Calibration and characterization of self-powered floating-gate sensor arrays for long-term fatigue monitoring

Measurement of cumulative loading statistics experienced by a structure is essential for monitoring long-term fatigue in biomechanical implants. However, the total power that can be harvested using typical in-vivo strain levels is less than 1 muW. In this paper we characterize the performance of a silicon floating-gate injector array that can be used in conjunction with a piezoelectric transducer to facilitate long- term, battery-less fatigue monitoring. Measured results from a fabricated prototype in a 0.5 mum CMOS process demonstrate that device can sense, compute and store loading statistics for over 70,000 of continuous simulated stress-strain cycles and this value can be increased beyond 10⁷ by appropriate scaling of the system parameters. The measured results also show excellent agreement with its theoretical model and the nominal power dissipation of the array was measured to be less than 800 nW.