Flexible electronics is a state-of-the-art concept for the next generation of wearable device, emphasizing the deformability, comfort and portability. Recent advances in intrinsically stretchable/flexible material and fancy structural mechanics design pave a promising avenue toward human-machine interface, biomedical engineering as well as daily life. To further realize the advantages, light, flexible and self-powered triboelectric nanogenerator (TENG) is placed great hopes to replace the conventional powering part. Nevertheless, the present TENGs are still poor in stretchability, miniaturization could reduce the strain but result in significantly decreasing performance, limiting its application scenarios such as tactile sensing and motion monitoring.

Structural mechanics design and strain simulation based on finite element analysis are feasible to improve the stretchability of TENG. In chapter 2 we introduced the design principle of structural mechanics design and strain simulation. In chapter 3, we reported a stretchable pressure sensor based on triboelectric effect and dots-distributed metallic electrodes, adopting contact-separation mode. The dots-distributed electrode based triboelectric nanogenerator (D-TENG) could be easily integrated with body and cloth, such as on the skin and under foot, to sense a broad range of activity-related strain information. The D-TENGs enable accurate detecting a broad range pressure from ~5 kPa to ~50 kPa with open-circuit voltage variation from several volts to tens of volts, and thus allow monitoring body daily actives such as joints’ bending, walking and running. These devices maintain stable and high-level signal outputs even after thousands cycles of measurement, proving the good stability. Simultaneously, the mechanical energy produced by our body motions could also be recollected by the D-TENG sensor for energy harvesting. Under an impulse tapping by finger (39.59 kPa), the induced voltage is sufficient to light up 15 LEDs. This work demonstrated a reliable design to improve the stretchability of electrode. What is more, based on structural mechanics design of electrode, the stretchability optimization needs furtherly demonstration by studying the stability of performance under deformations, which it is valuable for skin-integrated TENG.

Recent advances in engineering materials and devices that used in electronics skin (E-skin) have been successfully implanted into TENGs for realizing ultra-thin and skin-integrated tactile sensors. Ahead which two challenges still remain: poor stretchability result in unstable performance under skin deformations; fairly large size is required to guarantee high signal output and dilute crosstalk problem, leading to limited resolution for tactile mapping. In chapter 4, trampoline-inspired mechanics design and processing techniques in epidermal electronics are combined together to develop a thin, soft, stretchable self-powered tactile sensors based on TENG for E-skin. With the assistance of microstructure modifying by sandpapers, the TENG sensor exhibits great improved electrical performance and capable of distinguishing a broad range of pressure, with a great sensitivity of 0.367 mV Pa^-1. The resulted TENG sensor exhibits excellent stretchability and sensing stability with accurate unchanged signal outputs even under a high-level strain up to 35%. Demonstrations of the sensors associating with the integration with a glove for human-machine interfaces and the development of a 4 × 4 tactile array for pressure mapping and recognition of contact objects, offers great opportunity for next generation of self-powered E-skin.

In conclusion, the self-powered pressure sensors based on stretchable structural design and triboelectric effect have been developed, the devices could be integrated on human body and provide reliable pressure sensing even under deformations with skin, displayed their great potentials in various wearable sensing and power source, indicating a bright future in human-machine interface.