Miniature Fiber-Optic Pitot Tube Sensor

This paper presents a miniature fiber-optic Pitot tube for gas flow rate measurements created at the tip of an optical fiber. The proposed all-fiber sensor employs two in-fiber Fabry-Perot cavities/chambers. The first chamber is arranged as a differential pressure sensor using a thin flexible silica diaphragm and two side holes for measurement of the difference between stagnation and static pressure, while the second chamber acts as a reference sensor for compensation of changes in the gas refractive index. The entire sensor is fusion-spliced, and is made out of sections of silica fibers and silica capillaries. It is appropriate for mid to high-velocity microfluidic gas flow sensing where miniature size is essential. Sensor operation is demonstrated in a flow velocity range between 0 to 260 m/s with a resolution better than 1.5 m/s. The sensor has a diameter of only 200 μm.