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Methane leakage is also an issue for several other industries. However, hard wiring is not practical or cost effective and battery power is unacceptable due to the need for regular changes requiring engineers working in hazardous areas at great expense. The sustainability challenge of additional travel associated with device maintenance and disposal of used batteries in the millions is also environmentally unacceptable. Worker safety monitoring with lower-cost portable methane detectors requires bulky, rechargeable battery-powered devices that the industry is seeking to avoid for operational and environmental reasons. Various low-cost sensor technologies have been applied to methane sensing (catalytic, optical - non-dispersive infrared (NDIR), semiconducting metal oxide and electrochemical) with catalytic/pellistor sensors formerly being dominant but in recent years replaced by NDIR sensors overcoming issues of accuracy, susceptibility to poisoning, short lifetimes, power consumption, recalibration and requirement for oxygen presence. It also has the advantage of being a fail-to-safe technology. In this work, we present an optical NDIR gas sensor that uses a fast-response semiconductor light source/detector optopair operating at <1 mW power consumption, compatible with powering from photovoltaic based energy harvesting. This is a step change from current state-of-the-art gas sensor technologies and orders of magnitude lower than filament/thermopile based detectors. Fabrication of the sensor is discussed, including; semiconductor mid-IR optopair fabrication, mid-IR optical interference filter deposition and injection molded 2-mirror parabolic reflector optical system preparation. Sensor response to methane is discussed and light harvesting operation is demonstrated, enabling compatibility with wireless distributed methane sensor networks. |
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