Xudong Fan, an associate of biomedical engineering, points to the compressor that is part of the smart, portable gas sensor that he is developing. The device could one day be used to detect chemical weapon vapors or indicators of disease more precisely than current models do. It also consumes less power, which is crucial for stretching battery life in a mineshaft or an isolated clinic. Image credit: Joseph Xu, College of Engineering
These devices do all this by identifying and measuring airborne chemicals, and a new, more sensitive, smart model is under development at the University of Michigan. The smart sensor could detect chemical weapon vapors or indicators of disease better than the current design. It also consumes less power, crucial for stretching battery life down a mineshaft or in isolated clinics.
In the gold standard method of gas detection, chemicals are separated before they are measured, said Xudong "Sherman" Fan, a professor in the Department of Biomedical Engineering.
"In a vapor mixture, it’s very difficult to tell chemicals apart," he said.
The main advance of the sensor under development by Fan and his colleagues at U-M and the University of Missouri, Columbia, is a better approach to divvying up the chemicals. The researchers have demonstrated their concept on a table-top set-up, and they hope to produce a hand-held device in the future.
You can think of the different chemical vapors as tiny clouds, all overlapping in the original gas. In most gas sensors today, researchers separate the chemicals into smaller clouds by sending the gas through two tubes in sequence. A polymer coating on the inside of the first tube slows down heavier molecules, roughly separating the chemicals according to weight. The time it takes to get through the tube is the first clue to a chemical’s identity, Fan explained.
A pump and compressor collect gas from the first tube and then send it into the second tube at regular intervals. The second tube is typically coated with polar polymers, which are positively charged at one end and negatively charged at the other. This coating slows down polar gas molecules, allowing the non-polar molecules to pass through more quickly. With this second clue, the researchers can identify the chemicals in the gas.
The decision-maker added by Fan’s group consists of a detector and computer that watch for the beginnings and ends of partially separated chemical clouds. Under its direction, the compressor only runs when there is a complete cloud to send through. In addition to consuming one-tenth to one-hundredth of the energy expended by the compressor in typical systems, this approach makes data analysis easier by keeping all molecules of one type together, said Jing Liu, a graduate student in Fan’s group.
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