A Novel Flexible Microwave Sensor Chip for Simultaneous Monitoring of Oil Acidity and Water Content

This paper presents a square spiral-based flexible microwave sensor chip fabricated by MEMS technology. It can realize monitoring of oil acidity and water content at the same time with only a few millimeters size and can be bend suitable for various tubing wall shapes. The chosen shape and line width of the microwave sensor result in a great resolution in distinguish water content and acidity of oil. The results demonstrate several key sensing capability: (1) an excellent discriminating ability on water content at the frequency of approximately 5GHz without interference from oil acidity; (2) an excellent discriminating ability on acid value at 100 kHz without interference from water content in oil; (3) the electrode with a typical 25μm in width achieves the lowest detection limit and has the highest sensitivity. As shown from the results, the proposed microwave sensor can be potentially used in oil quality monitoring on all kinds of narrow occasions.