Interpreting and tracking nger motion in free space are important for human communication in the reality-virtuality continuum. End-user form-factor-free sensors integrated with neuromorphic computing capabilities can expedite the implementation of human-machine interfaces with accurate nger motion recognition. We introduce and design an ultra-exible TiO2 arti cial synapse array and organic proximity sensor conformably attachable to the nger skin surface for real-time nger motion recognition in free space. Ultra-exible synaptic device and sensor exhibit well-de ned synaptic and light-responsive electrical properties, along with mechanical robustness, and the synapse-sensor integration enables optical-electrical signal conversion. Accordingly, various nger motions for time-resolved digit patterns following a Eulerian trail in free space can be learned and recognized with up to ~95 % accuracy for different individuals at varying strains and repeated cycles. Our proposal may contribute to the development of human-machine interaction wearables for extended reality.
full textAs a fundamental way of human communication, nger motion has been used to convey intuitive nonverbal information, including expression and emphasis, for centuries 1,2 . In modern society, various expressions through nger motion (e.g., sign language and gesturing) have been combined with advanced sensing technology to transcend environmental and spatial limits 3-10 . Remarkably, real-time detection and interpretation of nger motion using a human-machine interface (HMI) endowed with advanced computational intelligence for signal processing appear promising for universal communication, helping people with disabilities adjust to their daily life and actual workspace 3,8 . When combined with the Internet of Things 3,4 and arti cial intelligence [5][6][7] , nger motion recognition can largely expand virtual societies in platforms such as the Metaverse 6,9,10 , which is an upcoming industry growth engine.To meaningfully connect human nger motion with machine operation, HMIs should be carefully designed based on the following speci cations: 1) form-factor-free user-oriented soft, lightweight, and mechanically robust sensors and neuromorphic electronic devices compatible with nger motions, 2) imperceptible integrated systems that do not restrict nger motion in three-dimensional (3D) free space, and 3) time-series processing of irregular motion signals and algorithms for accurate recognition regardless of the user and environment 11,12 . Developing a wearable HMI for the ngers satisfying these design speci cations can enhance nonverbal communication, especially in the reality-virtuality continuum 4,7,10,13 .Conventional detection and recognition of nger motion in free space generally rely on bulky HMIs that include 3D depth cameras 6,14 , infrared cameras 15 , inertial measurement units 16 , and other devices anchored to speci c positions, thus hindering detection owing to restricted elds of view 17 . Additionally, complex algorithms are required for distin...