The reported work experimentally investigates a method of more effective contactless mechanical frequency up-conversion that is based on multi-magnet plucking of a piezoelectric vibration energy harvester. Several moving excitation magnets are used to produce a periodic impulse train, which during a single plucking event consecutively deflects and then releases the cantilevered transducer to freely oscillate, thereby enabling enhanced micro-power generation performance. It was established that the proposed method is effective if a couple conditions are met. First, the transducer must be impulsively excited to produce resonant transient responses, which occurs when the ramping time of the magnetic impulse is close to the transducer rise time (defined as a quarter of the natural period). Second, the gap between the moving excitation magnets must be tuned to ensure that the impulse train period is as close to the natural period as possible. Measurements indicate that, in comparison to the conventional single-magnet plucking case, the consecutive excitation with three moving magnets leads to nearly six-fold (seven-fold) increase in average power output and total generated energy during the in-plane (out-of-plane) plucking regime.
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