Optical liquid-level sensor based on a designed light guide plate

An optical liquid-level sensor based on a designed light guide plate (LGP) is proposed and experimentally demonstrated. Light transmits between the two surfaces of the LGP as in an optical waveguide. The front surface of the LGP is planar and contacts the liquid, and the back surface is designed with microstructures to uniform the light distribution by scattering. The uniform light intensity that escapes from the LGP abruptly decreases at the liquid level. A linear charge-coupled device (CCD) near the back surface is used to detect the liquid level by detecting the abrupt decrease in the light intensity. The feasibility of the proposed sensor is proved by a ray-tracing simulation and an experiment. The sensor shows high linearity and accuracy with a measurement error of 0.12 mm. The measurement range can be extended flexibly.