A novel photonic skin sensor based on tapered micro nano fiber structure coated with sodium polyacrylate film

Biomimetic skin sensing devices play an important role in next-generation healthcare, robotics, and bioelectronics. In recent years, biomimetic skin-sensing technologies have gained significant attention due to their broad-ranging utility in the fields of healthcare and automation, and future wearable devices designed for health monitoring, robotic applications, and ultra-precise industrial positioning will necessitate the incorporation of flexible optical systems. A novel photonic skin flexible sensor (PSFS) based on partially neutralized sodium polyacrylate (PAS-50) is reported for the first time in this paper. In this study, a novel wearable sensor was designed for real-time detection of temperature and humidity. A single-mode tapered fiber (SMTF) structure based on the principle of evanescent wave is proposed for fast response and real-time monitoring of humidity and temperature. The sensor incorporates an optical micro/nanofiber (MNF) as the core sensing node, while a hydrophilic and ductile Sodium Polyacrylate (PAS) is chosen as the humidity-sensitive material that overcomes the limitation of commonly reported electrical, optical, and material-based flexible devices. Due to the strain amplification effect of the MNF, the sensitivity of the material to relative humidity (RH) is significantly improved, reaching 0.1411 dB/%. In addition, the temperature response exhibits outstanding sensitivity (0.4 dB/°C) in the human skin surface temperature range (30 ∼ 48 °C). Notably, the sensor exhibits a rapid response with a remarkable response time of 170 ms. The proposed PSFS presents novel opportunities for the advancement of future biomimetic skin devices, thus playing a pivotal role in the advancement of next-generation robotics and medical monitoring technologies.