Comparative Study of Frequency Response of Triboelectric and Piezoelectric Energy Harvesters

Piezoelectric and Triboelectric energy harvesters are efficient in scavenging useful electrical energy from the low-frequency mechanical vibrations scattered in our ambient. Several researchers have compared the performance of a standalone triboelectric and piezoelectric energy harvester operating under very low frequencies (< 5 Hz). However, there have been no reports of comparison between devices designed with the exact same topology and observing the variation in their relative frequency response under varying design parameters and operating conditions. In this paper, we present a comparative study of frequency response of the triboelectric nanogenerators and impact-driven piezoelectric generators. Both these devices are realized as a combination of a cantilever beam and an impact layer. They have a similar operating mechanism in the sense that they involve an impact between a vibrating beam and a rigid impact layer, but the inherent energy generation mechanism in both cases is very different. Due to this, we observe stark differences in the frequency response of these devices at different resonant frequencies and under varying gap lengths and acceleration amplitudes. We have initially explained the basic energy generation mechanism and developed an analytical model for the triboelectric and piezoelectric mechanisms. It is then solved numerically to predict the device operation and validated using device fabrication and experimentation. This is followed by observation, comparison and explanation of their contrasting frequency responses. This study is crucial as it assists in understanding the contrast that exists between the two energy harvesting mechanisms and will hopefully be useful while choosing and designing any piezoelectric/triboelectric device for powering low power wearable sensors from ultra-low frequency, wideband human motions.