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State of the Art

Tiny Forces to Be Reckoned With

Researchers at the National Institute of Standards and Technology give more than a fig about newtons—the international unit for measuring force. A new five-year initiative aims to develop an electronic method that can accurately measure the feeblest of forces, down to billionths of a newton (nanonewton).

A nanonewton is equal to the force exerted by a single blood cell in the Earth’s gravitational field. Much of the push for tools to measure such “micro forces” comes from the data-storage industry and two fast-developing areas: nanotechnology—the realm of almost infinitesimal devices—and microelectromechanical systems, MEMS—semiconductor-like hybrids that combine electronic and mechanical devices on a chip. Both technology areas will leverage slight forces with great effect, propelling tiny robots, for example, that inspect pipes or remove plaque from veins and arteries.

Small, unwanted forces may wreak havoc, however. Larger-than-anticipated stresses could cause surface cracks that disable a device or knock a MEMS machine out of service.

NIST researchers say they might be able to push current capabilities to measure forces down to 10 millionths of a newton. But their goal is to deliver highly accurate measurements of forces that are about 10,000 times smaller. Preliminary work points to a promising method for standardized measurements of micro forces: developing the electronic equivalent of a nanonewton by comparing a known electric current in a coil with the mass of an object in a gravitational field.

ASTM Committee E-8 on Fatigue and Fracture is working on standards related to MEMS. See the November 1999 issue of SN—“The Big Problem with Small Failures.” //