A vibration-based electromagnetic and piezoelectric hybrid energy harvester

This work presents the fabrication and testing of a vibration-based single energy hybrid harvester (VSEHH). Electromagnetic and piezoelectric transduction mechanisms are utilized for energy extraction in the developed harvester. Electromagnetic portion of the device composed of a permanent magnet, planar coil and wound coil, however, for piezoelectric portion polyvinylidene difluoride (PVDF) membrane is used. In the harvester the PVDF membrane having the magnet is kept loose in order to exploit the spring softening nonlinearity. At lower base excitation levels (less than 0.5g) the response of the VSEHH is linear, however, from 0.5 to 2.5g the harvester exhibits spring softening nonlinearity and at acceleration levels greater than 2.5g, the spring hardening nonlinearity is invoked. Because of nonlinear behavior of the harvester, the shift of resonant frequency, the sudden jump-up and jump-down phenomena result in the enhancement of the harvester's frequency bandwidth. Under sinusoidal excitation and at 123 Hz frequency and 4g acceleration, the electromagnetic portion of the harvester produced 40.6 mV load voltage and 212.7 mu W with planar coil and 73.5 mV load voltage and 319.1 mu W power with wound coil. Moreover, under the same vibrations condition a load voltage of 2930 mV and power of 57.6 mu W is generated by the piezoelectric portion of the harvester. Collectively, the harvester is capable of producing a power of 589.4 mu W and a power density of 334.13 mu W/cm(3). Furthermore, when subjected to broadband random vibrations, two central frequency peaks are produced, one is due to spring softening and the other corresponds to the spring hardening of the membrane.