Dynamic Inclinometer Based on Optofluidic Manipulation of Bubble-In-Fiber With Large Range and Fast Response for Posture Monitoring

A method for dynamic inclination measurement based on bubble-in-fiber (BiF) optofluidic manipulation is proposed. The photothermal interaction induces the solute Marangoni flow in binary mixed solution. Strong capture of the microbubble on the fiber-end is achieved. The two-beam Fabry-Perot interferometer (FPI) is formed by microbubble attracted by the end-face of the single-mode fiber (SMF). The BiF is always attracted to the fiber end-face, regardless of the change in inclination. The equilibrium position of the BiF at the end-face is affected by the inclination angle, which in turn changes the reflected light intensity coupled back to the SMF. The proposed “probe-type” dynamic inclination sensor has a wide range of inclination response from 0-90°. In addition, its superior dynamic performance makes it possible to measure human leg postures. The intensity-based demodulation has the unique advantage of being low-cost and commercially available. It is expected to be integrated with wearable devices, making it a perfect candidate for sensing the motion of an organism online.