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Beginning with a short historical sketch, electrodynamic energy harvesters with focus on vibration generators and volumes below 1 dm 3 are reviewed. The current challenges to generate up to several milliwatts of power from practically relevant flows and vibrations are addressed, and the variety of available solutions is sketched. Sixty-seven different harvester concepts from more than 130 publications are classified with respect to excitation, additional boundary conditions, design and fabrication. A chronological list of the harvester concepts with corresponding references provides an impression about the developments. Besides resonant harvester concepts, the review includes broadband approaches and mechanisms to harvest from flow. Finally, a short overview of harvesters in applications and first market ready concepts is given.

This article discusses how a nonhomogeneous magnetic field with a nonconstant flux gradient affects the behavior of electromagnetic vibration energy harvesters. Based on simulations, the authors show that this nonlinearity enables to increase the output power and bandwidth but not to effectively limit the oscillator vibration amplitude. The impact, however, depends on various system parameters, especially the mechanical damping. Comparing the results to an energy-harvesting prototype, one can conclude that, in practice, the linear model based on a homogeneous magnetic field provides a good estimate. The authors finally give suggestions about magnetic fields that are beneficial for energy harvesting.

The performance of more than 60 different electromagnetic energy harvesters described in more than 100 publications is benchmarked. The benchmarking is based on earlier published parameters from literature as well as on two novel parameters introduced in this paper. The former allow to compare different harvester conversion principles as well as harvesters of different electrodynamic design principles. The latter consider the impact of ambient and boundary conditions for the most important sub-group, namely the resonant electrodynamic harvesters. The special consideration of how the mechanical damping and the energy conversion effectiveness depend on these conditions enables a fairer benchmarking of this common harvester type. High performing prototypes are identified, and the key parameters are provided for explanation. Finally, beneficial design approaches and the main challenges to maximize the output power are pointed out.

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