Invited Paper VT-MoM1
Miniature Fiber Optic Pressure Sensors: Technologies and Applications

Monday, November 10, 2014, 8:20 am, Room 303

Compared with their electrical counterparts, fiber optical sensors offer many advantages including small size, immunity to electromagnetic interference, convenient light guiding through optical fibers, high sensitivity, high resolution, large bandwidth, and low noise. Recently, miniature fiber optic pressure sensors have attracted much attention for many applications including biomedical, surveillance, and industrial applications. Most of these sensors are based on a Fabry-Perot interferometer fabricated directly on an optical fiber end face with a silica/silicon (Si) diaphragm serving as a pressure transducer. Although these sensors have a small size (~100s micros in diameter), they suffer from important issues including low sensitivity due to the high elastic moduli of silica/Si (130-185 GPa), and high brittleness and easy breakage of the sensor elements.

In this paper, the research program at the Sensors and Actuators Laboratory (SAL) of the University of Maryland on miniature fiber optic pressure sensors based on polymer or grapheme diaphragms will be introduced. First, our work on polymer based miniature optical pressure sensors will be discussed. The polymer materials have superior elasticity and high fracture strength, which enables polymer based sensors to have superior sensitivity even at a small size and helps prevent cracking or breaking of the sensors. Furthermore, these sensors can be fabricated by using relatively simple and inexpensive processes. We have developed several unique low-cost micro-fabrication processes for these sensors, including self-aligned photolithography and UV molding process. By using simple and safe procedures, a polymer based Fabry-Perot cavity can be directly fabricated at the end of optical fiber, thus eliminating the necessity for complicated assembly of the sensing element and the optical fiber. Further, since polymer based sensors inherently suffer from temperature driftdue to the large thermal expansion coefficient of polymer materials, novel temperature compensation methods for the polymer based fiber optic pressure sensors will also be discussed. Second, miniature fiber optic pressure sensors utilizing a graphene diaphragm will be presented. Graphene is believed to be one of the strongest materials and the thinnest film in the universe, and it can be stretched by as much as 20%. These unique mechanical properties render graphene an excellent choice for miniature acoustic sensors with unprecedentedly high sensitivity, large bandwidth, and large dynamic range. Finally, the potential applications of these different sensors will be discussed.