By Emil Venere

A new technology enabling tiny machines called micro electromechanical systems to "self-calibrate" could make possible super-accurate and precise sensors for crime-scene forensics, environmental testing, and medical diagnostics.

The innovation might enable researchers to create a "nose-on-a-chip" for tracking criminal suspects, sensors for identifying hazardous solid or gaseous substances, as well as a new class of laboratory tools for specialists working in nanotechnology and biotechnology.

"In the everyday macroscopic world, we can accurately measure distance and mass because we have well-known standards such as rulers or weights that we use to calibrate devices that measure distances or forces," said Jason Vaughn Clark, an assistant professor of electrical and computer engineering and mechanical engineering. "But for the micro- or nanoscopic worlds, there have been no standards and no practical ways for measuring very small distances or forces."

The micro electromechanical systems, or MEMS, are promising for an array of high-tech applications.

Researchers previously have used various techniques to gauge the force and movement of tiny objects containing components so small they have to be measured on the scale of micrometers or nanometers, millionths or billionths of a meter, respectively. However, the accuracy of conventional techniques is typically off by 10% or more because of their inherent uncertainties, Clark said.

"And due to process variations within fabrication, no two microstructures have the same geometric and material properties," he said.

These small variations in microstructure geometry, stiffness, and mass can significantly affect performance.

"A 10% change in width can cause a 100% change in a microstructure's stiffness," Clark said. "Process variations have made it difficult for researchers to accurately predict the performance of MEMS."

The new technology created by Clark, called electro micro metrology—or EMM—is enabling engineers to account for process variations by determining the precise movement and force that's being applied to, or sensed by, a MEMS device.

"For the first time, MEMS can now truly self-calibrate without any external references," Clark said. "That is, our MEMS are able to determine their unique mechanical performance properties. And in doing so, they become very accurate sensors or actuators."

Research findings were detailed in two papers presented in June during a meeting of the Society of Experimental Mechanics in Indianapolis and at the Nanotech 2010 Conference and Expo in Anaheim, Calif. The work is based at the Birck Nanotechnology Center in Purdue's Discovery Park.