Abstract
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.
Highlights
Increasing demand for autonomous self-charging devices requires effective implementation of energy harvesting methods in order to reduce heavy reliance on inconvenient batteries
It is very difficult to ensure stable high-power generation with wearable piezoelectric vibration energy harvesters (P-VEHs) since human body parts move at very low frequencies and high amplitudes, piezoelectric transducers used in P-VEHs may deliver practically useable power levels only when excited to resonate at high frequencies (> 50-100 Hz), accompanied by very low vibration amplitudes [6,7,8]
This paper presents experimental demonstration of a more effective contactless mechanical frequency upconversion (MFU), which is based on multimagnet plucking
Summary
Increasing demand for autonomous self-charging devices requires effective implementation of energy harvesting methods in order to reduce heavy reliance on inconvenient batteries. It is very difficult to ensure stable high-power generation with wearable P-VEHs since human body parts move at very low frequencies (usually, up to several hertz) and high amplitudes, piezoelectric transducers used in P-VEHs may deliver practically useable power levels only when excited to resonate at high frequencies (> 50-100 Hz), accompanied by very low vibration amplitudes [6,7,8] This major mismatch between the excitation and operation conditions of the transducers is usually resolved by means of mechanical frequency upconversion (MFU) [9,10,11,12,13]. In order to measure generated voltage signals and derive average power output during different multi-magnet excitation conditions we used a cantilevered piezoceramic (PZT-5A) bimorph transducer made by Piezo Systems Inc. with the dimensions of 31.8 57.2 mm (Table 1) This type of transducer was chosen due to relatively high piezoelectric coefficients, permittivity and high electrical outputs, which are useable for vibration energy harvesting purposes [15].
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