University researchers have developed a way to improve sensors that are used to detect hazardous gas levels, zero in on narcotics and sniff out spoiled food.
A research project led by Dr. Mohammed Madani, an electrical engineering professor, has yielded an innovative method to insulate metal oxide semiconductor gas sensors.
Such “MOX” sensors trigger chemical reactions that identify and measure gaseous substances. They are used to locate explosives and chemicals, check air conditioners for leaking refrigerant, monitor air pollution, or signal the start of a fire.
The sensors, which are embedded in computer chips, outfit everything from large screening machines in airport terminals to small, hand-held breathalyzers.
“They can be used to detect almost any gaseous substance,” Madani said.
The sensors feature a film of tin oxide, zinc oxide, titanium oxide or any metal oxides. When a gas reaches a specific, minute level, the film reacts.
“Different metal oxides behave differently with different gases and different temperatures,” Madani said.
An exchange of electrons between the gas and the sensing layer material, at a given temperature that is regulated by the thin film heater, is enough to trigger the detection. The desired temperature is achieved by an “air gap” method.
The plates are suspended above an air pocket, held in place by four narrow strips protruding from each corner. The strips are, however, “delicate, easily damaged and often malfunction during fabrication or usage,” Madani said.
So, UL Lafayette researchers have devised an alternative insulation method. It involves layering a silicone wafer with a thin film of silica aerogel.
“It’s more durable, space efficient and practical. Silica aerogel is a better heat insulator than any substance that exists today,” Madani said. The most common aerogel is made from a synthetic form of silicon dioxide.
“Silica aerogel is very porous, light as air, but at the same time, it’s very tough,” Madani said.
Researchers have created a way to place a heating element atop the silica aerogel, eliminating the support bridges required with air-gap insulation.
Providing extra space is important, since a cluster of 21 metal oxides can detect the presence of nearly any gas, expanding the capabilities of one piece of equipment, making it more streamlined and more affordable.
A patent application for the insulation process is pending with the U.S. Patent and Trademark Office.