Modeling and experiment of a handy motion driven, frequency up-converting electromagnetic energy harvester using transverse impact by spherical ball

• A frequency up-converting electromagnetic energy harvester using transverse impact mechanism.
• Freely movable ball conquers the inconvenience in resonance issue at frequencies below 10 Hz.
• Could be implemented efficiently for hand-held and wearable devices with optimized design.

Power generation from human-body-induced vibration faces the challenges of low frequency and high amplitude with random excitation. In such cases, employing spring-mass structure as the low frequency oscillator is unrealizable and also unreliable. Impact based frequency up-conversion mechanisms have extensively been using to overcome the challenges. Random and direct impacts on the power generating element raise the questions on reliability, as well as efficiency of the energy harvesters. In order to meet these shortcomings, we have presented a handy motion driven electromagnetic energy harvester that also uses impact based frequency up-conversion mechanism; but instead of direct impact, it utilizes transverse impact by a freely movable spherical ball. Upon handy motion excitation, the ball vibrates along a fixed–fixed cantilever beam and pushes (by transverse impact) it at right angles while comes in contact with the parabolic top surface of a proof-mass attached to the beam, allowing it to vibrate at its higher resonant frequency. Relative motion between a magnet attached to the cantilever and a coil (placed below) induces voltage. A prototype energy harvester has been fabricated and characterized. At a periodic handy motion excitation of ∼2 g peak amplitude and frequency 5.8 Hz, it is capable of delivering maximum 103.55 μW average power (5.4 μW cm−3 power density) to 85 Ω matched load resistance. Experimental results reveal feasibility and reliable operation of the proposed frequency up-converting energy harvester in harvesting power from handy motion vibration. Further optimized design would be able to offer higher power density to be used efficiently for portable and wearable smart devices applications.