The U.S. Navy recently gave MicroStrain Inc., Williston, Vt., a $750,000 Small Business Innovation-Research (SBIR) Phase II contract to develop next-generation wireless strain sensors for tracking damage on Navy helicopters. Piezoelectric materials generate power for the sensor by converting cyclic strains to dc power, so the sensors operate indefinitely on rotating helicopter components without batteries.

By continuously monitoring strains on rotating components, the sensors can record operational loads, compute metal fatigue, and estimate remaining component life. Each sensor runs its own data-compression and fatigue algorithms, and its strain versus number of cycles (S-N) curve can be wirelessly uploaded. In recent demonstrations, the new gages were sampled at 40 Hz and had a 230-ft communications range while dissipating just 0.9 mW.

Tests took place on a helicopter pitch link, the rotating element that adjusts the rotor blade's angle of attack as the rotor turns. In tests replicating light use (straight and level flight), energy harvesters generated about 1 mW. The harvesters generated about 5 mW in tests replicating heavy use (pullups and gunnery turns).

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MicroStrain Inc., www.microstrain.com