Calculating Fatigue Damage with Wireless Sensors: Duty Cycling Vs. Down Sampling

Energy harvesting wireless sensor technology is an enabling development, with the potential to track accumulated damage on rotorcraft structures and critical components. Reducing the amount of power consumed by wireless sensor nodes allows the energy harvester's size and mass to be reduced, which, in turn enables the wireless sensors to be more deeply embedded, and to be used in more applications. This work provides a theoretical analysis of a fatigue tracking wireless sensor node that uses two distinct approaches to reducing its power consumption: 1) sampling at reduced rates (or down sampling) vs. 2) sampling at high rates in bursts (duty cycling). Our analysis was based on NASA H-60 pitch link flight test loads data collected at 357 Hz using slip rings. We analyzed data from eight different flight regimes, including autorotation, turns, and pushovers. For all eight flight regimes analyzed, we found that duty cycling significantly reduced power consumption while minimizing errors in estimating accumulated fatigue damage.