<p class="MsoNormal" style="text-align: justify; text-indent: .5in; line-height: 200%">In this article, a novel low-frequency, tunable, enhanced vibration energy harvester design is introduced as a power module for operating portable electronics and smart wearable devices. &nbsp;Since most sources of ambient vibrations around us are rich in low frequencies the power module presented in this work is specifically designed to target these low frequency oscillations, i.e. less than 5 Hz. Low frequency operation adds significant challenges to design process of energy harvesters; requiring an extremely soft spring and large mass and, therefore, resulting in large displacement and occupied volume. Nonetheless, the power module presented here overcomes this challenge through a unique spiral torsion spring system that allows for low frequency specialization while maintaining its small size, i.e. portable hand-held power module. Another crucial feature of the power module is its tunability; allowing it to operate in different modes in order to maximize electric power recovered from variety of daily activities.&nbsp; For example, while most forms of human activities occur at frequencies lower than 5 Hz the frequencies of these activities vary slightly (Walking: 1.9 Hz, Cycling: 2 Hz, Running: 3Hz, Hand shaking: 4.6 Hz). &nbsp;The spring system in the power module can be tuned using a spring tuning mechanism in order to achieve desired frequency response. For example, by adjusting the power module settings, one can tune the power module to reach a desired mode of operation that will guarantee frequency match between the resonant frequency of the power module and the excitation frequency imposed by the human activity (running, cycling, etc.,). The hand-held tunable power module offers additional desired features.&nbsp; For instance, the energy harvesting system inside the power module uses multiple coil sections with opposite winding direction, and multiple magnets that are arranged in a repulsive configuration. While the repulsing magnets arrangement yields a desired increase in the magnetic field gradient, the multiple coil section (with opposite winding direction) arrangement increases the voltage output without increasing the internal resistance of the coil. A desired low output impedance is achieved; ensuring output current that is large enough which to meet the threshold required to operate typical low-power sensors and portable electronics, i.e. 10 mA.</p><p class="MsoNormal" style="text-align: justify; text-indent: .5in; line-height: 200%">In this work we present our effort to design, model, fabircate, and characterize the power module. We also present field testing and real world demonstration of the power module while implemented as a power source for charging a smart phone from daily activities including running, cycling, driving, etc.</p>

Tunable Enhanced Vibration Energy Harvester as a Power Module for Portable Electronics and Iot Sensors

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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