Search Menu
Photonics Media Photonics Buyers' Guide Photonics EDU Photonics Spectra BioPhotonics EuroPhotonics Industrial Photonics Photonics Showcase Photonics ProdSpec Photonics Handbook
More News
Email Facebook Twitter Google+ LinkedIn Comments

Sensor Sniffs Out Fuel Vapors

Photonics Spectra
May 2001
Michael D. Wheeler

Fuel vapors pose a fire hazard to crews aboard military vehicles, especially because they use a middle-distillate fuel that is similar to commercial kerosene. Now researchers at the US Army Research Laboratory have developed a sensing method that uses a laser-mixing technique to perform fuel vapor measurements quickly and accurately.

The vapors from the middle-distillate fuel used in military vehicles are a significant fire hazard. Researchers at the US Army Research Laboratory have developed a laser-mixing technique that can detect fuel vapor quickly and cheaply.

The Army has investigated several methods to rapidly detect fuel vapor, including Fourier transform infrared (FTIR) spectroscopy. The drawbacks to FTIR are the size of the instrumentation and its inability to sample in remote or confined locations. Another approach is to use electrothermal or electrochemical sensors, which are inexpensive but which can yield inaccurate results for some fuel products.

"The sensor system we use is conceptually very similar to optical phone systems," explained Kevin L. McNesby, a researcher at the lab and co-author of a report that appeared in the Feb. 20 issue of Applied Optics. "We take several lasers, each emitting at a discrete wavelength corresponding to a known absorption in the target gas, and we turn each laser on and off at slightly different frequencies."

The technique mixes the output of the lasers in a single optical fiber, which is terminated with a gradient index lens that collimates the light. The light then travels through free space without excessive divergence.

After the light has traveled 10 to 100 cm, a mirror reflects it to a room-temperature photodetector, typically InGaAs for the spectral range of 1.5 to 1.8 µm. The electrical signal from the photodetector is demodulated, revealing the contribution to the signal from each wavelength of the light that was in the fiber. If the researchers know how much light was initially emitted, they can measure the wavelength-dependent absorption of the gas in its path and so determine the identity and quantity of any vapor that is present.

Telecom by-products

A technique based on infrared laser diodes has many benefits, McNesby explained. The sensors have high temporal resolution, and the lasers' microwatt output enables safe sampling. Moreover, because they are based on inexpensive fiber optics, lasers and detectors, a damaged module can be replaced cheaply.

Oddly, the technology bucks the historical trend in photonics, where military advances trickle down to industry. "All these advantages we employ are by-products of the [telecommunications] industry," McNesby said, "which has driven the tech base for diode laser spectroscopic techniques."

CommunicationsdefenseFuel vaporsResearch & TechnologySensors & DetectorsTech Pulse

Terms & Conditions Privacy Policy About Us Contact Us
back to top
Facebook Twitter Instagram LinkedIn YouTube RSS
©2018 Photonics Media, 100 West St., Pittsfield, MA, 01201 USA,

Photonics Media, Laurin Publishing
x Subscribe to Photonics Spectra magazine - FREE!
We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.