Recent advances in piezoelectric and triboelectric self-powered sensors for human-machine interface applications

The burgeoning internet of things (IoTs) and artificial intelligence (AI) technologies have prospered a variety of emerging applications. Human-machine interfaces (HMIs), for instance, enables users with intuitive, efficient, and friendly way to interact with machines, capable of instant information acquisition, processing, communication, and feedback, etc. These features require ultra-compact and high-performance transducers, and therefore self-powered sensors have become the key underlying technology for HMI applications. This review focuses on the piezoelectric, triboelectric, and hybrid self-powered sensors with particular attention to their microstructures and fabrication methods, showing that both traditional microfabrication and emerging fabrication methods like three-dimensional (3D) printing, electrospinning, and braiding have contributed to the planar, array, porous, fabric, and composite type self-powered sensors. Moreover, the integration method of piezoelectric and triboelectric sensor arrays (TSAs) is investigated. The crosstalk issue is highlighted, i.e. the signal interference between adjacent sensing units, and current solutions such as array design optimization, signal processing improvement, and material innovation to reduce crosstalk sensitivity have been reviewed through specific examples. Three categories of HMI applications have been outlined, including intelligent interaction, robotics, and human monitoring, with detailed explanations of how the self-powered sensors support these HMI applications. Through discussion of challenges and prospects, it is proposed that further coordinating the design and fabrication of micro devices with HMIs will potentially boost the intelligent application with even higher level of diversification, convenience, and interconnectivity.