Trio Closes In on Remote Chemical Sensor Project

Dr. James P. Smith

A collaboration among Sandia National Laboratories, the Massachusetts Institute of Technology in Cambridge and the Honeywell Technology Center in Minneapolis promises to produce a functioning prototype remote sensor by 2001 that will allow a person with binoculars to detect in seconds the nature of a gas being emitted by a smoke cloud. While remote chemical sensors are not new, this work-in-progress could do much of the spectral processing up front, allowing faster, more sensitive and selective results.

Broadband infrared light is incident upon a diffraction grating that is electronically programmed to produce the synthetic spectrum of a molecule.

The sensor will be based on two patents: one held by Mike Butler and Mike Sinclair of Sandia and Tony Ricco, formerly of Sandia, and the other held by Steve Senturia of MIT. The device will identify the presence of target chemicals in a smoke cloud 2 miles away. It will be small and capable of being mounted on a telescope or on binoculars. An obvious application is the identification of dangerous components in a gas cloud released over a battlefield.

Called a polychromator, the sensor will use a combination of optics and microelectromechanical systems (MEMS). About the size of a dime, the polychromator chip consists of approximately 1000 microscopic microelectromechanical grating elements on a silicon wafer manufactured with standard microlithographic techniques. Each 10-µm- wide element is 1 cm long and can be moved up and down. The deflection profile of the elements can be programmed to encode an infrared spectrum for correlation with the incoming light.

"Depending on the surface relief profile we build into the grating, we can diffract a particular spectrum," Sinclair said. "The advantage of using MEMS is that a single optical package can be programmed to find any one of several chemical signatures. The sensitivity of the polychromator should be at least as good as a regular spectrometer because we are actually looking at multiple wavelengths simultaneously."

"Strong teamwork is the key to success due to the complexity of the project," Butler said. "Honeywell is fabricating the MEMS devices; MIT is providing electromechanical design and characterization; and Sandia is working on the optical characterization and system integration." He said a multidisciplinary approach is required -- one that stresses communications and coordination of tasks. "This type of instrument has never been made before."

The Defense Advanced Research Projects Agency has funded the 4 1/2-year research and development project. The agency is the central organization for the US Department of Defense as it pursues R&D technology where risk and payoff are very high and where success may provide dramatic advances for traditional military roles and missions.