Optical Microfibers for Sensing Proximity and Contact in Human–Machine Interfaces

• Published in: ACS applied materials & interfaces 2022-03, Vol.14 (12), p.14447-14454
• Main Authors: Liu, Haitao, Song, Xingda, Wang, Xiaoyu, Wang, Shuhao, Yao, Ni, Li, Xiong, Fang, Wei, Tong, Limin, Zhang, Lei
• Format: Article
• Language: English
• Subjects: Functional Nanostructured Materials (including low-D carbon); Humans; Humidity; Mechanical Phenomena; Touch; Wearable Electronic Devices
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.1c23716

The monitoring of proximity-contact events is essential for human–machine interactions, intelligent robots, and healthcare monitoring. We report a dual-modal sensor made with two functionalized optical microfibers (MFs), which is inspired by the somatosensory system of human skin. The integrated sensor with a hierarchical structure gradationally detects finger approaching and touching by measuring the relative humidity (RH) and force-triggered light intensity variations. Specifically, the RH sensory part shows enhanced evanescent absorption, achieving a sensitive RH measurement with a fast response (110 ms), a high resolution (0.11%RH), and a wide working range (10–100%RH). Enabled by the transition from guided modes into radiation modes of the waveguiding MF, the force sensory part exhibits a high sensitivity (6.2%/kPa) and a fast response (up to 1.5 kHz). By using a real-time data processing unit, the proximity-contact sensor (PCS) achieves continuous detection of the full-contact events, including finger approaching, contacting, pressing, releasing, and leaving. As a proof of concept, the electromagnetic-interference-free PCS enables a smart switch system to recognize the proximity and contact of bare/gloved fingers. Moreover, skin humidity detection and respiration monitoring are realized. These initial results pave the way toward a category of optical collaborative devices ranging from human–machine interfaces to multifunctional on-skin healthcare sensors.