Magnetic resonance imaging reveals unusual strain in a human body. Now a related physical effect, called nuclear quadrupole resonance, may help check for strain in the composite materials that are becoming common in everything from bridges to airplanes. The method, being developed by San Diego-based Quantum Magnetics, requires an undisclosed additive to be mixed into the composite as it is being formed. When this substance is hit by radio waves, it emits a different frequency; the magnitude of the shift indicates the strain in the material.

In one potential application, radio devices could be permanently affixed to various points on a structure to check the strain continually. Alternatively, a mobile unit could check for strain at particular points during routine maintenance. A commercial strain-monitoring system is about two years off, says researcher Stephanie Vierkotter.