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In vibration energy harvesting systems, mechanical damping is reduced to minimum to get large electrical power output. However, small mechanical damping will result in a narrow bandwidth in the frequency domain. This will lead to non-ideal performance when the excitation frequency does not match with the natural frequency. In human body energy harvesting backpack, the human comfort will also have to take into consideration besides harvesting power. In this paper, we proposed an electrical damping tuning method for energy harvesting backpack. The electrical damping will change according to the excitation frequency to achieve high power output at lower frequency. In this way, the frequency bandwidth increases. At resonance and high frequency, the damping will be tuned to control the maximum stroke of the backpack. This will make the wearer feel comfortable while substantial power is harvested. The electrical damping tuning circuit senses the input frequency and tunes the electrical damping accordingly. The circuit design and the control strategy are described in detail. Experiment will be done to validate the design goals.
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