Comb-structured triboelectric nanogenerators for multi-directional energy scavenging from human movements.

A triboelectric nanogenerator (TENG) is an emerging energy harvesting technology utilizing multi-directional, wasted mechanical energies stemming from vibrations, winds, waves, body movements, etc. In this study, we report a comb-structured TENG (CTENG) capable of effectively scavenging multi-directional motions from human movements, which include walking, jumping, and running. By attaching CTENG to a person's calf, we obtain a root-mean-square (RMS) power value of 5.28 µW (i.e. 13.12 V and 0.4 µA) for 1 s during mild running action (~5 m/s), which is sufficient for powering 10 light emitting diodes (LEDs). We integrate a CTENG with a simple hand-held pendulum (HHP) system with a natural frequency of 5.5 Hz. The natural frequency and input energy of our HHP system can be easily controlled by changing the holder mass and initial bending displacement, thus producing different output behaviors for the CTENG. Under the optimal HHP-based CTENG system design, the maximum output reaches 116 V at 6.5 µA under 0.1 kg mass and 4 cm bending displacement conditions. The corresponding output energy is 52.7 µJ for an operation time of 10.8 s. Our HHP-CTENG system can sufficiently power 45 LEDs and shows different output performances by varying the driving velocity of a vehicle, thus demonstrating the possibility for a self-powered velocity monitoring system.

Moving objects by imagination? Amount of finger movement and pendulum length determine success in the Chevreul pendulum illusion.

Hand-held pendulums can seemingly oscillate on their own, without perceived conscious control. This illusion, named after Chevreul, is likely a result of ideomotor movements. While this phenomenon was originally assumed to have a supernatural basis, it has been accepted for over 150 years that the movements are self-generated. However, until now, recordings of the small movements that create these oscillations have not been performed. In this study, we examined how participants produce these unconscious oscillations using a motion capture system. As expected, the Chevreul pendulum illusion was produced when the fingers holding the pendulum generated an oscillating frequency close to the resonant frequency of the pendulum, where very small driving movements of the arm are sufficient to produce relatively large pendulum motion. We found that pendulum length significantly affected the ability to produce the illusion - participants were much more successful with a 40 cm compared to an 80 cm pendulum. Further, we found that participants that tended to move their fingers more were more successful in producing the illusion but did not find a connection between inter-joint coordination and ability to generate the illusion.