| This paper describes the design, development and characterization of a silicon-based ball-tip optical fiber sensor for monitoring ammonia concentration in solutions. It is an extrinsic optic fiber sensor which is based on the light transmission absorption mode. An effective method has been developed to mix the pH indicator with PDMS as the sensing material by using ultrasound stirring, and a tip coating approach has been successfully applied to attach the sensing material on the optical fiber tip. The size of the sensing element is less than 4mm2. However, the sensitivities of the sensor using the bromocresol purple are as low as 100ppb and 300ppb in the stagnant and dynamic solutions respectively. It also exhibits short response time, a good reversibility and long working life time. It detects ammonia within 10 seconds and shows more than 96% reversibility even though it is used for more than 20 days. An efficient calibration method has been invented to remove the interruptive factors such as temperature, pressure and light source input intensity alterations. |
