Human-motion energy harvesting is emerging as a promising solution for wearable electronics and devices, offering a sustainable power source that extends operational longevity and enhances durability. However, current techniques and prototypes have yet to achieve fully interactive, battery-free functionality. This paper presents a battery-free interactive gaming system powered by energy harvested from transient fingertip motion. To ensure the reactivity, interactivity, and stability of the fingertip motion harvester (FMH), we employ a multistable structure. The FMH unit provides a reliable energy solution by utilizing precharged potential energy within dynamically varying potential wells. Additionally, the integration of a bistable screen design facilitates seamless gaming experiences, decouples game logic from user interface mechanics, and ensures rapid system recovery after power interruptions. Beyond advancing fundamental research, this work pioneers a practical battery-free interaction paradigm based on fingertip motion, with potential for broader battery-free user interfaces and low-power interactive systems.

This demonstration showcases a battery-free wireless keyboard that utilizes the kinetic energy generated from key presses to generate electrical power. Each key incorporates a Quasi-Static Toggling harvester, which employs potential energy pre-charging to ensure a consistently reliable energy output. Extensive practical testing has confirmed that this keyboard exhibits responsiveness and low latency comparable to traditional wireless keyboards. This study represents a significant improvement over previous battery-free IoT applications that often compromised service quality, as it offers a stable energy-harvesting mechanism and provides a dependable framework for designing battery-free devices.

Vibration energy harvesters have been widely investigated to supply sustainable power for devices in the Internet of Things (IoT). Despite the advances in vibration energy harvesters, there still remain challenges in the design and optimization of energy harvesters to meet the increasing power demand of long-range IoT applications. In this article, an auxetic piezoelectric energy harvester with tapered thickness (TAEH) is proposed to improve the efficiency of energy harvesting by achieving the uniform stress and high average stress. Compared with traditional auxetic piezoelectric energy harvester with uniform thickness (UAEH), the stress distribution with tapered thickness is more uniform, which can contribute to a higher power output with lower maximum stress. Furthermore, the multiobjective optimization is used to further improve the average stress values without increasing the maximum stress, thus increasing the energy output. Finite element analysis is performed to validate the performance of the energy harvesters. In the experimental validation, it is found that with the tapered thickness introduced to the auxetic energy harvester, the maximum power output and power density of TAEH can be increased by 212.84% and 279.08%, respectively, compared with UAEH. After the optimization, these two indices of the optimized TAEH (OTAEH) are further increased by 24.32% and 27.59%, respectively. Specifically, a high power density of 0.148 mW/g is achieved in the OTAEH, indicating its high vibration energy harvesting performance with lightweight. Finally, it is demonstrated that the OTAEH can generate more than 40.94 mJ within 27.6 s to successfully power an IoT device for temperature sensing and long-range data transmission.