However, with the coupling effect strengthening, the frequency corresponding to peak spectral density is bigger than the natural frequency, and the 3dB bandwidth of harvester is much larger accordingly; moreover, the bandwidth decreases with EM load increasing while it rises firstly and fall later with PE load increasing, which reaches the maximum at the optimal load. The analysis results can provide certain criteria for hybrid piezoelectric-electromagnetic energy harvester design.