A miniaturized optical gas sensor for natural gas analysis

The depletion of domestic reserves and the growing use of sustainable resources forces a transition from the locally produced natural gas with a well-known composition toward the ‘new’ gas with a more flexible composition in the Netherlands. For safe combustion and proper billing, the natural gas must be monitored at both distribution points and households. This calls for a robust and low-cost gas sensor that does not require sample preparation or a lab technician to analyze the results.

Optical absorption spectroscopy is a widely used method for material identification due to its nondestructive and self-referencing properties. However, the gas cell, where the sample to be measured is stored, limits the miniaturization of spectrometers to maintain the sensitivity. The gas-filled linear variable optical filter (LVOF) functionally integrates a wideband optical filter and a gas cell by using the resonator cavity of the LVOF as a chamber. The highly reflective mirrors and high operating order of the LVOF enhances the physical dimensions of the cavity into an effective optical path comparable to an external gas cell. Therefore, when combined with a wideband emitter and a detector array, the gas-filled LVOF enables wafer-level spectroscopy with high sensitivity and selectivity.

In this dissertation, the design, fabrication and characterization of a gas-filled LVOF for the composition measurement of natural gas is described. The functionality of the sensor is demonstrated by actual gas measurements using the main constituents of natural gas; methane, ethane and propane.