Harvesting Low-Frequency (<5 Hz) Irregular Mechanical Energy: A Possible Killer Application of Triboelectric Nanogenerator

TLDR

EMGs and TENGs are the leading ambient mechanical energy harvesters, but their effectiveness varies with triggering frequency. The study compared EMG and TENG outputs under <5 Hz motion, finding EMG output scales with frequency squared while TENG output scales linearly with frequency. At low frequencies, TENGs outperform EMGs, delivering high, frequency‑independent voltages (>10–100 V) that can power devices, while EMGs produce insufficient voltage (<0.2–4 V), making TENGs lightweight, low‑cost, scalable and ideal for harvesting energy from human motion or ocean waves.

Abstract

Electromagnetic generators (EMGs) and triboelectric nanogenerators (TENGs) are the two most powerful approaches for harvesting ambient mechanical energy, but the effectiveness of each depends on the triggering frequency. Here, after systematically comparing the performances of EMGs and TENGs under low-frequency motion (<5 Hz), we demonstrated that the output performance of EMGs is proportional to the square of the frequency, while that of TENGs is approximately in proportion to the frequency. Therefore, the TENG has a much better performance than that of the EMG at low frequency (typically 0.1–3 Hz). Importantly, the extremely small output voltage of the EMG at low frequency makes it almost inapplicable to drive any electronic unit that requires a certain threshold voltage (∼0.2–4 V), so that most of the harvested energy is wasted. In contrast, a TENG has an output voltage that is usually high enough (>10–100 V) and independent of frequency so that most of the generated power can be effectively used to power the devices. Furthermore, a TENG also has advantages of light weight, low cost, and easy scale up through advanced structure designs. All these merits verify the possible killer application of a TENG for harvesting energy at low frequency from motions such as human motions for powering small electronics and possibly ocean waves for large-scale blue energy.