The ability to sense heat and touch is essential for healthcare, robotics, and human–machine interfaces. By taking advantage of the engineerable waveguiding properties, we design and fabricate a flexible optical microfiber sensor for simultaneous temperature and pressure measurement based on theoretical calculation. The sensor exhibits a high temperature sensitivity of 1.2 nm/°C by measuring the shift of a high-order mode cutoff wavelength in the short-wavelength range. In the case of pressure sensing, the sensor shows a sensitivity of 4.5% per kilopascal with a fast temporal frequency response of 1000 Hz owing to the strong evanescent wave guided outside the microfiber. The cross talk is negligible because the temperature and pressure signals are measured at different wavelengths based on different mechanisms. The properties of fast temporal response, high temperature, and pressure sensitivity enable the sensor for real-time skin temperature and wrist pulse measurements, which is critical to the accurate analysis of pulse waveforms. We believe the sensor will have great potential in wearable optical devices ranging from healthcare to humanoid robots.
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.
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