Measuring Tiny Motions of Tiny Objects

Credit: Brian Roxworthy, NIST/CNST

It’s relatively easy to measure small movements of large objects but much more difficult when the moving parts measure only a few billionths of a meter across. The ability to accurately measure tiny displacements of microscopic bodies has applications in sensing tiny amounts of biological or chemical agents that can harm humans, perfecting the movement of miniature robots and accurately deploying airbags in life-threatening accidents.

PML scientists have developed a device that measures the motion of super-tiny particles traversing distances almost unimaginably small—shorter than the diameter of a hydrogen atom, or less than one-millionth the width of a human hair. Not only can the handheld device sense the atomic-scale motion of its tiny parts with unprecedented precision, but the researchers have devised a method to mass produce the highly sensitive measuring tool.

The PML researchers used laser light to measure the motion of a microscopic gold particle embedded in a device similar to a miniature diving board. An air gap that the team had created between this structure and a thin gold sheet was so tiny that the laser light could not penetrate it. But the light excited groups of electrons in the gap to oscillate back and forth, like a plucked guitar string. The interaction with the electrons allowed the team to go beyond the standard limitations of light in locating and tracking the motion of particles smaller than the wavelength of the laser.