Investigation of nonlinear damping in vibration energy harvesters

Energy harvesting continually attracts more interest as a result of the development technologies such as wireless sensor network systems, condition-based monitoring (CBM) applications, structural monitoring systems, etc. Although there are many sources in the nature that can be used as ambient energy source like solar energy, wind energy and thermal energy, vibration based energy harvesters outshines among them because of its abundance and non-availability of solar energy every time. In a conventional vibration energy harvester with electromagnetic transduction mechanism, the electrical damping is linear. Because of some design challenges like limited travel span for the proof mass of the system and variable ambient vibration characteristics, many suggestions are offered up to now in order to increase the efficiency of these harvesters. Within this scope, in this study, using nonlinear electrical damping is proposed. In order to compare the efficiencies of the linearly and nonlinearly damped systems, they are both modelled and solved numerically in MATLAB environment. The simulations are carried on for both with and without including parasitic damping. Over a range of ambient vibration amplitudes and frequencies, power results are normalized and comparisons are made. It is seen that using nonlinear damping increases efficiency of the harvester in majority of the testing range when parasitic damping is not included in the analysis. As the nonlinearity of the damping increases, the efficiency of the system increases as well. When the effect of parasitic damping is examined, it is seen that as the amount of parasitic damping increases, the superiority of the nonlinear damping decreases. For the second part of the study, nonlinear damping is realized physically. An experimental setup that can hold five different coil loops and measure the open circuit voltages is design and built. For the experimental study, firstly, the relationships of the effect of magnet speed and coil turn numbers are established with initial experiments. After that an algorithm is written to calculate the desired coil configuration for a desired damping profile. The required configuration is calculated with DPF and tested experimentally with two different damping profiles one representing linear and other representing the nonlinear case. It is seen that the written algorithm successfully calculates the linear and nonlinear damping profiles. The results are then validated experimentally. As a result of this study, it is shown that nonlinear damping can be an effective and applicable way to increase the efficiencies of the vibration based energy harvesters in the future.