Bending the Straight into Curved: A Tree-Ring-Inspired Fully Printed Omnidirectional Triboelectric Nanogenerator with Ring-Nested Structure for All-In-One Wearable Self-Powered Systems and IoT Smart Packaging

The free-standing triboelectric nanogenerator (FS-TENG), known for its simple structure and a universal external friction layer, has gained attention in wearable electronics and IoT smart packaging. Nevertheless, the design of parallel electrodes limits sliding energy conversion from multiple angles. In this paper, inspired by the tree ring structure, a structurally simple omnidirectional triboelectric nanogenerator (O-TENG) was designed. By the "bending the straight into curved" approach, the traditional parallel straight electrodes of the FS-TENG are transformed into a ring-nested electrode structure, achieving sliding energy harvesting and electrical signal generation from arbitrary angles. The fully printed O-TENG by optimizing its dielectric properties for the friction layer, achieving a maximum open-circuit voltage and short-circuit current of 232.45 V and 1.37 µA, respectively. Thanks to the symmetrical ring-nested structure, the relative standard deviations of the open-circuit voltage and short-circuit current across multiple angles were only 2.63% and 4.52%. When integrated with micro-supercapacitors and printed on fabric, the O-TENG-powered system successfully ran a digital watch after 1006 s of motion. Furthermore, the system integrated a printed electrochromic device (ECD) to develop a motion-interactive optical modulation system, where the ECD changed from light blue to dark blue after 398 s of arm friction during running. Finally, the O-TENG, printed as a sensor tag on packaging, monitors multi-angle sliding motion. Therefore, the bio-inspired simplified O-TENG, associated with its fully printed fabrication and integration method, show great potential for novelty developments of wearable electronics and IoT smart packaging.