Mechanical energy conversion systems for triboelectric nanogenerators: Kinematic and vibrational designs

Triboelectric nanogenerators (TENGs) represent a promising next-generation renewable energy technology. So far, TENGs have been successfully used as highly sensitive and self-powered internet of things (IoT) sensors and portable/wearable power sources owing to their various merits, such as their light weight, freedom of material selection, low cost, and high-power conversion. The ability to take advantage of diverse mechanical input sources is another significant advantage of TENGs. However, the irregular magnitudes and frequencies of input sources are critical limitations that currently prevent utilizing TENGs in industrial or practical applications. In this review, we focus on mechanical energy conversion systems (MECS) for the regular or controlled operation of TENGs; to do this, we employ kinematics or vibrational theory. Once we control the mechanical operation of TENGs, we can predict the power production from these devices. Furthermore, mechanical frequency matching can greatly reduce power loss from electrical circuits. Motion control from, rotational to linear movement, can effectively provide high-frequency operation of contact-separation mode TENGs, enabling us to obtain sustainable and high-performance TENGs. Finally, resonant system designs for TENGs can produce the maximum output power. Thus, we discuss how to account for damping effects or non-linear impacts when designing a resonant system with TENGs. Finally, this review offers an effective way to avoid wasting irregular mechanical input sources for TENGs, making the practical commercialization of TENGs more feasible.