MEMS-based non-dispersive mid-infrared sensor for condition monitoring of lubricants

We present the development of a novel MEMS-based non-dispersive mid-infrared sensor for oil condition monitoring. Non-dispersive infrared sensors (NDIR sensors) are known for being rugged, compact, and low-cost compared to dis persive sensors or FTIR spectrometers. The sensor described here integrates all optical components into a single silicon device, allowing for a further decrease in size and cost. It can be conceptually divided into multiple segments that share a common fluidic channel. Each segment comprises a hotplate emitter, an optical bandpass filter, and a bolometer detector. The short distance of only 1.255 mm between each emitter and its detector allows a larger fraction of the emitted radiation to reach the detector, increasing signal strength compared to conventional sensor designs. The sensor’s basic functionality was validated using maritime engine oil, artificially contaminated with water, soot, and ethyl acetate, whichmimics the formation of carbonyl groups due to oxidation. The sensor successfully resolved concentrations as low as 80 ppm, 60 ppm, and 3500 ppm by weight, respectively, under an alternating voltage of 1 V to 10 V at 10 Hz.