Algorithm to suppress drift for micro-mirror and other intensity modulated hydrogen sensors

Abstract

Here, a method to suppress drift in intensity-modulated sensors is presented that preserves the advantages of such sensors including simplicity and low-cost components. This method is illustrated using metal hydride-based optical hydrogen sensors that can reliably, accurately, and quickly sense hydrogen across a large concentration range. These sensors rely on a metal hydride-sensing material that reversibly absorbs hydrogen when a hydrogen concentration is present. In turn, this causes a change in the optical properties which can be probed to determine the hydrogen concentration. To do this, two major methods exist: intensity- and frequency-modulated sensors. While intensity-modulated sensors are typically simpler and cheaper to fabricate, they may suffer from drifting light sources and unstable alignments. Using the fact that exposure to hydrogen reduces (increases) the optical transmission (reflectivity) of a Ta-based sensing material for blue/green light while it increases (decreases) the transmission for (near) infrared (IR) light, it is possible to differentiate between a changing hydrogen concentration and a drifting light source: Whereas the signal of both wavelengths is positively correlated for a drifting light source, the signal is negatively correlated when the hydrogen concentration changes. Using this algorithm, the drift on the signal can be reduced by a factor of 5 for intensity-modulated sensors. In a more general perspective, the wealth of information in the wavelength-dependent optical response allows for more advanced approaches to improve the signal and accuracy of (optical) sensors.