Abstract
Electronic skin, a class of wearable electronic sensors that mimic the functionalities of human skin, has made remarkable success in applications including health monitoring, human-machine interaction and electronic-biological interfaces. While electronic skin continues to achieve higher sensitivity and faster response, its ultimate performance is fundamentally limited by the nature of low-frequency AC currents. Herein, highly sensitive skin-like wearable optical sensors are demonstrated by embedding glass micro/nanofibers (MNFs) in thin layers of polydimethylsiloxane (PDMS). Enabled by the transition from guided modes into radiation modes of the waveguiding MNFs upon external stimuli, the skin-like optical sensors show ultrahigh sensitivity (1870 kPa-1), low detection limit (7 mPa) and fast response (10 μs) for pressure sensing, significantly exceeding the performance metrics of state-of-the-art electronic skins. Electromagnetic interference (EMI)-free detection of high-frequency vibrations, wrist pulse and human voice are realized. Moreover, a five-sensor optical data glove and a 2×2-MNF tactile sensor are demonstrated. These initial results pave the way toward a new category of optical devices ranging from ultrasensitive wearable sensors to optical skins.
Highlights
Over the past decades, breakthroughs in flexible electronics and nanotechnology have enabled wearable electronic sensors[1,2] that respond to external stimuli via capacitive[3], resistive[4], piezoelectric[5], and triboelectric[6] effects
We use a thin layer of PDMS, a highly flexible and biocompatible polymer with refractive index (n=1.40) slightly lower than that of silica (n=1.46), to enclose the MNF and isolate the evanescent fields, while maintaining high mechanical flexibility and low optical losses of the MNF (Fig. S2)
We have demonstrated a new class of wearable optical sensors that greatly surpasses conventional wearable sensors in sensitivity, response time and Electromagnetic interference (EMI) immunity
Summary
Breakthroughs in flexible electronics and nanotechnology have enabled wearable electronic sensors[1,2] that respond to external stimuli via capacitive[3], resistive[4], piezoelectric[5], and triboelectric[6] effects. Optical micro/nanofibers (MNFs), which are about 1 μm in diameter, are capable of guiding light with high flexibility[15]. Owing to their atomically-precise geometric uniformities, they offer waveguiding losses (e.g., 5 Gpa17) higher than spider silks (0.5–3.6 GPa18). We demonstrate a simple and general approach to wearable optical sensors by embedding glass MNFs in thin layers of polydimethylsiloxane (PDMS). Based on the transition from guided modes into radiation modes of the waveguiding MNFs upon external stimuli, the single-MNF optical sensors are demonstrated for pressure and vibration sensing with extraordinary high sensitivity and fast response. A five-sensor optical data glove and 2×2-MNF tactile sensors are demonstrated for controlling the movement of a mechanical hand and detecting the exact location of a touch, respectively
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