This paper reports a hula-hooping-like nonlinear buckled elastic string electromagnetic energy harvester for wideband vibration energy harvesting. The harvester is comprised of a magnetic rotor attached at the middle of a clamped-clamped buckled elastic string and a stator with an embedding coil array. Attributed to the geometric nonlinear characteristic of the elastic string, the harvester can convert the reciprocate vibration in arbitrary in-plane direction to a hula-hooping-like curvilinear translation plane motion. A hardening nonlinear wideband voltage response was demonstrated by sweep excitation from 5 ∼ 23 Hz. The output peak power for a single coil can reach 1.12 mW at a 5 ms −2 excitation. To overcome the phase delay effects between the voltages of three spatially distributed coils, they were rectified separately and connected serially or parallelly to provide the final output. An open circuit peak voltage of 0.53 V was obtained from the serial connection at a 4 ms −2 up-sweep excitation, under which a 100 µF capacitor was successfully charged to 0.35 V within 120 s. The omnidirectional energy scavenging performance of the harvester was further validated experimentally, suggesting its great promise for practical vibration energy harvesting.
The development of "smart" residential thermostats-both in terms of wider connectivity and higher intelligence-has revealed great opportunity for energy conservation, as well as providing comfort and convenience. This paper focuses on the interaction design of such a novel system, and analyzed user requirements for input, output, and level of intelligence systematically through both in-depth interviews and a survey.
Two-degrees-of-freedom magnetically coupled energy harvesters have been presented by several researches to achieve a broader response bandwidth. However, most two-degrees-of-freedom systems are composed of two piezoelectric beams, while in the low frequency operating environment with limited space, the dimension of the piezoelectric beam is limited which leads to high stiffness of the generated beam. Therefore, the output of dual-beam system is relatively low under low frequency and amplitude vibrations. This paper presents a magnetically coupled two-degrees-of-freedom energy harvester by using torsional spring. The proposed harvester consists of a piezoelectric beam with a tip magnet and an interacting magnet mounted on a rotatable bar with a torsional spring. The shape of the potential well changes with the rotation of the bar, facilitating the occurrence of the snap-through motion under low amplitude and wideband vibration excitation. What’s more, the stiffness of the torsional spring can be easily adjusted to make the designed harvester suitable for low frequency vibrations. Compared with the conventional bi-stable harvester, the presented harvester could easily overcome the potential barrier and generate larger power under low excitation intensity. Analytical, simulation, and experimental results demonstrate that the proposed energy harvester is capable of harvesting low frequency wideband vibration energy.
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