This paper reports the design of an electromagnetic vibration energy harvester that doubles the magnitude of output power generated by the prior four-bar magnet configuration. This enhancement was achieved with minor increase in volume by 23% and mass by 30%. The new ‘double cell’ design utilizes an additional pair of magnets to create a secondary air gap, or cell, for a second coil to vibrate within. To further reduce the dimensions of the device, two coils were attached to one common cantilever beam. These unique features lead to improvements of 66% in output power per unit volume (power density) and 27% increase in output power per unit volume and mass (specific power density), from 0.1 to 0.17 mW cm−3 and 0.41 to 0.51 mW cm−3 kg−1 respectively. Using the ANSYS multiphysics analysis, it was determined that for the double cell harvester, adding one additional pair of magnets created a small magnetic gradient between air gaps of 0.001 T which is insignificant in terms of electromagnetic damping. An analytical model was developed to optimize the magnitude of transformation factor and magnetic field gradient within the gap.

This paper reports the design of an electromagnetic vibration energy harvesting system that provides high power density and broad bandwidth. The ‘double cell’ harvester was chosen as the generator for this system. In order to harvest power over a broad range of frequencies, four ‘double cell’ harvesters with varying resonances were incorporated in the system architecture. The average AC to regulated DC power conversion efficiency across the 4 Hz bandwidth was 78%, which is one of the highest reported magnitudes for an electromagnetic vibration harvesting system. The magnetic flux density variation within the double cell array was modeled using the finite element method and compared to a single cell with equivalent tip mass and magnet volume. The double cell array was found to generate a similar magnitude of power to a single cell but three times higher bandwidth. The average generator conversion efficiency for the double cell array was 45.3%, which approaches the maximum theoretical limit of 50%.

High-performance low-cost multilayer textured Pb(Mg 1/3 Nb 2/3 )O 3 -PbZrO 3 -PbTiO 3 (PMN-PZT) piezoelectric ceramic benders were fabricated by combining templated grain growth (TGG) and low-temperature co-firing ceramics (LTCC) process. The d  g values of textured samples were 700-800% higher than that of the random counterpart, which results in 500-600% increase in the output power from vibration energy harvesting. The output power and power density of tri-layer textured sample at the acceleration of 0.43 g were measured to be 903 µW and 15.5 mW/cm 3 , respectively. The results demonstrate that the multilayer structure results in an increase in output current and a decrease in the matching resistive load.

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