This writeup was originally featured on Tech Briefs
Sensing of gases is a critical function but the technology hasn’t changed in decades. So, when I heard about a brand-new type of sensor from NevadaNano (Sparks, NV), I decided to interview Ben Rogers, their Director of Engineering.
MOLECULAR PROPERTY SPECTROMETER
They call their sensor, a MEMS-based device, the Molecular Property Spectrometer™ (MPS™).
The MPS Flammable Gas Sensor can detect and identify the concentrations of 12 of the most common combustible gases, including hydrogen; the MPS Methane Gas Sensor is designed to monitor methane leaks for the oil and gas industries; the MPS Refrigerant Gas Sensor detects mildly flammable low global warming refrigerants— all based on the same technology. According to Rogers, their sensor is far more accurate and reliable than the traditional Pellistor (catalytic bead sensor) and Nondispersive Infrared Sensor (NDIR). Most traditional sensors have a coating that excites some sort of chemical reaction. The problem is that over time, the sensing sites that enable the reaction can be ruined. The MPS, however, is an inert silicon-based surface, which doesn’t require any chemical reaction. It heats up, measures the thermodynamic properties of the air, and then cools back off again, so it can last for 10 years or more without any calibrating, according to Rogers.
IDENTIFYING A GAS
The MPS is built into about an inch-sized package, as shown in Figure 1. Air to be tested enters through the mesh screen at the top and impinges upon a suspended, tethered micro hotplate, which is the same diameter as a human hair — 100 microns across. The hotplate can be heated up to hundreds of degrees Celsius. The source of the heat is a Joule heater, in which an electric current is fed through a resistive element as shown in the inset of Figure 1. The current comes in on one of the tethers, swirls around and comes out on that trace. “We can measure the resistance of the hotplate, which gives us its temperature and also the power it took to reach that temperature,” said Rogers. The relationship between the temperature of the plate and the power required to reach that temperature is a function of the thermal conductivity of the air. READ MORE